From 2af7ba21563f1b7f011ffa9f0c08e4acb473eef3 Mon Sep 17 00:00:00 2001
From: Fedor Nezhivoi <gyzerok@users.noreply.github.com>
Date: Tue, 24 Jun 2025 20:05:24 +0700
Subject: [PATCH 001/148] fix: lift unsafe_state_mutation constraints for
 SvelteSet and SvelteMap created inside the derived (#16221)

Co-authored-by: Fedor Nezhivoi <f.nezhivoi@corp.vk.com>
---
 .changeset/fair-bats-visit.md                 |  5 ++++
 packages/svelte/src/reactivity/date.js        |  4 +--
 packages/svelte/src/reactivity/map.js         |  6 ++---
 packages/svelte/src/reactivity/set.js         |  6 ++---
 .../src/reactivity/url-search-params.js       |  4 +--
 packages/svelte/src/reactivity/url.js         | 18 ++++++-------
 .../side-effect-derived-array/_config.js      | 23 ++++++++++++++++
 .../side-effect-derived-array/main.svelte     | 25 +++++++++++++++++
 .../side-effect-derived-date/_config.js       | 23 ++++++++++++++++
 .../side-effect-derived-date/main.svelte      | 27 +++++++++++++++++++
 .../side-effect-derived-map/_config.js        | 23 ++++++++++++++++
 .../side-effect-derived-map/main.svelte       | 27 +++++++++++++++++++
 .../side-effect-derived-object/_config.js     | 23 ++++++++++++++++
 .../side-effect-derived-object/main.svelte    | 25 +++++++++++++++++
 .../side-effect-derived-primitive/_config.js  | 23 ++++++++++++++++
 .../side-effect-derived-primitive/main.svelte | 25 +++++++++++++++++
 .../side-effect-derived-set/_config.js        | 23 ++++++++++++++++
 .../side-effect-derived-set/main.svelte       | 27 +++++++++++++++++++
 .../_config.js                                | 23 ++++++++++++++++
 .../main.svelte                               | 27 +++++++++++++++++++
 .../side-effect-derived-url/_config.js        | 23 ++++++++++++++++
 .../side-effect-derived-url/main.svelte       | 27 +++++++++++++++++++
 22 files changed, 418 insertions(+), 19 deletions(-)
 create mode 100644 .changeset/fair-bats-visit.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-array/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-array/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-date/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-date/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-map/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-map/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-object/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-object/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-primitive/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-primitive/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-set/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-set/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-url-search-params/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-url-search-params/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-url/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-url/main.svelte

diff --git a/.changeset/fair-bats-visit.md b/.changeset/fair-bats-visit.md
new file mode 100644
index 0000000000..bc0a426395
--- /dev/null
+++ b/.changeset/fair-bats-visit.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+lift unsafe_state_mutation constraints for SvelteSet, SvelteMap, SvelteDate, SvelteURL and SvelteURLSearchParams created inside the derived
diff --git a/packages/svelte/src/reactivity/date.js b/packages/svelte/src/reactivity/date.js
index 4176f0ceec..8e2b5d41ab 100644
--- a/packages/svelte/src/reactivity/date.js
+++ b/packages/svelte/src/reactivity/date.js
@@ -1,6 +1,6 @@
 /** @import { Source } from '#client' */
 import { derived } from '../internal/client/index.js';
-import { source, set } from '../internal/client/reactivity/sources.js';
+import { set, state } from '../internal/client/reactivity/sources.js';
 import { tag } from '../internal/client/dev/tracing.js';
 import { active_reaction, get, set_active_reaction } from '../internal/client/runtime.js';
 import { DEV } from 'esm-env';
@@ -40,7 +40,7 @@ var inited = false;
  * ```
  */
 export class SvelteDate extends Date {
-	#time = source(super.getTime());
+	#time = state(super.getTime());
 
 	/** @type {Map<keyof Date, Source<unknown>>} */
 	#deriveds = new Map();
diff --git a/packages/svelte/src/reactivity/map.js b/packages/svelte/src/reactivity/map.js
index eed163dbf2..cd2fac163f 100644
--- a/packages/svelte/src/reactivity/map.js
+++ b/packages/svelte/src/reactivity/map.js
@@ -1,6 +1,6 @@
 /** @import { Source } from '#client' */
 import { DEV } from 'esm-env';
-import { set, source } from '../internal/client/reactivity/sources.js';
+import { set, source, state } from '../internal/client/reactivity/sources.js';
 import { label, tag } from '../internal/client/dev/tracing.js';
 import { get } from '../internal/client/runtime.js';
 import { increment } from './utils.js';
@@ -54,8 +54,8 @@ import { increment } from './utils.js';
 export class SvelteMap extends Map {
 	/** @type {Map<K, Source<number>>} */
 	#sources = new Map();
-	#version = source(0);
-	#size = source(0);
+	#version = state(0);
+	#size = state(0);
 
 	/**
 	 * @param {Iterable<readonly [K, V]> | null | undefined} [value]
diff --git a/packages/svelte/src/reactivity/set.js b/packages/svelte/src/reactivity/set.js
index fd22014cb3..8a656c2bc1 100644
--- a/packages/svelte/src/reactivity/set.js
+++ b/packages/svelte/src/reactivity/set.js
@@ -1,6 +1,6 @@
 /** @import { Source } from '#client' */
 import { DEV } from 'esm-env';
-import { source, set } from '../internal/client/reactivity/sources.js';
+import { source, set, state } from '../internal/client/reactivity/sources.js';
 import { label, tag } from '../internal/client/dev/tracing.js';
 import { get } from '../internal/client/runtime.js';
 import { increment } from './utils.js';
@@ -48,8 +48,8 @@ var inited = false;
 export class SvelteSet extends Set {
 	/** @type {Map<T, Source<boolean>>} */
 	#sources = new Map();
-	#version = source(0);
-	#size = source(0);
+	#version = state(0);
+	#size = state(0);
 
 	/**
 	 * @param {Iterable<T> | null | undefined} [value]
diff --git a/packages/svelte/src/reactivity/url-search-params.js b/packages/svelte/src/reactivity/url-search-params.js
index c77ff9c822..389da7cdb6 100644
--- a/packages/svelte/src/reactivity/url-search-params.js
+++ b/packages/svelte/src/reactivity/url-search-params.js
@@ -1,5 +1,5 @@
 import { DEV } from 'esm-env';
-import { source } from '../internal/client/reactivity/sources.js';
+import { state } from '../internal/client/reactivity/sources.js';
 import { tag } from '../internal/client/dev/tracing.js';
 import { get } from '../internal/client/runtime.js';
 import { get_current_url } from './url.js';
@@ -34,7 +34,7 @@ export const REPLACE = Symbol();
  * ```
  */
 export class SvelteURLSearchParams extends URLSearchParams {
-	#version = DEV ? tag(source(0), 'SvelteURLSearchParams version') : source(0);
+	#version = DEV ? tag(state(0), 'SvelteURLSearchParams version') : state(0);
 	#url = get_current_url();
 
 	#updating = false;
diff --git a/packages/svelte/src/reactivity/url.js b/packages/svelte/src/reactivity/url.js
index 56732a0402..dfede23f6e 100644
--- a/packages/svelte/src/reactivity/url.js
+++ b/packages/svelte/src/reactivity/url.js
@@ -1,5 +1,5 @@
 import { DEV } from 'esm-env';
-import { source, set } from '../internal/client/reactivity/sources.js';
+import { set, state } from '../internal/client/reactivity/sources.js';
 import { tag } from '../internal/client/dev/tracing.js';
 import { get } from '../internal/client/runtime.js';
 import { REPLACE, SvelteURLSearchParams } from './url-search-params.js';
@@ -40,14 +40,14 @@ export function get_current_url() {
  * ```
  */
 export class SvelteURL extends URL {
-	#protocol = source(super.protocol);
-	#username = source(super.username);
-	#password = source(super.password);
-	#hostname = source(super.hostname);
-	#port = source(super.port);
-	#pathname = source(super.pathname);
-	#hash = source(super.hash);
-	#search = source(super.search);
+	#protocol = state(super.protocol);
+	#username = state(super.username);
+	#password = state(super.password);
+	#hostname = state(super.hostname);
+	#port = state(super.port);
+	#pathname = state(super.pathname);
+	#hash = state(super.hash);
+	#search = state(super.search);
 	#searchParams;
 
 	/**
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-array/_config.js b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-array/_config.js
new file mode 100644
index 0000000000..5ad6f57e31
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-array/_config.js
@@ -0,0 +1,23 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true,
+		runes: true
+	},
+
+	test({ assert, target }) {
+		const [button1, button2] = target.querySelectorAll('button');
+
+		assert.throws(() => {
+			button1?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button2?.click();
+			flushSync();
+		});
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-array/main.svelte b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-array/main.svelte
new file mode 100644
index 0000000000..6468dbebc9
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-array/main.svelte
@@ -0,0 +1,25 @@
+<script>
+	let visibleExternal = $state(false);
+	let external = $state([]);
+	const throws = $derived.by(() => {
+		external.push(1);
+		return external;
+	});
+
+	let visibleInternal = $state(false)
+	const works = $derived.by(() => {
+		let internal = $state([]);
+		internal.push(1);
+		return internal;
+	});
+</script>
+
+<button onclick={() => (visibleExternal = true)}>external</button>
+{#if visibleExternal}
+	{throws}
+{/if}
+<button onclick={() => (visibleInternal = true)}>internal</button>
+{#if visibleInternal}
+	{works}
+{/if}
+
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-date/_config.js b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-date/_config.js
new file mode 100644
index 0000000000..5ad6f57e31
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-date/_config.js
@@ -0,0 +1,23 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true,
+		runes: true
+	},
+
+	test({ assert, target }) {
+		const [button1, button2] = target.querySelectorAll('button');
+
+		assert.throws(() => {
+			button1?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button2?.click();
+			flushSync();
+		});
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-date/main.svelte b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-date/main.svelte
new file mode 100644
index 0000000000..a3c6aa629f
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-date/main.svelte
@@ -0,0 +1,27 @@
+<script>
+	import { SvelteDate } from 'svelte/reactivity';
+
+	let visibleExternal = $state(false);
+	let external = new SvelteDate();
+	const throws = $derived.by(() => {
+		external.setTime(12345);
+		return external;
+	})
+
+	let visibleInternal = $state(false);
+	const works = $derived.by(() => {
+		let internal = new SvelteDate();
+		internal.setTime(12345);
+		return internal;
+	})
+</script>
+
+<button onclick={() => (visibleExternal = true)}>external</button>
+{#if visibleExternal}
+	{throws}
+{/if}
+<button onclick={() => (visibleInternal = true)}>internal</button>
+{#if visibleInternal}
+	{works}
+{/if}
+
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-map/_config.js b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-map/_config.js
new file mode 100644
index 0000000000..5ad6f57e31
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-map/_config.js
@@ -0,0 +1,23 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true,
+		runes: true
+	},
+
+	test({ assert, target }) {
+		const [button1, button2] = target.querySelectorAll('button');
+
+		assert.throws(() => {
+			button1?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button2?.click();
+			flushSync();
+		});
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-map/main.svelte b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-map/main.svelte
new file mode 100644
index 0000000000..bdd5ccb75c
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-map/main.svelte
@@ -0,0 +1,27 @@
+<script>
+	import { SvelteMap } from 'svelte/reactivity';
+
+	let visibleExternal = $state(false);
+	let external = new SvelteMap();
+	const throws = $derived.by(() => {
+		external.set(1, 1);
+		return external;
+	});
+
+	let visibleInternal = $state(false);
+	const works = $derived.by(() => {
+		let internal = new SvelteMap();
+		internal.set(1, 1);
+		return internal;
+	});
+</script>
+
+<button onclick={() => (visibleExternal = true)}>external</button>
+{#if visibleExternal}
+	{throws}
+{/if}
+<button onclick={() => (visibleInternal = true)}>internal</button>
+{#if visibleInternal}
+	{works}
+{/if}
+
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-object/_config.js b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-object/_config.js
new file mode 100644
index 0000000000..5ad6f57e31
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-object/_config.js
@@ -0,0 +1,23 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true,
+		runes: true
+	},
+
+	test({ assert, target }) {
+		const [button1, button2] = target.querySelectorAll('button');
+
+		assert.throws(() => {
+			button1?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button2?.click();
+			flushSync();
+		});
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-object/main.svelte b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-object/main.svelte
new file mode 100644
index 0000000000..2174bde59f
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-object/main.svelte
@@ -0,0 +1,25 @@
+<script>
+	let visibleExternal = $state(false);
+	let external = $state({ v: 1 });
+	const throws = $derived.by(() => {
+		external.v = 2;
+		return external;
+	});
+
+	let visibleInternal = $state(false)
+	const works = $derived.by(() => {
+		let internal = $state({ v: 1 });
+		internal.v = 2;
+		return internal;
+	});
+</script>
+
+<button onclick={() => (visibleExternal = true)}>external</button>
+{#if visibleExternal}
+	{throws}
+{/if}
+<button onclick={() => (visibleInternal = true)}>internal</button>
+{#if visibleInternal}
+	{works}
+{/if}
+
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-primitive/_config.js b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-primitive/_config.js
new file mode 100644
index 0000000000..5ad6f57e31
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-primitive/_config.js
@@ -0,0 +1,23 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true,
+		runes: true
+	},
+
+	test({ assert, target }) {
+		const [button1, button2] = target.querySelectorAll('button');
+
+		assert.throws(() => {
+			button1?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button2?.click();
+			flushSync();
+		});
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-primitive/main.svelte b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-primitive/main.svelte
new file mode 100644
index 0000000000..21de8b9d91
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-primitive/main.svelte
@@ -0,0 +1,25 @@
+<script>
+	let visibleExternal = $state(false);
+	let external = $state(1);
+	const throws = $derived.by(() => {
+		external = 2;
+		return external;
+	});
+
+	let visibleInternal = $state(false);
+	const works = $derived.by(() => {
+		let internal = $state(1);
+		internal = 2;
+		return internal;
+	});
+</script>
+
+<button onclick={() => (visibleExternal = true)}>external</button>
+{#if visibleExternal}
+	{throws}
+{/if}
+<button onclick={() => (visibleInternal = true)}>internal</button>
+{#if visibleInternal}
+	{works}
+{/if}
+
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-set/_config.js b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-set/_config.js
new file mode 100644
index 0000000000..5ad6f57e31
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-set/_config.js
@@ -0,0 +1,23 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true,
+		runes: true
+	},
+
+	test({ assert, target }) {
+		const [button1, button2] = target.querySelectorAll('button');
+
+		assert.throws(() => {
+			button1?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button2?.click();
+			flushSync();
+		});
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-set/main.svelte b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-set/main.svelte
new file mode 100644
index 0000000000..8564f6e7c4
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-set/main.svelte
@@ -0,0 +1,27 @@
+<script>
+	import { SvelteSet } from 'svelte/reactivity';
+
+	let visibleExternal = $state(false);
+	let external = new SvelteSet();
+	const throws = $derived.by(() => {
+		external.add(1);
+		return external;
+	})
+
+	let visibleInternal = $state(false);
+	const works = $derived.by(() => {
+		let internal = new SvelteSet();
+		internal.add(1);
+		return internal;
+	})
+</script>
+
+<button onclick={() => (visibleExternal = true)}>external</button>
+{#if visibleExternal}
+	{throws}
+{/if}
+<button onclick={() => (visibleInternal = true)}>internal</button>
+{#if visibleInternal}
+	{works}
+{/if}
+
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url-search-params/_config.js b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url-search-params/_config.js
new file mode 100644
index 0000000000..5ad6f57e31
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url-search-params/_config.js
@@ -0,0 +1,23 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true,
+		runes: true
+	},
+
+	test({ assert, target }) {
+		const [button1, button2] = target.querySelectorAll('button');
+
+		assert.throws(() => {
+			button1?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button2?.click();
+			flushSync();
+		});
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url-search-params/main.svelte b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url-search-params/main.svelte
new file mode 100644
index 0000000000..014a1e4e6d
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url-search-params/main.svelte
@@ -0,0 +1,27 @@
+<script>
+	import { SvelteURLSearchParams } from 'svelte/reactivity';
+
+	let visibleExternal = $state(false);
+	let external = new SvelteURLSearchParams();
+	const throws = $derived.by(() => {
+		external.append('foo', 'bar')
+		return external;
+	})
+
+	let visibleInternal = $state(false);
+	const works = $derived.by(() => {
+		let internal = new SvelteURLSearchParams();
+		internal.append('foo', 'bar')
+		return internal;
+	})
+</script>
+
+<button onclick={() => (visibleExternal = true)}>external</button>
+{#if visibleExternal}
+	{throws}
+{/if}
+<button onclick={() => (visibleInternal = true)}>internal</button>
+{#if visibleInternal}
+	{works}
+{/if}
+
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url/_config.js b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url/_config.js
new file mode 100644
index 0000000000..5ad6f57e31
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url/_config.js
@@ -0,0 +1,23 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true,
+		runes: true
+	},
+
+	test({ assert, target }) {
+		const [button1, button2] = target.querySelectorAll('button');
+
+		assert.throws(() => {
+			button1?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button2?.click();
+			flushSync();
+		});
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url/main.svelte b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url/main.svelte
new file mode 100644
index 0000000000..69ead384c3
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-url/main.svelte
@@ -0,0 +1,27 @@
+<script>
+	import { SvelteURL } from 'svelte/reactivity';
+
+	let visibleExternal = $state(false);
+	let external = new SvelteURL('https://svelte.dev');
+	const throws = $derived.by(() => {
+		external.host = 'kit.svelte.dev'
+		return external;
+	})
+
+	let visibleInternal = $state(false);
+	const works = $derived.by(() => {
+		let internal = new SvelteURL('https://svelte.dev');
+		internal.host = 'kit.svelte.dev'
+		return internal;
+	})
+</script>
+
+<button onclick={() => (visibleExternal = true)}>external</button>
+{#if visibleExternal}
+	{throws}
+{/if}
+<button onclick={() => (visibleInternal = true)}>internal</button>
+{#if visibleInternal}
+	{works}
+{/if}
+

From 922bee9a6d44c2a0313766a9a996411acf451408 Mon Sep 17 00:00:00 2001
From: Paolo Ricciuti <ricciutipaolo@gmail.com>
Date: Wed, 25 Jun 2025 11:35:03 +0200
Subject: [PATCH 002/148] fix: use fine grained for template if the component
 is not explicitly in legacy mode (#16232)

* fix: use fine grained for template if the component is not explicitly in legacy mode

* chore: add comment

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>

* fix: add `LabeledStatement` to `instance.ast` check

* fix: spread `keys`

* fix: snapshots

* fix: use `compileOption.runes` if defined + add other tests

---------

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
---
 .changeset/cold-dingos-dream.md               |  5 ++++
 .../src/compiler/phases/2-analyze/index.js    | 23 +++++++++++++++++++
 .../client/visitors/shared/utils.js           |  5 +++-
 .../svelte/src/compiler/phases/types.d.ts     |  1 +
 .../svelte/tests/runtime-legacy/shared.ts     |  5 +++-
 .../_config.js                                | 17 ++++++++++++++
 .../main.svelte                               |  8 +++++++
 .../test.svelte.js                            |  9 ++++++++
 .../_config.js                                | 17 ++++++++++++++
 .../main.svelte                               |  9 ++++++++
 .../test.svelte.js                            |  9 ++++++++
 .../_config.js                                | 17 ++++++++++++++
 .../main.svelte                               |  9 ++++++++
 .../test.svelte.js                            |  9 ++++++++
 .../_config.js                                | 17 ++++++++++++++
 .../main.svelte                               |  9 ++++++++
 .../test.svelte.js                            |  9 ++++++++
 .../_config.js                                | 17 ++++++++++++++
 .../main.svelte                               |  9 ++++++++
 .../test.svelte.js                            |  9 ++++++++
 .../_config.js                                | 17 ++++++++++++++
 .../main.svelte                               | 10 ++++++++
 .../test.svelte.js                            |  9 ++++++++
 .../_config.js                                | 17 ++++++++++++++
 .../main.svelte                               | 12 ++++++++++
 .../test.svelte.js                            |  9 ++++++++
 .../samples/legacy-runes-ambiguous/_config.js | 17 ++++++++++++++
 .../legacy-runes-ambiguous/main.svelte        |  7 ++++++
 .../legacy-runes-ambiguous/test.svelte.js     |  9 ++++++++
 .../purity/_expected/client/index.svelte.js   |  6 ++---
 30 files changed, 320 insertions(+), 6 deletions(-)
 create mode 100644 .changeset/cold-dingos-dream.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-explicit-false/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-explicit-false/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-explicit-false/test.svelte.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$props/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$props/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$props/test.svelte.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$restProps/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$restProps/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$restProps/test.svelte.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-const/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-const/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-const/test.svelte.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-labeled/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-labeled/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-labeled/test.svelte.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let-2/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let-2/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let-2/test.svelte.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let/test.svelte.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous/test.svelte.js

diff --git a/.changeset/cold-dingos-dream.md b/.changeset/cold-dingos-dream.md
new file mode 100644
index 0000000000..c48414abc2
--- /dev/null
+++ b/.changeset/cold-dingos-dream.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: use fine grained for template if the component is not explicitly in legacy mode
diff --git a/packages/svelte/src/compiler/phases/2-analyze/index.js b/packages/svelte/src/compiler/phases/2-analyze/index.js
index fded183b86..80adc10c1a 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/index.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/index.js
@@ -431,6 +431,29 @@ export function analyze_component(root, source, options) {
 		template,
 		elements: [],
 		runes,
+		// if we are not in runes mode but we have no reserved references ($$props, $$restProps)
+		// and no `export let` we might be in a wannabe runes component that is using runes in an external
+		// module...we need to fallback to the runic behavior
+		maybe_runes:
+			!runes &&
+			// if they explicitly disabled runes, use the legacy behavior
+			options.runes !== false &&
+			![...module.scope.references.keys()].some((name) =>
+				['$$props', '$$restProps'].includes(name)
+			) &&
+			!instance.ast.body.some(
+				(node) =>
+					node.type === 'LabeledStatement' ||
+					(node.type === 'ExportNamedDeclaration' &&
+						((node.declaration &&
+							node.declaration.type === 'VariableDeclaration' &&
+							node.declaration.kind === 'let') ||
+							node.specifiers.some(
+								(specifier) =>
+									specifier.local.type === 'Identifier' &&
+									instance.scope.get(specifier.local.name)?.declaration_kind === 'let'
+							)))
+			),
 		tracing: false,
 		classes: new Map(),
 		immutable: runes || options.immutable,
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
index 15982899c9..c861a51b7d 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
@@ -370,7 +370,10 @@ export function validate_mutation(node, context, expression) {
 export function build_expression(context, expression, metadata, state = context.state) {
 	const value = /** @type {Expression} */ (context.visit(expression, state));
 
-	if (context.state.analysis.runes) {
+	// Components not explicitly in legacy mode might be expected to be in runes mode (especially since we didn't
+	// adjust this behavior until recently, which broke people's existing components), so we also bail in this case.
+	// Kind of an in-between-mode.
+	if (context.state.analysis.runes || context.state.analysis.maybe_runes) {
 		return value;
 	}
 
diff --git a/packages/svelte/src/compiler/phases/types.d.ts b/packages/svelte/src/compiler/phases/types.d.ts
index 67cbd75ff8..8fa4bff619 100644
--- a/packages/svelte/src/compiler/phases/types.d.ts
+++ b/packages/svelte/src/compiler/phases/types.d.ts
@@ -51,6 +51,7 @@ export interface ComponentAnalysis extends Analysis {
 	/** Used for CSS pruning and scoping */
 	elements: Array<AST.RegularElement | AST.SvelteElement>;
 	runes: boolean;
+	maybe_runes: boolean;
 	tracing: boolean;
 	exports: Array<{ name: string; alias: string | null }>;
 	/** Whether the component uses `$$props` */
diff --git a/packages/svelte/tests/runtime-legacy/shared.ts b/packages/svelte/tests/runtime-legacy/shared.ts
index 11ea9f6dda..126992a0c0 100644
--- a/packages/svelte/tests/runtime-legacy/shared.ts
+++ b/packages/svelte/tests/runtime-legacy/shared.ts
@@ -158,7 +158,10 @@ async function common_setup(cwd: string, runes: boolean | undefined, config: Run
 		...config.compileOptions,
 		immutable: config.immutable,
 		accessors: 'accessors' in config ? config.accessors : true,
-		runes
+		runes:
+			config.compileOptions && 'runes' in config.compileOptions
+				? config.compileOptions.runes
+				: runes
 	};
 
 	// load_compiled can be used for debugging a test. It means the compiler will not run on the input
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-explicit-false/_config.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-explicit-false/_config.js
new file mode 100644
index 0000000000..904fea3f65
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-explicit-false/_config.js
@@ -0,0 +1,17 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client'],
+	compileOptions: {
+		runes: undefined
+	},
+	async test({ assert, target }) {
+		const p = target.querySelector('p');
+		const btn = target.querySelector('button');
+		flushSync(() => {
+			btn?.click();
+		});
+		assert.equal(p?.innerHTML, '0');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-explicit-false/main.svelte b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-explicit-false/main.svelte
new file mode 100644
index 0000000000..cb5837dcd6
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-explicit-false/main.svelte
@@ -0,0 +1,8 @@
+<svelte:options runes={false} />
+<script>
+	import { get, set } from "./test.svelte.js";
+</script>
+
+<p>{get()}</p>
+
+<button onclick={()=>set()}></button>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-explicit-false/test.svelte.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-explicit-false/test.svelte.js
new file mode 100644
index 0000000000..f0e7181c29
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-explicit-false/test.svelte.js
@@ -0,0 +1,9 @@
+let count = $state(0);
+
+export function get() {
+	return count;
+}
+
+export function set() {
+	count++;
+}
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$props/_config.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$props/_config.js
new file mode 100644
index 0000000000..904fea3f65
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$props/_config.js
@@ -0,0 +1,17 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client'],
+	compileOptions: {
+		runes: undefined
+	},
+	async test({ assert, target }) {
+		const p = target.querySelector('p');
+		const btn = target.querySelector('button');
+		flushSync(() => {
+			btn?.click();
+		});
+		assert.equal(p?.innerHTML, '0');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$props/main.svelte b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$props/main.svelte
new file mode 100644
index 0000000000..a7370b48d6
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$props/main.svelte
@@ -0,0 +1,9 @@
+<script>
+	import { get, set } from "./test.svelte.js";
+
+	$$props;
+</script>
+
+<p>{get()}</p>
+
+<button onclick={()=>set()}></button>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$props/test.svelte.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$props/test.svelte.js
new file mode 100644
index 0000000000..f0e7181c29
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$props/test.svelte.js
@@ -0,0 +1,9 @@
+let count = $state(0);
+
+export function get() {
+	return count;
+}
+
+export function set() {
+	count++;
+}
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$restProps/_config.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$restProps/_config.js
new file mode 100644
index 0000000000..904fea3f65
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$restProps/_config.js
@@ -0,0 +1,17 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client'],
+	compileOptions: {
+		runes: undefined
+	},
+	async test({ assert, target }) {
+		const p = target.querySelector('p');
+		const btn = target.querySelector('button');
+		flushSync(() => {
+			btn?.click();
+		});
+		assert.equal(p?.innerHTML, '0');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$restProps/main.svelte b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$restProps/main.svelte
new file mode 100644
index 0000000000..ccf9bd2864
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$restProps/main.svelte
@@ -0,0 +1,9 @@
+<script>
+	import { get, set } from "./test.svelte.js";
+
+	$$restProps;
+</script>
+
+<p>{get()}</p>
+
+<button onclick={()=>set()}></button>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$restProps/test.svelte.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$restProps/test.svelte.js
new file mode 100644
index 0000000000..f0e7181c29
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-$$restProps/test.svelte.js
@@ -0,0 +1,9 @@
+let count = $state(0);
+
+export function get() {
+	return count;
+}
+
+export function set() {
+	count++;
+}
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-const/_config.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-const/_config.js
new file mode 100644
index 0000000000..2d72de6d13
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-const/_config.js
@@ -0,0 +1,17 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client'],
+	compileOptions: {
+		runes: undefined
+	},
+	async test({ assert, target }) {
+		const p = target.querySelector('p');
+		const btn = target.querySelector('button');
+		flushSync(() => {
+			btn?.click();
+		});
+		assert.equal(p?.innerHTML, '1');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-const/main.svelte b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-const/main.svelte
new file mode 100644
index 0000000000..49aef81518
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-const/main.svelte
@@ -0,0 +1,9 @@
+<script>
+	import { get, set } from "./test.svelte.js";
+
+	export const x = 42;
+</script>
+
+<p>{get()}</p>
+
+<button onclick={()=>set()}></button>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-const/test.svelte.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-const/test.svelte.js
new file mode 100644
index 0000000000..f0e7181c29
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-const/test.svelte.js
@@ -0,0 +1,9 @@
+let count = $state(0);
+
+export function get() {
+	return count;
+}
+
+export function set() {
+	count++;
+}
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-labeled/_config.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-labeled/_config.js
new file mode 100644
index 0000000000..904fea3f65
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-labeled/_config.js
@@ -0,0 +1,17 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client'],
+	compileOptions: {
+		runes: undefined
+	},
+	async test({ assert, target }) {
+		const p = target.querySelector('p');
+		const btn = target.querySelector('button');
+		flushSync(() => {
+			btn?.click();
+		});
+		assert.equal(p?.innerHTML, '0');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-labeled/main.svelte b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-labeled/main.svelte
new file mode 100644
index 0000000000..f7cd0ede2e
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-labeled/main.svelte
@@ -0,0 +1,9 @@
+<script>
+	import { get, set } from "./test.svelte.js";
+
+	$: console.log("");
+</script>
+
+<p>{get()}</p>
+
+<button onclick={()=>set()}></button>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-labeled/test.svelte.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-labeled/test.svelte.js
new file mode 100644
index 0000000000..f0e7181c29
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-labeled/test.svelte.js
@@ -0,0 +1,9 @@
+let count = $state(0);
+
+export function get() {
+	return count;
+}
+
+export function set() {
+	count++;
+}
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let-2/_config.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let-2/_config.js
new file mode 100644
index 0000000000..904fea3f65
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let-2/_config.js
@@ -0,0 +1,17 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client'],
+	compileOptions: {
+		runes: undefined
+	},
+	async test({ assert, target }) {
+		const p = target.querySelector('p');
+		const btn = target.querySelector('button');
+		flushSync(() => {
+			btn?.click();
+		});
+		assert.equal(p?.innerHTML, '0');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let-2/main.svelte b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let-2/main.svelte
new file mode 100644
index 0000000000..36becde4a3
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let-2/main.svelte
@@ -0,0 +1,10 @@
+<script>
+	import { get, set } from "./test.svelte.js";
+
+	export let x = 42;
+</script>
+
+{x}
+<p>{get()}</p>
+
+<button onclick={()=>set()}></button>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let-2/test.svelte.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let-2/test.svelte.js
new file mode 100644
index 0000000000..f0e7181c29
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let-2/test.svelte.js
@@ -0,0 +1,9 @@
+let count = $state(0);
+
+export function get() {
+	return count;
+}
+
+export function set() {
+	count++;
+}
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let/_config.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let/_config.js
new file mode 100644
index 0000000000..904fea3f65
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let/_config.js
@@ -0,0 +1,17 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client'],
+	compileOptions: {
+		runes: undefined
+	},
+	async test({ assert, target }) {
+		const p = target.querySelector('p');
+		const btn = target.querySelector('button');
+		flushSync(() => {
+			btn?.click();
+		});
+		assert.equal(p?.innerHTML, '0');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let/main.svelte b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let/main.svelte
new file mode 100644
index 0000000000..1449b7d582
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let/main.svelte
@@ -0,0 +1,12 @@
+<script>
+	import { get, set } from "./test.svelte.js";
+
+	let x = 42;
+
+	export { x };
+</script>
+
+{x}
+<p>{get()}</p>
+
+<button onclick={()=>set()}></button>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let/test.svelte.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let/test.svelte.js
new file mode 100644
index 0000000000..f0e7181c29
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-let/test.svelte.js
@@ -0,0 +1,9 @@
+let count = $state(0);
+
+export function get() {
+	return count;
+}
+
+export function set() {
+	count++;
+}
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous/_config.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous/_config.js
new file mode 100644
index 0000000000..2d72de6d13
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous/_config.js
@@ -0,0 +1,17 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client'],
+	compileOptions: {
+		runes: undefined
+	},
+	async test({ assert, target }) {
+		const p = target.querySelector('p');
+		const btn = target.querySelector('button');
+		flushSync(() => {
+			btn?.click();
+		});
+		assert.equal(p?.innerHTML, '1');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous/main.svelte b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous/main.svelte
new file mode 100644
index 0000000000..698a852ac9
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous/main.svelte
@@ -0,0 +1,7 @@
+<script>
+	import { get, set } from "./test.svelte.js";
+</script>
+
+<p>{get()}</p>
+
+<button onclick={()=>set()}></button>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous/test.svelte.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous/test.svelte.js
new file mode 100644
index 0000000000..f0e7181c29
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous/test.svelte.js
@@ -0,0 +1,9 @@
+let count = $state(0);
+
+export function get() {
+	return count;
+}
+
+export function set() {
+	count++;
+}
diff --git a/packages/svelte/tests/snapshot/samples/purity/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/purity/_expected/client/index.svelte.js
index da6fdf44d8..a351851875 100644
--- a/packages/svelte/tests/snapshot/samples/purity/_expected/client/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/purity/_expected/client/index.svelte.js
@@ -8,13 +8,11 @@ export default function Purity($$anchor) {
 	var fragment = root();
 	var p = $.first_child(fragment);
 
-	p.textContent = (
-		$.untrack(() => Math.max(0, Math.min(0, 100)))
-	);
+	p.textContent = '0';
 
 	var p_1 = $.sibling(p, 2);
 
-	p_1.textContent = ($.untrack(() => location.href));
+	p_1.textContent = location.href;
 
 	var node = $.sibling(p_1, 2);
 

From 777e67b9487ffbc8f433e50752243fcb51d22392 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Wed, 25 Jun 2025 12:38:03 +0200
Subject: [PATCH 003/148] Version Packages (#16216)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/clever-dodos-jam.md  |  5 -----
 .changeset/cold-dingos-dream.md |  5 -----
 .changeset/fair-bats-visit.md   |  5 -----
 packages/svelte/CHANGELOG.md    | 10 ++++++++++
 packages/svelte/package.json    |  2 +-
 packages/svelte/src/version.js  |  2 +-
 6 files changed, 12 insertions(+), 17 deletions(-)
 delete mode 100644 .changeset/clever-dodos-jam.md
 delete mode 100644 .changeset/cold-dingos-dream.md
 delete mode 100644 .changeset/fair-bats-visit.md

diff --git a/.changeset/clever-dodos-jam.md b/.changeset/clever-dodos-jam.md
deleted file mode 100644
index bdeb979184..0000000000
--- a/.changeset/clever-dodos-jam.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: untrack `$inspect.with` and add check for unsafe mutation
diff --git a/.changeset/cold-dingos-dream.md b/.changeset/cold-dingos-dream.md
deleted file mode 100644
index c48414abc2..0000000000
--- a/.changeset/cold-dingos-dream.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: use fine grained for template if the component is not explicitly in legacy mode
diff --git a/.changeset/fair-bats-visit.md b/.changeset/fair-bats-visit.md
deleted file mode 100644
index bc0a426395..0000000000
--- a/.changeset/fair-bats-visit.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-lift unsafe_state_mutation constraints for SvelteSet, SvelteMap, SvelteDate, SvelteURL and SvelteURLSearchParams created inside the derived
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index b29ecc3fe3..e254be754f 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,15 @@
 # svelte
 
+## 5.34.8
+
+### Patch Changes
+
+- fix: untrack `$inspect.with` and add check for unsafe mutation ([#16209](https://github.com/sveltejs/svelte/pull/16209))
+
+- fix: use fine grained for template if the component is not explicitly in legacy mode ([#16232](https://github.com/sveltejs/svelte/pull/16232))
+
+- lift unsafe_state_mutation constraints for SvelteSet, SvelteMap, SvelteDate, SvelteURL and SvelteURLSearchParams created inside the derived ([#16221](https://github.com/sveltejs/svelte/pull/16221))
+
 ## 5.34.7
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index bdf7576e22..17a3e980c4 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.34.7",
+  "version": "5.34.8",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 748cc3ddd6..ec0126b17d 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.34.7';
+export const VERSION = '5.34.8';
 export const PUBLIC_VERSION = '5';

From facf528cb8a7289c8b3eaf036949a515f5ad2108 Mon Sep 17 00:00:00 2001
From: brunnerh <brunnerh@users.noreply.github.com>
Date: Wed, 25 Jun 2025 20:35:48 +0200
Subject: [PATCH 004/148] docs: Simplify TS config docs (#16236)

* Simplify TypeScript config requirements

Assignments are allowed in the constructor from 5.31.0 onward, so retaining the classes via ES2015 should be enough.

* Add  back a little bit of detail.
---
 documentation/docs/07-misc/03-typescript.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/documentation/docs/07-misc/03-typescript.md b/documentation/docs/07-misc/03-typescript.md
index fbf8817069..ff33885fb8 100644
--- a/documentation/docs/07-misc/03-typescript.md
+++ b/documentation/docs/07-misc/03-typescript.md
@@ -83,7 +83,7 @@ If you're using tools like Rollup or Webpack instead, install their respective S
 
 When using TypeScript, make sure your `tsconfig.json` is setup correctly.
 
-- Use a [`target`](https://www.typescriptlang.org/tsconfig/#target) of at least `ES2022`, or a `target` of at least `ES2015` alongside [`useDefineForClassFields`](https://www.typescriptlang.org/tsconfig/#useDefineForClassFields). This ensures that rune declarations on class fields are not messed with, which would break the Svelte compiler
+- Use a [`target`](https://www.typescriptlang.org/tsconfig/#target) of at least `ES2015` so classes are not compiled to functions
 - Set [`verbatimModuleSyntax`](https://www.typescriptlang.org/tsconfig/#verbatimModuleSyntax) to `true` so that imports are left as-is
 - Set [`isolatedModules`](https://www.typescriptlang.org/tsconfig/#isolatedModules) to `true` so that each file is looked at in isolation. TypeScript has a few features which require cross-file analysis and compilation, which the Svelte compiler and tooling like Vite don't do. 
 

From 0b2b9c724fef657af9371089e468d5c49c209e36 Mon Sep 17 00:00:00 2001
From: 7nik <kifiranet@gmail.com>
Date: Wed, 25 Jun 2025 21:38:26 +0300
Subject: [PATCH 005/148] chore: adjust linting (#16231)

* chore: adjust linting

* more nice treeshaking failure message

* lint
---
 .prettierignore                               |  4 +-
 eslint.config.js                              |  1 +
 .../svelte/scripts/check-treeshakeability.js  | 50 ++++++++++---------
 3 files changed, 30 insertions(+), 25 deletions(-)

diff --git a/.prettierignore b/.prettierignore
index d5c124353c..72cd10aca8 100644
--- a/.prettierignore
+++ b/.prettierignore
@@ -7,6 +7,7 @@ packages/**/config/*.js
 
 # packages/svelte
 packages/svelte/messages/**/*.md
+packages/svelte/scripts/_bundle.js
 packages/svelte/src/compiler/errors.js
 packages/svelte/src/compiler/warnings.js
 packages/svelte/src/internal/client/errors.js
@@ -25,8 +26,7 @@ packages/svelte/tests/hydration/samples/*/_expected.html
 packages/svelte/tests/hydration/samples/*/_override.html
 packages/svelte/types
 packages/svelte/compiler/index.js
-playgrounds/sandbox/input/**.svelte
-playgrounds/sandbox/output
+playgrounds/sandbox/src/*
 
 # sites/svelte.dev
 sites/svelte.dev/static/svelte-app.json
diff --git a/eslint.config.js b/eslint.config.js
index d6c977a36a..d7044fc9f1 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -87,6 +87,7 @@ export default [
 			'**/*.d.ts',
 			'**/tests',
 			'packages/svelte/scripts/process-messages/templates/*.js',
+			'packages/svelte/scripts/_bundle.js',
 			'packages/svelte/src/compiler/errors.js',
 			'packages/svelte/src/internal/client/errors.js',
 			'packages/svelte/src/internal/client/warnings.js',
diff --git a/packages/svelte/scripts/check-treeshakeability.js b/packages/svelte/scripts/check-treeshakeability.js
index 1501ee6954..e883496fe2 100644
--- a/packages/svelte/scripts/check-treeshakeability.js
+++ b/packages/svelte/scripts/check-treeshakeability.js
@@ -118,36 +118,40 @@ const bundle = await bundle_code(
 	).js.code
 );
 
-if (!bundle.includes('hydrate_node') && !bundle.includes('hydrate_next')) {
-	// eslint-disable-next-line no-console
-	console.error(`✅ Hydration code treeshakeable`);
-} else {
-	failed = true;
-	// eslint-disable-next-line no-console
-	console.error(`❌ Hydration code not treeshakeable`);
-}
+/**
+ * @param {string} case_name
+ * @param {string[]} strings
+ */
+function check_bundle(case_name, ...strings) {
+	for (const string of strings) {
+		const index = bundle.indexOf(string);
+		if (index >= 0) {
+			// eslint-disable-next-line no-console
+			console.error(`❌ ${case_name} not treeshakeable`);
+			failed = true;
 
-if (!bundle.includes('component_context.l')) {
-	// eslint-disable-next-line no-console
-	console.error(`✅ Legacy code treeshakeable`);
-} else {
-	failed = true;
+			let lines = bundle.slice(index - 500, index + 500).split('\n');
+			const target_line = lines.findIndex((line) => line.includes(string));
+			// mark the failed line
+			lines = lines
+				.map((line, i) => (i === target_line ? `> ${line}` : `| ${line}`))
+				.slice(target_line - 5, target_line + 6);
+			// eslint-disable-next-line no-console
+			console.error('The first failed line:\n' + lines.join('\n'));
+			return;
+		}
+	}
 	// eslint-disable-next-line no-console
-	console.error(`❌ Legacy code not treeshakeable`);
+	console.error(`✅ ${case_name} treeshakeable`);
 }
 
-if (!bundle.includes(`'CreatedAt'`)) {
-	// eslint-disable-next-line no-console
-	console.error(`✅ $inspect.trace code treeshakeable`);
-} else {
-	failed = true;
-	// eslint-disable-next-line no-console
-	console.error(`❌ $inspect.trace code not treeshakeable`);
-}
+check_bundle('Hydration code', 'hydrate_node', 'hydrate_next');
+check_bundle('Legacy code', 'component_context.l');
+check_bundle('$inspect.trace', `'CreatedAt'`);
 
 if (failed) {
 	// eslint-disable-next-line no-console
-	console.error(bundle);
+	console.error('Full bundle at', path.resolve('scripts/_bundle.js'));
 	fs.writeFileSync('scripts/_bundle.js', bundle);
 }
 

From da2feafe6765d2278ff053f62e6603a60b06833e Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 25 Jun 2025 14:40:52 -0400
Subject: [PATCH 006/148] chore: silence some pesky logs (#16241)

---
 .../samples/inspect-state-unsafe-mutation/_config.js        | 6 +++++-
 .../legacy-runes-ambiguous-export-labeled/_config.js        | 2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/packages/svelte/tests/runtime-runes/samples/inspect-state-unsafe-mutation/_config.js b/packages/svelte/tests/runtime-runes/samples/inspect-state-unsafe-mutation/_config.js
index 7e8fcd2d48..dcf3a8bc3d 100644
--- a/packages/svelte/tests/runtime-runes/samples/inspect-state-unsafe-mutation/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/inspect-state-unsafe-mutation/_config.js
@@ -5,5 +5,9 @@ export default test({
 	compileOptions: {
 		dev: true
 	},
-	error: 'state_unsafe_mutation'
+
+	error: 'state_unsafe_mutation',
+
+	// silence the logs
+	test({ logs }) {}
 });
diff --git a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-labeled/_config.js b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-labeled/_config.js
index 904fea3f65..c4cff665d2 100644
--- a/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-labeled/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/legacy-runes-ambiguous-export-labeled/_config.js
@@ -6,7 +6,7 @@ export default test({
 	compileOptions: {
 		runes: undefined
 	},
-	async test({ assert, target }) {
+	async test({ assert, target, logs }) {
 		const p = target.querySelector('p');
 		const btn = target.querySelector('button');
 		flushSync(() => {

From 213274a75ecc71dd86a31ba2dab4f594fc2cd265 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 26 Jun 2025 18:23:10 -0400
Subject: [PATCH 007/148] chore: reduce some select.value indirection (#16250)

---
 .../client/visitors/RegularElement.js         | 21 ++++++++-----------
 .../client/visitors/shared/utils.js           | 14 -------------
 2 files changed, 9 insertions(+), 26 deletions(-)

diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js
index 1aefff0db0..b0f285eb41 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js
@@ -25,7 +25,6 @@ import { process_children } from './shared/fragment.js';
 import {
 	build_render_statement,
 	build_template_chunk,
-	build_update_assignment,
 	get_expression_id,
 	memoize_expression
 } from './shared/utils.js';
@@ -657,17 +656,15 @@ function build_element_special_value_attribute(element, node_id, attribute, cont
 	}
 
 	if (has_state) {
-		const id = state.scope.generate(`${node_id.name}_value`);
-		build_update_assignment(
-			state,
-			id,
-			// `<option>` is a special case: The value property reflects to the DOM. If the value is set to undefined,
-			// that means the value should be set to the empty string. To be able to do that when the value is
-			// initially undefined, we need to set a value that is guaranteed to be different.
-			element === 'option' ? b.object([]) : undefined,
-			value,
-			update
-		);
+		const id = b.id(state.scope.generate(`${node_id.name}_value`));
+
+		// `<option>` is a special case: The value property reflects to the DOM. If the value is set to undefined,
+		// that means the value should be set to the empty string. To be able to do that when the value is
+		// initially undefined, we need to set a value that is guaranteed to be different.
+		const init = element === 'option' ? b.object([]) : undefined;
+
+		state.init.push(b.var(id, init));
+		state.update.push(b.if(b.binary('!==', id, b.assignment('=', id, value)), b.block([update])));
 	} else {
 		state.init.push(update);
 	}
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
index c861a51b7d..0bd9bfb128 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
@@ -165,20 +165,6 @@ export function parse_directive_name(name) {
 	return expression;
 }
 
-/**
- * @param {ComponentClientTransformState} state
- * @param {string} id
- * @param {Expression | undefined} init
- * @param {Expression} value
- * @param {ExpressionStatement} update
- */
-export function build_update_assignment(state, id, init, value, update) {
-	state.init.push(b.var(id, init));
-	state.update.push(
-		b.if(b.binary('!==', b.id(id), b.assignment('=', b.id(id), value)), b.block([update]))
-	);
-}
-
 /**
  * Serializes `bind:this` for components and elements.
  * @param {Identifier | MemberExpression | SequenceExpression} expression

From 32481bece6018887bd6291b80a4133ebc0a601eb Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 26 Jun 2025 19:59:30 -0400
Subject: [PATCH 008/148] chore: simplify `<select>` initialization (#16251)

* initialize option values before initing select values

* simplify init_select

* simplify

* tweak

* tidy up

* tweak

* on second thoughts just simplify it here
---
 .../client/visitors/RegularElement.js         | 46 ++++++++--------
 .../client/dom/elements/attributes.js         | 12 ++--
 .../client/dom/elements/bindings/select.js    | 55 +++++++------------
 3 files changed, 50 insertions(+), 63 deletions(-)

diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js
index b0f285eb41..ae8680f594 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js
@@ -22,12 +22,7 @@ import {
 	build_set_style
 } from './shared/element.js';
 import { process_children } from './shared/fragment.js';
-import {
-	build_render_statement,
-	build_template_chunk,
-	get_expression_id,
-	memoize_expression
-} from './shared/utils.js';
+import { build_render_statement, build_template_chunk, get_expression_id } from './shared/utils.js';
 import { visit_event_attribute } from './shared/events.js';
 
 /**
@@ -199,16 +194,16 @@ export function RegularElement(node, context) {
 
 	const node_id = context.state.node;
 
+	/** If true, needs `__value` for inputs */
+	const needs_special_value_handling =
+		node.name === 'option' ||
+		node.name === 'select' ||
+		bindings.has('group') ||
+		bindings.has('checked');
+
 	if (has_spread) {
 		build_attribute_effect(attributes, class_directives, style_directives, context, node, node_id);
 	} else {
-		/** If true, needs `__value` for inputs */
-		const needs_special_value_handling =
-			node.name === 'option' ||
-			node.name === 'select' ||
-			bindings.has('group') ||
-			bindings.has('checked');
-
 		for (const attribute of /** @type {AST.Attribute[]} */ (attributes)) {
 			if (is_event_attribute(attribute)) {
 				visit_event_attribute(attribute, context);
@@ -216,7 +211,6 @@ export function RegularElement(node, context) {
 			}
 
 			if (needs_special_value_handling && attribute.name === 'value') {
-				build_element_special_value_attribute(node.name, node_id, attribute, context);
 				continue;
 			}
 
@@ -391,6 +385,15 @@ export function RegularElement(node, context) {
 		context.state.update.push(b.stmt(b.assignment('=', dir, dir)));
 	}
 
+	if (!has_spread && needs_special_value_handling) {
+		for (const attribute of /** @type {AST.Attribute[]} */ (attributes)) {
+			if (attribute.name === 'value') {
+				build_element_special_value_attribute(node.name, node_id, attribute, context);
+				break;
+			}
+		}
+	}
+
 	context.state.template.pop_element();
 }
 
@@ -621,12 +624,7 @@ function build_element_special_value_attribute(element, node_id, attribute, cont
 		element === 'select' && attribute.value !== true && !is_text_attribute(attribute);
 
 	const { value, has_state } = build_attribute_value(attribute.value, context, (value, metadata) =>
-		metadata.has_call
-			? // if is a select with value we will also invoke `init_select` which need a reference before the template effect so we memoize separately
-				is_select_with_value
-				? memoize_expression(state, value)
-				: get_expression_id(state.expressions, value)
-			: value
+		metadata.has_call ? get_expression_id(state.expressions, value) : value
 	);
 
 	const evaluated = context.state.scope.evaluate(value);
@@ -651,10 +649,6 @@ function build_element_special_value_attribute(element, node_id, attribute, cont
 			: inner_assignment
 	);
 
-	if (is_select_with_value) {
-		state.init.push(b.stmt(b.call('$.init_select', node_id, b.thunk(value))));
-	}
-
 	if (has_state) {
 		const id = b.id(state.scope.generate(`${node_id.name}_value`));
 
@@ -668,4 +662,8 @@ function build_element_special_value_attribute(element, node_id, attribute, cont
 	} else {
 		state.init.push(update);
 	}
+
+	if (is_select_with_value) {
+		state.init.push(b.stmt(b.call('$.init_select', node_id)));
+	}
 }
diff --git a/packages/svelte/src/internal/client/dom/elements/attributes.js b/packages/svelte/src/internal/client/dom/elements/attributes.js
index 2d3d6a921d..5db685cf3e 100644
--- a/packages/svelte/src/internal/client/dom/elements/attributes.js
+++ b/packages/svelte/src/internal/client/dom/elements/attributes.js
@@ -20,7 +20,7 @@ import { clsx } from '../../../shared/attributes.js';
 import { set_class } from './class.js';
 import { set_style } from './style.js';
 import { ATTACHMENT_KEY, NAMESPACE_HTML } from '../../../../constants.js';
-import { block, branch, destroy_effect } from '../../reactivity/effects.js';
+import { block, branch, destroy_effect, effect } from '../../reactivity/effects.js';
 import { derived } from '../../reactivity/deriveds.js';
 import { init_select, select_option } from './bindings/select.js';
 
@@ -513,10 +513,12 @@ export function attribute_effect(
 	});
 
 	if (is_select) {
-		init_select(
-			/** @type {HTMLSelectElement} */ (element),
-			() => /** @type {Record<string | symbol, any>} */ (prev).value
-		);
+		var select = /** @type {HTMLSelectElement} */ (element);
+
+		effect(() => {
+			select_option(select, /** @type {Record<string | symbol, any>} */ (prev).value);
+			init_select(select);
+		});
 	}
 
 	inited = true;
diff --git a/packages/svelte/src/internal/client/dom/elements/bindings/select.js b/packages/svelte/src/internal/client/dom/elements/bindings/select.js
index e3263c65af..5e89686d86 100644
--- a/packages/svelte/src/internal/client/dom/elements/bindings/select.js
+++ b/packages/svelte/src/internal/client/dom/elements/bindings/select.js
@@ -1,6 +1,5 @@
-import { effect } from '../../../reactivity/effects.js';
+import { effect, teardown } from '../../../reactivity/effects.js';
 import { listen_to_event_and_reset_event } from './shared.js';
-import { untrack } from '../../../runtime.js';
 import { is } from '../../../proxy.js';
 import { is_array } from '../../../../shared/utils.js';
 import * as w from '../../../warnings.js';
@@ -51,40 +50,29 @@ export function select_option(select, value, mounting) {
  * current selection to the dom when it changes. Such
  * changes could for example occur when options are
  * inside an `#each` block.
- * @template V
  * @param {HTMLSelectElement} select
- * @param {() => V} [get_value]
  */
-export function init_select(select, get_value) {
-	let mounting = true;
-	effect(() => {
-		if (get_value) {
-			select_option(select, untrack(get_value), mounting);
-		}
-		mounting = false;
+export function init_select(select) {
+	var observer = new MutationObserver(() => {
+		// @ts-ignore
+		select_option(select, select.__value);
+		// Deliberately don't update the potential binding value,
+		// the model should be preserved unless explicitly changed
+	});
+
+	observer.observe(select, {
+		// Listen to option element changes
+		childList: true,
+		subtree: true, // because of <optgroup>
+		// Listen to option element value attribute changes
+		// (doesn't get notified of select value changes,
+		// because that property is not reflected as an attribute)
+		attributes: true,
+		attributeFilter: ['value']
+	});
 
-		var observer = new MutationObserver(() => {
-			// @ts-ignore
-			var value = select.__value;
-			select_option(select, value);
-			// Deliberately don't update the potential binding value,
-			// the model should be preserved unless explicitly changed
-		});
-
-		observer.observe(select, {
-			// Listen to option element changes
-			childList: true,
-			subtree: true, // because of <optgroup>
-			// Listen to option element value attribute changes
-			// (doesn't get notified of select value changes,
-			// because that property is not reflected as an attribute)
-			attributes: true,
-			attributeFilter: ['value']
-		});
-
-		return () => {
-			observer.disconnect();
-		};
+	teardown(() => {
+		observer.disconnect();
 	});
 }
 
@@ -136,7 +124,6 @@ export function bind_select_value(select, get, set = get) {
 		mounting = false;
 	});
 
-	// don't pass get_value, we already initialize it in the effect above
 	init_select(select);
 }
 

From 7019894fd9231cefcc0b4bbd13b6a2d8bb90ccb3 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Sat, 28 Jun 2025 01:37:23 +0200
Subject: [PATCH 009/148] fix: ensure unowned deriveds can add themselves as
 reactions while connected (#16249)

an unowned derived should still add itself as a reaction while it is properly connected, which means it can be cleaned up correctly - and this connection is indicated by it having reactions.

Fixes #15829 and potentially #15853
---
 .changeset/little-kings-smoke.md              |  5 +++
 .../svelte/src/internal/client/runtime.js     |  7 +++-
 packages/svelte/tests/signals/test.ts         | 39 +++++++++++++++++++
 3 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/little-kings-smoke.md

diff --git a/.changeset/little-kings-smoke.md b/.changeset/little-kings-smoke.md
new file mode 100644
index 0000000000..1e7f82352a
--- /dev/null
+++ b/.changeset/little-kings-smoke.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure unowned deriveds can add themselves as reactions while connected
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 56bc157f33..d057bfdf0d 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -294,7 +294,12 @@ export function update_reaction(reaction) {
 				reaction.deps = deps = new_deps;
 			}
 
-			if (!skip_reaction) {
+			if (
+				!skip_reaction ||
+				// Deriveds that already have reactions can cleanup, so we still add them as reactions
+				((flags & DERIVED) !== 0 &&
+					/** @type {import('#client').Derived} */ (reaction).reactions !== null)
+			) {
 				for (i = skipped_deps; i < deps.length; i++) {
 					(deps[i].reactions ??= []).push(reaction);
 				}
diff --git a/packages/svelte/tests/signals/test.ts b/packages/svelte/tests/signals/test.ts
index 78d7919e0f..719c936df0 100644
--- a/packages/svelte/tests/signals/test.ts
+++ b/packages/svelte/tests/signals/test.ts
@@ -112,6 +112,45 @@ describe('signals', () => {
 		};
 	});
 
+	test('unowned deriveds are not added as reactions but trigger effects', () => {
+		var obj = state<any>(undefined);
+
+		class C1 {
+			#v = state(0);
+			get v() {
+				return $.get(this.#v);
+			}
+			set v(v: number) {
+				set(this.#v, v);
+			}
+		}
+
+		return () => {
+			let d = derived(() => $.get(obj)?.v || '-');
+
+			const log: number[] = [];
+			assert.equal($.get(d), '-');
+
+			let destroy = effect_root(() => {
+				render_effect(() => {
+					log.push($.get(d));
+				});
+			});
+
+			set(obj, new C1());
+			flushSync();
+			assert.equal($.get(d), '-');
+			$.get(obj).v = 1;
+			flushSync();
+			assert.equal($.get(d), 1);
+			assert.deepEqual(log, ['-', 1]);
+			destroy();
+			// ensure we're not leaking reactions
+			assert.equal(obj.reactions, null);
+			assert.equal(d.reactions, null);
+		};
+	});
+
 	test('derived from state', () => {
 		const log: number[] = [];
 

From cf9f8c9c6b59544e0106634606d09a5e1a93375b Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Sat, 28 Jun 2025 10:35:51 +0200
Subject: [PATCH 010/148] Version Packages (#16257)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/little-kings-smoke.md | 5 -----
 packages/svelte/CHANGELOG.md     | 6 ++++++
 packages/svelte/package.json     | 2 +-
 packages/svelte/src/version.js   | 2 +-
 4 files changed, 8 insertions(+), 7 deletions(-)
 delete mode 100644 .changeset/little-kings-smoke.md

diff --git a/.changeset/little-kings-smoke.md b/.changeset/little-kings-smoke.md
deleted file mode 100644
index 1e7f82352a..0000000000
--- a/.changeset/little-kings-smoke.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: ensure unowned deriveds can add themselves as reactions while connected
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index e254be754f..ef64091ca3 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,11 @@
 # svelte
 
+## 5.34.9
+
+### Patch Changes
+
+- fix: ensure unowned deriveds can add themselves as reactions while connected ([#16249](https://github.com/sveltejs/svelte/pull/16249))
+
 ## 5.34.8
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 17a3e980c4..1d26663143 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.34.8",
+  "version": "5.34.9",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index ec0126b17d..1c0aed6e87 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.34.8';
+export const VERSION = '5.34.9';
 export const PUBLIC_VERSION = '5';

From e896c55b6cc1ec9064cd32ec097ea31d717e29e4 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 30 Jun 2025 08:59:35 -0400
Subject: [PATCH 011/148] chore: bump esrap (#16240)

* chore: bump esrap

* regenerate
---
 packages/svelte/package.json                  |   4 +-
 .../svelte/scripts/process-messages/index.js  | 318 +++++++++---------
 packages/svelte/src/compiler/errors.js        |   6 +-
 packages/svelte/src/compiler/index.js         |   3 +-
 packages/svelte/src/compiler/legacy.js        |   1 +
 .../src/compiler/phases/1-parse/acorn.js      |  61 +++-
 .../src/compiler/phases/1-parse/index.js      |   2 +
 .../compiler/phases/1-parse/read/context.js   |  11 +-
 .../phases/1-parse/read/expression.js         |  24 +-
 .../compiler/phases/1-parse/read/script.js    |   2 +-
 .../src/compiler/phases/1-parse/state/tag.js  |   7 +-
 .../src/compiler/phases/2-analyze/index.js    |  14 +-
 .../3-transform/client/transform-client.js    |   3 +
 .../src/compiler/phases/3-transform/index.js  |  22 +-
 .../3-transform/server/transform-server.js    |   3 +
 .../svelte/src/compiler/phases/types.d.ts     |   2 +
 .../svelte/src/compiler/types/template.d.ts   |  15 +-
 .../svelte/src/compiler/utils/mapped_code.js  |   9 +-
 packages/svelte/src/compiler/warnings.js      |  21 +-
 packages/svelte/src/internal/client/errors.js |  24 +-
 .../svelte/src/internal/client/warnings.js    |  24 +-
 packages/svelte/src/internal/server/errors.js |   3 +
 packages/svelte/src/internal/shared/errors.js |   6 +
 .../svelte/src/internal/shared/warnings.js    |  10 +-
 packages/svelte/tests/parser-modern/test.ts   |   2 +
 .../_expected/client/index.svelte.js          |   1 +
 .../_expected/server/index.svelte.js          |   1 +
 .../_expected/client/main.svelte.js           |   1 +
 .../_expected/server/main.svelte.js           |   1 +
 .../_expected/client/index.svelte.js          |   2 +
 .../_expected/server/index.svelte.js          |   2 +
 .../_expected/client/index.svelte.js          |   1 +
 .../_expected/client/index.svelte.js          |   4 +-
 .../_expected/server/index.svelte.js          |   4 +-
 packages/svelte/types/index.d.ts              |  15 +-
 pnpm-lock.yaml                                |  10 +-
 36 files changed, 398 insertions(+), 241 deletions(-)

diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 1d26663143..2d88d2a051 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -164,14 +164,14 @@
   "dependencies": {
     "@ampproject/remapping": "^2.3.0",
     "@jridgewell/sourcemap-codec": "^1.5.0",
+    "@sveltejs/acorn-typescript": "^1.0.5",
     "@types/estree": "^1.0.5",
     "acorn": "^8.12.1",
-    "@sveltejs/acorn-typescript": "^1.0.5",
     "aria-query": "^5.3.1",
     "axobject-query": "^4.1.0",
     "clsx": "^2.1.1",
     "esm-env": "^1.2.1",
-    "esrap": "^1.4.8",
+    "esrap": "^2.0.0",
     "is-reference": "^3.0.3",
     "locate-character": "^3.0.0",
     "magic-string": "^0.30.11",
diff --git a/packages/svelte/scripts/process-messages/index.js b/packages/svelte/scripts/process-messages/index.js
index 81c59271de..e705a1c921 100644
--- a/packages/svelte/scripts/process-messages/index.js
+++ b/packages/svelte/scripts/process-messages/index.js
@@ -1,9 +1,14 @@
+/** @import { Node } from 'esrap/languages/ts' */
+/** @import * as ESTree from 'estree' */
+/** @import { AST } from 'svelte/compiler' */
+
 // @ts-check
 import process from 'node:process';
 import fs from 'node:fs';
 import * as acorn from 'acorn';
 import { walk } from 'zimmerframe';
 import * as esrap from 'esrap';
+import ts from 'esrap/languages/ts';
 
 const DIR = '../../documentation/docs/98-reference/.generated';
 
@@ -97,79 +102,49 @@ function run() {
 			.readFileSync(new URL(`./templates/${name}.js`, import.meta.url), 'utf-8')
 			.replace(/\r\n/g, '\n');
 
-		/**
-		 * @type {Array<{
-		 * 	type: string;
-		 * 	value: string;
-		 * 	start: number;
-		 * 	end: number
-		 * }>}
-		 */
+		/** @type {AST.JSComment[]} */
 		const comments = [];
 
-		let ast = acorn.parse(source, {
-			ecmaVersion: 'latest',
-			sourceType: 'module',
-			onComment: (block, value, start, end) => {
-				if (block && /\n/.test(value)) {
-					let a = start;
-					while (a > 0 && source[a - 1] !== '\n') a -= 1;
-
-					let b = a;
-					while (/[ \t]/.test(source[b])) b += 1;
-
-					const indentation = source.slice(a, b);
-					value = value.replace(new RegExp(`^${indentation}`, 'gm'), '');
-				}
+		let ast = /** @type {ESTree.Node} */ (
+			/** @type {unknown} */ (
+				acorn.parse(source, {
+					ecmaVersion: 'latest',
+					sourceType: 'module',
+					locations: true,
+					onComment: comments
+				})
+			)
+		);
 
-				comments.push({ type: block ? 'Block' : 'Line', value, start, end });
+		comments.forEach((comment) => {
+			if (comment.type === 'Block') {
+				comment.value = comment.value.replace(/^\t+/gm, '');
 			}
 		});
 
 		ast = walk(ast, null, {
-			_(node, { next }) {
-				let comment;
-
-				while (comments[0] && comments[0].start < node.start) {
-					comment = comments.shift();
-					// @ts-expect-error
-					(node.leadingComments ||= []).push(comment);
-				}
-
-				next();
-
-				if (comments[0]) {
-					const slice = source.slice(node.end, comments[0].start);
-
-					if (/^[,) \t]*$/.test(slice)) {
-						// @ts-expect-error
-						node.trailingComments = [comments.shift()];
-					}
-				}
-			},
-			// @ts-expect-error
 			Identifier(node, context) {
 				if (node.name === 'CODES') {
-					return {
+					/** @type {ESTree.ArrayExpression} */
+					const array = {
 						type: 'ArrayExpression',
 						elements: Object.keys(messages[name]).map((code) => ({
 							type: 'Literal',
 							value: code
 						}))
 					};
+
+					return array;
 				}
 			}
 		});
 
-		if (comments.length > 0) {
-			// @ts-expect-error
-			(ast.trailingComments ||= []).push(...comments);
-		}
+		const body = /** @type {ESTree.Program} */ (ast).body;
 
 		const category = messages[name];
 
 		// find the `export function CODE` node
-		const index = ast.body.findIndex((node) => {
+		const index = body.findIndex((node) => {
 			if (
 				node.type === 'ExportNamedDeclaration' &&
 				node.declaration &&
@@ -181,8 +156,19 @@ function run() {
 
 		if (index === -1) throw new Error(`missing export function CODE in ${name}.js`);
 
-		const template_node = ast.body[index];
-		ast.body.splice(index, 1);
+		const template_node = body[index];
+		body.splice(index, 1);
+
+		const jsdoc = /** @type {AST.JSComment} */ (
+			comments.findLast((comment) => comment.start < /** @type {number} */ (template_node.start))
+		);
+
+		const printed = esrap.print(
+			/** @type {Node} */ (ast),
+			ts({
+				comments: comments.filter((comment) => comment !== jsdoc)
+			})
+		);
 
 		for (const code in category) {
 			const { messages } = category[code];
@@ -203,7 +189,7 @@ function run() {
 				};
 			});
 
-			/** @type {import('estree').Expression} */
+			/** @type {ESTree.Expression} */
 			let message = { type: 'Literal', value: '' };
 			let prev_vars;
 
@@ -221,10 +207,10 @@ function run() {
 
 				const parts = text.split(/(%\w+%)/);
 
-				/** @type {import('estree').Expression[]} */
+				/** @type {ESTree.Expression[]} */
 				const expressions = [];
 
-				/** @type {import('estree').TemplateElement[]} */
+				/** @type {ESTree.TemplateElement[]} */
 				const quasis = [];
 
 				for (let i = 0; i < parts.length; i += 1) {
@@ -244,7 +230,7 @@ function run() {
 					}
 				}
 
-				/** @type {import('estree').Expression} */
+				/** @type {ESTree.Expression} */
 				const expression = {
 					type: 'TemplateLiteral',
 					expressions,
@@ -272,138 +258,140 @@ function run() {
 				prev_vars = vars;
 			}
 
-			const clone = walk(/** @type {import('estree').Node} */ (template_node), null, {
-				// @ts-expect-error Block is a block comment, which is not recognised
-				Block(node, context) {
-					if (!node.value.includes('PARAMETER')) return;
-
-					const value = /** @type {string} */ (node.value)
-						.split('\n')
-						.map((line) => {
-							if (line === ' * MESSAGE') {
-								return messages[messages.length - 1]
-									.split('\n')
-									.map((line) => ` * ${line}`)
-									.join('\n');
-							}
+			const clone = /** @type {ESTree.Statement} */ (
+				walk(/** @type {ESTree.Node} */ (template_node), null, {
+					FunctionDeclaration(node, context) {
+						if (node.id.name !== 'CODE') return;
 
-							if (line.includes('PARAMETER')) {
-								return vars
-									.map((name, i) => {
-										const optional = i >= group[0].vars.length;
+						const params = [];
 
-										return optional
-											? ` * @param {string | undefined | null} [${name}]`
-											: ` * @param {string} ${name}`;
-									})
-									.join('\n');
+						for (const param of node.params) {
+							if (param.type === 'Identifier' && param.name === 'PARAMETER') {
+								params.push(...vars.map((name) => ({ type: 'Identifier', name })));
+							} else {
+								params.push(param);
 							}
+						}
 
-							return line;
-						})
-						.filter((x) => x !== '')
-						.join('\n');
+						return /** @type {ESTree.FunctionDeclaration} */ ({
+							.../** @type {ESTree.FunctionDeclaration} */ (context.next()),
+							params,
+							id: {
+								...node.id,
+								name: code
+							}
+						});
+					},
+					TemplateLiteral(node, context) {
+						/** @type {ESTree.TemplateElement} */
+						let quasi = {
+							type: 'TemplateElement',
+							value: {
+								...node.quasis[0].value
+							},
+							tail: node.quasis[0].tail
+						};
 
-					if (value !== node.value) {
-						return { ...node, value };
-					}
-				},
-				FunctionDeclaration(node, context) {
-					if (node.id.name !== 'CODE') return;
+						/** @type {ESTree.TemplateLiteral} */
+						let out = {
+							type: 'TemplateLiteral',
+							quasis: [quasi],
+							expressions: []
+						};
 
-					const params = [];
+						for (let i = 0; i < node.expressions.length; i += 1) {
+							const q = structuredClone(node.quasis[i + 1]);
+							const e = node.expressions[i];
 
-					for (const param of node.params) {
-						if (param.type === 'Identifier' && param.name === 'PARAMETER') {
-							params.push(...vars.map((name) => ({ type: 'Identifier', name })));
-						} else {
-							params.push(param);
-						}
-					}
+							if (e.type === 'Literal' && e.value === 'CODE') {
+								quasi.value.raw += code + q.value.raw;
+								continue;
+							}
 
-					return /** @type {import('estree').FunctionDeclaration} */ ({
-						.../** @type {import('estree').FunctionDeclaration} */ (context.next()),
-						params,
-						id: {
-							...node.id,
-							name: code
-						}
-					});
-				},
-				TemplateLiteral(node, context) {
-					/** @type {import('estree').TemplateElement} */
-					let quasi = {
-						type: 'TemplateElement',
-						value: {
-							...node.quasis[0].value
-						},
-						tail: node.quasis[0].tail
-					};
+							if (e.type === 'Identifier' && e.name === 'MESSAGE') {
+								if (message.type === 'Literal') {
+									const str = /** @type {string} */ (message.value).replace(/(`|\${)/g, '\\$1');
+									quasi.value.raw += str + q.value.raw;
+									continue;
+								}
+
+								if (message.type === 'TemplateLiteral') {
+									const m = structuredClone(message);
+									quasi.value.raw += m.quasis[0].value.raw;
+									out.quasis.push(...m.quasis.slice(1));
+									out.expressions.push(...m.expressions);
+									quasi = m.quasis[m.quasis.length - 1];
+									quasi.value.raw += q.value.raw;
+									continue;
+								}
+							}
 
-					/** @type {import('estree').TemplateLiteral} */
-					let out = {
-						type: 'TemplateLiteral',
-						quasis: [quasi],
-						expressions: []
-					};
+							out.quasis.push((quasi = q));
+							out.expressions.push(/** @type {ESTree.Expression} */ (context.visit(e)));
+						}
 
-					for (let i = 0; i < node.expressions.length; i += 1) {
-						const q = structuredClone(node.quasis[i + 1]);
-						const e = node.expressions[i];
+						return out;
+					},
+					Literal(node) {
+						if (node.value === 'CODE') {
+							return {
+								type: 'Literal',
+								value: code
+							};
+						}
+					},
+					Identifier(node) {
+						if (node.name !== 'MESSAGE') return;
+						return message;
+					}
+				})
+			);
 
-						if (e.type === 'Literal' && e.value === 'CODE') {
-							quasi.value.raw += code + q.value.raw;
-							continue;
+			const jsdoc_clone = {
+				...jsdoc,
+				value: /** @type {string} */ (jsdoc.value)
+					.split('\n')
+					.map((line) => {
+						if (line === ' * MESSAGE') {
+							return messages[messages.length - 1]
+								.split('\n')
+								.map((line) => ` * ${line}`)
+								.join('\n');
 						}
 
-						if (e.type === 'Identifier' && e.name === 'MESSAGE') {
-							if (message.type === 'Literal') {
-								const str = /** @type {string} */ (message.value).replace(/(`|\${)/g, '\\$1');
-								quasi.value.raw += str + q.value.raw;
-								continue;
-							}
+						if (line.includes('PARAMETER')) {
+							return vars
+								.map((name, i) => {
+									const optional = i >= group[0].vars.length;
 
-							if (message.type === 'TemplateLiteral') {
-								const m = structuredClone(message);
-								quasi.value.raw += m.quasis[0].value.raw;
-								out.quasis.push(...m.quasis.slice(1));
-								out.expressions.push(...m.expressions);
-								quasi = m.quasis[m.quasis.length - 1];
-								quasi.value.raw += q.value.raw;
-								continue;
-							}
+									return optional
+										? ` * @param {string | undefined | null} [${name}]`
+										: ` * @param {string} ${name}`;
+								})
+								.join('\n');
 						}
 
-						out.quasis.push((quasi = q));
-						out.expressions.push(/** @type {import('estree').Expression} */ (context.visit(e)));
-					}
+						return line;
+					})
+					.filter((x) => x !== '')
+					.join('\n')
+			};
 
-					return out;
-				},
-				Literal(node) {
-					if (node.value === 'CODE') {
-						return {
-							type: 'Literal',
-							value: code
-						};
-					}
-				},
-				Identifier(node) {
-					if (node.name !== 'MESSAGE') return;
-					return message;
-				}
-			});
+			const block = esrap.print(
+				// @ts-expect-error some bullshit
+				/** @type {ESTree.Program} */ ({ ...ast, body: [clone] }),
+				ts({ comments: [jsdoc_clone] })
+			).code;
 
-			// @ts-expect-error
-			ast.body.push(clone);
-		}
+			printed.code += `\n\n${block}`;
 
-		const module = esrap.print(ast);
+			body.push(clone);
+		}
 
 		fs.writeFileSync(
 			dest,
 			`/* This file is generated by scripts/process-messages/index.js. Do not edit! */\n\n` +
-				module.code,
+				printed.code,
 			'utf-8'
 		);
 	}
diff --git a/packages/svelte/src/compiler/errors.js b/packages/svelte/src/compiler/errors.js
index 25e72340c6..e9fa33b054 100644
--- a/packages/svelte/src/compiler/errors.js
+++ b/packages/svelte/src/compiler/errors.js
@@ -15,10 +15,12 @@ class InternalCompileError extends Error {
 	constructor(code, message, position) {
 		super(message);
 		this.stack = ''; // avoid unnecessary noise; don't set it as a class property or it becomes enumerable
+
 		// We want to extend from Error so that various bundler plugins properly handle it.
 		// But we also want to share the same object shape with that of warnings, therefore
 		// we create an instance of the shared class an copy over its properties.
 		this.#diagnostic = new CompileDiagnostic(code, message, position);
+
 		Object.assign(this, this.#diagnostic);
 		this.name = 'CompileError';
 	}
@@ -816,7 +818,9 @@ export function bind_invalid_expression(node) {
  * @returns {never}
  */
 export function bind_invalid_name(node, name, explanation) {
-	e(node, 'bind_invalid_name', `${explanation ? `\`bind:${name}\` is not a valid binding. ${explanation}` : `\`bind:${name}\` is not a valid binding`}\nhttps://svelte.dev/e/bind_invalid_name`);
+	e(node, 'bind_invalid_name', `${explanation
+		? `\`bind:${name}\` is not a valid binding. ${explanation}`
+		: `\`bind:${name}\` is not a valid binding`}\nhttps://svelte.dev/e/bind_invalid_name`);
 }
 
 /**
diff --git a/packages/svelte/src/compiler/index.js b/packages/svelte/src/compiler/index.js
index 756a88a824..429c6b4a6f 100644
--- a/packages/svelte/src/compiler/index.js
+++ b/packages/svelte/src/compiler/index.js
@@ -3,7 +3,6 @@
 /** @import { AST } from './public.js' */
 import { walk as zimmerframe_walk } from 'zimmerframe';
 import { convert } from './legacy.js';
-import { parse as parse_acorn } from './phases/1-parse/acorn.js';
 import { parse as _parse } from './phases/1-parse/index.js';
 import { remove_typescript_nodes } from './phases/1-parse/remove_typescript_nodes.js';
 import { analyze_component, analyze_module } from './phases/2-analyze/index.js';
@@ -69,7 +68,7 @@ export function compileModule(source, options) {
 	const validated = validate_module_options(options, '');
 	state.reset(source, validated);
 
-	const analysis = analyze_module(parse_acorn(source, false), validated);
+	const analysis = analyze_module(source, validated);
 	return transform_module(analysis, source, validated);
 }
 
diff --git a/packages/svelte/src/compiler/legacy.js b/packages/svelte/src/compiler/legacy.js
index f6b7e4b054..85345bca4a 100644
--- a/packages/svelte/src/compiler/legacy.js
+++ b/packages/svelte/src/compiler/legacy.js
@@ -451,6 +451,7 @@ export function convert(source, ast) {
 			SpreadAttribute(node) {
 				return { ...node, type: 'Spread' };
 			},
+			// @ts-ignore
 			StyleSheet(node, context) {
 				return {
 					...node,
diff --git a/packages/svelte/src/compiler/phases/1-parse/acorn.js b/packages/svelte/src/compiler/phases/1-parse/acorn.js
index 26a09abb66..77ce4a461c 100644
--- a/packages/svelte/src/compiler/phases/1-parse/acorn.js
+++ b/packages/svelte/src/compiler/phases/1-parse/acorn.js
@@ -1,18 +1,32 @@
 /** @import { Comment, Program } from 'estree' */
+/** @import { AST } from '#compiler' */
 import * as acorn from 'acorn';
 import { walk } from 'zimmerframe';
 import { tsPlugin } from '@sveltejs/acorn-typescript';
 
 const ParserWithTS = acorn.Parser.extend(tsPlugin());
 
+/**
+ * @typedef {Comment & {
+ *   start: number;
+ *   end: number;
+ * }} CommentWithLocation
+ */
+
 /**
  * @param {string} source
+ * @param {AST.JSComment[]} comments
  * @param {boolean} typescript
  * @param {boolean} [is_script]
  */
-export function parse(source, typescript, is_script) {
+export function parse(source, comments, typescript, is_script) {
 	const parser = typescript ? ParserWithTS : acorn.Parser;
-	const { onComment, add_comments } = get_comment_handlers(source);
+
+	const { onComment, add_comments } = get_comment_handlers(
+		source,
+		/** @type {CommentWithLocation[]} */ (comments)
+	);
+
 	// @ts-ignore
 	const parse_statement = parser.prototype.parseStatement;
 
@@ -53,13 +67,19 @@ export function parse(source, typescript, is_script) {
 
 /**
  * @param {string} source
+ * @param {Comment[]} comments
  * @param {boolean} typescript
  * @param {number} index
  * @returns {acorn.Expression & { leadingComments?: CommentWithLocation[]; trailingComments?: CommentWithLocation[]; }}
  */
-export function parse_expression_at(source, typescript, index) {
+export function parse_expression_at(source, comments, typescript, index) {
 	const parser = typescript ? ParserWithTS : acorn.Parser;
-	const { onComment, add_comments } = get_comment_handlers(source);
+
+	const { onComment, add_comments } = get_comment_handlers(
+		source,
+		/** @type {CommentWithLocation[]} */ (comments),
+		index
+	);
 
 	const ast = parser.parseExpressionAt(source, index, {
 		onComment,
@@ -78,26 +98,20 @@ export function parse_expression_at(source, typescript, index) {
  * to add them after the fact. They are needed in order to support `svelte-ignore` comments
  * in JS code and so that `prettier-plugin-svelte` doesn't remove all comments when formatting.
  * @param {string} source
+ * @param {CommentWithLocation[]} comments
+ * @param {number} index
  */
-function get_comment_handlers(source) {
-	/**
-	 * @typedef {Comment & {
-	 *   start: number;
-	 *   end: number;
-	 * }} CommentWithLocation
-	 */
-
-	/** @type {CommentWithLocation[]} */
-	const comments = [];
-
+function get_comment_handlers(source, comments, index = 0) {
 	return {
 		/**
 		 * @param {boolean} block
 		 * @param {string} value
 		 * @param {number} start
 		 * @param {number} end
+		 * @param {import('acorn').Position} [start_loc]
+		 * @param {import('acorn').Position} [end_loc]
 		 */
-		onComment: (block, value, start, end) => {
+		onComment: (block, value, start, end, start_loc, end_loc) => {
 			if (block && /\n/.test(value)) {
 				let a = start;
 				while (a > 0 && source[a - 1] !== '\n') a -= 1;
@@ -109,13 +123,26 @@ function get_comment_handlers(source) {
 				value = value.replace(new RegExp(`^${indentation}`, 'gm'), '');
 			}
 
-			comments.push({ type: block ? 'Block' : 'Line', value, start, end });
+			comments.push({
+				type: block ? 'Block' : 'Line',
+				value,
+				start,
+				end,
+				loc: {
+					start: /** @type {import('acorn').Position} */ (start_loc),
+					end: /** @type {import('acorn').Position} */ (end_loc)
+				}
+			});
 		},
 
 		/** @param {acorn.Node & { leadingComments?: CommentWithLocation[]; trailingComments?: CommentWithLocation[]; }} ast */
 		add_comments(ast) {
 			if (comments.length === 0) return;
 
+			comments = comments
+				.filter((comment) => comment.start >= index)
+				.map(({ type, value, start, end }) => ({ type, value, start, end }));
+
 			walk(ast, null, {
 				_(node, { next, path }) {
 					let comment;
diff --git a/packages/svelte/src/compiler/phases/1-parse/index.js b/packages/svelte/src/compiler/phases/1-parse/index.js
index 6cc5b58aa6..b8ae8199eb 100644
--- a/packages/svelte/src/compiler/phases/1-parse/index.js
+++ b/packages/svelte/src/compiler/phases/1-parse/index.js
@@ -1,4 +1,5 @@
 /** @import { AST } from '#compiler' */
+/** @import { Comment } from 'estree' */
 // @ts-expect-error acorn type definitions are borked in the release we use
 import { isIdentifierStart, isIdentifierChar } from 'acorn';
 import fragment from './state/fragment.js';
@@ -87,6 +88,7 @@ export class Parser {
 			type: 'Root',
 			fragment: create_fragment(),
 			options: null,
+			comments: [],
 			metadata: {
 				ts: this.ts
 			}
diff --git a/packages/svelte/src/compiler/phases/1-parse/read/context.js b/packages/svelte/src/compiler/phases/1-parse/read/context.js
index b118901830..282288e2a2 100644
--- a/packages/svelte/src/compiler/phases/1-parse/read/context.js
+++ b/packages/svelte/src/compiler/phases/1-parse/read/context.js
@@ -59,7 +59,12 @@ export default function read_pattern(parser) {
 			space_with_newline.slice(0, first_space) + space_with_newline.slice(first_space + 1);
 
 		const expression = /** @type {any} */ (
-			parse_expression_at(`${space_with_newline}(${pattern_string} = 1)`, parser.ts, start - 1)
+			parse_expression_at(
+				`${space_with_newline}(${pattern_string} = 1)`,
+				parser.root.comments,
+				parser.ts,
+				start - 1
+			)
 		).left;
 
 		expression.typeAnnotation = read_type_annotation(parser);
@@ -96,13 +101,13 @@ function read_type_annotation(parser) {
 		// parameters as part of a sequence expression instead, and will then error on optional
 		// parameters (`?:`). Therefore replace that sequence with something that will not error.
 		parser.template.slice(parser.index).replace(/\?\s*:/g, ':');
-	let expression = parse_expression_at(template, parser.ts, a);
+	let expression = parse_expression_at(template, parser.root.comments, parser.ts, a);
 
 	// `foo: bar = baz` gets mangled — fix it
 	if (expression.type === 'AssignmentExpression') {
 		let b = expression.right.start;
 		while (template[b] !== '=') b -= 1;
-		expression = parse_expression_at(template.slice(0, b), parser.ts, a);
+		expression = parse_expression_at(template.slice(0, b), parser.root.comments, parser.ts, a);
 	}
 
 	// `array as item: string, index` becomes `string, index`, which is mistaken as a sequence expression - fix that
diff --git a/packages/svelte/src/compiler/phases/1-parse/read/expression.js b/packages/svelte/src/compiler/phases/1-parse/read/expression.js
index a596cdf572..5d21f85792 100644
--- a/packages/svelte/src/compiler/phases/1-parse/read/expression.js
+++ b/packages/svelte/src/compiler/phases/1-parse/read/expression.js
@@ -34,12 +34,24 @@ export function get_loose_identifier(parser, opening_token) {
  */
 export default function read_expression(parser, opening_token, disallow_loose) {
 	try {
-		const node = parse_expression_at(parser.template, parser.ts, parser.index);
+		let comment_index = parser.root.comments.length;
+
+		const node = parse_expression_at(
+			parser.template,
+			parser.root.comments,
+			parser.ts,
+			parser.index
+		);
 
 		let num_parens = 0;
 
-		if (node.leadingComments !== undefined && node.leadingComments.length > 0) {
-			parser.index = node.leadingComments.at(-1).end;
+		let i = parser.root.comments.length;
+		while (i-- > comment_index) {
+			const comment = parser.root.comments[i];
+			if (comment.end < node.start) {
+				parser.index = comment.end;
+				break;
+			}
 		}
 
 		for (let i = parser.index; i < /** @type {number} */ (node.start); i += 1) {
@@ -47,9 +59,9 @@ export default function read_expression(parser, opening_token, disallow_loose) {
 		}
 
 		let index = /** @type {number} */ (node.end);
-		if (node.trailingComments !== undefined && node.trailingComments.length > 0) {
-			index = node.trailingComments.at(-1).end;
-		}
+
+		const last_comment = parser.root.comments.at(-1);
+		if (last_comment && last_comment.end > index) index = last_comment.end;
 
 		while (num_parens > 0) {
 			const char = parser.template[index];
diff --git a/packages/svelte/src/compiler/phases/1-parse/read/script.js b/packages/svelte/src/compiler/phases/1-parse/read/script.js
index 6290127811..9ce449f200 100644
--- a/packages/svelte/src/compiler/phases/1-parse/read/script.js
+++ b/packages/svelte/src/compiler/phases/1-parse/read/script.js
@@ -34,7 +34,7 @@ export function read_script(parser, start, attributes) {
 	let ast;
 
 	try {
-		ast = acorn.parse(source, parser.ts, true);
+		ast = acorn.parse(source, parser.root.comments, parser.ts, true);
 	} catch (err) {
 		parser.acorn_error(err);
 	}
diff --git a/packages/svelte/src/compiler/phases/1-parse/state/tag.js b/packages/svelte/src/compiler/phases/1-parse/state/tag.js
index 5d77d6a8f4..ba091ef7ec 100644
--- a/packages/svelte/src/compiler/phases/1-parse/state/tag.js
+++ b/packages/svelte/src/compiler/phases/1-parse/state/tag.js
@@ -398,7 +398,12 @@ function open(parser) {
 
 		let function_expression = matched
 			? /** @type {ArrowFunctionExpression} */ (
-					parse_expression_at(prelude + `${params} => {}`, parser.ts, params_start)
+					parse_expression_at(
+						prelude + `${params} => {}`,
+						parser.root.comments,
+						parser.ts,
+						params_start
+					)
 				)
 			: { params: [] };
 
diff --git a/packages/svelte/src/compiler/phases/2-analyze/index.js b/packages/svelte/src/compiler/phases/2-analyze/index.js
index 80adc10c1a..be1f1ee5bb 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/index.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/index.js
@@ -1,8 +1,9 @@
-/** @import { Expression, Node, Program } from 'estree' */
+/** @import { Comment, Expression, Node, Program } from 'estree' */
 /** @import { Binding, AST, ValidatedCompileOptions, ValidatedModuleCompileOptions } from '#compiler' */
 /** @import { AnalysisState, Visitors } from './types' */
 /** @import { Analysis, ComponentAnalysis, Js, ReactiveStatement, Template } from '../types' */
 import { walk } from 'zimmerframe';
+import { parse } from '../1-parse/acorn.js';
 import * as e from '../../errors.js';
 import * as w from '../../warnings.js';
 import { extract_identifiers } from '../../utils/ast.js';
@@ -231,11 +232,16 @@ function get_component_name(filename) {
 const RESERVED = ['$$props', '$$restProps', '$$slots'];
 
 /**
- * @param {Program} ast
+ * @param {string} source
  * @param {ValidatedModuleCompileOptions} options
  * @returns {Analysis}
  */
-export function analyze_module(ast, options) {
+export function analyze_module(source, options) {
+	/** @type {AST.JSComment[]} */
+	const comments = [];
+
+	const ast = parse(source, comments, false, false);
+
 	const { scope, scopes } = create_scopes(ast, new ScopeRoot(), false, null);
 
 	for (const [name, references] of scope.references) {
@@ -259,6 +265,7 @@ export function analyze_module(ast, options) {
 		runes: true,
 		immutable: true,
 		tracing: false,
+		comments,
 		classes: new Map()
 	};
 
@@ -429,6 +436,7 @@ export function analyze_component(root, source, options) {
 		module,
 		instance,
 		template,
+		comments: root.comments,
 		elements: [],
 		runes,
 		// if we are not in runes mode but we have no reserved references ($$props, $$restProps)
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js b/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
index e2e006c14b..e85a35cf8e 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
@@ -362,6 +362,9 @@ export function client_component(analysis, options) {
 		.../** @type {ESTree.Statement[]} */ (template.body)
 	]);
 
+	// trick esrap into including comments
+	component_block.loc = instance.loc;
+
 	if (!analysis.runes) {
 		// Bind static exports to props so that people can access them with bind:x
 		for (const { name, alias } of analysis.exports) {
diff --git a/packages/svelte/src/compiler/phases/3-transform/index.js b/packages/svelte/src/compiler/phases/3-transform/index.js
index f96fd64ec7..33665097ab 100644
--- a/packages/svelte/src/compiler/phases/3-transform/index.js
+++ b/packages/svelte/src/compiler/phases/3-transform/index.js
@@ -1,6 +1,8 @@
+/** @import { Node } from 'esrap/languages/ts' */
 /** @import { ValidatedCompileOptions, CompileResult, ValidatedModuleCompileOptions } from '#compiler' */
 /** @import { ComponentAnalysis, Analysis } from '../types' */
 import { print } from 'esrap';
+import ts from 'esrap/languages/ts';
 import { VERSION } from '../../../version.js';
 import { server_component, server_module } from './server/transform-server.js';
 import { client_component, client_module } from './client/transform-client.js';
@@ -34,7 +36,7 @@ export function transform_component(analysis, source, options) {
 
 	const js_source_name = get_source_name(options.filename, options.outputFilename, 'input.svelte');
 
-	const js = print(program, {
+	const js = print(/** @type {Node} */ (program), ts({ comments: analysis.comments }), {
 		// include source content; makes it easier/more robust looking up the source map code
 		// (else esrap does return null for source and sourceMapContent which may trip up tooling)
 		sourceMapContent: source,
@@ -93,13 +95,19 @@ export function transform_module(analysis, source, options) {
 		];
 	}
 
+	const js = print(/** @type {Node} */ (program), ts({ comments: analysis.comments }), {
+		// include source content; makes it easier/more robust looking up the source map code
+		// (else esrap does return null for source and sourceMapContent which may trip up tooling)
+		sourceMapContent: source,
+		sourceMapSource: get_source_name(options.filename, undefined, 'input.svelte.js')
+	});
+
+	// prepend comment
+	js.code = `/* ${basename} generated by Svelte v${VERSION} */\n${js.code}`;
+	js.map.mappings = ';' + js.map.mappings;
+
 	return {
-		js: print(program, {
-			// include source content; makes it easier/more robust looking up the source map code
-			// (else esrap does return null for source and sourceMapContent which may trip up tooling)
-			sourceMapContent: source,
-			sourceMapSource: get_source_name(options.filename, undefined, 'input.svelte.js')
-		}),
+		js,
 		css: null,
 		metadata: {
 			runes: true
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/transform-server.js b/packages/svelte/src/compiler/phases/3-transform/server/transform-server.js
index 7a3d6bef6c..86346b864c 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/transform-server.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/transform-server.js
@@ -242,6 +242,9 @@ export function server_component(analysis, options) {
 		.../** @type {Statement[]} */ (template.body)
 	]);
 
+	// trick esrap into including comments
+	component_block.loc = instance.loc;
+
 	if (analysis.props_id) {
 		// need to be placed on first line of the component for hydration
 		component_block.body.unshift(
diff --git a/packages/svelte/src/compiler/phases/types.d.ts b/packages/svelte/src/compiler/phases/types.d.ts
index 8fa4bff619..661f363991 100644
--- a/packages/svelte/src/compiler/phases/types.d.ts
+++ b/packages/svelte/src/compiler/phases/types.d.ts
@@ -2,6 +2,7 @@ import type { AST, Binding, StateField } from '#compiler';
 import type {
 	AssignmentExpression,
 	ClassBody,
+	Comment,
 	Identifier,
 	LabeledStatement,
 	Node,
@@ -37,6 +38,7 @@ export interface Analysis {
 	runes: boolean;
 	immutable: boolean;
 	tracing: boolean;
+	comments: AST.JSComment[];
 
 	classes: Map<ClassBody, Map<string, StateField>>;
 
diff --git a/packages/svelte/src/compiler/types/template.d.ts b/packages/svelte/src/compiler/types/template.d.ts
index 2a7ec7b5c6..c9841e9d4e 100644
--- a/packages/svelte/src/compiler/types/template.d.ts
+++ b/packages/svelte/src/compiler/types/template.d.ts
@@ -72,6 +72,8 @@ export namespace AST {
 		instance: Script | null;
 		/** The parsed `<script module>` element, if exists */
 		module: Script | null;
+		/** Comments found in <script> and {expressions} */
+		comments: JSComment[];
 		/** @internal */
 		metadata: {
 			/** Whether the component was parsed with typescript */
@@ -537,6 +539,17 @@ export namespace AST {
 		attributes: Attribute[];
 	}
 
+	export interface JSComment {
+		type: 'Line' | 'Block';
+		value: string;
+		start: number;
+		end: number;
+		loc: {
+			start: { line: number; column: number };
+			end: { line: number; column: number };
+		};
+	}
+
 	export type AttributeLike = Attribute | SpreadAttribute | Directive;
 
 	export type Directive =
@@ -593,7 +606,7 @@ export namespace AST {
 		| AST.Comment
 		| Block;
 
-	export type SvelteNode = Node | TemplateNode | AST.Fragment | _CSS.Node;
+	export type SvelteNode = Node | TemplateNode | AST.Fragment | _CSS.Node | Script;
 
 	export type { _CSS as CSS };
 }
diff --git a/packages/svelte/src/compiler/utils/mapped_code.js b/packages/svelte/src/compiler/utils/mapped_code.js
index 089078af7f..f23e3be245 100644
--- a/packages/svelte/src/compiler/utils/mapped_code.js
+++ b/packages/svelte/src/compiler/utils/mapped_code.js
@@ -398,10 +398,13 @@ export function merge_with_preprocessor_map(result, options, source_name) {
 		// map may contain a different file name. Patch our map beforehand to align sources so merging
 		// with the preprocessor map works correctly.
 		result.map.sources = [file_basename];
-		result.map = apply_preprocessor_sourcemap(
-			file_basename,
+		Object.assign(
 			result.map,
-			/** @type {any} */ (options.sourcemap)
+			apply_preprocessor_sourcemap(
+				file_basename,
+				result.map,
+				/** @type {any} */ (options.sourcemap)
+			)
 		);
 		// After applying the preprocessor map, we need to do the inverse and make the sources
 		// relative to the input file again in case the output code is in a different directory.
diff --git a/packages/svelte/src/compiler/warnings.js b/packages/svelte/src/compiler/warnings.js
index 1226190891..8c03e12e71 100644
--- a/packages/svelte/src/compiler/warnings.js
+++ b/packages/svelte/src/compiler/warnings.js
@@ -1,12 +1,6 @@
 /* This file is generated by scripts/process-messages/index.js. Do not edit! */
 
-import {
-	warnings,
-	ignore_stack,
-	ignore_map,
-	warning_filter
-} from './state.js';
-
+import { warnings, ignore_stack, ignore_map, warning_filter } from './state.js';
 import { CompileDiagnostic } from './utils/compile_diagnostic.js';
 
 /** @typedef {{ start?: number, end?: number }} NodeLike */
@@ -40,6 +34,7 @@ function w(node, code, message) {
 	const warning = new InternalCompileWarning(code, message, node && node.start !== undefined ? [node.start, node.end ?? node.start] : undefined);
 
 	if (!warning_filter(warning)) return;
+
 	warnings.push(warning);
 }
 
@@ -496,7 +491,9 @@ export function a11y_role_supports_aria_props_implicit(node, attribute, role, na
  * @param {string | undefined | null} [suggestion]
  */
 export function a11y_unknown_aria_attribute(node, attribute, suggestion) {
-	w(node, 'a11y_unknown_aria_attribute', `${suggestion ? `Unknown aria attribute 'aria-${attribute}'. Did you mean '${suggestion}'?` : `Unknown aria attribute 'aria-${attribute}'`}\nhttps://svelte.dev/e/a11y_unknown_aria_attribute`);
+	w(node, 'a11y_unknown_aria_attribute', `${suggestion
+		? `Unknown aria attribute 'aria-${attribute}'. Did you mean '${suggestion}'?`
+		: `Unknown aria attribute 'aria-${attribute}'`}\nhttps://svelte.dev/e/a11y_unknown_aria_attribute`);
 }
 
 /**
@@ -506,7 +503,9 @@ export function a11y_unknown_aria_attribute(node, attribute, suggestion) {
  * @param {string | undefined | null} [suggestion]
  */
 export function a11y_unknown_role(node, role, suggestion) {
-	w(node, 'a11y_unknown_role', `${suggestion ? `Unknown role '${role}'. Did you mean '${suggestion}'?` : `Unknown role '${role}'`}\nhttps://svelte.dev/e/a11y_unknown_role`);
+	w(node, 'a11y_unknown_role', `${suggestion
+		? `Unknown role '${role}'. Did you mean '${suggestion}'?`
+		: `Unknown role '${role}'`}\nhttps://svelte.dev/e/a11y_unknown_role`);
 }
 
 /**
@@ -534,7 +533,9 @@ export function legacy_code(node, code, suggestion) {
  * @param {string | undefined | null} [suggestion]
  */
 export function unknown_code(node, code, suggestion) {
-	w(node, 'unknown_code', `${suggestion ? `\`${code}\` is not a recognised code (did you mean \`${suggestion}\`?)` : `\`${code}\` is not a recognised code`}\nhttps://svelte.dev/e/unknown_code`);
+	w(node, 'unknown_code', `${suggestion
+		? `\`${code}\` is not a recognised code (did you mean \`${suggestion}\`?)`
+		: `\`${code}\` is not a recognised code`}\nhttps://svelte.dev/e/unknown_code`);
 }
 
 /**
diff --git a/packages/svelte/src/internal/client/errors.js b/packages/svelte/src/internal/client/errors.js
index 962593b48d..a0ac021c03 100644
--- a/packages/svelte/src/internal/client/errors.js
+++ b/packages/svelte/src/internal/client/errors.js
@@ -11,6 +11,7 @@ export function bind_invalid_checkbox_value() {
 		const error = new Error(`bind_invalid_checkbox_value\nUsing \`bind:value\` together with a checkbox input is not allowed. Use \`bind:checked\` instead\nhttps://svelte.dev/e/bind_invalid_checkbox_value`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/bind_invalid_checkbox_value`);
@@ -29,6 +30,7 @@ export function bind_invalid_export(component, key, name) {
 		const error = new Error(`bind_invalid_export\nComponent ${component} has an export named \`${key}\` that a consumer component is trying to access using \`bind:${key}\`, which is disallowed. Instead, use \`bind:this\` (e.g. \`<${name} bind:this={component} />\`) and then access the property on the bound component instance (e.g. \`component.${key}\`)\nhttps://svelte.dev/e/bind_invalid_export`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/bind_invalid_export`);
@@ -47,6 +49,7 @@ export function bind_not_bindable(key, component, name) {
 		const error = new Error(`bind_not_bindable\nA component is attempting to bind to a non-bindable property \`${key}\` belonging to ${component} (i.e. \`<${name} bind:${key}={...}>\`). To mark a property as bindable: \`let { ${key} = $bindable() } = $props()\`\nhttps://svelte.dev/e/bind_not_bindable`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/bind_not_bindable`);
@@ -64,6 +67,7 @@ export function component_api_changed(method, component) {
 		const error = new Error(`component_api_changed\nCalling \`${method}\` on a component instance (of ${component}) is no longer valid in Svelte 5\nhttps://svelte.dev/e/component_api_changed`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/component_api_changed`);
@@ -81,6 +85,7 @@ export function component_api_invalid_new(component, name) {
 		const error = new Error(`component_api_invalid_new\nAttempted to instantiate ${component} with \`new ${name}\`, which is no longer valid in Svelte 5. If this component is not under your control, set the \`compatibility.componentApi\` compiler option to \`4\` to keep it working.\nhttps://svelte.dev/e/component_api_invalid_new`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/component_api_invalid_new`);
@@ -96,6 +101,7 @@ export function derived_references_self() {
 		const error = new Error(`derived_references_self\nA derived value cannot reference itself recursively\nhttps://svelte.dev/e/derived_references_self`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/derived_references_self`);
@@ -111,9 +117,12 @@ export function derived_references_self() {
  */
 export function each_key_duplicate(a, b, value) {
 	if (DEV) {
-		const error = new Error(`each_key_duplicate\n${value ? `Keyed each block has duplicate key \`${value}\` at indexes ${a} and ${b}` : `Keyed each block has duplicate key at indexes ${a} and ${b}`}\nhttps://svelte.dev/e/each_key_duplicate`);
+		const error = new Error(`each_key_duplicate\n${value
+			? `Keyed each block has duplicate key \`${value}\` at indexes ${a} and ${b}`
+			: `Keyed each block has duplicate key at indexes ${a} and ${b}`}\nhttps://svelte.dev/e/each_key_duplicate`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/each_key_duplicate`);
@@ -130,6 +139,7 @@ export function effect_in_teardown(rune) {
 		const error = new Error(`effect_in_teardown\n\`${rune}\` cannot be used inside an effect cleanup function\nhttps://svelte.dev/e/effect_in_teardown`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/effect_in_teardown`);
@@ -145,6 +155,7 @@ export function effect_in_unowned_derived() {
 		const error = new Error(`effect_in_unowned_derived\nEffect cannot be created inside a \`$derived\` value that was not itself created inside an effect\nhttps://svelte.dev/e/effect_in_unowned_derived`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/effect_in_unowned_derived`);
@@ -161,6 +172,7 @@ export function effect_orphan(rune) {
 		const error = new Error(`effect_orphan\n\`${rune}\` can only be used inside an effect (e.g. during component initialisation)\nhttps://svelte.dev/e/effect_orphan`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/effect_orphan`);
@@ -176,6 +188,7 @@ export function effect_update_depth_exceeded() {
 		const error = new Error(`effect_update_depth_exceeded\nMaximum update depth exceeded. This can happen when a reactive block or effect repeatedly sets a new value. Svelte limits the number of nested updates to prevent infinite loops\nhttps://svelte.dev/e/effect_update_depth_exceeded`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/effect_update_depth_exceeded`);
@@ -191,6 +204,7 @@ export function hydration_failed() {
 		const error = new Error(`hydration_failed\nFailed to hydrate the application\nhttps://svelte.dev/e/hydration_failed`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/hydration_failed`);
@@ -206,6 +220,7 @@ export function invalid_snippet() {
 		const error = new Error(`invalid_snippet\nCould not \`{@render}\` snippet due to the expression being \`null\` or \`undefined\`. Consider using optional chaining \`{@render snippet?.()}\`\nhttps://svelte.dev/e/invalid_snippet`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/invalid_snippet`);
@@ -222,6 +237,7 @@ export function lifecycle_legacy_only(name) {
 		const error = new Error(`lifecycle_legacy_only\n\`${name}(...)\` cannot be used in runes mode\nhttps://svelte.dev/e/lifecycle_legacy_only`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/lifecycle_legacy_only`);
@@ -238,6 +254,7 @@ export function props_invalid_value(key) {
 		const error = new Error(`props_invalid_value\nCannot do \`bind:${key}={undefined}\` when \`${key}\` has a fallback value\nhttps://svelte.dev/e/props_invalid_value`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/props_invalid_value`);
@@ -254,6 +271,7 @@ export function props_rest_readonly(property) {
 		const error = new Error(`props_rest_readonly\nRest element properties of \`$props()\` such as \`${property}\` are readonly\nhttps://svelte.dev/e/props_rest_readonly`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/props_rest_readonly`);
@@ -270,6 +288,7 @@ export function rune_outside_svelte(rune) {
 		const error = new Error(`rune_outside_svelte\nThe \`${rune}\` rune is only available inside \`.svelte\` and \`.svelte.js/ts\` files\nhttps://svelte.dev/e/rune_outside_svelte`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/rune_outside_svelte`);
@@ -285,6 +304,7 @@ export function state_descriptors_fixed() {
 		const error = new Error(`state_descriptors_fixed\nProperty descriptors defined on \`$state\` objects must contain \`value\` and always be \`enumerable\`, \`configurable\` and \`writable\`.\nhttps://svelte.dev/e/state_descriptors_fixed`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/state_descriptors_fixed`);
@@ -300,6 +320,7 @@ export function state_prototype_fixed() {
 		const error = new Error(`state_prototype_fixed\nCannot set prototype of \`$state\` object\nhttps://svelte.dev/e/state_prototype_fixed`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/state_prototype_fixed`);
@@ -315,6 +336,7 @@ export function state_unsafe_mutation() {
 		const error = new Error(`state_unsafe_mutation\nUpdating state inside \`$derived(...)\`, \`$inspect(...)\` or a template expression is forbidden. If the value should not be reactive, declare it without \`$state\`\nhttps://svelte.dev/e/state_unsafe_mutation`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/state_unsafe_mutation`);
diff --git a/packages/svelte/src/internal/client/warnings.js b/packages/svelte/src/internal/client/warnings.js
index e07892a4b0..74f9041b91 100644
--- a/packages/svelte/src/internal/client/warnings.js
+++ b/packages/svelte/src/internal/client/warnings.js
@@ -25,7 +25,13 @@ export function assignment_value_stale(property, location) {
  */
 export function binding_property_non_reactive(binding, location) {
 	if (DEV) {
-		console.warn(`%c[svelte] binding_property_non_reactive\n%c${location ? `\`${binding}\` (${location}) is binding to a non-reactive property` : `\`${binding}\` is binding to a non-reactive property`}\nhttps://svelte.dev/e/binding_property_non_reactive`, bold, normal);
+		console.warn(
+			`%c[svelte] binding_property_non_reactive\n%c${location
+				? `\`${binding}\` (${location}) is binding to a non-reactive property`
+				: `\`${binding}\` is binding to a non-reactive property`}\nhttps://svelte.dev/e/binding_property_non_reactive`,
+			bold,
+			normal
+		);
 	} else {
 		console.warn(`https://svelte.dev/e/binding_property_non_reactive`);
 	}
@@ -76,7 +82,13 @@ export function hydration_attribute_changed(attribute, html, value) {
  */
 export function hydration_html_changed(location) {
 	if (DEV) {
-		console.warn(`%c[svelte] hydration_html_changed\n%c${location ? `The value of an \`{@html ...}\` block ${location} changed between server and client renders. The client value will be ignored in favour of the server value` : 'The value of an `{@html ...}` block changed between server and client renders. The client value will be ignored in favour of the server value'}\nhttps://svelte.dev/e/hydration_html_changed`, bold, normal);
+		console.warn(
+			`%c[svelte] hydration_html_changed\n%c${location
+				? `The value of an \`{@html ...}\` block ${location} changed between server and client renders. The client value will be ignored in favour of the server value`
+				: 'The value of an `{@html ...}` block changed between server and client renders. The client value will be ignored in favour of the server value'}\nhttps://svelte.dev/e/hydration_html_changed`,
+			bold,
+			normal
+		);
 	} else {
 		console.warn(`https://svelte.dev/e/hydration_html_changed`);
 	}
@@ -88,7 +100,13 @@ export function hydration_html_changed(location) {
  */
 export function hydration_mismatch(location) {
 	if (DEV) {
-		console.warn(`%c[svelte] hydration_mismatch\n%c${location ? `Hydration failed because the initial UI does not match what was rendered on the server. The error occurred near ${location}` : 'Hydration failed because the initial UI does not match what was rendered on the server'}\nhttps://svelte.dev/e/hydration_mismatch`, bold, normal);
+		console.warn(
+			`%c[svelte] hydration_mismatch\n%c${location
+				? `Hydration failed because the initial UI does not match what was rendered on the server. The error occurred near ${location}`
+				: 'Hydration failed because the initial UI does not match what was rendered on the server'}\nhttps://svelte.dev/e/hydration_mismatch`,
+			bold,
+			normal
+		);
 	} else {
 		console.warn(`https://svelte.dev/e/hydration_mismatch`);
 	}
diff --git a/packages/svelte/src/internal/server/errors.js b/packages/svelte/src/internal/server/errors.js
index 38c545c84e..e47530c9aa 100644
--- a/packages/svelte/src/internal/server/errors.js
+++ b/packages/svelte/src/internal/server/errors.js
@@ -1,5 +1,7 @@
 /* This file is generated by scripts/process-messages/index.js. Do not edit! */
 
+
+
 /**
  * `%name%(...)` is not available on the server
  * @param {string} name
@@ -9,5 +11,6 @@ export function lifecycle_function_unavailable(name) {
 	const error = new Error(`lifecycle_function_unavailable\n\`${name}(...)\` is not available on the server\nhttps://svelte.dev/e/lifecycle_function_unavailable`);
 
 	error.name = 'Svelte error';
+
 	throw error;
 }
\ No newline at end of file
diff --git a/packages/svelte/src/internal/shared/errors.js b/packages/svelte/src/internal/shared/errors.js
index b8606fbf6f..6bcc35016a 100644
--- a/packages/svelte/src/internal/shared/errors.js
+++ b/packages/svelte/src/internal/shared/errors.js
@@ -11,6 +11,7 @@ export function invalid_default_snippet() {
 		const error = new Error(`invalid_default_snippet\nCannot use \`{@render children(...)}\` if the parent component uses \`let:\` directives. Consider using a named snippet instead\nhttps://svelte.dev/e/invalid_default_snippet`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/invalid_default_snippet`);
@@ -26,6 +27,7 @@ export function invalid_snippet_arguments() {
 		const error = new Error(`invalid_snippet_arguments\nA snippet function was passed invalid arguments. Snippets should only be instantiated via \`{@render ...}\`\nhttps://svelte.dev/e/invalid_snippet_arguments`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/invalid_snippet_arguments`);
@@ -42,6 +44,7 @@ export function lifecycle_outside_component(name) {
 		const error = new Error(`lifecycle_outside_component\n\`${name}(...)\` can only be used during component initialisation\nhttps://svelte.dev/e/lifecycle_outside_component`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/lifecycle_outside_component`);
@@ -57,6 +60,7 @@ export function snippet_without_render_tag() {
 		const error = new Error(`snippet_without_render_tag\nAttempted to render a snippet without a \`{@render}\` block. This would cause the snippet code to be stringified instead of its content being rendered to the DOM. To fix this, change \`{snippet}\` to \`{@render snippet()}\`.\nhttps://svelte.dev/e/snippet_without_render_tag`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/snippet_without_render_tag`);
@@ -73,6 +77,7 @@ export function store_invalid_shape(name) {
 		const error = new Error(`store_invalid_shape\n\`${name}\` is not a store with a \`subscribe\` method\nhttps://svelte.dev/e/store_invalid_shape`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/store_invalid_shape`);
@@ -88,6 +93,7 @@ export function svelte_element_invalid_this_value() {
 		const error = new Error(`svelte_element_invalid_this_value\nThe \`this\` prop on \`<svelte:element>\` must be a string, if defined\nhttps://svelte.dev/e/svelte_element_invalid_this_value`);
 
 		error.name = 'Svelte error';
+
 		throw error;
 	} else {
 		throw new Error(`https://svelte.dev/e/svelte_element_invalid_this_value`);
diff --git a/packages/svelte/src/internal/shared/warnings.js b/packages/svelte/src/internal/shared/warnings.js
index 281be08382..0acca44184 100644
--- a/packages/svelte/src/internal/shared/warnings.js
+++ b/packages/svelte/src/internal/shared/warnings.js
@@ -25,11 +25,15 @@ export function dynamic_void_element_content(tag) {
  */
 export function state_snapshot_uncloneable(properties) {
 	if (DEV) {
-		console.warn(`%c[svelte] state_snapshot_uncloneable\n%c${properties
-			? `The following properties cannot be cloned with \`$state.snapshot\` — the return value contains the originals:
+		console.warn(
+			`%c[svelte] state_snapshot_uncloneable\n%c${properties
+				? `The following properties cannot be cloned with \`$state.snapshot\` — the return value contains the originals:
 
 ${properties}`
-			: 'Value cannot be cloned with `$state.snapshot` — the original value was returned'}\nhttps://svelte.dev/e/state_snapshot_uncloneable`, bold, normal);
+				: 'Value cannot be cloned with `$state.snapshot` — the original value was returned'}\nhttps://svelte.dev/e/state_snapshot_uncloneable`,
+			bold,
+			normal
+		);
 	} else {
 		console.warn(`https://svelte.dev/e/state_snapshot_uncloneable`);
 	}
diff --git a/packages/svelte/tests/parser-modern/test.ts b/packages/svelte/tests/parser-modern/test.ts
index b47d4a4879..279ba7bc08 100644
--- a/packages/svelte/tests/parser-modern/test.ts
+++ b/packages/svelte/tests/parser-modern/test.ts
@@ -21,6 +21,8 @@ const { test, run } = suite<ParserTest>(async (config, cwd) => {
 		)
 	);
 
+	delete actual.comments;
+
 	// run `UPDATE_SNAPSHOTS=true pnpm test parser` to update parser tests
 	if (process.env.UPDATE_SNAPSHOTS) {
 		fs.writeFileSync(`${cwd}/output.json`, JSON.stringify(actual, null, '\t'));
diff --git a/packages/svelte/tests/snapshot/samples/bind-component-snippet/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/bind-component-snippet/_expected/client/index.svelte.js
index ba3f4b155a..a87a356d58 100644
--- a/packages/svelte/tests/snapshot/samples/bind-component-snippet/_expected/client/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/bind-component-snippet/_expected/client/index.svelte.js
@@ -22,6 +22,7 @@ export default function Bind_component_snippet($$anchor) {
 		get value() {
 			return $.get(value);
 		},
+
 		set value($$value) {
 			$.set(value, $$value, true);
 		}
diff --git a/packages/svelte/tests/snapshot/samples/bind-component-snippet/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/bind-component-snippet/_expected/server/index.svelte.js
index cadae2cf15..e2c0ee29a5 100644
--- a/packages/svelte/tests/snapshot/samples/bind-component-snippet/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/bind-component-snippet/_expected/server/index.svelte.js
@@ -16,6 +16,7 @@ export default function Bind_component_snippet($$payload) {
 			get value() {
 				return value;
 			},
+
 			set value($$value) {
 				value = $$value;
 				$$settled = false;
diff --git a/packages/svelte/tests/snapshot/samples/dynamic-attributes-casing/_expected/client/main.svelte.js b/packages/svelte/tests/snapshot/samples/dynamic-attributes-casing/_expected/client/main.svelte.js
index 28bb01fb18..d84b674f88 100644
--- a/packages/svelte/tests/snapshot/samples/dynamic-attributes-casing/_expected/client/main.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/dynamic-attributes-casing/_expected/client/main.svelte.js
@@ -6,6 +6,7 @@ var root = $.from_html(`<div></div> <svg></svg> <custom-element></custom-element
 export default function Main($$anchor) {
 	// needs to be a snapshot test because jsdom does auto-correct the attribute casing
 	let x = 'test';
+
 	let y = () => 'test';
 	var fragment = root();
 	var div = $.first_child(fragment);
diff --git a/packages/svelte/tests/snapshot/samples/dynamic-attributes-casing/_expected/server/main.svelte.js b/packages/svelte/tests/snapshot/samples/dynamic-attributes-casing/_expected/server/main.svelte.js
index 4ea5edb6a0..cf731d8187 100644
--- a/packages/svelte/tests/snapshot/samples/dynamic-attributes-casing/_expected/server/main.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/dynamic-attributes-casing/_expected/server/main.svelte.js
@@ -3,6 +3,7 @@ import * as $ from 'svelte/internal/server';
 export default function Main($$payload) {
 	// needs to be a snapshot test because jsdom does auto-correct the attribute casing
 	let x = 'test';
+
 	let y = () => 'test';
 
 	$$payload.out += `<div${$.attr('foobar', x)}></div> <svg${$.attr('viewBox', x)}></svg> <custom-element${$.attr('foobar', x)}></custom-element> <div${$.attr('foobar', y())}></div> <svg${$.attr('viewBox', y())}></svg> <custom-element${$.attr('foobar', y())}></custom-element>`;
diff --git a/packages/svelte/tests/snapshot/samples/function-prop-no-getter/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/function-prop-no-getter/_expected/client/index.svelte.js
index 762a23754c..218951b836 100644
--- a/packages/svelte/tests/snapshot/samples/function-prop-no-getter/_expected/client/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/function-prop-no-getter/_expected/client/index.svelte.js
@@ -14,6 +14,7 @@ export default function Function_prop_no_getter($$anchor) {
 		onmousedown: () => $.set(count, $.get(count) + 1),
 		onmouseup,
 		onmouseenter: () => $.set(count, plusOne($.get(count)), true),
+
 		children: ($$anchor, $$slotProps) => {
 			$.next();
 
@@ -22,6 +23,7 @@ export default function Function_prop_no_getter($$anchor) {
 			$.template_effect(() => $.set_text(text, `clicks: ${$.get(count) ?? ''}`));
 			$.append($$anchor, text);
 		},
+
 		$$slots: { default: true }
 	});
 }
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/function-prop-no-getter/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/function-prop-no-getter/_expected/server/index.svelte.js
index 88f6f55ee7..7d37abd97b 100644
--- a/packages/svelte/tests/snapshot/samples/function-prop-no-getter/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/function-prop-no-getter/_expected/server/index.svelte.js
@@ -13,9 +13,11 @@ export default function Function_prop_no_getter($$payload) {
 		onmousedown: () => count += 1,
 		onmouseup,
 		onmouseenter: () => count = plusOne(count),
+
 		children: ($$payload) => {
 			$$payload.out += `<!---->clicks: ${$.escape(count)}`;
 		},
+
 		$$slots: { default: true }
 	});
 }
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/functional-templating/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/functional-templating/_expected/client/index.svelte.js
index 792d5421e1..d4034dc55d 100644
--- a/packages/svelte/tests/snapshot/samples/functional-templating/_expected/client/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/functional-templating/_expected/client/index.svelte.js
@@ -6,6 +6,7 @@ var root = $.from_tree(
 	[
 		['h1', null, 'hello'],
 		' ',
+
 		[
 			'div',
 			{ class: 'potato' },
diff --git a/packages/svelte/tests/snapshot/samples/imports-in-modules/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/imports-in-modules/_expected/client/index.svelte.js
index ebbe191dcb..0eab38919c 100644
--- a/packages/svelte/tests/snapshot/samples/imports-in-modules/_expected/client/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/imports-in-modules/_expected/client/index.svelte.js
@@ -3,6 +3,4 @@ import 'svelte/internal/flags/legacy';
 import * as $ from 'svelte/internal/client';
 import { random } from './module.svelte';
 
-export default function Imports_in_modules($$anchor) {
-	
-}
\ No newline at end of file
+export default function Imports_in_modules($$anchor) {}
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/imports-in-modules/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/imports-in-modules/_expected/server/index.svelte.js
index 4cd6bc59d7..2ed863d68f 100644
--- a/packages/svelte/tests/snapshot/samples/imports-in-modules/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/imports-in-modules/_expected/server/index.svelte.js
@@ -1,6 +1,4 @@
 import * as $ from 'svelte/internal/server';
 import { random } from './module.svelte';
 
-export default function Imports_in_modules($$payload) {
-	
-}
\ No newline at end of file
+export default function Imports_in_modules($$payload) {}
\ No newline at end of file
diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index 1a83e0d0f1..3401efac04 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -1120,6 +1120,8 @@ declare module 'svelte/compiler' {
 			instance: Script | null;
 			/** The parsed `<script module>` element, if exists */
 			module: Script | null;
+			/** Comments found in <script> and {expressions} */
+			comments: JSComment[];
 		}
 
 		export interface SvelteOptions {
@@ -1437,6 +1439,17 @@ declare module 'svelte/compiler' {
 			attributes: Attribute[];
 		}
 
+		export interface JSComment {
+			type: 'Line' | 'Block';
+			value: string;
+			start: number;
+			end: number;
+			loc: {
+				start: { line: number; column: number };
+				end: { line: number; column: number };
+			};
+		}
+
 		export type AttributeLike = Attribute | SpreadAttribute | Directive;
 
 		export type Directive =
@@ -1493,7 +1506,7 @@ declare module 'svelte/compiler' {
 			| AST.Comment
 			| Block;
 
-		export type SvelteNode = Node | TemplateNode | AST.Fragment | _CSS.Node;
+		export type SvelteNode = Node | TemplateNode | AST.Fragment | _CSS.Node | Script;
 
 		export type { _CSS as CSS };
 	}
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index cfbc54df33..b7fb655b2d 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -87,8 +87,8 @@ importers:
         specifier: ^1.2.1
         version: 1.2.1
       esrap:
-        specifier: ^1.4.8
-        version: 1.4.8
+        specifier: ^2.0.0
+        version: 2.0.0
       is-reference:
         specifier: ^3.0.3
         version: 3.0.3
@@ -1261,8 +1261,8 @@ packages:
     resolution: {integrity: sha512-YQLXUplAwJgCydQ78IMJywZCceoqk1oH01OERdSAJc/7U2AylwjhSCLDEtqwg811idIS/9fIU5GjG73IgjKMVg==}
     engines: {node: '>=0.10'}
 
-  esrap@1.4.8:
-    resolution: {integrity: sha512-jlENbjZ7lqgJV9/OmgAtVqrFFMwsl70ctOgPIg5oTdQVGC13RSkMdtvAmu7ZTLax92c9ljnIG0xleEkdL69hwg==}
+  esrap@2.0.0:
+    resolution: {integrity: sha512-zhw1TDqno99Ld5wOpe0t47rzVyxfGc1fvxNzPsqk4idUf5dcAePkAyfTceLJaSTytjiWDu26S5tI+grjvymXJA==}
 
   esrecurse@4.3.0:
     resolution: {integrity: sha512-KmfKL3b6G+RXvP8N1vr3Tq1kL/oCFgn2NYXEtqP8/L3pKapUA4G8cFVaoF3SU323CD4XypR/ffioHmkti6/Tag==}
@@ -3622,7 +3622,7 @@ snapshots:
     dependencies:
       estraverse: 5.3.0
 
-  esrap@1.4.8:
+  esrap@2.0.0:
     dependencies:
       '@jridgewell/sourcemap-codec': 1.5.0
 

From 7c8be602be7c179a7f248aea078448413815e70a Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 30 Jun 2025 11:49:51 -0400
Subject: [PATCH 012/148] move config into svelte.config.js (#16265)

---
 playgrounds/sandbox/svelte.config.js | 5 +++++
 playgrounds/sandbox/vite.config.js   | 9 +--------
 2 files changed, 6 insertions(+), 8 deletions(-)
 create mode 100644 playgrounds/sandbox/svelte.config.js

diff --git a/playgrounds/sandbox/svelte.config.js b/playgrounds/sandbox/svelte.config.js
new file mode 100644
index 0000000000..65f739bdb6
--- /dev/null
+++ b/playgrounds/sandbox/svelte.config.js
@@ -0,0 +1,5 @@
+export default {
+	compilerOptions: {
+		hmr: true
+	}
+};
diff --git a/playgrounds/sandbox/vite.config.js b/playgrounds/sandbox/vite.config.js
index 51bfd0a212..5ce0204217 100644
--- a/playgrounds/sandbox/vite.config.js
+++ b/playgrounds/sandbox/vite.config.js
@@ -7,14 +7,7 @@ export default defineConfig({
 		minify: false
 	},
 
-	plugins: [
-		inspect(),
-		svelte({
-			compilerOptions: {
-				hmr: true
-			}
-		})
-	],
+	plugins: [inspect(), svelte()],
 
 	optimizeDeps: {
 		// svelte is a local workspace package, optimizing it would require dev server restarts with --force for every change

From b6731456595ffc43620d76f2afb115a19bb7553f Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 30 Jun 2025 15:47:25 -0400
Subject: [PATCH 013/148] feat: add `getAbortSignal()` (#16266)

* WIP getAbortSignal

* add test

* regenerate

* add error code

* changeset

* regenerate

* try this

* { stale: true }

* fix test

* lint

* abort synchronously in SSR

* make STALE_REACTION a `StaleReactionError extends Error`

* make non-optional

* Update packages/svelte/src/internal/server/abort-signal.js

Co-authored-by: Elliott Johnson <sejohnson@torchcloudconsulting.com>

---------

Co-authored-by: Elliott Johnson <sejohnson@torchcloudconsulting.com>
---
 .changeset/short-fireants-flow.md             |  5 ++
 .../98-reference/.generated/client-errors.md  |  6 ++
 .../svelte/messages/client-errors/errors.md   |  4 ++
 packages/svelte/src/index-client.js           | 33 ++++++++-
 packages/svelte/src/index-server.js           |  2 +
 .../svelte/src/internal/client/constants.js   |  6 ++
 packages/svelte/src/internal/client/errors.js | 16 +++++
 .../internal/client/reactivity/deriveds.js    |  3 +-
 .../src/internal/client/reactivity/effects.js |  9 ++-
 .../src/internal/client/reactivity/types.d.ts |  2 +
 .../svelte/src/internal/client/runtime.js     |  8 ++-
 .../src/internal/server/abort-signal.js       | 13 ++++
 packages/svelte/src/internal/server/index.js  | 71 ++++++++++---------
 .../samples/get-abort-signal/_config.js       | 34 +++++++++
 .../samples/get-abort-signal/main.svelte      | 33 +++++++++
 packages/svelte/types/index.d.ts              | 24 +++++++
 16 files changed, 231 insertions(+), 38 deletions(-)
 create mode 100644 .changeset/short-fireants-flow.md
 create mode 100644 packages/svelte/src/internal/server/abort-signal.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/get-abort-signal/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/get-abort-signal/main.svelte

diff --git a/.changeset/short-fireants-flow.md b/.changeset/short-fireants-flow.md
new file mode 100644
index 0000000000..b9955ff577
--- /dev/null
+++ b/.changeset/short-fireants-flow.md
@@ -0,0 +1,5 @@
+---
+'svelte': minor
+---
+
+feat: add `getAbortSignal()`
diff --git a/documentation/docs/98-reference/.generated/client-errors.md b/documentation/docs/98-reference/.generated/client-errors.md
index 111b0b8940..3f33e37d2e 100644
--- a/documentation/docs/98-reference/.generated/client-errors.md
+++ b/documentation/docs/98-reference/.generated/client-errors.md
@@ -74,6 +74,12 @@ Effect cannot be created inside a `$derived` value that was not itself created i
 Maximum update depth exceeded. This can happen when a reactive block or effect repeatedly sets a new value. Svelte limits the number of nested updates to prevent infinite loops
 ```
 
+### get_abort_signal_outside_reaction
+
+```
+`getAbortSignal()` can only be called inside an effect or derived
+```
+
 ### hydration_failed
 
 ```
diff --git a/packages/svelte/messages/client-errors/errors.md b/packages/svelte/messages/client-errors/errors.md
index 6d96770eba..47c2038d70 100644
--- a/packages/svelte/messages/client-errors/errors.md
+++ b/packages/svelte/messages/client-errors/errors.md
@@ -48,6 +48,10 @@ See the [migration guide](/docs/svelte/v5-migration-guide#Components-are-no-long
 
 > Maximum update depth exceeded. This can happen when a reactive block or effect repeatedly sets a new value. Svelte limits the number of nested updates to prevent infinite loops
 
+## get_abort_signal_outside_reaction
+
+> `getAbortSignal()` can only be called inside an effect or derived
+
 ## hydration_failed
 
 > Failed to hydrate the application
diff --git a/packages/svelte/src/index-client.js b/packages/svelte/src/index-client.js
index efd5628ae9..0d962aacd1 100644
--- a/packages/svelte/src/index-client.js
+++ b/packages/svelte/src/index-client.js
@@ -1,7 +1,7 @@
 /** @import { ComponentContext, ComponentContextLegacy } from '#client' */
 /** @import { EventDispatcher } from './index.js' */
 /** @import { NotFunction } from './internal/types.js' */
-import { untrack } from './internal/client/runtime.js';
+import { active_reaction, untrack } from './internal/client/runtime.js';
 import { is_array } from './internal/shared/utils.js';
 import { user_effect } from './internal/client/index.js';
 import * as e from './internal/client/errors.js';
@@ -44,6 +44,37 @@ if (DEV) {
 	throw_rune_error('$bindable');
 }
 
+/**
+ * Returns an [`AbortSignal`](https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal) that aborts when the current [derived](https://svelte.dev/docs/svelte/$derived) or [effect](https://svelte.dev/docs/svelte/$effect) re-runs or is destroyed.
+ *
+ * Must be called while a derived or effect is running.
+ *
+ * ```svelte
+ * <script>
+ * 	import { getAbortSignal } from 'svelte';
+ *
+ * 	let { id } = $props();
+ *
+ * 	async function getData(id) {
+ * 		const response = await fetch(`/items/${id}`, {
+ * 			signal: getAbortSignal()
+ * 		});
+ *
+ * 		return await response.json();
+ * 	}
+ *
+ * 	const data = $derived(await getData(id));
+ * </script>
+ * ```
+ */
+export function getAbortSignal() {
+	if (active_reaction === null) {
+		e.get_abort_signal_outside_reaction();
+	}
+
+	return (active_reaction.ac ??= new AbortController()).signal;
+}
+
 /**
  * `onMount`, like [`$effect`](https://svelte.dev/docs/svelte/$effect), schedules a function to run as soon as the component has been mounted to the DOM.
  * Unlike `$effect`, the provided function only runs once.
diff --git a/packages/svelte/src/index-server.js b/packages/svelte/src/index-server.js
index 0f1aff8f5a..e5039cf150 100644
--- a/packages/svelte/src/index-server.js
+++ b/packages/svelte/src/index-server.js
@@ -35,6 +35,8 @@ export function unmount() {
 
 export async function tick() {}
 
+export { getAbortSignal } from './internal/server/abort-signal.js';
+
 export { getAllContexts, getContext, hasContext, setContext } from './internal/server/context.js';
 
 export { createRawSnippet } from './internal/server/blocks/snippet.js';
diff --git a/packages/svelte/src/internal/client/constants.js b/packages/svelte/src/internal/client/constants.js
index 3ca915f98e..dd3d1b2df6 100644
--- a/packages/svelte/src/internal/client/constants.js
+++ b/packages/svelte/src/internal/client/constants.js
@@ -27,6 +27,12 @@ export const LEGACY_PROPS = Symbol('legacy props');
 export const LOADING_ATTR_SYMBOL = Symbol('');
 export const PROXY_PATH_SYMBOL = Symbol('proxy path');
 
+// allow users to ignore aborted signal errors if `reason.stale`
+export const STALE_REACTION = new (class StaleReactionError extends Error {
+	name = 'StaleReactionError';
+	message = 'The reaction that called `getAbortSignal()` was re-run or destroyed';
+})();
+
 export const ELEMENT_NODE = 1;
 export const TEXT_NODE = 3;
 export const COMMENT_NODE = 8;
diff --git a/packages/svelte/src/internal/client/errors.js b/packages/svelte/src/internal/client/errors.js
index a0ac021c03..5c3f5340e1 100644
--- a/packages/svelte/src/internal/client/errors.js
+++ b/packages/svelte/src/internal/client/errors.js
@@ -195,6 +195,22 @@ export function effect_update_depth_exceeded() {
 	}
 }
 
+/**
+ * `getAbortSignal()` can only be called inside an effect or derived
+ * @returns {never}
+ */
+export function get_abort_signal_outside_reaction() {
+	if (DEV) {
+		const error = new Error(`get_abort_signal_outside_reaction\n\`getAbortSignal()\` can only be called inside an effect or derived\nhttps://svelte.dev/e/get_abort_signal_outside_reaction`);
+
+		error.name = 'Svelte error';
+
+		throw error;
+	} else {
+		throw new Error(`https://svelte.dev/e/get_abort_signal_outside_reaction`);
+	}
+}
+
 /**
  * Failed to hydrate the application
  * @returns {never}
diff --git a/packages/svelte/src/internal/client/reactivity/deriveds.js b/packages/svelte/src/internal/client/reactivity/deriveds.js
index e9cea0df3e..d3123d24a1 100644
--- a/packages/svelte/src/internal/client/reactivity/deriveds.js
+++ b/packages/svelte/src/internal/client/reactivity/deriveds.js
@@ -53,7 +53,8 @@ export function derived(fn) {
 		rv: 0,
 		v: /** @type {V} */ (null),
 		wv: 0,
-		parent: parent_derived ?? active_effect
+		parent: parent_derived ?? active_effect,
+		ac: null
 	};
 
 	if (DEV && tracing_mode_flag) {
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index 03d073781d..a2806bde81 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -32,7 +32,8 @@ import {
 	HEAD_EFFECT,
 	MAYBE_DIRTY,
 	EFFECT_HAS_DERIVED,
-	BOUNDARY_EFFECT
+	BOUNDARY_EFFECT,
+	STALE_REACTION
 } from '#client/constants';
 import { set } from './sources.js';
 import * as e from '../errors.js';
@@ -106,7 +107,8 @@ function create_effect(type, fn, sync, push = true) {
 		prev: null,
 		teardown: null,
 		transitions: null,
-		wv: 0
+		wv: 0,
+		ac: null
 	};
 
 	if (DEV) {
@@ -397,6 +399,8 @@ export function destroy_effect_children(signal, remove_dom = false) {
 	signal.first = signal.last = null;
 
 	while (effect !== null) {
+		effect.ac?.abort(STALE_REACTION);
+
 		var next = effect.next;
 
 		if ((effect.f & ROOT_EFFECT) !== 0) {
@@ -478,6 +482,7 @@ export function destroy_effect(effect, remove_dom = true) {
 		effect.fn =
 		effect.nodes_start =
 		effect.nodes_end =
+		effect.ac =
 			null;
 }
 
diff --git a/packages/svelte/src/internal/client/reactivity/types.d.ts b/packages/svelte/src/internal/client/reactivity/types.d.ts
index 756bb98f09..88c84f27fe 100644
--- a/packages/svelte/src/internal/client/reactivity/types.d.ts
+++ b/packages/svelte/src/internal/client/reactivity/types.d.ts
@@ -40,6 +40,8 @@ export interface Reaction extends Signal {
 	fn: null | Function;
 	/** Signals that this signal reads from */
 	deps: null | Value[];
+	/** An AbortController that aborts when the signal is destroyed */
+	ac: null | AbortController;
 }
 
 export interface Derived<V = unknown> extends Value<V>, Reaction {
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index d057bfdf0d..3e70537d7c 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -22,7 +22,8 @@ import {
 	ROOT_EFFECT,
 	LEGACY_DERIVED_PROP,
 	DISCONNECTED,
-	EFFECT_IS_UPDATING
+	EFFECT_IS_UPDATING,
+	STALE_REACTION
 } from './constants.js';
 import { flush_tasks } from './dom/task.js';
 import { internal_set, old_values } from './reactivity/sources.js';
@@ -276,6 +277,11 @@ export function update_reaction(reaction) {
 
 	reaction.f |= EFFECT_IS_UPDATING;
 
+	if (reaction.ac !== null) {
+		reaction.ac.abort(STALE_REACTION);
+		reaction.ac = null;
+	}
+
 	try {
 		var result = /** @type {Function} */ (0, reaction.fn)();
 		var deps = reaction.deps;
diff --git a/packages/svelte/src/internal/server/abort-signal.js b/packages/svelte/src/internal/server/abort-signal.js
new file mode 100644
index 0000000000..da579b2592
--- /dev/null
+++ b/packages/svelte/src/internal/server/abort-signal.js
@@ -0,0 +1,13 @@
+import { STALE_REACTION } from '#client/constants';
+
+/** @type {AbortController | null} */
+export let controller = null;
+
+export function abort() {
+	controller?.abort(STALE_REACTION);
+	controller = null;
+}
+
+export function getAbortSignal() {
+	return (controller ??= new AbortController()).signal;
+}
diff --git a/packages/svelte/src/internal/server/index.js b/packages/svelte/src/internal/server/index.js
index 2ca85fff44..ceb516ebb0 100644
--- a/packages/svelte/src/internal/server/index.js
+++ b/packages/svelte/src/internal/server/index.js
@@ -18,6 +18,7 @@ import { validate_store } from '../shared/validate.js';
 import { is_boolean_attribute, is_raw_text_element, is_void } from '../../utils.js';
 import { reset_elements } from './dev.js';
 import { Payload } from './payload.js';
+import { abort } from './abort-signal.js';
 
 // https://html.spec.whatwg.org/multipage/syntax.html#attributes-2
 // https://infra.spec.whatwg.org/#noncharacter
@@ -66,50 +67,54 @@ export let on_destroy = [];
  * @returns {RenderOutput}
  */
 export function render(component, options = {}) {
-	const payload = new Payload(options.idPrefix ? options.idPrefix + '-' : '');
+	try {
+		const payload = new Payload(options.idPrefix ? options.idPrefix + '-' : '');
 
-	const prev_on_destroy = on_destroy;
-	on_destroy = [];
-	payload.out += BLOCK_OPEN;
+		const prev_on_destroy = on_destroy;
+		on_destroy = [];
+		payload.out += BLOCK_OPEN;
 
-	let reset_reset_element;
+		let reset_reset_element;
 
-	if (DEV) {
-		// prevent parent/child element state being corrupted by a bad render
-		reset_reset_element = reset_elements();
-	}
+		if (DEV) {
+			// prevent parent/child element state being corrupted by a bad render
+			reset_reset_element = reset_elements();
+		}
 
-	if (options.context) {
-		push();
-		/** @type {Component} */ (current_component).c = options.context;
-	}
+		if (options.context) {
+			push();
+			/** @type {Component} */ (current_component).c = options.context;
+		}
 
-	// @ts-expect-error
-	component(payload, options.props ?? {}, {}, {});
+		// @ts-expect-error
+		component(payload, options.props ?? {}, {}, {});
 
-	if (options.context) {
-		pop();
-	}
+		if (options.context) {
+			pop();
+		}
 
-	if (reset_reset_element) {
-		reset_reset_element();
-	}
+		if (reset_reset_element) {
+			reset_reset_element();
+		}
 
-	payload.out += BLOCK_CLOSE;
-	for (const cleanup of on_destroy) cleanup();
-	on_destroy = prev_on_destroy;
+		payload.out += BLOCK_CLOSE;
+		for (const cleanup of on_destroy) cleanup();
+		on_destroy = prev_on_destroy;
 
-	let head = payload.head.out + payload.head.title;
+		let head = payload.head.out + payload.head.title;
 
-	for (const { hash, code } of payload.css) {
-		head += `<style id="${hash}">${code}</style>`;
-	}
+		for (const { hash, code } of payload.css) {
+			head += `<style id="${hash}">${code}</style>`;
+		}
 
-	return {
-		head,
-		html: payload.out,
-		body: payload.out
-	};
+		return {
+			head,
+			html: payload.out,
+			body: payload.out
+		};
+	} finally {
+		abort();
+	}
 }
 
 /**
diff --git a/packages/svelte/tests/runtime-runes/samples/get-abort-signal/_config.js b/packages/svelte/tests/runtime-runes/samples/get-abort-signal/_config.js
new file mode 100644
index 0000000000..6a85e2615a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/get-abort-signal/_config.js
@@ -0,0 +1,34 @@
+import { test } from '../../test';
+
+export default test({
+	html: `<button>increment</button><p>loading...</p>`,
+
+	async test({ assert, target, variant, logs }) {
+		await new Promise((f) => setTimeout(f, 50));
+
+		if (variant === 'hydrate') {
+			assert.deepEqual(logs, [
+				'aborted',
+				'StaleReactionError',
+				'The reaction that called `getAbortSignal()` was re-run or destroyed'
+			]);
+		}
+
+		logs.length = 0;
+
+		const [button] = target.querySelectorAll('button');
+
+		await new Promise((f) => setTimeout(f, 50));
+		assert.htmlEqual(target.innerHTML, '<button>increment</button><p>0</p>');
+
+		button.click();
+		await new Promise((f) => setTimeout(f, 50));
+		assert.htmlEqual(target.innerHTML, '<button>increment</button><p>2</p>');
+
+		assert.deepEqual(logs, [
+			'aborted',
+			'StaleReactionError',
+			'The reaction that called `getAbortSignal()` was re-run or destroyed'
+		]);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/get-abort-signal/main.svelte b/packages/svelte/tests/runtime-runes/samples/get-abort-signal/main.svelte
new file mode 100644
index 0000000000..be5625125b
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/get-abort-signal/main.svelte
@@ -0,0 +1,33 @@
+<script>
+	import { getAbortSignal } from 'svelte';
+
+	let count = $state(0);
+
+	let delayed_count = $derived.by(async () => {
+		let c = count;
+
+		const signal = getAbortSignal();
+
+		await new Promise((f) => setTimeout(f));
+
+		if (signal.aborted) {
+			console.log('aborted', signal.reason.name, signal.reason.message);
+		}
+
+		return c;
+	});
+</script>
+
+<button onclick={async () => {
+	count += 1;
+	await Promise.resolve();
+	count += 1;
+}}>increment</button>
+
+{#await delayed_count}
+	<p>loading...</p>
+{:then count}
+	<p>{count}</p>
+{:catch error}
+	{console.log('this should never be rendered')}
+{/await}
diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index 3401efac04..432171ae0d 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -348,6 +348,30 @@ declare module 'svelte' {
 				 */
 				props: Props;
 			});
+	/**
+	 * Returns an [`AbortSignal`](https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal) that aborts when the current [derived](https://svelte.dev/docs/svelte/$derived) or [effect](https://svelte.dev/docs/svelte/$effect) re-runs or is destroyed.
+	 *
+	 * Must be called while a derived or effect is running.
+	 *
+	 * ```svelte
+	 * <script>
+	 * 	import { getAbortSignal } from 'svelte';
+	 *
+	 * 	let { id } = $props();
+	 *
+	 * 	async function getData(id) {
+	 * 		const response = await fetch(`/items/${id}`, {
+	 * 			signal: getAbortSignal()
+	 * 		});
+	 *
+	 * 		return await response.json();
+	 * 	}
+	 *
+	 * 	const data = $derived(await getData(id));
+	 * </script>
+	 * ```
+	 */
+	export function getAbortSignal(): AbortSignal;
 	/**
 	 * `onMount`, like [`$effect`](https://svelte.dev/docs/svelte/$effect), schedules a function to run as soon as the component has been mounted to the DOM.
 	 * Unlike `$effect`, the provided function only runs once.

From eb530c82c4e8870194cb919be4bc76600f0e0231 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 30 Jun 2025 16:04:44 -0400
Subject: [PATCH 014/148] chore: move stuff from `analysis` into global
 compiler state (#16268)

* break out locator stuff from the rest of global state

* move some stuff around

* tighten up

* make runes globally available

* make component_name globally available

* unused
---
 packages/svelte/src/compiler/index.js         | 14 ++++----
 packages/svelte/src/compiler/migrate/index.js |  5 ++-
 .../src/compiler/phases/1-parse/index.js      |  3 ++
 .../src/compiler/phases/2-analyze/index.js    | 17 +++++++++
 .../svelte/src/compiler/phases/types.d.ts     |  3 ++
 packages/svelte/src/compiler/state.js         | 35 +++++++++++++------
 6 files changed, 57 insertions(+), 20 deletions(-)

diff --git a/packages/svelte/src/compiler/index.js b/packages/svelte/src/compiler/index.js
index 429c6b4a6f..9ba23c1485 100644
--- a/packages/svelte/src/compiler/index.js
+++ b/packages/svelte/src/compiler/index.js
@@ -20,9 +20,8 @@ export { default as preprocess } from './preprocess/index.js';
  */
 export function compile(source, options) {
 	source = remove_bom(source);
-	state.reset_warning_filter(options.warningFilter);
+	state.reset_warnings(options.warningFilter);
 	const validated = validate_component_options(options, '');
-	state.reset(source, validated);
 
 	let parsed = _parse(source);
 
@@ -64,9 +63,8 @@ export function compile(source, options) {
  */
 export function compileModule(source, options) {
 	source = remove_bom(source);
-	state.reset_warning_filter(options.warningFilter);
+	state.reset_warnings(options.warningFilter);
 	const validated = validate_module_options(options, '');
-	state.reset(source, validated);
 
 	const analysis = analyze_module(source, validated);
 	return transform_module(analysis, source, validated);
@@ -96,6 +94,7 @@ export function compileModule(source, options) {
  * @returns {Record<string, any>}
  */
 
+// TODO 6.0 remove unused `filename`
 /**
  * The parse function parses a component, returning only its abstract syntax tree.
  *
@@ -104,14 +103,15 @@ export function compileModule(source, options) {
  *
  * The `loose` option, available since 5.13.0, tries to always return an AST even if the input will not successfully compile.
  *
+ * The `filename` option is unused and will be removed in Svelte 6.0.
+ *
  * @param {string} source
  * @param {{ filename?: string; rootDir?: string; modern?: boolean; loose?: boolean }} [options]
  * @returns {AST.Root | LegacyRoot}
  */
-export function parse(source, { filename, rootDir, modern, loose } = {}) {
+export function parse(source, { modern, loose } = {}) {
 	source = remove_bom(source);
-	state.reset_warning_filter(() => false);
-	state.reset(source, { filename: filename ?? '(unknown)', rootDir });
+	state.reset_warnings(() => false);
 
 	const ast = _parse(source, loose);
 	return to_public_ast(source, ast, modern);
diff --git a/packages/svelte/src/compiler/migrate/index.js b/packages/svelte/src/compiler/migrate/index.js
index 5ca9adb98b..fdc9734f85 100644
--- a/packages/svelte/src/compiler/migrate/index.js
+++ b/packages/svelte/src/compiler/migrate/index.js
@@ -9,7 +9,7 @@ import { parse } from '../phases/1-parse/index.js';
 import { regex_valid_component_name } from '../phases/1-parse/state/element.js';
 import { analyze_component } from '../phases/2-analyze/index.js';
 import { get_rune } from '../phases/scope.js';
-import { reset, reset_warning_filter } from '../state.js';
+import { reset, reset_warnings } from '../state.js';
 import {
 	extract_identifiers,
 	extract_all_identifiers_from_expression,
@@ -134,8 +134,7 @@ export function migrate(source, { filename, use_ts } = {}) {
 			return start + style_placeholder + end;
 		});
 
-		reset_warning_filter(() => false);
-		reset(source, { filename: filename ?? '(unknown)' });
+		reset_warnings(() => false);
 
 		let parsed = parse(source);
 
diff --git a/packages/svelte/src/compiler/phases/1-parse/index.js b/packages/svelte/src/compiler/phases/1-parse/index.js
index b8ae8199eb..77cc2bf3fa 100644
--- a/packages/svelte/src/compiler/phases/1-parse/index.js
+++ b/packages/svelte/src/compiler/phases/1-parse/index.js
@@ -9,6 +9,7 @@ import { create_fragment } from './utils/create.js';
 import read_options from './read/options.js';
 import { is_reserved } from '../../../utils.js';
 import { disallow_children } from '../2-analyze/visitors/shared/special-element.js';
+import * as state from '../../state.js';
 
 const regex_position_indicator = / \(\d+:\d+\)$/;
 
@@ -301,6 +302,8 @@ export class Parser {
  * @returns {AST.Root}
  */
 export function parse(template, loose = false) {
+	state.set_source(template);
+
 	const parser = new Parser(template, loose);
 	return parser.root;
 }
diff --git a/packages/svelte/src/compiler/phases/2-analyze/index.js b/packages/svelte/src/compiler/phases/2-analyze/index.js
index be1f1ee5bb..d73e273ec2 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/index.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/index.js
@@ -76,6 +76,7 @@ import { UseDirective } from './visitors/UseDirective.js';
 import { VariableDeclarator } from './visitors/VariableDeclarator.js';
 import is_reference from 'is-reference';
 import { mark_subtree_dynamic } from './visitors/shared/fragment.js';
+import * as state from '../../state.js';
 
 /**
  * @type {Visitors}
@@ -240,6 +241,7 @@ export function analyze_module(source, options) {
 	/** @type {AST.JSComment[]} */
 	const comments = [];
 
+	state.set_source(source);
 	const ast = parse(source, comments, false, false);
 
 	const { scope, scopes } = create_scopes(ast, new ScopeRoot(), false, null);
@@ -269,6 +271,13 @@ export function analyze_module(source, options) {
 		classes: new Map()
 	};
 
+	state.reset({
+		dev: options.dev,
+		filename: options.filename,
+		rootDir: options.rootDir,
+		runes: true
+	});
+
 	walk(
 		/** @type {Node} */ (ast),
 		{
@@ -506,6 +515,14 @@ export function analyze_component(root, source, options) {
 		snippets: new Set()
 	};
 
+	state.reset({
+		component_name: analysis.name,
+		dev: options.dev,
+		filename: options.filename,
+		rootDir: options.rootDir,
+		runes: true
+	});
+
 	if (!runes) {
 		// every exported `let` or `var` declaration becomes a prop, everything else becomes an export
 		for (const node of instance.ast.body) {
diff --git a/packages/svelte/src/compiler/phases/types.d.ts b/packages/svelte/src/compiler/phases/types.d.ts
index 661f363991..dba2559a17 100644
--- a/packages/svelte/src/compiler/phases/types.d.ts
+++ b/packages/svelte/src/compiler/phases/types.d.ts
@@ -34,7 +34,9 @@ export interface ReactiveStatement {
  */
 export interface Analysis {
 	module: Js;
+	/** @deprecated use `component_name` from `state.js` instead */
 	name: string; // TODO should this be filename? it's used in `compileModule` as well as `compile`
+	/** @deprecated use `runes` from `state.js` instead */
 	runes: boolean;
 	immutable: boolean;
 	tracing: boolean;
@@ -90,6 +92,7 @@ export interface ComponentAnalysis extends Analysis {
 		keyframes: string[];
 		has_global: boolean;
 	};
+	/** @deprecated use `source` from `state.js` instead */
 	source: string;
 	undefined_exports: Map<string, Node>;
 	/**
diff --git a/packages/svelte/src/compiler/state.js b/packages/svelte/src/compiler/state.js
index 1db3db917f..9095651ced 100644
--- a/packages/svelte/src/compiler/state.js
+++ b/packages/svelte/src/compiler/state.js
@@ -16,6 +16,8 @@ export let warnings = [];
  */
 export let filename;
 
+export let component_name = '<unknown>';
+
 /**
  * The original source code
  * @type {string}
@@ -28,8 +30,16 @@ export let source;
  */
 export let dev;
 
+export let runes = false;
+
 export let locator = getLocator('', { offsetLine: 1 });
 
+/** @param {string} value */
+export function set_source(value) {
+	source = value;
+	locator = getLocator(source, { offsetLine: 1 });
+}
+
 /**
  * @param {AST.SvelteNode & { start?: number | undefined }} node
  */
@@ -71,8 +81,9 @@ export function pop_ignore() {
  *
  * @param {(warning: Warning) => boolean} fn
  */
-export function reset_warning_filter(fn = () => true) {
+export function reset_warnings(fn = () => true) {
 	warning_filter = fn;
+	warnings = [];
 }
 
 /**
@@ -85,23 +96,27 @@ export function is_ignored(node, code) {
 }
 
 /**
- * @param {string} _source
- * @param {{ dev?: boolean; filename: string; rootDir?: string }} options
+ * @param {{
+ *   dev: boolean;
+ *   filename: string;
+ *   component_name?: string;
+ *   rootDir?: string;
+ *   runes: boolean;
+ * }} state
  */
-export function reset(_source, options) {
-	source = _source;
-	const root_dir = options.rootDir?.replace(/\\/g, '/');
-	filename = options.filename.replace(/\\/g, '/');
+export function reset(state) {
+	const root_dir = state.rootDir?.replace(/\\/g, '/');
+	filename = state.filename.replace(/\\/g, '/');
 
-	dev = !!options.dev;
+	dev = state.dev;
+	runes = state.runes;
+	component_name = state.component_name ?? '(unknown)';
 
 	if (typeof root_dir === 'string' && filename.startsWith(root_dir)) {
 		// make filename relative to rootDir
 		filename = filename.replace(root_dir, '').replace(/^[/\\]/, '');
 	}
 
-	locator = getLocator(source, { offsetLine: 1 });
-	warnings = [];
 	ignore_stack = [];
 	ignore_map.clear();
 }

From d427ffd8b96c5a5509ee602bd77d58a90f24e784 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 1 Jul 2025 10:37:37 -0400
Subject: [PATCH 015/148] chore: encapsulate expression memoization (#16269)

* chore: encapsulate expression memoization

* add comment

* tweak

* use b.id
---
 .../3-transform/client/transform-client.js    |  4 +-
 .../phases/3-transform/client/types.d.ts      |  5 +-
 .../3-transform/client/visitors/Fragment.js   |  4 +-
 .../client/visitors/RegularElement.js         | 61 ++++++++++---------
 .../client/visitors/SvelteElement.js          |  6 +-
 .../client/visitors/shared/element.js         | 37 +++++------
 .../client/visitors/shared/utils.js           | 52 ++++++++++++----
 7 files changed, 99 insertions(+), 70 deletions(-)

diff --git a/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js b/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
index e85a35cf8e..a9c0651e0f 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
@@ -168,9 +168,9 @@ export function client_component(analysis, options) {
 		// these are set inside the `Fragment` visitor, and cannot be used until then
 		init: /** @type {any} */ (null),
 		update: /** @type {any} */ (null),
-		expressions: /** @type {any} */ (null),
 		after_update: /** @type {any} */ (null),
-		template: /** @type {any} */ (null)
+		template: /** @type {any} */ (null),
+		memoizer: /** @type {any} */ (null)
 	};
 
 	const module = /** @type {ESTree.Program} */ (
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/types.d.ts b/packages/svelte/src/compiler/phases/3-transform/client/types.d.ts
index 2388ee1b00..cf5c942268 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/types.d.ts
+++ b/packages/svelte/src/compiler/phases/3-transform/client/types.d.ts
@@ -12,6 +12,7 @@ import type { AST, Namespace, ValidatedCompileOptions } from '#compiler';
 import type { TransformState } from '../types.js';
 import type { ComponentAnalysis } from '../../types.js';
 import type { Template } from './transform-template/template.js';
+import type { Memoizer } from './visitors/shared/utils.js';
 
 export interface ClientTransformState extends TransformState {
 	/**
@@ -49,8 +50,8 @@ export interface ComponentClientTransformState extends ClientTransformState {
 	readonly update: Statement[];
 	/** Stuff that happens after the render effect (control blocks, dynamic elements, bindings, actions, etc) */
 	readonly after_update: Statement[];
-	/** Expressions used inside the render effect */
-	readonly expressions: Expression[];
+	/** Memoized expressions */
+	readonly memoizer: Memoizer;
 	/** The HTML template string */
 	readonly template: Template;
 	readonly metadata: {
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/Fragment.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/Fragment.js
index 4825184d31..7cd2bd90ed 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/Fragment.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/Fragment.js
@@ -6,7 +6,7 @@ import * as b from '#compiler/builders';
 import { clean_nodes, infer_namespace } from '../../utils.js';
 import { transform_template } from '../transform-template/index.js';
 import { process_children } from './shared/fragment.js';
-import { build_render_statement } from './shared/utils.js';
+import { build_render_statement, Memoizer } from './shared/utils.js';
 import { Template } from '../transform-template/template.js';
 
 /**
@@ -64,8 +64,8 @@ export function Fragment(node, context) {
 		...context.state,
 		init: [],
 		update: [],
-		expressions: [],
 		after_update: [],
+		memoizer: new Memoizer(),
 		template: new Template(),
 		transform: { ...context.state.transform },
 		metadata: {
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js
index ae8680f594..eed2a75506 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js
@@ -22,7 +22,7 @@ import {
 	build_set_style
 } from './shared/element.js';
 import { process_children } from './shared/fragment.js';
-import { build_render_statement, build_template_chunk, get_expression_id } from './shared/utils.js';
+import { build_render_statement, build_template_chunk, Memoizer } from './shared/utils.js';
 import { visit_event_attribute } from './shared/events.js';
 
 /**
@@ -253,8 +253,7 @@ export function RegularElement(node, context) {
 				const { value, has_state } = build_attribute_value(
 					attribute.value,
 					context,
-					(value, metadata) =>
-						metadata.has_call ? get_expression_id(context.state.expressions, value) : value
+					(value, metadata) => (metadata.has_call ? context.state.memoizer.add(value) : value)
 				);
 
 				const update = build_element_attribute_update(node, node_id, name, value, attributes);
@@ -455,11 +454,15 @@ function setup_select_synchronization(value_binding, context) {
 
 /**
  * @param {AST.ClassDirective[]} class_directives
- * @param {Expression[]} expressions
  * @param {ComponentContext} context
+ * @param {Memoizer} memoizer
  * @return {ObjectExpression | Identifier}
  */
-export function build_class_directives_object(class_directives, expressions, context) {
+export function build_class_directives_object(
+	class_directives,
+	context,
+	memoizer = context.state.memoizer
+) {
 	let properties = [];
 	let has_call_or_state = false;
 
@@ -471,38 +474,40 @@ export function build_class_directives_object(class_directives, expressions, con
 
 	const directives = b.object(properties);
 
-	return has_call_or_state ? get_expression_id(expressions, directives) : directives;
+	return has_call_or_state ? memoizer.add(directives) : directives;
 }
 
 /**
  * @param {AST.StyleDirective[]} style_directives
- * @param {Expression[]} expressions
  * @param {ComponentContext} context
- * @return {ObjectExpression | ArrayExpression}}
+ * @param {Memoizer} memoizer
+ * @return {ObjectExpression | ArrayExpression | Identifier}}
  */
-export function build_style_directives_object(style_directives, expressions, context) {
-	let normal_properties = [];
-	let important_properties = [];
+export function build_style_directives_object(
+	style_directives,
+	context,
+	memoizer = context.state.memoizer
+) {
+	const normal = b.object([]);
+	const important = b.object([]);
 
-	for (const directive of style_directives) {
+	let has_call_or_state = false;
+
+	for (const d of style_directives) {
 		const expression =
-			directive.value === true
-				? build_getter({ name: directive.name, type: 'Identifier' }, context.state)
-				: build_attribute_value(directive.value, context, (value, metadata) =>
-						metadata.has_call ? get_expression_id(expressions, value) : value
-					).value;
-		const property = b.init(directive.name, expression);
-
-		if (directive.modifiers.includes('important')) {
-			important_properties.push(property);
-		} else {
-			normal_properties.push(property);
-		}
+			d.value === true
+				? build_getter(b.id(d.name), context.state)
+				: build_attribute_value(d.value, context).value;
+
+		const object = d.modifiers.includes('important') ? important : normal;
+		object.properties.push(b.init(d.name, expression));
+
+		has_call_or_state ||= d.metadata.expression.has_call || d.metadata.expression.has_state;
 	}
 
-	return important_properties.length
-		? b.array([b.object(normal_properties), b.object(important_properties)])
-		: b.object(normal_properties);
+	const directives = important.properties.length ? b.array([normal, important]) : normal;
+
+	return has_call_or_state ? memoizer.add(directives) : directives;
 }
 
 /**
@@ -624,7 +629,7 @@ function build_element_special_value_attribute(element, node_id, attribute, cont
 		element === 'select' && attribute.value !== true && !is_text_attribute(attribute);
 
 	const { value, has_state } = build_attribute_value(attribute.value, context, (value, metadata) =>
-		metadata.has_call ? get_expression_id(state.expressions, value) : value
+		metadata.has_call ? state.memoizer.add(value) : value
 	);
 
 	const evaluated = context.state.scope.evaluate(value);
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteElement.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteElement.js
index 7381553dbe..6af5f5770e 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteElement.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteElement.js
@@ -10,7 +10,7 @@ import {
 	build_attribute_effect,
 	build_set_class
 } from './shared/element.js';
-import { build_render_statement } from './shared/utils.js';
+import { build_render_statement, Memoizer } from './shared/utils.js';
 
 /**
  * @param {AST.SvelteElement} node
@@ -46,8 +46,8 @@ export function SvelteElement(node, context) {
 			node: element_id,
 			init: [],
 			update: [],
-			expressions: [],
-			after_update: []
+			after_update: [],
+			memoizer: new Memoizer()
 		}
 	};
 
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/element.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/element.js
index 10f942b7d4..d119b0457b 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/element.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/element.js
@@ -7,7 +7,7 @@ import { is_ignored } from '../../../../../state.js';
 import { is_event_attribute } from '../../../../../utils/ast.js';
 import * as b from '#compiler/builders';
 import { build_class_directives_object, build_style_directives_object } from '../RegularElement.js';
-import { build_expression, build_template_chunk, get_expression_id } from './utils.js';
+import { build_expression, build_template_chunk, Memoizer } from './utils.js';
 
 /**
  * @param {Array<AST.Attribute | AST.SpreadAttribute>} attributes
@@ -28,18 +28,12 @@ export function build_attribute_effect(
 	/** @type {ObjectExpression['properties']} */
 	const values = [];
 
-	/** @type {Expression[]} */
-	const expressions = [];
-
-	/** @param {Expression} value */
-	function memoize(value) {
-		return b.id(`$${expressions.push(value) - 1}`);
-	}
+	const memoizer = new Memoizer();
 
 	for (const attribute of attributes) {
 		if (attribute.type === 'Attribute') {
 			const { value } = build_attribute_value(attribute.value, context, (value, metadata) =>
-				metadata.has_call ? memoize(value) : value
+				metadata.has_call ? memoizer.add(value) : value
 			);
 
 			if (
@@ -57,7 +51,7 @@ export function build_attribute_effect(
 			let value = /** @type {Expression} */ (context.visit(attribute));
 
 			if (attribute.metadata.expression.has_call) {
-				value = memoize(value);
+				value = memoizer.add(value);
 			}
 
 			values.push(b.spread(value));
@@ -69,7 +63,7 @@ export function build_attribute_effect(
 			b.prop(
 				'init',
 				b.array([b.id('$.CLASS')]),
-				build_class_directives_object(class_directives, expressions, context)
+				build_class_directives_object(class_directives, context, memoizer)
 			)
 		);
 	}
@@ -79,21 +73,20 @@ export function build_attribute_effect(
 			b.prop(
 				'init',
 				b.array([b.id('$.STYLE')]),
-				build_style_directives_object(style_directives, expressions, context)
+				build_style_directives_object(style_directives, context, memoizer)
 			)
 		);
 	}
 
+	const ids = memoizer.apply();
+
 	context.state.init.push(
 		b.stmt(
 			b.call(
 				'$.attribute_effect',
 				element_id,
-				b.arrow(
-					expressions.map((_, i) => b.id(`$${i}`)),
-					b.object(values)
-				),
-				expressions.length > 0 && b.array(expressions.map((expression) => b.thunk(expression))),
+				b.arrow(ids, b.object(values)),
+				memoizer.sync_values(),
 				element.metadata.scoped &&
 					context.state.analysis.css.hash !== '' &&
 					b.literal(context.state.analysis.css.hash),
@@ -158,7 +151,7 @@ export function build_set_class(element, node_id, attribute, class_directives, c
 			value = b.call('$.clsx', value);
 		}
 
-		return metadata.has_call ? get_expression_id(context.state.expressions, value) : value;
+		return metadata.has_call ? context.state.memoizer.add(value) : value;
 	});
 
 	/** @type {Identifier | undefined} */
@@ -171,7 +164,7 @@ export function build_set_class(element, node_id, attribute, class_directives, c
 	let next;
 
 	if (class_directives.length) {
-		next = build_class_directives_object(class_directives, context.state.expressions, context);
+		next = build_class_directives_object(class_directives, context);
 		has_state ||= class_directives.some((d) => d.metadata.expression.has_state);
 
 		if (has_state) {
@@ -226,7 +219,7 @@ export function build_set_class(element, node_id, attribute, class_directives, c
  */
 export function build_set_style(node_id, attribute, style_directives, context) {
 	let { value, has_state } = build_attribute_value(attribute.value, context, (value, metadata) =>
-		metadata.has_call ? get_expression_id(context.state.expressions, value) : value
+		metadata.has_call ? context.state.memoizer.add(value) : value
 	);
 
 	/** @type {Identifier | undefined} */
@@ -235,11 +228,11 @@ export function build_set_style(node_id, attribute, style_directives, context) {
 	/** @type {ObjectExpression | Identifier | undefined} */
 	let prev;
 
-	/** @type {ArrayExpression | ObjectExpression | undefined} */
+	/** @type {Expression | undefined} */
 	let next;
 
 	if (style_directives.length) {
-		next = build_style_directives_object(style_directives, context.state.expressions, context);
+		next = build_style_directives_object(style_directives, context);
 		has_state ||= style_directives.some((d) => d.metadata.expression.has_state);
 
 		if (has_state) {
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
index 0bd9bfb128..b80466ccc9 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
@@ -21,12 +21,41 @@ export function memoize_expression(state, value) {
 }
 
 /**
- * Pushes `value` into `expressions` and returns a new id
- * @param {Expression[]} expressions
- * @param {Expression} value
+ * A utility for extracting complex expressions (such as call expressions)
+ * from templates and replacing them with `$0`, `$1` etc
  */
-export function get_expression_id(expressions, value) {
-	return b.id(`$${expressions.push(value) - 1}`);
+export class Memoizer {
+	/** @type {Array<{ id: Identifier, expression: Expression }>} */
+	#sync = [];
+
+	/**
+	 * @param {Expression} expression
+	 */
+	add(expression) {
+		const id = b.id('#'); // filled in later
+
+		this.#sync.push({ id, expression });
+
+		return id;
+	}
+
+	apply() {
+		return this.#sync.map((memo, i) => {
+			memo.id.name = `$${i}`;
+			return memo.id;
+		});
+	}
+
+	deriveds(runes = true) {
+		return this.#sync.map((memo) =>
+			b.let(memo.id, b.call(runes ? '$.derived' : '$.derived_safe_equal', b.thunk(memo.expression)))
+		);
+	}
+
+	sync_values() {
+		if (this.#sync.length === 0) return;
+		return b.array(this.#sync.map((memo) => b.thunk(memo.expression)));
+	}
 }
 
 /**
@@ -40,8 +69,7 @@ export function build_template_chunk(
 	values,
 	context,
 	state = context.state,
-	memoize = (value, metadata) =>
-		metadata.has_call ? get_expression_id(state.expressions, value) : value
+	memoize = (value, metadata) => (metadata.has_call ? state.memoizer.add(value) : value)
 ) {
 	/** @type {Expression[]} */
 	const expressions = [];
@@ -128,18 +156,20 @@ export function build_template_chunk(
  * @param {ComponentClientTransformState} state
  */
 export function build_render_statement(state) {
+	const ids = state.memoizer.apply();
+	const values = state.memoizer.sync_values();
+
 	return b.stmt(
 		b.call(
 			'$.template_effect',
 			b.arrow(
-				state.expressions.map((_, i) => b.id(`$${i}`)),
+				ids,
 				state.update.length === 1 && state.update[0].type === 'ExpressionStatement'
 					? state.update[0].expression
 					: b.block(state.update)
 			),
-			state.expressions.length > 0 &&
-				b.array(state.expressions.map((expression) => b.thunk(expression))),
-			state.expressions.length > 0 && !state.analysis.runes && b.id('$.derived_safe_equal')
+			values,
+			values && !state.analysis.runes && b.id('$.derived_safe_equal')
 		)
 	);
 }

From 11ec907fd57fec85e090d6a620743bd447f9d2ef Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 1 Jul 2025 14:20:19 -0400
Subject: [PATCH 016/148] chore: simplify props (#16270)

* simplify props

* simplify

* tweak

* reorder a bit

* simplify

* unused

* more

* more

* tweak

* also appears to be unnecessary

* changeset

* apparently this is also unnecessary

* explanatory comment
---
 .changeset/new-trees-behave.md                |   5 +
 .../svelte/src/internal/client/constants.js   |   2 -
 .../src/internal/client/reactivity/props.js   | 175 +++++++-----------
 .../svelte/src/internal/client/runtime.js     |  13 +-
 4 files changed, 73 insertions(+), 122 deletions(-)
 create mode 100644 .changeset/new-trees-behave.md

diff --git a/.changeset/new-trees-behave.md b/.changeset/new-trees-behave.md
new file mode 100644
index 0000000000..d5fab30f3e
--- /dev/null
+++ b/.changeset/new-trees-behave.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: simplify props
diff --git a/packages/svelte/src/internal/client/constants.js b/packages/svelte/src/internal/client/constants.js
index dd3d1b2df6..cd5e0d2244 100644
--- a/packages/svelte/src/internal/client/constants.js
+++ b/packages/svelte/src/internal/client/constants.js
@@ -15,8 +15,6 @@ export const DESTROYED = 1 << 14;
 export const EFFECT_RAN = 1 << 15;
 /** 'Transparent' effects do not create a transition boundary */
 export const EFFECT_TRANSPARENT = 1 << 16;
-/** Svelte 4 legacy mode props need to be handled with deriveds and be recognized elsewhere, hence the dedicated flag */
-export const LEGACY_DERIVED_PROP = 1 << 17;
 export const INSPECT_EFFECT = 1 << 18;
 export const HEAD_EFFECT = 1 << 19;
 export const EFFECT_HAS_DERIVED = 1 << 20;
diff --git a/packages/svelte/src/internal/client/reactivity/props.js b/packages/svelte/src/internal/client/reactivity/props.js
index f3111361c0..f51291b1cc 100644
--- a/packages/svelte/src/internal/client/reactivity/props.js
+++ b/packages/svelte/src/internal/client/reactivity/props.js
@@ -8,12 +8,11 @@ import {
 	PROPS_IS_UPDATED
 } from '../../../constants.js';
 import { get_descriptor, is_function } from '../../shared/utils.js';
-import { mutable_source, set, source, update } from './sources.js';
+import { set, source, update } from './sources.js';
 import { derived, derived_safe_equal } from './deriveds.js';
-import { get, captured_signals, untrack } from '../runtime.js';
-import { safe_equals } from './equality.js';
+import { get, untrack } from '../runtime.js';
 import * as e from '../errors.js';
-import { LEGACY_DERIVED_PROP, LEGACY_PROPS, STATE_SYMBOL } from '#client/constants';
+import { LEGACY_PROPS, STATE_SYMBOL } from '#client/constants';
 import { proxy } from '../proxy.js';
 import { capture_store_binding } from './store.js';
 import { legacy_mode_flag } from '../../flags/index.js';
@@ -260,89 +259,92 @@ function has_destroyed_component_ctx(current_value) {
  * @returns {(() => V | ((arg: V) => V) | ((arg: V, mutation: boolean) => V))}
  */
 export function prop(props, key, flags, fallback) {
-	var immutable = (flags & PROPS_IS_IMMUTABLE) !== 0;
 	var runes = !legacy_mode_flag || (flags & PROPS_IS_RUNES) !== 0;
 	var bindable = (flags & PROPS_IS_BINDABLE) !== 0;
 	var lazy = (flags & PROPS_IS_LAZY_INITIAL) !== 0;
-	var is_store_sub = false;
-	var prop_value;
-
-	if (bindable) {
-		[prop_value, is_store_sub] = capture_store_binding(() => /** @type {V} */ (props[key]));
-	} else {
-		prop_value = /** @type {V} */ (props[key]);
-	}
-
-	// Can be the case when someone does `mount(Component, props)` with `let props = $state({...})`
-	// or `createClassComponent(Component, props)`
-	var is_entry_props = STATE_SYMBOL in props || LEGACY_PROPS in props;
-
-	var setter =
-		(bindable &&
-			(get_descriptor(props, key)?.set ??
-				(is_entry_props && key in props && ((v) => (props[key] = v))))) ||
-		undefined;
 
 	var fallback_value = /** @type {V} */ (fallback);
 	var fallback_dirty = true;
-	var fallback_used = false;
 
 	var get_fallback = () => {
-		fallback_used = true;
 		if (fallback_dirty) {
 			fallback_dirty = false;
-			if (lazy) {
-				fallback_value = untrack(/** @type {() => V} */ (fallback));
-			} else {
-				fallback_value = /** @type {V} */ (fallback);
-			}
+
+			fallback_value = lazy
+				? untrack(/** @type {() => V} */ (fallback))
+				: /** @type {V} */ (fallback);
 		}
 
 		return fallback_value;
 	};
 
-	if (prop_value === undefined && fallback !== undefined) {
-		if (setter && runes) {
-			e.props_invalid_value(key);
-		}
+	/** @type {((v: V) => void) | undefined} */
+	var setter;
 
-		prop_value = get_fallback();
-		if (setter) setter(prop_value);
+	if (bindable) {
+		// Can be the case when someone does `mount(Component, props)` with `let props = $state({...})`
+		// or `createClassComponent(Component, props)`
+		var is_entry_props = STATE_SYMBOL in props || LEGACY_PROPS in props;
+
+		setter =
+			get_descriptor(props, key)?.set ??
+			(is_entry_props && key in props ? (v) => (props[key] = v) : undefined);
+	}
+
+	var initial_value;
+	var is_store_sub = false;
+
+	if (bindable) {
+		[initial_value, is_store_sub] = capture_store_binding(() => /** @type {V} */ (props[key]));
+	} else {
+		initial_value = /** @type {V} */ (props[key]);
+	}
+
+	if (initial_value === undefined && fallback !== undefined) {
+		initial_value = get_fallback();
+
+		if (setter) {
+			if (runes) e.props_invalid_value(key);
+			setter(initial_value);
+		}
 	}
 
 	/** @type {() => V} */
 	var getter;
+
 	if (runes) {
 		getter = () => {
 			var value = /** @type {V} */ (props[key]);
 			if (value === undefined) return get_fallback();
 			fallback_dirty = true;
-			fallback_used = false;
 			return value;
 		};
 	} else {
-		// Svelte 4 did not trigger updates when a primitive value was updated to the same value.
-		// Replicate that behavior through using a derived
-		var derived_getter = (immutable ? derived : derived_safe_equal)(
-			() => /** @type {V} */ (props[key])
-		);
-		derived_getter.f |= LEGACY_DERIVED_PROP;
 		getter = () => {
-			var value = get(derived_getter);
-			if (value !== undefined) fallback_value = /** @type {V} */ (undefined);
+			var value = /** @type {V} */ (props[key]);
+
+			if (value !== undefined) {
+				// in legacy mode, we don't revert to the fallback value
+				// if the prop goes from defined to undefined. The easiest
+				// way to model this is to make the fallback undefined
+				// as soon as the prop has a value
+				fallback_value = /** @type {V} */ (undefined);
+			}
+
 			return value === undefined ? fallback_value : value;
 		};
 	}
 
-	// easy mode — prop is never written to
-	if ((flags & PROPS_IS_UPDATED) === 0 && runes) {
+	// prop is never written to — we only need a getter
+	if ((flags & PROPS_IS_UPDATED) === 0) {
 		return getter;
 	}
 
-	// intermediate mode — prop is written to, but the parent component had
-	// `bind:foo` which means we can just call `$$props.foo = value` directly
+	// prop is written to, but the parent component had `bind:foo` which
+	// means we can just call `$$props.foo = value` directly
 	if (setter) {
 		var legacy_parent = props.$$legacy;
+
 		return function (/** @type {any} */ value, /** @type {boolean} */ mutation) {
 			if (arguments.length > 0) {
 				// We don't want to notify if the value was mutated and the parent is in runes mode.
@@ -352,82 +354,39 @@ export function prop(props, key, flags, fallback) {
 				if (!runes || !mutation || legacy_parent || is_store_sub) {
 					/** @type {Function} */ (setter)(mutation ? getter() : value);
 				}
+
 				return value;
-			} else {
-				return getter();
 			}
+
+			return getter();
 		};
 	}
 
-	// hard mode. this is where it gets ugly — the value in the child should
-	// synchronize with the parent, but it should also be possible to temporarily
-	// set the value to something else locally.
-	var from_child = false;
-	var was_from_child = false;
-
-	// The derived returns the current value. The underlying mutable
-	// source is written to from various places to persist this value.
-	var inner_current_value = mutable_source(prop_value);
-	var current_value = derived(() => {
-		var parent_value = getter();
-		var child_value = get(inner_current_value);
-
-		if (from_child) {
-			from_child = false;
-			was_from_child = true;
-			return child_value;
-		}
-
-		was_from_child = false;
-		return (inner_current_value.v = parent_value);
-	});
-
-	// Ensure we eagerly capture the initial value if it's bindable
-	if (bindable) {
-		get(current_value);
-	}
+	// prop is written to, but there's no binding, which means we
+	// create a derived that we can write to locally
+	var d = ((flags & PROPS_IS_IMMUTABLE) !== 0 ? derived : derived_safe_equal)(getter);
 
-	if (!immutable) current_value.equals = safe_equals;
+	// Capture the initial value if it's bindable
+	if (bindable) get(d);
 
 	return function (/** @type {any} */ value, /** @type {boolean} */ mutation) {
-		// legacy nonsense — need to ensure the source is invalidated when necessary
-		// also needed for when handling inspect logic so we can inspect the correct source signal
-		if (captured_signals !== null) {
-			// set this so that we don't reset to the parent value if `d`
-			// is invalidated because of `invalidate_inner_signals` (rather
-			// than because the parent or child value changed)
-			from_child = was_from_child;
-			// invoke getters so that signals are picked up by `invalidate_inner_signals`
-			getter();
-			get(inner_current_value);
-		}
-
 		if (arguments.length > 0) {
-			const new_value = mutation ? get(current_value) : runes && bindable ? proxy(value) : value;
-
-			if (!current_value.equals(new_value)) {
-				from_child = true;
-				set(inner_current_value, new_value);
-				// To ensure the fallback value is consistent when used with proxies, we
-				// update the local fallback_value, but only if the fallback is actively used
-				if (fallback_used && fallback_value !== undefined) {
-					fallback_value = new_value;
-				}
+			const new_value = mutation ? get(d) : runes && bindable ? proxy(value) : value;
 
-				if (has_destroyed_component_ctx(current_value)) {
-					return value;
-				}
+			set(d, new_value);
 
-				untrack(() => get(current_value)); // force a synchronisation immediately
+			if (fallback_value !== undefined) {
+				fallback_value = new_value;
 			}
 
 			return value;
 		}
 
-		if (has_destroyed_component_ctx(current_value)) {
-			return current_value.v;
+		// TODO is this still necessary post-#16263?
+		if (has_destroyed_component_ctx(d)) {
+			return d.v;
 		}
 
-		return get(current_value);
+		return get(d);
 	};
 }
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 3e70537d7c..5a798ba3e9 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -20,7 +20,6 @@ import {
 	STATE_SYMBOL,
 	BLOCK_EFFECT,
 	ROOT_EFFECT,
-	LEGACY_DERIVED_PROP,
 	DISCONNECTED,
 	EFFECT_IS_UPDATING,
 	STALE_REACTION
@@ -863,17 +862,7 @@ export function invalidate_inner_signals(fn) {
 	var captured = capture_signals(() => untrack(fn));
 
 	for (var signal of captured) {
-		// Go one level up because derived signals created as part of props in legacy mode
-		if ((signal.f & LEGACY_DERIVED_PROP) !== 0) {
-			for (const dep of /** @type {Derived} */ (signal).deps || []) {
-				if ((dep.f & DERIVED) === 0) {
-					// Use internal_set instead of set here and below to avoid mutation validation
-					internal_set(dep, dep.v);
-				}
-			}
-		} else {
-			internal_set(signal, signal.v);
-		}
+		internal_set(signal, signal.v);
 	}
 }
 

From 2f68131e9a780f139d6bdcf1b27854d850542671 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Tue, 1 Jul 2025 23:10:16 +0200
Subject: [PATCH 017/148] fix: revert props legacy mode regression (#16279)

#16270 removed a condition which seemed to keep passing the corresponding test, but it actually introduced a regression since the PROPS_IS_UPDATED is always set when accessors should be created, which is the case by default in legacy mode tests. Setting accessors to false in the test reveals the regression, so this reverts that part of the refactoring
---
 packages/svelte/src/internal/client/reactivity/props.js   | 8 +++++---
 .../runtime-legacy/samples/prop-no-change/_config.js      | 1 +
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/packages/svelte/src/internal/client/reactivity/props.js b/packages/svelte/src/internal/client/reactivity/props.js
index f51291b1cc..3501bcd3c7 100644
--- a/packages/svelte/src/internal/client/reactivity/props.js
+++ b/packages/svelte/src/internal/client/reactivity/props.js
@@ -336,7 +336,7 @@ export function prop(props, key, flags, fallback) {
 	}
 
 	// prop is never written to — we only need a getter
-	if ((flags & PROPS_IS_UPDATED) === 0) {
+	if (runes && (flags & PROPS_IS_UPDATED) === 0) {
 		return getter;
 	}
 
@@ -362,8 +362,10 @@ export function prop(props, key, flags, fallback) {
 		};
 	}
 
-	// prop is written to, but there's no binding, which means we
-	// create a derived that we can write to locally
+	// Either prop is written to, but there's no binding, which means we
+	// create a derived that we can write to locally.
+	// Or we are in legacy mode where we always create a derived to replicate that
+	// Svelte 4 did not trigger updates when a primitive value was updated to the same value.
 	var d = ((flags & PROPS_IS_IMMUTABLE) !== 0 ? derived : derived_safe_equal)(getter);
 
 	// Capture the initial value if it's bindable
diff --git a/packages/svelte/tests/runtime-legacy/samples/prop-no-change/_config.js b/packages/svelte/tests/runtime-legacy/samples/prop-no-change/_config.js
index 905c2a6226..84658336e2 100644
--- a/packages/svelte/tests/runtime-legacy/samples/prop-no-change/_config.js
+++ b/packages/svelte/tests/runtime-legacy/samples/prop-no-change/_config.js
@@ -2,6 +2,7 @@ import { flushSync } from 'svelte';
 import { test } from '../../test';
 
 export default test({
+	accessors: false,
 	test({ assert, logs, target }) {
 		assert.deepEqual(logs, ['primitive', 'object']);
 		target.querySelector('button')?.click();

From 9dddb31b4a9260a520d19e2955393da0aa1d7f3b Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Wed, 2 Jul 2025 08:07:08 -0400
Subject: [PATCH 018/148] Version Packages (#16276)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/new-trees-behave.md    |  5 -----
 .changeset/short-fireants-flow.md |  5 -----
 packages/svelte/CHANGELOG.md      | 10 ++++++++++
 packages/svelte/package.json      |  2 +-
 packages/svelte/src/version.js    |  2 +-
 5 files changed, 12 insertions(+), 12 deletions(-)
 delete mode 100644 .changeset/new-trees-behave.md
 delete mode 100644 .changeset/short-fireants-flow.md

diff --git a/.changeset/new-trees-behave.md b/.changeset/new-trees-behave.md
deleted file mode 100644
index d5fab30f3e..0000000000
--- a/.changeset/new-trees-behave.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-chore: simplify props
diff --git a/.changeset/short-fireants-flow.md b/.changeset/short-fireants-flow.md
deleted file mode 100644
index b9955ff577..0000000000
--- a/.changeset/short-fireants-flow.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': minor
----
-
-feat: add `getAbortSignal()`
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index ef64091ca3..7589eda728 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,15 @@
 # svelte
 
+## 5.35.0
+
+### Minor Changes
+
+- feat: add `getAbortSignal()` ([#16266](https://github.com/sveltejs/svelte/pull/16266))
+
+### Patch Changes
+
+- chore: simplify props ([#16270](https://github.com/sveltejs/svelte/pull/16270))
+
 ## 5.34.9
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 2d88d2a051..e8c28aeaa1 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.34.9",
+  "version": "5.35.0",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 1c0aed6e87..baa2dbd046 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.34.9';
+export const VERSION = '5.35.0';
 export const PUBLIC_VERSION = '5';

From 32882a956bc1283063d6da52401ac02b0aedefdb Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Wed, 2 Jul 2025 14:12:25 +0200
Subject: [PATCH 019/148] feat: add parent hierarchy to `__svelte_meta` objects
 at dev time (#16255)

* feat: add parent hierarchy to `__svelte_meta` objects at dev time

This adds a `parent` property to the `__svelte_meta` properties that are added to elements at dev time. This property represents the closest non-element parent the element is related to. For example for `{#if ...}<div>foo</div>{/if}` the `parent` of the div would be the line/column of the if block.
The parent is recursive and goes upwards (through component boundaries) until the root component is reached, which has no parent.

part of #11389

* oops

* Apply suggestions from code review

Co-authored-by: Rich Harris <rich.harris@vercel.com>

* tweak

* original component tag

* make render appear in tree, keep tree in sync when rerenders occur

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
---
 .changeset/hot-buses-end.md                   |   5 +
 .../3-transform/client/visitors/AwaitBlock.js |   8 +-
 .../3-transform/client/visitors/EachBlock.js  |   4 +-
 .../3-transform/client/visitors/IfBlock.js    |   4 +-
 .../3-transform/client/visitors/KeyBlock.js   |   8 +-
 .../3-transform/client/visitors/RenderTag.js  |  14 +-
 .../client/visitors/shared/component.js       |  10 +-
 .../client/visitors/shared/utils.js           |  35 +++-
 packages/svelte/src/compiler/state.js         |   3 +
 .../svelte/src/internal/client/context.js     |  40 +++-
 .../src/internal/client/dev/elements.js       |   2 +
 .../src/internal/client/dom/blocks/await.js   |  16 +-
 .../client/dom/blocks/svelte-element.js       |   3 +-
 packages/svelte/src/internal/client/index.js  |   2 +-
 .../src/internal/client/reactivity/effects.js |   8 +-
 .../src/internal/client/reactivity/types.d.ts |  10 +-
 .../svelte/src/internal/client/runtime.js     |   9 +-
 .../svelte/src/internal/client/types.d.ts     |   9 +
 .../samples/svelte-meta-parent/_config.js     | 186 ++++++++++++++++++
 .../samples/svelte-meta-parent/child.svelte   |   1 +
 .../samples/svelte-meta-parent/main.svelte    |  50 +++++
 .../svelte-meta-parent/passthrough.svelte     |   9 +
 22 files changed, 408 insertions(+), 28 deletions(-)
 create mode 100644 .changeset/hot-buses-end.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/child.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/passthrough.svelte

diff --git a/.changeset/hot-buses-end.md b/.changeset/hot-buses-end.md
new file mode 100644
index 0000000000..dd5a28fca8
--- /dev/null
+++ b/.changeset/hot-buses-end.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+feat: add parent hierarchy to `__svelte_meta` objects
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitBlock.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitBlock.js
index 7873cf3ddb..c550c8e17b 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitBlock.js
@@ -5,7 +5,7 @@ import { extract_identifiers } from '../../../../utils/ast.js';
 import * as b from '#compiler/builders';
 import { create_derived } from '../utils.js';
 import { get_value } from './shared/declarations.js';
-import { build_expression } from './shared/utils.js';
+import { build_expression, add_svelte_meta } from './shared/utils.js';
 
 /**
  * @param {AST.AwaitBlock} node
@@ -54,7 +54,7 @@ export function AwaitBlock(node, context) {
 	}
 
 	context.state.init.push(
-		b.stmt(
+		add_svelte_meta(
 			b.call(
 				'$.await',
 				context.state.node,
@@ -64,7 +64,9 @@ export function AwaitBlock(node, context) {
 					: b.null,
 				then_block,
 				catch_block
-			)
+			),
+			node,
+			'await'
 		)
 	);
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js
index 201c4b278f..353927b865 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js
@@ -13,7 +13,7 @@ import { dev } from '../../../../state.js';
 import { extract_paths, object } from '../../../../utils/ast.js';
 import * as b from '#compiler/builders';
 import { get_value } from './shared/declarations.js';
-import { build_expression } from './shared/utils.js';
+import { build_expression, add_svelte_meta } from './shared/utils.js';
 
 /**
  * @param {AST.EachBlock} node
@@ -337,7 +337,7 @@ export function EachBlock(node, context) {
 		);
 	}
 
-	context.state.init.push(b.stmt(b.call('$.each', ...args)));
+	context.state.init.push(add_svelte_meta(b.call('$.each', ...args), node, 'each'));
 }
 
 /**
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/IfBlock.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/IfBlock.js
index deab040e50..cfd2bb7b09 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/IfBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/IfBlock.js
@@ -2,7 +2,7 @@
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext } from '../types' */
 import * as b from '#compiler/builders';
-import { build_expression } from './shared/utils.js';
+import { build_expression, add_svelte_meta } from './shared/utils.js';
 
 /**
  * @param {AST.IfBlock} node
@@ -74,7 +74,7 @@ export function IfBlock(node, context) {
 		args.push(b.id('$$elseif'));
 	}
 
-	statements.push(b.stmt(b.call('$.if', ...args)));
+	statements.push(add_svelte_meta(b.call('$.if', ...args), node, 'if'));
 
 	context.state.init.push(b.block(statements));
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/KeyBlock.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/KeyBlock.js
index 2f17479c7e..3add1fbe93 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/KeyBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/KeyBlock.js
@@ -2,7 +2,7 @@
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext } from '../types' */
 import * as b from '#compiler/builders';
-import { build_expression } from './shared/utils.js';
+import { build_expression, add_svelte_meta } from './shared/utils.js';
 
 /**
  * @param {AST.KeyBlock} node
@@ -15,6 +15,10 @@ export function KeyBlock(node, context) {
 	const body = /** @type {Expression} */ (context.visit(node.fragment));
 
 	context.state.init.push(
-		b.stmt(b.call('$.key', context.state.node, b.thunk(key), b.arrow([b.id('$$anchor')], body)))
+		add_svelte_meta(
+			b.call('$.key', context.state.node, b.thunk(key), b.arrow([b.id('$$anchor')], body)),
+			node,
+			'key'
+		)
 	);
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/RenderTag.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/RenderTag.js
index c3615d9d50..7f1a4ae7ba 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/RenderTag.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/RenderTag.js
@@ -3,7 +3,7 @@
 /** @import { ComponentContext } from '../types' */
 import { unwrap_optional } from '../../../../utils/ast.js';
 import * as b from '#compiler/builders';
-import { build_expression } from './shared/utils.js';
+import { add_svelte_meta, build_expression } from './shared/utils.js';
 
 /**
  * @param {AST.RenderTag} node
@@ -48,16 +48,22 @@ export function RenderTag(node, context) {
 		}
 
 		context.state.init.push(
-			b.stmt(b.call('$.snippet', context.state.node, b.thunk(snippet_function), ...args))
+			add_svelte_meta(
+				b.call('$.snippet', context.state.node, b.thunk(snippet_function), ...args),
+				node,
+				'render'
+			)
 		);
 	} else {
 		context.state.init.push(
-			b.stmt(
+			add_svelte_meta(
 				(node.expression.type === 'CallExpression' ? b.call : b.maybe_call)(
 					snippet_function,
 					context.state.node,
 					...args
-				)
+				),
+				node,
+				'render'
 			)
 		);
 	}
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js
index cb6e4de478..aa3704b50b 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js
@@ -4,7 +4,12 @@
 import { dev, is_ignored } from '../../../../../state.js';
 import { get_attribute_chunks, object } from '../../../../../utils/ast.js';
 import * as b from '#compiler/builders';
-import { build_bind_this, memoize_expression, validate_binding } from '../shared/utils.js';
+import {
+	build_bind_this,
+	memoize_expression,
+	validate_binding,
+	add_svelte_meta
+} from '../shared/utils.js';
 import { build_attribute_value } from '../shared/element.js';
 import { build_event_handler } from './events.js';
 import { determine_slot } from '../../../../../utils/slot.js';
@@ -483,7 +488,8 @@ export function build_component(node, component_name, context) {
 		);
 	} else {
 		context.state.template.push_comment();
-		statements.push(b.stmt(fn(anchor)));
+
+		statements.push(add_svelte_meta(fn(anchor), node, 'component', { componentTag: node.name }));
 	}
 
 	return statements.length > 1 ? b.block(statements) : statements[0];
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
index b80466ccc9..de74fede0c 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
@@ -1,4 +1,4 @@
-/** @import { AssignmentExpression, Expression, ExpressionStatement, Identifier, MemberExpression, SequenceExpression, Literal, Super, UpdateExpression, Pattern } from 'estree' */
+/** @import { AssignmentExpression, Expression, Identifier, MemberExpression, SequenceExpression, Literal, Super, UpdateExpression, ExpressionStatement } from 'estree' */
 /** @import { AST, ExpressionMetadata } from '#compiler' */
 /** @import { ComponentClientTransformState, ComponentContext, Context } from '../../types' */
 import { walk } from 'zimmerframe';
@@ -7,7 +7,7 @@ import * as b from '#compiler/builders';
 import { sanitize_template_string } from '../../../../../utils/sanitize_template_string.js';
 import { regex_is_valid_identifier } from '../../../../patterns.js';
 import is_reference from 'is-reference';
-import { dev, is_ignored, locator } from '../../../../../state.js';
+import { dev, is_ignored, locator, component_name } from '../../../../../state.js';
 import { build_getter, create_derived } from '../../utils.js';
 
 /**
@@ -424,3 +424,34 @@ export function build_expression(context, expression, metadata, state = context.
 
 	return sequence;
 }
+
+/**
+ * Wraps a statement/expression with dev stack tracking in dev mode
+ * @param {Expression} expression - The function call to wrap (e.g., $.if, $.each, etc.)
+ * @param {{ start?: number }} node - AST node for location info
+ * @param {'component' | 'if' | 'each' | 'await' | 'key' | 'render'} type - Type of block/component
+ * @param {Record<string, number | string>} [additional] - Any additional properties to add to the dev stack entry
+ * @returns {ExpressionStatement} - Statement with or without dev stack wrapping
+ */
+export function add_svelte_meta(expression, node, type, additional) {
+	if (!dev) {
+		return b.stmt(expression);
+	}
+
+	const location = node.start !== undefined && locator(node.start);
+	if (!location) {
+		return b.stmt(expression);
+	}
+
+	return b.stmt(
+		b.call(
+			'$.add_svelte_meta',
+			b.arrow([], expression),
+			b.literal(type),
+			b.id(component_name),
+			b.literal(location.line),
+			b.literal(location.column),
+			additional && b.object(Object.entries(additional).map(([k, v]) => b.init(k, b.literal(v))))
+		)
+	);
+}
diff --git a/packages/svelte/src/compiler/state.js b/packages/svelte/src/compiler/state.js
index 9095651ced..5eb25dd6bb 100644
--- a/packages/svelte/src/compiler/state.js
+++ b/packages/svelte/src/compiler/state.js
@@ -16,6 +16,9 @@ export let warnings = [];
  */
 export let filename;
 
+/**
+ * The name of the component that is used in the `export default function ...` statement.
+ */
 export let component_name = '<unknown>';
 
 /**
diff --git a/packages/svelte/src/internal/client/context.js b/packages/svelte/src/internal/client/context.js
index 7c7213b7a2..e4220149ab 100644
--- a/packages/svelte/src/internal/client/context.js
+++ b/packages/svelte/src/internal/client/context.js
@@ -1,4 +1,4 @@
-/** @import { ComponentContext } from '#client' */
+/** @import { ComponentContext, DevStackEntry } from '#client' */
 
 import { DEV } from 'esm-env';
 import { lifecycle_outside_component } from '../shared/errors.js';
@@ -11,6 +11,7 @@ import {
 } from './runtime.js';
 import { effect, teardown } from './reactivity/effects.js';
 import { legacy_mode_flag } from '../flags/index.js';
+import { FILENAME } from '../../constants.js';
 
 /** @type {ComponentContext | null} */
 export let component_context = null;
@@ -20,6 +21,43 @@ export function set_component_context(context) {
 	component_context = context;
 }
 
+/** @type {DevStackEntry | null} */
+export let dev_stack = null;
+
+/** @param {DevStackEntry | null} stack */
+export function set_dev_stack(stack) {
+	dev_stack = stack;
+}
+
+/**
+ * Execute a callback with a new dev stack entry
+ * @param {() => any} callback - Function to execute
+ * @param {DevStackEntry['type']} type - Type of block/component
+ * @param {any} component - Component function
+ * @param {number} line - Line number
+ * @param {number} column - Column number
+ * @param {Record<string, any>} [additional] - Any additional properties to add to the dev stack entry
+ * @returns {any}
+ */
+export function add_svelte_meta(callback, type, component, line, column, additional) {
+	const parent = dev_stack;
+
+	dev_stack = {
+		type,
+		file: component[FILENAME],
+		line,
+		column,
+		parent,
+		...additional
+	};
+
+	try {
+		return callback();
+	} finally {
+		dev_stack = parent;
+	}
+}
+
 /**
  * The current component function. Different from current component context:
  * ```html
diff --git a/packages/svelte/src/internal/client/dev/elements.js b/packages/svelte/src/internal/client/dev/elements.js
index f70f893d1e..8dd54e0a2a 100644
--- a/packages/svelte/src/internal/client/dev/elements.js
+++ b/packages/svelte/src/internal/client/dev/elements.js
@@ -2,6 +2,7 @@
 import { COMMENT_NODE, DOCUMENT_FRAGMENT_NODE, ELEMENT_NODE } from '#client/constants';
 import { HYDRATION_END, HYDRATION_START, HYDRATION_START_ELSE } from '../../../constants.js';
 import { hydrating } from '../dom/hydration.js';
+import { dev_stack } from '../context.js';
 
 /**
  * @param {any} fn
@@ -28,6 +29,7 @@ export function add_locations(fn, filename, locations) {
 function assign_location(element, filename, location) {
 	// @ts-expect-error
 	element.__svelte_meta = {
+		parent: dev_stack,
 		loc: { file: filename, line: location[0], column: location[1] }
 	};
 
diff --git a/packages/svelte/src/internal/client/dom/blocks/await.js b/packages/svelte/src/internal/client/dom/blocks/await.js
index 47df5fc9a5..325224fff2 100644
--- a/packages/svelte/src/internal/client/dom/blocks/await.js
+++ b/packages/svelte/src/internal/client/dom/blocks/await.js
@@ -16,9 +16,11 @@ import { queue_micro_task } from '../task.js';
 import { HYDRATION_START_ELSE, UNINITIALIZED } from '../../../../constants.js';
 import {
 	component_context,
+	dev_stack,
 	is_runes,
 	set_component_context,
-	set_dev_current_component_function
+	set_dev_current_component_function,
+	set_dev_stack
 } from '../../context.js';
 
 const PENDING = 0;
@@ -45,6 +47,7 @@ export function await_block(node, get_input, pending_fn, then_fn, catch_fn) {
 
 	/** @type {any} */
 	var component_function = DEV ? component_context?.function : null;
+	var dev_original_stack = DEV ? dev_stack : null;
 
 	/** @type {V | Promise<V> | typeof UNINITIALIZED} */
 	var input = UNINITIALIZED;
@@ -75,7 +78,10 @@ export function await_block(node, get_input, pending_fn, then_fn, catch_fn) {
 			set_active_effect(effect);
 			set_active_reaction(effect); // TODO do we need both?
 			set_component_context(active_component_context);
-			if (DEV) set_dev_current_component_function(component_function);
+			if (DEV) {
+				set_dev_current_component_function(component_function);
+				set_dev_stack(dev_original_stack);
+			}
 		}
 
 		try {
@@ -107,7 +113,11 @@ export function await_block(node, get_input, pending_fn, then_fn, catch_fn) {
 			}
 		} finally {
 			if (restore) {
-				if (DEV) set_dev_current_component_function(null);
+				if (DEV) {
+					set_dev_current_component_function(null);
+					set_dev_stack(null);
+				}
+
 				set_component_context(null);
 				set_active_reaction(null);
 				set_active_effect(null);
diff --git a/packages/svelte/src/internal/client/dom/blocks/svelte-element.js b/packages/svelte/src/internal/client/dom/blocks/svelte-element.js
index ffa57b2d8b..231a3621b1 100644
--- a/packages/svelte/src/internal/client/dom/blocks/svelte-element.js
+++ b/packages/svelte/src/internal/client/dom/blocks/svelte-element.js
@@ -18,7 +18,7 @@ import {
 import { set_should_intro } from '../../render.js';
 import { current_each_item, set_current_each_item } from './each.js';
 import { active_effect } from '../../runtime.js';
-import { component_context } from '../../context.js';
+import { component_context, dev_stack } from '../../context.js';
 import { DEV } from 'esm-env';
 import { EFFECT_TRANSPARENT, ELEMENT_NODE } from '#client/constants';
 import { assign_nodes } from '../template.js';
@@ -107,6 +107,7 @@ export function element(node, get_tag, is_svg, render_fn, get_namespace, locatio
 				if (DEV && location) {
 					// @ts-expect-error
 					element.__svelte_meta = {
+						parent: dev_stack,
 						loc: {
 							file: filename,
 							line: location[0],
diff --git a/packages/svelte/src/internal/client/index.js b/packages/svelte/src/internal/client/index.js
index 60f9af9120..576a30fa77 100644
--- a/packages/svelte/src/internal/client/index.js
+++ b/packages/svelte/src/internal/client/index.js
@@ -1,6 +1,6 @@
 export { createAttachmentKey as attachment } from '../../attachments/index.js';
 export { FILENAME, HMR, NAMESPACE_SVG } from '../../constants.js';
-export { push, pop } from './context.js';
+export { push, pop, add_svelte_meta } from './context.js';
 export { assign, assign_and, assign_or, assign_nullish } from './dev/assign.js';
 export { cleanup_styles } from './dev/css.js';
 export { add_locations } from './dev/elements.js';
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index a2806bde81..a2de8940a6 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -41,7 +41,7 @@ import { DEV } from 'esm-env';
 import { define_property } from '../../shared/utils.js';
 import { get_next_sibling } from '../dom/operations.js';
 import { derived } from './deriveds.js';
-import { component_context, dev_current_component_function } from '../context.js';
+import { component_context, dev_current_component_function, dev_stack } from '../context.js';
 
 /**
  * @param {'$effect' | '$effect.pre' | '$inspect'} rune
@@ -359,7 +359,11 @@ export function template_effect(fn, thunks = [], d = derived) {
  * @param {number} flags
  */
 export function block(fn, flags = 0) {
-	return create_effect(RENDER_EFFECT | BLOCK_EFFECT | flags, fn, true);
+	var effect = create_effect(RENDER_EFFECT | BLOCK_EFFECT | flags, fn, true);
+	if (DEV) {
+		effect.dev_stack = dev_stack;
+	}
+	return effect;
 }
 
 /**
diff --git a/packages/svelte/src/internal/client/reactivity/types.d.ts b/packages/svelte/src/internal/client/reactivity/types.d.ts
index 88c84f27fe..80c4155705 100644
--- a/packages/svelte/src/internal/client/reactivity/types.d.ts
+++ b/packages/svelte/src/internal/client/reactivity/types.d.ts
@@ -1,4 +1,10 @@
-import type { ComponentContext, Dom, Equals, TemplateNode, TransitionManager } from '#client';
+import type {
+	ComponentContext,
+	DevStackEntry,
+	Equals,
+	TemplateNode,
+	TransitionManager
+} from '#client';
 
 export interface Signal {
 	/** Flags bitmask */
@@ -80,6 +86,8 @@ export interface Effect extends Reaction {
 	parent: Effect | null;
 	/** Dev only */
 	component_function?: any;
+	/** Dev only. Only set for certain block effects. Contains a reference to the stack that represents the render tree */
+	dev_stack?: DevStackEntry | null;
 }
 
 export type Source<V = unknown> = Value<V>;
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 5a798ba3e9..8e6242447e 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -34,12 +34,13 @@ import { tracing_expressions, get_stack } from './dev/tracing.js';
 import {
 	component_context,
 	dev_current_component_function,
+	dev_stack,
 	is_runes,
 	set_component_context,
-	set_dev_current_component_function
+	set_dev_current_component_function,
+	set_dev_stack
 } from './context.js';
 import { handle_error, invoke_error_boundary } from './error-handling.js';
-import { snapshot } from '../shared/clone.js';
 
 let is_flushing = false;
 
@@ -444,6 +445,9 @@ export function update_effect(effect) {
 	if (DEV) {
 		var previous_component_fn = dev_current_component_function;
 		set_dev_current_component_function(effect.component_function);
+		var previous_stack = /** @type {any} */ (dev_stack);
+		// only block effects have a dev stack, keep the current one otherwise
+		set_dev_stack(effect.dev_stack ?? dev_stack);
 	}
 
 	try {
@@ -478,6 +482,7 @@ export function update_effect(effect) {
 
 		if (DEV) {
 			set_dev_current_component_function(previous_component_fn);
+			set_dev_stack(previous_stack);
 		}
 	}
 }
diff --git a/packages/svelte/src/internal/client/types.d.ts b/packages/svelte/src/internal/client/types.d.ts
index 9703c2aac1..0b7310e172 100644
--- a/packages/svelte/src/internal/client/types.d.ts
+++ b/packages/svelte/src/internal/client/types.d.ts
@@ -187,4 +187,13 @@ export type SourceLocation =
 	| [line: number, column: number]
 	| [line: number, column: number, SourceLocation[]];
 
+export interface DevStackEntry {
+	file: string;
+	type: 'component' | 'if' | 'each' | 'await' | 'key' | 'render';
+	line: number;
+	column: number;
+	parent: DevStackEntry | null;
+	componentTag?: string;
+}
+
 export * from './reactivity/types';
diff --git a/packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/_config.js b/packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/_config.js
new file mode 100644
index 0000000000..eba85d5098
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/_config.js
@@ -0,0 +1,186 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client', 'hydrate'],
+	compileOptions: {
+		dev: true
+	},
+	html: `
+		<p>no parent</p>
+		<button>toggle</button>
+		<p>if</p>
+		<p>each</p>
+		<p>loading</p>
+		<p>key</p>
+		<p>hi</p>
+		<p>hi</p>
+		<p>hi</p>
+		<p>hi</p>
+		<p>hi</p>
+	`,
+
+	async test({ target, assert }) {
+		function check() {
+			const [main, if_, each, await_, key, child1, child2, child3, child4, dynamic] =
+				target.querySelectorAll('p');
+
+			// @ts-expect-error
+			assert.deepEqual(main.__svelte_meta.parent, null);
+
+			// @ts-expect-error
+			assert.deepEqual(if_.__svelte_meta.parent, {
+				file: 'main.svelte',
+				type: 'if',
+				line: 12,
+				column: 0,
+				parent: null
+			});
+
+			// @ts-expect-error
+			assert.deepEqual(each.__svelte_meta.parent, {
+				file: 'main.svelte',
+				type: 'each',
+				line: 16,
+				column: 0,
+				parent: null
+			});
+
+			// @ts-expect-error
+			assert.deepEqual(await_.__svelte_meta.parent, {
+				file: 'main.svelte',
+				type: 'await',
+				line: 20,
+				column: 0,
+				parent: null
+			});
+
+			// @ts-expect-error
+			assert.deepEqual(key.__svelte_meta.parent, {
+				file: 'main.svelte',
+				type: 'key',
+				line: 26,
+				column: 0,
+				parent: null
+			});
+
+			// @ts-expect-error
+			assert.deepEqual(child1.__svelte_meta.parent, {
+				file: 'main.svelte',
+				type: 'component',
+				componentTag: 'Child',
+				line: 30,
+				column: 0,
+				parent: null
+			});
+
+			// @ts-expect-error
+			assert.deepEqual(child2.__svelte_meta.parent, {
+				file: 'main.svelte',
+				type: 'component',
+				componentTag: 'Child',
+				line: 33,
+				column: 1,
+				parent: {
+					file: 'passthrough.svelte',
+					type: 'render',
+					line: 5,
+					column: 0,
+					parent: {
+						file: 'main.svelte',
+						type: 'component',
+						componentTag: 'Passthrough',
+						line: 32,
+						column: 0,
+						parent: null
+					}
+				}
+			});
+
+			// @ts-expect-error
+			assert.deepEqual(child3.__svelte_meta.parent, {
+				file: 'main.svelte',
+				type: 'component',
+				componentTag: 'Child',
+				line: 38,
+				column: 2,
+				parent: {
+					file: 'passthrough.svelte',
+					type: 'render',
+					line: 5,
+					column: 0,
+					parent: {
+						file: 'main.svelte',
+						type: 'component',
+						componentTag: 'Passthrough',
+						line: 37,
+						column: 1,
+						parent: {
+							file: 'passthrough.svelte',
+							type: 'render',
+							line: 5,
+							column: 0,
+							parent: {
+								file: 'main.svelte',
+								type: 'component',
+								componentTag: 'Passthrough',
+								line: 36,
+								column: 0,
+								parent: null
+							}
+						}
+					}
+				}
+			});
+
+			// @ts-expect-error
+			assert.deepEqual(child4.__svelte_meta.parent, {
+				file: 'passthrough.svelte',
+				type: 'render',
+				line: 8,
+				column: 1,
+				parent: {
+					file: 'passthrough.svelte',
+					type: 'if',
+					line: 7,
+					column: 0,
+					parent: {
+						file: 'main.svelte',
+						type: 'component',
+						componentTag: 'Passthrough',
+						line: 43,
+						column: 1,
+						parent: {
+							file: 'main.svelte',
+							type: 'if',
+							line: 42,
+							column: 0,
+							parent: null
+						}
+					}
+				}
+			});
+
+			// @ts-expect-error
+			assert.deepEqual(dynamic.__svelte_meta.parent, {
+				file: 'main.svelte',
+				type: 'component',
+				componentTag: 'x.y',
+				line: 50,
+				column: 0,
+				parent: null
+			});
+		}
+
+		await tick();
+		check();
+
+		// Test that stack is kept when re-rendering
+		const button = target.querySelector('button');
+		button?.click();
+		await tick();
+		button?.click();
+		await tick();
+		check();
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/child.svelte b/packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/child.svelte
new file mode 100644
index 0000000000..0df6def593
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/child.svelte
@@ -0,0 +1 @@
+<p>hi</p>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/main.svelte b/packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/main.svelte
new file mode 100644
index 0000000000..b9bd46d8f7
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/main.svelte
@@ -0,0 +1,50 @@
+<script>
+	import Child from "./child.svelte";
+	import Passthrough from "./passthrough.svelte";
+	let x = { y: Child }
+	let key = 'test';
+	let show = $state(true);
+</script>
+
+<p>no parent</p>
+<button onclick={() => show = !show}>toggle</button>
+
+{#if true}
+	<p>if</p>
+{/if}
+
+{#each [1]}
+	<p>each</p>
+{/each}
+
+{#await Promise.resolve()}
+	<p>loading</p>
+{:then}
+	<p>await</p>
+{/await}
+
+{#key key}
+	<p>key</p>
+{/key} 
+
+<Child />
+
+<Passthrough>
+	<Child />
+</Passthrough>
+
+<Passthrough>
+	<Passthrough>
+		<Child />
+	</Passthrough>
+</Passthrough>
+
+{#if show}
+	<Passthrough>
+		{#snippet named()}
+			<p>hi</p>
+		{/snippet}
+	</Passthrough>
+{/if}
+
+<x.y />
diff --git a/packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/passthrough.svelte b/packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/passthrough.svelte
new file mode 100644
index 0000000000..70ba81a4c1
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/passthrough.svelte
@@ -0,0 +1,9 @@
+<script>
+	let { children, named } = $props();
+</script>
+
+{@render children?.()}
+
+{#if true}
+	{@render named?.()}
+{/if}

From 49cba86e9b604f66bcd037e5eeb7a27788510b3b Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 2 Jul 2025 11:19:51 -0400
Subject: [PATCH 020/148] chore: rename EFFECT_HAS_DERIVED to EFFECT_PRESERVED
 (#16283)

---
 packages/svelte/src/internal/client/constants.js           | 2 +-
 packages/svelte/src/internal/client/reactivity/deriveds.js | 4 ++--
 packages/svelte/src/internal/client/reactivity/effects.js  | 4 ++--
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/packages/svelte/src/internal/client/constants.js b/packages/svelte/src/internal/client/constants.js
index cd5e0d2244..38db28fecf 100644
--- a/packages/svelte/src/internal/client/constants.js
+++ b/packages/svelte/src/internal/client/constants.js
@@ -17,7 +17,7 @@ export const EFFECT_RAN = 1 << 15;
 export const EFFECT_TRANSPARENT = 1 << 16;
 export const INSPECT_EFFECT = 1 << 18;
 export const HEAD_EFFECT = 1 << 19;
-export const EFFECT_HAS_DERIVED = 1 << 20;
+export const EFFECT_PRESERVED = 1 << 20;
 export const EFFECT_IS_UPDATING = 1 << 21;
 
 export const STATE_SYMBOL = Symbol('$state');
diff --git a/packages/svelte/src/internal/client/reactivity/deriveds.js b/packages/svelte/src/internal/client/reactivity/deriveds.js
index d3123d24a1..fdfc13c0e2 100644
--- a/packages/svelte/src/internal/client/reactivity/deriveds.js
+++ b/packages/svelte/src/internal/client/reactivity/deriveds.js
@@ -1,6 +1,6 @@
 /** @import { Derived, Effect } from '#client' */
 import { DEV } from 'esm-env';
-import { CLEAN, DERIVED, DIRTY, EFFECT_HAS_DERIVED, MAYBE_DIRTY, UNOWNED } from '#client/constants';
+import { CLEAN, DERIVED, DIRTY, EFFECT_PRESERVED, MAYBE_DIRTY, UNOWNED } from '#client/constants';
 import {
 	active_reaction,
 	active_effect,
@@ -38,7 +38,7 @@ export function derived(fn) {
 	} else {
 		// Since deriveds are evaluated lazily, any effects created inside them are
 		// created too late to ensure that the parent effect is added to the tree
-		active_effect.f |= EFFECT_HAS_DERIVED;
+		active_effect.f |= EFFECT_PRESERVED;
 	}
 
 	/** @type {Derived<V>} */
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index a2de8940a6..702c410ce8 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -31,7 +31,7 @@ import {
 	INSPECT_EFFECT,
 	HEAD_EFFECT,
 	MAYBE_DIRTY,
-	EFFECT_HAS_DERIVED,
+	EFFECT_PRESERVED,
 	BOUNDARY_EFFECT,
 	STALE_REACTION
 } from '#client/constants';
@@ -135,7 +135,7 @@ function create_effect(type, fn, sync, push = true) {
 		effect.first === null &&
 		effect.nodes_start === null &&
 		effect.teardown === null &&
-		(effect.f & (EFFECT_HAS_DERIVED | BOUNDARY_EFFECT)) === 0;
+		(effect.f & (EFFECT_PRESERVED | BOUNDARY_EFFECT)) === 0;
 
 	if (!inert && push) {
 		if (parent !== null) {

From 7914cb183554b16627bec40c8e91b163beaf0480 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 2 Jul 2025 12:16:53 -0400
Subject: [PATCH 021/148] chore: convert boundary implementation to a class
 (#16284)

* WIP class boundaries

* WIP

* WIP

* WIP

* unused

* unused

* unused
---
 .../internal/client/dom/blocks/boundary.js    | 233 +++++++++++-------
 .../src/internal/client/error-handling.js     |   4 +-
 .../src/internal/client/reactivity/effects.js |   1 +
 .../src/internal/client/reactivity/types.d.ts |   3 +
 4 files changed, 149 insertions(+), 92 deletions(-)

diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index d7a53da1d1..03cec4fd2f 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -1,6 +1,5 @@
 /** @import { Effect, TemplateNode, } from '#client' */
-
-import { BOUNDARY_EFFECT, EFFECT_TRANSPARENT } from '#client/constants';
+import { BOUNDARY_EFFECT, EFFECT_PRESERVED, EFFECT_TRANSPARENT } from '#client/constants';
 import { component_context, set_component_context } from '../../context.js';
 import { invoke_error_boundary } from '../../error-handling.js';
 import { block, branch, destroy_effect, pause_effect } from '../../reactivity/effects.js';
@@ -21,116 +20,170 @@ import {
 import { queue_micro_task } from '../task.js';
 
 /**
- * @param {Effect} boundary
- * @param {() => void} fn
+ * @typedef {{
+ * 	 onerror?: (error: unknown, reset: () => void) => void;
+ *   failed?: (anchor: Node, error: () => unknown, reset: () => () => void) => void;
+ * }} BoundaryProps
  */
-function with_boundary(boundary, fn) {
-	var previous_effect = active_effect;
-	var previous_reaction = active_reaction;
-	var previous_ctx = component_context;
-
-	set_active_effect(boundary);
-	set_active_reaction(boundary);
-	set_component_context(boundary.ctx);
-
-	try {
-		fn();
-	} finally {
-		set_active_effect(previous_effect);
-		set_active_reaction(previous_reaction);
-		set_component_context(previous_ctx);
-	}
-}
+
+var flags = EFFECT_TRANSPARENT | EFFECT_PRESERVED | BOUNDARY_EFFECT;
 
 /**
  * @param {TemplateNode} node
- * @param {{
- * 	 onerror?: (error: unknown, reset: () => void) => void,
- *   failed?: (anchor: Node, error: () => unknown, reset: () => () => void) => void
- * }} props
- * @param {((anchor: Node) => void)} boundary_fn
+ * @param {BoundaryProps} props
+ * @param {((anchor: Node) => void)} children
  * @returns {void}
  */
-export function boundary(node, props, boundary_fn) {
-	var anchor = node;
+export function boundary(node, props, children) {
+	new Boundary(node, props, children);
+}
+
+export class Boundary {
+	/** @type {TemplateNode} */
+	#anchor;
+
+	/** @type {TemplateNode} */
+	#hydrate_open;
+
+	/** @type {BoundaryProps} */
+	#props;
+
+	/** @type {((anchor: Node) => void)} */
+	#children;
 
 	/** @type {Effect} */
-	var boundary_effect;
-
-	block(() => {
-		var boundary = /** @type {Effect} */ (active_effect);
-		var hydrate_open = hydrate_node;
-		var is_creating_fallback = false;
-
-		// We re-use the effect's fn property to avoid allocation of an additional field
-		boundary.fn = (/** @type {unknown}} */ error) => {
-			var onerror = props.onerror;
-			let failed = props.failed;
-
-			// If we have nothing to capture the error, or if we hit an error while
-			// rendering the fallback, re-throw for another boundary to handle
-			if ((!onerror && !failed) || is_creating_fallback) {
-				throw error;
-			}
+	#effect;
 
-			var reset = () => {
-				pause_effect(boundary_effect);
+	/** @type {Effect | null} */
+	#main_effect = null;
 
-				with_boundary(boundary, () => {
-					is_creating_fallback = false;
-					boundary_effect = branch(() => boundary_fn(anchor));
-				});
-			};
+	/** @type {Effect | null} */
+	#failed_effect = null;
 
-			var previous_reaction = active_reaction;
+	#is_creating_fallback = false;
 
-			try {
-				set_active_reaction(null);
-				onerror?.(error, reset);
-			} finally {
-				set_active_reaction(previous_reaction);
+	/**
+	 * @param {TemplateNode} node
+	 * @param {BoundaryProps} props
+	 * @param {((anchor: Node) => void)} children
+	 */
+	constructor(node, props, children) {
+		this.#anchor = node;
+		this.#props = props;
+		this.#children = children;
+
+		this.#hydrate_open = hydrate_node;
+
+		this.#effect = block(() => {
+			/** @type {Effect} */ (active_effect).b = this;
+
+			if (hydrating) {
+				hydrate_next();
 			}
 
-			if (boundary_effect) {
-				destroy_effect(boundary_effect);
-			} else if (hydrating) {
-				set_hydrate_node(hydrate_open);
-				next();
-				set_hydrate_node(remove_nodes());
+			try {
+				this.#main_effect = branch(() => children(this.#anchor));
+			} catch (error) {
+				this.error(error);
 			}
+		}, flags);
 
-			if (failed) {
-				// Render the `failed` snippet in a microtask
-				queue_micro_task(() => {
-					with_boundary(boundary, () => {
-						is_creating_fallback = true;
-
-						try {
-							boundary_effect = branch(() => {
-								failed(
-									anchor,
-									() => error,
-									() => reset
-								);
-							});
-						} catch (error) {
-							invoke_error_boundary(error, /** @type {Effect} */ (boundary.parent));
-						}
-
-						is_creating_fallback = false;
-					});
+		if (hydrating) {
+			this.#anchor = hydrate_node;
+		}
+	}
+
+	/**
+	 * @param {() => Effect | null} fn
+	 */
+	#run(fn) {
+		var previous_effect = active_effect;
+		var previous_reaction = active_reaction;
+		var previous_ctx = component_context;
+
+		set_active_effect(this.#effect);
+		set_active_reaction(this.#effect);
+		set_component_context(this.#effect.ctx);
+
+		try {
+			return fn();
+		} finally {
+			set_active_effect(previous_effect);
+			set_active_reaction(previous_reaction);
+			set_component_context(previous_ctx);
+		}
+	}
+
+	/** @param {unknown} error */
+	error(error) {
+		var onerror = this.#props.onerror;
+		let failed = this.#props.failed;
+
+		const reset = () => {
+			if (this.#failed_effect !== null) {
+				pause_effect(this.#failed_effect, () => {
+					this.#failed_effect = null;
 				});
 			}
+
+			this.#main_effect = this.#run(() => {
+				this.#is_creating_fallback = false;
+				return branch(() => this.#children(this.#anchor));
+			});
 		};
 
-		if (hydrating) {
-			hydrate_next();
+		// If we have nothing to capture the error, or if we hit an error while
+		// rendering the fallback, re-throw for another boundary to handle
+		if (this.#is_creating_fallback || (!onerror && !failed)) {
+			throw error;
+		}
+
+		var previous_reaction = active_reaction;
+
+		try {
+			set_active_reaction(null);
+			onerror?.(error, reset);
+		} finally {
+			set_active_reaction(previous_reaction);
 		}
 
-		boundary_effect = branch(() => boundary_fn(anchor));
-	}, EFFECT_TRANSPARENT | BOUNDARY_EFFECT);
+		if (this.#main_effect) {
+			destroy_effect(this.#main_effect);
+			this.#main_effect = null;
+		}
 
-	if (hydrating) {
-		anchor = hydrate_node;
+		if (this.#failed_effect) {
+			destroy_effect(this.#failed_effect);
+			this.#failed_effect = null;
+		}
+
+		if (hydrating) {
+			set_hydrate_node(this.#hydrate_open);
+			next();
+			set_hydrate_node(remove_nodes());
+		}
+
+		if (failed) {
+			queue_micro_task(() => {
+				this.#failed_effect = this.#run(() => {
+					this.#is_creating_fallback = true;
+
+					try {
+						return branch(() => {
+							failed(
+								this.#anchor,
+								() => error,
+								() => reset
+							);
+						});
+					} catch (error) {
+						invoke_error_boundary(error, /** @type {Effect} */ (this.#effect.parent));
+						return null;
+					} finally {
+						this.#is_creating_fallback = false;
+					}
+				});
+			});
+		}
 	}
 }
diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index 99f3ed6cd4..378f7408ef 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -1,4 +1,5 @@
 /** @import { Effect } from '#client' */
+/** @import { Boundary } from './dom/blocks/boundary.js' */
 import { DEV } from 'esm-env';
 import { FILENAME } from '../../constants.js';
 import { is_firefox } from './dom/operations.js';
@@ -39,8 +40,7 @@ export function invoke_error_boundary(error, effect) {
 	while (effect !== null) {
 		if ((effect.f & BOUNDARY_EFFECT) !== 0) {
 			try {
-				// @ts-expect-error
-				effect.fn(error);
+				/** @type {Boundary} */ (effect.b).error(error);
 				return;
 			} catch {}
 		}
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index 702c410ce8..7570064c37 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -104,6 +104,7 @@ function create_effect(type, fn, sync, push = true) {
 		last: null,
 		next: null,
 		parent,
+		b: parent && parent.b,
 		prev: null,
 		teardown: null,
 		transitions: null,
diff --git a/packages/svelte/src/internal/client/reactivity/types.d.ts b/packages/svelte/src/internal/client/reactivity/types.d.ts
index 80c4155705..90f922df68 100644
--- a/packages/svelte/src/internal/client/reactivity/types.d.ts
+++ b/packages/svelte/src/internal/client/reactivity/types.d.ts
@@ -5,6 +5,7 @@ import type {
 	TemplateNode,
 	TransitionManager
 } from '#client';
+import type { Boundary } from '../dom/blocks/boundary';
 
 export interface Signal {
 	/** Flags bitmask */
@@ -84,6 +85,8 @@ export interface Effect extends Reaction {
 	last: null | Effect;
 	/** Parent effect */
 	parent: Effect | null;
+	/** The boundary this effect belongs to */
+	b: Boundary | null;
 	/** Dev only */
 	component_function?: any;
 	/** Dev only. Only set for certain block effects. Contains a reference to the stack that represents the render tree */

From dde791311d3c6a7b28e276548e6beb45a9f2e798 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 2 Jul 2025 13:06:45 -0400
Subject: [PATCH 022/148] chore: minor tweaks (#16285)

---
 packages/svelte/src/internal/client/constants.js | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/packages/svelte/src/internal/client/constants.js b/packages/svelte/src/internal/client/constants.js
index 38db28fecf..1cffa43940 100644
--- a/packages/svelte/src/internal/client/constants.js
+++ b/packages/svelte/src/internal/client/constants.js
@@ -15,17 +15,17 @@ export const DESTROYED = 1 << 14;
 export const EFFECT_RAN = 1 << 15;
 /** 'Transparent' effects do not create a transition boundary */
 export const EFFECT_TRANSPARENT = 1 << 16;
-export const INSPECT_EFFECT = 1 << 18;
-export const HEAD_EFFECT = 1 << 19;
-export const EFFECT_PRESERVED = 1 << 20;
-export const EFFECT_IS_UPDATING = 1 << 21;
+export const INSPECT_EFFECT = 1 << 17;
+export const HEAD_EFFECT = 1 << 18;
+export const EFFECT_PRESERVED = 1 << 19;
+export const EFFECT_IS_UPDATING = 1 << 20;
 
 export const STATE_SYMBOL = Symbol('$state');
 export const LEGACY_PROPS = Symbol('legacy props');
 export const LOADING_ATTR_SYMBOL = Symbol('');
 export const PROXY_PATH_SYMBOL = Symbol('proxy path');
 
-// allow users to ignore aborted signal errors if `reason.stale`
+/** allow users to ignore aborted signal errors if `reason.name === 'StaleReactionError` */
 export const STALE_REACTION = new (class StaleReactionError extends Error {
 	name = 'StaleReactionError';
 	message = 'The reaction that called `getAbortSignal()` was re-run or destroyed';

From 5ebbedf2051715f1df10a884976d7d23b1d7f5fc Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Wed, 2 Jul 2025 22:18:28 +0200
Subject: [PATCH 023/148] Version Packages (#16281)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/hot-buses-end.md    | 5 -----
 packages/svelte/CHANGELOG.md   | 6 ++++++
 packages/svelte/package.json   | 2 +-
 packages/svelte/src/version.js | 2 +-
 4 files changed, 8 insertions(+), 7 deletions(-)
 delete mode 100644 .changeset/hot-buses-end.md

diff --git a/.changeset/hot-buses-end.md b/.changeset/hot-buses-end.md
deleted file mode 100644
index dd5a28fca8..0000000000
--- a/.changeset/hot-buses-end.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-feat: add parent hierarchy to `__svelte_meta` objects
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 7589eda728..fb5d43c9dd 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,11 @@
 # svelte
 
+## 5.35.1
+
+### Patch Changes
+
+- feat: add parent hierarchy to `__svelte_meta` objects ([#16255](https://github.com/sveltejs/svelte/pull/16255))
+
 ## 5.35.0
 
 ### Minor Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index e8c28aeaa1..b1e57b9829 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.35.0",
+  "version": "5.35.1",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index baa2dbd046..2efcf03eb1 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.35.0';
+export const VERSION = '5.35.1';
 export const PUBLIC_VERSION = '5';

From eeb32a50d14d2ac69970b0e207746092a34d2fc3 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 3 Jul 2025 11:47:26 -0400
Subject: [PATCH 024/148] fix: bump esrap (#16295)

---
 .changeset/fifty-hats-watch.md |  5 +++++
 packages/svelte/package.json   |  2 +-
 pnpm-lock.yaml                 | 10 +++++-----
 3 files changed, 11 insertions(+), 6 deletions(-)
 create mode 100644 .changeset/fifty-hats-watch.md

diff --git a/.changeset/fifty-hats-watch.md b/.changeset/fifty-hats-watch.md
new file mode 100644
index 0000000000..83bb72e735
--- /dev/null
+++ b/.changeset/fifty-hats-watch.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: bump esrap
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index b1e57b9829..b6776a8fbc 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -171,7 +171,7 @@
     "axobject-query": "^4.1.0",
     "clsx": "^2.1.1",
     "esm-env": "^1.2.1",
-    "esrap": "^2.0.0",
+    "esrap": "^2.1.0",
     "is-reference": "^3.0.3",
     "locate-character": "^3.0.0",
     "magic-string": "^0.30.11",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index b7fb655b2d..87fb2b2667 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -87,8 +87,8 @@ importers:
         specifier: ^1.2.1
         version: 1.2.1
       esrap:
-        specifier: ^2.0.0
-        version: 2.0.0
+        specifier: ^2.1.0
+        version: 2.1.0
       is-reference:
         specifier: ^3.0.3
         version: 3.0.3
@@ -1261,8 +1261,8 @@ packages:
     resolution: {integrity: sha512-YQLXUplAwJgCydQ78IMJywZCceoqk1oH01OERdSAJc/7U2AylwjhSCLDEtqwg811idIS/9fIU5GjG73IgjKMVg==}
     engines: {node: '>=0.10'}
 
-  esrap@2.0.0:
-    resolution: {integrity: sha512-zhw1TDqno99Ld5wOpe0t47rzVyxfGc1fvxNzPsqk4idUf5dcAePkAyfTceLJaSTytjiWDu26S5tI+grjvymXJA==}
+  esrap@2.1.0:
+    resolution: {integrity: sha512-yzmPNpl7TBbMRC5Lj2JlJZNPml0tzqoqP5B1JXycNUwtqma9AKCO0M2wHrdgsHcy1WRW7S9rJknAMtByg3usgA==}
 
   esrecurse@4.3.0:
     resolution: {integrity: sha512-KmfKL3b6G+RXvP8N1vr3Tq1kL/oCFgn2NYXEtqP8/L3pKapUA4G8cFVaoF3SU323CD4XypR/ffioHmkti6/Tag==}
@@ -3622,7 +3622,7 @@ snapshots:
     dependencies:
       estraverse: 5.3.0
 
-  esrap@2.0.0:
+  esrap@2.1.0:
     dependencies:
       '@jridgewell/sourcemap-codec': 1.5.0
 

From 220e901a825a23df7c310cd5978d3141e573e645 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Thu, 3 Jul 2025 11:50:58 -0400
Subject: [PATCH 025/148] Version Packages (#16297)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/fifty-hats-watch.md | 5 -----
 packages/svelte/CHANGELOG.md   | 6 ++++++
 packages/svelte/package.json   | 2 +-
 packages/svelte/src/version.js | 2 +-
 4 files changed, 8 insertions(+), 7 deletions(-)
 delete mode 100644 .changeset/fifty-hats-watch.md

diff --git a/.changeset/fifty-hats-watch.md b/.changeset/fifty-hats-watch.md
deleted file mode 100644
index 83bb72e735..0000000000
--- a/.changeset/fifty-hats-watch.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: bump esrap
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index fb5d43c9dd..ad72bfabb0 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,11 @@
 # svelte
 
+## 5.35.2
+
+### Patch Changes
+
+- fix: bump esrap ([#16295](https://github.com/sveltejs/svelte/pull/16295))
+
 ## 5.35.1
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index b6776a8fbc..872c21a179 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.35.1",
+  "version": "5.35.2",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 2efcf03eb1..47c354c7a2 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.35.1';
+export const VERSION = '5.35.2';
 export const PUBLIC_VERSION = '5';

From 432763a03ebcb4c03e7c5084cb52aac6f1afaa22 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 3 Jul 2025 12:11:28 -0400
Subject: [PATCH 026/148] chore: `reaction_sources` -> `source_ownership`
 (#16287)

* reaction_sources -> source_ownership

* put equality statements first, it's faster
---
 .../src/internal/client/reactivity/sources.js |  4 +--
 .../svelte/src/internal/client/runtime.js     | 28 ++++++++++++-------
 2 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index 0db3530232..a86ccfee4f 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -11,7 +11,7 @@ import {
 	untrack,
 	increment_write_version,
 	update_effect,
-	reaction_sources,
+	source_ownership,
 	check_dirtiness,
 	untracking,
 	is_destroying_effect,
@@ -140,7 +140,7 @@ export function set(source, value, should_proxy = false) {
 		(!untracking || (active_reaction.f & INSPECT_EFFECT) !== 0) &&
 		is_runes() &&
 		(active_reaction.f & (DERIVED | BLOCK_EFFECT | INSPECT_EFFECT)) !== 0 &&
-		!(reaction_sources?.[1].includes(source) && reaction_sources[0] === active_reaction)
+		!(source_ownership?.reaction === active_reaction && source_ownership.sources.includes(source))
 	) {
 		e.state_unsafe_mutation();
 	}
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 8e6242447e..fce6c78b56 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -86,17 +86,17 @@ export function set_active_effect(effect) {
 /**
  * When sources are created within a reaction, reading and writing
  * them within that reaction should not cause a re-run
- * @type {null | [active_reaction: Reaction, sources: Source[]]}
+ * @type {null | { reaction: Reaction, sources: Source[] }}
  */
-export let reaction_sources = null;
+export let source_ownership = null;
 
 /** @param {Value} value */
 export function push_reaction_value(value) {
 	if (active_reaction !== null && active_reaction.f & EFFECT_IS_UPDATING) {
-		if (reaction_sources === null) {
-			reaction_sources = [active_reaction, [value]];
+		if (source_ownership === null) {
+			source_ownership = { reaction: active_reaction, sources: [value] };
 		} else {
-			reaction_sources[1].push(value);
+			source_ownership.sources.push(value);
 		}
 	}
 }
@@ -235,7 +235,12 @@ function schedule_possible_effect_self_invalidation(signal, effect, root = true)
 	for (var i = 0; i < reactions.length; i++) {
 		var reaction = reactions[i];
 
-		if (reaction_sources?.[1].includes(signal) && reaction_sources[0] === active_reaction) continue;
+		if (
+			source_ownership?.reaction === active_reaction &&
+			source_ownership.sources.includes(signal)
+		) {
+			continue;
+		}
 
 		if ((reaction.f & DERIVED) !== 0) {
 			schedule_possible_effect_self_invalidation(/** @type {Derived} */ (reaction), effect, false);
@@ -257,7 +262,7 @@ export function update_reaction(reaction) {
 	var previous_untracked_writes = untracked_writes;
 	var previous_reaction = active_reaction;
 	var previous_skip_reaction = skip_reaction;
-	var previous_reaction_sources = reaction_sources;
+	var previous_reaction_sources = source_ownership;
 	var previous_component_context = component_context;
 	var previous_untracking = untracking;
 
@@ -270,7 +275,7 @@ export function update_reaction(reaction) {
 		(flags & UNOWNED) !== 0 && (untracking || !is_updating_effect || active_reaction === null);
 	active_reaction = (flags & (BRANCH_EFFECT | ROOT_EFFECT)) === 0 ? reaction : null;
 
-	reaction_sources = null;
+	source_ownership = null;
 	set_component_context(reaction.ctx);
 	untracking = false;
 	read_version++;
@@ -358,7 +363,7 @@ export function update_reaction(reaction) {
 		untracked_writes = previous_untracked_writes;
 		active_reaction = previous_reaction;
 		skip_reaction = previous_skip_reaction;
-		reaction_sources = previous_reaction_sources;
+		source_ownership = previous_reaction_sources;
 		set_component_context(previous_component_context);
 		untracking = previous_untracking;
 
@@ -739,7 +744,10 @@ export function get(signal) {
 
 	// Register the dependency on the current reaction signal.
 	if (active_reaction !== null && !untracking) {
-		if (!reaction_sources?.[1].includes(signal) || reaction_sources[0] !== active_reaction) {
+		if (
+			source_ownership?.reaction !== active_reaction ||
+			!source_ownership?.sources.includes(signal)
+		) {
 			var deps = active_reaction.deps;
 			if (signal.rv < read_version) {
 				signal.rv = read_version;

From c3348aea06b5dcc13159b96053351f36d6cb6d71 Mon Sep 17 00:00:00 2001
From: 7nik <kifiranet@gmail.com>
Date: Fri, 4 Jul 2025 17:54:37 +0300
Subject: [PATCH 027/148] fix: do not proxify the value assigned to a derived
 (#16302)

---
 .changeset/new-wolves-punch.md                |  5 ++++
 .../client/visitors/AssignmentExpression.js   |  1 +
 .../samples/writable-derived-4/_config.js     | 23 +++++++++++++++++++
 .../samples/writable-derived-4/main.svelte    |  9 ++++++++
 4 files changed, 38 insertions(+)
 create mode 100644 .changeset/new-wolves-punch.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/writable-derived-4/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/writable-derived-4/main.svelte

diff --git a/.changeset/new-wolves-punch.md b/.changeset/new-wolves-punch.md
new file mode 100644
index 0000000000..c856038cbc
--- /dev/null
+++ b/.changeset/new-wolves-punch.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: do not proxify the value assigned to a derived
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/AssignmentExpression.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/AssignmentExpression.js
index ce190814f8..7d64d60bca 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/AssignmentExpression.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/AssignmentExpression.js
@@ -137,6 +137,7 @@ function build_assignment(operator, left, right, context) {
 				binding.kind !== 'prop' &&
 				binding.kind !== 'bindable_prop' &&
 				binding.kind !== 'raw_state' &&
+				binding.kind !== 'derived' &&
 				binding.kind !== 'store_sub' &&
 				context.state.analysis.runes &&
 				should_proxy(right, context.state.scope) &&
diff --git a/packages/svelte/tests/runtime-runes/samples/writable-derived-4/_config.js b/packages/svelte/tests/runtime-runes/samples/writable-derived-4/_config.js
new file mode 100644
index 0000000000..8d312ca73a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/writable-derived-4/_config.js
@@ -0,0 +1,23 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	test({ assert, target }) {
+		const [btn1, btn2, btn3] = target.getElementsByTagName('button');
+		const [div] = target.getElementsByTagName('div');
+
+		flushSync(() => btn1.click());
+		assert.equal(div.textContent, '1');
+		flushSync(() => btn2.click());
+		assert.equal(div.textContent, '1');
+		flushSync(() => btn3.click());
+		assert.equal(div.textContent, '2');
+
+		flushSync(() => btn1.click());
+		assert.equal(div.textContent, '2');
+		flushSync(() => btn2.click());
+		assert.equal(div.textContent, '2');
+		flushSync(() => btn3.click());
+		assert.equal(div.textContent, '3');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/writable-derived-4/main.svelte b/packages/svelte/tests/runtime-runes/samples/writable-derived-4/main.svelte
new file mode 100644
index 0000000000..a24f69ba77
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/writable-derived-4/main.svelte
@@ -0,0 +1,9 @@
+<script>
+	let count = $derived({ value: 1 });
+</script>
+
+<button onclick={() => count.value++}>mutate</button>
+<button onclick={() => count = count}>assign self</button>
+<button onclick={() => count = {...count} }>assign copy</button>
+
+<div>{count.value}</div>

From 834cd91b367172859b26d35a23aad4e87800b881 Mon Sep 17 00:00:00 2001
From: Paolo Ricciuti <ricciutipaolo@gmail.com>
Date: Sun, 6 Jul 2025 14:57:45 +0200
Subject: [PATCH 028/148] fix: account for mounting when `select_option` in
 `attribute_effect` (#16309)

---
 .changeset/curvy-carrots-prove.md                        | 5 +++++
 .../src/internal/client/dom/elements/attributes.js       | 5 +++--
 .../samples/select-spread-option-selected/_config.js     | 9 +++++++++
 .../samples/select-spread-option-selected/main.svelte    | 8 ++++++++
 4 files changed, 25 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/curvy-carrots-prove.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/select-spread-option-selected/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/select-spread-option-selected/main.svelte

diff --git a/.changeset/curvy-carrots-prove.md b/.changeset/curvy-carrots-prove.md
new file mode 100644
index 0000000000..7723990179
--- /dev/null
+++ b/.changeset/curvy-carrots-prove.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: account for mounting when `select_option` in `attribute_effect`
diff --git a/packages/svelte/src/internal/client/dom/elements/attributes.js b/packages/svelte/src/internal/client/dom/elements/attributes.js
index 5db685cf3e..c96338778f 100644
--- a/packages/svelte/src/internal/client/dom/elements/attributes.js
+++ b/packages/svelte/src/internal/client/dom/elements/attributes.js
@@ -514,9 +514,10 @@ export function attribute_effect(
 
 	if (is_select) {
 		var select = /** @type {HTMLSelectElement} */ (element);
-
+		var mounting = true;
 		effect(() => {
-			select_option(select, /** @type {Record<string | symbol, any>} */ (prev).value);
+			select_option(select, /** @type {Record<string | symbol, any>} */ (prev).value, mounting);
+			mounting = false;
 			init_select(select);
 		});
 	}
diff --git a/packages/svelte/tests/runtime-runes/samples/select-spread-option-selected/_config.js b/packages/svelte/tests/runtime-runes/samples/select-spread-option-selected/_config.js
new file mode 100644
index 0000000000..50da3ac095
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/select-spread-option-selected/_config.js
@@ -0,0 +1,9 @@
+import { ok, test } from '../../test';
+
+export default test({
+	async test({ assert, target, instance }) {
+		const select = target.querySelector('select');
+		ok(select);
+		assert.equal(select.selectedIndex, 1);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/select-spread-option-selected/main.svelte b/packages/svelte/tests/runtime-runes/samples/select-spread-option-selected/main.svelte
new file mode 100644
index 0000000000..e5fc6c5535
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/select-spread-option-selected/main.svelte
@@ -0,0 +1,8 @@
+<script>
+	let others = {onclick: ()=> {}}
+</script>
+
+<select {...others}>
+	<option>o1</option>
+	<option selected>o2</option>
+</select>

From 4a26edf54576152affe8649eca8c9b3d1a5b8015 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 7 Jul 2025 10:17:17 -0400
Subject: [PATCH 029/148] chore: remove unused `mounting` variable from
 `select_option` call (#16312)

---
 .../svelte/src/internal/client/dom/elements/attributes.js  | 7 +++----
 .../src/internal/client/dom/elements/bindings/select.js    | 4 ++--
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/packages/svelte/src/internal/client/dom/elements/attributes.js b/packages/svelte/src/internal/client/dom/elements/attributes.js
index c96338778f..66f484a59a 100644
--- a/packages/svelte/src/internal/client/dom/elements/attributes.js
+++ b/packages/svelte/src/internal/client/dom/elements/attributes.js
@@ -491,7 +491,7 @@ export function attribute_effect(
 		var current = set_attributes(element, prev, next, css_hash, skip_warning);
 
 		if (inited && is_select && 'value' in next) {
-			select_option(/** @type {HTMLSelectElement} */ (element), next.value, false);
+			select_option(/** @type {HTMLSelectElement} */ (element), next.value);
 		}
 
 		for (let symbol of Object.getOwnPropertySymbols(effects)) {
@@ -514,10 +514,9 @@ export function attribute_effect(
 
 	if (is_select) {
 		var select = /** @type {HTMLSelectElement} */ (element);
-		var mounting = true;
+
 		effect(() => {
-			select_option(select, /** @type {Record<string | symbol, any>} */ (prev).value, mounting);
-			mounting = false;
+			select_option(select, /** @type {Record<string | symbol, any>} */ (prev).value, true);
 			init_select(select);
 		});
 	}
diff --git a/packages/svelte/src/internal/client/dom/elements/bindings/select.js b/packages/svelte/src/internal/client/dom/elements/bindings/select.js
index 5e89686d86..e39fb865cd 100644
--- a/packages/svelte/src/internal/client/dom/elements/bindings/select.js
+++ b/packages/svelte/src/internal/client/dom/elements/bindings/select.js
@@ -9,9 +9,9 @@ import * as w from '../../../warnings.js';
  * @template V
  * @param {HTMLSelectElement} select
  * @param {V} value
- * @param {boolean} [mounting]
+ * @param {boolean} mounting
  */
-export function select_option(select, value, mounting) {
+export function select_option(select, value, mounting = false) {
 	if (select.multiple) {
 		// If value is null or undefined, keep the selection as is
 		if (value == undefined) {

From 63e48365fbad844f5a82cf5e5a994fdfd13f419b Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Mon, 7 Jul 2025 10:53:41 -0400
Subject: [PATCH 030/148] Version Packages (#16303)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/curvy-carrots-prove.md | 5 -----
 .changeset/new-wolves-punch.md    | 5 -----
 packages/svelte/CHANGELOG.md      | 8 ++++++++
 packages/svelte/package.json      | 2 +-
 packages/svelte/src/version.js    | 2 +-
 5 files changed, 10 insertions(+), 12 deletions(-)
 delete mode 100644 .changeset/curvy-carrots-prove.md
 delete mode 100644 .changeset/new-wolves-punch.md

diff --git a/.changeset/curvy-carrots-prove.md b/.changeset/curvy-carrots-prove.md
deleted file mode 100644
index 7723990179..0000000000
--- a/.changeset/curvy-carrots-prove.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: account for mounting when `select_option` in `attribute_effect`
diff --git a/.changeset/new-wolves-punch.md b/.changeset/new-wolves-punch.md
deleted file mode 100644
index c856038cbc..0000000000
--- a/.changeset/new-wolves-punch.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: do not proxify the value assigned to a derived
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index ad72bfabb0..4f1be5e299 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,13 @@
 # svelte
 
+## 5.35.3
+
+### Patch Changes
+
+- fix: account for mounting when `select_option` in `attribute_effect` ([#16309](https://github.com/sveltejs/svelte/pull/16309))
+
+- fix: do not proxify the value assigned to a derived ([#16302](https://github.com/sveltejs/svelte/pull/16302))
+
 ## 5.35.2
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 872c21a179..30a8f8833a 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.35.2",
+  "version": "5.35.3",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 47c354c7a2..d98b622908 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.35.2';
+export const VERSION = '5.35.3';
 export const PUBLIC_VERSION = '5';

From cf2ff5e8dc908395853e3a7cc2022fe3552f7062 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 7 Jul 2025 11:46:57 -0400
Subject: [PATCH 031/148] fix: abort and reschedule effect processing after
 state change in user effect (#16280)

* fix: abort and reschedule effect processing after state change in user effect

* failing test

* skip for now
---
 .changeset/cuddly-walls-tan.md                |  5 ++++
 .../svelte/src/internal/client/constants.js   |  1 +
 .../svelte/src/internal/client/context.js     |  4 ++--
 .../src/internal/client/reactivity/effects.js | 15 ++++++++----
 .../svelte/src/internal/client/runtime.js     | 15 +++++++++++-
 .../samples/effect-order-6/A.svelte           | 11 +++++++++
 .../samples/effect-order-6/B.svelte           |  9 ++++++++
 .../samples/effect-order-6/Child.svelte       | 20 ++++++++++++++++
 .../samples/effect-order-6/_config.js         | 13 +++++++++++
 .../samples/effect-order-6/main.svelte        | 23 +++++++++++++++++++
 .../samples/effect-order-7/A.svelte           |  9 ++++++++
 .../samples/effect-order-7/B.svelte           |  9 ++++++++
 .../samples/effect-order-7/Child.svelte       | 20 ++++++++++++++++
 .../samples/effect-order-7/_config.js         | 15 ++++++++++++
 .../samples/effect-order-7/main.svelte        | 22 ++++++++++++++++++
 15 files changed, 184 insertions(+), 7 deletions(-)
 create mode 100644 .changeset/cuddly-walls-tan.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/effect-order-6/A.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/effect-order-6/B.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/effect-order-6/Child.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/effect-order-6/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/effect-order-6/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/effect-order-7/A.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/effect-order-7/B.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/effect-order-7/Child.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/effect-order-7/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/effect-order-7/main.svelte

diff --git a/.changeset/cuddly-walls-tan.md b/.changeset/cuddly-walls-tan.md
new file mode 100644
index 0000000000..feececc052
--- /dev/null
+++ b/.changeset/cuddly-walls-tan.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: abort and reschedule effect processing after state change in user effect
diff --git a/packages/svelte/src/internal/client/constants.js b/packages/svelte/src/internal/client/constants.js
index 1cffa43940..a5a8b42972 100644
--- a/packages/svelte/src/internal/client/constants.js
+++ b/packages/svelte/src/internal/client/constants.js
@@ -19,6 +19,7 @@ export const INSPECT_EFFECT = 1 << 17;
 export const HEAD_EFFECT = 1 << 18;
 export const EFFECT_PRESERVED = 1 << 19;
 export const EFFECT_IS_UPDATING = 1 << 20;
+export const USER_EFFECT = 1 << 21;
 
 export const STATE_SYMBOL = Symbol('$state');
 export const LEGACY_PROPS = Symbol('legacy props');
diff --git a/packages/svelte/src/internal/client/context.js b/packages/svelte/src/internal/client/context.js
index e4220149ab..736b81c172 100644
--- a/packages/svelte/src/internal/client/context.js
+++ b/packages/svelte/src/internal/client/context.js
@@ -9,7 +9,7 @@ import {
 	set_active_effect,
 	set_active_reaction
 } from './runtime.js';
-import { effect, teardown } from './reactivity/effects.js';
+import { create_user_effect, teardown } from './reactivity/effects.js';
 import { legacy_mode_flag } from '../flags/index.js';
 import { FILENAME } from '../../constants.js';
 
@@ -191,7 +191,7 @@ export function pop(component) {
 					var component_effect = component_effects[i];
 					set_active_effect(component_effect.effect);
 					set_active_reaction(component_effect.reaction);
-					effect(component_effect.fn);
+					create_user_effect(component_effect.fn);
 				}
 			} finally {
 				set_active_effect(previous_effect);
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index 7570064c37..df2afd3e38 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -33,7 +33,8 @@ import {
 	MAYBE_DIRTY,
 	EFFECT_PRESERVED,
 	BOUNDARY_EFFECT,
-	STALE_REACTION
+	STALE_REACTION,
+	USER_EFFECT
 } from '#client/constants';
 import { set } from './sources.js';
 import * as e from '../errors.js';
@@ -200,11 +201,17 @@ export function user_effect(fn) {
 			reaction: active_reaction
 		});
 	} else {
-		var signal = effect(fn);
-		return signal;
+		return create_user_effect(fn);
 	}
 }
 
+/**
+ * @param {() => void | (() => void)} fn
+ */
+export function create_user_effect(fn) {
+	return create_effect(EFFECT | USER_EFFECT, fn, false);
+}
+
 /**
  * Internal representation of `$effect.pre(...)`
  * @param {() => void | (() => void)} fn
@@ -217,7 +224,7 @@ export function user_pre_effect(fn) {
 			value: '$effect.pre'
 		});
 	}
-	return render_effect(fn);
+	return create_effect(RENDER_EFFECT | USER_EFFECT, fn, true);
 }
 
 /** @param {() => void | (() => void)} fn */
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index fce6c78b56..c00ade5587 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -22,7 +22,8 @@ import {
 	ROOT_EFFECT,
 	DISCONNECTED,
 	EFFECT_IS_UPDATING,
-	STALE_REACTION
+	STALE_REACTION,
+	USER_EFFECT
 } from './constants.js';
 import { flush_tasks } from './dom/task.js';
 import { internal_set, old_values } from './reactivity/sources.js';
@@ -581,6 +582,8 @@ function flush_queued_effects(effects) {
 
 		if ((effect.f & (DESTROYED | INERT)) === 0) {
 			if (check_dirtiness(effect)) {
+				var wv = write_version;
+
 				update_effect(effect);
 
 				// Effects with no dependencies or teardown do not get added to the effect tree.
@@ -597,9 +600,19 @@ function flush_queued_effects(effects) {
 						effect.fn = null;
 					}
 				}
+
+				// if state is written in a user effect, abort and re-schedule, lest we run
+				// effects that should be removed as a result of the state change
+				if (write_version > wv && (effect.f & USER_EFFECT) !== 0) {
+					break;
+				}
 			}
 		}
 	}
+
+	for (; i < length; i += 1) {
+		schedule_effect(effects[i]);
+	}
 }
 
 /**
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-order-6/A.svelte b/packages/svelte/tests/runtime-runes/samples/effect-order-6/A.svelte
new file mode 100644
index 0000000000..2e789a0460
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-order-6/A.svelte
@@ -0,0 +1,11 @@
+<script>
+	import B from './B.svelte';
+
+	let { boolean, closed } = $props();
+
+	$effect(() => {
+		console.log(boolean);
+	});
+</script>
+
+<B {closed} />
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-order-6/B.svelte b/packages/svelte/tests/runtime-runes/samples/effect-order-6/B.svelte
new file mode 100644
index 0000000000..1fad19bc15
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-order-6/B.svelte
@@ -0,0 +1,9 @@
+<script>
+	import { close } from './Child.svelte';
+
+	let { closed } = $props();
+
+	$effect(() => {
+		if (closed) close();
+	});
+</script>
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-order-6/Child.svelte b/packages/svelte/tests/runtime-runes/samples/effect-order-6/Child.svelte
new file mode 100644
index 0000000000..b905b4b4d7
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-order-6/Child.svelte
@@ -0,0 +1,20 @@
+<script module>
+	let object = $state();
+
+	export function open() {
+		object = { boolean: true };
+	}
+
+	export function close() {
+		object = undefined;
+	}
+</script>
+
+<script>
+	let { children } = $props();
+</script>
+
+{#if object?.boolean}
+	<!-- error occurs here, this is executed when the if should already make it falsy -->
+	{@render children(object.boolean)}
+{/if}
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-order-6/_config.js b/packages/svelte/tests/runtime-runes/samples/effect-order-6/_config.js
new file mode 100644
index 0000000000..8f9077e954
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-order-6/_config.js
@@ -0,0 +1,13 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target, logs }) {
+		const [open, close] = target.querySelectorAll('button');
+
+		flushSync(() => open.click());
+		flushSync(() => close.click());
+
+		assert.deepEqual(logs, [true]);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-order-6/main.svelte b/packages/svelte/tests/runtime-runes/samples/effect-order-6/main.svelte
new file mode 100644
index 0000000000..eee487fa13
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-order-6/main.svelte
@@ -0,0 +1,23 @@
+<script>
+	import A from './A.svelte';
+	import Child, { open } from './Child.svelte';
+
+	let closed = $state(false);
+</script>
+
+<button onclick={open}>
+	open
+</button>
+
+<button onclick={() => closed = true}>
+	close
+</button>
+
+<hr>
+
+<Child>
+	{#snippet children(boolean)}
+		<A {closed} {boolean} />
+	{/snippet}
+</Child>
+
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-order-7/A.svelte b/packages/svelte/tests/runtime-runes/samples/effect-order-7/A.svelte
new file mode 100644
index 0000000000..54f4869d62
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-order-7/A.svelte
@@ -0,0 +1,9 @@
+<script>
+	import B from './B.svelte';
+
+	let { boolean, closed } = $props();
+</script>
+
+<span>{boolean}</span>
+
+<B {closed} />
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-order-7/B.svelte b/packages/svelte/tests/runtime-runes/samples/effect-order-7/B.svelte
new file mode 100644
index 0000000000..2a2e634db1
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-order-7/B.svelte
@@ -0,0 +1,9 @@
+<script>
+	import { close } from './Child.svelte';
+
+	let { closed } = $props();
+
+	$effect.pre(() => {
+		if (closed) close();
+	});
+</script>
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-order-7/Child.svelte b/packages/svelte/tests/runtime-runes/samples/effect-order-7/Child.svelte
new file mode 100644
index 0000000000..9606fd8602
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-order-7/Child.svelte
@@ -0,0 +1,20 @@
+<script module>
+	let object = $state();
+
+	export function open() {
+		object = { nested: { boolean: true } };
+	}
+
+	export function close() {
+		object = undefined;
+	}
+</script>
+
+<script>
+	let { children } = $props();
+</script>
+
+{#if object?.nested}
+	<!-- error occurs here, this is executed when the if should already make it falsy -->
+	{@render children(object.nested)}
+{/if}
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-order-7/_config.js b/packages/svelte/tests/runtime-runes/samples/effect-order-7/_config.js
new file mode 100644
index 0000000000..29c33c7b18
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-order-7/_config.js
@@ -0,0 +1,15 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	skip: true,
+
+	async test({ assert, target, logs }) {
+		const [open, close] = target.querySelectorAll('button');
+
+		flushSync(() => open.click());
+		flushSync(() => close.click());
+
+		assert.deepEqual(logs, [true]);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-order-7/main.svelte b/packages/svelte/tests/runtime-runes/samples/effect-order-7/main.svelte
new file mode 100644
index 0000000000..c9c45c50cf
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-order-7/main.svelte
@@ -0,0 +1,22 @@
+<script>
+	import A from './A.svelte';
+	import Child, { open } from './Child.svelte';
+
+	let closed = $state(false);
+</script>
+
+<button onclick={open}>
+	open
+</button>
+
+<button onclick={() => closed = true}>
+	close
+</button>
+
+<hr>
+
+<Child>
+	{#snippet children(nested)}
+		<A {closed} boolean={nested.boolean} />
+	{/snippet}
+</Child>

From eb094ba059d262e5583108a85b0e549b95dbd344 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Mon, 7 Jul 2025 12:37:51 -0400
Subject: [PATCH 032/148] Version Packages (#16313)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/cuddly-walls-tan.md | 5 -----
 packages/svelte/CHANGELOG.md   | 6 ++++++
 packages/svelte/package.json   | 2 +-
 packages/svelte/src/version.js | 2 +-
 4 files changed, 8 insertions(+), 7 deletions(-)
 delete mode 100644 .changeset/cuddly-walls-tan.md

diff --git a/.changeset/cuddly-walls-tan.md b/.changeset/cuddly-walls-tan.md
deleted file mode 100644
index feececc052..0000000000
--- a/.changeset/cuddly-walls-tan.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: abort and reschedule effect processing after state change in user effect
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 4f1be5e299..89ae380840 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,11 @@
 # svelte
 
+## 5.35.4
+
+### Patch Changes
+
+- fix: abort and reschedule effect processing after state change in user effect ([#16280](https://github.com/sveltejs/svelte/pull/16280))
+
 ## 5.35.3
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 30a8f8833a..aaf8f26fec 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.35.3",
+  "version": "5.35.4",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index d98b622908..c4111b9e8d 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.35.3';
+export const VERSION = '5.35.4';
 export const PUBLIC_VERSION = '5';

From 140462374a759d7c38262e9823a7db6c73bcc067 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 7 Jul 2025 13:32:15 -0400
Subject: [PATCH 033/148] fix: re-evaluate derived props during teardown
 (#16278)

* Store deriveds old value before updating them for consistency with directly assigned sources when reading in teardown functions

* Add tests for derived old values in teardown functions

* Add tests for props old values in onDestroy hooks to prevent regressions

* Add changeset

* Update comment

* remove extraneous tests - these pass with or without the src change

* revert

* WIP

* simplify props

* simplify

* tweak

* reorder a bit

* simplify

* unused

* more

* more

* tweak

* also appears to be unnecessary

* changeset

* fix

* Update .changeset/light-rivers-jump.md

* easier debugging

* fix

* WIP

* fix

---------

Co-authored-by: raythurnvoid <53383860+raythurnvoid@users.noreply.github.com>
---
 .changeset/light-rivers-jump.md               |  5 ++
 .../internal/client/reactivity/deriveds.js    |  3 +-
 .../src/internal/client/reactivity/props.js   | 80 ++++++++++++++-----
 .../svelte/src/internal/client/runtime.js     | 44 +++++++++-
 .../derived-cleanup-old-value/_config.js      | 22 +++++
 .../derived-cleanup-old-value/main.svelte     | 20 +++++
 .../effect-teardown-derived/Component.svelte  | 15 ++++
 .../effect-teardown-derived/_config.js        | 17 ++++
 .../effect-teardown-derived/main.svelte       | 13 +++
 9 files changed, 194 insertions(+), 25 deletions(-)
 create mode 100644 .changeset/light-rivers-jump.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/derived-cleanup-old-value/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/derived-cleanup-old-value/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/effect-teardown-derived/Component.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/effect-teardown-derived/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/effect-teardown-derived/main.svelte

diff --git a/.changeset/light-rivers-jump.md b/.changeset/light-rivers-jump.md
new file mode 100644
index 0000000000..2454d57156
--- /dev/null
+++ b/.changeset/light-rivers-jump.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: re-evaluate derived props during teardown
diff --git a/packages/svelte/src/internal/client/reactivity/deriveds.js b/packages/svelte/src/internal/client/reactivity/deriveds.js
index fdfc13c0e2..e563c77534 100644
--- a/packages/svelte/src/internal/client/reactivity/deriveds.js
+++ b/packages/svelte/src/internal/client/reactivity/deriveds.js
@@ -19,6 +19,7 @@ import { inspect_effects, set_inspect_effects } from './sources.js';
 import { get_stack } from '../dev/tracing.js';
 import { tracing_mode_flag } from '../../flags/index.js';
 import { component_context } from '../context.js';
+import { UNINITIALIZED } from '../../../constants.js';
 
 /**
  * @template V
@@ -51,7 +52,7 @@ export function derived(fn) {
 		fn,
 		reactions: null,
 		rv: 0,
-		v: /** @type {V} */ (null),
+		v: /** @type {V} */ (UNINITIALIZED),
 		wv: 0,
 		parent: parent_derived ?? active_effect,
 		ac: null
diff --git a/packages/svelte/src/internal/client/reactivity/props.js b/packages/svelte/src/internal/client/reactivity/props.js
index 3501bcd3c7..03daad5251 100644
--- a/packages/svelte/src/internal/client/reactivity/props.js
+++ b/packages/svelte/src/internal/client/reactivity/props.js
@@ -1,18 +1,26 @@
-/** @import { Derived, Source } from './types.js' */
+/** @import { ComponentContext } from '#client' */
+/** @import { Derived, Effect, Source } from './types.js' */
 import { DEV } from 'esm-env';
 import {
 	PROPS_IS_BINDABLE,
 	PROPS_IS_IMMUTABLE,
 	PROPS_IS_LAZY_INITIAL,
 	PROPS_IS_RUNES,
-	PROPS_IS_UPDATED
+	PROPS_IS_UPDATED,
+	UNINITIALIZED
 } from '../../../constants.js';
 import { get_descriptor, is_function } from '../../shared/utils.js';
 import { set, source, update } from './sources.js';
 import { derived, derived_safe_equal } from './deriveds.js';
-import { get, untrack } from '../runtime.js';
+import {
+	active_effect,
+	get,
+	is_destroying_effect,
+	set_active_effect,
+	untrack
+} from '../runtime.js';
 import * as e from '../errors.js';
-import { LEGACY_PROPS, STATE_SYMBOL } from '#client/constants';
+import { DESTROYED, LEGACY_PROPS, STATE_SYMBOL } from '#client/constants';
 import { proxy } from '../proxy.js';
 import { capture_store_binding } from './store.js';
 import { legacy_mode_flag } from '../../flags/index.js';
@@ -92,7 +100,7 @@ export function rest_props(props, exclude, name) {
 
 /**
  * The proxy handler for legacy $$restProps and $$props
- * @type {ProxyHandler<{ props: Record<string | symbol, unknown>, exclude: Array<string | symbol>, special: Record<string | symbol, (v?: unknown) => unknown>, version: Source<number> }>}}
+ * @type {ProxyHandler<{ props: Record<string | symbol, unknown>, exclude: Array<string | symbol>, special: Record<string | symbol, (v?: unknown) => unknown>, version: Source<number>, parent_effect: Effect }>}}
  */
 const legacy_rest_props_handler = {
 	get(target, key) {
@@ -102,17 +110,25 @@ const legacy_rest_props_handler = {
 	},
 	set(target, key, value) {
 		if (!(key in target.special)) {
-			// Handle props that can temporarily get out of sync with the parent
-			/** @type {Record<string, (v?: unknown) => unknown>} */
-			target.special[key] = prop(
-				{
-					get [key]() {
-						return target.props[key];
-					}
-				},
-				/** @type {string} */ (key),
-				PROPS_IS_UPDATED
-			);
+			var previous_effect = active_effect;
+
+			try {
+				set_active_effect(target.parent_effect);
+
+				// Handle props that can temporarily get out of sync with the parent
+				/** @type {Record<string, (v?: unknown) => unknown>} */
+				target.special[key] = prop(
+					{
+						get [key]() {
+							return target.props[key];
+						}
+					},
+					/** @type {string} */ (key),
+					PROPS_IS_UPDATED
+				);
+			} finally {
+				set_active_effect(previous_effect);
+			}
 		}
 
 		target.special[key](value);
@@ -151,7 +167,19 @@ const legacy_rest_props_handler = {
  * @returns {Record<string, unknown>}
  */
 export function legacy_rest_props(props, exclude) {
-	return new Proxy({ props, exclude, special: {}, version: source(0) }, legacy_rest_props_handler);
+	return new Proxy(
+		{
+			props,
+			exclude,
+			special: {},
+			version: source(0),
+			// TODO this is only necessary because we need to track component
+			// destruction inside `prop`, because of `bind:this`, but it
+			// seems likely that we can simplify `bind:this` instead
+			parent_effect: /** @type {Effect} */ (active_effect)
+		},
+		legacy_rest_props_handler
+	);
 }
 
 /**
@@ -366,16 +394,24 @@ export function prop(props, key, flags, fallback) {
 	// create a derived that we can write to locally.
 	// Or we are in legacy mode where we always create a derived to replicate that
 	// Svelte 4 did not trigger updates when a primitive value was updated to the same value.
-	var d = ((flags & PROPS_IS_IMMUTABLE) !== 0 ? derived : derived_safe_equal)(getter);
+	var overridden = false;
+
+	var d = ((flags & PROPS_IS_IMMUTABLE) !== 0 ? derived : derived_safe_equal)(() => {
+		overridden = false;
+		return getter();
+	});
 
 	// Capture the initial value if it's bindable
 	if (bindable) get(d);
 
+	var parent_effect = /** @type {Effect} */ (active_effect);
+
 	return function (/** @type {any} */ value, /** @type {boolean} */ mutation) {
 		if (arguments.length > 0) {
 			const new_value = mutation ? get(d) : runes && bindable ? proxy(value) : value;
 
 			set(d, new_value);
+			overridden = true;
 
 			if (fallback_value !== undefined) {
 				fallback_value = new_value;
@@ -384,8 +420,12 @@ export function prop(props, key, flags, fallback) {
 			return value;
 		}
 
-		// TODO is this still necessary post-#16263?
-		if (has_destroyed_component_ctx(d)) {
+		// special case — avoid recalculating the derived if we're in a
+		// teardown function and the prop was overridden locally, or the
+		// component was already destroyed (this latter part is necessary
+		// because `bind:this` can read props after the component has
+		// been destroyed. TODO simplify `bind:this`
+		if ((is_destroying_effect && overridden) || (parent_effect.f & DESTROYED) !== 0) {
 			return d.v;
 		}
 
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index c00ade5587..28fcf26e83 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -27,7 +27,7 @@ import {
 } from './constants.js';
 import { flush_tasks } from './dom/task.js';
 import { internal_set, old_values } from './reactivity/sources.js';
-import { destroy_derived_effects, update_derived } from './reactivity/deriveds.js';
+import { destroy_derived_effects, execute_derived, update_derived } from './reactivity/deriveds.js';
 import * as e from './errors.js';
 
 import { tracing_mode_flag } from '../flags/index.js';
@@ -42,6 +42,7 @@ import {
 	set_dev_stack
 } from './context.js';
 import { handle_error, invoke_error_boundary } from './error-handling.js';
+import { UNINITIALIZED } from '../../constants.js';
 
 let is_flushing = false;
 
@@ -795,7 +796,7 @@ export function get(signal) {
 		}
 	}
 
-	if (is_derived) {
+	if (is_derived && !is_destroying_effect) {
 		derived = /** @type {Derived} */ (signal);
 
 		if (check_dirtiness(derived)) {
@@ -836,13 +837,48 @@ export function get(signal) {
 		}
 	}
 
-	if (is_destroying_effect && old_values.has(signal)) {
-		return old_values.get(signal);
+	if (is_destroying_effect) {
+		if (old_values.has(signal)) {
+			return old_values.get(signal);
+		}
+
+		if (is_derived) {
+			derived = /** @type {Derived} */ (signal);
+
+			var value = derived.v;
+
+			// if the derived is dirty, or depends on the values that just changed, re-execute
+			if ((derived.f & CLEAN) !== 0 || depends_on_old_values(derived)) {
+				value = execute_derived(derived);
+			}
+
+			old_values.set(derived, value);
+
+			return value;
+		}
 	}
 
 	return signal.v;
 }
 
+/** @param {Derived} derived */
+function depends_on_old_values(derived) {
+	if (derived.v === UNINITIALIZED) return true; // we don't know, so assume the worst
+	if (derived.deps === null) return false;
+
+	for (const dep of derived.deps) {
+		if (old_values.has(dep)) {
+			return true;
+		}
+
+		if ((dep.f & DERIVED) !== 0 && depends_on_old_values(/** @type {Derived} */ (dep))) {
+			return true;
+		}
+	}
+
+	return false;
+}
+
 /**
  * Like `get`, but checks for `undefined`. Used for `var` declarations because they can be accessed before being declared
  * @template V
diff --git a/packages/svelte/tests/runtime-runes/samples/derived-cleanup-old-value/_config.js b/packages/svelte/tests/runtime-runes/samples/derived-cleanup-old-value/_config.js
new file mode 100644
index 0000000000..694dccdcf8
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/derived-cleanup-old-value/_config.js
@@ -0,0 +1,22 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, logs, target }) {
+		const [increment] = target.querySelectorAll('button');
+
+		flushSync(() => increment.click());
+		flushSync(() => increment.click());
+		flushSync(() => increment.click());
+
+		assert.deepEqual(logs, [
+			'count: 1',
+			'squared: 1',
+			'count: 2',
+			'squared: 4',
+			'count: 3',
+			'squared: 9',
+			'count: 4'
+		]);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/derived-cleanup-old-value/main.svelte b/packages/svelte/tests/runtime-runes/samples/derived-cleanup-old-value/main.svelte
new file mode 100644
index 0000000000..a4c58a8e99
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/derived-cleanup-old-value/main.svelte
@@ -0,0 +1,20 @@
+<script>
+	let count = $state(1);
+	let squared = $derived(count * count);
+
+	$effect(() => {
+		console.log(`count: ${count}`);
+
+		return () => {
+			console.log(`squared: ${squared}`);
+		};
+	});
+</script>
+
+<button onclick={() => count++}>increment</button>
+
+<p>count: {count}</p>
+
+{#if count % 2 === 0}
+	<p id="squared">squared: {squared}</p>
+{/if}
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-teardown-derived/Component.svelte b/packages/svelte/tests/runtime-runes/samples/effect-teardown-derived/Component.svelte
new file mode 100644
index 0000000000..3c863c7fc9
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-teardown-derived/Component.svelte
@@ -0,0 +1,15 @@
+<script>
+	let { message, count } = $props();
+
+	$effect(() => () => {
+		console.log(count, message);
+	});
+</script>
+
+<p>{count}</p>
+
+<!-- we need these so that the props are made into deriveds -->
+<button disabled onclick={() => {
+	count += 1;
+	message += '!';
+}}>update</button>
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-teardown-derived/_config.js b/packages/svelte/tests/runtime-runes/samples/effect-teardown-derived/_config.js
new file mode 100644
index 0000000000..1f6e5d1f7f
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-teardown-derived/_config.js
@@ -0,0 +1,17 @@
+import { test } from '../../test';
+import { flushSync } from 'svelte';
+
+export default test({
+	async test({ assert, target, logs }) {
+		const [increment, toggle] = target.querySelectorAll('button');
+
+		flushSync(() => toggle.click());
+		assert.deepEqual(logs, [0, 'hello']);
+
+		flushSync(() => toggle.click());
+		flushSync(() => increment.click());
+		flushSync(() => increment.click());
+
+		assert.deepEqual(logs, [0, 'hello', 1, 'hello']);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-teardown-derived/main.svelte b/packages/svelte/tests/runtime-runes/samples/effect-teardown-derived/main.svelte
new file mode 100644
index 0000000000..1a97d3e760
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-teardown-derived/main.svelte
@@ -0,0 +1,13 @@
+<script>
+	import Component from "./Component.svelte";
+
+	let message = $state('hello');
+	let count = $state(0);
+</script>
+
+<button onclick={() => count++}>{count}</button>
+<button onclick={() => message = message === 'hello' ? 'goodbye' : 'hello'}>{message}</button>
+
+{#if count < 2 && message === 'hello'}
+	<Component {count} {message} />
+{/if}

From c9098bcaa0cf7accf7de4a16f8b72671023e69e7 Mon Sep 17 00:00:00 2001
From: Paolo Ricciuti <ricciutipaolo@gmail.com>
Date: Wed, 9 Jul 2025 15:32:18 +0200
Subject: [PATCH 034/148] fix: use `state` instead of `source` in reactive
 classes (#16239)

* fix: use `state` instead of `source` in reactive classes

* fix: use `active_reaction` as indication to use `source` or `state`

* fix: cleanup `#initial_reaction` on `teardown` to free memory

* fix: use `#source` in `set` too

* unused

* chore: use WeakRef

* use update_version instead of WeakRef in SvelteSet/SvelteMap (#16324)

* tidy up

* tweak comment to remove active_reaction reference

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
---
 .../svelte/src/internal/client/runtime.js     |   6 +-
 packages/svelte/src/motion/spring.js          |  12 +-
 packages/svelte/src/motion/tweened.js         |   6 +-
 packages/svelte/src/reactivity/map.js         |  25 ++++-
 packages/svelte/src/reactivity/set.js         |  18 ++-
 .../side-effect-derived-map/_config.js        |  33 +++++-
 .../side-effect-derived-map/main.svelte       | 106 +++++++++++++++---
 .../side-effect-derived-set/_config.js        |  12 +-
 .../side-effect-derived-set/main.svelte       |  51 ++++++---
 .../side-effect-derived-spring/_config.js     |  23 ++++
 .../side-effect-derived-spring/main.svelte    |  26 +++++
 .../side-effect-derived-tween/_config.js      |  23 ++++
 .../side-effect-derived-tween/main.svelte     |  26 +++++
 13 files changed, 318 insertions(+), 49 deletions(-)
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-spring/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-spring/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-tween/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/side-effect-derived-tween/main.svelte

diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 28fcf26e83..cd7170d326 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -134,6 +134,8 @@ let write_version = 1;
 /** @type {number} Used to version each read of a source of derived to avoid duplicating depedencies inside a reaction */
 let read_version = 0;
 
+export let update_version = read_version;
+
 // If we are working with a get() chain that has no active container,
 // to prevent memory leaks, we skip adding the reaction.
 export let skip_reaction = false;
@@ -267,6 +269,7 @@ export function update_reaction(reaction) {
 	var previous_reaction_sources = source_ownership;
 	var previous_component_context = component_context;
 	var previous_untracking = untracking;
+	var previous_update_version = update_version;
 
 	var flags = reaction.f;
 
@@ -280,7 +283,7 @@ export function update_reaction(reaction) {
 	source_ownership = null;
 	set_component_context(reaction.ctx);
 	untracking = false;
-	read_version++;
+	update_version = ++read_version;
 
 	reaction.f |= EFFECT_IS_UPDATING;
 
@@ -368,6 +371,7 @@ export function update_reaction(reaction) {
 		source_ownership = previous_reaction_sources;
 		set_component_context(previous_component_context);
 		untracking = previous_untracking;
+		update_version = previous_update_version;
 
 		reaction.f ^= EFFECT_IS_UPDATING;
 	}
diff --git a/packages/svelte/src/motion/spring.js b/packages/svelte/src/motion/spring.js
index 0f3bc6fb9f..44be1a501b 100644
--- a/packages/svelte/src/motion/spring.js
+++ b/packages/svelte/src/motion/spring.js
@@ -5,7 +5,7 @@ import { writable } from '../store/shared/index.js';
 import { loop } from '../internal/client/loop.js';
 import { raf } from '../internal/client/timing.js';
 import { is_date } from './utils.js';
-import { set, source } from '../internal/client/reactivity/sources.js';
+import { set, state } from '../internal/client/reactivity/sources.js';
 import { render_effect } from '../internal/client/reactivity/effects.js';
 import { tag } from '../internal/client/dev/tracing.js';
 import { get } from '../internal/client/runtime.js';
@@ -170,9 +170,9 @@ export function spring(value, opts = {}) {
  * @since 5.8.0
  */
 export class Spring {
-	#stiffness = source(0.15);
-	#damping = source(0.8);
-	#precision = source(0.01);
+	#stiffness = state(0.15);
+	#damping = state(0.8);
+	#precision = state(0.01);
 
 	#current;
 	#target;
@@ -194,8 +194,8 @@ export class Spring {
 	 * @param {SpringOpts} [options]
 	 */
 	constructor(value, options = {}) {
-		this.#current = DEV ? tag(source(value), 'Spring.current') : source(value);
-		this.#target = DEV ? tag(source(value), 'Spring.target') : source(value);
+		this.#current = DEV ? tag(state(value), 'Spring.current') : state(value);
+		this.#target = DEV ? tag(state(value), 'Spring.target') : state(value);
 
 		if (typeof options.stiffness === 'number') this.#stiffness.v = clamp(options.stiffness, 0, 1);
 		if (typeof options.damping === 'number') this.#damping.v = clamp(options.damping, 0, 1);
diff --git a/packages/svelte/src/motion/tweened.js b/packages/svelte/src/motion/tweened.js
index 09bd06c325..437c22ec3b 100644
--- a/packages/svelte/src/motion/tweened.js
+++ b/packages/svelte/src/motion/tweened.js
@@ -6,7 +6,7 @@ import { raf } from '../internal/client/timing.js';
 import { loop } from '../internal/client/loop.js';
 import { linear } from '../easing/index.js';
 import { is_date } from './utils.js';
-import { set, source } from '../internal/client/reactivity/sources.js';
+import { set, state } from '../internal/client/reactivity/sources.js';
 import { tag } from '../internal/client/dev/tracing.js';
 import { get, render_effect } from 'svelte/internal/client';
 import { DEV } from 'esm-env';
@@ -191,8 +191,8 @@ export class Tween {
 	 * @param {TweenedOptions<T>} options
 	 */
 	constructor(value, options = {}) {
-		this.#current = source(value);
-		this.#target = source(value);
+		this.#current = state(value);
+		this.#target = state(value);
 		this.#defaults = options;
 
 		if (DEV) {
diff --git a/packages/svelte/src/reactivity/map.js b/packages/svelte/src/reactivity/map.js
index cd2fac163f..4fa2dfd7b2 100644
--- a/packages/svelte/src/reactivity/map.js
+++ b/packages/svelte/src/reactivity/map.js
@@ -2,7 +2,7 @@
 import { DEV } from 'esm-env';
 import { set, source, state } from '../internal/client/reactivity/sources.js';
 import { label, tag } from '../internal/client/dev/tracing.js';
-import { get } from '../internal/client/runtime.js';
+import { get, update_version } from '../internal/client/runtime.js';
 import { increment } from './utils.js';
 
 /**
@@ -56,6 +56,7 @@ export class SvelteMap extends Map {
 	#sources = new Map();
 	#version = state(0);
 	#size = state(0);
+	#update_version = update_version || -1;
 
 	/**
 	 * @param {Iterable<readonly [K, V]> | null | undefined} [value]
@@ -79,6 +80,19 @@ export class SvelteMap extends Map {
 		}
 	}
 
+	/**
+	 * If the source is being created inside the same reaction as the SvelteMap instance,
+	 * we use `state` so that it will not be a dependency of the reaction. Otherwise we
+	 * use `source` so it will be.
+	 *
+	 * @template T
+	 * @param {T} value
+	 * @returns {Source<T>}
+	 */
+	#source(value) {
+		return update_version === this.#update_version ? state(value) : source(value);
+	}
+
 	/** @param {K} key */
 	has(key) {
 		var sources = this.#sources;
@@ -87,7 +101,7 @@ export class SvelteMap extends Map {
 		if (s === undefined) {
 			var ret = super.get(key);
 			if (ret !== undefined) {
-				s = source(0);
+				s = this.#source(0);
 
 				if (DEV) {
 					tag(s, `SvelteMap get(${label(key)})`);
@@ -123,7 +137,7 @@ export class SvelteMap extends Map {
 		if (s === undefined) {
 			var ret = super.get(key);
 			if (ret !== undefined) {
-				s = source(0);
+				s = this.#source(0);
 
 				if (DEV) {
 					tag(s, `SvelteMap get(${label(key)})`);
@@ -154,7 +168,7 @@ export class SvelteMap extends Map {
 		var version = this.#version;
 
 		if (s === undefined) {
-			s = source(0);
+			s = this.#source(0);
 
 			if (DEV) {
 				tag(s, `SvelteMap get(${label(key)})`);
@@ -219,8 +233,7 @@ export class SvelteMap extends Map {
 		if (this.#size.v !== sources.size) {
 			for (var key of super.keys()) {
 				if (!sources.has(key)) {
-					var s = source(0);
-
+					var s = this.#source(0);
 					if (DEV) {
 						tag(s, `SvelteMap get(${label(key)})`);
 					}
diff --git a/packages/svelte/src/reactivity/set.js b/packages/svelte/src/reactivity/set.js
index 8a656c2bc1..9e3c330beb 100644
--- a/packages/svelte/src/reactivity/set.js
+++ b/packages/svelte/src/reactivity/set.js
@@ -2,7 +2,7 @@
 import { DEV } from 'esm-env';
 import { source, set, state } from '../internal/client/reactivity/sources.js';
 import { label, tag } from '../internal/client/dev/tracing.js';
-import { get } from '../internal/client/runtime.js';
+import { get, update_version } from '../internal/client/runtime.js';
 import { increment } from './utils.js';
 
 var read_methods = ['forEach', 'isDisjointFrom', 'isSubsetOf', 'isSupersetOf'];
@@ -50,6 +50,7 @@ export class SvelteSet extends Set {
 	#sources = new Map();
 	#version = state(0);
 	#size = state(0);
+	#update_version = update_version || -1;
 
 	/**
 	 * @param {Iterable<T> | null | undefined} [value]
@@ -75,6 +76,19 @@ export class SvelteSet extends Set {
 		if (!inited) this.#init();
 	}
 
+	/**
+	 * If the source is being created inside the same reaction as the SvelteSet instance,
+	 * we use `state` so that it will not be a dependency of the reaction. Otherwise we
+	 * use `source` so it will be.
+	 *
+	 * @template T
+	 * @param {T} value
+	 * @returns {Source<T>}
+	 */
+	#source(value) {
+		return update_version === this.#update_version ? state(value) : source(value);
+	}
+
 	// We init as part of the first instance so that we can treeshake this class
 	#init() {
 		inited = true;
@@ -116,7 +130,7 @@ export class SvelteSet extends Set {
 				return false;
 			}
 
-			s = source(true);
+			s = this.#source(true);
 
 			if (DEV) {
 				tag(s, `SvelteSet has(${label(value)})`);
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-map/_config.js b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-map/_config.js
index 5ad6f57e31..c10dc7fb55 100644
--- a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-map/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-map/_config.js
@@ -8,7 +8,8 @@ export default test({
 	},
 
 	test({ assert, target }) {
-		const [button1, button2] = target.querySelectorAll('button');
+		const [button1, button2, button3, button4, button5, button6, button7, button8] =
+			target.querySelectorAll('button');
 
 		assert.throws(() => {
 			button1?.click();
@@ -19,5 +20,35 @@ export default test({
 			button2?.click();
 			flushSync();
 		});
+
+		assert.throws(() => {
+			button3?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button4?.click();
+			flushSync();
+		});
+
+		assert.throws(() => {
+			button5?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button6?.click();
+			flushSync();
+		});
+
+		assert.throws(() => {
+			button7?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button8?.click();
+			flushSync();
+		});
 	}
 });
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-map/main.svelte b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-map/main.svelte
index bdd5ccb75c..c37f37ceb6 100644
--- a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-map/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-map/main.svelte
@@ -1,27 +1,101 @@
 <script>
 	import { SvelteMap } from 'svelte/reactivity';
 
-	let visibleExternal = $state(false);
-	let external = new SvelteMap();
-	const throws = $derived.by(() => {
-		external.set(1, 1);
-		return external;
+	let outside_basic = $state(false);
+	let outside_basic_map = new SvelteMap();
+	const throw_basic = $derived.by(() => {
+		outside_basic_map.set(1, 1);
+		return outside_basic_map;
 	});
 
-	let visibleInternal = $state(false);
-	const works = $derived.by(() => {
-		let internal = new SvelteMap();
-		internal.set(1, 1);
-		return internal;
+	let inside_basic = $state(false);
+	const works_basic = $derived.by(() => {
+		let inside = new SvelteMap();
+		inside.set(1, 1);
+		return inside;
+	});
+
+	let outside_has = $state(false);
+	let outside_has_map = new SvelteMap([[1, 1]]);
+	const throw_has = $derived.by(() => {
+		outside_has_map.has(1);
+		outside_has_map.set(1, 2);
+		return outside_has_map;
+	});
+
+	let inside_has = $state(false);
+	const works_has = $derived.by(() => {
+		let inside = new SvelteMap([[1, 1]]);
+		inside.has(1);
+		inside.set(1, 1);
+		return inside;
+	});
+
+	let outside_get = $state(false);
+	let outside_get_map = new SvelteMap([[1, 1]]);
+	const throw_get = $derived.by(() => {
+		outside_get_map.get(1);
+		outside_get_map.set(1, 2);
+		return outside_get_map;
+	});
+
+	let inside_get = $state(false);
+	const works_get = $derived.by(() => {
+		let inside = new SvelteMap([[1, 1]]);
+		inside.get(1);
+		inside.set(1, 1);
+		return inside;
+	});
+
+	let outside_values = $state(false);
+	let outside_values_map = new SvelteMap([[1, 1]]);
+	const throw_values = $derived.by(() => {
+		outside_values_map.values(1);
+		outside_values_map.set(1, 2);
+		return outside_values_map;
+	});
+
+	let inside_values = $state(false);
+	const works_values = $derived.by(() => {
+		let inside = new SvelteMap([[1, 1]]);
+		inside.values();
+		inside.set(1, 1);
+		return inside;
 	});
 </script>
 
-<button onclick={() => (visibleExternal = true)}>external</button>
-{#if visibleExternal}
-	{throws}
+<button onclick={() => (outside_basic = true)}>external</button>
+{#if outside_basic}
+	{throw_basic}
+{/if}
+<button onclick={() => (inside_basic = true)}>internal</button>
+{#if inside_basic}
+	{works_basic}
+{/if}
+
+<button onclick={() => (outside_has = true)}>external</button>
+{#if outside_has}
+	{throw_has}
 {/if}
-<button onclick={() => (visibleInternal = true)}>internal</button>
-{#if visibleInternal}
-	{works}
+<button onclick={() => (inside_has = true)}>internal</button>
+{#if inside_has}
+	{works_has}
 {/if}
 
+<button onclick={() => (outside_get = true)}>external</button>
+{#if outside_get}
+	{throw_get}
+{/if}
+<button onclick={() => (inside_get = true)}>internal</button>
+{#if inside_get}
+	{works_get}
+{/if}
+
+<button onclick={() => (outside_values = true)}>external</button>
+{#if outside_values}
+	{throw_values}
+{/if}
+<button onclick={() => (inside_values = true)}>internal</button>
+{#if inside_values}
+	{works_values}
+{/if}
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-set/_config.js b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-set/_config.js
index 5ad6f57e31..5cf066fb8a 100644
--- a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-set/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-set/_config.js
@@ -8,7 +8,7 @@ export default test({
 	},
 
 	test({ assert, target }) {
-		const [button1, button2] = target.querySelectorAll('button');
+		const [button1, button2, button3, button4] = target.querySelectorAll('button');
 
 		assert.throws(() => {
 			button1?.click();
@@ -19,5 +19,15 @@ export default test({
 			button2?.click();
 			flushSync();
 		});
+
+		assert.throws(() => {
+			button3?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button4?.click();
+			flushSync();
+		});
 	}
 });
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-set/main.svelte b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-set/main.svelte
index 8564f6e7c4..1d6735ba64 100644
--- a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-set/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-set/main.svelte
@@ -1,27 +1,52 @@
 <script>
 	import { SvelteSet } from 'svelte/reactivity';
 
-	let visibleExternal = $state(false);
-	let external = new SvelteSet();
-	const throws = $derived.by(() => {
-		external.add(1);
-		return external;
+	let outside_basic = $state(false);
+	let outside_basic_set = new SvelteSet();
+	const throws_basic = $derived.by(() => {
+		outside_basic_set.add(1);
+		return outside_basic_set;
 	})
 
-	let visibleInternal = $state(false);
-	const works = $derived.by(() => {
+	let inside_basic = $state(false);
+	const works_basic = $derived.by(() => {
 		let internal = new SvelteSet();
 		internal.add(1);
 		return internal;
 	})
+
+	let outside_has_delete = $state(false);
+	let outside_has_delete_set = new SvelteSet([1]);
+	const throws_has_delete = $derived.by(() => {
+		outside_has_delete_set.has(1);
+		outside_has_delete_set.delete(1);
+		return outside_has_delete_set;
+	})
+
+	let inside_has_delete = $state(false);
+	const works_has_delete = $derived.by(() => {
+		let internal = new SvelteSet([1]);
+		internal.has(1);
+		internal.delete(1);
+		return internal;
+	})
 </script>
 
-<button onclick={() => (visibleExternal = true)}>external</button>
-{#if visibleExternal}
-	{throws}
+<button onclick={() => (outside_basic = true)}>external</button>
+{#if outside_basic}
+	{throws_basic}
+{/if}
+<button onclick={() => (inside_basic = true)}>internal</button>
+{#if inside_basic}
+	{works_basic}
+{/if}
+
+<button onclick={() => (outside_has_delete = true)}>external</button>
+{#if outside_has_delete}
+	{throws_has_delete}
 {/if}
-<button onclick={() => (visibleInternal = true)}>internal</button>
-{#if visibleInternal}
-	{works}
+<button onclick={() => (inside_has_delete = true)}>internal</button>
+{#if inside_has_delete}
+	{works_has_delete}
 {/if}
 
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-spring/_config.js b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-spring/_config.js
new file mode 100644
index 0000000000..5ad6f57e31
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-spring/_config.js
@@ -0,0 +1,23 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true,
+		runes: true
+	},
+
+	test({ assert, target }) {
+		const [button1, button2] = target.querySelectorAll('button');
+
+		assert.throws(() => {
+			button1?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button2?.click();
+			flushSync();
+		});
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-spring/main.svelte b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-spring/main.svelte
new file mode 100644
index 0000000000..b0818deca9
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-spring/main.svelte
@@ -0,0 +1,26 @@
+<script>
+	import { Spring } from 'svelte/motion';
+
+	let outside_basic = $state(false);
+	let outside_basic_spring = new Spring(0);
+	const throws_basic = $derived.by(() => {
+		outside_basic_spring.set(1);
+		return outside_basic_spring;
+	})
+
+	let inside_basic = $state(false);
+	const works_basic = $derived.by(() => {
+		let internal = new Spring(0);
+		internal.set(1);
+		return internal;
+	})
+</script>
+
+<button onclick={() => (outside_basic = true)}>external</button>
+{#if outside_basic}
+	{throws_basic}
+{/if}
+<button onclick={() => (inside_basic = true)}>internal</button>
+{#if inside_basic}
+	{works_basic}
+{/if}
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-tween/_config.js b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-tween/_config.js
new file mode 100644
index 0000000000..5ad6f57e31
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-tween/_config.js
@@ -0,0 +1,23 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true,
+		runes: true
+	},
+
+	test({ assert, target }) {
+		const [button1, button2] = target.querySelectorAll('button');
+
+		assert.throws(() => {
+			button1?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+
+		assert.doesNotThrow(() => {
+			button2?.click();
+			flushSync();
+		});
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-derived-tween/main.svelte b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-tween/main.svelte
new file mode 100644
index 0000000000..bd007f2b50
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-derived-tween/main.svelte
@@ -0,0 +1,26 @@
+<script>
+	import { Tween } from 'svelte/motion';
+
+	let outside_basic = $state(false);
+	let outside_basic_tween = new Tween(0);
+	const throws_basic = $derived.by(() => {
+		outside_basic_tween.set(1);
+		return outside_basic_tween;
+	})
+
+	let inside_basic = $state(false);
+	const works_basic = $derived.by(() => {
+		let internal = new Tween(0);
+		internal.set(1);
+		return internal;
+	})
+</script>
+
+<button onclick={() => (outside_basic = true)}>external</button>
+{#if outside_basic}
+	{throws_basic}
+{/if}
+<button onclick={() => (inside_basic = true)}>internal</button>
+{#if inside_basic}
+	{works_basic}
+{/if}
\ No newline at end of file

From 9d176b50080ed075d97ed96a15e2109b3db69886 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 9 Jul 2025 09:37:29 -0400
Subject: [PATCH 035/148] chore: changeset for #16239 (#16325)

---
 .changeset/gorgeous-birds-brake.md | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 .changeset/gorgeous-birds-brake.md

diff --git a/.changeset/gorgeous-birds-brake.md b/.changeset/gorgeous-birds-brake.md
new file mode 100644
index 0000000000..8365cc0e6a
--- /dev/null
+++ b/.changeset/gorgeous-birds-brake.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: associate sources in Spring/Tween/SvelteMap/SvelteSet with correct reaction

From fab2091743d48f682d470cccb1a99590ce6bac32 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Wed, 9 Jul 2025 09:41:08 -0400
Subject: [PATCH 036/148] Version Packages (#16314)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/gorgeous-birds-brake.md | 5 -----
 .changeset/light-rivers-jump.md    | 5 -----
 packages/svelte/CHANGELOG.md       | 8 ++++++++
 packages/svelte/package.json       | 2 +-
 packages/svelte/src/version.js     | 2 +-
 5 files changed, 10 insertions(+), 12 deletions(-)
 delete mode 100644 .changeset/gorgeous-birds-brake.md
 delete mode 100644 .changeset/light-rivers-jump.md

diff --git a/.changeset/gorgeous-birds-brake.md b/.changeset/gorgeous-birds-brake.md
deleted file mode 100644
index 8365cc0e6a..0000000000
--- a/.changeset/gorgeous-birds-brake.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: associate sources in Spring/Tween/SvelteMap/SvelteSet with correct reaction
diff --git a/.changeset/light-rivers-jump.md b/.changeset/light-rivers-jump.md
deleted file mode 100644
index 2454d57156..0000000000
--- a/.changeset/light-rivers-jump.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: re-evaluate derived props during teardown
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 89ae380840..19aa1466c0 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,13 @@
 # svelte
 
+## 5.35.5
+
+### Patch Changes
+
+- fix: associate sources in Spring/Tween/SvelteMap/SvelteSet with correct reaction ([#16325](https://github.com/sveltejs/svelte/pull/16325))
+
+- fix: re-evaluate derived props during teardown ([#16278](https://github.com/sveltejs/svelte/pull/16278))
+
 ## 5.35.4
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index aaf8f26fec..4ac497ed41 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.35.4",
+  "version": "5.35.5",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index c4111b9e8d..eb68753d71 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.35.4';
+export const VERSION = '5.35.5';
 export const PUBLIC_VERSION = '5';

From 71ed9e4648705ac79f1f834b8530d0d3ee06ffa2 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 9 Jul 2025 20:56:33 -0400
Subject: [PATCH 037/148] chore: simplify/optimize source_ownership occurrence
 (#16328)

---
 packages/svelte/src/internal/client/runtime.js | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index cd7170d326..d6e7325ba3 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -236,16 +236,13 @@ function schedule_possible_effect_self_invalidation(signal, effect, root = true)
 	var reactions = signal.reactions;
 	if (reactions === null) return;
 
+	if (source_ownership?.reaction === active_reaction && source_ownership.sources.includes(signal)) {
+		return;
+	}
+
 	for (var i = 0; i < reactions.length; i++) {
 		var reaction = reactions[i];
 
-		if (
-			source_ownership?.reaction === active_reaction &&
-			source_ownership.sources.includes(signal)
-		) {
-			continue;
-		}
-
 		if ((reaction.f & DERIVED) !== 0) {
 			schedule_possible_effect_self_invalidation(/** @type {Derived} */ (reaction), effect, false);
 		} else if (effect === reaction) {

From 86b06cb6945816ec8182544ba101cd38679f96a1 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 10 Jul 2025 01:58:42 -0400
Subject: [PATCH 038/148] chore: dry out transition `get_options` (#16329)

---
 .../src/internal/client/dom/elements/transitions.js   | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/packages/svelte/src/internal/client/dom/elements/transitions.js b/packages/svelte/src/internal/client/dom/elements/transitions.js
index 38100e982c..00fad9ffdb 100644
--- a/packages/svelte/src/internal/client/dom/elements/transitions.js
+++ b/packages/svelte/src/internal/client/dom/elements/transitions.js
@@ -209,21 +209,14 @@ export function transition(flags, element, get_fn, get_params) {
 	var outro;
 
 	function get_options() {
-		var previous_reaction = active_reaction;
-		var previous_effect = active_effect;
-		set_active_reaction(null);
-		set_active_effect(null);
-		try {
+		return without_reactive_context(() => {
 			// If a transition is still ongoing, we use the existing options rather than generating
 			// new ones. This ensures that reversible transitions reverse smoothly, rather than
 			// jumping to a new spot because (for example) a different `duration` was used
 			return (current_options ??= get_fn()(element, get_params?.() ?? /** @type {P} */ ({}), {
 				direction
 			}));
-		} finally {
-			set_active_reaction(previous_reaction);
-			set_active_effect(previous_effect);
-		}
+		});
 	}
 
 	/** @type {TransitionManager} */

From c3361bfdb7adc3f2df6ec831fb54f2ca614880e9 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 10 Jul 2025 01:59:57 -0400
Subject: [PATCH 039/148] chore: remove component_context.d (#16330)

---
 packages/svelte/src/internal/client/context.js          | 9 ++-------
 packages/svelte/src/internal/client/reactivity/props.js | 8 --------
 packages/svelte/src/internal/client/types.d.ts          | 2 --
 3 files changed, 2 insertions(+), 17 deletions(-)

diff --git a/packages/svelte/src/internal/client/context.js b/packages/svelte/src/internal/client/context.js
index 736b81c172..d79d827fee 100644
--- a/packages/svelte/src/internal/client/context.js
+++ b/packages/svelte/src/internal/client/context.js
@@ -139,16 +139,15 @@ export function getAllContexts() {
  * @returns {void}
  */
 export function push(props, runes = false, fn) {
-	var ctx = (component_context = {
+	component_context = {
 		p: component_context,
 		c: null,
-		d: false,
 		e: null,
 		m: false,
 		s: props,
 		x: null,
 		l: null
-	});
+	};
 
 	if (legacy_mode_flag && !runes) {
 		component_context.l = {
@@ -159,10 +158,6 @@ export function push(props, runes = false, fn) {
 		};
 	}
 
-	teardown(() => {
-		/** @type {ComponentContext} */ (ctx).d = true;
-	});
-
 	if (DEV) {
 		// component function
 		component_context.function = fn;
diff --git a/packages/svelte/src/internal/client/reactivity/props.js b/packages/svelte/src/internal/client/reactivity/props.js
index 03daad5251..f39d45bb04 100644
--- a/packages/svelte/src/internal/client/reactivity/props.js
+++ b/packages/svelte/src/internal/client/reactivity/props.js
@@ -268,14 +268,6 @@ export function spread_props(...props) {
 	return new Proxy({ props }, spread_props_handler);
 }
 
-/**
- * @param {Derived} current_value
- * @returns {boolean}
- */
-function has_destroyed_component_ctx(current_value) {
-	return current_value.ctx?.d ?? false;
-}
-
 /**
  * This function is responsible for synchronizing a possibly bound prop with the inner component state.
  * It is used whenever the compiler sees that the component writes to the prop, or when it has a default prop_value.
diff --git a/packages/svelte/src/internal/client/types.d.ts b/packages/svelte/src/internal/client/types.d.ts
index 0b7310e172..bcbd0ac8a3 100644
--- a/packages/svelte/src/internal/client/types.d.ts
+++ b/packages/svelte/src/internal/client/types.d.ts
@@ -14,8 +14,6 @@ export type ComponentContext = {
 	p: null | ComponentContext;
 	/** context */
 	c: null | Map<unknown, unknown>;
-	/** destroyed */
-	d: boolean;
 	/** deferred effects */
 	e: null | Array<{
 		fn: () => void | (() => void);

From 0cafe34c92dd21b532702bf6bc27cce108e25ea0 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 10 Jul 2025 07:44:07 -0400
Subject: [PATCH 040/148] chore: DRY out increment logic (#16332)

---
 packages/svelte/src/internal/client/proxy.js     | 16 ++++------------
 .../src/internal/client/reactivity/sources.js    |  8 ++++++++
 .../svelte/src/reactivity/create-subscriber.js   |  3 +--
 packages/svelte/src/reactivity/map.js            |  3 +--
 packages/svelte/src/reactivity/set.js            |  3 +--
 .../svelte/src/reactivity/url-search-params.js   |  3 +--
 packages/svelte/src/reactivity/utils.js          |  7 -------
 7 files changed, 16 insertions(+), 27 deletions(-)
 delete mode 100644 packages/svelte/src/reactivity/utils.js

diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index d9063aee34..97c8da9d33 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -8,7 +8,7 @@ import {
 	is_array,
 	object_prototype
 } from '../shared/utils.js';
-import { state as source, set } from './reactivity/sources.js';
+import { state as source, set, increment } from './reactivity/sources.js';
 import { PROXY_PATH_SYMBOL, STATE_SYMBOL } from '#client/constants';
 import { UNINITIALIZED } from '../../constants.js';
 import * as e from './errors.js';
@@ -118,7 +118,7 @@ export function proxy(value) {
 				if (prop in target) {
 					const s = with_parent(() => source(UNINITIALIZED, stack));
 					sources.set(prop, s);
-					update_version(version);
+					increment(version);
 
 					if (DEV) {
 						tag(s, get_label(path, prop));
@@ -136,7 +136,7 @@ export function proxy(value) {
 					}
 				}
 				set(s, UNINITIALIZED);
-				update_version(version);
+				increment(version);
 			}
 
 			return true;
@@ -304,7 +304,7 @@ export function proxy(value) {
 					}
 				}
 
-				update_version(version);
+				increment(version);
 			}
 
 			return true;
@@ -343,14 +343,6 @@ function get_label(path, prop) {
 	return /^\d+$/.test(prop) ? `${path}[${prop}]` : `${path}['${prop}']`;
 }
 
-/**
- * @param {Source<number>} signal
- * @param {1 | -1} [d]
- */
-function update_version(signal, d = 1) {
-	set(signal, signal.v + d);
-}
-
 /**
  * @param {any} value
  */
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index a86ccfee4f..9f08354cc0 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -259,6 +259,14 @@ export function update_pre(source, d = 1) {
 	return set(source, d === 1 ? ++value : --value);
 }
 
+/**
+ * Silently (without using `get`) increment a source
+ * @param {Source<number>} source
+ */
+export function increment(source) {
+	set(source, source.v + 1);
+}
+
 /**
  * @param {Value} signal
  * @param {number} status should be DIRTY or MAYBE_DIRTY
diff --git a/packages/svelte/src/reactivity/create-subscriber.js b/packages/svelte/src/reactivity/create-subscriber.js
index 491ffb45cb..67a92ceb7b 100644
--- a/packages/svelte/src/reactivity/create-subscriber.js
+++ b/packages/svelte/src/reactivity/create-subscriber.js
@@ -1,8 +1,7 @@
 import { get, tick, untrack } from '../internal/client/runtime.js';
 import { effect_tracking, render_effect } from '../internal/client/reactivity/effects.js';
-import { source } from '../internal/client/reactivity/sources.js';
+import { source, increment } from '../internal/client/reactivity/sources.js';
 import { tag } from '../internal/client/dev/tracing.js';
-import { increment } from './utils.js';
 import { DEV } from 'esm-env';
 
 /**
diff --git a/packages/svelte/src/reactivity/map.js b/packages/svelte/src/reactivity/map.js
index 4fa2dfd7b2..014b5e7c7c 100644
--- a/packages/svelte/src/reactivity/map.js
+++ b/packages/svelte/src/reactivity/map.js
@@ -1,9 +1,8 @@
 /** @import { Source } from '#client' */
 import { DEV } from 'esm-env';
-import { set, source, state } from '../internal/client/reactivity/sources.js';
+import { set, source, state, increment } from '../internal/client/reactivity/sources.js';
 import { label, tag } from '../internal/client/dev/tracing.js';
 import { get, update_version } from '../internal/client/runtime.js';
-import { increment } from './utils.js';
 
 /**
  * A reactive version of the built-in [`Map`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) object.
diff --git a/packages/svelte/src/reactivity/set.js b/packages/svelte/src/reactivity/set.js
index 9e3c330beb..d7c2deeaae 100644
--- a/packages/svelte/src/reactivity/set.js
+++ b/packages/svelte/src/reactivity/set.js
@@ -1,9 +1,8 @@
 /** @import { Source } from '#client' */
 import { DEV } from 'esm-env';
-import { source, set, state } from '../internal/client/reactivity/sources.js';
+import { source, set, state, increment } from '../internal/client/reactivity/sources.js';
 import { label, tag } from '../internal/client/dev/tracing.js';
 import { get, update_version } from '../internal/client/runtime.js';
-import { increment } from './utils.js';
 
 var read_methods = ['forEach', 'isDisjointFrom', 'isSubsetOf', 'isSupersetOf'];
 var set_like_methods = ['difference', 'intersection', 'symmetricDifference', 'union'];
diff --git a/packages/svelte/src/reactivity/url-search-params.js b/packages/svelte/src/reactivity/url-search-params.js
index 389da7cdb6..2381e11875 100644
--- a/packages/svelte/src/reactivity/url-search-params.js
+++ b/packages/svelte/src/reactivity/url-search-params.js
@@ -1,9 +1,8 @@
 import { DEV } from 'esm-env';
-import { state } from '../internal/client/reactivity/sources.js';
+import { state, increment } from '../internal/client/reactivity/sources.js';
 import { tag } from '../internal/client/dev/tracing.js';
 import { get } from '../internal/client/runtime.js';
 import { get_current_url } from './url.js';
-import { increment } from './utils.js';
 
 export const REPLACE = Symbol();
 
diff --git a/packages/svelte/src/reactivity/utils.js b/packages/svelte/src/reactivity/utils.js
deleted file mode 100644
index cd55e0e0ba..0000000000
--- a/packages/svelte/src/reactivity/utils.js
+++ /dev/null
@@ -1,7 +0,0 @@
-/** @import { Source } from '#client' */
-import { set } from '../internal/client/reactivity/sources.js';
-
-/** @param {Source<number>} source */
-export function increment(source) {
-	set(source, source.v + 1);
-}

From 8da222f46021fd2bd3e69048557a229c20a2fe94 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 10 Jul 2025 08:57:33 -0400
Subject: [PATCH 041/148] chore: simplify component pop (#16331)

* chore: simplify pop

* shuffle

* remove .m flag on component context

* unused

* shuffle

* simplify

* context is never null in pop

* changeset
---
 .changeset/new-candles-marry.md               |  5 ++
 .../svelte/src/internal/client/context.js     | 50 ++++++++-----------
 .../src/internal/client/reactivity/effects.js | 18 ++-----
 .../svelte/src/internal/client/types.d.ts     |  8 +--
 4 files changed, 30 insertions(+), 51 deletions(-)
 create mode 100644 .changeset/new-candles-marry.md

diff --git a/.changeset/new-candles-marry.md b/.changeset/new-candles-marry.md
new file mode 100644
index 0000000000..4d55980c72
--- /dev/null
+++ b/.changeset/new-candles-marry.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: simplify internal component `pop()`
diff --git a/packages/svelte/src/internal/client/context.js b/packages/svelte/src/internal/client/context.js
index d79d827fee..6876a89f57 100644
--- a/packages/svelte/src/internal/client/context.js
+++ b/packages/svelte/src/internal/client/context.js
@@ -143,7 +143,6 @@ export function push(props, runes = false, fn) {
 		p: component_context,
 		c: null,
 		e: null,
-		m: false,
 		s: props,
 		x: null,
 		l: null
@@ -171,37 +170,28 @@ export function push(props, runes = false, fn) {
  * @returns {T}
  */
 export function pop(component) {
-	const context_stack_item = component_context;
-	if (context_stack_item !== null) {
-		if (component !== undefined) {
-			context_stack_item.x = component;
-		}
-		const component_effects = context_stack_item.e;
-		if (component_effects !== null) {
-			var previous_effect = active_effect;
-			var previous_reaction = active_reaction;
-			context_stack_item.e = null;
-			try {
-				for (var i = 0; i < component_effects.length; i++) {
-					var component_effect = component_effects[i];
-					set_active_effect(component_effect.effect);
-					set_active_reaction(component_effect.reaction);
-					create_user_effect(component_effect.fn);
-				}
-			} finally {
-				set_active_effect(previous_effect);
-				set_active_reaction(previous_reaction);
-			}
-		}
-		component_context = context_stack_item.p;
-		if (DEV) {
-			dev_current_component_function = context_stack_item.p?.function ?? null;
+	var context = /** @type {ComponentContext} */ (component_context);
+	var effects = context.e;
+
+	if (effects !== null) {
+		context.e = null;
+
+		for (var fn of effects) {
+			create_user_effect(fn);
 		}
-		context_stack_item.m = true;
 	}
-	// Micro-optimization: Don't set .a above to the empty object
-	// so it can be garbage-collected when the return here is unused
-	return component || /** @type {T} */ ({});
+
+	if (component !== undefined) {
+		context.x = component;
+	}
+
+	component_context = context.p;
+
+	if (DEV) {
+		dev_current_component_function = component_context?.function ?? null;
+	}
+
+	return component ?? /** @type {T} */ ({});
 }
 
 /** @returns {boolean} */
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index df2afd3e38..51c6805529 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -179,28 +179,18 @@ export function teardown(fn) {
 export function user_effect(fn) {
 	validate_effect('$effect');
 
-	// Non-nested `$effect(...)` in a component should be deferred
-	// until the component is mounted
-	var defer =
-		active_effect !== null &&
-		(active_effect.f & BRANCH_EFFECT) !== 0 &&
-		component_context !== null &&
-		!component_context.m;
-
 	if (DEV) {
 		define_property(fn, 'name', {
 			value: '$effect'
 		});
 	}
 
-	if (defer) {
+	if (!active_reaction && active_effect && (active_effect.f & BRANCH_EFFECT) !== 0) {
+		// Top-level `$effect(...)` in a component — defer until mount
 		var context = /** @type {ComponentContext} */ (component_context);
-		(context.e ??= []).push({
-			fn,
-			effect: active_effect,
-			reaction: active_reaction
-		});
+		(context.e ??= []).push(fn);
 	} else {
+		// Everything else — create immediately
 		return create_user_effect(fn);
 	}
 }
diff --git a/packages/svelte/src/internal/client/types.d.ts b/packages/svelte/src/internal/client/types.d.ts
index bcbd0ac8a3..a42f91343c 100644
--- a/packages/svelte/src/internal/client/types.d.ts
+++ b/packages/svelte/src/internal/client/types.d.ts
@@ -15,13 +15,7 @@ export type ComponentContext = {
 	/** context */
 	c: null | Map<unknown, unknown>;
 	/** deferred effects */
-	e: null | Array<{
-		fn: () => void | (() => void);
-		effect: null | Effect;
-		reaction: null | Reaction;
-	}>;
-	/** mounted */
-	m: boolean;
+	e: null | Array<() => void | (() => void)>;
 	/**
 	 * props — needed for legacy mode lifecycle functions, and for `createEventDispatcher`
 	 * @deprecated remove in 6.0

From 0e7e873a1b9a4b5c999ccc2525172d658fc73e25 Mon Sep 17 00:00:00 2001
From: "Dominik G." <dominik.goepel@gmx.de>
Date: Thu, 10 Jul 2025 15:41:47 +0200
Subject: [PATCH 042/148] chore: update svelte-ecosystem-ci trigger (#16315)

---
 .github/workflows/ecosystem-ci-trigger.yml | 43 +++++++++++++++-------
 1 file changed, 30 insertions(+), 13 deletions(-)

diff --git a/.github/workflows/ecosystem-ci-trigger.yml b/.github/workflows/ecosystem-ci-trigger.yml
index 71df3242e8..7c6b740370 100644
--- a/.github/workflows/ecosystem-ci-trigger.yml
+++ b/.github/workflows/ecosystem-ci-trigger.yml
@@ -8,9 +8,17 @@ jobs:
   trigger:
     runs-on: ubuntu-latest
     if: github.repository == 'sveltejs/svelte' && github.event.issue.pull_request && startsWith(github.event.comment.body, '/ecosystem-ci run')
+    permissions:
+      issues: write # to add / delete reactions
+      pull-requests: read # to read PR data
+      actions: read # to check workflow status
+      contents: read # to clone the repo
     steps:
-      - uses: GitHubSecurityLab/actions-permissions/monitor@v1
-      - uses: actions/github-script@v6
+      - name: monitor action permissions
+        uses: GitHubSecurityLab/actions-permissions/monitor@v1
+      - name: check user authorization # user needs triage permission
+        uses: actions/github-script@v7
+        id: check-permissions
         with:
           script: |
             const user = context.payload.sender.login
@@ -29,7 +37,7 @@ jobs:
             }
 
             if (hasTriagePermission) {
-              console.log('Allowed')
+              console.log('User is allowed. Adding +1 reaction.')
               await github.rest.reactions.createForIssueComment({
                 owner: context.repo.owner,
                 repo: context.repo.repo,
@@ -37,16 +45,18 @@ jobs:
                 content: '+1',
               })
             } else {
-              console.log('Not allowed')
+              console.log('User is not allowed. Adding -1 reaction.')
               await github.rest.reactions.createForIssueComment({
                 owner: context.repo.owner,
                 repo: context.repo.repo,
                 comment_id: context.payload.comment.id,
                 content: '-1',
               })
-              throw new Error('not allowed')
+              throw new Error('User does not have the necessary permissions.')
             }
-      - uses: actions/github-script@v6
+
+      - name: Get PR Data
+        uses: actions/github-script@v7
         id: get-pr-data
         with:
           script: |
@@ -59,21 +69,27 @@ jobs:
             return {
               num: context.issue.number,
               branchName: pr.head.ref,
+              commit: pr.head.sha,
               repo: pr.head.repo.full_name
             }
-      - id: generate-token
-        uses: tibdex/github-app-token@b62528385c34dbc9f38e5f4225ac829252d1ea92 #keep pinned for security reasons, currently 1.8.0
+
+      - name: Generate Token
+        id: generate-token
+        uses: actions/create-github-app-token@v2
         with:
-          app_id: ${{ secrets.ECOSYSTEM_CI_GITHUB_APP_ID }}
-          private_key: ${{ secrets.ECOSYSTEM_CI_GITHUB_APP_PRIVATE_KEY }}
-          repository: '${{ github.repository_owner }}/svelte-ecosystem-ci'
-      - uses: actions/github-script@v6
+          app-id: ${{ secrets.ECOSYSTEM_CI_GITHUB_APP_ID }}
+          private-key: ${{ secrets.ECOSYSTEM_CI_GITHUB_APP_PRIVATE_KEY }}
+          repositories: |
+            svelte
+            svelte-ecosystem-ci
+
+      - name: Trigger Downstream Workflow
+        uses: actions/github-script@v7
         id: trigger
         env:
           COMMENT: ${{ github.event.comment.body }}
         with:
           github-token: ${{ steps.generate-token.outputs.token }}
-          result-encoding: string
           script: |
             const comment = process.env.COMMENT.trim()
             const prData = ${{ steps.get-pr-data.outputs.result }}
@@ -89,6 +105,7 @@ jobs:
                 prNumber: '' + prData.num,
                 branchName: prData.branchName,
                 repo: prData.repo,
+                commit: prData.commit,
                 suite: suite === '' ? '-' : suite
               }
             })

From 443e76e4baa6b57739b263d4dbb74868508ec2e1 Mon Sep 17 00:00:00 2001
From: "Dominik G." <dominik.goepel@gmx.de>
Date: Thu, 10 Jul 2025 16:56:41 +0200
Subject: [PATCH 043/148] fix: set write permission for PR in
 ecosystem-ci-trigger workflow (#16337)

* fix: set write permission for PR in ecosystem-ci-trigger workflow

* chore: match wording with vites trigger
---
 .github/workflows/ecosystem-ci-trigger.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/ecosystem-ci-trigger.yml b/.github/workflows/ecosystem-ci-trigger.yml
index 7c6b740370..9be1f00104 100644
--- a/.github/workflows/ecosystem-ci-trigger.yml
+++ b/.github/workflows/ecosystem-ci-trigger.yml
@@ -10,7 +10,7 @@ jobs:
     if: github.repository == 'sveltejs/svelte' && github.event.issue.pull_request && startsWith(github.event.comment.body, '/ecosystem-ci run')
     permissions:
       issues: write # to add / delete reactions
-      pull-requests: read # to read PR data
+      pull-requests: write # to read PR data, and to add labels
       actions: read # to check workflow status
       contents: read # to clone the repo
     steps:

From 6f0aec527177d4c3ec56b94d1e8b21d28266bbb7 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 10 Jul 2025 12:36:10 -0400
Subject: [PATCH 044/148] chore: simplify source ownership (#16333)

* simplify source ownership

* rename

* changeset

* make it unnecessary to hand onto `current_sources` past the initial update
---
 .changeset/eight-walls-mate.md                |  5 ++++
 packages/svelte/src/internal/client/proxy.js  | 29 +++++++++++++++----
 .../src/internal/client/reactivity/sources.js |  4 +--
 .../svelte/src/internal/client/runtime.js     | 28 +++++++++---------
 4 files changed, 45 insertions(+), 21 deletions(-)
 create mode 100644 .changeset/eight-walls-mate.md

diff --git a/.changeset/eight-walls-mate.md b/.changeset/eight-walls-mate.md
new file mode 100644
index 0000000000..a7de4e6278
--- /dev/null
+++ b/.changeset/eight-walls-mate.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: simplify reaction/source ownership tracking
diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index 97c8da9d33..5da1b7e188 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -1,6 +1,13 @@
 /** @import { Source } from '#client' */
 import { DEV } from 'esm-env';
-import { get, active_effect, active_reaction, set_active_reaction } from './runtime.js';
+import {
+	get,
+	active_effect,
+	update_version,
+	active_reaction,
+	set_update_version,
+	set_active_reaction
+} from './runtime.js';
 import {
 	array_prototype,
 	get_descriptor,
@@ -41,7 +48,7 @@ export function proxy(value) {
 	var version = source(0);
 
 	var stack = DEV && tracing_mode_flag ? get_stack('CreatedAt') : null;
-	var reaction = active_reaction;
+	var parent_version = update_version;
 
 	/**
 	 * Executes the proxy in the context of the reaction it was originally created in, if any
@@ -49,13 +56,23 @@ export function proxy(value) {
 	 * @param {() => T} fn
 	 */
 	var with_parent = (fn) => {
-		var previous_reaction = active_reaction;
-		set_active_reaction(reaction);
+		if (update_version === parent_version) {
+			return fn();
+		}
+
+		// child source is being created after the initial proxy —
+		// prevent it from being associated with the current reaction
+		var reaction = active_reaction;
+		var version = update_version;
+
+		set_active_reaction(null);
+		set_update_version(parent_version);
 
-		/** @type {T} */
 		var result = fn();
 
-		set_active_reaction(previous_reaction);
+		set_active_reaction(reaction);
+		set_update_version(version);
+
 		return result;
 	};
 
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index 9f08354cc0..f84312e31c 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -11,7 +11,7 @@ import {
 	untrack,
 	increment_write_version,
 	update_effect,
-	source_ownership,
+	current_sources,
 	check_dirtiness,
 	untracking,
 	is_destroying_effect,
@@ -140,7 +140,7 @@ export function set(source, value, should_proxy = false) {
 		(!untracking || (active_reaction.f & INSPECT_EFFECT) !== 0) &&
 		is_runes() &&
 		(active_reaction.f & (DERIVED | BLOCK_EFFECT | INSPECT_EFFECT)) !== 0 &&
-		!(source_ownership?.reaction === active_reaction && source_ownership.sources.includes(source))
+		!current_sources?.includes(source)
 	) {
 		e.state_unsafe_mutation();
 	}
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index d6e7325ba3..6477e2942a 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -88,17 +88,17 @@ export function set_active_effect(effect) {
 /**
  * When sources are created within a reaction, reading and writing
  * them within that reaction should not cause a re-run
- * @type {null | { reaction: Reaction, sources: Source[] }}
+ * @type {null | Source[]}
  */
-export let source_ownership = null;
+export let current_sources = null;
 
 /** @param {Value} value */
 export function push_reaction_value(value) {
 	if (active_reaction !== null && active_reaction.f & EFFECT_IS_UPDATING) {
-		if (source_ownership === null) {
-			source_ownership = { reaction: active_reaction, sources: [value] };
+		if (current_sources === null) {
+			current_sources = [value];
 		} else {
-			source_ownership.sources.push(value);
+			current_sources.push(value);
 		}
 	}
 }
@@ -136,6 +136,11 @@ let read_version = 0;
 
 export let update_version = read_version;
 
+/** @param {number} value */
+export function set_update_version(value) {
+	update_version = value;
+}
+
 // If we are working with a get() chain that has no active container,
 // to prevent memory leaks, we skip adding the reaction.
 export let skip_reaction = false;
@@ -236,7 +241,7 @@ function schedule_possible_effect_self_invalidation(signal, effect, root = true)
 	var reactions = signal.reactions;
 	if (reactions === null) return;
 
-	if (source_ownership?.reaction === active_reaction && source_ownership.sources.includes(signal)) {
+	if (current_sources?.includes(signal)) {
 		return;
 	}
 
@@ -263,7 +268,7 @@ export function update_reaction(reaction) {
 	var previous_untracked_writes = untracked_writes;
 	var previous_reaction = active_reaction;
 	var previous_skip_reaction = skip_reaction;
-	var previous_reaction_sources = source_ownership;
+	var previous_sources = current_sources;
 	var previous_component_context = component_context;
 	var previous_untracking = untracking;
 	var previous_update_version = update_version;
@@ -277,7 +282,7 @@ export function update_reaction(reaction) {
 		(flags & UNOWNED) !== 0 && (untracking || !is_updating_effect || active_reaction === null);
 	active_reaction = (flags & (BRANCH_EFFECT | ROOT_EFFECT)) === 0 ? reaction : null;
 
-	source_ownership = null;
+	current_sources = null;
 	set_component_context(reaction.ctx);
 	untracking = false;
 	update_version = ++read_version;
@@ -365,7 +370,7 @@ export function update_reaction(reaction) {
 		untracked_writes = previous_untracked_writes;
 		active_reaction = previous_reaction;
 		skip_reaction = previous_skip_reaction;
-		source_ownership = previous_reaction_sources;
+		current_sources = previous_sources;
 		set_component_context(previous_component_context);
 		untracking = previous_untracking;
 		update_version = previous_update_version;
@@ -759,10 +764,7 @@ export function get(signal) {
 
 	// Register the dependency on the current reaction signal.
 	if (active_reaction !== null && !untracking) {
-		if (
-			source_ownership?.reaction !== active_reaction ||
-			!source_ownership?.sources.includes(signal)
-		) {
+		if (!current_sources?.includes(signal)) {
 			var deps = active_reaction.deps;
 			if (signal.rv < read_version) {
 				signal.rv = read_version;

From ca1eb55e970243dbed1c032e038860218325d63a Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Thu, 10 Jul 2025 20:41:02 -0400
Subject: [PATCH 045/148] Version Packages (#16334)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/eight-walls-mate.md  | 5 -----
 .changeset/new-candles-marry.md | 5 -----
 packages/svelte/CHANGELOG.md    | 8 ++++++++
 packages/svelte/package.json    | 2 +-
 packages/svelte/src/version.js  | 2 +-
 5 files changed, 10 insertions(+), 12 deletions(-)
 delete mode 100644 .changeset/eight-walls-mate.md
 delete mode 100644 .changeset/new-candles-marry.md

diff --git a/.changeset/eight-walls-mate.md b/.changeset/eight-walls-mate.md
deleted file mode 100644
index a7de4e6278..0000000000
--- a/.changeset/eight-walls-mate.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-chore: simplify reaction/source ownership tracking
diff --git a/.changeset/new-candles-marry.md b/.changeset/new-candles-marry.md
deleted file mode 100644
index 4d55980c72..0000000000
--- a/.changeset/new-candles-marry.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-chore: simplify internal component `pop()`
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 19aa1466c0..8f158c528f 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,13 @@
 # svelte
 
+## 5.35.6
+
+### Patch Changes
+
+- chore: simplify reaction/source ownership tracking ([#16333](https://github.com/sveltejs/svelte/pull/16333))
+
+- chore: simplify internal component `pop()` ([#16331](https://github.com/sveltejs/svelte/pull/16331))
+
 ## 5.35.5
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 4ac497ed41..4eed145f3f 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.35.5",
+  "version": "5.35.6",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index eb68753d71..266b0b9491 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.35.5';
+export const VERSION = '5.35.6';
 export const PUBLIC_VERSION = '5';

From e802d3b2cc0b6b5f96f853833fc6852705554a6c Mon Sep 17 00:00:00 2001
From: "Ahmad S." <navorite@gmail.com>
Date: Fri, 11 Jul 2025 20:31:22 +0300
Subject: [PATCH 046/148] chore: replace inline regex with variable (#16340)

* chore: replace inline regex with variable

* Update packages/svelte/src/compiler/phases/patterns.js

Co-authored-by: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>

* Update a11y.js

* Update a11y.js

---------

Co-authored-by: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
---
 .changeset/tiny-news-whisper.md                             | 5 +++++
 .../src/compiler/phases/2-analyze/visitors/shared/a11y.js   | 6 ++++--
 packages/svelte/src/compiler/phases/patterns.js             | 2 ++
 3 files changed, 11 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/tiny-news-whisper.md

diff --git a/.changeset/tiny-news-whisper.md b/.changeset/tiny-news-whisper.md
new file mode 100644
index 0000000000..8bf877085d
--- /dev/null
+++ b/.changeset/tiny-news-whisper.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: replace inline regex with variable
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y.js
index 1f58a28cad..e103e3eb80 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y.js
@@ -6,7 +6,9 @@ import { roles as roles_map, aria, elementRoles } from 'aria-query';
 import { AXObjects, AXObjectRoles, elementAXObjects } from 'axobject-query';
 import {
 	regex_heading_tags,
+	regex_js_prefix,
 	regex_not_whitespace,
+	regex_redundant_img_alt,
 	regex_starts_with_vowel,
 	regex_whitespaces
 } from '../../../patterns.js';
@@ -1011,7 +1013,7 @@ export function check_element(node, context) {
 		if (href) {
 			const href_value = get_static_text_value(href);
 			if (href_value !== null) {
-				if (href_value === '' || href_value === '#' || /^\W*javascript:/i.test(href_value)) {
+				if (href_value === '' || href_value === '#' || regex_js_prefix.test(href_value)) {
 					w.a11y_invalid_attribute(href, href_value, href.name);
 				}
 			}
@@ -1061,7 +1063,7 @@ export function check_element(node, context) {
 		const alt_attribute = get_static_text_value(attribute_map.get('alt'));
 		const aria_hidden = get_static_value(attribute_map.get('aria-hidden'));
 		if (alt_attribute && !aria_hidden && !has_spread) {
-			if (/\b(image|picture|photo)\b/i.test(alt_attribute)) {
+			if (regex_redundant_img_alt.test(alt_attribute)) {
 				w.a11y_img_redundant_alt(node);
 			}
 		}
diff --git a/packages/svelte/src/compiler/phases/patterns.js b/packages/svelte/src/compiler/phases/patterns.js
index 2bee717131..448be7f949 100644
--- a/packages/svelte/src/compiler/phases/patterns.js
+++ b/packages/svelte/src/compiler/phases/patterns.js
@@ -23,3 +23,5 @@ export const regex_heading_tags = /^h[1-6]$/;
 export const regex_illegal_attribute_character = /(^[0-9-.])|[\^$@%&#?!|()[\]{}^*+~;]/;
 export const regex_bidirectional_control_characters =
 	/[\u202a\u202b\u202c\u202d\u202e\u2066\u2067\u2068\u2069]+/g;
+export const regex_js_prefix = /^\W*javascript:/i;
+export const regex_redundant_img_alt = /\b(image|picture|photo)\b/i;

From 96c1a10042475c4ef8b55dfdca8538a25e792626 Mon Sep 17 00:00:00 2001
From: "Ahmad S." <navorite@gmail.com>
Date: Fri, 11 Jul 2025 20:41:59 +0300
Subject: [PATCH 047/148] fix: silence autofocus a11y warning inside `<dialog>`
 (#16341)

---
 .changeset/cuddly-humans-end.md                            | 5 +++++
 .../src/compiler/phases/2-analyze/visitors/shared/a11y.js  | 2 +-
 .../tests/validator/samples/a11y-no-autofocus/input.svelte | 7 ++++++-
 3 files changed, 12 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/cuddly-humans-end.md

diff --git a/.changeset/cuddly-humans-end.md b/.changeset/cuddly-humans-end.md
new file mode 100644
index 0000000000..d02e08de7a
--- /dev/null
+++ b/.changeset/cuddly-humans-end.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: silence autofocus a11y warning inside `<dialog>`
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y.js
index e103e3eb80..152e679bf5 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y.js
@@ -877,7 +877,7 @@ export function check_element(node, context) {
 		}
 
 		// no-autofocus
-		if (name === 'autofocus') {
+		if (name === 'autofocus' && node.name !== 'dialog' && !is_parent(context.path, ['dialog'])) {
 			w.a11y_autofocus(attribute);
 		}
 
diff --git a/packages/svelte/tests/validator/samples/a11y-no-autofocus/input.svelte b/packages/svelte/tests/validator/samples/a11y-no-autofocus/input.svelte
index 769dbe8c5b..7b1dccd1e8 100644
--- a/packages/svelte/tests/validator/samples/a11y-no-autofocus/input.svelte
+++ b/packages/svelte/tests/validator/samples/a11y-no-autofocus/input.svelte
@@ -1 +1,6 @@
-<div autofocus></div>
\ No newline at end of file
+<div autofocus></div>
+<dialog autofocus>
+</dialog>
+<dialog>
+	<input autofocus>
+</dialog>

From 58baf80a70433a27a58bf5a642b4ccfd0c23349b Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Sun, 13 Jul 2025 02:40:26 -0700
Subject: [PATCH 048/148] docs: add note about proxying state proxies (#16354)

---
 documentation/docs/02-runes/02-$state.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/documentation/docs/02-runes/02-$state.md b/documentation/docs/02-runes/02-$state.md
index 8e6c91fad7..7c4571e575 100644
--- a/documentation/docs/02-runes/02-$state.md
+++ b/documentation/docs/02-runes/02-$state.md
@@ -50,7 +50,7 @@ todos.push({
 });
 ```
 
-> [!NOTE] When you update properties of proxies, the original object is _not_ mutated.
+> [!NOTE] When you update properties of proxies, the original object is _not_ mutated. If you desire to use your own proxy handlers in a state proxy, [you should wrap the object _after_ wrapping it in `$state`](https://svelte.dev/playground/hello-world?version=latest#H4sIAAAAAAAACpWR3WoDIRCFX2UqhWyIJL3erAulL9C7XnQLMe5ksbUqOpsfln33YuyGFNJC8UKdc2bOhw7Myk9kJXsJ0nttO9jcR5KEG9AWJDwHdzwxznbaYGTl68Do5JM_FRifuh-9X8Y9Gkq1rYx4q66cJbQUWcmqqIL2VDe2IYMEbvuOikBADi-GJDSkXG-phId0G-frye2DO2psQYDFQ0Ys8gQO350dUkEydEg82T0GOs0nsSG9g2IqgxACZueo2ZUlpdvoDC6N64qsg1QKY8T2bpZp8gpIfbCQ85Zn50Ud82HkeY83uDjspenxv3jXcSDyjPWf9L1vJf0GH666J-jLu1ery4dV257IWXBWGa0-xFDMQdTTn2ScxWKsn86ROsLwQxqrVR5QM84Ij8TKFD2-cUZSm4O2LSt30kQcvwCgCmfZnAIAAA==).
 
 Note that if you destructure a reactive value, the references are not reactive — as in normal JavaScript, they are evaluated at the point of destructuring:
 

From 61f75651d6a4f1106a55c2cd357751d473729e55 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Sun, 13 Jul 2025 12:48:08 -0400
Subject: [PATCH 049/148] chore: re-export shared errors (#16356)

---
 .../process-messages/templates/client-errors.js       |  2 ++
 .../process-messages/templates/server-errors.js       |  2 ++
 packages/svelte/src/index-client.js                   | 11 +++++------
 packages/svelte/src/internal/client/context.js        |  4 ++--
 packages/svelte/src/internal/client/dev/validation.js |  7 ++++---
 packages/svelte/src/internal/client/errors.js         |  2 ++
 packages/svelte/src/internal/server/context.js        |  2 +-
 packages/svelte/src/internal/server/dev.js            |  4 ++--
 packages/svelte/src/internal/server/errors.js         |  2 +-
 packages/svelte/src/legacy/legacy-client.js           |  4 ++--
 10 files changed, 23 insertions(+), 17 deletions(-)

diff --git a/packages/svelte/scripts/process-messages/templates/client-errors.js b/packages/svelte/scripts/process-messages/templates/client-errors.js
index c72e9f9d5e..ef749b4ba3 100644
--- a/packages/svelte/scripts/process-messages/templates/client-errors.js
+++ b/packages/svelte/scripts/process-messages/templates/client-errors.js
@@ -1,5 +1,7 @@
 import { DEV } from 'esm-env';
 
+export * from '../shared/errors.js';
+
 /**
  * MESSAGE
  * @param {string} PARAMETER
diff --git a/packages/svelte/scripts/process-messages/templates/server-errors.js b/packages/svelte/scripts/process-messages/templates/server-errors.js
index 6fb7924564..0bbe801abc 100644
--- a/packages/svelte/scripts/process-messages/templates/server-errors.js
+++ b/packages/svelte/scripts/process-messages/templates/server-errors.js
@@ -1,3 +1,5 @@
+export * from '../shared/errors.js';
+
 /**
  * MESSAGE
  * @param {string} PARAMETER
diff --git a/packages/svelte/src/index-client.js b/packages/svelte/src/index-client.js
index 0d962aacd1..ae1caf16d9 100644
--- a/packages/svelte/src/index-client.js
+++ b/packages/svelte/src/index-client.js
@@ -5,7 +5,6 @@ import { active_reaction, untrack } from './internal/client/runtime.js';
 import { is_array } from './internal/shared/utils.js';
 import { user_effect } from './internal/client/index.js';
 import * as e from './internal/client/errors.js';
-import { lifecycle_outside_component } from './internal/shared/errors.js';
 import { legacy_mode_flag } from './internal/flags/index.js';
 import { component_context } from './internal/client/context.js';
 import { DEV } from 'esm-env';
@@ -91,7 +90,7 @@ export function getAbortSignal() {
  */
 export function onMount(fn) {
 	if (component_context === null) {
-		lifecycle_outside_component('onMount');
+		e.lifecycle_outside_component('onMount');
 	}
 
 	if (legacy_mode_flag && component_context.l !== null) {
@@ -115,7 +114,7 @@ export function onMount(fn) {
  */
 export function onDestroy(fn) {
 	if (component_context === null) {
-		lifecycle_outside_component('onDestroy');
+		e.lifecycle_outside_component('onDestroy');
 	}
 
 	onMount(() => () => untrack(fn));
@@ -158,7 +157,7 @@ function create_custom_event(type, detail, { bubbles = false, cancelable = false
 export function createEventDispatcher() {
 	const active_component_context = component_context;
 	if (active_component_context === null) {
-		lifecycle_outside_component('createEventDispatcher');
+		e.lifecycle_outside_component('createEventDispatcher');
 	}
 
 	return (type, detail, options) => {
@@ -196,7 +195,7 @@ export function createEventDispatcher() {
  */
 export function beforeUpdate(fn) {
 	if (component_context === null) {
-		lifecycle_outside_component('beforeUpdate');
+		e.lifecycle_outside_component('beforeUpdate');
 	}
 
 	if (component_context.l === null) {
@@ -219,7 +218,7 @@ export function beforeUpdate(fn) {
  */
 export function afterUpdate(fn) {
 	if (component_context === null) {
-		lifecycle_outside_component('afterUpdate');
+		e.lifecycle_outside_component('afterUpdate');
 	}
 
 	if (component_context.l === null) {
diff --git a/packages/svelte/src/internal/client/context.js b/packages/svelte/src/internal/client/context.js
index 6876a89f57..eae326f9bb 100644
--- a/packages/svelte/src/internal/client/context.js
+++ b/packages/svelte/src/internal/client/context.js
@@ -1,7 +1,7 @@
 /** @import { ComponentContext, DevStackEntry } from '#client' */
 
 import { DEV } from 'esm-env';
-import { lifecycle_outside_component } from '../shared/errors.js';
+import * as e from './errors.js';
 import { source } from './reactivity/sources.js';
 import {
 	active_effect,
@@ -205,7 +205,7 @@ export function is_runes() {
  */
 function get_or_init_context_map(name) {
 	if (component_context === null) {
-		lifecycle_outside_component(name);
+		e.lifecycle_outside_component(name);
 	}
 
 	return (component_context.c ??= new Map(get_parent_context(component_context) || undefined));
diff --git a/packages/svelte/src/internal/client/dev/validation.js b/packages/svelte/src/internal/client/dev/validation.js
index e41e4c4628..60d140c718 100644
--- a/packages/svelte/src/internal/client/dev/validation.js
+++ b/packages/svelte/src/internal/client/dev/validation.js
@@ -1,15 +1,16 @@
-import { invalid_snippet_arguments } from '../../shared/errors.js';
+import * as e from '../errors.js';
 /**
  * @param {Node} anchor
  * @param {...(()=>any)[]} args
  */
 export function validate_snippet_args(anchor, ...args) {
 	if (typeof anchor !== 'object' || !(anchor instanceof Node)) {
-		invalid_snippet_arguments();
+		e.invalid_snippet_arguments();
 	}
+
 	for (let arg of args) {
 		if (typeof arg !== 'function') {
-			invalid_snippet_arguments();
+			e.invalid_snippet_arguments();
 		}
 	}
 }
diff --git a/packages/svelte/src/internal/client/errors.js b/packages/svelte/src/internal/client/errors.js
index 5c3f5340e1..64dc34e8d0 100644
--- a/packages/svelte/src/internal/client/errors.js
+++ b/packages/svelte/src/internal/client/errors.js
@@ -2,6 +2,8 @@
 
 import { DEV } from 'esm-env';
 
+export *  from '../shared/errors.js';
+
 /**
  * Using `bind:value` together with a checkbox input is not allowed. Use `bind:checked` instead
  * @returns {never}
diff --git a/packages/svelte/src/internal/server/context.js b/packages/svelte/src/internal/server/context.js
index 4e547f48cb..bae93beb53 100644
--- a/packages/svelte/src/internal/server/context.js
+++ b/packages/svelte/src/internal/server/context.js
@@ -1,7 +1,7 @@
 /** @import { Component } from '#server' */
 import { DEV } from 'esm-env';
 import { on_destroy } from './index.js';
-import * as e from '../shared/errors.js';
+import * as e from './errors.js';
 
 /** @type {Component | null} */
 export var current_component = null;
diff --git a/packages/svelte/src/internal/server/dev.js b/packages/svelte/src/internal/server/dev.js
index efc761d7c5..3c320f9698 100644
--- a/packages/svelte/src/internal/server/dev.js
+++ b/packages/svelte/src/internal/server/dev.js
@@ -5,7 +5,7 @@ import {
 	is_tag_valid_with_parent
 } from '../../html-tree-validation.js';
 import { current_component } from './context.js';
-import { invalid_snippet_arguments } from '../shared/errors.js';
+import * as e from './errors.js';
 import { HeadPayload, Payload } from './payload.js';
 
 /**
@@ -102,6 +102,6 @@ export function validate_snippet_args(payload) {
 		// for some reason typescript consider the type of payload as never after the first instanceof
 		!(payload instanceof Payload || /** @type {any} */ (payload) instanceof HeadPayload)
 	) {
-		invalid_snippet_arguments();
+		e.invalid_snippet_arguments();
 	}
 }
diff --git a/packages/svelte/src/internal/server/errors.js b/packages/svelte/src/internal/server/errors.js
index e47530c9aa..458937218f 100644
--- a/packages/svelte/src/internal/server/errors.js
+++ b/packages/svelte/src/internal/server/errors.js
@@ -1,6 +1,6 @@
 /* This file is generated by scripts/process-messages/index.js. Do not edit! */
 
-
+export *  from '../shared/errors.js';
 
 /**
  * `%name%(...)` is not available on the server
diff --git a/packages/svelte/src/legacy/legacy-client.js b/packages/svelte/src/legacy/legacy-client.js
index 45c478ecab..61acbeaa28 100644
--- a/packages/svelte/src/legacy/legacy-client.js
+++ b/packages/svelte/src/legacy/legacy-client.js
@@ -4,8 +4,8 @@ import { user_pre_effect } from '../internal/client/reactivity/effects.js';
 import { mutable_source, set } from '../internal/client/reactivity/sources.js';
 import { hydrate, mount, unmount } from '../internal/client/render.js';
 import { active_effect, flushSync, get, set_signal_status } from '../internal/client/runtime.js';
-import { lifecycle_outside_component } from '../internal/shared/errors.js';
 import { define_property, is_array } from '../internal/shared/utils.js';
+import * as e from '../internal/client/errors.js';
 import * as w from '../internal/client/warnings.js';
 import { DEV } from 'esm-env';
 import { FILENAME } from '../constants.js';
@@ -245,7 +245,7 @@ export function handlers(...handlers) {
 export function createBubbler() {
 	const active_component_context = component_context;
 	if (active_component_context === null) {
-		lifecycle_outside_component('createBubbler');
+		e.lifecycle_outside_component('createBubbler');
 	}
 
 	return (/**@type {string}*/ type) => (/**@type {Event}*/ event) => {

From 4ef53a75a9f7428efe169ab2e037e87508c3ac87 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Sun, 13 Jul 2025 15:15:02 -0400
Subject: [PATCH 050/148] chore: tidy up some stuff (#16357)

* chore: tidy up some stuff

* shut up dumbass
---
 packages/svelte/knip.json                           | 4 ----
 packages/svelte/src/compiler/phases/scope.js        | 6 +++---
 packages/svelte/src/internal/client/context.js      | 9 +--------
 packages/svelte/src/internal/server/abort-signal.js | 2 +-
 packages/svelte/src/internal/shared/validate.js     | 2 --
 packages/svelte/src/utils.js                        | 2 +-
 6 files changed, 6 insertions(+), 19 deletions(-)

diff --git a/packages/svelte/knip.json b/packages/svelte/knip.json
index 7a27a64a91..0d1bf17e9f 100644
--- a/packages/svelte/knip.json
+++ b/packages/svelte/knip.json
@@ -1,10 +1,6 @@
 {
 	"$schema": "https://unpkg.com/knip@5/schema.json",
 	"entry": [
-		"src/*/index.js",
-		"src/index-client.ts",
-		"src/index-server.ts",
-		"src/index.d.ts",
 		"tests/**/*.js",
 		"tests/**/*.ts",
 		"!tests/**/*.svelte",
diff --git a/packages/svelte/src/compiler/phases/scope.js b/packages/svelte/src/compiler/phases/scope.js
index 8a2cc39ba7..662924b52c 100644
--- a/packages/svelte/src/compiler/phases/scope.js
+++ b/packages/svelte/src/compiler/phases/scope.js
@@ -18,9 +18,9 @@ import { validate_identifier_name } from './2-analyze/visitors/shared/utils.js';
 
 const UNKNOWN = Symbol('unknown');
 /** Includes `BigInt` */
-export const NUMBER = Symbol('number');
-export const STRING = Symbol('string');
-export const FUNCTION = Symbol('string');
+const NUMBER = Symbol('number');
+const STRING = Symbol('string');
+const FUNCTION = Symbol('string');
 
 /** @type {Record<string, [type: NUMBER | STRING | UNKNOWN, fn?: Function]>} */
 const globals = {
diff --git a/packages/svelte/src/internal/client/context.js b/packages/svelte/src/internal/client/context.js
index eae326f9bb..a9ceafcd11 100644
--- a/packages/svelte/src/internal/client/context.js
+++ b/packages/svelte/src/internal/client/context.js
@@ -1,15 +1,8 @@
 /** @import { ComponentContext, DevStackEntry } from '#client' */
-
 import { DEV } from 'esm-env';
 import * as e from './errors.js';
 import { source } from './reactivity/sources.js';
-import {
-	active_effect,
-	active_reaction,
-	set_active_effect,
-	set_active_reaction
-} from './runtime.js';
-import { create_user_effect, teardown } from './reactivity/effects.js';
+import { create_user_effect } from './reactivity/effects.js';
 import { legacy_mode_flag } from '../flags/index.js';
 import { FILENAME } from '../../constants.js';
 
diff --git a/packages/svelte/src/internal/server/abort-signal.js b/packages/svelte/src/internal/server/abort-signal.js
index da579b2592..a769a46e3d 100644
--- a/packages/svelte/src/internal/server/abort-signal.js
+++ b/packages/svelte/src/internal/server/abort-signal.js
@@ -1,7 +1,7 @@
 import { STALE_REACTION } from '#client/constants';
 
 /** @type {AbortController | null} */
-export let controller = null;
+let controller = null;
 
 export function abort() {
 	controller?.abort(STALE_REACTION);
diff --git a/packages/svelte/src/internal/shared/validate.js b/packages/svelte/src/internal/shared/validate.js
index bbb237594b..8f3e2807e7 100644
--- a/packages/svelte/src/internal/shared/validate.js
+++ b/packages/svelte/src/internal/shared/validate.js
@@ -1,5 +1,3 @@
-/** @import { TemplateNode } from '#client' */
-/** @import { Getters } from '#shared' */
 import { is_void } from '../../utils.js';
 import * as w from './warnings.js';
 import * as e from './errors.js';
diff --git a/packages/svelte/src/utils.js b/packages/svelte/src/utils.js
index 921eaec57c..2fc21220f0 100644
--- a/packages/svelte/src/utils.js
+++ b/packages/svelte/src/utils.js
@@ -428,7 +428,7 @@ export function is_mathml(name) {
 	return MATHML_ELEMENTS.includes(name);
 }
 
-export const STATE_CREATION_RUNES = /** @type {const} */ ([
+const STATE_CREATION_RUNES = /** @type {const} */ ([
 	'$state',
 	'$state.raw',
 	'$derived',

From a23599a196380ce7fc3fb374dac4daee173776b7 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Sun, 13 Jul 2025 18:20:29 -0400
Subject: [PATCH 051/148] fix: don't show adjusted error messages in boundaries
 (#16360)

---
 .changeset/large-balloons-agree.md            |  5 ++
 .../src/internal/client/error-handling.js     | 47 ++++++++++++-------
 .../samples/error-boundary-3/_config.js       |  2 +-
 .../samples/error-boundary-3/main.svelte      |  6 +--
 4 files changed, 38 insertions(+), 22 deletions(-)
 create mode 100644 .changeset/large-balloons-agree.md

diff --git a/.changeset/large-balloons-agree.md b/.changeset/large-balloons-agree.md
new file mode 100644
index 0000000000..9355336862
--- /dev/null
+++ b/.changeset/large-balloons-agree.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: don't show adjusted error messages in boundaries
diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index 378f7408ef..b12f21adfc 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -7,14 +7,16 @@ import { BOUNDARY_EFFECT, EFFECT_RAN } from './constants.js';
 import { define_property, get_descriptor } from '../shared/utils.js';
 import { active_effect } from './runtime.js';
 
+const adjustments = new WeakMap();
+
 /**
  * @param {unknown} error
  */
 export function handle_error(error) {
 	var effect = /** @type {Effect} */ (active_effect);
 
-	if (DEV && error instanceof Error) {
-		adjust_error(error, effect);
+	if (DEV && error instanceof Error && !adjustments.has(error)) {
+		adjustments.set(error, get_adjustments(error, effect));
 	}
 
 	if ((effect.f & EFFECT_RAN) === 0) {
@@ -48,21 +50,19 @@ export function invoke_error_boundary(error, effect) {
 		effect = effect.parent;
 	}
 
+	if (error instanceof Error) {
+		apply_adjustments(error);
+	}
+
 	throw error;
 }
 
-/** @type {WeakSet<Error>} */
-const adjusted_errors = new WeakSet();
-
 /**
  * Add useful information to the error message/stack in development
  * @param {Error} error
  * @param {Effect} effect
  */
-function adjust_error(error, effect) {
-	if (adjusted_errors.has(error)) return;
-	adjusted_errors.add(error);
-
+function get_adjustments(error, effect) {
 	const message_descriptor = get_descriptor(error, 'message');
 
 	// if the message was already changed and it's not configurable we can't change it
@@ -78,17 +78,28 @@ function adjust_error(error, effect) {
 		context = context.p;
 	}
 
-	define_property(error, 'message', {
-		value: error.message + `\n${component_stack}\n`
-	});
+	return {
+		message: error.message + `\n${component_stack}\n`,
+		stack: error.stack
+			?.split('\n')
+			.filter((line) => !line.includes('svelte/src/internal'))
+			.join('\n')
+	};
+}
+
+/**
+ * @param {Error} error
+ */
+function apply_adjustments(error) {
+	const adjusted = adjustments.get(error);
+
+	if (adjusted) {
+		define_property(error, 'message', {
+			value: adjusted.message
+		});
 
-	if (error.stack) {
-		// Filter out internal modules
 		define_property(error, 'stack', {
-			value: error.stack
-				.split('\n')
-				.filter((line) => !line.includes('svelte/src/internal'))
-				.join('\n')
+			value: adjusted.stack
 		});
 	}
 }
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-3/_config.js b/packages/svelte/tests/runtime-runes/samples/error-boundary-3/_config.js
index 040e13676e..06da8f667c 100644
--- a/packages/svelte/tests/runtime-runes/samples/error-boundary-3/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-3/_config.js
@@ -9,6 +9,6 @@ export default test({
 		flushSync();
 
 		assert.deepEqual(logs, ['error caught']);
-		assert.htmlEqual(target.innerHTML, `<div>Fallback!</div><button>+</button>`);
+		assert.htmlEqual(target.innerHTML, `<div>oh no!</div><button>+</button>`);
 	}
 });
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-3/main.svelte b/packages/svelte/tests/runtime-runes/samples/error-boundary-3/main.svelte
index bad84666c0..bc7fe072c4 100644
--- a/packages/svelte/tests/runtime-runes/samples/error-boundary-3/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-3/main.svelte
@@ -1,6 +1,6 @@
 <script>
 	function throw_error() {
-		throw new Error('test')
+		throw new Error('oh no!')
 	}
 
 	let count = $state(0);
@@ -9,8 +9,8 @@
 <svelte:boundary onerror={(e) => console.log('error caught')}>
 	{count > 0 ? throw_error() : null}
 
-	{#snippet failed()}
-		<div>Fallback!</div>
+	{#snippet failed(e)}
+		<div>{e.message}</div>
 	{/snippet}
 </svelte:boundary>
 

From 3f3cf9ff36608ecec9d45e3777eabc074e99f5e5 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Sun, 13 Jul 2025 18:21:10 -0400
Subject: [PATCH 052/148] chore: rename check_dirtiness -> is_dirty (#16359)

---
 .../svelte/src/internal/client/reactivity/effects.js   |  4 ++--
 .../svelte/src/internal/client/reactivity/sources.js   |  4 ++--
 packages/svelte/src/internal/client/runtime.js         | 10 +++++-----
 3 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index 51c6805529..b6a40a68be 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -1,6 +1,6 @@
 /** @import { ComponentContext, ComponentContextLegacy, Derived, Effect, TemplateNode, TransitionManager } from '#client' */
 import {
-	check_dirtiness,
+	is_dirty,
 	active_effect,
 	active_reaction,
 	update_effect,
@@ -307,7 +307,7 @@ export function legacy_pre_effect_reset() {
 				set_signal_status(effect, MAYBE_DIRTY);
 			}
 
-			if (check_dirtiness(effect)) {
+			if (is_dirty(effect)) {
 				update_effect(effect);
 			}
 
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index f84312e31c..c04443c93e 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -12,7 +12,7 @@ import {
 	increment_write_version,
 	update_effect,
 	current_sources,
-	check_dirtiness,
+	is_dirty,
 	untracking,
 	is_destroying_effect,
 	push_reaction_value
@@ -218,7 +218,7 @@ export function internal_set(source, value) {
 				if ((effect.f & CLEAN) !== 0) {
 					set_signal_status(effect, MAYBE_DIRTY);
 				}
-				if (check_dirtiness(effect)) {
+				if (is_dirty(effect)) {
 					update_effect(effect);
 				}
 			}
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 6477e2942a..5eca31e8cf 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -163,7 +163,7 @@ export function increment_write_version() {
  * @param {Reaction} reaction
  * @returns {boolean}
  */
-export function check_dirtiness(reaction) {
+export function is_dirty(reaction) {
 	var flags = reaction.f;
 
 	if ((flags & DIRTY) !== 0) {
@@ -212,7 +212,7 @@ export function check_dirtiness(reaction) {
 			for (i = 0; i < length; i++) {
 				dependency = dependencies[i];
 
-				if (check_dirtiness(/** @type {Derived} */ (dependency))) {
+				if (is_dirty(/** @type {Derived} */ (dependency))) {
 					update_derived(/** @type {Derived} */ (dependency));
 				}
 
@@ -588,7 +588,7 @@ function flush_queued_effects(effects) {
 		var effect = effects[i];
 
 		if ((effect.f & (DESTROYED | INERT)) === 0) {
-			if (check_dirtiness(effect)) {
+			if (is_dirty(effect)) {
 				var wv = write_version;
 
 				update_effect(effect);
@@ -675,7 +675,7 @@ function process_effects(root) {
 			} else if (is_branch) {
 				effect.f ^= CLEAN;
 			} else {
-				if (check_dirtiness(effect)) {
+				if (is_dirty(effect)) {
 					update_effect(effect);
 				}
 			}
@@ -802,7 +802,7 @@ export function get(signal) {
 	if (is_derived && !is_destroying_effect) {
 		derived = /** @type {Derived} */ (signal);
 
-		if (check_dirtiness(derived)) {
+		if (is_dirty(derived)) {
 			update_derived(derived);
 		}
 	}

From df5801c5fef7735fa67b016ebf0fea5acb8f2fc2 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 14 Jul 2025 09:50:55 -0400
Subject: [PATCH 053/148] chore: remove unused option validators (#16361)

---
 .../svelte/src/compiler/validate-options.js   | 27 -------------------
 1 file changed, 27 deletions(-)

diff --git a/packages/svelte/src/compiler/validate-options.js b/packages/svelte/src/compiler/validate-options.js
index 85305d7ce9..1fd89139d5 100644
--- a/packages/svelte/src/compiler/validate-options.js
+++ b/packages/svelte/src/compiler/validate-options.js
@@ -241,19 +241,6 @@ function validator(fallback, fn) {
 	};
 }
 
-/**
- * @param {number} fallback
- * @returns {Validator}
- */
-function number(fallback) {
-	return validator(fallback, (input, keypath) => {
-		if (typeof input !== 'number') {
-			throw_error(`${keypath} should be a number, if specified`);
-		}
-		return input;
-	});
-}
-
 /**
  * @param {string | undefined} fallback
  * @param {boolean} allow_empty
@@ -273,20 +260,6 @@ function string(fallback, allow_empty = true) {
 	});
 }
 
-/**
- * @param {string[]} fallback
- * @returns {Validator}
- */
-function string_array(fallback) {
-	return validator(fallback, (input, keypath) => {
-		if (input && !Array.isArray(input)) {
-			throw_error(`${keypath} should be a string array, if specified`);
-		}
-
-		return input;
-	});
-}
-
 /**
  * @param {boolean | undefined} fallback
  * @returns {Validator}

From f6a2599ee13ba58b959ce690d9f26acc1c698d63 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 14 Jul 2025 09:53:30 -0400
Subject: [PATCH 054/148] chore: remove memoize_expression (#16358)

---
 .../client/visitors/SlotElement.js            | 25 ++++++-------
 .../client/visitors/shared/component.js       | 37 +++++++++----------
 .../client/visitors/shared/utils.js           | 12 +-----
 3 files changed, 30 insertions(+), 44 deletions(-)

diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/SlotElement.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/SlotElement.js
index 401cfde428..e37cdb2bea 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/SlotElement.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/SlotElement.js
@@ -1,9 +1,9 @@
-/** @import { BlockStatement, Expression, ExpressionStatement, Literal, Property } from 'estree' */
+/** @import { BlockStatement, Expression, ExpressionStatement, Literal, Property, Statement } from 'estree' */
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext } from '../types' */
 import * as b from '#compiler/builders';
 import { build_attribute_value } from './shared/element.js';
-import { memoize_expression } from './shared/utils.js';
+import { Memoizer } from './shared/utils.js';
 
 /**
  * @param {AST.SlotElement} node
@@ -22,7 +22,7 @@ export function SlotElement(node, context) {
 	/** @type {ExpressionStatement[]} */
 	const lets = [];
 
-	let is_default = true;
+	const memoizer = new Memoizer();
 
 	let name = b.literal('default');
 
@@ -33,12 +33,11 @@ export function SlotElement(node, context) {
 			const { value, has_state } = build_attribute_value(
 				attribute.value,
 				context,
-				(value, metadata) => (metadata.has_call ? memoize_expression(context.state, value) : value)
+				(value, metadata) => (metadata.has_call ? b.call('$.get', memoizer.add(value)) : value)
 			);
 
 			if (attribute.name === 'name') {
 				name = /** @type {Literal} */ (value);
-				is_default = false;
 			} else if (attribute.name !== 'slot') {
 				if (has_state) {
 					props.push(b.get(attribute.name, [b.return(value)]));
@@ -51,9 +50,14 @@ export function SlotElement(node, context) {
 		}
 	}
 
+	memoizer.apply();
+
 	// Let bindings first, they can be used on attributes
 	context.state.init.push(...lets);
 
+	/** @type {Statement[]} */
+	const statements = memoizer.deriveds(context.state.analysis.runes);
+
 	const props_expression =
 		spreads.length === 0 ? b.object(props) : b.call('$.spread_props', b.object(props), ...spreads);
 
@@ -62,14 +66,9 @@ export function SlotElement(node, context) {
 			? b.null
 			: b.arrow([b.id('$$anchor')], /** @type {BlockStatement} */ (context.visit(node.fragment)));
 
-	const slot = b.call(
-		'$.slot',
-		context.state.node,
-		b.id('$$props'),
-		name,
-		props_expression,
-		fallback
+	statements.push(
+		b.stmt(b.call('$.slot', context.state.node, b.id('$$props'), name, props_expression, fallback))
 	);
 
-	context.state.init.push(b.stmt(slot));
+	context.state.init.push(statements.length === 1 ? statements[0] : b.block(statements));
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js
index aa3704b50b..6b52db55ba 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js
@@ -4,12 +4,7 @@
 import { dev, is_ignored } from '../../../../../state.js';
 import { get_attribute_chunks, object } from '../../../../../utils/ast.js';
 import * as b from '#compiler/builders';
-import {
-	build_bind_this,
-	memoize_expression,
-	validate_binding,
-	add_svelte_meta
-} from '../shared/utils.js';
+import { add_svelte_meta, build_bind_this, Memoizer, validate_binding } from '../shared/utils.js';
 import { build_attribute_value } from '../shared/element.js';
 import { build_event_handler } from './events.js';
 import { determine_slot } from '../../../../../utils/slot.js';
@@ -48,6 +43,8 @@ export function build_component(node, component_name, context) {
 	/** @type {Record<string, Expression[]>} */
 	const events = {};
 
+	const memoizer = new Memoizer();
+
 	/** @type {Property[]} */
 	const custom_css_props = [];
 
@@ -133,15 +130,13 @@ export function build_component(node, component_name, context) {
 		} else if (attribute.type === 'SpreadAttribute') {
 			const expression = /** @type {Expression} */ (context.visit(attribute));
 			if (attribute.metadata.expression.has_state) {
-				let value = expression;
-
-				if (attribute.metadata.expression.has_call) {
-					const id = b.id(context.state.scope.generate('spread_element'));
-					context.state.init.push(b.var(id, b.call('$.derived', b.thunk(value))));
-					value = b.call('$.get', id);
-				}
-
-				props_and_spreads.push(b.thunk(value));
+				props_and_spreads.push(
+					b.thunk(
+						attribute.metadata.expression.has_call
+							? b.call('$.get', memoizer.add(expression))
+							: expression
+					)
+				);
 			} else {
 				props_and_spreads.push(expression);
 			}
@@ -150,10 +145,10 @@ export function build_component(node, component_name, context) {
 				custom_css_props.push(
 					b.init(
 						attribute.name,
-						build_attribute_value(attribute.value, context, (value, metadata) =>
+						build_attribute_value(attribute.value, context, (value, metadata) => {
 							// TODO put the derived in the local block
-							metadata.has_call ? memoize_expression(context.state, value) : value
-						).value
+							return metadata.has_call ? b.call('$.get', memoizer.add(value)) : value;
+						}).value
 					)
 				);
 				continue;
@@ -184,7 +179,7 @@ export function build_component(node, component_name, context) {
 						);
 					});
 
-					return should_wrap_in_derived ? memoize_expression(context.state, value) : value;
+					return should_wrap_in_derived ? b.call('$.get', memoizer.add(value)) : value;
 				}
 			);
 
@@ -444,7 +439,7 @@ export function build_component(node, component_name, context) {
 		};
 	}
 
-	const statements = [...snippet_declarations];
+	const statements = [...snippet_declarations, ...memoizer.deriveds(context.state.analysis.runes)];
 
 	if (is_component_dynamic) {
 		const prev = fn;
@@ -492,5 +487,7 @@ export function build_component(node, component_name, context) {
 		statements.push(add_svelte_meta(fn(anchor), node, 'component', { componentTag: node.name }));
 	}
 
+	memoizer.apply();
+
 	return statements.length > 1 ? b.block(statements) : statements[0];
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
index de74fede0c..eed806339d 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
@@ -8,17 +8,7 @@ import { sanitize_template_string } from '../../../../../utils/sanitize_template
 import { regex_is_valid_identifier } from '../../../../patterns.js';
 import is_reference from 'is-reference';
 import { dev, is_ignored, locator, component_name } from '../../../../../state.js';
-import { build_getter, create_derived } from '../../utils.js';
-
-/**
- * @param {ComponentClientTransformState} state
- * @param {Expression} value
- */
-export function memoize_expression(state, value) {
-	const id = b.id(state.scope.generate('expression'));
-	state.init.push(b.const(id, create_derived(state, b.thunk(value))));
-	return b.call('$.get', id);
-}
+import { build_getter } from '../../utils.js';
 
 /**
  * A utility for extracting complex expressions (such as call expressions)

From 6d8f39f8d2e7c78cb5dc4bbfea8ae76150351b2b Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Mon, 14 Jul 2025 12:36:21 -0400
Subject: [PATCH 055/148] Version Packages (#16347)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/cuddly-humans-end.md    |  5 -----
 .changeset/large-balloons-agree.md |  5 -----
 .changeset/tiny-news-whisper.md    |  5 -----
 packages/svelte/CHANGELOG.md       | 10 ++++++++++
 packages/svelte/package.json       |  2 +-
 packages/svelte/src/version.js     |  2 +-
 6 files changed, 12 insertions(+), 17 deletions(-)
 delete mode 100644 .changeset/cuddly-humans-end.md
 delete mode 100644 .changeset/large-balloons-agree.md
 delete mode 100644 .changeset/tiny-news-whisper.md

diff --git a/.changeset/cuddly-humans-end.md b/.changeset/cuddly-humans-end.md
deleted file mode 100644
index d02e08de7a..0000000000
--- a/.changeset/cuddly-humans-end.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: silence autofocus a11y warning inside `<dialog>`
diff --git a/.changeset/large-balloons-agree.md b/.changeset/large-balloons-agree.md
deleted file mode 100644
index 9355336862..0000000000
--- a/.changeset/large-balloons-agree.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: don't show adjusted error messages in boundaries
diff --git a/.changeset/tiny-news-whisper.md b/.changeset/tiny-news-whisper.md
deleted file mode 100644
index 8bf877085d..0000000000
--- a/.changeset/tiny-news-whisper.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-chore: replace inline regex with variable
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 8f158c528f..7b822ee9b1 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,15 @@
 # svelte
 
+## 5.35.7
+
+### Patch Changes
+
+- fix: silence autofocus a11y warning inside `<dialog>` ([#16341](https://github.com/sveltejs/svelte/pull/16341))
+
+- fix: don't show adjusted error messages in boundaries ([#16360](https://github.com/sveltejs/svelte/pull/16360))
+
+- chore: replace inline regex with variable ([#16340](https://github.com/sveltejs/svelte/pull/16340))
+
 ## 5.35.6
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 4eed145f3f..44957964b7 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.35.6",
+  "version": "5.35.7",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 266b0b9491..0674d46652 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.35.6';
+export const VERSION = '5.35.7';
 export const PUBLIC_VERSION = '5';

From 82f648157e50a1498082dd24b78594f7a18e39a5 Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Mon, 14 Jul 2025 12:06:00 -0700
Subject: [PATCH 056/148] chore: clean up a11y analysis code (#16345)

* chore: clean up a11y analysis code

* lint

* apply changes from #16340 and #16341

* `utils.js` -> `index.js`

* remove unused exports

* remove unused exports

* newlines are free :)

* consolidate loops

* put the exported function up top

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
---
 .changeset/warm-olives-applaud.md             |    5 +
 .../2-analyze/visitors/RegularElement.js      |    2 +-
 .../2-analyze/visitors/SvelteElement.js       |    2 +-
 .../visitors/shared/a11y/constants.js         |  319 ++++
 .../shared/{a11y.js => a11y/index.js}         | 1529 +++++++----------
 5 files changed, 975 insertions(+), 882 deletions(-)
 create mode 100644 .changeset/warm-olives-applaud.md
 create mode 100644 packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y/constants.js
 rename packages/svelte/src/compiler/phases/2-analyze/visitors/shared/{a11y.js => a11y/index.js} (55%)

diff --git a/.changeset/warm-olives-applaud.md b/.changeset/warm-olives-applaud.md
new file mode 100644
index 0000000000..63a7803b99
--- /dev/null
+++ b/.changeset/warm-olives-applaud.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: clean up a11y analysis code
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/RegularElement.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/RegularElement.js
index d5689e5d55..fab5d46e1b 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/RegularElement.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/RegularElement.js
@@ -9,7 +9,7 @@ import * as e from '../../../errors.js';
 import * as w from '../../../warnings.js';
 import { create_attribute, is_custom_element_node } from '../../nodes.js';
 import { regex_starts_with_newline } from '../../patterns.js';
-import { check_element } from './shared/a11y.js';
+import { check_element } from './shared/a11y/index.js';
 import { validate_element } from './shared/element.js';
 import { mark_subtree_dynamic } from './shared/fragment.js';
 
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteElement.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteElement.js
index c45859408c..f2e298f7ea 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteElement.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteElement.js
@@ -2,7 +2,7 @@
 /** @import { Context } from '../types' */
 import { NAMESPACE_MATHML, NAMESPACE_SVG } from '../../../../constants.js';
 import { is_text_attribute } from '../../../utils/ast.js';
-import { check_element } from './shared/a11y.js';
+import { check_element } from './shared/a11y/index.js';
 import { validate_element } from './shared/element.js';
 import { mark_subtree_dynamic } from './shared/fragment.js';
 
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y/constants.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y/constants.js
new file mode 100644
index 0000000000..a1b70f2207
--- /dev/null
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y/constants.js
@@ -0,0 +1,319 @@
+/** @import { ARIARoleRelationConcept  } from 'aria-query' */
+import { roles as roles_map, elementRoles } from 'aria-query';
+// @ts-expect-error package doesn't provide typings
+import { AXObjects, elementAXObjects } from 'axobject-query';
+
+export const aria_attributes =
+	'activedescendant atomic autocomplete busy checked colcount colindex colspan controls current describedby description details disabled dropeffect errormessage expanded flowto grabbed haspopup hidden invalid keyshortcuts label labelledby level live modal multiline multiselectable orientation owns placeholder posinset pressed readonly relevant required roledescription rowcount rowindex rowspan selected setsize sort valuemax valuemin valuenow valuetext'.split(
+		' '
+	);
+
+/** @type {Record<string, string[]>} */
+export const a11y_required_attributes = {
+	a: ['href'],
+	area: ['alt', 'aria-label', 'aria-labelledby'],
+	// html-has-lang
+	html: ['lang'],
+	// iframe-has-title
+	iframe: ['title'],
+	img: ['alt'],
+	object: ['title', 'aria-label', 'aria-labelledby']
+};
+
+export const a11y_distracting_elements = ['blink', 'marquee'];
+
+// this excludes `<a>` and `<button>` because they are handled separately
+export const a11y_required_content = [
+	// heading-has-content
+	'h1',
+	'h2',
+	'h3',
+	'h4',
+	'h5',
+	'h6'
+];
+
+export const a11y_labelable = [
+	'button',
+	'input',
+	'keygen',
+	'meter',
+	'output',
+	'progress',
+	'select',
+	'textarea'
+];
+
+export const a11y_interactive_handlers = [
+	// Keyboard events
+	'keypress',
+	'keydown',
+	'keyup',
+	// Click events
+	'click',
+	'contextmenu',
+	'dblclick',
+	'drag',
+	'dragend',
+	'dragenter',
+	'dragexit',
+	'dragleave',
+	'dragover',
+	'dragstart',
+	'drop',
+	'mousedown',
+	'mouseenter',
+	'mouseleave',
+	'mousemove',
+	'mouseout',
+	'mouseover',
+	'mouseup'
+];
+
+export const a11y_recommended_interactive_handlers = [
+	'click',
+	'mousedown',
+	'mouseup',
+	'keypress',
+	'keydown',
+	'keyup'
+];
+
+export const a11y_nested_implicit_semantics = new Map([
+	['header', 'banner'],
+	['footer', 'contentinfo']
+]);
+
+export const a11y_implicit_semantics = new Map([
+	['a', 'link'],
+	['area', 'link'],
+	['article', 'article'],
+	['aside', 'complementary'],
+	['body', 'document'],
+	['button', 'button'],
+	['datalist', 'listbox'],
+	['dd', 'definition'],
+	['dfn', 'term'],
+	['dialog', 'dialog'],
+	['details', 'group'],
+	['dt', 'term'],
+	['fieldset', 'group'],
+	['figure', 'figure'],
+	['form', 'form'],
+	['h1', 'heading'],
+	['h2', 'heading'],
+	['h3', 'heading'],
+	['h4', 'heading'],
+	['h5', 'heading'],
+	['h6', 'heading'],
+	['hr', 'separator'],
+	['img', 'img'],
+	['li', 'listitem'],
+	['link', 'link'],
+	['main', 'main'],
+	['menu', 'list'],
+	['meter', 'progressbar'],
+	['nav', 'navigation'],
+	['ol', 'list'],
+	['option', 'option'],
+	['optgroup', 'group'],
+	['output', 'status'],
+	['progress', 'progressbar'],
+	['section', 'region'],
+	['summary', 'button'],
+	['table', 'table'],
+	['tbody', 'rowgroup'],
+	['textarea', 'textbox'],
+	['tfoot', 'rowgroup'],
+	['thead', 'rowgroup'],
+	['tr', 'row'],
+	['ul', 'list']
+]);
+
+export const menuitem_type_to_implicit_role = new Map([
+	['command', 'menuitem'],
+	['checkbox', 'menuitemcheckbox'],
+	['radio', 'menuitemradio']
+]);
+
+export const input_type_to_implicit_role = new Map([
+	['button', 'button'],
+	['image', 'button'],
+	['reset', 'button'],
+	['submit', 'button'],
+	['checkbox', 'checkbox'],
+	['radio', 'radio'],
+	['range', 'slider'],
+	['number', 'spinbutton'],
+	['email', 'textbox'],
+	['search', 'searchbox'],
+	['tel', 'textbox'],
+	['text', 'textbox'],
+	['url', 'textbox']
+]);
+
+/**
+ * Exceptions to the rule which follows common A11y conventions
+ * TODO make this configurable by the user
+ * @type {Record<string, string[]>}
+ */
+export const a11y_non_interactive_element_to_interactive_role_exceptions = {
+	ul: ['listbox', 'menu', 'menubar', 'radiogroup', 'tablist', 'tree', 'treegrid'],
+	ol: ['listbox', 'menu', 'menubar', 'radiogroup', 'tablist', 'tree', 'treegrid'],
+	li: ['menuitem', 'option', 'row', 'tab', 'treeitem'],
+	table: ['grid'],
+	td: ['gridcell'],
+	fieldset: ['radiogroup', 'presentation']
+};
+
+export const combobox_if_list = ['email', 'search', 'tel', 'text', 'url'];
+
+// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#autofilling-form-controls:-the-autocomplete-attribute
+export const address_type_tokens = ['shipping', 'billing'];
+
+export const autofill_field_name_tokens = [
+	'',
+	'on',
+	'off',
+	'name',
+	'honorific-prefix',
+	'given-name',
+	'additional-name',
+	'family-name',
+	'honorific-suffix',
+	'nickname',
+	'username',
+	'new-password',
+	'current-password',
+	'one-time-code',
+	'organization-title',
+	'organization',
+	'street-address',
+	'address-line1',
+	'address-line2',
+	'address-line3',
+	'address-level4',
+	'address-level3',
+	'address-level2',
+	'address-level1',
+	'country',
+	'country-name',
+	'postal-code',
+	'cc-name',
+	'cc-given-name',
+	'cc-additional-name',
+	'cc-family-name',
+	'cc-number',
+	'cc-exp',
+	'cc-exp-month',
+	'cc-exp-year',
+	'cc-csc',
+	'cc-type',
+	'transaction-currency',
+	'transaction-amount',
+	'language',
+	'bday',
+	'bday-day',
+	'bday-month',
+	'bday-year',
+	'sex',
+	'url',
+	'photo'
+];
+
+export const contact_type_tokens = ['home', 'work', 'mobile', 'fax', 'pager'];
+
+export const autofill_contact_field_name_tokens = [
+	'tel',
+	'tel-country-code',
+	'tel-national',
+	'tel-area-code',
+	'tel-local',
+	'tel-local-prefix',
+	'tel-local-suffix',
+	'tel-extension',
+	'email',
+	'impp'
+];
+
+export const ElementInteractivity = /** @type {const} */ ({
+	Interactive: 'interactive',
+	NonInteractive: 'non-interactive',
+	Static: 'static'
+});
+
+export const invisible_elements = ['meta', 'html', 'script', 'style'];
+
+export const aria_roles = roles_map.keys();
+
+export const abstract_roles = aria_roles.filter((role) => roles_map.get(role)?.abstract);
+
+const non_abstract_roles = aria_roles.filter((name) => !abstract_roles.includes(name));
+
+export const non_interactive_roles = non_abstract_roles
+	.filter((name) => {
+		const role = roles_map.get(name);
+		return (
+			// 'toolbar' does not descend from widget, but it does support
+			// aria-activedescendant, thus in practice we treat it as a widget.
+			// focusable tabpanel elements are recommended if any panels in a set contain content where the first element in the panel is not focusable.
+			// 'generic' is meant to have no semantic meaning.
+			// 'cell' is treated as CellRole by the AXObject which is interactive, so we treat 'cell' it as interactive as well.
+			!['toolbar', 'tabpanel', 'generic', 'cell'].includes(name) &&
+			!role?.superClass.some((classes) => classes.includes('widget') || classes.includes('window'))
+		);
+	})
+	.concat(
+		// The `progressbar` is descended from `widget`, but in practice, its
+		// value is always `readonly`, so we treat it as a non-interactive role.
+		'progressbar'
+	);
+
+export const interactive_roles = non_abstract_roles.filter(
+	(name) =>
+		!non_interactive_roles.includes(name) &&
+		// 'generic' is meant to have no semantic meaning.
+		name !== 'generic'
+);
+
+export const presentation_roles = ['presentation', 'none'];
+
+/** @type {ARIARoleRelationConcept[]} */
+export const non_interactive_element_role_schemas = [];
+
+/** @type {ARIARoleRelationConcept[]} */
+export const interactive_element_role_schemas = [];
+
+for (const [schema, roles] of elementRoles.entries()) {
+	if ([...roles].every((role) => role !== 'generic' && non_interactive_roles.includes(role))) {
+		non_interactive_element_role_schemas.push(schema);
+	}
+
+	if ([...roles].every((role) => interactive_roles.includes(role))) {
+		interactive_element_role_schemas.push(schema);
+	}
+}
+
+const interactive_ax_objects = [...AXObjects.keys()].filter(
+	(name) => AXObjects.get(name).type === 'widget'
+);
+
+/** @type {ARIARoleRelationConcept[]} */
+export const interactive_element_ax_object_schemas = [];
+
+/** @type {ARIARoleRelationConcept[]} */
+export const non_interactive_element_ax_object_schemas = [];
+
+const non_interactive_ax_objects = [...AXObjects.keys()].filter((name) =>
+	['windows', 'structure'].includes(AXObjects.get(name).type)
+);
+
+for (const [schema, ax_object] of elementAXObjects.entries()) {
+	if ([...ax_object].every((role) => interactive_ax_objects.includes(role))) {
+		interactive_element_ax_object_schemas.push(schema);
+	}
+
+	if ([...ax_object].every((role) => non_interactive_ax_objects.includes(role))) {
+		non_interactive_element_ax_object_schemas.push(schema);
+	}
+}
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y/index.js
similarity index 55%
rename from packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y.js
rename to packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y/index.js
index 152e679bf5..5db31314d4 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y/index.js
@@ -1,688 +1,53 @@
-/** @import { Context } from '../../types.js' */
 /** @import { AST } from '#compiler' */
+/** @import { Context } from '../../../types.js' */
 /** @import { ARIARoleDefinitionKey, ARIARoleRelationConcept, ARIAProperty, ARIAPropertyDefinition, ARIARoleDefinition } from 'aria-query' */
-import { roles as roles_map, aria, elementRoles } from 'aria-query';
-// @ts-expect-error package doesn't provide typings
-import { AXObjects, AXObjectRoles, elementAXObjects } from 'axobject-query';
-import {
-	regex_heading_tags,
-	regex_js_prefix,
-	regex_not_whitespace,
-	regex_redundant_img_alt,
-	regex_starts_with_vowel,
-	regex_whitespaces
-} from '../../../patterns.js';
-import * as w from '../../../../warnings.js';
-import fuzzymatch from '../../../1-parse/utils/fuzzymatch.js';
-import { is_event_attribute, is_text_attribute } from '../../../../utils/ast.js';
-import { walk } from 'zimmerframe';
-import { list } from '../../../../utils/string.js';
-import { is_content_editable_binding } from '../../../../../utils.js';
-
-const aria_roles = roles_map.keys();
-const abstract_roles = aria_roles.filter((role) => roles_map.get(role)?.abstract);
-const non_abstract_roles = aria_roles.filter((name) => !abstract_roles.includes(name));
-const non_interactive_roles = non_abstract_roles
-	.filter((name) => {
-		const role = roles_map.get(name);
-		return (
-			// 'toolbar' does not descend from widget, but it does support
-			// aria-activedescendant, thus in practice we treat it as a widget.
-			// focusable tabpanel elements are recommended if any panels in a set contain content where the first element in the panel is not focusable.
-			// 'generic' is meant to have no semantic meaning.
-			// 'cell' is treated as CellRole by the AXObject which is interactive, so we treat 'cell' it as interactive as well.
-			!['toolbar', 'tabpanel', 'generic', 'cell'].includes(name) &&
-			!role?.superClass.some((classes) => classes.includes('widget') || classes.includes('window'))
-		);
-	})
-	.concat(
-		// The `progressbar` is descended from `widget`, but in practice, its
-		// value is always `readonly`, so we treat it as a non-interactive role.
-		'progressbar'
-	);
-const interactive_roles = non_abstract_roles.filter(
-	(name) =>
-		!non_interactive_roles.includes(name) &&
-		// 'generic' is meant to have no semantic meaning.
-		name !== 'generic'
-);
-
-/**
- * @param {ARIARoleDefinitionKey} role
- */
-function is_non_interactive_roles(role) {
-	return non_interactive_roles.includes(role);
-}
-
-/**
- * @param {ARIARoleDefinitionKey} role
- */
-function is_interactive_roles(role) {
-	return interactive_roles.includes(role);
-}
-
-/**
- * @param {ARIARoleDefinitionKey} role
- */
-function is_abstract_role(role) {
-	return abstract_roles.includes(role);
-}
-
-const presentation_roles = ['presentation', 'none'];
-
-/**
- * @param {ARIARoleDefinitionKey} role
- */
-function is_presentation_role(role) {
-	return presentation_roles.includes(role);
-}
-
-/**
- * @param {string} tag_name
- * @param {Map<string, AST.Attribute>} attribute_map
- */
-function is_hidden_from_screen_reader(tag_name, attribute_map) {
-	if (tag_name === 'input') {
-		const type = get_static_value(attribute_map.get('type'));
-		if (type === 'hidden') {
-			return true;
-		}
-	}
-
-	const aria_hidden = attribute_map.get('aria-hidden');
-	if (!aria_hidden) return false;
-	const aria_hidden_value = get_static_value(aria_hidden);
-	if (aria_hidden_value === null) return true;
-	return aria_hidden_value === true || aria_hidden_value === 'true';
-}
-
-/**
- * @param {Map<string, AST.Attribute>} attribute_map
- */
-function has_disabled_attribute(attribute_map) {
-	const disabled_attr_value = get_static_value(attribute_map.get('disabled'));
-	if (disabled_attr_value) {
-		return true;
-	}
-
-	const aria_disabled_attr = attribute_map.get('aria-disabled');
-	if (aria_disabled_attr) {
-		const aria_disabled_attr_value = get_static_value(aria_disabled_attr);
-		if (aria_disabled_attr_value === 'true') {
-			return true;
-		}
-	}
-	return false;
-}
-
-/**
- * @type {ARIARoleRelationConcept[]}
- */
-const non_interactive_element_role_schemas = [];
-elementRoles.entries().forEach(([schema, roles]) => {
-	if ([...roles].every((role) => role !== 'generic' && non_interactive_roles.includes(role))) {
-		non_interactive_element_role_schemas.push(schema);
-	}
-});
-
-/**
- * @type {ARIARoleRelationConcept[]}
- */
-const interactive_element_role_schemas = [];
-elementRoles.entries().forEach(([schema, roles]) => {
-	if ([...roles].every((role) => interactive_roles.includes(role))) {
-		interactive_element_role_schemas.push(schema);
-	}
-});
-const interactive_ax_objects = [...AXObjects.keys()].filter(
-	(name) => AXObjects.get(name).type === 'widget'
-);
-const non_interactive_ax_objects = [...AXObjects.keys()].filter((name) =>
-	['windows', 'structure'].includes(AXObjects.get(name).type)
-);
-
-/**
- * @type {ARIARoleRelationConcept[]}
- */
-const interactive_element_ax_object_schemas = [];
-elementAXObjects.entries().forEach(
-	/**
-	 * @param {any} _
-	 */
-	([schema, ax_object]) => {
-		if ([...ax_object].every((role) => interactive_ax_objects.includes(role))) {
-			interactive_element_ax_object_schemas.push(schema);
-		}
-	}
-);
-
-/**
- * @type {ARIARoleRelationConcept[]}
- */
-const non_interactive_element_ax_object_schemas = [];
-elementAXObjects.entries().forEach(
-	/**
-	 * @param {any} _
-	 */
-	([schema, ax_object]) => {
-		if ([...ax_object].every((role) => non_interactive_ax_objects.includes(role))) {
-			non_interactive_element_ax_object_schemas.push(schema);
-		}
-	}
-);
-
-/**
- * @param {ARIARoleRelationConcept} schema
- * @param {string} tag_name
- * @param {Map<string, AST.Attribute>} attribute_map
- */
-function match_schema(schema, tag_name, attribute_map) {
-	if (schema.name !== tag_name) return false;
-	if (!schema.attributes) return true;
-	return schema.attributes.every((schema_attribute) => {
-		const attribute = attribute_map.get(schema_attribute.name);
-		if (!attribute) return false;
-		if (schema_attribute.value && schema_attribute.value !== get_static_text_value(attribute)) {
-			return false;
-		}
-		return true;
-	});
-}
-
-const ElementInteractivity = /** @type {const} */ ({
-	Interactive: 'interactive',
-	NonInteractive: 'non-interactive',
-	Static: 'static'
-});
-
-/**
- * @param {string} tag_name
- * @param {Map<string, AST.Attribute>} attribute_map
- * @returns {ElementInteractivity[keyof ElementInteractivity]}
- */
-function element_interactivity(tag_name, attribute_map) {
-	if (
-		interactive_element_role_schemas.some((schema) => match_schema(schema, tag_name, attribute_map))
-	) {
-		return ElementInteractivity.Interactive;
-	}
-	if (
-		tag_name !== 'header' &&
-		non_interactive_element_role_schemas.some((schema) =>
-			match_schema(schema, tag_name, attribute_map)
-		)
-	) {
-		return ElementInteractivity.NonInteractive;
-	}
-	if (
-		interactive_element_ax_object_schemas.some((schema) =>
-			match_schema(schema, tag_name, attribute_map)
-		)
-	) {
-		return ElementInteractivity.Interactive;
-	}
-	if (
-		non_interactive_element_ax_object_schemas.some((schema) =>
-			match_schema(schema, tag_name, attribute_map)
-		)
-	) {
-		return ElementInteractivity.NonInteractive;
-	}
-	return ElementInteractivity.Static;
-}
-
-/**
- * @param {string} tag_name
- * @param {Map<string, AST.Attribute>} attribute_map
- * @returns {boolean}
- */
-function is_interactive_element(tag_name, attribute_map) {
-	return element_interactivity(tag_name, attribute_map) === ElementInteractivity.Interactive;
-}
-
-/**
- * @param {string} tag_name
- * @param {Map<string, AST.Attribute>} attribute_map
- * @returns {boolean}
- */
-function is_non_interactive_element(tag_name, attribute_map) {
-	return element_interactivity(tag_name, attribute_map) === ElementInteractivity.NonInteractive;
-}
-
-/**
- * @param {string} tag_name
- * @param {Map<string, AST.Attribute>} attribute_map
- * @returns {boolean}
- */
-function is_static_element(tag_name, attribute_map) {
-	return element_interactivity(tag_name, attribute_map) === ElementInteractivity.Static;
-}
-
-/**
- * @param {ARIARoleDefinitionKey} role
- * @param {string} tag_name
- * @param {Map<string, AST.Attribute>} attribute_map
- */
-function is_semantic_role_element(role, tag_name, attribute_map) {
-	for (const [schema, ax_object] of elementAXObjects.entries()) {
-		if (
-			schema.name === tag_name &&
-			(!schema.attributes ||
-				schema.attributes.every(
-					/** @param {any} attr */
-					(attr) =>
-						attribute_map.has(attr.name) &&
-						get_static_value(attribute_map.get(attr.name)) === attr.value
-				))
-		) {
-			for (const name of ax_object) {
-				const roles = AXObjectRoles.get(name);
-				if (roles) {
-					for (const { name } of roles) {
-						if (name === role) {
-							return true;
-						}
-					}
-				}
-			}
-		}
-	}
-	return false;
-}
-
-// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#autofilling-form-controls:-the-autocomplete-attribute
-const address_type_tokens = ['shipping', 'billing'];
-const autofill_field_name_tokens = [
-	'',
-	'on',
-	'off',
-	'name',
-	'honorific-prefix',
-	'given-name',
-	'additional-name',
-	'family-name',
-	'honorific-suffix',
-	'nickname',
-	'username',
-	'new-password',
-	'current-password',
-	'one-time-code',
-	'organization-title',
-	'organization',
-	'street-address',
-	'address-line1',
-	'address-line2',
-	'address-line3',
-	'address-level4',
-	'address-level3',
-	'address-level2',
-	'address-level1',
-	'country',
-	'country-name',
-	'postal-code',
-	'cc-name',
-	'cc-given-name',
-	'cc-additional-name',
-	'cc-family-name',
-	'cc-number',
-	'cc-exp',
-	'cc-exp-month',
-	'cc-exp-year',
-	'cc-csc',
-	'cc-type',
-	'transaction-currency',
-	'transaction-amount',
-	'language',
-	'bday',
-	'bday-day',
-	'bday-month',
-	'bday-year',
-	'sex',
-	'url',
-	'photo'
-];
-const contact_type_tokens = ['home', 'work', 'mobile', 'fax', 'pager'];
-const autofill_contact_field_name_tokens = [
-	'tel',
-	'tel-country-code',
-	'tel-national',
-	'tel-area-code',
-	'tel-local',
-	'tel-local-prefix',
-	'tel-local-suffix',
-	'tel-extension',
-	'email',
-	'impp'
-];
-
-/**
- * @param {null | true | string} autocomplete
- */
-function is_valid_autocomplete(autocomplete) {
-	if (autocomplete === true) {
-		return false;
-	} else if (!autocomplete) {
-		return true; // dynamic value
-	}
-	const tokens = autocomplete.trim().toLowerCase().split(regex_whitespaces);
-	if (typeof tokens[0] === 'string' && tokens[0].startsWith('section-')) {
-		tokens.shift();
-	}
-	if (address_type_tokens.includes(tokens[0])) {
-		tokens.shift();
-	}
-	if (autofill_field_name_tokens.includes(tokens[0])) {
-		tokens.shift();
-	} else {
-		if (contact_type_tokens.includes(tokens[0])) {
-			tokens.shift();
-		}
-		if (autofill_contact_field_name_tokens.includes(tokens[0])) {
-			tokens.shift();
-		} else {
-			return false;
-		}
-	}
-	if (tokens[0] === 'webauthn') {
-		tokens.shift();
-	}
-	return tokens.length === 0;
-}
-
-const aria_attributes =
-	'activedescendant atomic autocomplete busy checked colcount colindex colspan controls current describedby description details disabled dropeffect errormessage expanded flowto grabbed haspopup hidden invalid keyshortcuts label labelledby level live modal multiline multiselectable orientation owns placeholder posinset pressed readonly relevant required roledescription rowcount rowindex rowspan selected setsize sort valuemax valuemin valuenow valuetext'.split(
-		' '
-	);
-/** @type {Record<string, string[]>} */
-const a11y_required_attributes = {
-	a: ['href'],
-	area: ['alt', 'aria-label', 'aria-labelledby'],
-	// html-has-lang
-	html: ['lang'],
-	// iframe-has-title
-	iframe: ['title'],
-	img: ['alt'],
-	object: ['title', 'aria-label', 'aria-labelledby']
-};
-const a11y_distracting_elements = ['blink', 'marquee'];
-
-// this excludes `<a>` and `<button>` because they are handled separately
-const a11y_required_content = [
-	// heading-has-content
-	'h1',
-	'h2',
-	'h3',
-	'h4',
-	'h5',
-	'h6'
-];
-const a11y_labelable = [
-	'button',
-	'input',
-	'keygen',
-	'meter',
-	'output',
-	'progress',
-	'select',
-	'textarea'
-];
-const a11y_interactive_handlers = [
-	// Keyboard events
-	'keypress',
-	'keydown',
-	'keyup',
-	// Click events
-	'click',
-	'contextmenu',
-	'dblclick',
-	'drag',
-	'dragend',
-	'dragenter',
-	'dragexit',
-	'dragleave',
-	'dragover',
-	'dragstart',
-	'drop',
-	'mousedown',
-	'mouseenter',
-	'mouseleave',
-	'mousemove',
-	'mouseout',
-	'mouseover',
-	'mouseup'
-];
-const a11y_recommended_interactive_handlers = [
-	'click',
-	'mousedown',
-	'mouseup',
-	'keypress',
-	'keydown',
-	'keyup'
-];
-const a11y_nested_implicit_semantics = new Map([
-	['header', 'banner'],
-	['footer', 'contentinfo']
-]);
-const a11y_implicit_semantics = new Map([
-	['a', 'link'],
-	['area', 'link'],
-	['article', 'article'],
-	['aside', 'complementary'],
-	['body', 'document'],
-	['button', 'button'],
-	['datalist', 'listbox'],
-	['dd', 'definition'],
-	['dfn', 'term'],
-	['dialog', 'dialog'],
-	['details', 'group'],
-	['dt', 'term'],
-	['fieldset', 'group'],
-	['figure', 'figure'],
-	['form', 'form'],
-	['h1', 'heading'],
-	['h2', 'heading'],
-	['h3', 'heading'],
-	['h4', 'heading'],
-	['h5', 'heading'],
-	['h6', 'heading'],
-	['hr', 'separator'],
-	['img', 'img'],
-	['li', 'listitem'],
-	['link', 'link'],
-	['main', 'main'],
-	['menu', 'list'],
-	['meter', 'progressbar'],
-	['nav', 'navigation'],
-	['ol', 'list'],
-	['option', 'option'],
-	['optgroup', 'group'],
-	['output', 'status'],
-	['progress', 'progressbar'],
-	['section', 'region'],
-	['summary', 'button'],
-	['table', 'table'],
-	['tbody', 'rowgroup'],
-	['textarea', 'textbox'],
-	['tfoot', 'rowgroup'],
-	['thead', 'rowgroup'],
-	['tr', 'row'],
-	['ul', 'list']
-]);
-const menuitem_type_to_implicit_role = new Map([
-	['command', 'menuitem'],
-	['checkbox', 'menuitemcheckbox'],
-	['radio', 'menuitemradio']
-]);
-const input_type_to_implicit_role = new Map([
-	['button', 'button'],
-	['image', 'button'],
-	['reset', 'button'],
-	['submit', 'button'],
-	['checkbox', 'checkbox'],
-	['radio', 'radio'],
-	['range', 'slider'],
-	['number', 'spinbutton'],
-	['email', 'textbox'],
-	['search', 'searchbox'],
-	['tel', 'textbox'],
-	['text', 'textbox'],
-	['url', 'textbox']
-]);
-
-/**
- * Exceptions to the rule which follows common A11y conventions
- * TODO make this configurable by the user
- * @type {Record<string, string[]>}
- */
-const a11y_non_interactive_element_to_interactive_role_exceptions = {
-	ul: ['listbox', 'menu', 'menubar', 'radiogroup', 'tablist', 'tree', 'treegrid'],
-	ol: ['listbox', 'menu', 'menubar', 'radiogroup', 'tablist', 'tree', 'treegrid'],
-	li: ['menuitem', 'option', 'row', 'tab', 'treeitem'],
-	table: ['grid'],
-	td: ['gridcell'],
-	fieldset: ['radiogroup', 'presentation']
-};
-
-const combobox_if_list = ['email', 'search', 'tel', 'text', 'url'];
-
-/** @param {Map<string, AST.Attribute>} attribute_map */
-function input_implicit_role(attribute_map) {
-	const type_attribute = attribute_map.get('type');
-	if (!type_attribute) return;
-	const type = get_static_text_value(type_attribute);
-	if (!type) return;
-	const list_attribute_exists = attribute_map.has('list');
-	if (list_attribute_exists && combobox_if_list.includes(type)) {
-		return 'combobox';
-	}
-	return input_type_to_implicit_role.get(type);
-}
-
-/** @param {Map<string, AST.Attribute>} attribute_map */
-function menuitem_implicit_role(attribute_map) {
-	const type_attribute = attribute_map.get('type');
-	if (!type_attribute) return;
-	const type = get_static_text_value(type_attribute);
-	if (!type) return;
-	return menuitem_type_to_implicit_role.get(type);
-}
-
-/**
- * @param {string} name
- * @param {Map<string, AST.Attribute>} attribute_map
- */
-function get_implicit_role(name, attribute_map) {
-	if (name === 'menuitem') {
-		return menuitem_implicit_role(attribute_map);
-	} else if (name === 'input') {
-		return input_implicit_role(attribute_map);
-	} else {
-		return a11y_implicit_semantics.get(name);
-	}
-}
-
-const invisible_elements = ['meta', 'html', 'script', 'style'];
-
-/**
- * @param {AST.SvelteNode[]} path
- * @param {string[]} elements
- */
-function is_parent(path, elements) {
-	let i = path.length;
-	while (i--) {
-		const parent = path[i];
-		if (parent.type === 'SvelteElement') return true; // unknown, play it safe, so we don't warn
-		if (parent.type === 'RegularElement') {
-			return elements.includes(parent.name);
-		}
-	}
-	return false;
-}
-
-/**
- * @param {AST.Attribute} attribute
- * @param {ARIAProperty} name
- * @param {ARIAPropertyDefinition} schema
- * @param {string | true | null} value
- */
-function validate_aria_attribute_value(attribute, name, schema, value) {
-	const type = schema.type;
-
-	if (value === null) return;
-	if (value === true) value = '';
-
-	if (type === 'boolean' && value !== 'true' && value !== 'false') {
-		w.a11y_incorrect_aria_attribute_type_boolean(attribute, name);
-	} else if (type === 'integer' && (value === '' || !Number.isInteger(+value))) {
-		w.a11y_incorrect_aria_attribute_type_integer(attribute, name);
-	} else if (type === 'number' && (value === '' || isNaN(+value))) {
-		w.a11y_incorrect_aria_attribute_type(attribute, name, 'number');
-	} else if ((type === 'string' || type === 'id') && value === '') {
-		w.a11y_incorrect_aria_attribute_type(attribute, name, 'non-empty string');
-	} else if (type === 'idlist' && value === '') {
-		w.a11y_incorrect_aria_attribute_type_idlist(attribute, name);
-	} else if (type === 'token') {
-		const values = (schema.values ?? []).map((value) => value.toString());
-		if (!values.includes(value.toLowerCase())) {
-			w.a11y_incorrect_aria_attribute_type_token(
-				attribute,
-				name,
-				list(values.map((v) => `"${v}"`))
-			);
-		}
-	} else if (type === 'tokenlist') {
-		const values = (schema.values ?? []).map((value) => value.toString());
-		if (
-			value
-				.toLowerCase()
-				.split(regex_whitespaces)
-				.some((value) => !values.includes(value))
-		) {
-			w.a11y_incorrect_aria_attribute_type_tokenlist(
-				attribute,
-				name,
-				list(values.map((v) => `"${v}"`))
-			);
-		}
-	} else if (type === 'tristate' && value !== 'true' && value !== 'false' && value !== 'mixed') {
-		w.a11y_incorrect_aria_attribute_type_tristate(attribute, name);
-	}
-}
-
-/**
- * @param {AST.RegularElement |AST.SvelteElement} node
- * @param {string[]} attributes
- * @param {string} name
- */
-function warn_missing_attribute(node, attributes, name = node.name) {
-	const article =
-		regex_starts_with_vowel.test(attributes[0]) || attributes[0] === 'href' ? 'an' : 'a';
-	const sequence =
-		attributes.length > 1
-			? attributes.slice(0, -1).join(', ') + ` or ${attributes[attributes.length - 1]}`
-			: attributes[0];
-
-	w.a11y_missing_attribute(node, name, article, sequence);
-}
-
-/**
- * @param {AST.Attribute | undefined} attribute
- */
-function get_static_value(attribute) {
-	if (!attribute) return null;
-	if (attribute.value === true) return true;
-	if (is_text_attribute(attribute)) return attribute.value[0].data;
-	return null;
-}
-
-/**
- * @param {AST.Attribute | undefined} attribute
- */
-function get_static_text_value(attribute) {
-	const value = get_static_value(attribute);
-	if (value === true) return null;
-	return value;
-}
+import {
+	a11y_distracting_elements,
+	a11y_implicit_semantics,
+	a11y_interactive_handlers,
+	a11y_labelable,
+	a11y_nested_implicit_semantics,
+	a11y_non_interactive_element_to_interactive_role_exceptions,
+	a11y_recommended_interactive_handlers,
+	a11y_required_attributes,
+	a11y_required_content,
+	abstract_roles,
+	address_type_tokens,
+	aria_attributes,
+	aria_roles,
+	autofill_contact_field_name_tokens,
+	autofill_field_name_tokens,
+	combobox_if_list,
+	contact_type_tokens,
+	ElementInteractivity,
+	input_type_to_implicit_role,
+	interactive_element_ax_object_schemas,
+	interactive_element_role_schemas,
+	interactive_roles,
+	invisible_elements,
+	menuitem_type_to_implicit_role,
+	non_interactive_element_ax_object_schemas,
+	non_interactive_element_role_schemas,
+	non_interactive_roles,
+	presentation_roles
+} from './constants.js';
+import { roles as roles_map, aria } from 'aria-query';
+// @ts-expect-error package doesn't provide typings
+import { AXObjectRoles, elementAXObjects } from 'axobject-query';
+import {
+	regex_heading_tags,
+	regex_js_prefix,
+	regex_not_whitespace,
+	regex_redundant_img_alt,
+	regex_starts_with_vowel,
+	regex_whitespaces
+} from '../../../../patterns.js';
+import { is_event_attribute, is_text_attribute } from '../../../../../utils/ast.js';
+import { list } from '../../../../../utils/string.js';
+import { walk } from 'zimmerframe';
+import fuzzymatch from '../../../../1-parse/utils/fuzzymatch.js';
+import { is_content_editable_binding } from '../../../../../../utils.js';
+import * as w from '../../../../../warnings.js';
 
 /**
  * @param {AST.RegularElement | AST.SvelteElement} node
@@ -705,22 +70,33 @@ export function check_element(node, context) {
 	let has_contenteditable_binding = false;
 
 	for (const attribute of node.attributes) {
-		if (attribute.type === 'SpreadAttribute') {
-			has_spread = true;
-		} else if (attribute.type === 'OnDirective') {
-			handlers.add(attribute.name);
-		} else if (attribute.type === 'Attribute') {
-			if (is_event_attribute(attribute)) {
-				handlers.add(attribute.name.slice(2));
-			} else {
-				attributes.push(attribute);
-				attribute_map.set(attribute.name, attribute);
-				if (attribute.name === 'contenteditable') {
-					has_contenteditable_attr = true;
+		switch (attribute.type) {
+			case 'Attribute': {
+				if (is_event_attribute(attribute)) {
+					handlers.add(attribute.name.slice(2));
+				} else {
+					attributes.push(attribute);
+					attribute_map.set(attribute.name, attribute);
+					if (attribute.name === 'contenteditable') {
+						has_contenteditable_attr = true;
+					}
+				}
+				break;
+			}
+			case 'SpreadAttribute': {
+				has_spread = true;
+				break;
+			}
+			case 'BindDirective': {
+				if (is_content_editable_binding(attribute.name)) {
+					has_contenteditable_binding = true;
 				}
+				break;
+			}
+			case 'OnDirective': {
+				handlers.add(attribute.name);
+				break;
 			}
-		} else if (attribute.type === 'BindDirective' && is_content_editable_binding(attribute.name)) {
-			has_contenteditable_binding = true;
 		}
 	}
 
@@ -765,15 +141,18 @@ export function check_element(node, context) {
 			}
 		}
 
-		// aria-role
-		if (name === 'role') {
-			if (invisible_elements.includes(node.name)) {
-				// aria-unsupported-elements
-				w.a11y_misplaced_role(attribute, node.name);
-			}
+		switch (name) {
+			// aria-role
+			case 'role': {
+				if (invisible_elements.includes(node.name)) {
+					// aria-unsupported-elements
+					w.a11y_misplaced_role(attribute, node.name);
+				}
 
-			const value = get_static_value(attribute);
-			if (typeof value === 'string') {
+				const value = get_static_value(attribute);
+				if (typeof value !== 'string') {
+					break;
+				}
 				for (const c_r of value.split(regex_whitespaces)) {
 					const current_role = /** @type {ARIARoleDefinitionKey} current_role */ (c_r);
 
@@ -868,30 +247,35 @@ export function check_element(node, context) {
 						w.a11y_no_noninteractive_element_to_interactive_role(node, node.name, current_role);
 					}
 				}
+				break;
 			}
-		}
-
-		// no-access-key
-		if (name === 'accesskey') {
-			w.a11y_accesskey(attribute);
-		}
-
-		// no-autofocus
-		if (name === 'autofocus' && node.name !== 'dialog' && !is_parent(context.path, ['dialog'])) {
-			w.a11y_autofocus(attribute);
-		}
-
-		// scope
-		if (name === 'scope' && !is_dynamic_element && node.name !== 'th') {
-			w.a11y_misplaced_scope(attribute);
-		}
-
-		// tabindex-no-positive
-		if (name === 'tabindex') {
-			const value = get_static_value(attribute);
-			// @ts-ignore todo is tabindex=true correct case?
-			if (!isNaN(value) && +value > 0) {
-				w.a11y_positive_tabindex(attribute);
+			// no-access-key
+			case 'accesskey': {
+				w.a11y_accesskey(attribute);
+				break;
+			}
+			// no-autofocus
+			case 'autofocus': {
+				if (node.name !== 'dialog' && !is_parent(context.path, ['dialog'])) {
+					w.a11y_autofocus(attribute);
+				}
+				break;
+			}
+			// scope
+			case 'scope': {
+				if (!is_dynamic_element && node.name !== 'th') {
+					w.a11y_misplaced_scope(attribute);
+				}
+				break;
+			}
+			// tabindex-no-positive
+			case 'tabindex': {
+				const value = get_static_value(attribute);
+				// @ts-ignore todo is tabindex=true correct case?
+				if (!isNaN(value) && +value > 0) {
+					w.a11y_positive_tabindex(attribute);
+				}
+				break;
 			}
 		}
 	}
@@ -989,174 +373,429 @@ export function check_element(node, context) {
 		}
 	}
 
-	if (!has_spread && handlers.has('mouseover') && !handlers.has('focus')) {
-		w.a11y_mouse_events_have_key_events(node, 'mouseover', 'focus');
+	if (!has_spread && handlers.has('mouseover') && !handlers.has('focus')) {
+		w.a11y_mouse_events_have_key_events(node, 'mouseover', 'focus');
+	}
+
+	if (!has_spread && handlers.has('mouseout') && !handlers.has('blur')) {
+		w.a11y_mouse_events_have_key_events(node, 'mouseout', 'blur');
+	}
+
+	// element-specific checks
+	const is_labelled = attribute_map.has('aria-label') || attribute_map.has('aria-labelledby');
+
+	switch (node.name) {
+		case 'a':
+		case 'button': {
+			const is_hidden = get_static_value(attribute_map.get('aria-hidden')) === 'true';
+			if (!has_spread && !is_hidden && !is_labelled && !has_content(node)) {
+				w.a11y_consider_explicit_label(node);
+			}
+			if (node.name === 'button') {
+				break;
+			}
+			const href = attribute_map.get('href') || attribute_map.get('xlink:href');
+			if (href) {
+				const href_value = get_static_text_value(href);
+				if (href_value !== null) {
+					if (href_value === '' || href_value === '#' || regex_js_prefix.test(href_value)) {
+						w.a11y_invalid_attribute(href, href_value, href.name);
+					}
+				}
+			} else if (!has_spread) {
+				const id_attribute = get_static_value(attribute_map.get('id'));
+				const name_attribute = get_static_value(attribute_map.get('name'));
+				const aria_disabled_attribute = get_static_value(attribute_map.get('aria-disabled'));
+				if (!id_attribute && !name_attribute && aria_disabled_attribute !== 'true') {
+					warn_missing_attribute(node, ['href']);
+				}
+			}
+			break;
+		}
+		case 'input': {
+			const type = attribute_map.get('type');
+			const type_value = get_static_text_value(type);
+			if (type_value === 'image' && !has_spread) {
+				const required_attributes = ['alt', 'aria-label', 'aria-labelledby'];
+				const has_attribute = required_attributes.some((name) => attribute_map.has(name));
+				if (!has_attribute) {
+					warn_missing_attribute(node, required_attributes, 'input type="image"');
+				}
+			}
+			// autocomplete-valid
+			const autocomplete = attribute_map.get('autocomplete');
+			if (type && autocomplete) {
+				const autocomplete_value = get_static_value(autocomplete);
+				if (!is_valid_autocomplete(autocomplete_value)) {
+					w.a11y_autocomplete_valid(
+						autocomplete,
+						/** @type {string} */ (autocomplete_value),
+						type_value ?? '...'
+					);
+				}
+			}
+			break;
+		}
+		case 'img': {
+			const alt_attribute = get_static_text_value(attribute_map.get('alt'));
+			const aria_hidden = get_static_value(attribute_map.get('aria-hidden'));
+			if (alt_attribute && !aria_hidden && !has_spread) {
+				if (regex_redundant_img_alt.test(alt_attribute)) {
+					w.a11y_img_redundant_alt(node);
+				}
+			}
+			break;
+		}
+		case 'label': {
+			/** @param {AST.TemplateNode} node */
+			const has_input_child = (node) => {
+				let has = false;
+				walk(
+					node,
+					{},
+					{
+						_(node, { next }) {
+							if (
+								node.type === 'SvelteElement' ||
+								node.type === 'SlotElement' ||
+								node.type === 'Component' ||
+								node.type === 'RenderTag' ||
+								(node.type === 'RegularElement' &&
+									(a11y_labelable.includes(node.name) || node.name === 'slot'))
+							) {
+								has = true;
+							} else {
+								next();
+							}
+						}
+					}
+				);
+				return has;
+			};
+			if (!has_spread && !attribute_map.has('for') && !has_input_child(node)) {
+				w.a11y_label_has_associated_control(node);
+			}
+			break;
+		}
+		case 'video': {
+			const aria_hidden_attribute = attribute_map.get('aria-hidden');
+			const aria_hidden_exist = aria_hidden_attribute && get_static_value(aria_hidden_attribute);
+			if (attribute_map.has('muted') || aria_hidden_exist === 'true' || has_spread) {
+				return;
+			}
+			let has_caption = false;
+			const track = /** @type {AST.RegularElement | undefined} */ (
+				node.fragment.nodes.find((i) => i.type === 'RegularElement' && i.name === 'track')
+			);
+			if (track) {
+				has_caption = track.attributes.some(
+					(a) =>
+						a.type === 'SpreadAttribute' ||
+						(a.type === 'Attribute' && a.name === 'kind' && get_static_value(a) === 'captions')
+				);
+			}
+			if (!has_caption) {
+				w.a11y_media_has_caption(node);
+			}
+			break;
+		}
+		case 'figcaption': {
+			if (!is_parent(context.path, ['figure'])) {
+				w.a11y_figcaption_parent(node);
+			}
+			break;
+		}
+		case 'figure': {
+			const children = node.fragment.nodes.filter((node) => {
+				if (node.type === 'Comment') return false;
+				if (node.type === 'Text') return regex_not_whitespace.test(node.data);
+				return true;
+			});
+			const index = children.findIndex(
+				(child) => child.type === 'RegularElement' && child.name === 'figcaption'
+			);
+			if (index !== -1 && index !== 0 && index !== children.length - 1) {
+				w.a11y_figcaption_index(children[index]);
+			}
+			break;
+		}
+	}
+
+	if (!has_spread && node.name !== 'a') {
+		const required_attributes = a11y_required_attributes[node.name];
+		if (required_attributes) {
+			const has_attribute = required_attributes.some((name) => attribute_map.has(name));
+			if (!has_attribute) {
+				warn_missing_attribute(node, required_attributes);
+			}
+		}
+	}
+
+	if (a11y_distracting_elements.includes(node.name)) {
+		// no-distracting-elements
+		w.a11y_distracting_elements(node, node.name);
+	}
+
+	// Check content
+	if (
+		!has_spread &&
+		!is_labelled &&
+		!has_contenteditable_binding &&
+		a11y_required_content.includes(node.name) &&
+		!has_content(node)
+	) {
+		w.a11y_missing_content(node, node.name);
+	}
+}
+
+/**
+ * @param {ARIARoleDefinitionKey} role
+ */
+function is_presentation_role(role) {
+	return presentation_roles.includes(role);
+}
+
+/**
+ * @param {string} tag_name
+ * @param {Map<string, AST.Attribute>} attribute_map
+ */
+function is_hidden_from_screen_reader(tag_name, attribute_map) {
+	if (tag_name === 'input') {
+		const type = get_static_value(attribute_map.get('type'));
+		if (type === 'hidden') {
+			return true;
+		}
+	}
+
+	const aria_hidden = attribute_map.get('aria-hidden');
+	if (!aria_hidden) return false;
+	const aria_hidden_value = get_static_value(aria_hidden);
+	if (aria_hidden_value === null) return true;
+	return aria_hidden_value === true || aria_hidden_value === 'true';
+}
+
+/**
+ * @param {Map<string, AST.Attribute>} attribute_map
+ */
+function has_disabled_attribute(attribute_map) {
+	const disabled_attr_value = get_static_value(attribute_map.get('disabled'));
+	if (disabled_attr_value) {
+		return true;
+	}
+
+	const aria_disabled_attr = attribute_map.get('aria-disabled');
+	if (aria_disabled_attr) {
+		const aria_disabled_attr_value = get_static_value(aria_disabled_attr);
+		if (aria_disabled_attr_value === 'true') {
+			return true;
+		}
+	}
+	return false;
+}
+
+/**
+ * @param {string} tag_name
+ * @param {Map<string, AST.Attribute>} attribute_map
+ * @returns {ElementInteractivity[keyof ElementInteractivity]}
+ */
+function element_interactivity(tag_name, attribute_map) {
+	if (
+		interactive_element_role_schemas.some((schema) => match_schema(schema, tag_name, attribute_map))
+	) {
+		return ElementInteractivity.Interactive;
+	}
+	if (
+		tag_name !== 'header' &&
+		non_interactive_element_role_schemas.some((schema) =>
+			match_schema(schema, tag_name, attribute_map)
+		)
+	) {
+		return ElementInteractivity.NonInteractive;
+	}
+	if (
+		interactive_element_ax_object_schemas.some((schema) =>
+			match_schema(schema, tag_name, attribute_map)
+		)
+	) {
+		return ElementInteractivity.Interactive;
+	}
+	if (
+		non_interactive_element_ax_object_schemas.some((schema) =>
+			match_schema(schema, tag_name, attribute_map)
+		)
+	) {
+		return ElementInteractivity.NonInteractive;
+	}
+	return ElementInteractivity.Static;
+}
+
+/**
+ * @param {string} tag_name
+ * @param {Map<string, AST.Attribute>} attribute_map
+ * @returns {boolean}
+ */
+function is_interactive_element(tag_name, attribute_map) {
+	return element_interactivity(tag_name, attribute_map) === ElementInteractivity.Interactive;
+}
+
+/**
+ * @param {string} tag_name
+ * @param {Map<string, AST.Attribute>} attribute_map
+ * @returns {boolean}
+ */
+function is_non_interactive_element(tag_name, attribute_map) {
+	return element_interactivity(tag_name, attribute_map) === ElementInteractivity.NonInteractive;
+}
+
+/**
+ * @param {string} tag_name
+ * @param {Map<string, AST.Attribute>} attribute_map
+ * @returns {boolean}
+ */
+function is_static_element(tag_name, attribute_map) {
+	return element_interactivity(tag_name, attribute_map) === ElementInteractivity.Static;
+}
+
+/**
+ * @param {ARIARoleDefinitionKey} role
+ * @param {string} tag_name
+ * @param {Map<string, AST.Attribute>} attribute_map
+ */
+function is_semantic_role_element(role, tag_name, attribute_map) {
+	for (const [schema, ax_object] of elementAXObjects.entries()) {
+		if (
+			schema.name === tag_name &&
+			(!schema.attributes ||
+				schema.attributes.every(
+					/** @param {any} attr */
+					(attr) =>
+						attribute_map.has(attr.name) &&
+						get_static_value(attribute_map.get(attr.name)) === attr.value
+				))
+		) {
+			for (const name of ax_object) {
+				const roles = AXObjectRoles.get(name);
+				if (roles) {
+					for (const { name } of roles) {
+						if (name === role) {
+							return true;
+						}
+					}
+				}
+			}
+		}
+	}
+	return false;
+}
+
+/**
+ * @param {null | true | string} autocomplete
+ */
+function is_valid_autocomplete(autocomplete) {
+	if (autocomplete === true) {
+		return false;
+	} else if (!autocomplete) {
+		return true; // dynamic value
 	}
-
-	if (!has_spread && handlers.has('mouseout') && !handlers.has('blur')) {
-		w.a11y_mouse_events_have_key_events(node, 'mouseout', 'blur');
+	const tokens = autocomplete.trim().toLowerCase().split(regex_whitespaces);
+	if (typeof tokens[0] === 'string' && tokens[0].startsWith('section-')) {
+		tokens.shift();
 	}
-
-	// element-specific checks
-	const is_labelled = attribute_map.has('aria-label') || attribute_map.has('aria-labelledby');
-
-	if (node.name === 'a' || node.name === 'button') {
-		const is_hidden = get_static_value(attribute_map.get('aria-hidden')) === 'true';
-
-		if (!has_spread && !is_hidden && !is_labelled && !has_content(node)) {
-			w.a11y_consider_explicit_label(node);
-		}
+	if (address_type_tokens.includes(tokens[0])) {
+		tokens.shift();
 	}
-
-	if (node.name === 'a') {
-		const href = attribute_map.get('href') || attribute_map.get('xlink:href');
-		if (href) {
-			const href_value = get_static_text_value(href);
-			if (href_value !== null) {
-				if (href_value === '' || href_value === '#' || regex_js_prefix.test(href_value)) {
-					w.a11y_invalid_attribute(href, href_value, href.name);
-				}
-			}
-		} else if (!has_spread) {
-			const id_attribute = get_static_value(attribute_map.get('id'));
-			const name_attribute = get_static_value(attribute_map.get('name'));
-			const aria_disabled_attribute = get_static_value(attribute_map.get('aria-disabled'));
-			if (!id_attribute && !name_attribute && aria_disabled_attribute !== 'true') {
-				warn_missing_attribute(node, ['href']);
-			}
+	if (autofill_field_name_tokens.includes(tokens[0])) {
+		tokens.shift();
+	} else {
+		if (contact_type_tokens.includes(tokens[0])) {
+			tokens.shift();
 		}
-	} else if (!has_spread) {
-		const required_attributes = a11y_required_attributes[node.name];
-		if (required_attributes) {
-			const has_attribute = required_attributes.some((name) => attribute_map.has(name));
-			if (!has_attribute) {
-				warn_missing_attribute(node, required_attributes);
-			}
+		if (autofill_contact_field_name_tokens.includes(tokens[0])) {
+			tokens.shift();
+		} else {
+			return false;
 		}
 	}
-
-	if (node.name === 'input') {
-		const type = attribute_map.get('type');
-		const type_value = get_static_text_value(type);
-		if (type_value === 'image' && !has_spread) {
-			const required_attributes = ['alt', 'aria-label', 'aria-labelledby'];
-			const has_attribute = required_attributes.some((name) => attribute_map.has(name));
-			if (!has_attribute) {
-				warn_missing_attribute(node, required_attributes, 'input type="image"');
-			}
-		}
-		// autocomplete-valid
-		const autocomplete = attribute_map.get('autocomplete');
-		if (type && autocomplete) {
-			const autocomplete_value = get_static_value(autocomplete);
-			if (!is_valid_autocomplete(autocomplete_value)) {
-				w.a11y_autocomplete_valid(
-					autocomplete,
-					/** @type {string} */ (autocomplete_value),
-					type_value ?? '...'
-				);
-			}
-		}
+	if (tokens[0] === 'webauthn') {
+		tokens.shift();
 	}
+	return tokens.length === 0;
+}
 
-	if (node.name === 'img') {
-		const alt_attribute = get_static_text_value(attribute_map.get('alt'));
-		const aria_hidden = get_static_value(attribute_map.get('aria-hidden'));
-		if (alt_attribute && !aria_hidden && !has_spread) {
-			if (regex_redundant_img_alt.test(alt_attribute)) {
-				w.a11y_img_redundant_alt(node);
-			}
-		}
+/** @param {Map<string, AST.Attribute>} attribute_map */
+function input_implicit_role(attribute_map) {
+	const type_attribute = attribute_map.get('type');
+	if (!type_attribute) return;
+	const type = get_static_text_value(type_attribute);
+	if (!type) return;
+	const list_attribute_exists = attribute_map.has('list');
+	if (list_attribute_exists && combobox_if_list.includes(type)) {
+		return 'combobox';
 	}
+	return input_type_to_implicit_role.get(type);
+}
 
-	if (node.name === 'label') {
-		/** @param {AST.TemplateNode} node */
-		const has_input_child = (node) => {
-			let has = false;
-			walk(
-				node,
-				{},
-				{
-					_(node, { next }) {
-						if (
-							node.type === 'SvelteElement' ||
-							node.type === 'SlotElement' ||
-							node.type === 'Component' ||
-							node.type === 'RenderTag' ||
-							(node.type === 'RegularElement' &&
-								(a11y_labelable.includes(node.name) || node.name === 'slot'))
-						) {
-							has = true;
-						} else {
-							next();
-						}
-					}
-				}
-			);
-			return has;
-		};
-		if (!has_spread && !attribute_map.has('for') && !has_input_child(node)) {
-			w.a11y_label_has_associated_control(node);
-		}
-	}
+/** @param {Map<string, AST.Attribute>} attribute_map */
+function menuitem_implicit_role(attribute_map) {
+	const type_attribute = attribute_map.get('type');
+	if (!type_attribute) return;
+	const type = get_static_text_value(type_attribute);
+	if (!type) return;
+	return menuitem_type_to_implicit_role.get(type);
+}
 
-	if (node.name === 'video') {
-		const aria_hidden_attribute = attribute_map.get('aria-hidden');
-		const aria_hidden_exist = aria_hidden_attribute && get_static_value(aria_hidden_attribute);
-		if (attribute_map.has('muted') || aria_hidden_exist === 'true' || has_spread) {
-			return;
-		}
-		let has_caption = false;
-		const track = /** @type {AST.RegularElement | undefined} */ (
-			node.fragment.nodes.find((i) => i.type === 'RegularElement' && i.name === 'track')
-		);
-		if (track) {
-			has_caption = track.attributes.some(
-				(a) =>
-					a.type === 'SpreadAttribute' ||
-					(a.type === 'Attribute' && a.name === 'kind' && get_static_value(a) === 'captions')
-			);
-		}
-		if (!has_caption) {
-			w.a11y_media_has_caption(node);
-		}
+/**
+ * @param {string} name
+ * @param {Map<string, AST.Attribute>} attribute_map
+ */
+function get_implicit_role(name, attribute_map) {
+	if (name === 'menuitem') {
+		return menuitem_implicit_role(attribute_map);
+	} else if (name === 'input') {
+		return input_implicit_role(attribute_map);
+	} else {
+		return a11y_implicit_semantics.get(name);
 	}
+}
 
-	if (node.name === 'figcaption') {
-		if (!is_parent(context.path, ['figure'])) {
-			w.a11y_figcaption_parent(node);
-		}
-	}
+/**
+ * @param {ARIARoleDefinitionKey} role
+ */
+function is_non_interactive_roles(role) {
+	return non_interactive_roles.includes(role);
+}
 
-	if (node.name === 'figure') {
-		const children = node.fragment.nodes.filter((node) => {
-			if (node.type === 'Comment') return false;
-			if (node.type === 'Text') return regex_not_whitespace.test(node.data);
-			return true;
-		});
-		const index = children.findIndex(
-			(child) => child.type === 'RegularElement' && child.name === 'figcaption'
-		);
-		if (index !== -1 && index !== 0 && index !== children.length - 1) {
-			w.a11y_figcaption_index(children[index]);
-		}
-	}
+/**
+ * @param {ARIARoleDefinitionKey} role
+ */
+function is_interactive_roles(role) {
+	return interactive_roles.includes(role);
+}
 
-	if (a11y_distracting_elements.includes(node.name)) {
-		// no-distracting-elements
-		w.a11y_distracting_elements(node, node.name);
-	}
+/**
+ * @param {ARIARoleDefinitionKey} role
+ */
+function is_abstract_role(role) {
+	return abstract_roles.includes(role);
+}
 
-	// Check content
-	if (
-		!has_spread &&
-		!is_labelled &&
-		!has_contenteditable_binding &&
-		a11y_required_content.includes(node.name) &&
-		!has_content(node)
-	) {
-		w.a11y_missing_content(node, node.name);
-	}
+/**
+ * @param {AST.Attribute | undefined} attribute
+ */
+function get_static_text_value(attribute) {
+	const value = get_static_value(attribute);
+	if (value === true) return null;
+	return value;
+}
+
+/**
+ * @param {AST.Attribute | undefined} attribute
+ */
+function get_static_value(attribute) {
+	if (!attribute) return null;
+	if (attribute.value === true) return true;
+	if (is_text_attribute(attribute)) return attribute.value[0].data;
+	return null;
 }
 
 /**
@@ -1188,3 +827,133 @@ function has_content(element) {
 		return true;
 	}
 }
+
+/**
+ * @param {ARIARoleRelationConcept} schema
+ * @param {string} tag_name
+ * @param {Map<string, AST.Attribute>} attribute_map
+ */
+function match_schema(schema, tag_name, attribute_map) {
+	if (schema.name !== tag_name) return false;
+	if (!schema.attributes) return true;
+	return schema.attributes.every((schema_attribute) => {
+		const attribute = attribute_map.get(schema_attribute.name);
+		if (!attribute) return false;
+		if (schema_attribute.value && schema_attribute.value !== get_static_text_value(attribute)) {
+			return false;
+		}
+		return true;
+	});
+}
+
+/**
+ * @param {AST.SvelteNode[]} path
+ * @param {string[]} elements
+ */
+function is_parent(path, elements) {
+	let i = path.length;
+	while (i--) {
+		const parent = path[i];
+		if (parent.type === 'SvelteElement') return true; // unknown, play it safe, so we don't warn
+		if (parent.type === 'RegularElement') {
+			return elements.includes(parent.name);
+		}
+	}
+	return false;
+}
+
+/**
+ * @param {AST.Attribute} attribute
+ * @param {ARIAProperty} name
+ * @param {ARIAPropertyDefinition} schema
+ * @param {string | true | null} value
+ */
+function validate_aria_attribute_value(attribute, name, schema, value) {
+	const type = schema.type;
+
+	if (value === null) return;
+	if (value === true) value = '';
+
+	switch (type) {
+		case 'id':
+		case 'string': {
+			if (value === '') {
+				w.a11y_incorrect_aria_attribute_type(attribute, name, 'non-empty string');
+			}
+			break;
+		}
+		case 'number': {
+			if (value === '' || isNaN(+value)) {
+				w.a11y_incorrect_aria_attribute_type(attribute, name, 'number');
+			}
+			break;
+		}
+		case 'boolean': {
+			if (value !== 'true' && value !== 'false') {
+				w.a11y_incorrect_aria_attribute_type_boolean(attribute, name);
+			}
+			break;
+		}
+		case 'idlist': {
+			if (value === '') {
+				w.a11y_incorrect_aria_attribute_type_idlist(attribute, name);
+			}
+			break;
+		}
+		case 'integer': {
+			if (value === '' || !Number.isInteger(+value)) {
+				w.a11y_incorrect_aria_attribute_type_integer(attribute, name);
+			}
+			break;
+		}
+		case 'token': {
+			const values = (schema.values ?? []).map((value) => value.toString());
+			if (!values.includes(value.toLowerCase())) {
+				w.a11y_incorrect_aria_attribute_type_token(
+					attribute,
+					name,
+					list(values.map((v) => `"${v}"`))
+				);
+			}
+			break;
+		}
+		case 'tokenlist': {
+			const values = (schema.values ?? []).map((value) => value.toString());
+			if (
+				value
+					.toLowerCase()
+					.split(regex_whitespaces)
+					.some((value) => !values.includes(value))
+			) {
+				w.a11y_incorrect_aria_attribute_type_tokenlist(
+					attribute,
+					name,
+					list(values.map((v) => `"${v}"`))
+				);
+			}
+			break;
+		}
+		case 'tristate': {
+			if (value !== 'true' && value !== 'false' && value !== 'mixed') {
+				w.a11y_incorrect_aria_attribute_type_tristate(attribute, name);
+			}
+			break;
+		}
+	}
+}
+
+/**
+ * @param {AST.RegularElement |AST.SvelteElement} node
+ * @param {string[]} attributes
+ * @param {string} name
+ */
+function warn_missing_attribute(node, attributes, name = node.name) {
+	const article =
+		regex_starts_with_vowel.test(attributes[0]) || attributes[0] === 'href' ? 'an' : 'a';
+	const sequence =
+		attributes.length > 1
+			? attributes.slice(0, -1).join(', ') + ` or ${attributes[attributes.length - 1]}`
+			: attributes[0];
+
+	w.a11y_missing_attribute(node, name, article, sequence);
+}

From 0672e48223171f86b309e3de84c1c3846eee0bda Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 14 Jul 2025 15:58:44 -0400
Subject: [PATCH 057/148] feat: allow `await` in components (#15844)

* tidy

* tidy

* yes it can, apparently

* tidy up

* unused

* complete merge

* WIP

* simplify

* debugging help

* WIP

* unused

* partial merge

* WIP

* fix

* add test

* rename

* fix

* unused

* oops

* chore: merge main into async branch (#16197)

* chore: merge main into async branch

* adjust test

* fix: make effects depend on state created inside them (#16198)

* make effects depend on state created inside them

* fix, add github action

* disable test in async mode

* make batch.#deferred private

* fix settled when awaits occur inside pending boundary

* tweak

* change behaviour of `tick()` to be requestAnimationFrame-based

* get rid of a bunch of Promise.resolve chains

* more

* more

* fix test

* disallow `flushSync()` inside effects

* regenerate

* handle errors in block expressions

* make validate_each_keys async-aware

* for unowned deriveds, throw errors lazily

* rename ASYNC_ERROR -> ERROR_VALUE, and avoid conflicts with other flags now that it's used with deriveds as well as sources

* invoke boundary directly

* local effect pending

* update test

* fix

* fix

* fix weird bug in tests

* delete old changeset that somehow got left over here

* Update .changeset/eleven-weeks-dance.md

* update error details

* unused

* simplify

* tweak

* tweak

* tweak

* tweak

* tidy up

* handle errors in async block expressions

* tweak

* groundwork for async attribute_effect

* dry out

* fix async directives

* tidy up

* initialize option values before initing select values

* simplify init_select

* simplify

* tweak

* tidy up

* tweak

* on second thoughts just simplify it here

* tidy

* handle awaits in `<slot>`

* unused

* tidy up

* tidy up

* dry out

* dry out

* Revert "dry out"

This reverts commit 25855163bf7d915492f62d3d0e5370ed74e65132.

* dry out

* dry out

* use let for block-scoped stuff

* dry out

* dry out

* tidy up

* only wrap awaits in `$.save` when necessary

* oops

* remove TODO comment (just checked)

* oops, leftover

* simplify

* unused

* remove logging

* tweak

* unused

* unused

* remove logging

* partial fix

* fix

* remove unused EFFECT_HAS_DERIVED

* Update packages/svelte/src/reactivity/create-subscriber.js

Co-authored-by: Elliott Johnson <sejohnson@torchcloudconsulting.com>

* Update packages/svelte/src/index-client.js

Co-authored-by: Elliott Johnson <sejohnson@torchcloudconsulting.com>

* Update packages/svelte/src/internal/client/runtime.js

Co-authored-by: Elliott Johnson <sejohnson@torchcloudconsulting.com>

* unused

* Update packages/svelte/src/internal/client/reactivity/sources.js

Co-authored-by: Elliott Johnson <sejohnson@torchcloudconsulting.com>

* Update packages/svelte/src/internal/client/reactivity/deriveds.js

Co-authored-by: Elliott Johnson <sejohnson@torchcloudconsulting.com>

* Update packages/svelte/src/internal/client/reactivity/deriveds.js

Co-authored-by: Elliott Johnson <sejohnson@torchcloudconsulting.com>

* prettier

* unused

* fix flags

* tweak

* tweak

* unused

* fix

* no idea what a 'boundary micro task' is or why it was deemed necessary but evidently it isn't

* remove queue_boundary_micro_task

* oops

* note

* tidy up

* remove TODO

* make method private

* simplify

* flesh out await_reactivity_loss warning

* tweak

* update test

* fix

* null out from_async_derived in more places

* tidy up test

* failing test

* unused

* fix test

* fix

* simplify. no idea what the async_mode_flag stuff is about, but it appears unnecessary

* add async_derived_orphan error

* regenerate

* flesh out await_outside_boundary message

* add some JSDoc

* only update `$effect.pending()` if someone is listening, since it causes a double flush and makes debugging harder

* tweak logic to make it clearer why and when we commit a batch

* add a couple of comments

* false -> 0

* add comment

* unused

* silence warning

* add effect_pending_outside_reaction error

* Update packages/svelte/src/compiler/types/index.d.ts

Co-authored-by: Elliott Johnson <sejohnson@torchcloudconsulting.com>

* suspend batch, not boundary

* rename from_async_derived -> current_async_derived

* tweak

* remove TODO - this method is only called when pending snippet exists

* use error boundary for test - vitest does some weird error swallowing afaict

* flush less often

* restore -> activate

* remove TODO

* move batch-related code into batch.js

* make flush_queued_root_effects a method of batch

* make process_effects a method of batch

* make stuff private

* unused

* regenerate

* update test

* more JSDoc

* add more JSDoc

* branch and block effects do not also need to be render effects

* tidy up

* simplify

* unused

* move code where it belongs

* remove, for now

* fix

* only apply error adjustments when error escapes boundaries

* remove EFFECT_IS_UPDATING

* is_dirty is a better name than check_dirtiness

* duplicates are rare and harmless

* apparently we no longer need the merging logic? we can simplify and fix stuff by removing it

* tidy

* don't commit stale batches

* add skipped failing test

* partial merge

* WIP

* WIP

* WIP

* tweak

* tidy up

* dont update derived status when time-travelling

* tidy up

* tidy up

* tag async deriveds

* tweak

* bail out of secondary flushes

* re-run blocks on subsequent flushes

* add test

* fix

* add tests, one failing

* fix

* flesh out await_waterfall message

* tidy up

* dry out

* unused

* tweak

* tidy up

* TODO

* tweak

* tidy up

* remove TODO

* unused export

* add optimisation back

* revert unneeded changes

* revert

* update some tests

* more

* more

* move some code

* rename

* WIP

* unset context synchronously

* remove unused argument

* Apply suggestions from code review

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>

* add comment

* add comment

* use queue_micro_task in createSubscriber

* Update packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitExpression.js

Co-authored-by: Elliott Johnson <sejohnson@torchcloudconsulting.com>

* prettier

---------

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
Co-authored-by: Simon Holthausen <simon.holthausen@vercel.com>
Co-authored-by: Elliott Johnson <sejohnson@torchcloudconsulting.com>
---
 .changeset/eleven-weeks-dance.md              |   5 +
 .github/workflows/ci.yml                      |  17 +
 .../98-reference/.generated/client-errors.md  |  36 ++
 .../.generated/client-warnings.md             |  61 ++
 .../98-reference/.generated/compile-errors.md |  12 +
 .../98-reference/.generated/shared-errors.md  |  20 +
 eslint.config.js                              |   3 +-
 .../svelte/messages/client-errors/errors.md   |  28 +
 .../messages/client-warnings/warnings.md      |  57 ++
 .../svelte/messages/compile-errors/script.md  |   8 +
 .../svelte/messages/shared-errors/errors.md   |  18 +
 packages/svelte/package.json                  |   3 +
 packages/svelte/src/compiler/errors.js        |  18 +
 packages/svelte/src/compiler/migrate/index.js |   5 +-
 .../compiler/phases/1-parse/state/element.js  |   2 +
 .../src/compiler/phases/2-analyze/index.js    |  32 +-
 .../2-analyze/visitors/AwaitExpression.js     |  30 +
 .../2-analyze/visitors/CallExpression.js      |  22 +-
 .../2-analyze/visitors/StyleDirective.js      |   1 +
 .../2-analyze/visitors/SvelteBoundary.js      |   2 +-
 .../2-analyze/visitors/SvelteElement.js       |  14 +-
 .../3-transform/client/transform-client.js    |  70 +-
 .../phases/3-transform/client/types.d.ts      |   9 +-
 .../client/visitors/AwaitExpression.js        | 126 ++++
 .../client/visitors/CallExpression.js         |  10 +-
 .../3-transform/client/visitors/EachBlock.js  |  31 +-
 .../3-transform/client/visitors/Fragment.js   |   4 +-
 .../client/visitors/FunctionDeclaration.js    |   2 +-
 .../3-transform/client/visitors/HtmlTag.js    |  19 +-
 .../3-transform/client/visitors/IfBlock.js    |  42 +-
 .../3-transform/client/visitors/KeyBlock.js   |  28 +-
 .../client/visitors/RegularElement.js         |  21 +-
 .../3-transform/client/visitors/RenderTag.js  |  59 +-
 .../client/visitors/SlotElement.js            |  22 +-
 .../client/visitors/SvelteBoundary.js         |   4 +-
 .../client/visitors/SvelteElement.js          |  41 +-
 .../client/visitors/VariableDeclaration.js    |  44 +-
 .../client/visitors/shared/component.js       |  46 +-
 .../client/visitors/shared/element.js         |  25 +-
 .../client/visitors/shared/function.js        |   2 +-
 .../client/visitors/shared/utils.js           |  35 +-
 .../3-transform/server/transform-server.js    |   2 +
 .../server/visitors/AwaitExpression.js        |  25 +
 .../server/visitors/CallExpression.js         |   4 +
 .../3-transform/server/visitors/IfBlock.js    |  27 +-
 .../server/visitors/SvelteBoundary.js         |  29 +-
 packages/svelte/src/compiler/phases/nodes.js  |   3 +-
 packages/svelte/src/compiler/phases/scope.js  |  19 +
 .../svelte/src/compiler/phases/types.d.ts     |   9 +-
 packages/svelte/src/compiler/types/index.d.ts |   7 +
 .../svelte/src/compiler/types/template.d.ts   |   1 +
 .../svelte/src/compiler/utils/builders.js     |  36 +-
 .../svelte/src/compiler/validate-options.js   |   6 +-
 packages/svelte/src/constants.js              |   2 +
 packages/svelte/src/index-client.js           |   4 +-
 packages/svelte/src/index-server.js           |   2 +
 .../svelte/src/internal/client/constants.js   |   9 +-
 .../svelte/src/internal/client/context.js     |  28 +-
 .../svelte/src/internal/client/dev/debug.js   |   3 +
 .../svelte/src/internal/client/dev/tracing.js |   4 +-
 .../src/internal/client/dom/blocks/async.js   |  26 +
 .../src/internal/client/dom/blocks/await.js   |   3 +-
 .../internal/client/dom/blocks/boundary.js    | 207 +++++-
 .../src/internal/client/dom/blocks/each.js    | 202 ++++--
 .../src/internal/client/dom/blocks/if.js      | 119 ++--
 .../src/internal/client/dom/blocks/key.js     |  44 +-
 .../client/dom/blocks/svelte-component.js     |  43 +-
 .../client/dom/elements/attributes.js         |  81 +--
 .../client/dom/elements/bindings/input.js     |   9 +
 .../src/internal/client/dom/operations.js     |  19 +-
 .../src/internal/client/error-handling.js     |  21 +-
 packages/svelte/src/internal/client/errors.js |  64 ++
 packages/svelte/src/internal/client/index.js  |  15 +-
 .../src/internal/client/reactivity/async.js   | 127 ++++
 .../src/internal/client/reactivity/batch.js   | 603 ++++++++++++++++++
 .../internal/client/reactivity/deriveds.js    | 172 ++++-
 .../src/internal/client/reactivity/effects.js |  97 +--
 .../src/internal/client/reactivity/sources.js |  11 +-
 .../svelte/src/internal/client/runtime.js     | 462 +++++---------
 .../svelte/src/internal/client/types.d.ts     |   4 +-
 .../svelte/src/internal/client/warnings.js    |  25 +
 packages/svelte/src/internal/flags/async.js   |   3 +
 packages/svelte/src/internal/flags/index.js   |  10 +
 packages/svelte/src/internal/server/index.js  |   2 +
 packages/svelte/src/internal/shared/errors.js |  16 +
 packages/svelte/src/legacy/legacy-client.js   |   9 +-
 .../src/reactivity/create-subscriber.js       |   5 +-
 packages/svelte/src/utils.js                  |   1 +
 packages/svelte/tests/helpers.js              |   5 +-
 .../samples/transition-abort/_config.js       |   2 +
 .../svelte/tests/runtime-legacy/shared.ts     |  46 +-
 .../samples/async-abort-signal/_config.js     |  23 +
 .../samples/async-abort-signal/main.svelte    |  29 +
 .../async-attribute-without-state/_config.js  |  18 +
 .../async-attribute-without-state/main.svelte |   7 +
 .../samples/async-attribute/_config.js        |  29 +
 .../samples/async-attribute/main.svelte       |  15 +
 .../_config.js                                |  27 +
 .../main.svelte                               |  28 +
 .../async-block-reject-during-init/_config.js |  10 +
 .../main.svelte                               |   8 +
 .../_config.js                                |  28 +
 .../main.svelte                               |  29 +
 .../samples/async-block-rerun/_config.js      |  53 ++
 .../samples/async-block-rerun/main.svelte     |  45 ++
 .../samples/async-child-effect/_config.js     |  55 ++
 .../samples/async-child-effect/main.svelte    |  26 +
 .../samples/async-class-directive/_config.js  |  20 +
 .../samples/async-class-directive/main.svelte |  11 +
 .../samples/async-derived-in-if/Child.svelte  |   5 +
 .../samples/async-derived-in-if/_config.js    |  19 +
 .../samples/async-derived-in-if/main.svelte   |  17 +
 .../Child.svelte                              |   9 +
 .../_config.js                                |  33 +
 .../main.svelte                               |  20 +
 .../samples/async-derived-module/Child.svelte |  20 +
 .../samples/async-derived-module/_config.js   |  93 +++
 .../samples/async-derived-module/main.svelte  |  21 +
 .../async-derived-module/state.svelte.js      |   9 +
 .../async-derived-unchanging/Component.svelte |  29 +
 .../async-derived-unchanging/_config.js       |  33 +
 .../async-derived-unchanging/main.svelte      |  11 +
 .../samples/async-derived/Child.svelte        |  15 +
 .../samples/async-derived/_config.js          |  48 ++
 .../samples/async-derived/main.svelte         |  21 +
 .../samples/async-each-await-item/_config.js  |  31 +
 .../samples/async-each-await-item/main.svelte |  39 ++
 .../samples/async-each-keyed/_config.js       |  41 ++
 .../samples/async-each-keyed/main.svelte      |  24 +
 .../samples/async-each/_config.js             |  48 ++
 .../samples/async-each/main.svelte            |  17 +
 .../_config.js                                |  11 +
 .../main.svelte                               |   8 +
 .../samples/async-error-recovery/_config.js   |  87 +++
 .../samples/async-error-recovery/main.svelte  |  24 +
 .../samples/async-error/_config.js            |  34 +
 .../samples/async-error/main.svelte           |  20 +
 .../samples/async-expression/_config.js       |  56 ++
 .../samples/async-expression/main.svelte      |  19 +
 .../samples/async-html-tag/_config.js         |  51 ++
 .../samples/async-html-tag/main.svelte        |  15 +
 .../runtime-runes/samples/async-if/_config.js |  31 +
 .../samples/async-if/main.svelte              |  19 +
 .../samples/async-key/_config.js              |  46 ++
 .../samples/async-key/main.svelte             |  17 +
 .../_config.js                                |  35 +
 .../main.svelte                               |  17 +
 .../_config.js                                |  30 +
 .../main.svelte                               |  31 +
 .../samples/async-nested-derived/Child.svelte |  11 +
 .../samples/async-nested-derived/_config.js   |  14 +
 .../samples/async-nested-derived/main.svelte  |  15 +
 .../samples/async-prop/Child.svelte           |   5 +
 .../samples/async-prop/_config.js             |  51 ++
 .../samples/async-prop/main.svelte            |  17 +
 .../samples/async-reactivity-loss/_config.js  |  24 +
 .../samples/async-reactivity-loss/main.svelte |  20 +
 .../samples/async-redirect-initial/_config.js |  51 ++
 .../async-redirect-initial/main.svelte        |  43 ++
 .../samples/async-redirect/_config.js         |  52 ++
 .../samples/async-redirect/main.svelte        |  43 ++
 .../samples/async-render-tag/_config.js       |  51 ++
 .../samples/async-render-tag/main.svelte      |  19 +
 .../samples/async-slot/Child.svelte           |   1 +
 .../samples/async-slot/_config.js             |  13 +
 .../samples/async-slot/main.svelte            |  13 +
 .../samples/async-stale-derived-2/_config.js  |  58 ++
 .../samples/async-stale-derived-2/main.svelte |  34 +
 .../samples/async-stale-derived/_config.js    |  52 ++
 .../samples/async-stale-derived/main.svelte   |  26 +
 .../samples/async-svelte-element/_config.js   |  51 ++
 .../samples/async-svelte-element/main.svelte  |  15 +
 .../async-top-level-in-if/Child.svelte        |   7 +
 .../samples/async-top-level-in-if/_config.js  |  40 ++
 .../samples/async-top-level-in-if/main.svelte |  20 +
 .../samples/async-top-level/Child.svelte      |   7 +
 .../samples/async-top-level/_config.js        |  14 +
 .../samples/async-top-level/main.svelte       |  15 +
 .../async-unresolved-promise/_config.js       |  32 +
 .../async-unresolved-promise/main.svelte      |  19 +
 .../async-waterfall-on-init/_config.js        |  42 ++
 .../async-waterfall-on-init/main.svelte       |  22 +
 .../async-with-sync-derived/_config.js        |  53 ++
 .../async-with-sync-derived/main.svelte       |  19 +
 .../samples/effect-cleanup/_config.js         |   9 +-
 .../samples/effect-cleanup/main.svelte        |   2 +-
 .../samples/error-boundary-18/_config.js      |   2 +
 .../set-context-after-await/Child.svelte      |  11 +
 .../set-context-after-await/_config.js        |  12 +
 .../set-context-after-await/main.svelte       |  11 +
 .../set-context-after-mount/_config.js        |  16 +
 .../set-context-after-mount/main.svelte       |  20 +
 .../samples/tick-timing/_config.js            |   2 +
 .../samples/untrack-own-deriveds/_config.js   |   2 +
 packages/svelte/tests/signals/test.ts         |  76 ++-
 packages/svelte/tests/store/test.ts           |   9 +-
 packages/svelte/tests/suite.ts                |   6 +-
 packages/svelte/types/index.d.ts              |  61 +-
 playgrounds/sandbox/index.html                |   6 +
 playgrounds/sandbox/run.js                    |  15 +-
 playgrounds/sandbox/ssr-common.js             |  17 +
 playgrounds/sandbox/ssr-dev.js                |   1 +
 playgrounds/sandbox/ssr-prod.js               |   1 +
 playgrounds/sandbox/svelte.config.js          |   6 +-
 204 files changed, 5777 insertions(+), 799 deletions(-)
 create mode 100644 .changeset/eleven-weeks-dance.md
 create mode 100644 packages/svelte/src/compiler/phases/2-analyze/visitors/AwaitExpression.js
 create mode 100644 packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitExpression.js
 create mode 100644 packages/svelte/src/compiler/phases/3-transform/server/visitors/AwaitExpression.js
 create mode 100644 packages/svelte/src/internal/client/dom/blocks/async.js
 create mode 100644 packages/svelte/src/internal/client/reactivity/async.js
 create mode 100644 packages/svelte/src/internal/client/reactivity/batch.js
 create mode 100644 packages/svelte/src/internal/flags/async.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-abort-signal/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-abort-signal/main.svelte
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 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-prop/Child.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-prop/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-prop/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-reactivity-loss/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-reactivity-loss/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-redirect-initial/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-redirect-initial/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-redirect/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-redirect/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-render-tag/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-render-tag/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-slot/Child.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-slot/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-slot/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-stale-derived-2/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-stale-derived-2/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-stale-derived/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-stale-derived/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-svelte-element/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-svelte-element/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-top-level-in-if/Child.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-top-level-in-if/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-top-level-in-if/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-top-level/Child.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-top-level/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-top-level/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-unresolved-promise/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-unresolved-promise/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-waterfall-on-init/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-waterfall-on-init/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-with-sync-derived/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-with-sync-derived/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/set-context-after-await/Child.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/set-context-after-await/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/set-context-after-await/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/set-context-after-mount/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/set-context-after-mount/main.svelte
 create mode 100644 playgrounds/sandbox/ssr-common.js

diff --git a/.changeset/eleven-weeks-dance.md b/.changeset/eleven-weeks-dance.md
new file mode 100644
index 0000000000..91245df0eb
--- /dev/null
+++ b/.changeset/eleven-weeks-dance.md
@@ -0,0 +1,5 @@
+---
+'svelte': minor
+---
+
+feat: support `await` in components when using the `experimental.async` compiler option
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c0e1d36760..046ad335f3 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -43,6 +43,23 @@ jobs:
       - run: pnpm test
         env:
           CI: true
+  TestNoAsync:
+    permissions: {}
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - uses: actions/checkout@v4
+      - uses: pnpm/action-setup@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: pnpm
+      - run: pnpm install --frozen-lockfile
+      - run: pnpm playwright install chromium
+      - run: pnpm test runtime-runes
+        env:
+          CI: true
+          SVELTE_NO_ASYNC: true
   Lint:
     permissions: {}
     runs-on: ubuntu-latest
diff --git a/documentation/docs/98-reference/.generated/client-errors.md b/documentation/docs/98-reference/.generated/client-errors.md
index 3f33e37d2e..c7d6ec8ac9 100644
--- a/documentation/docs/98-reference/.generated/client-errors.md
+++ b/documentation/docs/98-reference/.generated/client-errors.md
@@ -1,5 +1,17 @@
 <!-- This file is generated by scripts/process-messages/index.js. Do not edit! -->
 
+### async_derived_orphan
+
+```
+Cannot create a `$derived(...)` with an `await` expression outside of an effect tree
+```
+
+In Svelte there are two types of reaction — [`$derived`](/docs/svelte/$derived) and [`$effect`](/docs/svelte/$effect). Deriveds can be created anywhere, because they run _lazily_ and can be [garbage collected](https://developer.mozilla.org/en-US/docs/Glossary/Garbage_collection) if nothing references them. Effects, by contrast, keep running eagerly whenever their dependencies change, until they are destroyed.
+
+Because of this, effects can only be created inside other effects (or [effect roots](/docs/svelte/$effect#$effect.root), such as the one that is created when you first mount a component) so that Svelte knows when to destroy them.
+
+Some sleight of hand occurs when a derived contains an `await` expression: Since waiting until we read `{await getPromise()}` to call `getPromise` would be too late, we use an effect to instead call it proactively, notifying Svelte when the value is available. But since we're using an effect, we can only create asynchronous deriveds inside another effect.
+
 ### bind_invalid_checkbox_value
 
 ```
@@ -68,12 +80,28 @@ Effect cannot be created inside a `$derived` value that was not itself created i
 `%rune%` can only be used inside an effect (e.g. during component initialisation)
 ```
 
+### effect_pending_outside_reaction
+
+```
+`$effect.pending()` can only be called inside an effect or derived
+```
+
 ### effect_update_depth_exceeded
 
 ```
 Maximum update depth exceeded. This can happen when a reactive block or effect repeatedly sets a new value. Svelte limits the number of nested updates to prevent infinite loops
 ```
 
+### flush_sync_in_effect
+
+```
+Cannot use `flushSync` inside an effect
+```
+
+The `flushSync()` function can be used to flush any pending effects synchronously. It cannot be used if effects are currently being flushed — in other words, you can call it after a state change but _not_ inside an effect.
+
+This restriction only applies when using the `experimental.async` option, which will be active by default in Svelte 6.
+
 ### get_abort_signal_outside_reaction
 
 ```
@@ -116,6 +144,14 @@ Rest element properties of `$props()` such as `%property%` are readonly
 The `%rune%` rune is only available inside `.svelte` and `.svelte.js/ts` files
 ```
 
+### set_context_after_init
+
+```
+`setContext` must be called when a component first initializes, not in a subsequent effect or after an `await` expression
+```
+
+This restriction only applies when using the `experimental.async` option, which will be active by default in Svelte 6.
+
 ### state_descriptors_fixed
 
 ```
diff --git a/documentation/docs/98-reference/.generated/client-warnings.md b/documentation/docs/98-reference/.generated/client-warnings.md
index fe90b0db38..1c75faef53 100644
--- a/documentation/docs/98-reference/.generated/client-warnings.md
+++ b/documentation/docs/98-reference/.generated/client-warnings.md
@@ -34,6 +34,67 @@ function add() {
 }
 ```
 
+### await_reactivity_loss
+
+```
+Detected reactivity loss when reading `%name%`. This happens when state is read in an async function after an earlier `await`
+```
+
+Svelte's signal-based reactivity works by tracking which bits of state are read when a template or `$derived(...)` expression executes. If an expression contains an `await`, Svelte transforms it such that any state _after_ the `await` is also tracked — in other words, in a case like this...
+
+```js
+let total = $derived(await a + b);
+```
+
+...both `a` and `b` are tracked, even though `b` is only read once `a` has resolved, after the initial execution.
+
+This does _not_ apply to an `await` that is not 'visible' inside the expression. In a case like this...
+
+```js
+async function sum() {
+	return await a + b;
+}
+
+let total = $derived(await sum());
+```
+
+...`total` will depend on `a` (which is read immediately) but not `b` (which is not). The solution is to pass the values into the function:
+
+```js
+async function sum(a, b) {
+	return await a + b;
+}
+
+let total = $derived(await sum(a, b));
+```
+
+### await_waterfall
+
+```
+An async derived, `%name%` (%location%) was not read immediately after it resolved. This often indicates an unnecessary waterfall, which can slow down your app
+```
+
+In a case like this...
+
+```js
+let a = $derived(await one());
+let b = $derived(await two());
+```
+
+...the second `$derived` will not be created until the first one has resolved. Since `await two()` does not depend on the value of `a`, this delay, often described as a 'waterfall', is unnecessary.
+
+(Note that if the values of `await one()` and `await two()` subsequently change, they can do so concurrently — the waterfall only occurs when the deriveds are first created.)
+
+You can solve this by creating the promises first and _then_ awaiting them:
+
+```js
+let aPromise = $derived(one());
+let bPromise = $derived(two());
+
+let a = $derived(await aPromise);
+let b = $derived(await bPromise);
+```
+
 ### binding_property_non_reactive
 
 ```
diff --git a/documentation/docs/98-reference/.generated/compile-errors.md b/documentation/docs/98-reference/.generated/compile-errors.md
index db848a0299..20f57770d1 100644
--- a/documentation/docs/98-reference/.generated/compile-errors.md
+++ b/documentation/docs/98-reference/.generated/compile-errors.md
@@ -480,6 +480,12 @@ Expected token %token%
 Expected whitespace
 ```
 
+### experimental_async
+
+```
+Cannot use `await` in deriveds and template expressions, or at the top level of a component, unless the `experimental.async` compiler option is `true`
+```
+
 ### export_undefined
 
 ```
@@ -534,6 +540,12 @@ The arguments keyword cannot be used within the template or at the top level of
 %message%
 ```
 
+### legacy_await_invalid
+
+```
+Cannot use `await` in deriveds and template expressions, or at the top level of a component, unless in runes mode
+```
+
 ### legacy_export_invalid
 
 ```
diff --git a/documentation/docs/98-reference/.generated/shared-errors.md b/documentation/docs/98-reference/.generated/shared-errors.md
index 6c31aaafd0..de34b3f5da 100644
--- a/documentation/docs/98-reference/.generated/shared-errors.md
+++ b/documentation/docs/98-reference/.generated/shared-errors.md
@@ -1,5 +1,25 @@
 <!-- This file is generated by scripts/process-messages/index.js. Do not edit! -->
 
+### await_outside_boundary
+
+```
+Cannot await outside a `<svelte:boundary>` with a `pending` snippet
+```
+
+The `await` keyword can only appear in a `$derived(...)` or template expression, or at the top level of a component's `<script>` block, if it is inside a [`<svelte:boundary>`](/docs/svelte/svelte-boundary) that has a `pending` snippet:
+
+```svelte
+<svelte:boundary>
+	<p>{await getData()}</p>
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
+```
+
+This restriction may be lifted in a future version of Svelte.
+
 ### invalid_default_snippet
 
 ```
diff --git a/eslint.config.js b/eslint.config.js
index d7044fc9f1..41d98fa428 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -49,12 +49,13 @@ export default [
 		},
 		rules: {
 			'@typescript-eslint/await-thenable': 'error',
-			'@typescript-eslint/prefer-promise-reject-errors': 'error',
 			'@typescript-eslint/require-await': 'error',
 			'no-console': 'error',
 			'lube/svelte-naming-convention': ['error', { fixSameNames: true }],
 			// eslint isn't that well-versed with JSDoc to know that `foo: /** @type{..} */ (foo)` isn't a violation of this rule, so turn it off
 			'object-shorthand': 'off',
+			// eslint is being a dummy here too
+			'@typescript-eslint/prefer-promise-reject-errors': 'off',
 			'no-var': 'off',
 
 			// TODO: enable these rules and run `pnpm lint:fix`
diff --git a/packages/svelte/messages/client-errors/errors.md b/packages/svelte/messages/client-errors/errors.md
index 47c2038d70..2ce25dbd53 100644
--- a/packages/svelte/messages/client-errors/errors.md
+++ b/packages/svelte/messages/client-errors/errors.md
@@ -1,3 +1,13 @@
+## async_derived_orphan
+
+> Cannot create a `$derived(...)` with an `await` expression outside of an effect tree
+
+In Svelte there are two types of reaction — [`$derived`](/docs/svelte/$derived) and [`$effect`](/docs/svelte/$effect). Deriveds can be created anywhere, because they run _lazily_ and can be [garbage collected](https://developer.mozilla.org/en-US/docs/Glossary/Garbage_collection) if nothing references them. Effects, by contrast, keep running eagerly whenever their dependencies change, until they are destroyed.
+
+Because of this, effects can only be created inside other effects (or [effect roots](/docs/svelte/$effect#$effect.root), such as the one that is created when you first mount a component) so that Svelte knows when to destroy them.
+
+Some sleight of hand occurs when a derived contains an `await` expression: Since waiting until we read `{await getPromise()}` to call `getPromise` would be too late, we use an effect to instead call it proactively, notifying Svelte when the value is available. But since we're using an effect, we can only create asynchronous deriveds inside another effect.
+
 ## bind_invalid_checkbox_value
 
 > Using `bind:value` together with a checkbox input is not allowed. Use `bind:checked` instead
@@ -44,10 +54,22 @@ See the [migration guide](/docs/svelte/v5-migration-guide#Components-are-no-long
 
 > `%rune%` can only be used inside an effect (e.g. during component initialisation)
 
+## effect_pending_outside_reaction
+
+> `$effect.pending()` can only be called inside an effect or derived
+
 ## effect_update_depth_exceeded
 
 > Maximum update depth exceeded. This can happen when a reactive block or effect repeatedly sets a new value. Svelte limits the number of nested updates to prevent infinite loops
 
+## flush_sync_in_effect
+
+> Cannot use `flushSync` inside an effect
+
+The `flushSync()` function can be used to flush any pending effects synchronously. It cannot be used if effects are currently being flushed — in other words, you can call it after a state change but _not_ inside an effect.
+
+This restriction only applies when using the `experimental.async` option, which will be active by default in Svelte 6.
+
 ## get_abort_signal_outside_reaction
 
 > `getAbortSignal()` can only be called inside an effect or derived
@@ -76,6 +98,12 @@ See the [migration guide](/docs/svelte/v5-migration-guide#Components-are-no-long
 
 > The `%rune%` rune is only available inside `.svelte` and `.svelte.js/ts` files
 
+## set_context_after_init
+
+> `setContext` must be called when a component first initializes, not in a subsequent effect or after an `await` expression
+
+This restriction only applies when using the `experimental.async` option, which will be active by default in Svelte 6.
+
 ## state_descriptors_fixed
 
 > Property descriptors defined on `$state` objects must contain `value` and always be `enumerable`, `configurable` and `writable`.
diff --git a/packages/svelte/messages/client-warnings/warnings.md b/packages/svelte/messages/client-warnings/warnings.md
index f1901271d1..498c19a547 100644
--- a/packages/svelte/messages/client-warnings/warnings.md
+++ b/packages/svelte/messages/client-warnings/warnings.md
@@ -30,6 +30,63 @@ function add() {
 }
 ```
 
+## await_reactivity_loss
+
+> Detected reactivity loss when reading `%name%`. This happens when state is read in an async function after an earlier `await`
+
+Svelte's signal-based reactivity works by tracking which bits of state are read when a template or `$derived(...)` expression executes. If an expression contains an `await`, Svelte transforms it such that any state _after_ the `await` is also tracked — in other words, in a case like this...
+
+```js
+let total = $derived(await a + b);
+```
+
+...both `a` and `b` are tracked, even though `b` is only read once `a` has resolved, after the initial execution.
+
+This does _not_ apply to an `await` that is not 'visible' inside the expression. In a case like this...
+
+```js
+async function sum() {
+	return await a + b;
+}
+
+let total = $derived(await sum());
+```
+
+...`total` will depend on `a` (which is read immediately) but not `b` (which is not). The solution is to pass the values into the function:
+
+```js
+async function sum(a, b) {
+	return await a + b;
+}
+
+let total = $derived(await sum(a, b));
+```
+
+## await_waterfall
+
+> An async derived, `%name%` (%location%) was not read immediately after it resolved. This often indicates an unnecessary waterfall, which can slow down your app
+
+In a case like this...
+
+```js
+let a = $derived(await one());
+let b = $derived(await two());
+```
+
+...the second `$derived` will not be created until the first one has resolved. Since `await two()` does not depend on the value of `a`, this delay, often described as a 'waterfall', is unnecessary.
+
+(Note that if the values of `await one()` and `await two()` subsequently change, they can do so concurrently — the waterfall only occurs when the deriveds are first created.)
+
+You can solve this by creating the promises first and _then_ awaiting them:
+
+```js
+let aPromise = $derived(one());
+let bPromise = $derived(two());
+
+let a = $derived(await aPromise);
+let b = $derived(await bPromise);
+```
+
 ## binding_property_non_reactive
 
 > `%binding%` is binding to a non-reactive property
diff --git a/packages/svelte/messages/compile-errors/script.md b/packages/svelte/messages/compile-errors/script.md
index e11975aef2..2b0c5eafdf 100644
--- a/packages/svelte/messages/compile-errors/script.md
+++ b/packages/svelte/messages/compile-errors/script.md
@@ -70,6 +70,10 @@ This turned out to be buggy and unpredictable, particularly when working with de
 
 > `$effect()` can only be used as an expression statement
 
+## experimental_async
+
+> Cannot use `await` in deriveds and template expressions, or at the top level of a component, unless the `experimental.async` compiler option is `true`
+
 ## export_undefined
 
 > `%name%` is not defined
@@ -98,6 +102,10 @@ This turned out to be buggy and unpredictable, particularly when working with de
 
 > The arguments keyword cannot be used within the template or at the top level of a component
 
+## legacy_await_invalid
+
+> Cannot use `await` in deriveds and template expressions, or at the top level of a component, unless in runes mode
+
 ## legacy_export_invalid
 
 > Cannot use `export let` in runes mode — use `$props()` instead
diff --git a/packages/svelte/messages/shared-errors/errors.md b/packages/svelte/messages/shared-errors/errors.md
index 4b4d332202..f9160671d3 100644
--- a/packages/svelte/messages/shared-errors/errors.md
+++ b/packages/svelte/messages/shared-errors/errors.md
@@ -1,3 +1,21 @@
+## await_outside_boundary
+
+> Cannot await outside a `<svelte:boundary>` with a `pending` snippet
+
+The `await` keyword can only appear in a `$derived(...)` or template expression, or at the top level of a component's `<script>` block, if it is inside a [`<svelte:boundary>`](/docs/svelte/svelte-boundary) that has a `pending` snippet:
+
+```svelte
+<svelte:boundary>
+	<p>{await getData()}</p>
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
+```
+
+This restriction may be lifted in a future version of Svelte.
+
 ## invalid_default_snippet
 
 > Cannot use `{@render children(...)}` if the parent component uses `let:` directives. Consider using a named snippet instead
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 44957964b7..0dc8b20f98 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -59,6 +59,9 @@
     "./internal/disclose-version": {
       "default": "./src/internal/disclose-version.js"
     },
+    "./internal/flags/async": {
+      "default": "./src/internal/flags/async.js"
+    },
     "./internal/flags/legacy": {
       "default": "./src/internal/flags/legacy.js"
     },
diff --git a/packages/svelte/src/compiler/errors.js b/packages/svelte/src/compiler/errors.js
index e9fa33b054..599d3e8248 100644
--- a/packages/svelte/src/compiler/errors.js
+++ b/packages/svelte/src/compiler/errors.js
@@ -170,6 +170,15 @@ export function effect_invalid_placement(node) {
 	e(node, 'effect_invalid_placement', `\`$effect()\` can only be used as an expression statement\nhttps://svelte.dev/e/effect_invalid_placement`);
 }
 
+/**
+ * Cannot use `await` in deriveds and template expressions, or at the top level of a component, unless the `experimental.async` compiler option is `true`
+ * @param {null | number | NodeLike} node
+ * @returns {never}
+ */
+export function experimental_async(node) {
+	e(node, 'experimental_async', `Cannot use \`await\` in deriveds and template expressions, or at the top level of a component, unless the \`experimental.async\` compiler option is \`true\`\nhttps://svelte.dev/e/experimental_async`);
+}
+
 /**
  * `%name%` is not defined
  * @param {null | number | NodeLike} node
@@ -235,6 +244,15 @@ export function invalid_arguments_usage(node) {
 	e(node, 'invalid_arguments_usage', `The arguments keyword cannot be used within the template or at the top level of a component\nhttps://svelte.dev/e/invalid_arguments_usage`);
 }
 
+/**
+ * Cannot use `await` in deriveds and template expressions, or at the top level of a component, unless in runes mode
+ * @param {null | number | NodeLike} node
+ * @returns {never}
+ */
+export function legacy_await_invalid(node) {
+	e(node, 'legacy_await_invalid', `Cannot use \`await\` in deriveds and template expressions, or at the top level of a component, unless in runes mode\nhttps://svelte.dev/e/legacy_await_invalid`);
+}
+
 /**
  * Cannot use `export let` in runes mode — use `$props()` instead
  * @param {null | number | NodeLike} node
diff --git a/packages/svelte/src/compiler/migrate/index.js b/packages/svelte/src/compiler/migrate/index.js
index fdc9734f85..0e2fe019ed 100644
--- a/packages/svelte/src/compiler/migrate/index.js
+++ b/packages/svelte/src/compiler/migrate/index.js
@@ -145,7 +145,10 @@ export function migrate(source, { filename, use_ts } = {}) {
 			...validate_component_options({}, ''),
 			...parsed_options,
 			customElementOptions,
-			filename: filename ?? '(unknown)'
+			filename: filename ?? '(unknown)',
+			experimental: {
+				async: true
+			}
 		};
 
 		const str = new MagicString(source);
diff --git a/packages/svelte/src/compiler/phases/1-parse/state/element.js b/packages/svelte/src/compiler/phases/1-parse/state/element.js
index 6b6c9160d8..87332f647d 100644
--- a/packages/svelte/src/compiler/phases/1-parse/state/element.js
+++ b/packages/svelte/src/compiler/phases/1-parse/state/element.js
@@ -295,6 +295,8 @@ export default function element(parser) {
 		} else {
 			element.tag = get_attribute_expression(definition);
 		}
+
+		element.metadata.expression = create_expression_metadata();
 	}
 
 	if (is_top_level_script_or_style) {
diff --git a/packages/svelte/src/compiler/phases/2-analyze/index.js b/packages/svelte/src/compiler/phases/2-analyze/index.js
index d73e273ec2..258b59018a 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/index.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/index.js
@@ -1,4 +1,4 @@
-/** @import { Comment, Expression, Node, Program } from 'estree' */
+/** @import { Expression, Node, Program } from 'estree' */
 /** @import { Binding, AST, ValidatedCompileOptions, ValidatedModuleCompileOptions } from '#compiler' */
 /** @import { AnalysisState, Visitors } from './types' */
 /** @import { Analysis, ComponentAnalysis, Js, ReactiveStatement, Template } from '../types' */
@@ -22,6 +22,7 @@ import { AssignmentExpression } from './visitors/AssignmentExpression.js';
 import { AttachTag } from './visitors/AttachTag.js';
 import { Attribute } from './visitors/Attribute.js';
 import { AwaitBlock } from './visitors/AwaitBlock.js';
+import { AwaitExpression } from './visitors/AwaitExpression.js';
 import { BindDirective } from './visitors/BindDirective.js';
 import { CallExpression } from './visitors/CallExpression.js';
 import { ClassBody } from './visitors/ClassBody.js';
@@ -140,6 +141,7 @@ const visitors = {
 	AttachTag,
 	Attribute,
 	AwaitBlock,
+	AwaitExpression,
 	BindDirective,
 	CallExpression,
 	ClassBody,
@@ -211,9 +213,14 @@ function js(script, root, allow_reactive_declarations, parent) {
 		body: []
 	};
 
-	const { scope, scopes } = create_scopes(ast, root, allow_reactive_declarations, parent);
+	const { scope, scopes, has_await } = create_scopes(
+		ast,
+		root,
+		allow_reactive_declarations,
+		parent
+	);
 
-	return { ast, scope, scopes };
+	return { ast, scope, scopes, has_await };
 }
 
 /**
@@ -244,7 +251,7 @@ export function analyze_module(source, options) {
 	state.set_source(source);
 	const ast = parse(source, comments, false, false);
 
-	const { scope, scopes } = create_scopes(ast, new ScopeRoot(), false, null);
+	const { scope, scopes, has_await } = create_scopes(ast, new ScopeRoot(), false, null);
 
 	for (const [name, references] of scope.references) {
 		if (name[0] !== '$' || RESERVED.includes(name)) continue;
@@ -261,12 +268,13 @@ export function analyze_module(source, options) {
 
 	/** @type {Analysis} */
 	const analysis = {
-		module: { ast, scope, scopes },
+		module: { ast, scope, scopes, has_await },
 		name: options.filename,
 		accessors: false,
 		runes: true,
 		immutable: true,
 		tracing: false,
+		async_deriveds: new Set(),
 		comments,
 		classes: new Map()
 	};
@@ -314,7 +322,12 @@ export function analyze_component(root, source, options) {
 	const module = js(root.module, scope_root, false, null);
 	const instance = js(root.instance, scope_root, true, module.scope);
 
-	const { scope, scopes } = create_scopes(root.fragment, scope_root, false, instance.scope);
+	const { scope, scopes, has_await } = create_scopes(
+		root.fragment,
+		scope_root,
+		false,
+		instance.scope
+	);
 
 	/** @type {Template} */
 	const template = { ast: root.fragment, scope, scopes };
@@ -422,7 +435,9 @@ export function analyze_component(root, source, options) {
 
 	const component_name = get_component_name(options.filename);
 
-	const runes = options.runes ?? Array.from(module.scope.references.keys()).some(is_rune);
+	const runes =
+		options.runes ??
+		(has_await || instance.has_await || Array.from(module.scope.references.keys()).some(is_rune));
 
 	if (!runes) {
 		for (let check of synthetic_stores_legacy_check) {
@@ -512,7 +527,8 @@ export function analyze_component(root, source, options) {
 		source,
 		undefined_exports: new Map(),
 		snippet_renderers: new Map(),
-		snippets: new Set()
+		snippets: new Set(),
+		async_deriveds: new Set()
 	};
 
 	state.reset({
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/AwaitExpression.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/AwaitExpression.js
new file mode 100644
index 0000000000..af7d0307e9
--- /dev/null
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/AwaitExpression.js
@@ -0,0 +1,30 @@
+/** @import { AwaitExpression } from 'estree' */
+/** @import { Context } from '../types' */
+import * as e from '../../../errors.js';
+
+/**
+ * @param {AwaitExpression} node
+ * @param {Context} context
+ */
+export function AwaitExpression(node, context) {
+	let suspend = context.state.ast_type === 'instance' && context.state.function_depth === 1;
+
+	if (context.state.expression) {
+		context.state.expression.has_await = true;
+		suspend = true;
+	}
+
+	// disallow top-level `await` or `await` in template expressions
+	// unless a) in runes mode and b) opted into `experimental.async`
+	if (suspend) {
+		if (!context.state.options.experimental.async) {
+			e.experimental_async(node);
+		}
+
+		if (!context.state.analysis.runes) {
+			e.legacy_await_invalid(node);
+		}
+	}
+
+	context.next();
+}
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/CallExpression.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/CallExpression.js
index 33abb52cac..9b6337b9ed 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/CallExpression.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/CallExpression.js
@@ -7,6 +7,7 @@ import { get_parent } from '../../../utils/ast.js';
 import { is_pure, is_safe_identifier } from './shared/utils.js';
 import { dev, locate_node, source } from '../../../state.js';
 import * as b from '#compiler/builders';
+import { create_expression_metadata } from '../../nodes.js';
 
 /**
  * @param {CallExpression} node
@@ -163,6 +164,13 @@ export function CallExpression(node, context) {
 
 			break;
 
+		case '$effect.pending':
+			if (context.state.expression) {
+				context.state.expression.has_state = true;
+			}
+
+			break;
+
 		case '$inspect':
 			if (node.arguments.length < 1) {
 				e.rune_invalid_arguments_length(node, rune, 'one or more arguments');
@@ -227,7 +235,19 @@ export function CallExpression(node, context) {
 	}
 
 	// `$inspect(foo)` or `$derived(foo) should not trigger the `static-state-reference` warning
-	if (rune === '$inspect' || rune === '$derived') {
+	if (rune === '$derived') {
+		const expression = create_expression_metadata();
+
+		context.next({
+			...context.state,
+			function_depth: context.state.function_depth + 1,
+			expression
+		});
+
+		if (expression.has_await) {
+			context.state.analysis.async_deriveds.add(node);
+		}
+	} else if (rune === '$inspect') {
 		context.next({ ...context.state, function_depth: context.state.function_depth + 1 });
 	} else {
 		context.next();
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/StyleDirective.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/StyleDirective.js
index 7d6eb5be99..9699d3c03b 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/StyleDirective.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/StyleDirective.js
@@ -32,6 +32,7 @@ export function StyleDirective(node, context) {
 
 			node.metadata.expression.has_state ||= chunk.metadata.expression.has_state;
 			node.metadata.expression.has_call ||= chunk.metadata.expression.has_call;
+			node.metadata.expression.has_await ||= chunk.metadata.expression.has_await;
 		}
 	}
 }
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteBoundary.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteBoundary.js
index d50cb80cb8..35af96ba12 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteBoundary.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteBoundary.js
@@ -2,7 +2,7 @@
 /** @import { Context } from '../types' */
 import * as e from '../../../errors.js';
 
-const valid = ['onerror', 'failed'];
+const valid = ['onerror', 'failed', 'pending'];
 
 /**
  * @param {AST.SvelteBoundary} node
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteElement.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteElement.js
index f2e298f7ea..3f7b0ec6b8 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteElement.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteElement.js
@@ -62,5 +62,17 @@ export function SvelteElement(node, context) {
 
 	mark_subtree_dynamic(context.path);
 
-	context.next({ ...context.state, parent_element: null });
+	context.visit(node.tag, {
+		...context.state,
+		expression: node.metadata.expression
+	});
+
+	for (const attribute of node.attributes) {
+		context.visit(attribute);
+	}
+
+	context.visit(node.fragment, {
+		...context.state,
+		parent_element: null
+	});
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js b/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
index a9c0651e0f..c42d1b95d8 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
@@ -12,6 +12,7 @@ import { ArrowFunctionExpression } from './visitors/ArrowFunctionExpression.js';
 import { AssignmentExpression } from './visitors/AssignmentExpression.js';
 import { Attribute } from './visitors/Attribute.js';
 import { AwaitBlock } from './visitors/AwaitBlock.js';
+import { AwaitExpression } from './visitors/AwaitExpression.js';
 import { BinaryExpression } from './visitors/BinaryExpression.js';
 import { BindDirective } from './visitors/BindDirective.js';
 import { BlockStatement } from './visitors/BlockStatement.js';
@@ -88,6 +89,7 @@ const visitors = {
 	AssignmentExpression,
 	Attribute,
 	AwaitBlock,
+	AwaitExpression,
 	BinaryExpression,
 	BindDirective,
 	BlockStatement,
@@ -162,6 +164,7 @@ export function client_component(analysis, options) {
 		state_fields: new Map(),
 		transform: {},
 		in_constructor: false,
+		in_derived: false,
 		instance_level_snippets: [],
 		module_level_snippets: [],
 
@@ -350,7 +353,7 @@ export function client_component(analysis, options) {
 	const push_args = [b.id('$$props'), b.literal(analysis.runes)];
 	if (dev) push_args.push(b.id(analysis.name));
 
-	const component_block = b.block([
+	let component_block = b.block([
 		...store_setup,
 		...legacy_reactive_declarations,
 		...group_binding_declarations,
@@ -358,10 +361,49 @@ export function client_component(analysis, options) {
 		.../** @type {ESTree.Statement[]} */ (instance.body),
 		analysis.runes || !analysis.needs_context
 			? b.empty
-			: b.stmt(b.call('$.init', analysis.immutable ? b.true : undefined)),
-		.../** @type {ESTree.Statement[]} */ (template.body)
+			: b.stmt(b.call('$.init', analysis.immutable ? b.true : undefined))
 	]);
 
+	const should_inject_context =
+		dev ||
+		analysis.needs_context ||
+		analysis.reactive_statements.size > 0 ||
+		component_returned_object.length > 0;
+
+	let should_inject_props =
+		should_inject_context ||
+		analysis.needs_props ||
+		analysis.uses_props ||
+		analysis.uses_rest_props ||
+		analysis.uses_slots ||
+		analysis.slot_names.size > 0;
+
+	if (analysis.instance.has_await) {
+		const body = b.function_declaration(
+			b.id('$$body'),
+			should_inject_props ? [b.id('$$anchor'), b.id('$$props')] : [b.id('$$anchor')],
+			b.block([
+				b.var('$$unsuspend', b.call('$.suspend')),
+				...component_block.body,
+				b.if(b.call('$.aborted'), b.return()),
+				.../** @type {ESTree.Statement[]} */ (template.body),
+				b.stmt(b.call('$$unsuspend'))
+			]),
+			true
+		);
+
+		state.hoisted.push(body);
+
+		component_block = b.block([
+			b.var('fragment', b.call('$.comment')),
+			b.var('node', b.call('$.first_child', b.id('fragment'))),
+			b.stmt(b.call(body.id, b.id('node'), should_inject_props && b.id('$$props'))),
+			b.stmt(b.call('$.append', b.id('$$anchor'), b.id('fragment')))
+		]);
+	} else {
+		component_block.body.push(.../** @type {ESTree.Statement[]} */ (template.body));
+	}
+
 	// trick esrap into including comments
 	component_block.loc = instance.loc;
 
@@ -398,12 +440,6 @@ export function client_component(analysis, options) {
 		);
 	}
 
-	const should_inject_context =
-		dev ||
-		analysis.needs_context ||
-		analysis.reactive_statements.size > 0 ||
-		component_returned_object.length > 0;
-
 	// we want the cleanup function for the stores to run as the very last thing
 	// so that it can effectively clean up the store subscription even after the user effects runs
 	if (should_inject_context) {
@@ -469,14 +505,6 @@ export function client_component(analysis, options) {
 		component_block.body.unshift(b.const('$$slots', b.call('$.sanitize_slots', b.id('$$props'))));
 	}
 
-	let should_inject_props =
-		should_inject_context ||
-		analysis.needs_props ||
-		analysis.uses_props ||
-		analysis.uses_rest_props ||
-		analysis.uses_slots ||
-		analysis.slot_names.size > 0;
-
 	// Merge hoisted statements into module body.
 	// Ensure imports are on top, with the order preserved, then module body, then hoisted statements
 	/** @type {ESTree.ImportDeclaration[]} */
@@ -537,6 +565,10 @@ export function client_component(analysis, options) {
 		);
 	}
 
+	if (options.experimental.async) {
+		body.unshift(b.imports([], 'svelte/internal/flags/async'));
+	}
+
 	if (!analysis.runes) {
 		body.unshift(b.imports([], 'svelte/internal/flags/legacy'));
 	}
@@ -670,7 +702,9 @@ export function client_module(analysis, options) {
 		scopes: analysis.module.scopes,
 		state_fields: new Map(),
 		transform: {},
-		in_constructor: false
+		in_constructor: false,
+		in_derived: false,
+		is_instance: false
 	};
 
 	const module = /** @type {ESTree.Program} */ (
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/types.d.ts b/packages/svelte/src/compiler/phases/3-transform/client/types.d.ts
index cf5c942268..e691be169b 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/types.d.ts
+++ b/packages/svelte/src/compiler/phases/3-transform/client/types.d.ts
@@ -21,6 +21,14 @@ export interface ClientTransformState extends TransformState {
 	 */
 	readonly in_constructor: boolean;
 
+	/**
+	 * True if we're directly inside a `$derived(...)` expression (but not `$derived.by(...)`)
+	 */
+	readonly in_derived: boolean;
+
+	/** `true` if we're transforming the contents of `<script>` */
+	readonly is_instance: boolean;
+
 	readonly transform: Record<
 		string,
 		{
@@ -41,7 +49,6 @@ export interface ComponentClientTransformState extends ClientTransformState {
 	readonly options: ValidatedCompileOptions;
 	readonly hoisted: Array<Statement | ModuleDeclaration>;
 	readonly events: Set<string>;
-	readonly is_instance: boolean;
 	readonly store_to_invalidate?: string;
 
 	/** Stuff that happens before the render effect(s) */
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitExpression.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitExpression.js
new file mode 100644
index 0000000000..803d317ad4
--- /dev/null
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitExpression.js
@@ -0,0 +1,126 @@
+/** @import { AwaitExpression, Expression, Property, SpreadElement } from 'estree' */
+/** @import { Context } from '../types' */
+import { dev, is_ignored } from '../../../../state.js';
+import * as b from '../../../../utils/builders.js';
+
+/**
+ * @param {AwaitExpression} node
+ * @param {Context} context
+ */
+export function AwaitExpression(node, context) {
+	const argument = /** @type {Expression} */ (context.visit(node.argument));
+
+	const tla = context.state.is_instance && context.state.scope.function_depth === 1;
+
+	// preserve context for
+	//   a) top-level await and
+	//   b) awaits that precede other expressions in template or `$derived(...)`
+	if (tla || (is_reactive_expression(context) && !is_last_evaluated_expression(context, node))) {
+		return b.call(b.await(b.call('$.save', argument)));
+	}
+
+	// in dev, note which values are read inside a reactive expression,
+	// but don't track them
+	else if (dev && !is_ignored(node, 'await_reactivity_loss')) {
+		return b.call(b.await(b.call('$.track_reactivity_loss', argument)));
+	}
+
+	return argument === node.argument ? node : { ...node, argument };
+}
+
+/**
+ * @param {Context} context
+ */
+function is_reactive_expression(context) {
+	if (context.state.in_derived) {
+		return true;
+	}
+
+	let i = context.path.length;
+
+	while (i--) {
+		const parent = context.path[i];
+
+		if (
+			parent.type === 'ArrowFunctionExpression' ||
+			parent.type === 'FunctionExpression' ||
+			parent.type === 'FunctionDeclaration'
+		) {
+			return false;
+		}
+
+		// @ts-expect-error we could probably use a neater/more robust mechanism
+		if (parent.metadata) {
+			return true;
+		}
+	}
+
+	return false;
+}
+
+/**
+ * @param {Context} context
+ * @param {Expression | SpreadElement | Property} node
+ */
+function is_last_evaluated_expression(context, node) {
+	let i = context.path.length;
+
+	while (i--) {
+		const parent = /** @type {Expression | Property | SpreadElement} */ (context.path[i]);
+
+		// @ts-expect-error we could probably use a neater/more robust mechanism
+		if (parent.metadata) {
+			return true;
+		}
+
+		switch (parent.type) {
+			case 'ArrayExpression':
+				if (node !== parent.elements.at(-1)) return false;
+				break;
+
+			case 'AssignmentExpression':
+			case 'BinaryExpression':
+			case 'LogicalExpression':
+				if (node === parent.left) return false;
+				break;
+
+			case 'CallExpression':
+			case 'NewExpression':
+				if (node !== parent.arguments.at(-1)) return false;
+				break;
+
+			case 'ConditionalExpression':
+				if (node === parent.test) return false;
+				break;
+
+			case 'MemberExpression':
+				if (parent.computed && node === parent.object) return false;
+				break;
+
+			case 'ObjectExpression':
+				if (node !== parent.properties.at(-1)) return false;
+				break;
+
+			case 'Property':
+				if (node === parent.key) return false;
+				break;
+
+			case 'SequenceExpression':
+				if (node !== parent.expressions.at(-1)) return false;
+				break;
+
+			case 'TaggedTemplateExpression':
+				if (node !== parent.quasi.expressions.at(-1)) return false;
+				break;
+
+			case 'TemplateLiteral':
+				if (node !== parent.expressions.at(-1)) return false;
+				break;
+
+			default:
+				return false;
+		}
+
+		node = parent;
+	}
+}
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/CallExpression.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/CallExpression.js
index 665be9e23b..3e2f1414e6 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/CallExpression.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/CallExpression.js
@@ -44,10 +44,11 @@ export function CallExpression(node, context) {
 
 		case '$derived':
 		case '$derived.by': {
-			let fn = /** @type {Expression} */ (context.visit(node.arguments[0]));
-			if (rune === '$derived') fn = b.thunk(fn);
+			let fn = /** @type {Expression} */ (
+				context.visit(node.arguments[0], { ...context.state, in_derived: rune === '$derived' })
+			);
 
-			return b.call('$.derived', fn);
+			return b.call('$.derived', rune === '$derived' ? b.thunk(fn) : fn);
 		}
 
 		case '$state.snapshot':
@@ -63,6 +64,9 @@ export function CallExpression(node, context) {
 				.../** @type {Expression[]} */ (node.arguments.map((arg) => context.visit(arg)))
 			);
 
+		case '$effect.pending':
+			return b.call('$.pending');
+
 		case '$inspect':
 		case '$inspect().with':
 			return transform_inspect_rune(node, context);
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js
index 353927b865..225a4f617c 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js
@@ -312,11 +312,9 @@ export function EachBlock(node, context) {
 		declarations.push(b.let(node.index, index));
 	}
 
-	if (dev && node.metadata.keyed) {
-		context.state.init.push(
-			b.stmt(b.call('$.validate_each_keys', b.thunk(collection), key_function))
-		);
-	}
+	const { has_await } = node.metadata.expression;
+	const get_collection = b.thunk(collection, has_await);
+	const thunk = has_await ? b.thunk(b.call('$.get', b.id('$$collection'))) : get_collection;
 
 	const render_args = [b.id('$$anchor'), item];
 	if (uses_index || collection_id) render_args.push(index);
@@ -326,7 +324,7 @@ export function EachBlock(node, context) {
 	const args = [
 		context.state.node,
 		b.literal(flags),
-		b.thunk(collection),
+		thunk,
 		key_function,
 		b.arrow(render_args, b.block(declarations.concat(block.body)))
 	];
@@ -337,7 +335,26 @@ export function EachBlock(node, context) {
 		);
 	}
 
-	context.state.init.push(add_svelte_meta(b.call('$.each', ...args), node, 'each'));
+	const statements = [add_svelte_meta(b.call('$.each', ...args), node, 'each')];
+
+	if (dev && node.metadata.keyed) {
+		statements.unshift(b.stmt(b.call('$.validate_each_keys', thunk, key_function)));
+	}
+
+	if (has_await) {
+		context.state.init.push(
+			b.stmt(
+				b.call(
+					'$.async',
+					context.state.node,
+					b.array([get_collection]),
+					b.arrow([context.state.node, b.id('$$collection')], b.block(statements))
+				)
+			)
+		);
+	} else {
+		context.state.init.push(...statements);
+	}
 }
 
 /**
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/Fragment.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/Fragment.js
index 7cd2bd90ed..0b10c02ffb 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/Fragment.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/Fragment.js
@@ -47,9 +47,7 @@ export function Fragment(node, context) {
 	const is_single_element = trimmed.length === 1 && trimmed[0].type === 'RegularElement';
 	const is_single_child_not_needing_template =
 		trimmed.length === 1 &&
-		(trimmed[0].type === 'SvelteFragment' ||
-			trimmed[0].type === 'TitleElement' ||
-			(trimmed[0].type === 'IfBlock' && trimmed[0].elseif));
+		(trimmed[0].type === 'SvelteFragment' || trimmed[0].type === 'TitleElement');
 
 	const template_name = context.state.scope.root.unique('root'); // TODO infer name from parent
 
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/FunctionDeclaration.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/FunctionDeclaration.js
index 5dc8fa5cf9..cd299a710b 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/FunctionDeclaration.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/FunctionDeclaration.js
@@ -8,7 +8,7 @@ import * as b from '#compiler/builders';
  * @param {ComponentContext} context
  */
 export function FunctionDeclaration(node, context) {
-	const state = { ...context.state, in_constructor: false };
+	const state = { ...context.state, in_constructor: false, in_derived: false };
 
 	if (node.metadata?.hoisted === true) {
 		const params = build_hoisted_params(node, context);
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/HtmlTag.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/HtmlTag.js
index fb59967996..64e84ef2ff 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/HtmlTag.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/HtmlTag.js
@@ -11,7 +11,9 @@ import { build_expression } from './shared/utils.js';
 export function HtmlTag(node, context) {
 	context.state.template.push_comment();
 
+	const { has_await } = node.metadata.expression;
 	const expression = build_expression(context, node.expression, node.metadata.expression);
+	const html = has_await ? b.call('$.get', b.id('$$html')) : expression;
 
 	const is_svg = context.state.metadata.namespace === 'svg';
 	const is_mathml = context.state.metadata.namespace === 'mathml';
@@ -20,7 +22,7 @@ export function HtmlTag(node, context) {
 		b.call(
 			'$.html',
 			context.state.node,
-			b.thunk(expression),
+			b.thunk(html),
 			is_svg && b.true,
 			is_mathml && b.true,
 			is_ignored(node, 'hydration_html_changed') && b.true
@@ -28,5 +30,18 @@ export function HtmlTag(node, context) {
 	);
 
 	// push into init, so that bindings run afterwards, which might trigger another run and override hydration
-	context.state.init.push(statement);
+	if (node.metadata.expression.has_await) {
+		context.state.init.push(
+			b.stmt(
+				b.call(
+					'$.async',
+					context.state.node,
+					b.array([b.thunk(expression, true)]),
+					b.arrow([context.state.node, b.id('$$html')], b.block([statement]))
+				)
+			)
+		);
+	} else {
+		context.state.init.push(statement);
+	}
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/IfBlock.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/IfBlock.js
index cfd2bb7b09..3dd36b180b 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/IfBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/IfBlock.js
@@ -13,37 +13,32 @@ export function IfBlock(node, context) {
 	const statements = [];
 
 	const consequent = /** @type {BlockStatement} */ (context.visit(node.consequent));
-	const consequent_id = context.state.scope.generate('consequent');
+	const consequent_id = b.id(context.state.scope.generate('consequent'));
 
-	statements.push(b.var(b.id(consequent_id), b.arrow([b.id('$$anchor')], consequent)));
+	statements.push(b.var(consequent_id, b.arrow([b.id('$$anchor')], consequent)));
 
 	let alternate_id;
 
 	if (node.alternate) {
-		alternate_id = context.state.scope.generate('alternate');
 		const alternate = /** @type {BlockStatement} */ (context.visit(node.alternate));
-		const nodes = node.alternate.nodes;
-
-		let alternate_args = [b.id('$$anchor')];
-		if (nodes.length === 1 && nodes[0].type === 'IfBlock' && nodes[0].elseif) {
-			alternate_args.push(b.id('$$elseif'));
-		}
-
-		statements.push(b.var(b.id(alternate_id), b.arrow(alternate_args, alternate)));
+		alternate_id = b.id(context.state.scope.generate('alternate'));
+		statements.push(b.var(alternate_id, b.arrow([b.id('$$anchor')], alternate)));
 	}
 
-	const test = build_expression(context, node.test, node.metadata.expression);
+	const { has_await } = node.metadata.expression;
+	const expression = build_expression(context, node.test, node.metadata.expression);
+	const test = has_await ? b.call('$.get', b.id('$$condition')) : expression;
 
 	/** @type {Expression[]} */
 	const args = [
-		node.elseif ? b.id('$$anchor') : context.state.node,
+		context.state.node,
 		b.arrow(
 			[b.id('$$render')],
 			b.block([
 				b.if(
 					test,
-					b.stmt(b.call(b.id('$$render'), b.id(consequent_id))),
-					alternate_id ? b.stmt(b.call(b.id('$$render'), b.id(alternate_id), b.false)) : undefined
+					b.stmt(b.call('$$render', consequent_id)),
+					alternate_id && b.stmt(b.call('$$render', alternate_id, b.literal(false)))
 				)
 			])
 		)
@@ -71,10 +66,23 @@ export function IfBlock(node, context) {
 		// ...even though they're logically equivalent. In the first case, the
 		// transition will only play when `y` changes, but in the second it
 		// should play when `x` or `y` change — both are considered 'local'
-		args.push(b.id('$$elseif'));
+		args.push(b.true);
 	}
 
 	statements.push(add_svelte_meta(b.call('$.if', ...args), node, 'if'));
 
-	context.state.init.push(b.block(statements));
+	if (has_await) {
+		context.state.init.push(
+			b.stmt(
+				b.call(
+					'$.async',
+					context.state.node,
+					b.array([b.thunk(expression, true)]),
+					b.arrow([context.state.node, b.id('$$condition')], b.block(statements))
+				)
+			)
+		);
+	} else {
+		context.state.init.push(b.block(statements));
+	}
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/KeyBlock.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/KeyBlock.js
index 3add1fbe93..52850090e3 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/KeyBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/KeyBlock.js
@@ -11,14 +11,28 @@ import { build_expression, add_svelte_meta } from './shared/utils.js';
 export function KeyBlock(node, context) {
 	context.state.template.push_comment();
 
-	const key = build_expression(context, node.expression, node.metadata.expression);
+	const { has_await } = node.metadata.expression;
+
+	const expression = build_expression(context, node.expression, node.metadata.expression);
+	const key = b.thunk(has_await ? b.call('$.get', b.id('$$key')) : expression);
 	const body = /** @type {Expression} */ (context.visit(node.fragment));
 
-	context.state.init.push(
-		add_svelte_meta(
-			b.call('$.key', context.state.node, b.thunk(key), b.arrow([b.id('$$anchor')], body)),
-			node,
-			'key'
-		)
+	let statement = add_svelte_meta(
+		b.call('$.key', context.state.node, key, b.arrow([b.id('$$anchor')], body)),
+		node,
+		'key'
 	);
+
+	if (has_await) {
+		statement = b.stmt(
+			b.call(
+				'$.async',
+				context.state.node,
+				b.array([b.thunk(expression, true)]),
+				b.arrow([context.state.node, b.id('$$key')], b.block([statement]))
+			)
+		);
+	}
+
+	context.state.init.push(statement);
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js
index eed2a75506..4296aa959e 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js
@@ -253,7 +253,10 @@ export function RegularElement(node, context) {
 				const { value, has_state } = build_attribute_value(
 					attribute.value,
 					context,
-					(value, metadata) => (metadata.has_call ? context.state.memoizer.add(value) : value)
+					(value, metadata) =>
+						metadata.has_call || metadata.has_await
+							? context.state.memoizer.add(value, metadata.has_await)
+							: value
 				);
 
 				const update = build_element_attribute_update(node, node_id, name, value, attributes);
@@ -319,7 +322,11 @@ export function RegularElement(node, context) {
 	// (e.g. `<span>{location}</span>`), set `textContent` programmatically
 	const use_text_content =
 		trimmed.every((node) => node.type === 'Text' || node.type === 'ExpressionTag') &&
-		trimmed.every((node) => node.type === 'Text' || !node.metadata.expression.has_state) &&
+		trimmed.every(
+			(node) =>
+				node.type === 'Text' ||
+				(!node.metadata.expression.has_state && !node.metadata.expression.has_await)
+		) &&
 		trimmed.some((node) => node.type === 'ExpressionTag');
 
 	if (use_text_content) {
@@ -465,16 +472,18 @@ export function build_class_directives_object(
 ) {
 	let properties = [];
 	let has_call_or_state = false;
+	let has_await = false;
 
 	for (const d of class_directives) {
 		const expression = /** @type Expression */ (context.visit(d.expression));
 		properties.push(b.init(d.name, expression));
 		has_call_or_state ||= d.metadata.expression.has_call || d.metadata.expression.has_state;
+		has_await ||= d.metadata.expression.has_await;
 	}
 
 	const directives = b.object(properties);
 
-	return has_call_or_state ? memoizer.add(directives) : directives;
+	return has_call_or_state || has_await ? memoizer.add(directives, has_await) : directives;
 }
 
 /**
@@ -492,6 +501,7 @@ export function build_style_directives_object(
 	const important = b.object([]);
 
 	let has_call_or_state = false;
+	let has_await = false;
 
 	for (const d of style_directives) {
 		const expression =
@@ -503,11 +513,12 @@ export function build_style_directives_object(
 		object.properties.push(b.init(d.name, expression));
 
 		has_call_or_state ||= d.metadata.expression.has_call || d.metadata.expression.has_state;
+		has_await ||= d.metadata.expression.has_await;
 	}
 
 	const directives = important.properties.length ? b.array([normal, important]) : normal;
 
-	return has_call_or_state ? memoizer.add(directives) : directives;
+	return has_call_or_state || has_await ? memoizer.add(directives, has_await) : directives;
 }
 
 /**
@@ -629,7 +640,7 @@ function build_element_special_value_attribute(element, node_id, attribute, cont
 		element === 'select' && attribute.value !== true && !is_text_attribute(attribute);
 
 	const { value, has_state } = build_attribute_value(attribute.value, context, (value, metadata) =>
-		metadata.has_call ? state.memoizer.add(value) : value
+		metadata.has_call || metadata.has_await ? state.memoizer.add(value, metadata.has_await) : value
 	);
 
 	const evaluated = context.state.scope.evaluate(value);
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/RenderTag.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/RenderTag.js
index 7f1a4ae7ba..b7a6e65557 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/RenderTag.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/RenderTag.js
@@ -1,9 +1,9 @@
-/** @import { Expression } from 'estree' */
+/** @import { Expression, Statement } from 'estree' */
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext } from '../types' */
 import { unwrap_optional } from '../../../../utils/ast.js';
 import * as b from '#compiler/builders';
-import { add_svelte_meta, build_expression } from './shared/utils.js';
+import { add_svelte_meta, build_expression, Memoizer } from './shared/utils.js';
 
 /**
  * @param {AST.RenderTag} node
@@ -12,32 +12,34 @@ import { add_svelte_meta, build_expression } from './shared/utils.js';
 export function RenderTag(node, context) {
 	context.state.template.push_comment();
 
-	const expression = unwrap_optional(node.expression);
-
-	const callee = expression.callee;
-	const raw_args = expression.arguments;
+	const call = unwrap_optional(node.expression);
 
 	/** @type {Expression[]} */
 	let args = [];
-	for (let i = 0; i < raw_args.length; i++) {
-		let thunk = b.thunk(
-			build_expression(context, /** @type {Expression} */ (raw_args[i]), node.metadata.arguments[i])
-		);
 
-		const { has_call } = node.metadata.arguments[i];
+	const memoizer = new Memoizer();
+
+	for (let i = 0; i < call.arguments.length; i++) {
+		const arg = /** @type {Expression} */ (call.arguments[i]);
+		const metadata = node.metadata.arguments[i];
 
-		if (has_call) {
-			const id = b.id(context.state.scope.generate('render_arg'));
-			context.state.init.push(b.var(id, b.call('$.derived_safe_equal', thunk)));
-			args.push(b.thunk(b.call('$.get', id)));
-		} else {
-			args.push(thunk);
+		let expression = build_expression(context, arg, metadata);
+
+		if (metadata.has_await || metadata.has_call) {
+			expression = b.call('$.get', memoizer.add(expression, metadata.has_await));
 		}
+
+		args.push(b.thunk(expression));
 	}
 
+	memoizer.apply();
+
+	/** @type {Statement[]} */
+	const statements = memoizer.deriveds(context.state.analysis.runes);
+
 	let snippet_function = build_expression(
 		context,
-		/** @type {Expression} */ (callee),
+		/** @type {Expression} */ (call.callee),
 		node.metadata.expression
 	);
 
@@ -47,7 +49,7 @@ export function RenderTag(node, context) {
 			snippet_function = b.logical('??', snippet_function, b.id('$.noop'));
 		}
 
-		context.state.init.push(
+		statements.push(
 			add_svelte_meta(
 				b.call('$.snippet', context.state.node, b.thunk(snippet_function), ...args),
 				node,
@@ -55,7 +57,7 @@ export function RenderTag(node, context) {
 			)
 		);
 	} else {
-		context.state.init.push(
+		statements.push(
 			add_svelte_meta(
 				(node.expression.type === 'CallExpression' ? b.call : b.maybe_call)(
 					snippet_function,
@@ -67,4 +69,21 @@ export function RenderTag(node, context) {
 			)
 		);
 	}
+
+	const async_values = memoizer.async_values();
+
+	if (async_values) {
+		context.state.init.push(
+			b.stmt(
+				b.call(
+					'$.async',
+					context.state.node,
+					memoizer.async_values(),
+					b.arrow([context.state.node, ...memoizer.async_ids()], b.block(statements))
+				)
+			)
+		);
+	} else {
+		context.state.init.push(statements.length === 1 ? statements[0] : b.block(statements));
+	}
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/SlotElement.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/SlotElement.js
index e37cdb2bea..a5c0974738 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/SlotElement.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/SlotElement.js
@@ -33,7 +33,10 @@ export function SlotElement(node, context) {
 			const { value, has_state } = build_attribute_value(
 				attribute.value,
 				context,
-				(value, metadata) => (metadata.has_call ? b.call('$.get', memoizer.add(value)) : value)
+				(value, metadata) =>
+					metadata.has_call || metadata.has_await
+						? b.call('$.get', memoizer.add(value, metadata.has_await))
+						: value
 			);
 
 			if (attribute.name === 'name') {
@@ -70,5 +73,20 @@ export function SlotElement(node, context) {
 		b.stmt(b.call('$.slot', context.state.node, b.id('$$props'), name, props_expression, fallback))
 	);
 
-	context.state.init.push(statements.length === 1 ? statements[0] : b.block(statements));
+	const async_values = memoizer.async_values();
+
+	if (async_values) {
+		context.state.init.push(
+			b.stmt(
+				b.call(
+					'$.async',
+					context.state.node,
+					async_values,
+					b.arrow([context.state.node, ...memoizer.async_ids()], b.block(statements))
+				)
+			)
+		);
+	} else {
+		context.state.init.push(statements.length === 1 ? statements[0] : b.block(statements));
+	}
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteBoundary.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteBoundary.js
index 1480648ce5..d37b990440 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteBoundary.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteBoundary.js
@@ -1,4 +1,4 @@
-/** @import { BlockStatement, Statement, Expression, FunctionDeclaration, VariableDeclaration, ArrowFunctionExpression } from 'estree' */
+/** @import { BlockStatement, Statement, Expression, VariableDeclaration } from 'estree' */
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext } from '../types' */
 import { dev } from '../../../../state.js';
@@ -71,7 +71,7 @@ export function SvelteBoundary(node, context) {
 
 			hoisted.push(snippet);
 
-			if (child.expression.name === 'failed') {
+			if (['failed', 'pending'].includes(child.expression.name)) {
 				props.properties.push(b.prop('init', child.expression, child.expression));
 			}
 
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteElement.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteElement.js
index 6af5f5770e..2062519bb6 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteElement.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteElement.js
@@ -32,7 +32,7 @@ export function SvelteElement(node, context) {
 	const style_directives = [];
 
 	/** @type {ExpressionStatement[]} */
-	const lets = [];
+	const statements = [];
 
 	// Create a temporary context which picks up the init/update statements.
 	// They'll then be added to the function parameter of $.element
@@ -64,7 +64,7 @@ export function SvelteElement(node, context) {
 		} else if (attribute.type === 'StyleDirective') {
 			style_directives.push(attribute);
 		} else if (attribute.type === 'LetDirective') {
-			lets.push(/** @type {ExpressionStatement} */ (context.visit(attribute)));
+			statements.push(/** @type {ExpressionStatement} */ (context.visit(attribute)));
 		} else if (attribute.type === 'OnDirective') {
 			const handler = /** @type {Expression} */ (context.visit(attribute, inner_context.state));
 			inner_context.state.after_update.push(b.stmt(handler));
@@ -73,9 +73,6 @@ export function SvelteElement(node, context) {
 		}
 	}
 
-	// Let bindings first, they can be used on attributes
-	context.state.init.push(...lets); // create computeds in the outer context; the dynamic element is the single child of this slot
-
 	if (
 		attributes.length === 1 &&
 		attributes[0].type === 'Attribute' &&
@@ -96,14 +93,10 @@ export function SvelteElement(node, context) {
 		);
 	}
 
-	const get_tag = b.thunk(/** @type {Expression} */ (context.visit(node.tag)));
+	const { has_await } = node.metadata.expression;
 
-	if (dev) {
-		if (node.fragment.nodes.length > 0) {
-			context.state.init.push(b.stmt(b.call('$.validate_void_dynamic_element', get_tag)));
-		}
-		context.state.init.push(b.stmt(b.call('$.validate_dynamic_element_tag', get_tag)));
-	}
+	const expression = /** @type {Expression} */ (context.visit(node.tag));
+	const get_tag = b.thunk(has_await ? b.call('$.get', b.id('$$tag')) : expression);
 
 	/** @type {Statement[]} */
 	const inner = inner_context.state.init;
@@ -123,9 +116,16 @@ export function SvelteElement(node, context) {
 		).body
 	);
 
+	if (dev) {
+		if (node.fragment.nodes.length > 0) {
+			statements.push(b.stmt(b.call('$.validate_void_dynamic_element', get_tag)));
+		}
+		statements.push(b.stmt(b.call('$.validate_dynamic_element_tag', get_tag)));
+	}
+
 	const location = dev && locator(node.start);
 
-	context.state.init.push(
+	statements.push(
 		b.stmt(
 			b.call(
 				'$.element',
@@ -138,4 +138,19 @@ export function SvelteElement(node, context) {
 			)
 		)
 	);
+
+	if (has_await) {
+		context.state.init.push(
+			b.stmt(
+				b.call(
+					'$.async',
+					context.state.node,
+					b.array([b.thunk(expression, true)]),
+					b.arrow([context.state.node, b.id('$$tag')], b.block(statements))
+				)
+			)
+		);
+	} else {
+		context.state.init.push(statements.length === 1 ? statements[0] : b.block(statements));
+	}
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
index 53f18d42e4..19a7de5715 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
@@ -1,7 +1,7 @@
 /** @import { CallExpression, Expression, Identifier, Literal, VariableDeclaration, VariableDeclarator } from 'estree' */
 /** @import { Binding } from '#compiler' */
-/** @import { ComponentClientTransformState, ComponentContext } from '../types' */
-import { dev } from '../../../../state.js';
+/** @import { ComponentContext } from '../types' */
+import { dev, is_ignored, locate_node } from '../../../../state.js';
 import { extract_paths } from '../../../../utils/ast.js';
 import * as b from '#compiler/builders';
 import * as assert from '../../../../utils/assert.js';
@@ -20,7 +20,7 @@ export function VariableDeclaration(node, context) {
 
 	if (context.state.analysis.runes) {
 		for (const declarator of node.declarations) {
-			const init = declarator.init;
+			const init = /** @type {Expression} */ (declarator.init);
 			const rune = get_rune(init, context.state.scope);
 
 			if (
@@ -194,16 +194,38 @@ export function VariableDeclaration(node, context) {
 			}
 
 			if (rune === '$derived' || rune === '$derived.by') {
+				const is_async = context.state.analysis.async_deriveds.has(
+					/** @type {CallExpression} */ (init)
+				);
+
 				if (declarator.id.type === 'Identifier') {
-					let expression = /** @type {Expression} */ (context.visit(value));
-					if (rune === '$derived') expression = b.thunk(expression);
-					const call = b.call('$.derived', expression);
-					declarations.push(
-						b.declarator(
-							declarator.id,
-							dev ? b.call('$.tag', call, b.literal(declarator.id.name)) : call
-						)
+					let expression = /** @type {Expression} */ (
+						context.visit(value, {
+							...context.state,
+							in_derived: rune === '$derived'
+						})
 					);
+
+					if (is_async) {
+						const location = dev && !is_ignored(init, 'await_waterfall') && locate_node(init);
+						let call = b.call(
+							'$.async_derived',
+							b.thunk(expression, true),
+							location ? b.literal(location) : undefined
+						);
+
+						call = b.call(b.await(b.call('$.save', call)));
+						if (dev) call = b.call('$.tag', call, b.literal(declarator.id.name));
+
+						declarations.push(b.declarator(declarator.id, call));
+					} else {
+						if (rune === '$derived') expression = b.thunk(expression);
+
+						let call = b.call('$.derived', expression);
+						if (dev) call = b.call('$.tag', call, b.literal(declarator.id.name));
+
+						declarations.push(b.declarator(declarator.id, call));
+					}
 				} else {
 					const init = /** @type {CallExpression} */ (declarator.init);
 
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js
index 6b52db55ba..7feeebdbbc 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js
@@ -129,11 +129,12 @@ export function build_component(node, component_name, context) {
 			(events[attribute.name] ||= []).push(handler);
 		} else if (attribute.type === 'SpreadAttribute') {
 			const expression = /** @type {Expression} */ (context.visit(attribute));
+
 			if (attribute.metadata.expression.has_state) {
 				props_and_spreads.push(
 					b.thunk(
-						attribute.metadata.expression.has_call
-							? b.call('$.get', memoizer.add(expression))
+						attribute.metadata.expression.has_await || attribute.metadata.expression.has_call
+							? b.call('$.get', memoizer.add(expression, attribute.metadata.expression.has_await))
 							: expression
 					)
 				);
@@ -147,7 +148,9 @@ export function build_component(node, component_name, context) {
 						attribute.name,
 						build_attribute_value(attribute.value, context, (value, metadata) => {
 							// TODO put the derived in the local block
-							return metadata.has_call ? b.call('$.get', memoizer.add(value)) : value;
+							return metadata.has_call || metadata.has_await
+								? b.call('$.get', memoizer.add(value, metadata.has_await))
+								: value;
 						}).value
 					)
 				);
@@ -166,20 +169,24 @@ export function build_component(node, component_name, context) {
 				attribute.value,
 				context,
 				(value, metadata) => {
-					if (!metadata.has_state) return value;
+					if (!metadata.has_state && !metadata.has_await) return value;
 
 					// When we have a non-simple computation, anything other than an Identifier or Member expression,
 					// then there's a good chance it needs to be memoized to avoid over-firing when read within the
 					// child component (e.g. `active={i === index}`)
-					const should_wrap_in_derived = get_attribute_chunks(attribute.value).some((n) => {
-						return (
-							n.type === 'ExpressionTag' &&
-							n.expression.type !== 'Identifier' &&
-							n.expression.type !== 'MemberExpression'
-						);
-					});
-
-					return should_wrap_in_derived ? b.call('$.get', memoizer.add(value)) : value;
+					const should_wrap_in_derived =
+						metadata.has_await ||
+						get_attribute_chunks(attribute.value).some((n) => {
+							return (
+								n.type === 'ExpressionTag' &&
+								n.expression.type !== 'Identifier' &&
+								n.expression.type !== 'MemberExpression'
+							);
+						});
+
+					return should_wrap_in_derived
+						? b.call('$.get', memoizer.add(value, metadata.has_await))
+						: value;
 				}
 			);
 
@@ -489,5 +496,18 @@ export function build_component(node, component_name, context) {
 
 	memoizer.apply();
 
+	const async_values = memoizer.async_values();
+
+	if (async_values) {
+		return b.stmt(
+			b.call(
+				'$.async',
+				anchor,
+				async_values,
+				b.arrow([b.id('$$anchor'), ...memoizer.async_ids()], b.block(statements))
+			)
+		);
+	}
+
 	return statements.length > 1 ? b.block(statements) : statements[0];
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/element.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/element.js
index d119b0457b..9143a57025 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/element.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/element.js
@@ -1,4 +1,4 @@
-/** @import { ArrayExpression, Expression, Identifier, ObjectExpression } from 'estree' */
+/** @import { Expression, Identifier, ObjectExpression } from 'estree' */
 /** @import { AST, ExpressionMetadata } from '#compiler' */
 /** @import { ComponentContext } from '../../types' */
 import { escape_html } from '../../../../../../escaping.js';
@@ -33,7 +33,7 @@ export function build_attribute_effect(
 	for (const attribute of attributes) {
 		if (attribute.type === 'Attribute') {
 			const { value } = build_attribute_value(attribute.value, context, (value, metadata) =>
-				metadata.has_call ? memoizer.add(value) : value
+				metadata.has_call || metadata.has_await ? memoizer.add(value, metadata.has_await) : value
 			);
 
 			if (
@@ -50,8 +50,8 @@ export function build_attribute_effect(
 		} else {
 			let value = /** @type {Expression} */ (context.visit(attribute));
 
-			if (attribute.metadata.expression.has_call) {
-				value = memoizer.add(value);
+			if (attribute.metadata.expression.has_call || attribute.metadata.expression.has_await) {
+				value = memoizer.add(value, attribute.metadata.expression.has_await);
 			}
 
 			values.push(b.spread(value));
@@ -87,6 +87,7 @@ export function build_attribute_effect(
 				element_id,
 				b.arrow(ids, b.object(values)),
 				memoizer.sync_values(),
+				memoizer.async_values(),
 				element.metadata.scoped &&
 					context.state.analysis.css.hash !== '' &&
 					b.literal(context.state.analysis.css.hash),
@@ -118,7 +119,7 @@ export function build_attribute_value(value, context, memoize = (value) => value
 
 		return {
 			value: memoize(expression, chunk.metadata.expression),
-			has_state: chunk.metadata.expression.has_state
+			has_state: chunk.metadata.expression.has_state || chunk.metadata.expression.has_await
 		};
 	}
 
@@ -151,7 +152,9 @@ export function build_set_class(element, node_id, attribute, class_directives, c
 			value = b.call('$.clsx', value);
 		}
 
-		return metadata.has_call ? context.state.memoizer.add(value) : value;
+		return metadata.has_call || metadata.has_await
+			? context.state.memoizer.add(value, metadata.has_await)
+			: value;
 	});
 
 	/** @type {Identifier | undefined} */
@@ -165,7 +168,9 @@ export function build_set_class(element, node_id, attribute, class_directives, c
 
 	if (class_directives.length) {
 		next = build_class_directives_object(class_directives, context);
-		has_state ||= class_directives.some((d) => d.metadata.expression.has_state);
+		has_state ||= class_directives.some(
+			(d) => d.metadata.expression.has_state || d.metadata.expression.has_await
+		);
 
 		if (has_state) {
 			previous_id = b.id(context.state.scope.generate('classes'));
@@ -219,7 +224,7 @@ export function build_set_class(element, node_id, attribute, class_directives, c
  */
 export function build_set_style(node_id, attribute, style_directives, context) {
 	let { value, has_state } = build_attribute_value(attribute.value, context, (value, metadata) =>
-		metadata.has_call ? context.state.memoizer.add(value) : value
+		metadata.has_call ? context.state.memoizer.add(value, metadata.has_await) : value
 	);
 
 	/** @type {Identifier | undefined} */
@@ -233,7 +238,9 @@ export function build_set_style(node_id, attribute, style_directives, context) {
 
 	if (style_directives.length) {
 		next = build_style_directives_object(style_directives, context);
-		has_state ||= style_directives.some((d) => d.metadata.expression.has_state);
+		has_state ||= style_directives.some(
+			(d) => d.metadata.expression.has_state || d.metadata.expression.has_await
+		);
 
 		if (has_state) {
 			previous_id = b.id(context.state.scope.generate('styles'));
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/function.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/function.js
index a0e9d0bf5e..691ac0b01e 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/function.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/function.js
@@ -9,7 +9,7 @@ import { build_hoisted_params } from '../../utils.js';
 export const visit_function = (node, context) => {
 	const metadata = node.metadata;
 
-	let state = { ...context.state, in_constructor: false };
+	let state = { ...context.state, in_constructor: false, in_derived: false };
 
 	if (node.type === 'FunctionExpression') {
 		const parent = /** @type {Node} */ (context.path.at(-1));
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
index eed806339d..014547cf2d 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js
@@ -18,19 +18,23 @@ export class Memoizer {
 	/** @type {Array<{ id: Identifier, expression: Expression }>} */
 	#sync = [];
 
+	/** @type {Array<{ id: Identifier, expression: Expression }>} */
+	#async = [];
+
 	/**
 	 * @param {Expression} expression
+	 * @param {boolean} has_await
 	 */
-	add(expression) {
+	add(expression, has_await) {
 		const id = b.id('#'); // filled in later
 
-		this.#sync.push({ id, expression });
+		(has_await ? this.#async : this.#sync).push({ id, expression });
 
 		return id;
 	}
 
 	apply() {
-		return this.#sync.map((memo, i) => {
+		return [...this.#async, ...this.#sync].map((memo, i) => {
 			memo.id.name = `$${i}`;
 			return memo.id;
 		});
@@ -42,6 +46,15 @@ export class Memoizer {
 		);
 	}
 
+	async_ids() {
+		return this.#async.map((memo) => memo.id);
+	}
+
+	async_values() {
+		if (this.#async.length === 0) return;
+		return b.array(this.#async.map((memo) => b.thunk(memo.expression, true)));
+	}
+
 	sync_values() {
 		if (this.#sync.length === 0) return;
 		return b.array(this.#sync.map((memo) => b.thunk(memo.expression)));
@@ -59,7 +72,8 @@ export function build_template_chunk(
 	values,
 	context,
 	state = context.state,
-	memoize = (value, metadata) => (metadata.has_call ? state.memoizer.add(value) : value)
+	memoize = (value, metadata) =>
+		metadata.has_call || metadata.has_await ? state.memoizer.add(value, metadata.has_await) : value
 ) {
 	/** @type {Expression[]} */
 	const expressions = [];
@@ -68,6 +82,7 @@ export function build_template_chunk(
 	const quasis = [quasi];
 
 	let has_state = false;
+	let has_await = false;
 
 	for (let i = 0; i < values.length; i++) {
 		const node = values[i];
@@ -90,7 +105,8 @@ export function build_template_chunk(
 
 			const evaluated = state.scope.evaluate(value);
 
-			has_state ||= node.metadata.expression.has_state && !evaluated.is_known;
+			has_await ||= node.metadata.expression.has_await;
+			has_state ||= has_await || (node.metadata.expression.has_state && !evaluated.is_known);
 
 			if (values.length === 1) {
 				// If we have a single expression, then pass that in directly to possibly avoid doing
@@ -146,8 +162,9 @@ export function build_template_chunk(
  * @param {ComponentClientTransformState} state
  */
 export function build_render_statement(state) {
-	const ids = state.memoizer.apply();
-	const values = state.memoizer.sync_values();
+	const { memoizer } = state;
+
+	const ids = memoizer.apply();
 
 	return b.stmt(
 		b.call(
@@ -158,8 +175,8 @@ export function build_render_statement(state) {
 					? state.update[0].expression
 					: b.block(state.update)
 			),
-			values,
-			values && !state.analysis.runes && b.id('$.derived_safe_equal')
+			memoizer.sync_values(),
+			memoizer.async_values()
 		)
 	);
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/transform-server.js b/packages/svelte/src/compiler/phases/3-transform/server/transform-server.js
index 86346b864c..10c92242d4 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/transform-server.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/transform-server.js
@@ -10,6 +10,7 @@ import { dev, filename } from '../../../state.js';
 import { render_stylesheet } from '../css/index.js';
 import { AssignmentExpression } from './visitors/AssignmentExpression.js';
 import { AwaitBlock } from './visitors/AwaitBlock.js';
+import { AwaitExpression } from './visitors/AwaitExpression.js';
 import { CallExpression } from './visitors/CallExpression.js';
 import { ClassBody } from './visitors/ClassBody.js';
 import { Component } from './visitors/Component.js';
@@ -44,6 +45,7 @@ import { SvelteBoundary } from './visitors/SvelteBoundary.js';
 const global_visitors = {
 	_: set_scope,
 	AssignmentExpression,
+	AwaitExpression,
 	CallExpression,
 	ClassBody,
 	ExpressionStatement,
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/AwaitExpression.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/AwaitExpression.js
new file mode 100644
index 0000000000..9135892dbd
--- /dev/null
+++ b/packages/svelte/src/compiler/phases/3-transform/server/visitors/AwaitExpression.js
@@ -0,0 +1,25 @@
+/** @import { AwaitExpression } from 'estree' */
+/** @import { Context } from '../types.js' */
+import * as b from '../../../../utils/builders.js';
+
+/**
+ * @param {AwaitExpression} node
+ * @param {Context} context
+ */
+export function AwaitExpression(node, context) {
+	// if `await` is inside a function, or inside `<script module>`,
+	// allow it, otherwise error
+	if (
+		context.state.scope.function_depth === 0 ||
+		context.path.some(
+			(node) =>
+				node.type === 'ArrowFunctionExpression' ||
+				node.type === 'FunctionDeclaration' ||
+				node.type === 'FunctionExpression'
+		)
+	) {
+		return context.next();
+	}
+
+	return b.call('$.await_outside_boundary');
+}
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/CallExpression.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/CallExpression.js
index 35c79988b0..41d3202ce9 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/visitors/CallExpression.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/visitors/CallExpression.js
@@ -25,6 +25,10 @@ export function CallExpression(node, context) {
 		return b.arrow([], b.block([]));
 	}
 
+	if (rune === '$effect.pending') {
+		return b.literal(0);
+	}
+
 	if (rune === '$state' || rune === '$state.raw') {
 		return node.arguments[0] ? context.visit(node.arguments[0]) : b.void0;
 	}
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/IfBlock.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/IfBlock.js
index eb51c941f5..508dcc0fdd 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/visitors/IfBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/visitors/IfBlock.js
@@ -10,29 +10,18 @@ import { block_close, block_open } from './shared/utils.js';
  * @param {ComponentContext} context
  */
 export function IfBlock(node, context) {
+	const test = /** @type {Expression} */ (context.visit(node.test));
 	const consequent = /** @type {BlockStatement} */ (context.visit(node.consequent));
-	consequent.body.unshift(b.stmt(b.assignment('+=', b.id('$$payload.out'), block_open)));
-	let if_statement = b.if(/** @type {Expression} */ (context.visit(node.test)), consequent);
 
-	context.state.template.push(if_statement, block_close);
+	const alternate = node.alternate
+		? /** @type {BlockStatement} */ (context.visit(node.alternate))
+		: b.block([]);
 
-	let index = 1;
-	let alt = node.alternate;
-	while (alt && alt.nodes.length === 1 && alt.nodes[0].type === 'IfBlock' && alt.nodes[0].elseif) {
-		const elseif = alt.nodes[0];
-		const alternate = /** @type {BlockStatement} */ (context.visit(elseif.consequent));
-		alternate.body.unshift(
-			b.stmt(b.assignment('+=', b.id('$$payload.out'), b.literal(`<!--[${index++}-->`)))
-		);
-		if_statement = if_statement.alternate = b.if(
-			/** @type {Expression} */ (context.visit(elseif.test)),
-			alternate
-		);
-		alt = elseif.alternate;
-	}
+	consequent.body.unshift(b.stmt(b.assignment('+=', b.id('$$payload.out'), block_open)));
 
-	if_statement.alternate = alt ? /** @type {BlockStatement} */ (context.visit(alt)) : b.block([]);
-	if_statement.alternate.body.unshift(
+	alternate.body.unshift(
 		b.stmt(b.assignment('+=', b.id('$$payload.out'), b.literal(BLOCK_OPEN_ELSE)))
 	);
+
+	context.state.template.push(b.if(test, consequent, alternate), block_close);
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/SvelteBoundary.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/SvelteBoundary.js
index 734740c1b1..6e814d6384 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/visitors/SvelteBoundary.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/visitors/SvelteBoundary.js
@@ -3,15 +3,36 @@
 /** @import { ComponentContext } from '../types' */
 import { BLOCK_CLOSE, BLOCK_OPEN } from '../../../../../internal/server/hydration.js';
 import * as b from '#compiler/builders';
+import { build_attribute_value } from './shared/utils.js';
 
 /**
  * @param {AST.SvelteBoundary} node
  * @param {ComponentContext} context
  */
 export function SvelteBoundary(node, context) {
-	context.state.template.push(
-		b.literal(BLOCK_OPEN),
-		/** @type {BlockStatement} */ (context.visit(node.fragment)),
-		b.literal(BLOCK_CLOSE)
+	context.state.template.push(b.literal(BLOCK_OPEN));
+
+	// if this has a `pending` snippet, render it
+	const pending_attribute = /** @type {AST.Attribute} */ (
+		node.attributes.find((node) => node.type === 'Attribute' && node.name === 'pending')
+	);
+
+	const pending_snippet = /** @type {AST.SnippetBlock} */ (
+		node.fragment.nodes.find(
+			(node) => node.type === 'SnippetBlock' && node.expression.name === 'pending'
+		)
 	);
+
+	if (pending_attribute) {
+		const value = build_attribute_value(pending_attribute.value, context, false, true);
+		context.state.template.push(b.call(value, b.id('$$payload')));
+	} else if (pending_snippet) {
+		context.state.template.push(
+			/** @type {BlockStatement} */ (context.visit(pending_snippet.body))
+		);
+	} else {
+		context.state.template.push(/** @type {BlockStatement} */ (context.visit(node.fragment)));
+	}
+
+	context.state.template.push(b.literal(BLOCK_CLOSE));
 }
diff --git a/packages/svelte/src/compiler/phases/nodes.js b/packages/svelte/src/compiler/phases/nodes.js
index c35f194b75..4874554ff0 100644
--- a/packages/svelte/src/compiler/phases/nodes.js
+++ b/packages/svelte/src/compiler/phases/nodes.js
@@ -66,7 +66,8 @@ export function create_expression_metadata() {
 		has_state: false,
 		has_call: false,
 		has_member_expression: false,
-		has_assignment: false
+		has_assignment: false,
+		has_await: false
 	};
 }
 
diff --git a/packages/svelte/src/compiler/phases/scope.js b/packages/svelte/src/compiler/phases/scope.js
index 662924b52c..700e098e45 100644
--- a/packages/svelte/src/compiler/phases/scope.js
+++ b/packages/svelte/src/compiler/phases/scope.js
@@ -933,7 +933,25 @@ export function create_scopes(ast, root, allow_reactive_declarations, parent) {
 		}
 	};
 
+	let has_await = false;
+
 	walk(ast, state, {
+		AwaitExpression(node, context) {
+			// this doesn't _really_ belong here, but it allows us to
+			// automatically opt into runes mode on encountering
+			// blocking awaits, without doing an additional walk
+			// before the analysis occurs
+			// TODO remove this in Svelte 7.0 or whenever we get rid of legacy support
+			has_await ||= context.path.every(
+				({ type }) =>
+					type !== 'ArrowFunctionExpression' &&
+					type !== 'FunctionExpression' &&
+					type !== 'FunctionDeclaration'
+			);
+
+			context.next();
+		},
+
 		// references
 		Identifier(node, { path, state }) {
 			const parent = path.at(-1);
@@ -1290,6 +1308,7 @@ export function create_scopes(ast, root, allow_reactive_declarations, parent) {
 	}
 
 	return {
+		has_await,
 		scope,
 		scopes
 	};
diff --git a/packages/svelte/src/compiler/phases/types.d.ts b/packages/svelte/src/compiler/phases/types.d.ts
index dba2559a17..4cbbc362c7 100644
--- a/packages/svelte/src/compiler/phases/types.d.ts
+++ b/packages/svelte/src/compiler/phases/types.d.ts
@@ -1,21 +1,19 @@
 import type { AST, Binding, StateField } from '#compiler';
 import type {
-	AssignmentExpression,
+	CallExpression,
 	ClassBody,
-	Comment,
 	Identifier,
 	LabeledStatement,
 	Node,
 	Program
 } from 'estree';
 import type { Scope, ScopeRoot } from './scope.js';
-import type { StateCreationRuneName } from '../../utils.js';
-import type { AnalysisState } from './2-analyze/types.js';
 
 export interface Js {
 	ast: Program;
 	scope: Scope;
 	scopes: Map<AST.SvelteNode, Scope>;
+	has_await: boolean;
 }
 
 export interface Template {
@@ -46,6 +44,9 @@ export interface Analysis {
 
 	// TODO figure out if we can move this to ComponentAnalysis
 	accessors: boolean;
+
+	/** A set of deriveds that contain `await` expressions */
+	async_deriveds: Set<CallExpression>;
 }
 
 export interface ComponentAnalysis extends Analysis {
diff --git a/packages/svelte/src/compiler/types/index.d.ts b/packages/svelte/src/compiler/types/index.d.ts
index 558ee558f7..c4f41b724a 100644
--- a/packages/svelte/src/compiler/types/index.d.ts
+++ b/packages/svelte/src/compiler/types/index.d.ts
@@ -224,6 +224,11 @@ export interface ModuleCompileOptions {
 	 * Use this to filter out warnings. Return `true` to keep the warning, `false` to discard it.
 	 */
 	warningFilter?: (warning: Warning) => boolean;
+	/** Experimental options */
+	experimental?: {
+		/** Allow `await` keyword in deriveds, template expressions, and the top level of components */
+		async?: boolean;
+	};
 }
 
 // The following two somewhat scary looking types ensure that certain types are required but can be undefined still
@@ -287,6 +292,8 @@ export interface ExpressionMetadata {
 	has_state: boolean;
 	/** True if the expression involves a call expression (often, it will need to be wrapped in a derived) */
 	has_call: boolean;
+	/** True if the expression contains `await` */
+	has_await: boolean;
 	/** True if the expression includes a member expression */
 	has_member_expression: boolean;
 	/** True if the expression includes an assignment or an update */
diff --git a/packages/svelte/src/compiler/types/template.d.ts b/packages/svelte/src/compiler/types/template.d.ts
index c9841e9d4e..de06a41469 100644
--- a/packages/svelte/src/compiler/types/template.d.ts
+++ b/packages/svelte/src/compiler/types/template.d.ts
@@ -366,6 +366,7 @@ export namespace AST {
 		tag: Expression;
 		/** @internal */
 		metadata: {
+			expression: ExpressionMetadata;
 			/**
 			 * `true` if this is an svg element. The boolean may not be accurate because
 			 * the tag is dynamic, but we do our best to infer it from the template.
diff --git a/packages/svelte/src/compiler/utils/builders.js b/packages/svelte/src/compiler/utils/builders.js
index 736738d19f..c241cdb445 100644
--- a/packages/svelte/src/compiler/utils/builders.js
+++ b/packages/svelte/src/compiler/utils/builders.js
@@ -1,4 +1,5 @@
 /** @import * as ESTree from 'estree' */
+import { walk } from 'zimmerframe';
 import { regex_is_valid_identifier } from '../phases/patterns.js';
 import { sanitize_template_string } from './sanitize_template_string.js';
 
@@ -30,16 +31,17 @@ export function assignment_pattern(left, right) {
 /**
  * @param {Array<ESTree.Pattern>} params
  * @param {ESTree.BlockStatement | ESTree.Expression} body
+ * @param {boolean} async
  * @returns {ESTree.ArrowFunctionExpression}
  */
-export function arrow(params, body) {
+export function arrow(params, body, async = false) {
 	return {
 		type: 'ArrowFunctionExpression',
 		params,
 		body,
 		expression: body.type !== 'BlockStatement',
 		generator: false,
-		async: false,
+		async,
 		metadata: /** @type {any} */ (null) // should not be used by codegen
 	};
 }
@@ -100,7 +102,7 @@ export function labeled(name, body) {
 
 /**
  * @param {string | ESTree.Expression} callee
- * @param {...(ESTree.Expression | ESTree.SpreadElement | false | undefined)} args
+ * @param {...(ESTree.Expression | ESTree.SpreadElement | false | undefined | null)} args
  * @returns {ESTree.CallExpression}
  */
 export function call(callee, ...args) {
@@ -216,16 +218,17 @@ export function export_default(declaration) {
  * @param {ESTree.Identifier} id
  * @param {ESTree.Pattern[]} params
  * @param {ESTree.BlockStatement} body
+ * @param {boolean} async
  * @returns {ESTree.FunctionDeclaration}
  */
-export function function_declaration(id, params, body) {
+export function function_declaration(id, params, body, async = false) {
 	return {
 		type: 'FunctionDeclaration',
 		id,
 		params,
 		body,
 		generator: false,
-		async: false,
+		async,
 		metadata: /** @type {any} */ (null) // should not be used by codegen
 	};
 }
@@ -421,19 +424,32 @@ export function template(elements, expressions) {
  * @returns {ESTree.Expression}
  */
 export function thunk(expression, async = false) {
-	const fn = arrow([], expression);
-	if (async) fn.async = true;
-	return unthunk(fn);
+	return unthunk(arrow([], expression, async));
 }
 
 /**
  * Replace "(arg) => func(arg)" to "func"
- * @param {ESTree.Expression} expression
+ * @param {ESTree.ArrowFunctionExpression} expression
  * @returns {ESTree.Expression}
  */
 export function unthunk(expression) {
+	// optimize `async () => await x()`, but not `async () => await x(await y)`
+	if (expression.async && expression.body.type === 'AwaitExpression') {
+		let has_await = false;
+
+		walk(expression.body.argument, null, {
+			AwaitExpression(_node, context) {
+				has_await = true;
+				context.stop();
+			}
+		});
+
+		if (!has_await) {
+			return unthunk(arrow(expression.params, expression.body.argument));
+		}
+	}
+
 	if (
-		expression.type === 'ArrowFunctionExpression' &&
 		expression.async === false &&
 		expression.body.type === 'CallExpression' &&
 		expression.body.callee.type === 'Identifier' &&
diff --git a/packages/svelte/src/compiler/validate-options.js b/packages/svelte/src/compiler/validate-options.js
index 1fd89139d5..ed83375d22 100644
--- a/packages/svelte/src/compiler/validate-options.js
+++ b/packages/svelte/src/compiler/validate-options.js
@@ -41,7 +41,11 @@ const common = {
 		return input;
 	}),
 
-	warningFilter: fun(() => true)
+	warningFilter: fun(() => true),
+
+	experimental: object({
+		async: boolean(false)
+	})
 };
 
 export const validate_module_options =
diff --git a/packages/svelte/src/constants.js b/packages/svelte/src/constants.js
index 4e1785723c..69cd213940 100644
--- a/packages/svelte/src/constants.js
+++ b/packages/svelte/src/constants.js
@@ -42,6 +42,8 @@ export const NAMESPACE_MATHML = 'http://www.w3.org/1998/Math/MathML';
 // we use a list of ignorable runtime warnings because not every runtime warning
 // can be ignored and we want to keep the validation for svelte-ignore in place
 export const IGNORABLE_RUNTIME_WARNINGS = /** @type {const} */ ([
+	'await_waterfall',
+	'await_reactivity_loss',
 	'state_snapshot_uncloneable',
 	'binding_property_non_reactive',
 	'hydration_attribute_changed',
diff --git a/packages/svelte/src/index-client.js b/packages/svelte/src/index-client.js
index ae1caf16d9..397a81c319 100644
--- a/packages/svelte/src/index-client.js
+++ b/packages/svelte/src/index-client.js
@@ -237,8 +237,8 @@ function init_update_callbacks(context) {
 	return (l.u ??= { a: [], b: [], m: [] });
 }
 
-export { flushSync } from './internal/client/runtime.js';
+export { flushSync } from './internal/client/reactivity/batch.js';
 export { getContext, getAllContexts, hasContext, setContext } from './internal/client/context.js';
 export { hydrate, mount, unmount } from './internal/client/render.js';
-export { tick, untrack } from './internal/client/runtime.js';
+export { tick, untrack, settled } from './internal/client/runtime.js';
 export { createRawSnippet } from './internal/client/dom/blocks/snippet.js';
diff --git a/packages/svelte/src/index-server.js b/packages/svelte/src/index-server.js
index e5039cf150..1342e502d7 100644
--- a/packages/svelte/src/index-server.js
+++ b/packages/svelte/src/index-server.js
@@ -35,6 +35,8 @@ export function unmount() {
 
 export async function tick() {}
 
+export async function settled() {}
+
 export { getAbortSignal } from './internal/server/abort-signal.js';
 
 export { getAllContexts, getContext, hasContext, setContext } from './internal/server/context.js';
diff --git a/packages/svelte/src/internal/client/constants.js b/packages/svelte/src/internal/client/constants.js
index a5a8b42972..50a7a21ae8 100644
--- a/packages/svelte/src/internal/client/constants.js
+++ b/packages/svelte/src/internal/client/constants.js
@@ -18,8 +18,13 @@ export const EFFECT_TRANSPARENT = 1 << 16;
 export const INSPECT_EFFECT = 1 << 17;
 export const HEAD_EFFECT = 1 << 18;
 export const EFFECT_PRESERVED = 1 << 19;
-export const EFFECT_IS_UPDATING = 1 << 20;
-export const USER_EFFECT = 1 << 21;
+export const USER_EFFECT = 1 << 20;
+
+// Flags used for async
+export const REACTION_IS_UPDATING = 1 << 21;
+export const ASYNC = 1 << 22;
+
+export const ERROR_VALUE = 1 << 23;
 
 export const STATE_SYMBOL = Symbol('$state');
 export const LEGACY_PROPS = Symbol('legacy props');
diff --git a/packages/svelte/src/internal/client/context.js b/packages/svelte/src/internal/client/context.js
index a9ceafcd11..cad75546d4 100644
--- a/packages/svelte/src/internal/client/context.js
+++ b/packages/svelte/src/internal/client/context.js
@@ -1,10 +1,11 @@
-/** @import { ComponentContext, DevStackEntry } from '#client' */
+/** @import { ComponentContext, DevStackEntry, Effect } from '#client' */
 import { DEV } from 'esm-env';
 import * as e from './errors.js';
-import { source } from './reactivity/sources.js';
+import { active_effect, active_reaction } from './runtime.js';
 import { create_user_effect } from './reactivity/effects.js';
-import { legacy_mode_flag } from '../flags/index.js';
+import { async_mode_flag, legacy_mode_flag } from '../flags/index.js';
 import { FILENAME } from '../../constants.js';
+import { BRANCH_EFFECT, EFFECT_RAN } from './constants.js';
 
 /** @type {ComponentContext | null} */
 export let component_context = null;
@@ -96,6 +97,16 @@ export function getContext(key) {
  */
 export function setContext(key, context) {
 	const context_map = get_or_init_context_map('setContext');
+
+	if (async_mode_flag) {
+		var flags = /** @type {Effect} */ (active_effect).f;
+		var valid = !active_reaction && (flags & BRANCH_EFFECT) !== 0 && (flags & EFFECT_RAN) === 0;
+
+		if (!valid) {
+			e.set_context_after_init();
+		}
+	}
+
 	context_map.set(key, context);
 	return context;
 }
@@ -138,18 +149,9 @@ export function push(props, runes = false, fn) {
 		e: null,
 		s: props,
 		x: null,
-		l: null
+		l: legacy_mode_flag && !runes ? { s: null, u: null, $: [] } : null
 	};
 
-	if (legacy_mode_flag && !runes) {
-		component_context.l = {
-			s: null,
-			u: null,
-			r1: [],
-			r2: source(false)
-		};
-	}
-
 	if (DEV) {
 		// component function
 		component_context.function = fn;
diff --git a/packages/svelte/src/internal/client/dev/debug.js b/packages/svelte/src/internal/client/dev/debug.js
index fbde87a2d7..c47080ed2f 100644
--- a/packages/svelte/src/internal/client/dev/debug.js
+++ b/packages/svelte/src/internal/client/dev/debug.js
@@ -7,6 +7,7 @@ import {
 	CLEAN,
 	DERIVED,
 	EFFECT,
+	ASYNC,
 	MAYBE_DIRTY,
 	RENDER_EFFECT,
 	ROOT_EFFECT
@@ -39,6 +40,8 @@ export function log_effect_tree(effect, depth = 0) {
 		label = 'boundary';
 	} else if ((flags & BLOCK_EFFECT) !== 0) {
 		label = 'block';
+	} else if ((flags & ASYNC) !== 0) {
+		label = 'async';
 	} else if ((flags & BRANCH_EFFECT) !== 0) {
 		label = 'branch';
 	} else if ((flags & RENDER_EFFECT) !== 0) {
diff --git a/packages/svelte/src/internal/client/dev/tracing.js b/packages/svelte/src/internal/client/dev/tracing.js
index 5834f5bffd..128942ceb2 100644
--- a/packages/svelte/src/internal/client/dev/tracing.js
+++ b/packages/svelte/src/internal/client/dev/tracing.js
@@ -2,7 +2,7 @@
 import { UNINITIALIZED } from '../../../constants.js';
 import { snapshot } from '../../shared/clone.js';
 import { define_property } from '../../shared/utils.js';
-import { DERIVED, PROXY_PATH_SYMBOL, STATE_SYMBOL } from '#client/constants';
+import { DERIVED, ASYNC, PROXY_PATH_SYMBOL, STATE_SYMBOL } from '#client/constants';
 import { effect_tracking } from '../reactivity/effects.js';
 import { active_reaction, captured_signals, set_captured_signals, untrack } from '../runtime.js';
 
@@ -26,7 +26,7 @@ function log_entry(signal, entry) {
 		return;
 	}
 
-	const type = (signal.f & DERIVED) !== 0 ? '$derived' : '$state';
+	const type = (signal.f & (DERIVED | ASYNC)) !== 0 ? '$derived' : '$state';
 	const current_reaction = /** @type {Reaction} */ (active_reaction);
 	const dirty = signal.wv > current_reaction.wv || current_reaction.wv === 0;
 	const style = dirty
diff --git a/packages/svelte/src/internal/client/dom/blocks/async.js b/packages/svelte/src/internal/client/dom/blocks/async.js
new file mode 100644
index 0000000000..82f107ab29
--- /dev/null
+++ b/packages/svelte/src/internal/client/dom/blocks/async.js
@@ -0,0 +1,26 @@
+/** @import { TemplateNode, Value } from '#client' */
+import { flatten } from '../../reactivity/async.js';
+import { get } from '../../runtime.js';
+import { get_pending_boundary } from './boundary.js';
+
+/**
+ * @param {TemplateNode} node
+ * @param {Array<() => Promise<any>>} expressions
+ * @param {(anchor: TemplateNode, ...deriveds: Value[]) => void} fn
+ */
+export function async(node, expressions, fn) {
+	var boundary = get_pending_boundary();
+
+	boundary.update_pending_count(1);
+
+	flatten([], expressions, (values) => {
+		try {
+			// get values eagerly to avoid creating blocks if they reject
+			for (const d of values) get(d);
+
+			fn(node, ...values);
+		} finally {
+			boundary.update_pending_count(-1);
+		}
+	});
+}
diff --git a/packages/svelte/src/internal/client/dom/blocks/await.js b/packages/svelte/src/internal/client/dom/blocks/await.js
index 325224fff2..4f68db57b1 100644
--- a/packages/svelte/src/internal/client/dom/blocks/await.js
+++ b/packages/svelte/src/internal/client/dom/blocks/await.js
@@ -3,7 +3,7 @@ import { DEV } from 'esm-env';
 import { is_promise } from '../../../shared/utils.js';
 import { block, branch, pause_effect, resume_effect } from '../../reactivity/effects.js';
 import { internal_set, mutable_source, source } from '../../reactivity/sources.js';
-import { flushSync, set_active_effect, set_active_reaction } from '../../runtime.js';
+import { set_active_effect, set_active_reaction } from '../../runtime.js';
 import {
 	hydrate_next,
 	hydrate_node,
@@ -22,6 +22,7 @@ import {
 	set_dev_current_component_function,
 	set_dev_stack
 } from '../../context.js';
+import { flushSync } from '../../reactivity/batch.js';
 
 const PENDING = 0;
 const THEN = 1;
diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 03cec4fd2f..5ed0515210 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -1,4 +1,4 @@
-/** @import { Effect, TemplateNode, } from '#client' */
+/** @import { Effect, Source, TemplateNode, } from '#client' */
 import { BOUNDARY_EFFECT, EFFECT_PRESERVED, EFFECT_TRANSPARENT } from '#client/constants';
 import { component_context, set_component_context } from '../../context.js';
 import { invoke_error_boundary } from '../../error-handling.js';
@@ -6,6 +6,7 @@ import { block, branch, destroy_effect, pause_effect } from '../../reactivity/ef
 import {
 	active_effect,
 	active_reaction,
+	get,
 	set_active_effect,
 	set_active_reaction
 } from '../../runtime.js';
@@ -17,12 +18,20 @@ import {
 	remove_nodes,
 	set_hydrate_node
 } from '../hydration.js';
+import { get_next_sibling } from '../operations.js';
 import { queue_micro_task } from '../task.js';
+import * as e from '../../errors.js';
+import { DEV } from 'esm-env';
+import { Batch } from '../../reactivity/batch.js';
+import { internal_set, source } from '../../reactivity/sources.js';
+import { tag } from '../../dev/tracing.js';
+import { createSubscriber } from '../../../../reactivity/create-subscriber.js';
 
 /**
  * @typedef {{
  * 	 onerror?: (error: unknown, reset: () => void) => void;
  *   failed?: (anchor: Node, error: () => unknown, reset: () => () => void) => void;
+ *   pending?: (anchor: Node) => void;
  * }} BoundaryProps
  */
 
@@ -39,6 +48,11 @@ export function boundary(node, props, children) {
 }
 
 export class Boundary {
+	pending = false;
+
+	/** @type {Boundary | null} */
+	parent;
+
 	/** @type {TemplateNode} */
 	#anchor;
 
@@ -57,11 +71,39 @@ export class Boundary {
 	/** @type {Effect | null} */
 	#main_effect = null;
 
+	/** @type {Effect | null} */
+	#pending_effect = null;
+
 	/** @type {Effect | null} */
 	#failed_effect = null;
 
+	/** @type {DocumentFragment | null} */
+	#offscreen_fragment = null;
+
+	#pending_count = 0;
 	#is_creating_fallback = false;
 
+	/**
+	 * A source containing the number of pending async deriveds/expressions.
+	 * Only created if `$effect.pending()` is used inside the boundary,
+	 * otherwise updating the source results in needless `Batch.ensure()`
+	 * calls followed by no-op flushes
+	 * @type {Source<number> | null}
+	 */
+	#effect_pending = null;
+
+	#effect_pending_subscriber = createSubscriber(() => {
+		this.#effect_pending = source(this.#pending_count);
+
+		if (DEV) {
+			tag(this.#effect_pending, '$effect.pending()');
+		}
+
+		return () => {
+			this.#effect_pending = null;
+		};
+	});
+
 	/**
 	 * @param {TemplateNode} node
 	 * @param {BoundaryProps} props
@@ -74,6 +116,10 @@ export class Boundary {
 
 		this.#hydrate_open = hydrate_node;
 
+		this.parent = /** @type {Effect} */ (active_effect).b;
+
+		this.pending = !!this.#props.pending;
+
 		this.#effect = block(() => {
 			/** @type {Effect} */ (active_effect).b = this;
 
@@ -81,10 +127,43 @@ export class Boundary {
 				hydrate_next();
 			}
 
-			try {
-				this.#main_effect = branch(() => children(this.#anchor));
-			} catch (error) {
-				this.error(error);
+			const pending = this.#props.pending;
+
+			if (hydrating && pending) {
+				this.#pending_effect = branch(() => pending(this.#anchor));
+
+				// future work: when we have some form of async SSR, we will
+				// need to use hydration boundary comments to report whether
+				// the pending or main block was rendered for a given
+				// boundary, and hydrate accordingly
+				queueMicrotask(() => {
+					this.#main_effect = this.#run(() => {
+						Batch.ensure();
+						return branch(() => this.#children(this.#anchor));
+					});
+
+					if (this.#pending_count > 0) {
+						this.#show_pending_snippet();
+					} else {
+						pause_effect(/** @type {Effect} */ (this.#pending_effect), () => {
+							this.#pending_effect = null;
+						});
+
+						this.pending = false;
+					}
+				});
+			} else {
+				try {
+					this.#main_effect = branch(() => children(this.#anchor));
+				} catch (error) {
+					this.error(error);
+				}
+
+				if (this.#pending_count > 0) {
+					this.#show_pending_snippet();
+				} else {
+					this.pending = false;
+				}
 			}
 		}, flags);
 
@@ -93,6 +172,10 @@ export class Boundary {
 		}
 	}
 
+	has_pending_snippet() {
+		return !!this.#props.pending;
+	}
+
 	/**
 	 * @param {() => Effect | null} fn
 	 */
@@ -114,22 +197,85 @@ export class Boundary {
 		}
 	}
 
+	#show_pending_snippet() {
+		const pending = /** @type {(anchor: Node) => void} */ (this.#props.pending);
+
+		if (this.#main_effect !== null) {
+			this.#offscreen_fragment = document.createDocumentFragment();
+			move_effect(this.#main_effect, this.#offscreen_fragment);
+		}
+
+		if (this.#pending_effect === null) {
+			this.#pending_effect = branch(() => pending(this.#anchor));
+		}
+	}
+
+	/** @param {1 | -1} d */
+	#update_pending_count(d) {
+		this.#pending_count += d;
+
+		if (this.#pending_count === 0) {
+			this.pending = false;
+
+			if (this.#pending_effect) {
+				pause_effect(this.#pending_effect, () => {
+					this.#pending_effect = null;
+				});
+			}
+
+			if (this.#offscreen_fragment) {
+				this.#anchor.before(this.#offscreen_fragment);
+				this.#offscreen_fragment = null;
+			}
+		}
+	}
+
+	/** @param {1 | -1} d */
+	update_pending_count(d) {
+		if (this.has_pending_snippet()) {
+			this.#update_pending_count(d);
+		} else if (this.parent) {
+			this.parent.#update_pending_count(d);
+		}
+
+		queueMicrotask(() => {
+			if (this.#effect_pending) {
+				internal_set(this.#effect_pending, this.#pending_count);
+			}
+		});
+	}
+
+	get_effect_pending() {
+		this.#effect_pending_subscriber();
+		return get(/** @type {Source<number>} */ (this.#effect_pending));
+	}
+
 	/** @param {unknown} error */
 	error(error) {
 		var onerror = this.#props.onerror;
 		let failed = this.#props.failed;
 
 		const reset = () => {
+			this.#pending_count = 0;
+
 			if (this.#failed_effect !== null) {
 				pause_effect(this.#failed_effect, () => {
 					this.#failed_effect = null;
 				});
 			}
 
+			this.pending = true;
+
 			this.#main_effect = this.#run(() => {
 				this.#is_creating_fallback = false;
 				return branch(() => this.#children(this.#anchor));
 			});
+
+			if (this.#pending_count > 0) {
+				this.#show_pending_snippet();
+			} else {
+				this.pending = false;
+			}
 		};
 
 		// If we have nothing to capture the error, or if we hit an error while
@@ -152,6 +298,11 @@ export class Boundary {
 			this.#main_effect = null;
 		}
 
+		if (this.#pending_effect) {
+			destroy_effect(this.#pending_effect);
+			this.#pending_effect = null;
+		}
+
 		if (this.#failed_effect) {
 			destroy_effect(this.#failed_effect);
 			this.#failed_effect = null;
@@ -187,3 +338,49 @@ export class Boundary {
 		}
 	}
 }
+
+/**
+ *
+ * @param {Effect} effect
+ * @param {DocumentFragment} fragment
+ */
+function move_effect(effect, fragment) {
+	var node = effect.nodes_start;
+	var end = effect.nodes_end;
+
+	while (node !== null) {
+		/** @type {TemplateNode | null} */
+		var next = node === end ? null : /** @type {TemplateNode} */ (get_next_sibling(node));
+
+		fragment.append(node);
+		node = next;
+	}
+}
+
+export function get_pending_boundary() {
+	var boundary = /** @type {Effect} */ (active_effect).b;
+
+	while (boundary !== null && !boundary.has_pending_snippet()) {
+		boundary = boundary.parent;
+	}
+
+	if (boundary === null) {
+		e.await_outside_boundary();
+	}
+
+	return boundary;
+}
+
+export function pending() {
+	if (active_effect === null) {
+		e.effect_pending_outside_reaction();
+	}
+
+	var boundary = active_effect.b;
+
+	if (boundary === null) {
+		return 0; // TODO eventually we will need this to be global
+	}
+
+	return boundary.get_effect_pending();
+}
diff --git a/packages/svelte/src/internal/client/dom/blocks/each.js b/packages/svelte/src/internal/client/dom/blocks/each.js
index 7b12be58e8..43c75e2a37 100644
--- a/packages/svelte/src/internal/client/dom/blocks/each.js
+++ b/packages/svelte/src/internal/client/dom/blocks/each.js
@@ -1,4 +1,5 @@
 /** @import { EachItem, EachState, Effect, MaybeSource, Source, TemplateNode, TransitionManager, Value } from '#client' */
+/** @import { Batch } from '../../reactivity/batch.js'; */
 import {
 	EACH_INDEX_REACTIVE,
 	EACH_IS_ANIMATED,
@@ -21,7 +22,8 @@ import {
 	clear_text_content,
 	create_text,
 	get_first_child,
-	get_next_sibling
+	get_next_sibling,
+	should_defer_append
 } from '../operations.js';
 import {
 	block,
@@ -39,6 +41,7 @@ import { queue_micro_task } from '../task.js';
 import { active_effect, get } from '../../runtime.js';
 import { DEV } from 'esm-env';
 import { derived_safe_equal } from '../../reactivity/deriveds.js';
+import { current_batch } from '../../reactivity/batch.js';
 
 /**
  * The row of a keyed each block that is currently updating. We track this
@@ -66,9 +69,10 @@ export function index(_, i) {
  * @param {EachState} state
  * @param {EachItem[]} items
  * @param {null | Node} controlled_anchor
- * @param {Map<any, EachItem>} items_map
  */
-function pause_effects(state, items, controlled_anchor, items_map) {
+function pause_effects(state, items, controlled_anchor) {
+	var items_map = state.items;
+
 	/** @type {TransitionManager[]} */
 	var transitions = [];
 	var length = items.length;
@@ -137,6 +141,9 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
 
 	var was_empty = false;
 
+	/** @type {Map<any, EachItem>} */
+	var offscreen_items = new Map();
+
 	// TODO: ideally we could use derived for runes mode but because of the ability
 	// to use a store which can be mutated, we can't do that here as mutating a store
 	// will still result in the collection array being the same from the store
@@ -146,8 +153,45 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
 		return is_array(collection) ? collection : collection == null ? [] : array_from(collection);
 	});
 
+	/** @type {V[]} */
+	var array;
+
+	/** @type {Effect} */
+	var each_effect;
+
+	function commit() {
+		reconcile(
+			each_effect,
+			array,
+			state,
+			offscreen_items,
+			anchor,
+			render_fn,
+			flags,
+			get_key,
+			get_collection
+		);
+
+		if (fallback_fn !== null) {
+			if (array.length === 0) {
+				if (fallback) {
+					resume_effect(fallback);
+				} else {
+					fallback = branch(() => fallback_fn(anchor));
+				}
+			} else if (fallback !== null) {
+				pause_effect(fallback, () => {
+					fallback = null;
+				});
+			}
+		}
+	}
+
 	block(() => {
-		var array = get(each_array);
+		// store a reference to the effect so that we can update the start/end nodes in reconciliation
+		each_effect ??= /** @type {Effect} */ (active_effect);
+
+		array = get(each_array);
 		var length = array.length;
 
 		if (was_empty && length === 0) {
@@ -219,21 +263,56 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
 			}
 		}
 
-		if (!hydrating) {
-			reconcile(array, state, anchor, render_fn, flags, get_key, get_collection);
-		}
+		if (hydrating) {
+			if (length === 0 && fallback_fn) {
+				fallback = branch(() => fallback_fn(anchor));
+			}
+		} else {
+			if (should_defer_append()) {
+				var keys = new Set();
+				var batch = /** @type {Batch} */ (current_batch);
+
+				for (i = 0; i < length; i += 1) {
+					value = array[i];
+					key = get_key(value, i);
+
+					var existing = state.items.get(key) ?? offscreen_items.get(key);
+
+					if (existing) {
+						// update before reconciliation, to trigger any async updates
+						if ((flags & (EACH_ITEM_REACTIVE | EACH_INDEX_REACTIVE)) !== 0) {
+							update_item(existing, value, i, flags);
+						}
+					} else {
+						item = create_item(
+							null,
+							state,
+							null,
+							null,
+							value,
+							key,
+							i,
+							render_fn,
+							flags,
+							get_collection,
+							true
+						);
+
+						offscreen_items.set(key, item);
+					}
 
-		if (fallback_fn !== null) {
-			if (length === 0) {
-				if (fallback) {
-					resume_effect(fallback);
-				} else {
-					fallback = branch(() => fallback_fn(anchor));
+					keys.add(key);
 				}
-			} else if (fallback !== null) {
-				pause_effect(fallback, () => {
-					fallback = null;
-				});
+
+				for (const [key, item] of state.items) {
+					if (!keys.has(key)) {
+						batch.skipped_effects.add(item.e);
+					}
+				}
+
+				batch.add_callback(commit);
+			} else {
+				commit();
 			}
 		}
 
@@ -259,8 +338,10 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
 /**
  * Add, remove, or reorder items output by an each block as its input changes
  * @template V
+ * @param {Effect} each_effect
  * @param {Array<V>} array
  * @param {EachState} state
+ * @param {Map<any, EachItem>} offscreen_items
  * @param {Element | Comment | Text} anchor
  * @param {(anchor: Node, item: MaybeSource<V>, index: number | Source<number>, collection: () => V[]) => void} render_fn
  * @param {number} flags
@@ -268,7 +349,17 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
  * @param {() => V[]} get_collection
  * @returns {void}
  */
-function reconcile(array, state, anchor, render_fn, flags, get_key, get_collection) {
+function reconcile(
+	each_effect,
+	array,
+	state,
+	offscreen_items,
+	anchor,
+	render_fn,
+	flags,
+	get_key,
+	get_collection
+) {
 	var is_animated = (flags & EACH_IS_ANIMATED) !== 0;
 	var should_update = (flags & (EACH_ITEM_REACTIVE | EACH_INDEX_REACTIVE)) !== 0;
 
@@ -320,23 +411,39 @@ function reconcile(array, state, anchor, render_fn, flags, get_key, get_collecti
 	for (i = 0; i < length; i += 1) {
 		value = array[i];
 		key = get_key(value, i);
+
 		item = items.get(key);
 
 		if (item === undefined) {
-			var child_anchor = current ? /** @type {TemplateNode} */ (current.e.nodes_start) : anchor;
-
-			prev = create_item(
-				child_anchor,
-				state,
-				prev,
-				prev === null ? state.first : prev.next,
-				value,
-				key,
-				i,
-				render_fn,
-				flags,
-				get_collection
-			);
+			var pending = offscreen_items.get(key);
+
+			if (pending !== undefined) {
+				offscreen_items.delete(key);
+				items.set(key, pending);
+
+				var next = prev ? prev.next : current;
+
+				link(state, prev, pending);
+				link(state, pending, next);
+
+				move(pending, next, anchor);
+				prev = pending;
+			} else {
+				var child_anchor = current ? /** @type {TemplateNode} */ (current.e.nodes_start) : anchor;
+
+				prev = create_item(
+					child_anchor,
+					state,
+					prev,
+					prev === null ? state.first : prev.next,
+					value,
+					key,
+					i,
+					render_fn,
+					flags,
+					get_collection
+				);
+			}
 
 			items.set(key, prev);
 
@@ -455,7 +562,7 @@ function reconcile(array, state, anchor, render_fn, flags, get_key, get_collecti
 				}
 			}
 
-			pause_effects(state, to_destroy, controlled_anchor, items);
+			pause_effects(state, to_destroy, controlled_anchor);
 		}
 	}
 
@@ -468,8 +575,14 @@ function reconcile(array, state, anchor, render_fn, flags, get_key, get_collecti
 		});
 	}
 
-	/** @type {Effect} */ (active_effect).first = state.first && state.first.e;
-	/** @type {Effect} */ (active_effect).last = prev && prev.e;
+	each_effect.first = state.first && state.first.e;
+	each_effect.last = prev && prev.e;
+
+	for (var unused of offscreen_items.values()) {
+		destroy_effect(unused.e);
+	}
+
+	offscreen_items.clear();
 }
 
 /**
@@ -493,7 +606,7 @@ function update_item(item, value, index, type) {
 
 /**
  * @template V
- * @param {Node} anchor
+ * @param {Node | null} anchor
  * @param {EachState} state
  * @param {EachItem | null} prev
  * @param {EachItem | null} next
@@ -503,6 +616,7 @@ function update_item(item, value, index, type) {
  * @param {(anchor: Node, item: V | Source<V>, index: number | Value<number>, collection: () => V[]) => void} render_fn
  * @param {number} flags
  * @param {() => V[]} get_collection
+ * @param {boolean} [deferred]
  * @returns {EachItem}
  */
 function create_item(
@@ -515,7 +629,8 @@ function create_item(
 	index,
 	render_fn,
 	flags,
-	get_collection
+	get_collection,
+	deferred
 ) {
 	var previous_each_item = current_each_item;
 	var reactive = (flags & EACH_ITEM_REACTIVE) !== 0;
@@ -549,13 +664,20 @@ function create_item(
 	current_each_item = item;
 
 	try {
-		item.e = branch(() => render_fn(anchor, v, i, get_collection), hydrating);
+		if (anchor === null) {
+			var fragment = document.createDocumentFragment();
+			fragment.append((anchor = create_text()));
+		}
+
+		item.e = branch(() => render_fn(/** @type {Node} */ (anchor), v, i, get_collection), hydrating);
 
 		item.e.prev = prev && prev.e;
 		item.e.next = next && next.e;
 
 		if (prev === null) {
-			state.first = item;
+			if (!deferred) {
+				state.first = item;
+			}
 		} else {
 			prev.next = item;
 			prev.e.next = item.e;
@@ -583,7 +705,7 @@ function move(item, next, anchor) {
 	var dest = next ? /** @type {TemplateNode} */ (next.e.nodes_start) : anchor;
 	var node = /** @type {TemplateNode} */ (item.e.nodes_start);
 
-	while (node !== end) {
+	while (node !== null && node !== end) {
 		var next_node = /** @type {TemplateNode} */ (get_next_sibling(node));
 		dest.before(node);
 		node = next_node;
diff --git a/packages/svelte/src/internal/client/dom/blocks/if.js b/packages/svelte/src/internal/client/dom/blocks/if.js
index bf1098c3f4..6ba9ad4936 100644
--- a/packages/svelte/src/internal/client/dom/blocks/if.js
+++ b/packages/svelte/src/internal/client/dom/blocks/if.js
@@ -1,4 +1,5 @@
 /** @import { Effect, TemplateNode } from '#client' */
+/** @import { Batch } from '../../reactivity/batch.js'; */
 import { EFFECT_TRANSPARENT } from '#client/constants';
 import {
 	hydrate_next,
@@ -10,16 +11,20 @@ import {
 	set_hydrating
 } from '../hydration.js';
 import { block, branch, pause_effect, resume_effect } from '../../reactivity/effects.js';
-import { HYDRATION_START, HYDRATION_START_ELSE, UNINITIALIZED } from '../../../../constants.js';
+import { HYDRATION_START_ELSE, UNINITIALIZED } from '../../../../constants.js';
+import { create_text, should_defer_append } from '../operations.js';
+import { current_batch } from '../../reactivity/batch.js';
+
+// TODO reinstate https://github.com/sveltejs/svelte/pull/15250
 
 /**
  * @param {TemplateNode} node
- * @param {(branch: (fn: (anchor: Node, elseif?: [number,number]) => void, flag?: boolean) => void) => void} fn
- * @param {[number,number]} [elseif]
+ * @param {(branch: (fn: (anchor: Node) => void, flag?: boolean) => void) => void} fn
+ * @param {boolean} [elseif] True if this is an `{:else if ...}` block rather than an `{#if ...}`, as that affects which transitions are considered 'local'
  * @returns {void}
  */
-export function if_block(node, fn, [root_index, hydrate_index] = [0, 0]) {
-	if (hydrating && root_index === 0) {
+export function if_block(node, fn, elseif = false) {
+	if (hydrating) {
 		hydrate_next();
 	}
 
@@ -34,45 +39,56 @@ export function if_block(node, fn, [root_index, hydrate_index] = [0, 0]) {
 	/** @type {UNINITIALIZED | boolean | null} */
 	var condition = UNINITIALIZED;
 
-	var flags = root_index > 0 ? EFFECT_TRANSPARENT : 0;
+	var flags = elseif ? EFFECT_TRANSPARENT : 0;
 
 	var has_branch = false;
 
-	const set_branch = (
-		/** @type {(anchor: Node, elseif?: [number,number]) => void} */ fn,
-		flag = true
-	) => {
+	const set_branch = (/** @type {(anchor: Node) => void} */ fn, flag = true) => {
 		has_branch = true;
 		update_branch(flag, fn);
 	};
 
+	/** @type {DocumentFragment | null} */
+	var offscreen_fragment = null;
+
+	function commit() {
+		if (offscreen_fragment !== null) {
+			// remove the anchor
+			/** @type {Text} */ (offscreen_fragment.lastChild).remove();
+
+			anchor.before(offscreen_fragment);
+			offscreen_fragment = null;
+		}
+
+		var active = condition ? consequent_effect : alternate_effect;
+		var inactive = condition ? alternate_effect : consequent_effect;
+
+		if (active) {
+			resume_effect(active);
+		}
+
+		if (inactive) {
+			pause_effect(inactive, () => {
+				if (condition) {
+					alternate_effect = null;
+				} else {
+					consequent_effect = null;
+				}
+			});
+		}
+	}
+
 	const update_branch = (
 		/** @type {boolean | null} */ new_condition,
-		/** @type {null | ((anchor: Node, elseif?: [number,number]) => void)} */ fn
+		/** @type {null | ((anchor: Node) => void)} */ fn
 	) => {
 		if (condition === (condition = new_condition)) return;
 
 		/** Whether or not there was a hydration mismatch. Needs to be a `let` or else it isn't treeshaken out */
 		let mismatch = false;
 
-		if (hydrating && hydrate_index !== -1) {
-			if (root_index === 0) {
-				const data = read_hydration_instruction(anchor);
-
-				if (data === HYDRATION_START) {
-					hydrate_index = 0;
-				} else if (data === HYDRATION_START_ELSE) {
-					hydrate_index = Infinity;
-				} else {
-					hydrate_index = parseInt(data.substring(1));
-					if (hydrate_index !== hydrate_index) {
-						// if hydrate_index is NaN
-						// we set an invalid index to force mismatch
-						hydrate_index = condition ? Infinity : -1;
-					}
-				}
-			}
-			const is_else = hydrate_index > root_index;
+		if (hydrating) {
+			const is_else = read_hydration_instruction(anchor) === HYDRATION_START_ELSE;
 
 			if (!!condition === is_else) {
 				// Hydration mismatch: remove everything inside the anchor and start fresh.
@@ -82,34 +98,35 @@ export function if_block(node, fn, [root_index, hydrate_index] = [0, 0]) {
 				set_hydrate_node(anchor);
 				set_hydrating(false);
 				mismatch = true;
-				hydrate_index = -1; // ignore hydration in next else if
 			}
 		}
 
-		if (condition) {
-			if (consequent_effect) {
-				resume_effect(consequent_effect);
-			} else if (fn) {
-				consequent_effect = branch(() => fn(anchor));
-			}
+		var defer = should_defer_append();
+		var target = anchor;
 
-			if (alternate_effect) {
-				pause_effect(alternate_effect, () => {
-					alternate_effect = null;
-				});
-			}
+		if (defer) {
+			offscreen_fragment = document.createDocumentFragment();
+			offscreen_fragment.append((target = create_text()));
+		}
+
+		if (condition) {
+			consequent_effect ??= fn && branch(() => fn(target));
 		} else {
-			if (alternate_effect) {
-				resume_effect(alternate_effect);
-			} else if (fn) {
-				alternate_effect = branch(() => fn(anchor, [root_index + 1, hydrate_index]));
-			}
+			alternate_effect ??= fn && branch(() => fn(target));
+		}
 
-			if (consequent_effect) {
-				pause_effect(consequent_effect, () => {
-					consequent_effect = null;
-				});
-			}
+		if (defer) {
+			var batch = /** @type {Batch} */ (current_batch);
+
+			var active = condition ? consequent_effect : alternate_effect;
+			var inactive = condition ? alternate_effect : consequent_effect;
+
+			if (active) batch.skipped_effects.delete(active);
+			if (inactive) batch.skipped_effects.add(inactive);
+
+			batch.add_callback(commit);
+		} else {
+			commit();
 		}
 
 		if (mismatch) {
diff --git a/packages/svelte/src/internal/client/dom/blocks/key.js b/packages/svelte/src/internal/client/dom/blocks/key.js
index a697163548..5e3c42019f 100644
--- a/packages/svelte/src/internal/client/dom/blocks/key.js
+++ b/packages/svelte/src/internal/client/dom/blocks/key.js
@@ -1,9 +1,12 @@
 /** @import { Effect, TemplateNode } from '#client' */
+/** @import { Batch } from '../../reactivity/batch.js'; */
 import { UNINITIALIZED } from '../../../../constants.js';
 import { block, branch, pause_effect } from '../../reactivity/effects.js';
 import { not_equal, safe_not_equal } from '../../reactivity/equality.js';
 import { is_runes } from '../../context.js';
 import { hydrate_next, hydrate_node, hydrating } from '../hydration.js';
+import { create_text, should_defer_append } from '../operations.js';
+import { current_batch } from '../../reactivity/batch.js';
 
 /**
  * @template V
@@ -12,7 +15,7 @@ import { hydrate_next, hydrate_node, hydrating } from '../hydration.js';
  * @param {(anchor: Node) => TemplateNode | void} render_fn
  * @returns {void}
  */
-export function key_block(node, get_key, render_fn) {
+export function key(node, get_key, render_fn) {
 	if (hydrating) {
 		hydrate_next();
 	}
@@ -25,15 +28,48 @@ export function key_block(node, get_key, render_fn) {
 	/** @type {Effect} */
 	var effect;
 
+	/** @type {Effect} */
+	var pending_effect;
+
+	/** @type {DocumentFragment | null} */
+	var offscreen_fragment = null;
+
 	var changed = is_runes() ? not_equal : safe_not_equal;
 
+	function commit() {
+		if (effect) {
+			pause_effect(effect);
+		}
+
+		if (offscreen_fragment !== null) {
+			// remove the anchor
+			/** @type {Text} */ (offscreen_fragment.lastChild).remove();
+
+			anchor.before(offscreen_fragment);
+			offscreen_fragment = null;
+		}
+
+		effect = pending_effect;
+	}
+
 	block(() => {
 		if (changed(key, (key = get_key()))) {
-			if (effect) {
-				pause_effect(effect);
+			var target = anchor;
+
+			var defer = should_defer_append();
+
+			if (defer) {
+				offscreen_fragment = document.createDocumentFragment();
+				offscreen_fragment.append((target = create_text()));
 			}
 
-			effect = branch(() => render_fn(anchor));
+			pending_effect = branch(() => render_fn(target));
+
+			if (defer) {
+				/** @type {Batch} */ (current_batch).add_callback(commit);
+			} else {
+				commit();
+			}
 		}
 	});
 
diff --git a/packages/svelte/src/internal/client/dom/blocks/svelte-component.js b/packages/svelte/src/internal/client/dom/blocks/svelte-component.js
index ad21436505..f16da9c427 100644
--- a/packages/svelte/src/internal/client/dom/blocks/svelte-component.js
+++ b/packages/svelte/src/internal/client/dom/blocks/svelte-component.js
@@ -1,7 +1,10 @@
 /** @import { TemplateNode, Dom, Effect } from '#client' */
+/** @import { Batch } from '../../reactivity/batch.js'; */
 import { EFFECT_TRANSPARENT } from '#client/constants';
 import { block, branch, pause_effect } from '../../reactivity/effects.js';
+import { current_batch } from '../../reactivity/batch.js';
 import { hydrate_next, hydrate_node, hydrating } from '../hydration.js';
+import { create_text, should_defer_append } from '../operations.js';
 
 /**
  * @template P
@@ -24,16 +27,50 @@ export function component(node, get_component, render_fn) {
 	/** @type {Effect | null} */
 	var effect;
 
-	block(() => {
-		if (component === (component = get_component())) return;
+	/** @type {DocumentFragment | null} */
+	var offscreen_fragment = null;
 
+	/** @type {Effect | null} */
+	var pending_effect = null;
+
+	function commit() {
 		if (effect) {
 			pause_effect(effect);
 			effect = null;
 		}
 
+		if (offscreen_fragment) {
+			// remove the anchor
+			/** @type {Text} */ (offscreen_fragment.lastChild).remove();
+
+			anchor.before(offscreen_fragment);
+			offscreen_fragment = null;
+		}
+
+		effect = pending_effect;
+		pending_effect = null;
+	}
+
+	block(() => {
+		if (component === (component = get_component())) return;
+
+		var defer = should_defer_append();
+
 		if (component) {
-			effect = branch(() => render_fn(anchor, component));
+			var target = anchor;
+
+			if (defer) {
+				offscreen_fragment = document.createDocumentFragment();
+				offscreen_fragment.append((target = create_text()));
+			}
+
+			pending_effect = branch(() => render_fn(target, component));
+		}
+
+		if (defer) {
+			/** @type {Batch} */ (current_batch).add_callback(commit);
+		} else {
+			commit();
 		}
 	}, EFFECT_TRANSPARENT);
 
diff --git a/packages/svelte/src/internal/client/dom/elements/attributes.js b/packages/svelte/src/internal/client/dom/elements/attributes.js
index 66f484a59a..22e532f5e4 100644
--- a/packages/svelte/src/internal/client/dom/elements/attributes.js
+++ b/packages/svelte/src/internal/client/dom/elements/attributes.js
@@ -21,8 +21,8 @@ import { set_class } from './class.js';
 import { set_style } from './style.js';
 import { ATTACHMENT_KEY, NAMESPACE_HTML } from '../../../../constants.js';
 import { block, branch, destroy_effect, effect } from '../../reactivity/effects.js';
-import { derived } from '../../reactivity/deriveds.js';
 import { init_select, select_option } from './bindings/select.js';
+import { flatten } from '../../reactivity/async.js';
 
 export const CLASS = Symbol('class');
 export const STYLE = Symbol('style');
@@ -462,66 +462,67 @@ export function set_attributes(element, prev, next, css_hash, skip_warning = fal
 /**
  * @param {Element & ElementCSSInlineStyle} element
  * @param {(...expressions: any) => Record<string | symbol, any>} fn
- * @param {Array<() => any>} thunks
+ * @param {Array<() => any>} sync
+ * @param {Array<() => Promise<any>>} async
  * @param {string} [css_hash]
  * @param {boolean} [skip_warning]
  */
 export function attribute_effect(
 	element,
 	fn,
-	thunks = [],
+	sync = [],
+	async = [],
 	css_hash,
-	skip_warning = false,
-	d = derived
+	skip_warning = false
 ) {
-	const deriveds = thunks.map(d);
+	flatten(sync, async, (values) => {
+		/** @type {Record<string | symbol, any> | undefined} */
+		var prev = undefined;
 
-	/** @type {Record<string | symbol, any> | undefined} */
-	var prev = undefined;
+		/** @type {Record<symbol, Effect>} */
+		var effects = {};
 
-	/** @type {Record<symbol, Effect>} */
-	var effects = {};
+		var is_select = element.nodeName === 'SELECT';
+		var inited = false;
 
-	var is_select = element.nodeName === 'SELECT';
-	var inited = false;
+		block(() => {
+			var next = fn(...values.map(get));
+			/** @type {Record<string | symbol, any>} */
+			var current = set_attributes(element, prev, next, css_hash, skip_warning);
 
-	block(() => {
-		var next = fn(...deriveds.map(get));
-		/** @type {Record<string | symbol, any>} */
-		var current = set_attributes(element, prev, next, css_hash, skip_warning);
+			if (inited && is_select && 'value' in next) {
+				select_option(/** @type {HTMLSelectElement} */ (element), next.value);
+			}
 
-		if (inited && is_select && 'value' in next) {
-			select_option(/** @type {HTMLSelectElement} */ (element), next.value);
-		}
+			for (let symbol of Object.getOwnPropertySymbols(effects)) {
+				if (!next[symbol]) destroy_effect(effects[symbol]);
+			}
 
-		for (let symbol of Object.getOwnPropertySymbols(effects)) {
-			if (!next[symbol]) destroy_effect(effects[symbol]);
-		}
+			for (let symbol of Object.getOwnPropertySymbols(next)) {
+				var n = next[symbol];
 
-		for (let symbol of Object.getOwnPropertySymbols(next)) {
-			var n = next[symbol];
+				if (symbol.description === ATTACHMENT_KEY && (!prev || n !== prev[symbol])) {
+					if (effects[symbol]) destroy_effect(effects[symbol]);
+					effects[symbol] = branch(() => attach(element, () => n));
+				}
 
-			if (symbol.description === ATTACHMENT_KEY && (!prev || n !== prev[symbol])) {
-				if (effects[symbol]) destroy_effect(effects[symbol]);
-				effects[symbol] = branch(() => attach(element, () => n));
+				current[symbol] = n;
 			}
 
-			current[symbol] = n;
-		}
-
-		prev = current;
-	});
+			prev = current;
+		});
 
-	if (is_select) {
-		var select = /** @type {HTMLSelectElement} */ (element);
+		if (is_select) {
+			var select = /** @type {HTMLSelectElement} */ (element);
 
-		effect(() => {
-			select_option(select, /** @type {Record<string | symbol, any>} */ (prev).value, true);
-			init_select(select);
-		});
-	}
+			effect(() => {
+				select_option(select, /** @type {Record<string | symbol, any>} */ (prev).value, true);
+				init_select(select);
+			});
+		}
 
-	inited = true;
+		inited = true;
+	});
 }
 
 /**
diff --git a/packages/svelte/src/internal/client/dom/elements/bindings/input.js b/packages/svelte/src/internal/client/dom/elements/bindings/input.js
index f1992007ed..569d1179e6 100644
--- a/packages/svelte/src/internal/client/dom/elements/bindings/input.js
+++ b/packages/svelte/src/internal/client/dom/elements/bindings/input.js
@@ -64,6 +64,15 @@ export function bind_value(input, get, set = get) {
 
 		var value = get();
 
+		if (input === document.activeElement) {
+			// Never rewrite the contents of a focused input. We can get here if, for example,
+			// an update is deferred because of async work depending on the input:
+			//
+			// <input bind:value={query}>
+			// <p>{await find(query)}</p>
+			return;
+		}
+
 		if (is_numberlike_input(input) && value === to_number(input.value)) {
 			// handles 0 vs 00 case (see https://github.com/sveltejs/svelte/issues/9959)
 			return;
diff --git a/packages/svelte/src/internal/client/dom/operations.js b/packages/svelte/src/internal/client/dom/operations.js
index 4b35f0802f..fb269e47e0 100644
--- a/packages/svelte/src/internal/client/dom/operations.js
+++ b/packages/svelte/src/internal/client/dom/operations.js
@@ -1,9 +1,11 @@
-/** @import { TemplateNode } from '#client' */
+/** @import { Effect, TemplateNode } from '#client' */
 import { hydrate_node, hydrating, set_hydrate_node } from './hydration.js';
 import { DEV } from 'esm-env';
 import { init_array_prototype_warnings } from '../dev/equality.js';
 import { get_descriptor, is_extensible } from '../../shared/utils.js';
-import { TEXT_NODE } from '#client/constants';
+import { active_effect } from '../runtime.js';
+import { async_mode_flag } from '../../flags/index.js';
+import { TEXT_NODE, EFFECT_RAN } from '#client/constants';
 
 // export these for reference in the compiled code, making global name deduplication unnecessary
 /** @type {Window} */
@@ -204,6 +206,19 @@ export function clear_text_content(node) {
 	node.textContent = '';
 }
 
+/**
+ * Returns `true` if we're updating the current block, for example `condition` in
+ * an `{#if condition}` block just changed. In this case, the branch should be
+ * appended (or removed) at the same time as other updates within the
+ * current `<svelte:boundary>`
+ */
+export function should_defer_append() {
+	if (!async_mode_flag) return false;
+
+	var flags = /** @type {Effect} */ (active_effect).f;
+	return (flags & EFFECT_RAN) !== 0;
+}
+
 /**
  *
  * @param {string} tag
diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index b12f21adfc..a512839181 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -1,11 +1,11 @@
-/** @import { Effect } from '#client' */
+/** @import { Derived, Effect } from '#client' */
 /** @import { Boundary } from './dom/blocks/boundary.js' */
 import { DEV } from 'esm-env';
 import { FILENAME } from '../../constants.js';
 import { is_firefox } from './dom/operations.js';
-import { BOUNDARY_EFFECT, EFFECT_RAN } from './constants.js';
+import { ERROR_VALUE, BOUNDARY_EFFECT, EFFECT_RAN } from './constants.js';
 import { define_property, get_descriptor } from '../shared/utils.js';
-import { active_effect } from './runtime.js';
+import { active_effect, active_reaction } from './runtime.js';
 
 const adjustments = new WeakMap();
 
@@ -13,7 +13,13 @@ const adjustments = new WeakMap();
  * @param {unknown} error
  */
 export function handle_error(error) {
-	var effect = /** @type {Effect} */ (active_effect);
+	var effect = active_effect;
+
+	// for unowned deriveds, don't throw until we read the value
+	if (effect === null) {
+		/** @type {Derived} */ (active_reaction).f |= ERROR_VALUE;
+		return error;
+	}
 
 	if (DEV && error instanceof Error && !adjustments.has(error)) {
 		adjustments.set(error, get_adjustments(error, effect));
@@ -23,11 +29,14 @@ export function handle_error(error) {
 		// if the error occurred while creating this subtree, we let it
 		// bubble up until it hits a boundary that can handle it
 		if ((effect.f & BOUNDARY_EFFECT) === 0) {
+			if (!effect.parent && error instanceof Error) {
+				apply_adjustments(error);
+			}
+
 			throw error;
 		}
 
-		// @ts-expect-error
-		effect.fn(error);
+		/** @type {Boundary} */ (effect.b).error(error);
 	} else {
 		// otherwise we bubble up the effect tree ourselves
 		invoke_error_boundary(error, effect);
diff --git a/packages/svelte/src/internal/client/errors.js b/packages/svelte/src/internal/client/errors.js
index 64dc34e8d0..a491dc683d 100644
--- a/packages/svelte/src/internal/client/errors.js
+++ b/packages/svelte/src/internal/client/errors.js
@@ -4,6 +4,22 @@ import { DEV } from 'esm-env';
 
 export *  from '../shared/errors.js';
 
+/**
+ * Cannot create a `$derived(...)` with an `await` expression outside of an effect tree
+ * @returns {never}
+ */
+export function async_derived_orphan() {
+	if (DEV) {
+		const error = new Error(`async_derived_orphan\nCannot create a \`$derived(...)\` with an \`await\` expression outside of an effect tree\nhttps://svelte.dev/e/async_derived_orphan`);
+
+		error.name = 'Svelte error';
+
+		throw error;
+	} else {
+		throw new Error(`https://svelte.dev/e/async_derived_orphan`);
+	}
+}
+
 /**
  * Using `bind:value` together with a checkbox input is not allowed. Use `bind:checked` instead
  * @returns {never}
@@ -181,6 +197,22 @@ export function effect_orphan(rune) {
 	}
 }
 
+/**
+ * `$effect.pending()` can only be called inside an effect or derived
+ * @returns {never}
+ */
+export function effect_pending_outside_reaction() {
+	if (DEV) {
+		const error = new Error(`effect_pending_outside_reaction\n\`$effect.pending()\` can only be called inside an effect or derived\nhttps://svelte.dev/e/effect_pending_outside_reaction`);
+
+		error.name = 'Svelte error';
+
+		throw error;
+	} else {
+		throw new Error(`https://svelte.dev/e/effect_pending_outside_reaction`);
+	}
+}
+
 /**
  * Maximum update depth exceeded. This can happen when a reactive block or effect repeatedly sets a new value. Svelte limits the number of nested updates to prevent infinite loops
  * @returns {never}
@@ -197,6 +229,22 @@ export function effect_update_depth_exceeded() {
 	}
 }
 
+/**
+ * Cannot use `flushSync` inside an effect
+ * @returns {never}
+ */
+export function flush_sync_in_effect() {
+	if (DEV) {
+		const error = new Error(`flush_sync_in_effect\nCannot use \`flushSync\` inside an effect\nhttps://svelte.dev/e/flush_sync_in_effect`);
+
+		error.name = 'Svelte error';
+
+		throw error;
+	} else {
+		throw new Error(`https://svelte.dev/e/flush_sync_in_effect`);
+	}
+}
+
 /**
  * `getAbortSignal()` can only be called inside an effect or derived
  * @returns {never}
@@ -313,6 +361,22 @@ export function rune_outside_svelte(rune) {
 	}
 }
 
+/**
+ * `setContext` must be called when a component first initializes, not in a subsequent effect or after an `await` expression
+ * @returns {never}
+ */
+export function set_context_after_init() {
+	if (DEV) {
+		const error = new Error(`set_context_after_init\n\`setContext\` must be called when a component first initializes, not in a subsequent effect or after an \`await\` expression\nhttps://svelte.dev/e/set_context_after_init`);
+
+		error.name = 'Svelte error';
+
+		throw error;
+	} else {
+		throw new Error(`https://svelte.dev/e/set_context_after_init`);
+	}
+}
+
 /**
  * Property descriptors defined on `$state` objects must contain `value` and always be `enumerable`, `configurable` and `writable`.
  * @returns {never}
diff --git a/packages/svelte/src/internal/client/index.js b/packages/svelte/src/internal/client/index.js
index 576a30fa77..cddb432a98 100644
--- a/packages/svelte/src/internal/client/index.js
+++ b/packages/svelte/src/internal/client/index.js
@@ -9,10 +9,11 @@ export { create_ownership_validator } from './dev/ownership.js';
 export { check_target, legacy_api } from './dev/legacy.js';
 export { trace, tag, tag_proxy } from './dev/tracing.js';
 export { inspect } from './dev/inspect.js';
+export { async } from './dom/blocks/async.js';
 export { validate_snippet_args } from './dev/validation.js';
 export { await_block as await } from './dom/blocks/await.js';
 export { if_block as if } from './dom/blocks/if.js';
-export { key_block as key } from './dom/blocks/key.js';
+export { key } from './dom/blocks/key.js';
 export { css_props } from './dom/blocks/css-props.js';
 export { index, each } from './dom/blocks/each.js';
 export { html } from './dom/blocks/html.js';
@@ -97,8 +98,15 @@ export {
 	props_id,
 	with_script
 } from './dom/template.js';
-export { user_derived as derived, derived_safe_equal } from './reactivity/deriveds.js';
+export { save, track_reactivity_loss } from './reactivity/async.js';
+export { flushSync as flush, suspend } from './reactivity/batch.js';
 export {
+	async_derived,
+	user_derived as derived,
+	derived_safe_equal
+} from './reactivity/deriveds.js';
+export {
+	aborted,
 	effect_tracking,
 	effect_root,
 	legacy_pre_effect,
@@ -129,13 +137,12 @@ export {
 	update_store,
 	mark_store_binding
 } from './reactivity/store.js';
-export { boundary } from './dom/blocks/boundary.js';
+export { boundary, pending } from './dom/blocks/boundary.js';
 export { set_text } from './render.js';
 export {
 	get,
 	safe_get,
 	invalidate_inner_signals,
-	flushSync as flush,
 	tick,
 	untrack,
 	exclude_from_object,
diff --git a/packages/svelte/src/internal/client/reactivity/async.js b/packages/svelte/src/internal/client/reactivity/async.js
new file mode 100644
index 0000000000..c200f10dba
--- /dev/null
+++ b/packages/svelte/src/internal/client/reactivity/async.js
@@ -0,0 +1,127 @@
+/** @import { Effect, Value } from '#client' */
+
+import { DESTROYED } from '#client/constants';
+import { DEV } from 'esm-env';
+import { component_context, is_runes, set_component_context } from '../context.js';
+import { get_pending_boundary } from '../dom/blocks/boundary.js';
+import { invoke_error_boundary } from '../error-handling.js';
+import {
+	active_effect,
+	active_reaction,
+	set_active_effect,
+	set_active_reaction
+} from '../runtime.js';
+import { current_batch } from './batch.js';
+import {
+	async_derived,
+	current_async_effect,
+	derived,
+	derived_safe_equal,
+	set_from_async_derived
+} from './deriveds.js';
+
+/**
+ *
+ * @param {Array<() => any>} sync
+ * @param {Array<() => Promise<any>>} async
+ * @param {(values: Value[]) => any} fn
+ */
+export function flatten(sync, async, fn) {
+	const d = is_runes() ? derived : derived_safe_equal;
+
+	if (async.length === 0) {
+		fn(sync.map(d));
+		return;
+	}
+
+	var batch = current_batch;
+	var parent = /** @type {Effect} */ (active_effect);
+
+	var restore = capture();
+	var boundary = get_pending_boundary();
+
+	Promise.all(async.map((expression) => async_derived(expression)))
+		.then((result) => {
+			batch?.activate();
+
+			restore();
+
+			try {
+				fn([...sync.map(d), ...result]);
+			} catch (error) {
+				// ignore errors in blocks that have already been destroyed
+				if ((parent.f & DESTROYED) === 0) {
+					invoke_error_boundary(error, parent);
+				}
+			}
+
+			batch?.deactivate();
+			unset_context();
+		})
+		.catch((error) => {
+			boundary.error(error);
+		});
+}
+
+/**
+ * Captures the current effect context so that we can restore it after
+ * some asynchronous work has happened (so that e.g. `await a + b`
+ * causes `b` to be registered as a dependency).
+ */
+function capture() {
+	var previous_effect = active_effect;
+	var previous_reaction = active_reaction;
+	var previous_component_context = component_context;
+
+	return function restore() {
+		set_active_effect(previous_effect);
+		set_active_reaction(previous_reaction);
+		set_component_context(previous_component_context);
+
+		if (DEV) {
+			set_from_async_derived(null);
+		}
+	};
+}
+
+/**
+ * Wraps an `await` expression in such a way that the effect context that was
+ * active before the expression evaluated can be reapplied afterwards —
+ * `await a + b` becomes `(await $.save(a))() + b`
+ * @template T
+ * @param {Promise<T>} promise
+ * @returns {Promise<() => T>}
+ */
+export async function save(promise) {
+	var restore = capture();
+	var value = await promise;
+
+	return () => {
+		restore();
+		return value;
+	};
+}
+
+/**
+ * Reset `current_async_effect` after the `promise` resolves, so
+ * that we can emit `await_reactivity_loss` warnings
+ * @template T
+ * @param {Promise<T>} promise
+ * @returns {Promise<() => T>}
+ */
+export async function track_reactivity_loss(promise) {
+	var previous_async_effect = current_async_effect;
+	var value = await promise;
+
+	return () => {
+		set_from_async_derived(previous_async_effect);
+		return value;
+	};
+}
+
+export function unset_context() {
+	set_active_effect(null);
+	set_active_reaction(null);
+	set_component_context(null);
+	if (DEV) set_from_async_derived(null);
+}
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
new file mode 100644
index 0000000000..1126946ce9
--- /dev/null
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -0,0 +1,603 @@
+/** @import { Derived, Effect, Source } from '#client' */
+import {
+	BLOCK_EFFECT,
+	BRANCH_EFFECT,
+	CLEAN,
+	DESTROYED,
+	DIRTY,
+	EFFECT,
+	ASYNC,
+	INERT,
+	RENDER_EFFECT,
+	ROOT_EFFECT,
+	USER_EFFECT
+} from '#client/constants';
+import { async_mode_flag } from '../../flags/index.js';
+import { deferred, define_property } from '../../shared/utils.js';
+import { get_pending_boundary } from '../dom/blocks/boundary.js';
+import {
+	active_effect,
+	is_dirty,
+	is_updating_effect,
+	set_is_updating_effect,
+	set_signal_status,
+	update_effect,
+	write_version
+} from '../runtime.js';
+import * as e from '../errors.js';
+import { flush_tasks } from '../dom/task.js';
+import { DEV } from 'esm-env';
+import { invoke_error_boundary } from '../error-handling.js';
+import { old_values } from './sources.js';
+import { unlink_effect } from './effects.js';
+import { unset_context } from './async.js';
+
+/** @type {Set<Batch>} */
+const batches = new Set();
+
+/** @type {Batch | null} */
+export let current_batch = null;
+
+/**
+ * When time travelling, we re-evaluate deriveds based on the temporary
+ * values of their dependencies rather than their actual values, and cache
+ * the results in this map rather than on the deriveds themselves
+ * @type {Map<Derived, any> | null}
+ */
+export let batch_deriveds = null;
+
+/** @type {Effect[]} Stack of effects, dev only */
+export let dev_effect_stack = [];
+
+/** @type {Effect[]} */
+let queued_root_effects = [];
+
+/** @type {Effect | null} */
+let last_scheduled_effect = null;
+
+let is_flushing = false;
+
+export class Batch {
+	/**
+	 * The current values of any sources that are updated in this batch
+	 * They keys of this map are identical to `this.#previous`
+	 * @type {Map<Source, any>}
+	 */
+	#current = new Map();
+
+	/**
+	 * The values of any sources that are updated in this batch _before_ those updates took place.
+	 * They keys of this map are identical to `this.#current`
+	 * @type {Map<Source, any>}
+	 */
+	#previous = new Map();
+
+	/**
+	 * When the batch is committed (and the DOM is updated), we need to remove old branches
+	 * and append new ones by calling the functions added inside (if/each/key/etc) blocks
+	 * @type {Set<() => void>}
+	 */
+	#callbacks = new Set();
+
+	/**
+	 * The number of async effects that are currently in flight
+	 */
+	#pending = 0;
+
+	/**
+	 * A deferred that resolves when the batch is committed, used with `settled()`
+	 * TODO replace with Promise.withResolvers once supported widely enough
+	 * @type {{ promise: Promise<void>, resolve: (value?: any) => void, reject: (reason: unknown) => void } | null}
+	 */
+	#deferred = null;
+
+	/**
+	 * True if an async effect inside this batch resolved and
+	 * its parent branch was already deleted
+	 */
+	#neutered = false;
+
+	/**
+	 * Async effects (created inside `async_derived`) encountered during processing.
+	 * These run after the rest of the batch has updated, since they should
+	 * always have the latest values
+	 * @type {Effect[]}
+	 */
+	#async_effects = [];
+
+	/**
+	 * The same as `#async_effects`, but for effects inside a newly-created
+	 * `<svelte:boundary>` — these do not prevent the batch from committing
+	 * @type {Effect[]}
+	 */
+	#boundary_async_effects = [];
+
+	/**
+	 * Template effects and `$effect.pre` effects, which run when
+	 * a batch is committed
+	 * @type {Effect[]}
+	 */
+	#render_effects = [];
+
+	/**
+	 * The same as `#render_effects`, but for `$effect` (which runs after)
+	 * @type {Effect[]}
+	 */
+	#effects = [];
+
+	/**
+	 * Block effects, which may need to re-run on subsequent flushes
+	 * in order to update internal sources (e.g. each block items)
+	 * @type {Effect[]}
+	 */
+	#block_effects = [];
+
+	/**
+	 * A set of branches that still exist, but will be destroyed when this batch
+	 * is committed — we skip over these during `process`
+	 * @type {Set<Effect>}
+	 */
+	skipped_effects = new Set();
+
+	/**
+	 *
+	 * @param {Effect[]} root_effects
+	 */
+	#process(root_effects) {
+		queued_root_effects = [];
+
+		/** @type {Map<Source, { v: unknown, wv: number }> | null} */
+		var current_values = null;
+
+		// if there are multiple batches, we are 'time travelling' —
+		// we need to undo the changes belonging to any batch
+		// other than the current one
+		if (batches.size > 1) {
+			current_values = new Map();
+			batch_deriveds = new Map();
+
+			for (const [source, current] of this.#current) {
+				current_values.set(source, { v: source.v, wv: source.wv });
+				source.v = current;
+			}
+
+			for (const batch of batches) {
+				if (batch === this) continue;
+
+				for (const [source, previous] of batch.#previous) {
+					if (!current_values.has(source)) {
+						current_values.set(source, { v: source.v, wv: source.wv });
+						source.v = previous;
+					}
+				}
+			}
+		}
+
+		for (const root of root_effects) {
+			this.#traverse_effect_tree(root);
+		}
+
+		// if we didn't start any new async work, and no async work
+		// is outstanding from a previous flush, commit
+		if (this.#async_effects.length === 0 && this.#pending === 0) {
+			var render_effects = this.#render_effects;
+			var effects = this.#effects;
+
+			this.#render_effects = [];
+			this.#effects = [];
+			this.#block_effects = [];
+
+			this.#commit();
+
+			flush_queued_effects(render_effects);
+			flush_queued_effects(effects);
+
+			this.#deferred?.resolve();
+		} else {
+			// otherwise mark effects clean so they get scheduled on the next run
+			for (const e of this.#render_effects) set_signal_status(e, CLEAN);
+			for (const e of this.#effects) set_signal_status(e, CLEAN);
+			for (const e of this.#block_effects) set_signal_status(e, CLEAN);
+		}
+
+		if (current_values) {
+			for (const [source, { v, wv }] of current_values) {
+				// reset the source to the current value (unless
+				// it got a newer value as a result of effects running)
+				if (source.wv <= wv) {
+					source.v = v;
+				}
+			}
+
+			batch_deriveds = null;
+		}
+
+		for (const effect of this.#async_effects) {
+			update_effect(effect);
+		}
+
+		for (const effect of this.#boundary_async_effects) {
+			update_effect(effect);
+		}
+
+		this.#async_effects = [];
+		this.#boundary_async_effects = [];
+	}
+
+	/**
+	 * Traverse the effect tree, executing effects or stashing
+	 * them for later execution as appropriate
+	 * @param {Effect} root
+	 */
+	#traverse_effect_tree(root) {
+		root.f ^= CLEAN;
+
+		var effect = root.first;
+
+		while (effect !== null) {
+			var flags = effect.f;
+			var is_branch = (flags & (BRANCH_EFFECT | ROOT_EFFECT)) !== 0;
+			var is_skippable_branch = is_branch && (flags & CLEAN) !== 0;
+
+			var skip = is_skippable_branch || (flags & INERT) !== 0 || this.skipped_effects.has(effect);
+
+			if (!skip && effect.fn !== null) {
+				if (is_branch) {
+					effect.f ^= CLEAN;
+				} else if ((flags & EFFECT) !== 0) {
+					this.#effects.push(effect);
+				} else if (async_mode_flag && (flags & RENDER_EFFECT) !== 0) {
+					this.#render_effects.push(effect);
+				} else if (is_dirty(effect)) {
+					if ((flags & ASYNC) !== 0) {
+						var effects = effect.b?.pending ? this.#boundary_async_effects : this.#async_effects;
+						effects.push(effect);
+					} else {
+						if ((effect.f & BLOCK_EFFECT) !== 0) this.#block_effects.push(effect);
+						update_effect(effect);
+					}
+				}
+
+				var child = effect.first;
+
+				if (child !== null) {
+					effect = child;
+					continue;
+				}
+			}
+
+			var parent = effect.parent;
+			effect = effect.next;
+
+			while (effect === null && parent !== null) {
+				effect = parent.next;
+				parent = parent.parent;
+			}
+		}
+	}
+
+	/**
+	 * Associate a change to a given source with the current
+	 * batch, noting its previous and current values
+	 * @param {Source} source
+	 * @param {any} value
+	 */
+	capture(source, value) {
+		if (!this.#previous.has(source)) {
+			this.#previous.set(source, value);
+		}
+
+		this.#current.set(source, source.v);
+	}
+
+	activate() {
+		current_batch = this;
+	}
+
+	deactivate() {
+		current_batch = null;
+	}
+
+	neuter() {
+		this.#neutered = true;
+	}
+
+	flush() {
+		if (queued_root_effects.length > 0) {
+			this.flush_effects();
+		} else {
+			this.#commit();
+		}
+
+		if (current_batch !== this) {
+			// this can happen if a `flushSync` occurred during `this.flush_effects()`,
+			// which is permitted in legacy mode despite being a terrible idea
+			return;
+		}
+
+		if (this.#pending === 0) {
+			batches.delete(this);
+		}
+
+		current_batch = null;
+	}
+
+	flush_effects() {
+		var was_updating_effect = is_updating_effect;
+		is_flushing = true;
+
+		try {
+			var flush_count = 0;
+			set_is_updating_effect(true);
+
+			while (queued_root_effects.length > 0) {
+				if (flush_count++ > 1000) {
+					infinite_loop_guard();
+				}
+
+				this.#process(queued_root_effects);
+				old_values.clear();
+			}
+		} finally {
+			is_flushing = false;
+			set_is_updating_effect(was_updating_effect);
+
+			last_scheduled_effect = null;
+			if (DEV) {
+				dev_effect_stack = [];
+			}
+		}
+	}
+
+	/**
+	 * Append and remove branches to/from the DOM
+	 */
+	#commit() {
+		if (!this.#neutered) {
+			for (const fn of this.#callbacks) {
+				fn();
+			}
+		}
+
+		this.#callbacks.clear();
+	}
+
+	increment() {
+		this.#pending += 1;
+	}
+
+	decrement() {
+		this.#pending -= 1;
+
+		if (this.#pending === 0) {
+			for (const e of this.#render_effects) {
+				set_signal_status(e, DIRTY);
+				schedule_effect(e);
+			}
+
+			for (const e of this.#effects) {
+				set_signal_status(e, DIRTY);
+				schedule_effect(e);
+			}
+
+			for (const e of this.#block_effects) {
+				set_signal_status(e, DIRTY);
+				schedule_effect(e);
+			}
+
+			this.#render_effects = [];
+			this.#effects = [];
+
+			this.flush();
+		}
+	}
+
+	/** @param {() => void} fn */
+	add_callback(fn) {
+		this.#callbacks.add(fn);
+	}
+
+	settled() {
+		return (this.#deferred ??= deferred()).promise;
+	}
+
+	static ensure() {
+		if (current_batch === null) {
+			const batch = (current_batch = new Batch());
+			batches.add(current_batch);
+
+			queueMicrotask(() => {
+				if (current_batch !== batch) {
+					// a flushSync happened in the meantime
+					return;
+				}
+
+				batch.flush();
+			});
+		}
+
+		return current_batch;
+	}
+}
+
+/**
+ * Synchronously flush any pending updates.
+ * Returns void if no callback is provided, otherwise returns the result of calling the callback.
+ * @template [T=void]
+ * @param {(() => T) | undefined} [fn]
+ * @returns {T}
+ */
+export function flushSync(fn) {
+	if (async_mode_flag && active_effect !== null) {
+		e.flush_sync_in_effect();
+	}
+
+	var result;
+
+	const batch = Batch.ensure();
+
+	if (fn) {
+		batch.flush_effects();
+
+		result = fn();
+	}
+
+	while (true) {
+		flush_tasks();
+
+		if (queued_root_effects.length === 0) {
+			if (batch === current_batch) {
+				batch.flush();
+			}
+
+			// this would be reset in `batch.flush_effects()` but since we are early returning here,
+			// we need to reset it here as well in case the first time there's 0 queued root effects
+			last_scheduled_effect = null;
+
+			if (DEV) {
+				dev_effect_stack = [];
+			}
+
+			return /** @type {T} */ (result);
+		}
+
+		batch.flush_effects();
+	}
+}
+
+function log_effect_stack() {
+	// eslint-disable-next-line no-console
+	console.error(
+		'Last ten effects were: ',
+		dev_effect_stack.slice(-10).map((d) => d.fn)
+	);
+	dev_effect_stack = [];
+}
+
+function infinite_loop_guard() {
+	try {
+		e.effect_update_depth_exceeded();
+	} catch (error) {
+		if (DEV) {
+			// stack is garbage, ignore. Instead add a console.error message.
+			define_property(error, 'stack', {
+				value: ''
+			});
+		}
+		// Try and handle the error so it can be caught at a boundary, that's
+		// if there's an effect available from when it was last scheduled
+		if (last_scheduled_effect !== null) {
+			if (DEV) {
+				try {
+					invoke_error_boundary(error, last_scheduled_effect);
+				} catch (e) {
+					// Only log the effect stack if the error is re-thrown
+					log_effect_stack();
+					throw e;
+				}
+			} else {
+				invoke_error_boundary(error, last_scheduled_effect);
+			}
+		} else {
+			if (DEV) {
+				log_effect_stack();
+			}
+			throw error;
+		}
+	}
+}
+
+/**
+ * @param {Array<Effect>} effects
+ * @returns {void}
+ */
+function flush_queued_effects(effects) {
+	var length = effects.length;
+	if (length === 0) return;
+
+	for (var i = 0; i < length; i++) {
+		var effect = effects[i];
+
+		if ((effect.f & (DESTROYED | INERT)) === 0) {
+			if (is_dirty(effect)) {
+				var wv = write_version;
+
+				update_effect(effect);
+
+				// Effects with no dependencies or teardown do not get added to the effect tree.
+				// Deferred effects (e.g. `$effect(...)`) _are_ added to the tree because we
+				// don't know if we need to keep them until they are executed. Doing the check
+				// here (rather than in `update_effect`) allows us to skip the work for
+				// immediate effects.
+				if (effect.deps === null && effect.first === null && effect.nodes_start === null) {
+					if (effect.teardown === null) {
+						// remove this effect from the graph
+						unlink_effect(effect);
+					} else {
+						// keep the effect in the graph, but free up some memory
+						effect.fn = null;
+					}
+				}
+
+				// if state is written in a user effect, abort and re-schedule, lest we run
+				// effects that should be removed as a result of the state change
+				if (write_version > wv && (effect.f & USER_EFFECT) !== 0) {
+					break;
+				}
+			}
+		}
+	}
+
+	for (; i < length; i += 1) {
+		schedule_effect(effects[i]);
+	}
+}
+
+/**
+ * @param {Effect} signal
+ * @returns {void}
+ */
+export function schedule_effect(signal) {
+	var effect = (last_scheduled_effect = signal);
+
+	while (effect.parent !== null) {
+		effect = effect.parent;
+		var flags = effect.f;
+
+		// if the effect is being scheduled because a parent (each/await/etc) block
+		// updated an internal source, bail out or we'll cause a second flush
+		if (is_flushing && effect === active_effect && (flags & BLOCK_EFFECT) !== 0) {
+			return;
+		}
+
+		if ((flags & (ROOT_EFFECT | BRANCH_EFFECT)) !== 0) {
+			if ((flags & CLEAN) === 0) return;
+			effect.f ^= CLEAN;
+		}
+	}
+
+	queued_root_effects.push(effect);
+}
+
+export function suspend() {
+	var boundary = get_pending_boundary();
+	var batch = /** @type {Batch} */ (current_batch);
+	var pending = boundary.pending;
+
+	boundary.update_pending_count(1);
+	if (!pending) batch.increment();
+
+	return function unsuspend() {
+		boundary.update_pending_count(-1);
+		if (!pending) batch.decrement();
+
+		unset_context();
+	};
+}
+
+/**
+ * Forcibly remove all current batches, to prevent cross-talk between tests
+ */
+export function clear() {
+	batches.clear();
+}
diff --git a/packages/svelte/src/internal/client/reactivity/deriveds.js b/packages/svelte/src/internal/client/reactivity/deriveds.js
index e563c77534..fa6a9e02a1 100644
--- a/packages/svelte/src/internal/client/reactivity/deriveds.js
+++ b/packages/svelte/src/internal/client/reactivity/deriveds.js
@@ -1,6 +1,17 @@
-/** @import { Derived, Effect } from '#client' */
+/** @import { Derived, Effect, Source } from '#client' */
+/** @import { Batch } from './batch.js'; */
 import { DEV } from 'esm-env';
-import { CLEAN, DERIVED, DIRTY, EFFECT_PRESERVED, MAYBE_DIRTY, UNOWNED } from '#client/constants';
+import {
+	ERROR_VALUE,
+	CLEAN,
+	DERIVED,
+	DIRTY,
+	EFFECT_PRESERVED,
+	MAYBE_DIRTY,
+	STALE_REACTION,
+	UNOWNED,
+	ASYNC
+} from '#client/constants';
 import {
 	active_reaction,
 	active_effect,
@@ -14,12 +25,26 @@ import {
 } from '../runtime.js';
 import { equals, safe_equals } from './equality.js';
 import * as e from '../errors.js';
-import { destroy_effect } from './effects.js';
-import { inspect_effects, set_inspect_effects } from './sources.js';
+import * as w from '../warnings.js';
+import { async_effect, destroy_effect } from './effects.js';
+import { inspect_effects, internal_set, set_inspect_effects, source } from './sources.js';
 import { get_stack } from '../dev/tracing.js';
 import { tracing_mode_flag } from '../../flags/index.js';
+import { Boundary } from '../dom/blocks/boundary.js';
 import { component_context } from '../context.js';
 import { UNINITIALIZED } from '../../../constants.js';
+import { batch_deriveds, current_batch } from './batch.js';
+import { unset_context } from './async.js';
+
+/** @type {Effect | null} */
+export let current_async_effect = null;
+
+/** @param {Effect | null} v */
+export function set_from_async_derived(v) {
+	current_async_effect = v;
+}
+
+export const recent_async_deriveds = new Set();
 
 /**
  * @template V
@@ -65,6 +90,135 @@ export function derived(fn) {
 	return signal;
 }
 
+/**
+ * @template V
+ * @param {() => V | Promise<V>} fn
+ * @param {string} [location] If provided, print a warning if the value is not read immediately after update
+ * @returns {Promise<Source<V>>}
+ */
+/*#__NO_SIDE_EFFECTS__*/
+export function async_derived(fn, location) {
+	let parent = /** @type {Effect | null} */ (active_effect);
+
+	if (parent === null) {
+		e.async_derived_orphan();
+	}
+
+	var boundary = /** @type {Boundary} */ (parent.b);
+
+	var promise = /** @type {Promise<V>} */ (/** @type {unknown} */ (undefined));
+	var signal = source(/** @type {V} */ (UNINITIALIZED));
+
+	/** @type {Promise<V> | null} */
+	var prev = null;
+
+	// only suspend in async deriveds created on initialisation
+	var should_suspend = !active_reaction;
+
+	async_effect(() => {
+		if (DEV) current_async_effect = active_effect;
+
+		try {
+			var p = fn();
+		} catch (error) {
+			p = Promise.reject(error);
+		}
+
+		if (DEV) current_async_effect = null;
+
+		var r = () => p;
+		promise = prev?.then(r, r) ?? Promise.resolve(p);
+
+		prev = promise;
+
+		var batch = /** @type {Batch} */ (current_batch);
+		var pending = boundary.pending;
+
+		if (should_suspend) {
+			boundary.update_pending_count(1);
+			if (!pending) batch.increment();
+		}
+
+		/**
+		 * @param {any} value
+		 * @param {unknown} error
+		 */
+		const handler = (value, error = undefined) => {
+			prev = null;
+
+			current_async_effect = null;
+
+			if (!pending) batch.activate();
+
+			if (error) {
+				if (error !== STALE_REACTION) {
+					signal.f |= ERROR_VALUE;
+
+					// @ts-expect-error the error is the wrong type, but we don't care
+					internal_set(signal, error);
+				}
+			} else {
+				if ((signal.f & ERROR_VALUE) !== 0) {
+					signal.f ^= ERROR_VALUE;
+				}
+
+				internal_set(signal, value);
+
+				if (DEV && location !== undefined) {
+					recent_async_deriveds.add(signal);
+
+					setTimeout(() => {
+						if (recent_async_deriveds.has(signal)) {
+							w.await_waterfall(/** @type {string} */ (signal.label), location);
+							recent_async_deriveds.delete(signal);
+						}
+					});
+				}
+			}
+
+			if (should_suspend) {
+				boundary.update_pending_count(-1);
+				if (!pending) batch.decrement();
+			}
+
+			unset_context();
+		};
+
+		promise.then(handler, (e) => handler(null, e || 'unknown'));
+
+		if (batch) {
+			return () => {
+				queueMicrotask(() => batch.neuter());
+			};
+		}
+	});
+
+	if (DEV) {
+		// add a flag that lets this be printed as a derived
+		// when using `$inspect.trace()`
+		signal.f |= ASYNC;
+	}
+
+	return new Promise((fulfil) => {
+		/** @param {Promise<V>} p */
+		function next(p) {
+			function go() {
+				if (p === promise) {
+					fulfil(signal);
+				} else {
+					// if the effect re-runs before the initial promise
+					// resolves, delay resolution until we have a value
+					next(promise);
+				}
+			}
+
+			p.then(go, go);
+		}
+
+		next(promise);
+	});
+}
+
 /**
  * @template V
  * @param {() => V} fn
@@ -185,8 +339,12 @@ export function update_derived(derived) {
 	// cleanup function, or it will cache a stale value
 	if (is_destroying_effect) return;
 
-	var status =
-		(skip_reaction || (derived.f & UNOWNED) !== 0) && derived.deps !== null ? MAYBE_DIRTY : CLEAN;
+	if (batch_deriveds !== null) {
+		batch_deriveds.set(derived, derived.v);
+	} else {
+		var status =
+			(skip_reaction || (derived.f & UNOWNED) !== 0) && derived.deps !== null ? MAYBE_DIRTY : CLEAN;
 
-	set_signal_status(derived, status);
+		set_signal_status(derived, status);
+	}
 }
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index b6a40a68be..c4edd2bf8d 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -7,7 +7,6 @@ import {
 	get,
 	is_destroying_effect,
 	remove_reactions,
-	schedule_effect,
 	set_active_reaction,
 	set_is_destroying_effect,
 	set_signal_status,
@@ -32,17 +31,17 @@ import {
 	HEAD_EFFECT,
 	MAYBE_DIRTY,
 	EFFECT_PRESERVED,
-	BOUNDARY_EFFECT,
 	STALE_REACTION,
-	USER_EFFECT
+	USER_EFFECT,
+	ASYNC
 } from '#client/constants';
-import { set } from './sources.js';
 import * as e from '../errors.js';
 import { DEV } from 'esm-env';
 import { define_property } from '../../shared/utils.js';
 import { get_next_sibling } from '../dom/operations.js';
-import { derived } from './deriveds.js';
 import { component_context, dev_current_component_function, dev_stack } from '../context.js';
+import { Batch, schedule_effect } from './batch.js';
+import { flatten } from './async.js';
 
 /**
  * @param {'$effect' | '$effect.pre' | '$inspect'} rune
@@ -93,6 +92,10 @@ function create_effect(type, fn, sync, push = true) {
 		}
 	}
 
+	if (parent !== null && (parent.f & INERT) !== 0) {
+		type |= INERT;
+	}
+
 	/** @type {Effect} */
 	var effect = {
 		ctx: component_context,
@@ -137,7 +140,7 @@ function create_effect(type, fn, sync, push = true) {
 		effect.first === null &&
 		effect.nodes_start === null &&
 		effect.teardown === null &&
-		(effect.f & (EFFECT_PRESERVED | BOUNDARY_EFFECT)) === 0;
+		(effect.f & EFFECT_PRESERVED) === 0;
 
 	if (!inert && push) {
 		if (parent !== null) {
@@ -185,8 +188,13 @@ export function user_effect(fn) {
 		});
 	}
 
-	if (!active_reaction && active_effect && (active_effect.f & BRANCH_EFFECT) !== 0) {
-		// Top-level `$effect(...)` in a component — defer until mount
+	// Non-nested `$effect(...)` in a component should be deferred
+	// until the component is mounted
+	var flags = /** @type {Effect} */ (active_effect).f;
+	var defer = !active_reaction && (flags & BRANCH_EFFECT) !== 0 && (flags & EFFECT_RAN) === 0;
+
+	if (defer) {
+		// Top-level `$effect(...)` in an unmounted component — defer until mount
 		var context = /** @type {ComponentContext} */ (component_context);
 		(context.e ??= []).push(fn);
 	} else {
@@ -228,6 +236,7 @@ export function inspect_effect(fn) {
  * @returns {() => void}
  */
 export function effect_root(fn) {
+	Batch.ensure();
 	const effect = create_effect(ROOT_EFFECT, fn, true);
 
 	return () => {
@@ -241,6 +250,7 @@ export function effect_root(fn) {
  * @returns {(options?: { outro?: boolean }) => Promise<void>}
  */
 export function component_root(fn) {
+	Batch.ensure();
 	const effect = create_effect(ROOT_EFFECT, fn, true);
 
 	return (options = {}) => {
@@ -274,9 +284,10 @@ export function effect(fn) {
 export function legacy_pre_effect(deps, fn) {
 	var context = /** @type {ComponentContextLegacy} */ (component_context);
 
-	/** @type {{ effect: null | Effect, ran: boolean }} */
-	var token = { effect: null, ran: false };
-	context.l.r1.push(token);
+	/** @type {{ effect: null | Effect, ran: boolean, deps: () => any }} */
+	var token = { effect: null, ran: false, deps };
+
+	context.l.$.push(token);
 
 	token.effect = render_effect(() => {
 		deps();
@@ -286,7 +297,6 @@ export function legacy_pre_effect(deps, fn) {
 		if (token.ran) return;
 
 		token.ran = true;
-		set(context.l.r2, true);
 		untrack(fn);
 	});
 }
@@ -295,10 +305,10 @@ export function legacy_pre_effect_reset() {
 	var context = /** @type {ComponentContextLegacy} */ (component_context);
 
 	render_effect(() => {
-		if (!get(context.l.r2)) return;
-
 		// Run dirty `$:` statements
-		for (var token of context.l.r1) {
+		for (var token of context.l.$) {
+			token.deps();
+
 			var effect = token.effect;
 
 			// If the effect is CLEAN, then make it MAYBE_DIRTY. This ensures we traverse through
@@ -313,8 +323,6 @@ export function legacy_pre_effect_reset() {
 
 			token.ran = false;
 		}
-
-		context.l.r2.v = false; // set directly to avoid rerunning this effect
 	});
 }
 
@@ -322,34 +330,27 @@ export function legacy_pre_effect_reset() {
  * @param {() => void | (() => void)} fn
  * @returns {Effect}
  */
-export function render_effect(fn) {
-	return create_effect(RENDER_EFFECT, fn, true);
+export function async_effect(fn) {
+	return create_effect(ASYNC | EFFECT_PRESERVED, fn, true);
 }
 
 /**
- * @param {(...expressions: any) => void | (() => void)} fn
- * @param {Array<() => any>} thunks
- * @param {<T>(fn: () => T) => Derived<T>} d
+ * @param {() => void | (() => void)} fn
  * @returns {Effect}
  */
-export function template_effect(fn, thunks = [], d = derived) {
-	if (DEV) {
-		// wrap the effect so that we can decorate stack trace with `in {expression}`
-		// (TODO maybe there's a better approach?)
-		return render_effect(() => {
-			var outer = /** @type {Effect} */ (active_effect);
-			var inner = () => fn(...deriveds.map(get));
-
-			define_property(outer.fn, 'name', { value: '{expression}' });
-			define_property(inner, 'name', { value: '{expression}' });
-
-			const deriveds = thunks.map(d);
-			block(inner);
-		});
-	}
+export function render_effect(fn, flags = 0) {
+	return create_effect(RENDER_EFFECT | flags, fn, true);
+}
 
-	const deriveds = thunks.map(d);
-	return block(() => fn(...deriveds.map(get)));
+/**
+ * @param {(...expressions: any) => void | (() => void)} fn
+ * @param {Array<() => any>} sync
+ * @param {Array<() => Promise<any>>} async
+ */
+export function template_effect(fn, sync = [], async = []) {
+	flatten(sync, async, (values) => {
+		create_effect(RENDER_EFFECT, () => fn(...values.map(get)), true);
+	});
 }
 
 /**
@@ -357,7 +358,7 @@ export function template_effect(fn, thunks = [], d = derived) {
  * @param {number} flags
  */
 export function block(fn, flags = 0) {
-	var effect = create_effect(RENDER_EFFECT | BLOCK_EFFECT | flags, fn, true);
+	var effect = create_effect(BLOCK_EFFECT | flags, fn, true);
 	if (DEV) {
 		effect.dev_stack = dev_stack;
 	}
@@ -369,7 +370,7 @@ export function block(fn, flags = 0) {
  * @param {boolean} [push]
  */
 export function branch(fn, push = true) {
-	return create_effect(RENDER_EFFECT | BRANCH_EFFECT, fn, true, push);
+	return create_effect(BRANCH_EFFECT, fn, true, push);
 }
 
 /**
@@ -606,6 +607,15 @@ function resume_children(effect, local) {
 	if ((effect.f & INERT) === 0) return;
 	effect.f ^= INERT;
 
+	// If a dependency of this effect changed while it was paused,
+	// schedule the effect to update. we don't use `is_dirty`
+	// here because we don't want to eagerly recompute a derived like
+	// `{#if foo}{foo.bar()}{/if}` if `foo` is now `undefined
+	if ((effect.f & CLEAN) === 0) {
+		set_signal_status(effect, DIRTY);
+		schedule_effect(effect);
+	}
+
 	var child = effect.first;
 
 	while (child !== null) {
@@ -626,3 +636,8 @@ function resume_children(effect, local) {
 		}
 	}
 }
+
+export function aborted() {
+	var effect = /** @type {Effect} */ (active_effect);
+	return (effect.f & DESTROYED) !== 0;
+}
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index c04443c93e..29c657bdd0 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -5,7 +5,6 @@ import {
 	active_effect,
 	untracked_writes,
 	get,
-	schedule_effect,
 	set_untracked_writes,
 	set_signal_status,
 	untrack,
@@ -27,12 +26,14 @@ import {
 	UNOWNED,
 	MAYBE_DIRTY,
 	BLOCK_EFFECT,
-	ROOT_EFFECT
+	ROOT_EFFECT,
+	ASYNC
 } from '#client/constants';
 import * as e from '../errors.js';
 import { legacy_mode_flag, tracing_mode_flag } from '../../flags/index.js';
 import { get_stack, tag_proxy } from '../dev/tracing.js';
 import { component_context, is_runes } from '../context.js';
+import { Batch, schedule_effect } from './batch.js';
 import { proxy } from '../proxy.js';
 import { execute_derived } from './deriveds.js';
 
@@ -139,7 +140,7 @@ export function set(source, value, should_proxy = false) {
 		// to ensure we error if state is set inside an inspect effect
 		(!untracking || (active_reaction.f & INSPECT_EFFECT) !== 0) &&
 		is_runes() &&
-		(active_reaction.f & (DERIVED | BLOCK_EFFECT | INSPECT_EFFECT)) !== 0 &&
+		(active_reaction.f & (DERIVED | BLOCK_EFFECT | ASYNC | INSPECT_EFFECT)) !== 0 &&
 		!current_sources?.includes(source)
 	) {
 		e.state_unsafe_mutation();
@@ -172,6 +173,9 @@ export function internal_set(source, value) {
 
 		source.v = value;
 
+		const batch = Batch.ensure();
+		batch.capture(source, old_value);
+
 		if (DEV && tracing_mode_flag) {
 			source.updated = get_stack('UpdatedAt');
 
@@ -218,6 +222,7 @@ export function internal_set(source, value) {
 				if ((effect.f & CLEAN) !== 0) {
 					set_signal_status(effect, MAYBE_DIRTY);
 				}
+
 				if (is_dirty(effect)) {
 					update_effect(effect);
 				}
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 5eca31e8cf..b5f6822207 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -1,36 +1,36 @@
 /** @import { Derived, Effect, Reaction, Signal, Source, Value } from '#client' */
 import { DEV } from 'esm-env';
-import { define_property, get_descriptors, get_prototype_of, index_of } from '../shared/utils.js';
+import { get_descriptors, get_prototype_of, index_of } from '../shared/utils.js';
 import {
 	destroy_block_effect_children,
 	destroy_effect_children,
-	execute_effect_teardown,
-	unlink_effect
+	execute_effect_teardown
 } from './reactivity/effects.js';
 import {
-	EFFECT,
 	DIRTY,
 	MAYBE_DIRTY,
 	CLEAN,
 	DERIVED,
 	UNOWNED,
 	DESTROYED,
-	INERT,
 	BRANCH_EFFECT,
 	STATE_SYMBOL,
 	BLOCK_EFFECT,
 	ROOT_EFFECT,
 	DISCONNECTED,
-	EFFECT_IS_UPDATING,
+	REACTION_IS_UPDATING,
 	STALE_REACTION,
-	USER_EFFECT
+	ERROR_VALUE
 } from './constants.js';
-import { flush_tasks } from './dom/task.js';
 import { internal_set, old_values } from './reactivity/sources.js';
-import { destroy_derived_effects, execute_derived, update_derived } from './reactivity/deriveds.js';
-import * as e from './errors.js';
-
-import { tracing_mode_flag } from '../flags/index.js';
+import {
+	destroy_derived_effects,
+	execute_derived,
+	current_async_effect,
+	recent_async_deriveds,
+	update_derived
+} from './reactivity/deriveds.js';
+import { async_mode_flag, tracing_mode_flag } from '../flags/index.js';
 import { tracing_expressions, get_stack } from './dev/tracing.js';
 import {
 	component_context,
@@ -41,15 +41,23 @@ import {
 	set_dev_current_component_function,
 	set_dev_stack
 } from './context.js';
-import { handle_error, invoke_error_boundary } from './error-handling.js';
+import * as w from './warnings.js';
+import {
+	Batch,
+	batch_deriveds,
+	dev_effect_stack,
+	flushSync,
+	schedule_effect
+} from './reactivity/batch.js';
+import { handle_error } from './error-handling.js';
 import { UNINITIALIZED } from '../../constants.js';
 
-let is_flushing = false;
+export let is_updating_effect = false;
 
-/** @type {Effect | null} */
-let last_scheduled_effect = null;
-
-let is_updating_effect = false;
+/** @param {boolean} value */
+export function set_is_updating_effect(value) {
+	is_updating_effect = value;
+}
 
 export let is_destroying_effect = false;
 
@@ -58,15 +66,6 @@ export function set_is_destroying_effect(value) {
 	is_destroying_effect = value;
 }
 
-// Handle effect queues
-
-/** @type {Effect[]} */
-let queued_root_effects = [];
-
-/** @type {Effect[]} Stack of effects, dev only */
-let dev_effect_stack = [];
-// Handle signal reactivity tree dependencies and reactions
-
 /** @type {null | Reaction} */
 export let active_reaction = null;
 
@@ -94,7 +93,7 @@ export let current_sources = null;
 
 /** @param {Value} value */
 export function push_reaction_value(value) {
-	if (active_reaction !== null && active_reaction.f & EFFECT_IS_UPDATING) {
+	if (active_reaction !== null && (!async_mode_flag || (active_reaction.f & DERIVED) !== 0)) {
 		if (current_sources === null) {
 			current_sources = [value];
 		} else {
@@ -129,7 +128,7 @@ export function set_untracked_writes(value) {
  * @type {number} Used by sources and deriveds for handling updates.
  * Version starts from 1 so that unowned deriveds differentiate between a created effect and a run one for tracing
  **/
-let write_version = 1;
+export let write_version = 1;
 
 /** @type {number} Used to version each read of a source of derived to avoid duplicating depedencies inside a reaction */
 let read_version = 0;
@@ -182,8 +181,12 @@ export function is_dirty(reaction) {
 			var length = dependencies.length;
 
 			// If we are working with a disconnected or an unowned signal that is now connected (due to an active effect)
-			// then we need to re-connect the reaction to the dependency
-			if (is_disconnected || is_unowned_connected) {
+			// then we need to re-connect the reaction to the dependency, unless the effect has already been destroyed
+			// (which can happen if the derived is read by an async derived)
+			if (
+				(is_disconnected || is_unowned_connected) &&
+				(active_effect === null || (active_effect.f & DESTROYED) === 0)
+			) {
 				var derived = /** @type {Derived} */ (reaction);
 				var parent = derived.parent;
 
@@ -241,7 +244,7 @@ function schedule_possible_effect_self_invalidation(signal, effect, root = true)
 	var reactions = signal.reactions;
 	if (reactions === null) return;
 
-	if (current_sources?.includes(signal)) {
+	if (!async_mode_flag && current_sources?.includes(signal)) {
 		return;
 	}
 
@@ -287,14 +290,13 @@ export function update_reaction(reaction) {
 	untracking = false;
 	update_version = ++read_version;
 
-	reaction.f |= EFFECT_IS_UPDATING;
-
 	if (reaction.ac !== null) {
 		reaction.ac.abort(STALE_REACTION);
 		reaction.ac = null;
 	}
 
 	try {
+		reaction.f |= REACTION_IS_UPDATING;
 		var result = /** @type {Function} */ (0, reaction.fn)();
 		var deps = reaction.deps;
 
@@ -361,10 +363,15 @@ export function update_reaction(reaction) {
 			}
 		}
 
+		if ((reaction.f & ERROR_VALUE) !== 0) {
+			reaction.f ^= ERROR_VALUE;
+		}
+
 		return result;
 	} catch (error) {
-		handle_error(error);
+		return handle_error(error);
 	} finally {
+		reaction.f ^= REACTION_IS_UPDATING;
 		new_deps = previous_deps;
 		skipped_deps = previous_skipped_deps;
 		untracked_writes = previous_untracked_writes;
@@ -374,8 +381,6 @@ export function update_reaction(reaction) {
 		set_component_context(previous_component_context);
 		untracking = previous_untracking;
 		update_version = previous_update_version;
-
-		reaction.f ^= EFFECT_IS_UPDATING;
 	}
 }
 
@@ -400,6 +405,7 @@ function remove_reaction(signal, dependency) {
 			}
 		}
 	}
+
 	// If the derived has no reactions, then we can disconnect it from the graph,
 	// allowing it to either reconnect in the future, or be GC'd by the VM.
 	if (
@@ -500,253 +506,29 @@ export function update_effect(effect) {
 	}
 }
 
-function log_effect_stack() {
-	// eslint-disable-next-line no-console
-	console.error(
-		'Last ten effects were: ',
-		dev_effect_stack.slice(-10).map((d) => d.fn)
-	);
-	dev_effect_stack = [];
-}
-
-function infinite_loop_guard() {
-	try {
-		e.effect_update_depth_exceeded();
-	} catch (error) {
-		if (DEV) {
-			// stack is garbage, ignore. Instead add a console.error message.
-			define_property(error, 'stack', {
-				value: ''
-			});
-		}
-		// Try and handle the error so it can be caught at a boundary, that's
-		// if there's an effect available from when it was last scheduled
-		if (last_scheduled_effect !== null) {
-			if (DEV) {
-				try {
-					invoke_error_boundary(error, last_scheduled_effect);
-				} catch (e) {
-					// Only log the effect stack if the error is re-thrown
-					log_effect_stack();
-					throw e;
-				}
-			} else {
-				invoke_error_boundary(error, last_scheduled_effect);
-			}
-		} else {
-			if (DEV) {
-				log_effect_stack();
-			}
-			throw error;
-		}
-	}
-}
-
-function flush_queued_root_effects() {
-	var was_updating_effect = is_updating_effect;
-
-	try {
-		var flush_count = 0;
-		is_updating_effect = true;
-
-		while (queued_root_effects.length > 0) {
-			if (flush_count++ > 1000) {
-				infinite_loop_guard();
-			}
-
-			var root_effects = queued_root_effects;
-			var length = root_effects.length;
-
-			queued_root_effects = [];
-
-			for (var i = 0; i < length; i++) {
-				var collected_effects = process_effects(root_effects[i]);
-				flush_queued_effects(collected_effects);
-			}
-			old_values.clear();
-		}
-	} finally {
-		is_flushing = false;
-		is_updating_effect = was_updating_effect;
-
-		last_scheduled_effect = null;
-		if (DEV) {
-			dev_effect_stack = [];
-		}
-	}
-}
-
 /**
- * @param {Array<Effect>} effects
- * @returns {void}
- */
-function flush_queued_effects(effects) {
-	var length = effects.length;
-	if (length === 0) return;
-
-	for (var i = 0; i < length; i++) {
-		var effect = effects[i];
-
-		if ((effect.f & (DESTROYED | INERT)) === 0) {
-			if (is_dirty(effect)) {
-				var wv = write_version;
-
-				update_effect(effect);
-
-				// Effects with no dependencies or teardown do not get added to the effect tree.
-				// Deferred effects (e.g. `$effect(...)`) _are_ added to the tree because we
-				// don't know if we need to keep them until they are executed. Doing the check
-				// here (rather than in `update_effect`) allows us to skip the work for
-				// immediate effects.
-				if (effect.deps === null && effect.first === null && effect.nodes_start === null) {
-					if (effect.teardown === null) {
-						// remove this effect from the graph
-						unlink_effect(effect);
-					} else {
-						// keep the effect in the graph, but free up some memory
-						effect.fn = null;
-					}
-				}
-
-				// if state is written in a user effect, abort and re-schedule, lest we run
-				// effects that should be removed as a result of the state change
-				if (write_version > wv && (effect.f & USER_EFFECT) !== 0) {
-					break;
-				}
-			}
-		}
-	}
-
-	for (; i < length; i += 1) {
-		schedule_effect(effects[i]);
-	}
-}
-
-/**
- * @param {Effect} signal
- * @returns {void}
- */
-export function schedule_effect(signal) {
-	if (!is_flushing) {
-		is_flushing = true;
-		queueMicrotask(flush_queued_root_effects);
-	}
-
-	var effect = (last_scheduled_effect = signal);
-
-	while (effect.parent !== null) {
-		effect = effect.parent;
-		var flags = effect.f;
-
-		if ((flags & (ROOT_EFFECT | BRANCH_EFFECT)) !== 0) {
-			if ((flags & CLEAN) === 0) return;
-			effect.f ^= CLEAN;
-		}
-	}
-
-	queued_root_effects.push(effect);
-}
-
-/**
- *
- * This function both runs render effects and collects user effects in topological order
- * from the starting effect passed in. Effects will be collected when they match the filtered
- * bitwise flag passed in only. The collected effects array will be populated with all the user
- * effects to be flushed.
- *
- * @param {Effect} root
- * @returns {Effect[]}
- */
-function process_effects(root) {
-	/** @type {Effect[]} */
-	var effects = [];
-
-	/** @type {Effect | null} */
-	var effect = root;
-
-	while (effect !== null) {
-		var flags = effect.f;
-		var is_branch = (flags & (BRANCH_EFFECT | ROOT_EFFECT)) !== 0;
-		var is_skippable_branch = is_branch && (flags & CLEAN) !== 0;
-
-		if (!is_skippable_branch && (flags & INERT) === 0) {
-			if ((flags & EFFECT) !== 0) {
-				effects.push(effect);
-			} else if (is_branch) {
-				effect.f ^= CLEAN;
-			} else {
-				if (is_dirty(effect)) {
-					update_effect(effect);
-				}
-			}
-
-			/** @type {Effect | null} */
-			var child = effect.first;
-
-			if (child !== null) {
-				effect = child;
-				continue;
-			}
-		}
-
-		var parent = effect.parent;
-		effect = effect.next;
-
-		while (effect === null && parent !== null) {
-			effect = parent.next;
-			parent = parent.parent;
-		}
-	}
-
-	return effects;
-}
-
-/**
- * Synchronously flush any pending updates.
- * Returns void if no callback is provided, otherwise returns the result of calling the callback.
- * @template [T=void]
- * @param {(() => T) | undefined} [fn]
- * @returns {T}
+ * Returns a promise that resolves once any pending state changes have been applied.
+ * @returns {Promise<void>}
  */
-export function flushSync(fn) {
-	var result;
-
-	if (fn) {
-		is_flushing = true;
-		flush_queued_root_effects();
-
-		is_flushing = true;
-		result = fn();
+export async function tick() {
+	if (async_mode_flag) {
+		return new Promise((f) => requestAnimationFrame(() => f()));
 	}
 
-	while (true) {
-		flush_tasks();
-
-		if (queued_root_effects.length === 0) {
-			// this would be reset in `flush_queued_root_effects` but since we are early returning here,
-			// we need to reset it here as well in case the first time there's 0 queued root effects
-			is_flushing = false;
-			last_scheduled_effect = null;
-			if (DEV) {
-				dev_effect_stack = [];
-			}
-			return /** @type {T} */ (result);
-		}
+	await Promise.resolve();
 
-		is_flushing = true;
-		flush_queued_root_effects();
-	}
+	// By calling flushSync we guarantee that any pending state changes are applied after one tick.
+	// TODO look into whether we can make flushing subsequent updates synchronously in the future.
+	flushSync();
 }
 
 /**
- * Returns a promise that resolves once any pending state changes have been applied.
+ * Returns a promise that resolves once any state changes, and asynchronous work resulting from them,
+ * have resolved and the DOM has been updated
  * @returns {Promise<void>}
  */
-export async function tick() {
-	await Promise.resolve();
-	// By calling flushSync we guarantee that any pending state changes are applied after one tick.
-	// TODO look into whether we can make flushing subsequent updates synchronously in the future.
-	flushSync();
+export function settled() {
+	return Batch.ensure().settled();
 }
 
 /**
@@ -764,22 +546,44 @@ export function get(signal) {
 
 	// Register the dependency on the current reaction signal.
 	if (active_reaction !== null && !untracking) {
-		if (!current_sources?.includes(signal)) {
+		// if we're in a derived that is being read inside an _async_ derived,
+		// it's possible that the effect was already destroyed. In this case,
+		// we don't add the dependency, because that would create a memory leak
+		var destroyed = active_effect !== null && (active_effect.f & DESTROYED) !== 0;
+
+		if (!destroyed && !current_sources?.includes(signal)) {
 			var deps = active_reaction.deps;
-			if (signal.rv < read_version) {
-				signal.rv = read_version;
-				// If the signal is accessing the same dependencies in the same
-				// order as it did last time, increment `skipped_deps`
-				// rather than updating `new_deps`, which creates GC cost
-				if (new_deps === null && deps !== null && deps[skipped_deps] === signal) {
-					skipped_deps++;
-				} else if (new_deps === null) {
-					new_deps = [signal];
-				} else if (!skip_reaction || !new_deps.includes(signal)) {
-					// Normally we can push duplicated dependencies to `new_deps`, but if we're inside
-					// an unowned derived because skip_reaction is true, then we need to ensure that
-					// we don't have duplicates
-					new_deps.push(signal);
+
+			if ((active_reaction.f & REACTION_IS_UPDATING) !== 0) {
+				// we're in the effect init/update cycle
+				if (signal.rv < read_version) {
+					signal.rv = read_version;
+
+					// If the signal is accessing the same dependencies in the same
+					// order as it did last time, increment `skipped_deps`
+					// rather than updating `new_deps`, which creates GC cost
+					if (new_deps === null && deps !== null && deps[skipped_deps] === signal) {
+						skipped_deps++;
+					} else if (new_deps === null) {
+						new_deps = [signal];
+					} else if (!skip_reaction || !new_deps.includes(signal)) {
+						// Normally we can push duplicated dependencies to `new_deps`, but if we're inside
+						// an unowned derived because skip_reaction is true, then we need to ensure that
+						// we don't have duplicates
+						new_deps.push(signal);
+					}
+				}
+			} else {
+				// we're adding a dependency outside the init/update cycle
+				// (i.e. after an `await`)
+				(active_reaction.deps ??= []).push(signal);
+
+				var reactions = signal.reactions;
+
+				if (reactions === null) {
+					signal.reactions = [active_reaction];
+				} else if (!reactions.includes(active_reaction)) {
+					reactions.push(active_reaction);
 				}
 			}
 		}
@@ -799,42 +603,50 @@ export function get(signal) {
 		}
 	}
 
-	if (is_derived && !is_destroying_effect) {
-		derived = /** @type {Derived} */ (signal);
+	if (DEV) {
+		if (current_async_effect) {
+			var tracking = (current_async_effect.f & REACTION_IS_UPDATING) !== 0;
+			var was_read = current_async_effect.deps?.includes(signal);
 
-		if (is_dirty(derived)) {
-			update_derived(derived);
+			if (!tracking && !was_read) {
+				w.await_reactivity_loss(/** @type {string} */ (signal.label));
+
+				var trace = get_stack('TracedAt');
+				// eslint-disable-next-line no-console
+				if (trace) console.warn(trace);
+			}
 		}
-	}
 
-	if (
-		DEV &&
-		tracing_mode_flag &&
-		!untracking &&
-		tracing_expressions !== null &&
-		active_reaction !== null &&
-		tracing_expressions.reaction === active_reaction
-	) {
-		// Used when mapping state between special blocks like `each`
-		if (signal.trace) {
-			signal.trace();
-		} else {
-			var trace = get_stack('TracedAt');
+		recent_async_deriveds.delete(signal);
 
-			if (trace) {
-				var entry = tracing_expressions.entries.get(signal);
+		if (
+			tracing_mode_flag &&
+			!untracking &&
+			tracing_expressions !== null &&
+			active_reaction !== null &&
+			tracing_expressions.reaction === active_reaction
+		) {
+			// Used when mapping state between special blocks like `each`
+			if (signal.trace) {
+				signal.trace();
+			} else {
+				trace = get_stack('TracedAt');
 
-				if (entry === undefined) {
-					entry = { traces: [] };
-					tracing_expressions.entries.set(signal, entry);
-				}
+				if (trace) {
+					var entry = tracing_expressions.entries.get(signal);
+
+					if (entry === undefined) {
+						entry = { traces: [] };
+						tracing_expressions.entries.set(signal, entry);
+					}
 
-				var last = entry.traces[entry.traces.length - 1];
+					var last = entry.traces[entry.traces.length - 1];
 
-				// traces can be duplicated, e.g. by `snapshot` invoking both
-				// both `getOwnPropertyDescriptor` and `get` traps at once
-				if (trace.stack !== last?.stack) {
-					entry.traces.push(trace);
+					// traces can be duplicated, e.g. by `snapshot` invoking both
+					// both `getOwnPropertyDescriptor` and `get` traps at once
+					if (trace.stack !== last?.stack) {
+						entry.traces.push(trace);
+					}
 				}
 			}
 		}
@@ -859,6 +671,20 @@ export function get(signal) {
 
 			return value;
 		}
+	} else if (is_derived) {
+		derived = /** @type {Derived} */ (signal);
+
+		if (batch_deriveds?.has(derived)) {
+			return batch_deriveds.get(derived);
+		}
+
+		if (is_dirty(derived)) {
+			update_derived(derived);
+		}
+	}
+
+	if ((signal.f & ERROR_VALUE) !== 0) {
+		throw signal.v;
 	}
 
 	return signal.v;
diff --git a/packages/svelte/src/internal/client/types.d.ts b/packages/svelte/src/internal/client/types.d.ts
index a42f91343c..d24218c4d3 100644
--- a/packages/svelte/src/internal/client/types.d.ts
+++ b/packages/svelte/src/internal/client/types.d.ts
@@ -43,9 +43,7 @@ export type ComponentContext = {
 			m: Array<() => any>;
 		};
 		/** `$:` statements */
-		r1: any[];
-		/** This tracks whether `$:` statements have run in the current cycle, to ensure they only run once */
-		r2: Source<boolean>;
+		$: any[];
 	};
 	/**
 	 * dev mode only: the component function
diff --git a/packages/svelte/src/internal/client/warnings.js b/packages/svelte/src/internal/client/warnings.js
index 74f9041b91..dfd50a8722 100644
--- a/packages/svelte/src/internal/client/warnings.js
+++ b/packages/svelte/src/internal/client/warnings.js
@@ -18,6 +18,31 @@ export function assignment_value_stale(property, location) {
 	}
 }
 
+/**
+ * Detected reactivity loss when reading `%name%`. This happens when state is read in an async function after an earlier `await`
+ * @param {string} name
+ */
+export function await_reactivity_loss(name) {
+	if (DEV) {
+		console.warn(`%c[svelte] await_reactivity_loss\n%cDetected reactivity loss when reading \`${name}\`. This happens when state is read in an async function after an earlier \`await\`\nhttps://svelte.dev/e/await_reactivity_loss`, bold, normal);
+	} else {
+		console.warn(`https://svelte.dev/e/await_reactivity_loss`);
+	}
+}
+
+/**
+ * An async derived, `%name%` (%location%) was not read immediately after it resolved. This often indicates an unnecessary waterfall, which can slow down your app
+ * @param {string} name
+ * @param {string} location
+ */
+export function await_waterfall(name, location) {
+	if (DEV) {
+		console.warn(`%c[svelte] await_waterfall\n%cAn async derived, \`${name}\` (${location}) was not read immediately after it resolved. This often indicates an unnecessary waterfall, which can slow down your app\nhttps://svelte.dev/e/await_waterfall`, bold, normal);
+	} else {
+		console.warn(`https://svelte.dev/e/await_waterfall`);
+	}
+}
+
 /**
  * `%binding%` (%location%) is binding to a non-reactive property
  * @param {string} binding
diff --git a/packages/svelte/src/internal/flags/async.js b/packages/svelte/src/internal/flags/async.js
new file mode 100644
index 0000000000..ca4ff9286a
--- /dev/null
+++ b/packages/svelte/src/internal/flags/async.js
@@ -0,0 +1,3 @@
+import { enable_async_mode_flag } from './index.js';
+
+enable_async_mode_flag();
diff --git a/packages/svelte/src/internal/flags/index.js b/packages/svelte/src/internal/flags/index.js
index 017840f2d9..ce7bba604b 100644
--- a/packages/svelte/src/internal/flags/index.js
+++ b/packages/svelte/src/internal/flags/index.js
@@ -1,6 +1,16 @@
+export let async_mode_flag = false;
 export let legacy_mode_flag = false;
 export let tracing_mode_flag = false;
 
+export function enable_async_mode_flag() {
+	async_mode_flag = true;
+}
+
+/** ONLY USE THIS DURING TESTING */
+export function disable_async_mode_flag() {
+	async_mode_flag = false;
+}
+
 export function enable_legacy_mode_flag() {
 	legacy_mode_flag = true;
 }
diff --git a/packages/svelte/src/internal/server/index.js b/packages/svelte/src/internal/server/index.js
index ceb516ebb0..9942882d26 100644
--- a/packages/svelte/src/internal/server/index.js
+++ b/packages/svelte/src/internal/server/index.js
@@ -520,6 +520,8 @@ export {
 
 export { escape_html as escape };
 
+export { await_outside_boundary } from '../shared/errors.js';
+
 /**
  * @template T
  * @param {()=>T} fn
diff --git a/packages/svelte/src/internal/shared/errors.js b/packages/svelte/src/internal/shared/errors.js
index 6bcc35016a..66685cb00b 100644
--- a/packages/svelte/src/internal/shared/errors.js
+++ b/packages/svelte/src/internal/shared/errors.js
@@ -2,6 +2,22 @@
 
 import { DEV } from 'esm-env';
 
+/**
+ * Cannot await outside a `<svelte:boundary>` with a `pending` snippet
+ * @returns {never}
+ */
+export function await_outside_boundary() {
+	if (DEV) {
+		const error = new Error(`await_outside_boundary\nCannot await outside a \`<svelte:boundary>\` with a \`pending\` snippet\nhttps://svelte.dev/e/await_outside_boundary`);
+
+		error.name = 'Svelte error';
+
+		throw error;
+	} else {
+		throw new Error(`https://svelte.dev/e/await_outside_boundary`);
+	}
+}
+
 /**
  * Cannot use `{@render children(...)}` if the parent component uses `let:` directives. Consider using a named snippet instead
  * @returns {never}
diff --git a/packages/svelte/src/legacy/legacy-client.js b/packages/svelte/src/legacy/legacy-client.js
index 61acbeaa28..d4a053d1aa 100644
--- a/packages/svelte/src/legacy/legacy-client.js
+++ b/packages/svelte/src/legacy/legacy-client.js
@@ -3,13 +3,15 @@ import { DIRTY, LEGACY_PROPS, MAYBE_DIRTY } from '../internal/client/constants.j
 import { user_pre_effect } from '../internal/client/reactivity/effects.js';
 import { mutable_source, set } from '../internal/client/reactivity/sources.js';
 import { hydrate, mount, unmount } from '../internal/client/render.js';
-import { active_effect, flushSync, get, set_signal_status } from '../internal/client/runtime.js';
+import { active_effect, get, set_signal_status } from '../internal/client/runtime.js';
+import { flushSync } from '../internal/client/reactivity/batch.js';
 import { define_property, is_array } from '../internal/shared/utils.js';
 import * as e from '../internal/client/errors.js';
 import * as w from '../internal/client/warnings.js';
 import { DEV } from 'esm-env';
 import { FILENAME } from '../constants.js';
 import { component_context, dev_current_component_function } from '../internal/client/context.js';
+import { async_mode_flag } from '../internal/flags/index.js';
 
 /**
  * Takes the same options as a Svelte 4 component and the component function and returns a Svelte 4 compatible component.
@@ -119,8 +121,9 @@ class Svelte4Component {
 			recover: options.recover
 		});
 
-		// We don't flushSync for custom element wrappers or if the user doesn't want it
-		if (!options?.props?.$$host || options.sync === false) {
+		// We don't flushSync for custom element wrappers or if the user doesn't want it,
+		// or if we're in async mode since `flushSync()` will fail
+		if (!async_mode_flag && (!options?.props?.$$host || options.sync === false)) {
 			flushSync();
 		}
 
diff --git a/packages/svelte/src/reactivity/create-subscriber.js b/packages/svelte/src/reactivity/create-subscriber.js
index 67a92ceb7b..afcea9c5b4 100644
--- a/packages/svelte/src/reactivity/create-subscriber.js
+++ b/packages/svelte/src/reactivity/create-subscriber.js
@@ -3,6 +3,7 @@ import { effect_tracking, render_effect } from '../internal/client/reactivity/ef
 import { source, increment } from '../internal/client/reactivity/sources.js';
 import { tag } from '../internal/client/dev/tracing.js';
 import { DEV } from 'esm-env';
+import { queue_micro_task } from '../internal/client/dom/task.js';
 
 /**
  * Returns a `subscribe` function that, if called in an effect (including expressions in the template),
@@ -68,8 +69,8 @@ export function createSubscriber(start) {
 				subscribers += 1;
 
 				return () => {
-					tick().then(() => {
-						// Only count down after timeout, else we would reach 0 before our own render effect reruns,
+					queue_micro_task(() => {
+						// Only count down after a microtask, else we would reach 0 before our own render effect reruns,
 						// but reach 1 again when the tick callback of the prior teardown runs. That would mean we
 						// re-subcribe unnecessarily and create a memory leak because the old subscription is never cleaned up.
 						subscribers -= 1;
diff --git a/packages/svelte/src/utils.js b/packages/svelte/src/utils.js
index 2fc21220f0..cd79cfc274 100644
--- a/packages/svelte/src/utils.js
+++ b/packages/svelte/src/utils.js
@@ -445,6 +445,7 @@ const RUNES = /** @type {const} */ ([
 	'$effect.pre',
 	'$effect.tracking',
 	'$effect.root',
+	'$effect.pending',
 	'$inspect',
 	'$inspect().with',
 	'$inspect.trace',
diff --git a/packages/svelte/tests/helpers.js b/packages/svelte/tests/helpers.js
index 2d825dbb7c..410838829e 100644
--- a/packages/svelte/tests/helpers.js
+++ b/packages/svelte/tests/helpers.js
@@ -86,7 +86,8 @@ export async function compile_directory(
 				const compiled = compileModule(text, {
 					filename: opts.filename,
 					generate: opts.generate,
-					dev: opts.dev
+					dev: opts.dev,
+					experimental: opts.experimental
 				});
 				write(out, compiled.js.code.replace(`v${VERSION}`, 'VERSION'));
 			} else {
@@ -193,6 +194,8 @@ if (typeof window !== 'undefined') {
 
 export const fragments = /** @type {'html' | 'tree'} */ (process.env.FRAGMENTS) ?? 'html';
 
+export const async_mode = process.env.SVELTE_NO_ASYNC !== 'true';
+
 /**
  * @param {any[]} logs
  */
diff --git a/packages/svelte/tests/runtime-legacy/samples/transition-abort/_config.js b/packages/svelte/tests/runtime-legacy/samples/transition-abort/_config.js
index e35b08f2a8..dccf5ca669 100644
--- a/packages/svelte/tests/runtime-legacy/samples/transition-abort/_config.js
+++ b/packages/svelte/tests/runtime-legacy/samples/transition-abort/_config.js
@@ -27,6 +27,8 @@ export default test({
 			array: ['a', 'b', 'c']
 		});
 
+		raf.tick(25);
+
 		raf.tick(50);
 		assert.htmlEqual(
 			target.innerHTML,
diff --git a/packages/svelte/tests/runtime-legacy/shared.ts b/packages/svelte/tests/runtime-legacy/shared.ts
index 126992a0c0..8d7b3544bc 100644
--- a/packages/svelte/tests/runtime-legacy/shared.ts
+++ b/packages/svelte/tests/runtime-legacy/shared.ts
@@ -3,14 +3,15 @@ import { setImmediate } from 'node:timers/promises';
 import { globSync } from 'tinyglobby';
 import { createClassComponent } from 'svelte/legacy';
 import { proxy } from 'svelte/internal/client';
-import { flushSync, hydrate, mount, unmount, untrack } from 'svelte';
+import { flushSync, hydrate, mount, unmount } from 'svelte';
 import { render } from 'svelte/server';
 import { afterAll, assert, beforeAll } from 'vitest';
-import { compile_directory, fragments } from '../helpers.js';
+import { async_mode, compile_directory, fragments } from '../helpers.js';
 import { assert_html_equal, assert_html_equal_with_options } from '../html_equal.js';
 import { raf } from '../animation-helpers.js';
 import type { CompileOptions } from '#compiler';
 import { suite_with_variants, type BaseTest } from '../suite.js';
+import { clear } from '../../src/internal/client/reactivity/batch.js';
 
 type Assert = typeof import('vitest').assert & {
 	htmlEqual(a: string, b: string, description?: string): void;
@@ -25,12 +26,30 @@ type Assert = typeof import('vitest').assert & {
 	): void;
 };
 
+// TODO remove this shim when we can
+// @ts-expect-error
+Promise.withResolvers = () => {
+	let resolve;
+	let reject;
+
+	const promise = new Promise((f, r) => {
+		resolve = f;
+		reject = r;
+	});
+
+	return { promise, resolve, reject };
+};
+
 export interface RuntimeTest<Props extends Record<string, any> = Record<string, any>>
 	extends BaseTest {
 	/** Use e.g. `mode: ['client']` to indicate that this test should never run in server/hydrate modes */
 	mode?: Array<'server' | 'client' | 'hydrate'>;
 	/** Temporarily skip specific modes, without skipping the entire test */
 	skip_mode?: Array<'server' | 'client' | 'hydrate'>;
+	/** Skip if running with process.env.NO_ASYNC */
+	skip_no_async?: boolean;
+	/** Skip if running without process.env.NO_ASYNC */
+	skip_async?: boolean;
 	html?: string;
 	ssrHtml?: string;
 	compileOptions?: Partial<CompileOptions>;
@@ -107,7 +126,15 @@ let console_error = console.error;
 export function runtime_suite(runes: boolean) {
 	return suite_with_variants<RuntimeTest, 'hydrate' | 'ssr' | 'dom', CompileOptions>(
 		['dom', 'hydrate', 'ssr'],
-		(variant, config) => {
+		(variant, config, test_name) => {
+			if (!async_mode && (config.skip_no_async || test_name.startsWith('async-'))) {
+				return true;
+			}
+
+			if (async_mode && config.skip_async) {
+				return true;
+			}
+
 			if (variant === 'hydrate') {
 				if (config.mode && !config.mode.includes('hydrate')) return 'no-test';
 				if (config.skip_mode?.includes('hydrate')) return true;
@@ -154,6 +181,9 @@ async function common_setup(cwd: string, runes: boolean | undefined, config: Run
 		rootDir: cwd,
 		dev: force_hmr ? true : undefined,
 		hmr: force_hmr ? true : undefined,
+		experimental: {
+			async: runes && async_mode
+		},
 		fragments,
 		...config.compileOptions,
 		immutable: config.immutable,
@@ -215,7 +245,7 @@ async function run_test_variant(
 		if (str.slice(0, i).includes('warnings') || config.warnings) {
 			// eslint-disable-next-line no-console
 			console.warn = (...args) => {
-				if (args[0].startsWith('%c[svelte]')) {
+				if (typeof args[0] === 'string' && args[0].startsWith('%c[svelte]')) {
 					// TODO convert this to structured data, for more robust comparison?
 
 					let message = args[0];
@@ -397,6 +427,12 @@ async function run_test_variant(
 			try {
 				if (config.test) {
 					flushSync();
+
+					if (variant === 'hydrate' && cwd.includes('async-')) {
+						// wait for pending boundaries to render
+						await Promise.resolve();
+					}
+
 					await config.test({
 						// @ts-expect-error TS doesn't get it
 						assert: {
@@ -486,6 +522,8 @@ async function run_test_variant(
 		console.log = console_log;
 		console.warn = console_warn;
 		console.error = console_error;
+
+		clear();
 	}
 }
 
diff --git a/packages/svelte/tests/runtime-runes/samples/async-abort-signal/_config.js b/packages/svelte/tests/runtime-runes/samples/async-abort-signal/_config.js
new file mode 100644
index 0000000000..a947a91ab8
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-abort-signal/_config.js
@@ -0,0 +1,23 @@
+import { settled, tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target, logs }) {
+		const [reset, resolve] = target.querySelectorAll('button');
+
+		reset.click();
+		await settled();
+		assert.deepEqual(logs, ['aborted']);
+
+		resolve.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>resolve</button>
+				<h1>hello</h1>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-abort-signal/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-abort-signal/main.svelte
new file mode 100644
index 0000000000..d8d77bf0e9
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-abort-signal/main.svelte
@@ -0,0 +1,29 @@
+<script>
+	import { getAbortSignal } from 'svelte';
+
+	let deferred = $state(Promise.withResolvers());
+
+	function load(deferred) {
+		const signal = getAbortSignal();
+
+		return new Promise((fulfil, reject) => {
+			signal.onabort = (e) => {
+				console.log('aborted');
+				reject(e.currentTarget.reason);
+			};
+
+			deferred.promise.then(fulfil, reject);
+		});
+	}
+</script>
+
+<button onclick={() => deferred = Promise.withResolvers()}>reset</button>
+<button onclick={() => deferred.resolve('hello')}>resolve</button>
+
+<svelte:boundary>
+	<h1>{await load(deferred)}</h1>
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-attribute-without-state/_config.js b/packages/svelte/tests/runtime-runes/samples/async-attribute-without-state/_config.js
new file mode 100644
index 0000000000..3de81a507b
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-attribute-without-state/_config.js
@@ -0,0 +1,18 @@
+import { flushSync, tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `
+		<p>pending</p>
+	`,
+
+	async test({ assert, target }) {
+		await Promise.resolve();
+		await Promise.resolve();
+		await Promise.resolve();
+		await Promise.resolve();
+		flushSync();
+
+		assert.htmlEqual(target.innerHTML, '<p data-foo="bar">hello</p>');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-attribute-without-state/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-attribute-without-state/main.svelte
new file mode 100644
index 0000000000..00a11cac43
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-attribute-without-state/main.svelte
@@ -0,0 +1,7 @@
+<svelte:boundary>
+	<p data-foo={await 'bar'}>hello</p>
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-attribute/_config.js b/packages/svelte/tests/runtime-runes/samples/async-attribute/_config.js
new file mode 100644
index 0000000000..0a64738409
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-attribute/_config.js
@@ -0,0 +1,29 @@
+import { tick } from 'svelte';
+import { ok, test } from '../../test';
+
+export default test({
+	html: `
+		<button>cool</button>
+		<button>neat</button>
+		<button>reset</button>
+		<p>pending</p>
+	`,
+
+	async test({ assert, target }) {
+		const [cool, neat, reset] = target.querySelectorAll('button');
+
+		cool.click();
+		await tick();
+
+		const p = target.querySelector('p');
+		ok(p);
+		assert.htmlEqual(p.outerHTML, '<p class="cool">hello</p>');
+
+		reset.click();
+		assert.htmlEqual(p.outerHTML, '<p class="cool">hello</p>');
+
+		neat.click();
+		await tick();
+		assert.htmlEqual(p.outerHTML, '<p class="neat">hello</p>');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-attribute/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-attribute/main.svelte
new file mode 100644
index 0000000000..6332a9802d
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-attribute/main.svelte
@@ -0,0 +1,15 @@
+<script>
+	let deferred = $state(Promise.withResolvers());
+</script>
+
+<button onclick={() => deferred.resolve('cool')}>cool</button>
+<button onclick={() => deferred.resolve('neat')}>neat</button>
+<button onclick={() => deferred = Promise.withResolvers()}>reset</button>
+
+<svelte:boundary>
+	<p class={await deferred.promise}>hello</p>
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-block-destroy-during-init/_config.js b/packages/svelte/tests/runtime-runes/samples/async-block-destroy-during-init/_config.js
new file mode 100644
index 0000000000..a29c99860d
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-block-destroy-during-init/_config.js
@@ -0,0 +1,27 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const [increment, shift] = target.querySelectorAll('button');
+
+		increment.click();
+		await tick();
+
+		shift.click();
+		await tick();
+
+		shift.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<button>shift</button>
+				<p>false</p>
+				<p>1</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-block-destroy-during-init/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-block-destroy-during-init/main.svelte
new file mode 100644
index 0000000000..a93eb7dc25
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-block-destroy-during-init/main.svelte
@@ -0,0 +1,28 @@
+<script>
+	let count = $state(0);
+
+	let deferreds = [];
+
+	function push() {
+		const deferred = Promise.withResolvers();
+		deferreds.push(deferred);
+		return deferred.promise;
+	}
+</script>
+
+<button onclick={() => count += 1}>increment</button>
+<button onclick={() => deferreds.shift()?.resolve(count)}>shift</button>
+
+<svelte:boundary>
+	{#if count % 2 === 0}
+		<p>true</p>
+		<p>{await push()}</p>
+	{:else}
+		<p>false</p>
+		<p>{await push()}</p>
+	{/if}
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-block-reject-during-init/_config.js b/packages/svelte/tests/runtime-runes/samples/async-block-reject-during-init/_config.js
new file mode 100644
index 0000000000..e2718a35d2
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-block-reject-during-init/_config.js
@@ -0,0 +1,10 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		assert.htmlEqual(target.innerHTML, 'loading');
+		await tick();
+		assert.htmlEqual(target.innerHTML, 'nope');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-block-reject-during-init/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-block-reject-during-init/main.svelte
new file mode 100644
index 0000000000..412da7268e
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-block-reject-during-init/main.svelte
@@ -0,0 +1,8 @@
+<svelte:boundary>
+	{#if await Promise.reject(new Error('nope'))}
+		hi
+	{/if}
+
+	{#snippet pending()}loading{/snippet}
+	{#snippet failed(e)}{e.message}{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-block-reject-each-during-init/_config.js b/packages/svelte/tests/runtime-runes/samples/async-block-reject-each-during-init/_config.js
new file mode 100644
index 0000000000..c5dae7fee2
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-block-reject-each-during-init/_config.js
@@ -0,0 +1,28 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const [increment, resolve, reject] = target.querySelectorAll('button');
+
+		increment.click();
+		await tick();
+
+		reject.click();
+		await tick();
+
+		resolve.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<button>resolve</button>
+				<button>reject</button>
+				<p>false</p>
+				<p>1</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-block-reject-each-during-init/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-block-reject-each-during-init/main.svelte
new file mode 100644
index 0000000000..1ad6cb84de
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-block-reject-each-during-init/main.svelte
@@ -0,0 +1,29 @@
+<script>
+	let count = $state(0);
+
+	let deferreds = [];
+
+	function push() {
+		const deferred = Promise.withResolvers();
+		deferreds.push(deferred);
+		return deferred.promise;
+	}
+</script>
+
+<button onclick={() => count += 1}>increment</button>
+<button onclick={() => deferreds.shift()?.resolve([count])}>resolve</button>
+<button onclick={() => deferreds.shift()?.reject(new Error('oops'))}>reject</button>
+
+<svelte:boundary>
+	{#if count % 2 === 0}
+		<p>true</p>
+		{#each await push() as count}<p>{count}</p>{/each}
+	{:else}
+		<p>false</p>
+		{#each await push() as count}<p>{count}</p>{/each}
+	{/if}
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-block-rerun/_config.js b/packages/svelte/tests/runtime-runes/samples/async-block-rerun/_config.js
new file mode 100644
index 0000000000..18175de4dc
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-block-rerun/_config.js
@@ -0,0 +1,53 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const [override, release, resolve] = target.querySelectorAll('button');
+
+		resolve.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>override</button>
+				<button>release</button>
+				<button>resolve</button>
+				<p>before</p>
+				<p>before</p>
+			`
+		);
+
+		override.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>override</button>
+				<button>release</button>
+				<button>resolve</button>
+				<p>during</p>
+				<p>during</p>
+			`
+		);
+
+		release.click();
+		await tick();
+
+		resolve.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>override</button>
+				<button>release</button>
+				<button>resolve</button>
+				<p>after</p>
+				<p>after</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-block-rerun/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-block-rerun/main.svelte
new file mode 100644
index 0000000000..256ad68f4a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-block-rerun/main.svelte
@@ -0,0 +1,45 @@
+<script lang=ts>
+	let deferred = Promise.withResolvers();
+	let value = $state();
+	let override = $state();
+	let current = $derived(override ?? value);
+	let promise = $state(update(['before']));
+
+	async function update (v) {
+		deferred = Promise.withResolvers();
+		await deferred.promise;
+		value = v;
+	};
+
+	function indirect() {
+		override;
+		return promise.then(() => current);
+	}
+</script>
+
+<button onclick={() => {
+	override = ['during'];
+}}>override</button>
+
+<button onclick={() => {
+	override = null;
+	promise = update(['after']);
+}}>release</button>
+
+<button onclick={() => {
+	deferred.resolve(null);
+}}>resolve</button>
+
+<svelte:boundary>
+	{#each await indirect() as entry}
+		<p>{entry}</p>
+	{/each}
+
+	{#each current as entry}
+		<p>{entry}</p>
+	{/each}
+
+	{#snippet pending()}
+		<p>pending...</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-child-effect/_config.js b/packages/svelte/tests/runtime-runes/samples/async-child-effect/_config.js
new file mode 100644
index 0000000000..325cb1dcd6
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-child-effect/_config.js
@@ -0,0 +1,55 @@
+import { flushSync, tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `
+		<button>shift</button>
+		<p>loading</p>
+	`,
+
+	async test({ assert, target }) {
+		target.querySelector('button')?.click();
+		await tick();
+
+		const [button1, button2] = target.querySelectorAll('button');
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>shift</button>
+				<button>+</button>
+				<p>A</p>
+				<p>a</p>
+			`
+		);
+
+		flushSync(() => button2.click());
+		flushSync(() => button2.click());
+
+		button1.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>shift</button>
+				<button>+</button>
+				<p>AA</p>
+				<p>aa</p>
+			`
+		);
+
+		button1.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>shift</button>
+				<button>+</button>
+				<p>AAA</p>
+				<p>aaa</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-child-effect/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-child-effect/main.svelte
new file mode 100644
index 0000000000..edb0eaea44
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-child-effect/main.svelte
@@ -0,0 +1,26 @@
+<script>
+	let input = $state('a');
+
+	let queue = [];
+
+	function push(value) {
+		const deferred = Promise.withResolvers();
+		queue.push(() => deferred.resolve(value));
+		return deferred.promise;
+	}
+</script>
+
+<button onclick={() => queue.shift()()}>shift</button>
+
+<svelte:boundary>
+	<button onclick={() => input += 'a'}>+</button>
+	<p>{await push(input.toUpperCase())}</p>
+
+	{#if true}
+		<p>{input}</p>
+	{/if}
+
+	{#snippet pending()}
+		<p>loading</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-class-directive/_config.js b/packages/svelte/tests/runtime-runes/samples/async-class-directive/_config.js
new file mode 100644
index 0000000000..3186ed2069
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-class-directive/_config.js
@@ -0,0 +1,20 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `loading`,
+
+	async test({ assert, target }) {
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<div class="one">one</div>
+				<div class="two">two</div>
+				<div style="color: red;">red</div>
+				<div style="color: blue;">blue</div>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-class-directive/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-class-directive/main.svelte
new file mode 100644
index 0000000000..f0f27e4830
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-class-directive/main.svelte
@@ -0,0 +1,11 @@
+<svelte:boundary>
+	<div class:one={await true} {...{}}>one</div>
+	<div class:two={await true}>two</div>
+
+	<div style:color={await 'red'} {...{}}>red</div>
+	<div style:color={await 'blue'}>blue</div>
+
+	{#snippet pending()}
+		loading
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-in-if/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-derived-in-if/Child.svelte
new file mode 100644
index 0000000000..fb47377513
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-in-if/Child.svelte
@@ -0,0 +1,5 @@
+<script>
+	let n = $derived(await 1);
+</script>
+
+<p>{n}</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-in-if/_config.js b/packages/svelte/tests/runtime-runes/samples/async-derived-in-if/_config.js
new file mode 100644
index 0000000000..914b311c97
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-in-if/_config.js
@@ -0,0 +1,19 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const button = target.querySelector('button');
+
+		button?.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>show</button>
+				<p>1</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-in-if/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-derived-in-if/main.svelte
new file mode 100644
index 0000000000..a53381c2d5
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-in-if/main.svelte
@@ -0,0 +1,17 @@
+<script>
+	import Child from './Child.svelte';
+
+	let show = $state(false);
+</script>
+
+<button onclick={() => show = true}>show</button>
+
+<svelte:boundary>
+	{#if show}
+		<Child />
+	{/if}
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-invalidation-during-init/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-derived-invalidation-during-init/Child.svelte
new file mode 100644
index 0000000000..ffcd8b46b4
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-invalidation-during-init/Child.svelte
@@ -0,0 +1,9 @@
+<script>
+	let { promise } = $props();
+
+	let d = $derived({
+		value: await promise
+	});
+</script>
+
+<p>{(await d).value}</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-invalidation-during-init/_config.js b/packages/svelte/tests/runtime-runes/samples/async-derived-invalidation-during-init/_config.js
new file mode 100644
index 0000000000..fee8e2e6bf
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-invalidation-during-init/_config.js
@@ -0,0 +1,33 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `
+		<button>switch to d2</button>
+		<button>resolve d1</button>
+		<button>resolve d2</button>
+		<p>pending</p>
+	`,
+
+	async test({ assert, target, errors }) {
+		const [toggle, resolve1, resolve2] = target.querySelectorAll('button');
+
+		toggle.click();
+		resolve1.click();
+		resolve2.click();
+
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>switch to d2</button>
+				<button>resolve d1</button>
+				<button>resolve d2</button>
+				<p>two</p>
+			`
+		);
+
+		assert.deepEqual(errors, []);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-invalidation-during-init/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-derived-invalidation-during-init/main.svelte
new file mode 100644
index 0000000000..9babdb2fe2
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-invalidation-during-init/main.svelte
@@ -0,0 +1,20 @@
+<script>
+	import Child from './Child.svelte';
+
+	let d1 = $state(Promise.withResolvers());
+	let d2 = $state(Promise.withResolvers());
+
+	let deferred = $state.raw(d1);
+</script>
+
+<button onclick={() => deferred = d2}>switch to d2</button>
+<button onclick={() => d1.resolve('one')}>resolve d1</button>
+<button onclick={() => d2.resolve('two')}>resolve d2</button>
+
+<svelte:boundary>
+	<Child promise={deferred.promise} />
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-module/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-derived-module/Child.svelte
new file mode 100644
index 0000000000..f803a30c37
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-module/Child.svelte
@@ -0,0 +1,20 @@
+<script>
+	import { create_derived } from './state.svelte.js';
+
+	let { promise, num } = $props();
+
+	let derived = await create_derived(
+		() => promise,
+		() => num
+	);
+
+	$effect(() => {
+		console.log(`$effect ${derived.value} ${num}`);
+	});
+
+	$effect.pre(() => {
+		console.log(`$effect.pre ${derived.value} ${num}`);
+	});
+</script>
+
+<p>{derived.value}{console.log(`template ${derived.value} ${num}`)}</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-module/_config.js b/packages/svelte/tests/runtime-runes/samples/async-derived-module/_config.js
new file mode 100644
index 0000000000..f7d1d28fde
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-module/_config.js
@@ -0,0 +1,93 @@
+import { flushSync, tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `
+		<button>reset</button>
+		<button>a</button>
+		<button>b</button>
+		<button>increment</button>
+		<p>pending</p>
+	`,
+
+	async test({ assert, target, logs }) {
+		const [reset, a, b, increment] = target.querySelectorAll('button');
+
+		a.click();
+
+		// TODO why is this necessary? why isn't `await tick()` enough?
+		await Promise.resolve();
+		await Promise.resolve();
+		await Promise.resolve();
+		await Promise.resolve();
+		await Promise.resolve();
+		await Promise.resolve();
+		await Promise.resolve();
+		await Promise.resolve();
+		flushSync();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>a</button>
+				<button>b</button>
+				<button>increment</button>
+				<p>42</p>
+			`
+		);
+
+		increment.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>a</button>
+				<button>b</button>
+				<button>increment</button>
+				<p>84</p>
+			`
+		);
+
+		reset.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>a</button>
+				<button>b</button>
+				<button>increment</button>
+				<p>84</p>
+			`
+		);
+
+		b.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>a</button>
+				<button>b</button>
+				<button>increment</button>
+				<p>86</p>
+			`
+		);
+
+		assert.deepEqual(logs, [
+			'outside boundary 1',
+			'$effect.pre 42 1',
+			'template 42 1',
+			'$effect 42 1',
+			'$effect.pre 84 2',
+			'template 84 2',
+			'outside boundary 2',
+			'$effect 84 2',
+			'$effect.pre 86 2',
+			'template 86 2',
+			'$effect 86 2'
+		]);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-module/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-derived-module/main.svelte
new file mode 100644
index 0000000000..2c83e1d23d
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-module/main.svelte
@@ -0,0 +1,21 @@
+<script>
+	import Child from './Child.svelte';
+
+	let num = $state(1);
+	let deferred = $state(Promise.withResolvers());
+</script>
+
+<button onclick={() => deferred = Promise.withResolvers()}>reset</button>
+<button onclick={() => deferred.resolve(42)}>a</button>
+<button onclick={() => deferred.resolve(43)}>b</button>
+<button onclick={() => num += 1}>increment</button>
+
+<svelte:boundary>
+	<Child promise={deferred.promise} {num} />
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
+
+{console.log(`outside boundary ${num}`)}
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-module/state.svelte.js b/packages/svelte/tests/runtime-runes/samples/async-derived-module/state.svelte.js
new file mode 100644
index 0000000000..a53fbb8c6f
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-module/state.svelte.js
@@ -0,0 +1,9 @@
+export async function create_derived(get_promise, get_num) {
+	let value = $derived((await get_promise()) * get_num());
+
+	return {
+		get value() {
+			return value;
+		}
+	};
+}
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-unchanging/Component.svelte b/packages/svelte/tests/runtime-runes/samples/async-derived-unchanging/Component.svelte
new file mode 100644
index 0000000000..a90a9dedf7
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-unchanging/Component.svelte
@@ -0,0 +1,29 @@
+<script lang="ts">
+	let queue: Array<{ deferred: PromiseWithResolvers<number>; value: number }> = [];
+	let inited = false;
+
+	function push(value: number) {
+		const deferred = Promise.withResolvers<number>();
+		queue.push({ deferred, value });
+
+		if (!inited) {
+			inited = true;
+			shift();
+		}
+
+		return deferred.promise;
+	}
+
+	function shift() {
+		const next = queue.shift();
+		next?.deferred.resolve(next.value);
+	}
+
+	let n = $state(0);
+	let current = $derived(await push(n));
+</script>
+
+<button onclick={shift}>shift</button>
+<button onclick={() => n += 1}>increment</button>
+
+<p>{n}: {Math.min(current, 3)}</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-unchanging/_config.js b/packages/svelte/tests/runtime-runes/samples/async-derived-unchanging/_config.js
new file mode 100644
index 0000000000..016c311f98
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-unchanging/_config.js
@@ -0,0 +1,33 @@
+import { flushSync, tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `<p>pending...</p>`,
+
+	async test({ assert, target }) {
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>shift</button>
+				<button>increment</button>
+				<p>0: 0</p>
+			`
+		);
+
+		const [shift, increment] = target.querySelectorAll('button');
+		const [p] = target.querySelectorAll('p');
+
+		for (let i = 1; i < 5; i += 1) {
+			flushSync(() => increment.click());
+		}
+
+		for (let i = 1; i < 5; i += 1) {
+			shift.click();
+			await tick();
+
+			assert.equal(p.innerHTML, `${i}: ${Math.min(i, 3)}`);
+		}
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-unchanging/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-derived-unchanging/main.svelte
new file mode 100644
index 0000000000..2d5ddca4db
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-unchanging/main.svelte
@@ -0,0 +1,11 @@
+<script>
+	import Component from './Component.svelte';
+</script>
+
+<svelte:boundary>
+	<Component />
+
+	{#snippet pending()}
+		<p>pending...</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-derived/Child.svelte
new file mode 100644
index 0000000000..b59fd7c08f
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived/Child.svelte
@@ -0,0 +1,15 @@
+<script>
+	let { promise, num } = $props();
+
+	let value = $derived(num + (await promise));
+
+	$effect(() => {
+		console.log(`$effect ${value} ${num}`);
+	});
+
+	$effect.pre(() => {
+		console.log(`$effect.pre ${value} ${num}`);
+	});
+</script>
+
+<p>{value}{console.log(`template ${value} ${num}`)}</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived/_config.js b/packages/svelte/tests/runtime-runes/samples/async-derived/_config.js
new file mode 100644
index 0000000000..7239643464
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived/_config.js
@@ -0,0 +1,48 @@
+import { flushSync, settled, tick } from 'svelte';
+import { ok, test } from '../../test';
+
+export default test({
+	html: `
+		<button>resolve a</button>
+		<button>resolve b</button>
+		<button>reset</button>
+		<button>increment</button>
+		<p>pending</p>
+	`,
+
+	async test({ assert, target, logs }) {
+		const [resolve_a, resolve_b, reset, increment] = target.querySelectorAll('button');
+
+		flushSync(() => resolve_a.click());
+		await tick();
+
+		const p = target.querySelector('p');
+		ok(p);
+		assert.htmlEqual(p.innerHTML, '1a');
+
+		flushSync(() => increment.click());
+		await tick();
+		assert.htmlEqual(p.innerHTML, '2a');
+
+		reset.click();
+		assert.htmlEqual(p.innerHTML, '2a');
+
+		resolve_b.click();
+		await tick();
+		assert.htmlEqual(p.innerHTML, '2b');
+
+		assert.deepEqual(logs, [
+			'outside boundary 1',
+			'$effect.pre 1a 1',
+			'template 1a 1',
+			'$effect 1a 1',
+			'$effect.pre 2a 2',
+			'template 2a 2',
+			'outside boundary 2',
+			'$effect 2a 2',
+			'$effect.pre 2b 2',
+			'template 2b 2',
+			'$effect 2b 2'
+		]);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-derived/main.svelte
new file mode 100644
index 0000000000..1404ae0299
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived/main.svelte
@@ -0,0 +1,21 @@
+<script>
+	import Child from './Child.svelte';
+
+	let deferred = $state(Promise.withResolvers());
+	let num = $state(1);
+</script>
+
+<button onclick={() => deferred.resolve('a')}>resolve a</button>
+<button onclick={() => deferred.resolve('b')}>resolve b</button>
+<button onclick={() => deferred = Promise.withResolvers()}>reset</button>
+<button onclick={() => num += 1}>increment</button>
+
+<svelte:boundary>
+	<Child promise={deferred.promise} {num} />
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
+
+{console.log(`outside boundary ${num}`)}
diff --git a/packages/svelte/tests/runtime-runes/samples/async-each-await-item/_config.js b/packages/svelte/tests/runtime-runes/samples/async-each-await-item/_config.js
new file mode 100644
index 0000000000..54aa68eeb2
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-each-await-item/_config.js
@@ -0,0 +1,31 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `<button>step 1</button><button>step 2</button><button>step 3</button><p>pending</p>`,
+
+	async test({ assert, target }) {
+		const [button1, button2, button3] = target.querySelectorAll('button');
+
+		button1.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>step 1</button><button>step 2</button><button>step 3</button><p>a</p><p>b</p><p>c</p>'
+		);
+
+		button2.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>step 1</button><button>step 2</button><button>step 3</button><p>a</p><p>b</p><p>c</p>'
+		);
+
+		button3.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>step 1</button><button>step 2</button><button>step 3</button><p>b</p><p>c</p><p>d</p><p>e</p>'
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-each-await-item/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-each-await-item/main.svelte
new file mode 100644
index 0000000000..eddcf2b749
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-each-await-item/main.svelte
@@ -0,0 +1,39 @@
+<script>
+	let items = $state([
+		Promise.withResolvers(),
+		Promise.withResolvers(),
+		Promise.withResolvers()
+	]);
+</script>
+
+<button onclick={() => {
+	items[0].resolve('a');
+	items[1].resolve('b');
+	items[2].resolve('c');
+}}>step 1</button>
+
+<button onclick={() => {
+	items = [
+		Promise.withResolvers(),
+		Promise.withResolvers(),
+		Promise.withResolvers(),
+		Promise.withResolvers()
+	]
+}}>step 2</button>
+
+<button onclick={() => {
+	items[0].resolve('b');
+	items[1].resolve('c');
+	items[2].resolve('d');
+	items[3].resolve('e');
+}}>step 3</button>
+
+<svelte:boundary>
+	{#each items as deferred}
+		<p>{await deferred.promise}</p>
+	{/each}
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-each-keyed/_config.js b/packages/svelte/tests/runtime-runes/samples/async-each-keyed/_config.js
new file mode 100644
index 0000000000..43d3a0f876
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-each-keyed/_config.js
@@ -0,0 +1,41 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true
+	},
+
+	html: `
+		<button>reset</button>
+		<button>one</button>
+		<button>two</button>
+		<button>three</button>
+		<p>pending</p>
+	`,
+
+	async test({ assert, target }) {
+		const [reset, one, two, three] = target.querySelectorAll('button');
+
+		one.click();
+		await tick();
+
+		const [div] = target.querySelectorAll('div');
+		assert.htmlEqual(div.innerHTML, '<p>a</p><p>b</p><p>c</p>');
+
+		reset.click();
+		await tick();
+		assert.htmlEqual(div.innerHTML, '<p>a</p><p>b</p><p>c</p>');
+
+		two.click();
+		await tick();
+		assert.htmlEqual(div.innerHTML, '<p>d</p><p>e</p><p>f</p><p>g</p>');
+
+		reset.click();
+		await tick();
+		three.click();
+		await tick();
+
+		assert.include(target.innerHTML, '<p>each_key_duplicate');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-each-keyed/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-each-keyed/main.svelte
new file mode 100644
index 0000000000..e2f8263780
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-each-keyed/main.svelte
@@ -0,0 +1,24 @@
+<script>
+	let deferred = $state(Promise.withResolvers());
+</script>
+
+<button onclick={() => deferred = Promise.withResolvers()}>reset</button>
+<button onclick={() => deferred.resolve(['a', 'b', 'c'])}>one</button>
+<button onclick={() => deferred.resolve(['d', 'e', 'f', 'g'])}>two</button>
+<button onclick={() => deferred.resolve(['d', 'e', 'f', 'd'])}>three</button>
+
+<svelte:boundary>
+	<div>
+		{#each await deferred.promise as item (item)}
+			<p>{item}</p>
+		{/each}
+	</div>
+
+	{#snippet failed(e)}
+		<p>{e.message}</p>
+	{/snippet}
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-each/_config.js b/packages/svelte/tests/runtime-runes/samples/async-each/_config.js
new file mode 100644
index 0000000000..50aa055130
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-each/_config.js
@@ -0,0 +1,48 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `
+		<button>reset</button>
+		<button>abc</button>
+		<button>defg</button>
+		<p>pending</p>
+	`,
+
+	async test({ assert, target }) {
+		const [reset, abc, defg] = target.querySelectorAll('button');
+
+		abc.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>abc</button>
+				<button>defg</button>
+				<p>a</p><p>b</p><p>c</p>`
+		);
+
+		reset.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>abc</button>
+				<button>defg</button>
+				<p>a</p><p>b</p><p>c</p>`
+		);
+
+		defg.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>abc</button>
+				<button>defg</button>
+				<p>d</p><p>e</p><p>f</p><p>g</p>`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-each/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-each/main.svelte
new file mode 100644
index 0000000000..8e4412811a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-each/main.svelte
@@ -0,0 +1,17 @@
+<script>
+	let deferred = $state(Promise.withResolvers());
+</script>
+
+<button onclick={() => deferred = Promise.withResolvers()}>reset</button>
+<button onclick={() => deferred.resolve(['a', 'b', 'c'])}>abc</button>
+<button onclick={() => deferred.resolve(['d', 'e', 'f', 'g'])}>defg</button>
+
+<svelte:boundary>
+	{#each await deferred.promise as item}
+		<p>{item}</p>
+	{/each}
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-error-in-block-expression/_config.js b/packages/svelte/tests/runtime-runes/samples/async-error-in-block-expression/_config.js
new file mode 100644
index 0000000000..2679785cff
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-error-in-block-expression/_config.js
@@ -0,0 +1,11 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `loading`,
+
+	async test({ assert, target }) {
+		await tick();
+		assert.htmlEqual(target.innerHTML, 'oops');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-error-in-block-expression/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-error-in-block-expression/main.svelte
new file mode 100644
index 0000000000..a49a5c9540
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-error-in-block-expression/main.svelte
@@ -0,0 +1,8 @@
+<svelte:boundary>
+	{#each (await Promise.reject(new Error('oops'))) as x}
+		hi
+	{/each}
+
+	{#snippet pending()}loading{/snippet}
+	{#snippet failed()}oops{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-error-recovery/_config.js b/packages/svelte/tests/runtime-runes/samples/async-error-recovery/_config.js
new file mode 100644
index 0000000000..1613bf9c61
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-error-recovery/_config.js
@@ -0,0 +1,87 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `
+		<button>clicks: 0</button>
+		<p>pending...</p>
+	`,
+
+	compileOptions: {
+		// this tests some behaviour that was broken in dev
+		dev: true
+	},
+
+	async test({ assert, target }) {
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>clicks: 0</button>
+				<p>0</p>
+			`
+		);
+
+		let [button] = target.querySelectorAll('button');
+		let [p] = target.querySelectorAll('p');
+
+		button.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>clicks: 1</button>
+				<p>1</p>
+			`
+		);
+
+		button.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>clicks: 2</button>
+				<p>2</p>
+			`
+		);
+
+		button.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>clicks: 3</button>
+				<button>retry</button>
+			`
+		);
+
+		const [button1, button2] = target.querySelectorAll('button');
+
+		button1.click();
+		await tick();
+
+		button2.click();
+		await tick();
+
+		[p] = target.querySelectorAll('p');
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>clicks: 4</button>
+				<p>4</p>
+			`
+		);
+
+		button1.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>clicks: 5</button>
+				<p>5</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-error-recovery/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-error-recovery/main.svelte
new file mode 100644
index 0000000000..d5246d330e
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-error-recovery/main.svelte
@@ -0,0 +1,24 @@
+<script lang=ts>
+	let count = $state(0);
+
+	function process(count) {
+		if (count === 3) throw new Error('kaboom');
+		return count;
+	}
+</script>
+
+<button onclick={() => count++}>
+	clicks: {count}
+</button>
+
+<svelte:boundary>
+	<p>{await process(count)}</p>
+
+	{#snippet pending()}
+		<p>pending...</p>
+	{/snippet}
+
+	{#snippet failed(error, reset)}
+		<button onclick={reset}>retry</button>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-error/_config.js b/packages/svelte/tests/runtime-runes/samples/async-error/_config.js
new file mode 100644
index 0000000000..dfbd238eeb
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-error/_config.js
@@ -0,0 +1,34 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `<button>step 1</button><button>step 2</button><button>step 3</button><p>pending</p>`,
+
+	async test({ assert, target }) {
+		let [button1, button2, button3] = target.querySelectorAll('button');
+
+		button1.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>step 1</button><button>step 2</button><button>step 3</button><p>oops!</p><button data-id="reset">reset</button>'
+		);
+
+		button2.click();
+
+		const reset = /** @type {HTMLButtonElement} */ (target.querySelector('[data-id="reset"]'));
+		reset.click();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>step 1</button><button>step 2</button><button>step 3</button><p>pending</p>'
+		);
+
+		button3.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>step 1</button><button>step 2</button><button>step 3</button><h1>wheee</h1>'
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-error/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-error/main.svelte
new file mode 100644
index 0000000000..9af5bbaa16
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-error/main.svelte
@@ -0,0 +1,20 @@
+<script>
+	let deferred = $state(Promise.withResolvers());
+</script>
+
+<button onclick={() => deferred.reject(new Error('oops!'))}>step 1</button>
+<button onclick={() => deferred = Promise.withResolvers()}>step 2</button>
+<button onclick={() => deferred.resolve('wheee')}>step 3</button>
+
+<svelte:boundary>
+	<h1>{await deferred.promise}</h1>
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+
+	{#snippet failed(error, reset)}
+		<p>{error.message}</p>
+		<button data-id="reset" onclick={reset}>reset</button>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-expression/_config.js b/packages/svelte/tests/runtime-runes/samples/async-expression/_config.js
new file mode 100644
index 0000000000..3a66ea709f
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-expression/_config.js
@@ -0,0 +1,56 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `
+		<button>reset</button>
+		<button>hello</button>
+		<button>goodbye</button>
+		<p>pending</p>
+	`,
+
+	async test({ assert, target, raf }) {
+		const [reset, hello, goodbye] = target.querySelectorAll('button');
+
+		hello.click();
+		raf.tick(0);
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>hello</button>
+				<button>goodbye</button>
+				<h1>hello</h1>
+			`
+		);
+
+		reset.click();
+		raf.tick(0);
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>hello</button>
+				<button>goodbye</button>
+				<h1>hello</h1>
+				<p>updating...</p>
+			`
+		);
+
+		goodbye.click();
+		await Promise.resolve();
+		raf.tick(0);
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>hello</button>
+				<button>goodbye</button>
+				<h1>goodbye</h1>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-expression/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-expression/main.svelte
new file mode 100644
index 0000000000..42536ab02a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-expression/main.svelte
@@ -0,0 +1,19 @@
+<script>
+	let deferred = $state(Promise.withResolvers());
+</script>
+
+<button onclick={() => deferred = Promise.withResolvers()}>reset</button>
+<button onclick={() => deferred.resolve('hello')}>hello</button>
+<button onclick={() => deferred.resolve('goodbye')}>goodbye</button>
+
+<svelte:boundary>
+	<h1>{await deferred.promise}</h1>
+
+	{#if $effect.pending()}
+		<p>updating...</p>
+	{/if}
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-html-tag/_config.js b/packages/svelte/tests/runtime-runes/samples/async-html-tag/_config.js
new file mode 100644
index 0000000000..f5b1f3d2c4
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-html-tag/_config.js
@@ -0,0 +1,51 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `
+		<button>reset</button>
+		<button>hello</button>
+		<button>goodbye</button>
+		<p>pending</p>
+	`,
+
+	async test({ assert, target }) {
+		const [reset, hello, goodbye] = target.querySelectorAll('button');
+
+		hello.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>hello</button>
+				<button>goodbye</button>
+				<h1>hello</h1>
+			`
+		);
+
+		reset.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>hello</button>
+				<button>goodbye</button>
+				<h1>hello</h1>
+			`
+		);
+
+		goodbye.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>hello</button>
+				<button>goodbye</button>
+				<h1>goodbye</h1>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-html-tag/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-html-tag/main.svelte
new file mode 100644
index 0000000000..980bb16d5c
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-html-tag/main.svelte
@@ -0,0 +1,15 @@
+<script>
+	let deferred = $state(Promise.withResolvers());
+</script>
+
+<button onclick={() => deferred = Promise.withResolvers()}>reset</button>
+<button onclick={() => deferred.resolve('hello')}>hello</button>
+<button onclick={() => deferred.resolve('goodbye')}>goodbye</button>
+
+<svelte:boundary>
+	<h1>{@html await deferred.promise}</h1>
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-if/_config.js b/packages/svelte/tests/runtime-runes/samples/async-if/_config.js
new file mode 100644
index 0000000000..3cd67952c3
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-if/_config.js
@@ -0,0 +1,31 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `<button>reset</button><button>true</button><button>false</button><p>pending</p>`,
+
+	async test({ assert, target }) {
+		const [reset, t, f] = target.querySelectorAll('button');
+
+		t.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>reset</button><button>true</button><button>false</button><h1>yes</h1>'
+		);
+
+		reset.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>reset</button><button>true</button><button>false</button><h1>yes</h1>'
+		);
+
+		f.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>reset</button><button>true</button><button>false</button><h1>no</h1>'
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-if/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-if/main.svelte
new file mode 100644
index 0000000000..21a4cbef97
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-if/main.svelte
@@ -0,0 +1,19 @@
+<script>
+	let deferred = $state(Promise.withResolvers());
+</script>
+
+<button onclick={() => deferred = Promise.withResolvers()}>reset</button>
+<button onclick={() => deferred.resolve(true)}>true</button>
+<button onclick={() => deferred.resolve(false)}>false</button>
+
+<svelte:boundary>
+	{#if await deferred.promise}
+		<h1>yes</h1>
+	{:else}
+		<h1>no</h1>
+	{/if}
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-key/_config.js b/packages/svelte/tests/runtime-runes/samples/async-key/_config.js
new file mode 100644
index 0000000000..e7e5db3dd8
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-key/_config.js
@@ -0,0 +1,46 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `
+		<button>reset</button>
+		<button>1</button>
+		<button>2</button>
+		<p>pending</p>
+	`,
+
+	async test({ assert, target }) {
+		const [reset, one, two] = target.querySelectorAll('button');
+
+		const html = `
+			<button>reset</button>
+			<button>1</button>
+			<button>2</button>
+			<h1>hello</h1>
+		`;
+
+		one.click();
+		await tick();
+		assert.htmlEqual(target.innerHTML, html);
+
+		const h1 = target.querySelector('h1');
+
+		reset.click();
+		await tick();
+		assert.htmlEqual(target.innerHTML, html);
+
+		one.click();
+		await tick();
+		assert.htmlEqual(target.innerHTML, html);
+		assert.equal(target.querySelector('h1'), h1);
+
+		reset.click();
+		await tick();
+		assert.htmlEqual(target.innerHTML, html);
+
+		two.click();
+		await tick();
+		assert.htmlEqual(target.innerHTML, html);
+		assert.notEqual(target.querySelector('h1'), h1);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-key/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-key/main.svelte
new file mode 100644
index 0000000000..5fbdbd47d0
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-key/main.svelte
@@ -0,0 +1,17 @@
+<script>
+	let deferred = $state(Promise.withResolvers());
+</script>
+
+<button onclick={() => deferred = Promise.withResolvers()}>reset</button>
+<button onclick={() => deferred.resolve(1)}>1</button>
+<button onclick={() => deferred.resolve(2)}>2</button>
+
+<svelte:boundary>
+	{#key await deferred.promise}
+		<h1>hello</h1>
+	{/key}
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-linear-order-different-deriveds/_config.js b/packages/svelte/tests/runtime-runes/samples/async-linear-order-different-deriveds/_config.js
new file mode 100644
index 0000000000..cb8e0cfca9
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-linear-order-different-deriveds/_config.js
@@ -0,0 +1,35 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `<button>both</button><button>a</button><button>b</button><p>loading...</p>`,
+
+	async test({ assert, target }) {
+		const [both, a, b] = target.querySelectorAll('button');
+
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>both</button><button>a</button><button>b</button>
+				<p>1 * 2 = 2</p>
+				<p>2 * 2 = 4</p>
+			`
+		);
+
+		both.click();
+		b.click();
+
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>both</button><button>a</button><button>b</button>
+				<p>2 * 2 = 4</p>
+				<p>4 * 2 = 8</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-linear-order-different-deriveds/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-linear-order-different-deriveds/main.svelte
new file mode 100644
index 0000000000..432eed976c
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-linear-order-different-deriveds/main.svelte
@@ -0,0 +1,17 @@
+<script>
+	let a = $state(1);
+	let b = $state(2);
+</script>
+
+<button onclick={() => {a += 1; b += 1;}}>both</button>
+<button onclick={() => {a += 1;}}>a</button>
+<button onclick={() => {b += 1;}}>b</button>
+
+<svelte:boundary>
+	<p>{a} * 2 = {await (a * 2)}</p>
+	<p>{b} * 2 = {b * 2}</p>
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-linear-order-same-derived/_config.js b/packages/svelte/tests/runtime-runes/samples/async-linear-order-same-derived/_config.js
new file mode 100644
index 0000000000..5e522ebdb5
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-linear-order-same-derived/_config.js
@@ -0,0 +1,30 @@
+import { flushSync, tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const [a, b, reset1, reset2, resolve1, resolve2] = target.querySelectorAll('button');
+
+		resolve1.click();
+		await tick();
+
+		const p = /** @type {HTMLElement} */ (target.querySelector('#test'));
+
+		assert.htmlEqual(p.innerHTML, '1 + 2 = 3');
+
+		flushSync(() => reset1.click());
+		flushSync(() => a.click());
+		flushSync(() => reset2.click());
+		flushSync(() => b.click());
+
+		resolve2.click();
+		await tick();
+
+		assert.htmlEqual(p.innerHTML, '1 + 2 = 3');
+
+		resolve1.click();
+		await tick();
+
+		assert.htmlEqual(p.innerHTML, '2 + 3 = 5');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-linear-order-same-derived/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-linear-order-same-derived/main.svelte
new file mode 100644
index 0000000000..cc82db0d75
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-linear-order-same-derived/main.svelte
@@ -0,0 +1,31 @@
+<script>
+	let delay = 1000;
+	let a = $state(1);
+	let b = $state(2);
+
+	let d1 = Promise.withResolvers();
+	let d2 = Promise.withResolvers();
+	let deferred = d1;
+
+	async function add(a, b) {
+		await deferred.promise;
+		return a + b;
+	}
+</script>
+
+<button onclick={() => a++}>a++</button>
+<button onclick={() => b++}>b++</button>
+
+<button onclick={() => deferred = d1 = Promise.withResolvers()}>reset 1</button>
+<button onclick={() => deferred = d2 = Promise.withResolvers()}>reset 2</button>
+
+<button onclick={() => d1.resolve()}>resolve 1</button>
+<button onclick={() => d2.resolve()}>resolve 2</button>
+
+<svelte:boundary>
+	<p id="test">{a} + {b} = {await add(a, b)}</p>
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-nested-derived/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-nested-derived/Child.svelte
new file mode 100644
index 0000000000..546494f4c3
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-nested-derived/Child.svelte
@@ -0,0 +1,11 @@
+<script>
+	let { count } = $props();
+
+	async function x() {
+		let d = $derived(await new Promise((f) => {}));
+	}
+
+	let indirect = $derived(x() && count);
+</script>
+
+<p>{indirect}</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-nested-derived/_config.js b/packages/svelte/tests/runtime-runes/samples/async-nested-derived/_config.js
new file mode 100644
index 0000000000..172b44e6e3
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-nested-derived/_config.js
@@ -0,0 +1,14 @@
+import { flushSync, tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+		assert.htmlEqual(target.innerHTML, '<button>0</button><p>0</p>');
+
+		const button = target.querySelector('button');
+
+		flushSync(() => button?.click());
+		assert.htmlEqual(target.innerHTML, '<button>1</button><p>1</p>');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-nested-derived/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-nested-derived/main.svelte
new file mode 100644
index 0000000000..f6b0afe98c
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-nested-derived/main.svelte
@@ -0,0 +1,15 @@
+<script>
+	import Child from './Child.svelte';
+
+	let count = $state(0);
+</script>
+
+<button onclick={() => count += 1}>{count}</button>
+
+<svelte:boundary>
+	<Child {count} />
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-prop/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-prop/Child.svelte
new file mode 100644
index 0000000000..85d212b1a8
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-prop/Child.svelte
@@ -0,0 +1,5 @@
+<script>
+	let { value } = $props();
+</script>
+
+<h1>{value}</h1>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-prop/_config.js b/packages/svelte/tests/runtime-runes/samples/async-prop/_config.js
new file mode 100644
index 0000000000..66690c120c
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-prop/_config.js
@@ -0,0 +1,51 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `
+		<button>reset</button>
+		<button>hello</button>
+		<button>again</button>
+		<p>pending</p>
+	`,
+
+	async test({ assert, target }) {
+		const [reset, hello, again] = target.querySelectorAll('button');
+
+		hello.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>hello</button>
+				<button>again</button>
+				<h1>hello</h1>
+			`
+		);
+
+		reset.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>hello</button>
+				<button>again</button>
+				<h1>hello</h1>
+			`
+		);
+
+		again.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>hello</button>
+				<button>again</button>
+				<h1>hello again</h1>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-prop/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-prop/main.svelte
new file mode 100644
index 0000000000..38388607ce
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-prop/main.svelte
@@ -0,0 +1,17 @@
+<script>
+	import Child from './Child.svelte';
+
+	let deferred = $state(Promise.withResolvers());
+</script>
+
+<button onclick={() => deferred = Promise.withResolvers()}>reset</button>
+<button onclick={() => deferred.resolve('hello')}>hello</button>
+<button onclick={() => deferred.resolve('hello again')}>again</button>
+
+<svelte:boundary>
+	<Child value={await deferred.promise} />
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss/_config.js b/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss/_config.js
new file mode 100644
index 0000000000..f8a7cfd479
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss/_config.js
@@ -0,0 +1,24 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true
+	},
+
+	html: `<button>a</button><button>b</button><p>pending</p>`,
+
+	async test({ assert, target, warnings }) {
+		await tick();
+		assert.htmlEqual(target.innerHTML, '<button>a</button><button>b</button><h1>3</h1><p>3</p>');
+
+		assert.equal(
+			warnings[0],
+			'Detected reactivity loss when reading `b`. This happens when state is read in an async function after an earlier `await`'
+		);
+
+		assert.equal(warnings[1].name, 'TracedAtError');
+
+		assert.equal(warnings.length, 2);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss/main.svelte
new file mode 100644
index 0000000000..bdb1b095c9
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss/main.svelte
@@ -0,0 +1,20 @@
+<script>
+	let a = $state(1);
+	let b = $state(2);
+
+	async function a_plus_b() {
+		return await a + await b;
+	}
+</script>
+
+<button onclick={() => a++}>a</button>
+<button onclick={() => b++}>b</button>
+
+<svelte:boundary>
+	<h1>{await a_plus_b()}</h1>
+	<p>{await a + await b}</p>
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-redirect-initial/_config.js b/packages/svelte/tests/runtime-runes/samples/async-redirect-initial/_config.js
new file mode 100644
index 0000000000..17bb79af08
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-redirect-initial/_config.js
@@ -0,0 +1,51 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const [a, b, c, ok] = target.querySelectorAll('button');
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<h1>b</h1>
+				<button>a</button>
+				<button>b</button>
+				<button>c</button>
+				<button>ok</button>
+				<p>pending...</p>
+			`
+		);
+
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<h1>c</h1>
+				<button>a</button>
+				<button>b</button>
+				<button>c</button>
+				<button>ok</button>
+				<p>c</p>
+			`
+		);
+
+		ok.click();
+
+		b.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<h1>b</h1>
+				<button>a</button>
+				<button>b</button>
+				<button>c</button>
+				<button>ok</button>
+				<p>b</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-redirect-initial/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-redirect-initial/main.svelte
new file mode 100644
index 0000000000..b1bb291e2e
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-redirect-initial/main.svelte
@@ -0,0 +1,43 @@
+<script lang=ts>
+	let route = $state('b');
+	let ok = $state(false);
+
+	function goto(r) {
+		return Promise.resolve().then(() => {
+			route = r;
+			throw new Error('nope');
+		});
+	}
+</script>
+
+<h1>{route}</h1>
+<button onclick={() => route = 'a'}>a</button>
+<button onclick={() => route = 'b'}>b</button>
+<button onclick={() => route = 'c'}>c</button>
+<button onclick={() => ok = true}>ok</button>
+
+<svelte:boundary>
+	{#if route === 'a'}
+		<p>a</p>
+	{/if}
+
+	{#if route === 'b'}
+		{#if ok}
+			<p>b</p>
+		{:else}
+			{await goto('c')}
+		{/if}
+	{/if}
+
+	{#if route === 'c'}
+		<p>c</p>
+	{/if}
+
+	{#snippet pending()}
+		<p>pending...</p>
+	{/snippet}
+
+	{#snippet failed(error, reset)}
+		<button onclick={reset}>retry</button>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-redirect/_config.js b/packages/svelte/tests/runtime-runes/samples/async-redirect/_config.js
new file mode 100644
index 0000000000..ebbe642860
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-redirect/_config.js
@@ -0,0 +1,52 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<h1>a</h1>
+				<button>a</button>
+				<button>b</button>
+				<button>c</button>
+				<button>ok</button>
+				<p>a</p>
+			`
+		);
+
+		const [a, b, c, ok] = target.querySelectorAll('button');
+
+		b.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<h1>c</h1>
+				<button>a</button>
+				<button>b</button>
+				<button>c</button>
+				<button>ok</button>
+				<p>c</p>
+			`
+		);
+
+		ok.click();
+
+		b.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<h1>b</h1>
+				<button>a</button>
+				<button>b</button>
+				<button>c</button>
+				<button>ok</button>
+				<p>b</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-redirect/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-redirect/main.svelte
new file mode 100644
index 0000000000..bf5fdf9ed3
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-redirect/main.svelte
@@ -0,0 +1,43 @@
+<script lang=ts>
+	let route = $state('a');
+	let ok = $state(false);
+
+	function goto(r) {
+		return Promise.resolve().then(() => {
+			route = r;
+			throw new Error('nope');
+		});
+	}
+</script>
+
+<h1>{route}</h1>
+<button onclick={() => route = 'a'}>a</button>
+<button onclick={() => route = 'b'}>b</button>
+<button onclick={() => route = 'c'}>c</button>
+<button onclick={() => ok = true}>ok</button>
+
+<svelte:boundary>
+	{#if route === 'a'}
+		<p>a</p>
+	{/if}
+
+	{#if route === 'b'}
+		{#if ok}
+			<p>b</p>
+		{:else}
+			{await goto('c')}
+		{/if}
+	{/if}
+
+	{#if route === 'c'}
+		<p>c</p>
+	{/if}
+
+	{#snippet pending()}
+		<p>pending...</p>
+	{/snippet}
+
+	{#snippet failed(error, reset)}
+		<button onclick={reset}>retry</button>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-render-tag/_config.js b/packages/svelte/tests/runtime-runes/samples/async-render-tag/_config.js
new file mode 100644
index 0000000000..6f3473f592
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-render-tag/_config.js
@@ -0,0 +1,51 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `
+		<button>reset</button>
+		<button>hello</button>
+		<button>wheee</button>
+		<p>pending</p>
+	`,
+
+	async test({ assert, target }) {
+		const [reset, hello, wheee] = target.querySelectorAll('button');
+
+		hello.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>hello</button>
+				<button>wheee</button>
+				<h1>hello</h1>
+			`
+		);
+
+		reset.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>hello</button>
+				<button>wheee</button>
+				<h1>hello</h1>
+			`
+		);
+
+		wheee.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>hello</button>
+				<button>wheee</button>
+				<h1>wheee</h1>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-render-tag/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-render-tag/main.svelte
new file mode 100644
index 0000000000..b59bc319d8
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-render-tag/main.svelte
@@ -0,0 +1,19 @@
+<script>
+	let deferred = $state(Promise.withResolvers());
+</script>
+
+<button onclick={() => deferred = Promise.withResolvers()}>reset</button>
+<button onclick={() => deferred.resolve('hello')}>hello</button>
+<button onclick={() => deferred.resolve('wheee')}>wheee</button>
+
+{#snippet hello(message)}
+	<h1>{message}</h1>
+{/snippet}
+
+<svelte:boundary>
+	{@render hello(await deferred.promise)}
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-slot/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-slot/Child.svelte
new file mode 100644
index 0000000000..c32f869f63
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-slot/Child.svelte
@@ -0,0 +1 @@
+<slot message={await 'hello'}></slot>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-slot/_config.js b/packages/svelte/tests/runtime-runes/samples/async-slot/_config.js
new file mode 100644
index 0000000000..3d54d24259
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-slot/_config.js
@@ -0,0 +1,13 @@
+import { tick } from 'svelte';
+import { ok, test } from '../../test';
+
+export default test({
+	html: `
+		<p>loading...</p>
+	`,
+
+	async test({ assert, target }) {
+		await tick();
+		assert.htmlEqual(target.innerHTML, '<p>hello</p>');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-slot/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-slot/main.svelte
new file mode 100644
index 0000000000..badd60746d
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-slot/main.svelte
@@ -0,0 +1,13 @@
+<script>
+	import Child from './Child.svelte';
+</script>
+
+<svelte:boundary>
+	<Child let:message>
+		<p>{message}</p>
+	</Child>
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-stale-derived-2/_config.js b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-2/_config.js
new file mode 100644
index 0000000000..8276c5be41
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-2/_config.js
@@ -0,0 +1,58 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	skip: true, // TODO this one is tricky
+
+	async test({ assert, target }) {
+		const [increment, a, b] = target.querySelectorAll('button');
+
+		a.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<button>shift a</button>
+				<button>shift b</button>
+				<p>a: 0</p>
+			`
+		);
+
+		increment.click();
+		await tick();
+
+		increment.click();
+		await tick();
+
+		increment.click();
+		await tick();
+
+		a.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<button>shift a</button>
+				<button>shift b</button>
+				<p>a: 0</p>
+			`
+		);
+
+		b.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<button>shift a</button>
+				<button>shift b</button>
+				<p>b: 0</p
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-stale-derived-2/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-2/main.svelte
new file mode 100644
index 0000000000..c9d4f2b096
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-2/main.svelte
@@ -0,0 +1,34 @@
+<script lang="ts">
+	let count = $state(0);
+
+	let a = [];
+	let b = [];
+
+	function push(deferreds, value) {
+		const deferred = Promise.withResolvers();
+		deferreds.push({ deferred, value });
+		return deferred.promise;
+	}
+</script>
+
+<button onclick={() => count += 1}>increment</button>
+<button onclick={() => {
+	const d = a.shift();
+	d?.deferred.resolve(d.value);
+}}>shift a</button>
+<button onclick={() => {
+	const d = b.shift();
+	d?.deferred.resolve(d.value);
+}}>shift b</button>
+
+<svelte:boundary>
+	{#if count % 2 === 0}
+		<p>a: {await push(a, count)}</p>
+	{:else}
+		<p>b: {await push(b, count)}</p>
+	{/if}
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-stale-derived/_config.js b/packages/svelte/tests/runtime-runes/samples/async-stale-derived/_config.js
new file mode 100644
index 0000000000..884b27d865
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-stale-derived/_config.js
@@ -0,0 +1,52 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+
+		const [increment, shift] = target.querySelectorAll('button');
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<button>shift</button>
+				<p>0</p>
+			`
+		);
+
+		increment.click();
+		await tick();
+
+		increment.click();
+		await tick();
+
+		increment.click();
+		await tick();
+
+		shift.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<button>shift</button>
+				<p>2</p>
+			`
+		);
+
+		shift.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<button>shift</button>
+				<p>delayed: 3</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-stale-derived/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-stale-derived/main.svelte
new file mode 100644
index 0000000000..eeefffbee6
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-stale-derived/main.svelte
@@ -0,0 +1,26 @@
+<script lang="ts">
+	let count = $state(0);
+
+	let deferreds = [];
+
+	function push() {
+		const deferred = Promise.withResolvers();
+		deferreds.push(deferred);
+		return deferred.promise;
+	}
+</script>
+
+<button onclick={() => count += 1}>increment</button>
+<button onclick={() => deferreds.shift()?.resolve(count)}>shift</button>
+
+<svelte:boundary>
+	{#if count % 2}
+		<p>delayed: {await push()}</p>
+	{:else}
+		<p>{await count}</p>
+	{/if}
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-svelte-element/_config.js b/packages/svelte/tests/runtime-runes/samples/async-svelte-element/_config.js
new file mode 100644
index 0000000000..dc25be10c8
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-svelte-element/_config.js
@@ -0,0 +1,51 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `
+		<button>reset</button>
+		<button>h1</button>
+		<button>h2</button>
+		<p>pending</p>
+	`,
+
+	async test({ assert, target }) {
+		const [reset, h1, h2] = target.querySelectorAll('button');
+
+		h1.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>h1</button>
+				<button>h2</button>
+				<h1>hello</h1>
+			`
+		);
+
+		reset.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>h1</button>
+				<button>h2</button>
+				<h1>hello</h1>
+			`
+		);
+
+		h2.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>reset</button>
+				<button>h1</button>
+				<button>h2</button>
+				<h2>hello</h2>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-svelte-element/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-svelte-element/main.svelte
new file mode 100644
index 0000000000..f8165784dc
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-svelte-element/main.svelte
@@ -0,0 +1,15 @@
+<script>
+	let deferred = $state(Promise.withResolvers());
+</script>
+
+<button onclick={() => deferred = Promise.withResolvers()}>reset</button>
+<button onclick={() => deferred.resolve('h1')}>h1</button>
+<button onclick={() => deferred.resolve('h2')}>h2</button>
+
+<svelte:boundary>
+	<svelte:element this={await deferred.promise}>hello</svelte:element>
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-top-level-in-if/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-top-level-in-if/Child.svelte
new file mode 100644
index 0000000000..7ad618f130
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-top-level-in-if/Child.svelte
@@ -0,0 +1,7 @@
+<script>
+	let { promise } = $props();
+
+	let value = await promise;
+</script>
+
+<p>{value}</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-top-level-in-if/_config.js b/packages/svelte/tests/runtime-runes/samples/async-top-level-in-if/_config.js
new file mode 100644
index 0000000000..73c9b50a69
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-top-level-in-if/_config.js
@@ -0,0 +1,40 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const [toggle, hello] = target.querySelectorAll('button');
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+			<button>toggle</button>
+			<button>hello</button>
+		`
+		);
+
+		toggle.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+			<button>toggle</button>
+			<button>hello</button>
+		`
+		);
+
+		hello.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+			<button>toggle</button>
+			<button>hello</button>
+			<p>condition is true</p>
+			<p>hello</p>
+		`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-top-level-in-if/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-top-level-in-if/main.svelte
new file mode 100644
index 0000000000..d111ce6fe3
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-top-level-in-if/main.svelte
@@ -0,0 +1,20 @@
+<script>
+	import Child from './Child.svelte';
+
+	let condition = $state(false);
+	let deferred = $state(Promise.withResolvers());
+</script>
+
+<button onclick={() => condition = !condition}>toggle</button>
+<button onclick={() => deferred.resolve('hello')}>hello</button>
+
+<svelte:boundary>
+	{#if condition}
+		<p>condition is {condition}</p>
+		<Child promise={deferred.promise} />
+	{/if}
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-top-level/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-top-level/Child.svelte
new file mode 100644
index 0000000000..7ad618f130
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-top-level/Child.svelte
@@ -0,0 +1,7 @@
+<script>
+	let { promise } = $props();
+
+	let value = await promise;
+</script>
+
+<p>{value}</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-top-level/_config.js b/packages/svelte/tests/runtime-runes/samples/async-top-level/_config.js
new file mode 100644
index 0000000000..b2200201c6
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-top-level/_config.js
@@ -0,0 +1,14 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `<button>hello</button><p>pending</p>`,
+
+	async test({ assert, target }) {
+		const [hello] = target.querySelectorAll('button');
+
+		hello.click();
+		await tick();
+		assert.htmlEqual(target.innerHTML, '<button>hello</button><p>hello</p>');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-top-level/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-top-level/main.svelte
new file mode 100644
index 0000000000..78ad3ba04a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-top-level/main.svelte
@@ -0,0 +1,15 @@
+<script>
+	import Child from './Child.svelte';
+
+	let deferred = $state(Promise.withResolvers());
+</script>
+
+<button onclick={() => deferred.resolve('hello')}>hello</button>
+
+<svelte:boundary>
+	<Child promise={deferred.promise} />
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-unresolved-promise/_config.js b/packages/svelte/tests/runtime-runes/samples/async-unresolved-promise/_config.js
new file mode 100644
index 0000000000..e9ccbba2b6
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-unresolved-promise/_config.js
@@ -0,0 +1,32 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+
+		const [increment] = target.querySelectorAll('button');
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<p>0</p>
+			`
+		);
+
+		increment.click();
+		await tick();
+
+		increment.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<p>2</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-unresolved-promise/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-unresolved-promise/main.svelte
new file mode 100644
index 0000000000..e0619a1fe4
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-unresolved-promise/main.svelte
@@ -0,0 +1,19 @@
+<script>
+	let count = $state(0);
+</script>
+
+<button onclick={() => count += 1}>
+	increment
+</button>
+
+<svelte:boundary>
+	{#if count % 2}
+		<p>{await new Promise(() => {})}</p>
+	{:else}
+		<p>{await count}</p>
+	{/if}
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-waterfall-on-init/_config.js b/packages/svelte/tests/runtime-runes/samples/async-waterfall-on-init/_config.js
new file mode 100644
index 0000000000..e2c8b851c1
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-waterfall-on-init/_config.js
@@ -0,0 +1,42 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `
+		<button>resolve 1</button>
+		<button>resolve 2</button>
+		<hr>
+		<p>pending</p>
+	`,
+
+	async test({ assert, target }) {
+		const [button1, button2] = target.querySelectorAll('button');
+
+		button1.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>resolve 1</button>
+				<button>resolve 2</button>
+				<hr>
+				<p>pending</p>
+			`
+		);
+
+		button2.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>resolve 1</button>
+				<button>resolve 2</button>
+				<hr>
+				<button>0</button>
+				<p>true</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-waterfall-on-init/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-waterfall-on-init/main.svelte
new file mode 100644
index 0000000000..86af9bb07e
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-waterfall-on-init/main.svelte
@@ -0,0 +1,22 @@
+<script>
+	let d1 = Promise.withResolvers();
+	let d2 = Promise.withResolvers();
+
+	let count = $state(0);
+</script>
+
+<button onclick={() => d1.resolve(true)}>resolve 1</button>
+<button onclick={() => d2.resolve(true)}>resolve 2</button>
+
+<hr>
+
+<svelte:boundary>
+	{#if await d1.promise}
+		<button onclick={() => count += 1}>{count}</button>
+		<p>{await d2.promise}</p>
+	{/if}
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-with-sync-derived/_config.js b/packages/svelte/tests/runtime-runes/samples/async-with-sync-derived/_config.js
new file mode 100644
index 0000000000..837dd976e2
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-with-sync-derived/_config.js
@@ -0,0 +1,53 @@
+import { flushSync, tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `<p>loading...</p>`,
+
+	async test({ assert, target }) {
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>log</button>
+				<button>x 1</button>
+				<button>other 1</button>
+				<p>1</p>
+				<p>1</p>
+				<p>1</p>
+			`
+		);
+
+		const [log, x, other] = target.querySelectorAll('button');
+
+		flushSync(() => x.click());
+		flushSync(() => other.click());
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>log</button>
+				<button>x 1</button>
+				<button>other 2</button>
+				<p>1</p>
+				<p>1</p>
+				<p>1</p>
+			`
+		);
+
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>log</button>
+				<button>x 2</button>
+				<button>other 2</button>
+				<p>2</p>
+				<p>2</p>
+				<p>2</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-with-sync-derived/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-with-sync-derived/main.svelte
new file mode 100644
index 0000000000..764007e082
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-with-sync-derived/main.svelte
@@ -0,0 +1,19 @@
+<script>
+	let x = $state(1);
+	let y = $derived(x);
+	let other = $state(1);
+</script>
+
+<svelte:boundary>
+	<button onclick={() => console.log({ x, y })}>log</button>
+	<button onclick={() => x += 1}>x {x}</button>
+	<button onclick={() => other += 1}>other {other}</button>
+
+	<p>{x}</p>
+	<p>{await x}</p>
+	<p>{y}</p>
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-cleanup/_config.js b/packages/svelte/tests/runtime-runes/samples/effect-cleanup/_config.js
index e55733c148..416f61d23a 100644
--- a/packages/svelte/tests/runtime-runes/samples/effect-cleanup/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/effect-cleanup/_config.js
@@ -1,3 +1,4 @@
+import { async_mode } from '../../../helpers';
 import { test } from '../../test';
 import { flushSync } from 'svelte';
 
@@ -10,6 +11,12 @@ export default test({
 		flushSync(() => {
 			b1.click();
 		});
-		assert.deepEqual(logs, ['init 0']);
+
+		// With async mode (which is on by default for runtime-runes) this works as expected, without it
+		// it works differently: https://github.com/sveltejs/svelte/pull/15564
+		assert.deepEqual(
+			logs,
+			async_mode ? ['init 0', 'cleanup 0', null, 'init 2', 'cleanup 2', null, 'init 4'] : ['init 0']
+		);
 	}
 });
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-cleanup/main.svelte b/packages/svelte/tests/runtime-runes/samples/effect-cleanup/main.svelte
index 2cdcfdfb58..da38374f82 100644
--- a/packages/svelte/tests/runtime-runes/samples/effect-cleanup/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/effect-cleanup/main.svelte
@@ -14,4 +14,4 @@
 	})
 </script>
 
-<button on:click={() => count++ }>Click</button>
+<button onclick={() => count++ }>Click</button>
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-18/_config.js b/packages/svelte/tests/runtime-runes/samples/error-boundary-18/_config.js
index e092d0e7c7..f34668ec45 100644
--- a/packages/svelte/tests/runtime-runes/samples/error-boundary-18/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-18/_config.js
@@ -2,6 +2,8 @@ import { flushSync } from 'svelte';
 import { test } from '../../test';
 
 export default test({
+	skip: true, // TODO unskip once tagged values are in and we can fix this properly
+
 	test({ assert, target }) {
 		let btn = target.querySelector('button');
 
diff --git a/packages/svelte/tests/runtime-runes/samples/set-context-after-await/Child.svelte b/packages/svelte/tests/runtime-runes/samples/set-context-after-await/Child.svelte
new file mode 100644
index 0000000000..122a316726
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/set-context-after-await/Child.svelte
@@ -0,0 +1,11 @@
+<script>
+	import { setContext } from 'svelte';
+
+	await Promise.resolve();
+
+	try {
+		setContext('potato', {});
+	} catch (e) {
+		console.log(e.message);
+	}
+</script>
diff --git a/packages/svelte/tests/runtime-runes/samples/set-context-after-await/_config.js b/packages/svelte/tests/runtime-runes/samples/set-context-after-await/_config.js
new file mode 100644
index 0000000000..1bf7e71176
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/set-context-after-await/_config.js
@@ -0,0 +1,12 @@
+import { test } from '../../test';
+
+export default test({
+	skip_no_async: true,
+	async test({ assert, logs }) {
+		await Promise.resolve();
+		await Promise.resolve();
+		await Promise.resolve();
+
+		assert.ok(logs[0].startsWith('set_context_after_init'));
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/set-context-after-await/main.svelte b/packages/svelte/tests/runtime-runes/samples/set-context-after-await/main.svelte
new file mode 100644
index 0000000000..65d0e623cf
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/set-context-after-await/main.svelte
@@ -0,0 +1,11 @@
+<script>
+	import Child from './Child.svelte';
+</script>
+
+<svelte:boundary>
+	<Child />
+
+	{#snippet pending()}
+		...
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/set-context-after-mount/_config.js b/packages/svelte/tests/runtime-runes/samples/set-context-after-mount/_config.js
new file mode 100644
index 0000000000..4569f42a73
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/set-context-after-mount/_config.js
@@ -0,0 +1,16 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+import { async_mode } from '../../../helpers';
+
+export default test({
+	async test({ target, assert, logs }) {
+		const button = target.querySelector('button');
+
+		flushSync(() => button?.click());
+		assert.ok(
+			async_mode
+				? logs[0].startsWith('set_context_after_init')
+				: logs[0] === 'works without experimental async but really shouldnt'
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/set-context-after-mount/main.svelte b/packages/svelte/tests/runtime-runes/samples/set-context-after-mount/main.svelte
new file mode 100644
index 0000000000..0c3b6c3a0f
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/set-context-after-mount/main.svelte
@@ -0,0 +1,20 @@
+<script>
+	import { setContext } from 'svelte';
+
+	let condition = $state(false);
+
+	$effect(() => {
+		if (condition) {
+			try {
+				setContext('potato', {});
+				console.log('works without experimental async but really shouldnt')
+			} catch (e) {
+				console.log(e.message);
+			}
+		}
+	});
+</script>
+
+<button onclick={() => condition = !condition}>
+	{condition}
+</button>
diff --git a/packages/svelte/tests/runtime-runes/samples/tick-timing/_config.js b/packages/svelte/tests/runtime-runes/samples/tick-timing/_config.js
index 339cec55c5..25414d4b47 100644
--- a/packages/svelte/tests/runtime-runes/samples/tick-timing/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/tick-timing/_config.js
@@ -3,6 +3,8 @@ import { test, ok } from '../../test';
 
 // Tests that tick only resolves after all pending effects have been cleared
 export default test({
+	skip: true, // weirdly, this works if you run it by itself
+
 	async test({ assert, target }) {
 		const btn = target.querySelector('button');
 		ok(btn);
diff --git a/packages/svelte/tests/runtime-runes/samples/untrack-own-deriveds/_config.js b/packages/svelte/tests/runtime-runes/samples/untrack-own-deriveds/_config.js
index 18062b86fb..b728c3c0be 100644
--- a/packages/svelte/tests/runtime-runes/samples/untrack-own-deriveds/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/untrack-own-deriveds/_config.js
@@ -2,6 +2,8 @@ import { flushSync } from 'svelte';
 import { test } from '../../test';
 
 export default test({
+	// In async mode we _do_ want to run effects that react to their own state changing
+	skip_async: true,
 	test({ assert, target, logs }) {
 		const button = target.querySelector('button');
 
diff --git a/packages/svelte/tests/signals/test.ts b/packages/svelte/tests/signals/test.ts
index 719c936df0..937324727b 100644
--- a/packages/svelte/tests/signals/test.ts
+++ b/packages/svelte/tests/signals/test.ts
@@ -6,16 +6,18 @@ import {
 	effect,
 	effect_root,
 	render_effect,
-	user_effect
+	user_effect,
+	user_pre_effect
 } from '../../src/internal/client/reactivity/effects';
 import { state, set, update, update_pre } from '../../src/internal/client/reactivity/sources';
-import type { Derived, Effect, Value } from '../../src/internal/client/types';
+import type { Derived, Effect, Source, Value } from '../../src/internal/client/types';
 import { proxy } from '../../src/internal/client/proxy';
 import { derived } from '../../src/internal/client/reactivity/deriveds';
 import { snapshot } from '../../src/internal/shared/clone.js';
 import { SvelteSet } from '../../src/reactivity/set';
 import { DESTROYED } from '../../src/internal/client/constants';
 import { noop } from 'svelte/internal/client';
+import { disable_async_mode_flag, enable_async_mode_flag } from '../../src/internal/flags';
 
 /**
  * @param runes runes mode
@@ -557,7 +559,7 @@ describe('signals', () => {
 		};
 	});
 
-	test('schedules rerun when writing to signal before reading it', (runes) => {
+	test.skip('schedules rerun when writing to signal before reading it', (runes) => {
 		if (!runes) return () => {};
 
 		const error = console.error;
@@ -1049,31 +1051,85 @@ describe('signals', () => {
 		};
 	});
 
-	test('effects do not depend on state they own', () => {
+	test('effects do depend on state they own', (runes) => {
+		// This behavior is important for use cases like a Resource class
+		// which shares its instance between multiple effects and triggers
+		// rerenders by self-invalidating its state.
+		const log: number[] = [];
+
+		let count: any;
+
+		if (runes) {
+			// We will make this the new default behavior once it's stable but until then
+			// we need to keep the old behavior to not break existing code.
+			enable_async_mode_flag();
+		}
+
+		effect(() => {
+			if (!count || $.get<number>(count) < 2) {
+				count ||= state(0);
+				log.push($.get(count));
+				set(count, $.get<number>(count) + 1);
+			}
+		});
+
+		return () => {
+			try {
+				flushSync();
+				if (runes) {
+					assert.deepEqual(log, [0, 1]);
+				} else {
+					assert.deepEqual(log, [0]);
+				}
+			} finally {
+				disable_async_mode_flag();
+			}
+		};
+	});
+
+	test('nested effects depend on state of upper effects', () => {
+		const logs: number[] = [];
+		let raw: Source<number>;
+		let proxied: { current: number };
+
 		user_effect(() => {
-			const value = state(0);
-			set(value, $.get(value) + 1);
+			raw = state(0);
+			proxied = proxy({ current: 0 });
+
+			// We need those separate, else one working and rerunning the effect
+			// could mask the other one not rerunning
+			user_effect(() => {
+				logs.push($.get(raw));
+			});
+
+			user_effect(() => {
+				logs.push(proxied.current);
+			});
 		});
 
 		return () => {
 			flushSync();
+			set(raw, $.get(raw) + 1);
+			proxied.current += 1;
+			flushSync();
+			assert.deepEqual(logs, [0, 0, 1, 1]);
 		};
 	});
 
 	test('nested effects depend on state of upper effects', () => {
 		const logs: number[] = [];
 
-		user_effect(() => {
+		user_pre_effect(() => {
 			const raw = state(0);
 			const proxied = proxy({ current: 0 });
 
 			// We need those separate, else one working and rerunning the effect
 			// could mask the other one not rerunning
-			user_effect(() => {
+			user_pre_effect(() => {
 				logs.push($.get(raw));
 			});
 
-			user_effect(() => {
+			user_pre_effect(() => {
 				logs.push(proxied.current);
 			});
 
@@ -1081,7 +1137,7 @@ describe('signals', () => {
 			// together with the reading effects
 			flushSync();
 
-			user_effect(() => {
+			user_pre_effect(() => {
 				$.untrack(() => {
 					set(raw, $.get(raw) + 1);
 					proxied.current += 1;
diff --git a/packages/svelte/tests/store/test.ts b/packages/svelte/tests/store/test.ts
index 77cecca7e5..ecb22c1be6 100644
--- a/packages/svelte/tests/store/test.ts
+++ b/packages/svelte/tests/store/test.ts
@@ -11,6 +11,7 @@ import {
 } from 'svelte/store';
 import { source, set } from '../../src/internal/client/reactivity/sources';
 import * as $ from '../../src/internal/client/runtime';
+import { flushSync } from '../../src/internal/client/reactivity/batch';
 import { effect_root, render_effect } from 'svelte/internal/client';
 
 describe('writable', () => {
@@ -602,7 +603,7 @@ describe('toStore', () => {
 		assert.deepEqual(log, [0]);
 
 		set(count, 1);
-		$.flushSync();
+		flushSync();
 		assert.deepEqual(log, [0, 1]);
 
 		unsubscribe();
@@ -625,7 +626,7 @@ describe('toStore', () => {
 		assert.deepEqual(log, [0]);
 
 		set(count, 1);
-		$.flushSync();
+		flushSync();
 		assert.deepEqual(log, [0, 1]);
 
 		store.set(2);
@@ -654,11 +655,11 @@ describe('fromStore', () => {
 		assert.deepEqual(log, [0]);
 
 		store.set(1);
-		$.flushSync();
+		flushSync();
 		assert.deepEqual(log, [0, 1]);
 
 		count.current = 2;
-		$.flushSync();
+		flushSync();
 		assert.deepEqual(log, [0, 1, 2]);
 
 		assert.equal(get(store), 2);
diff --git a/packages/svelte/tests/suite.ts b/packages/svelte/tests/suite.ts
index 0ae06e727f..6954b8b683 100644
--- a/packages/svelte/tests/suite.ts
+++ b/packages/svelte/tests/suite.ts
@@ -35,7 +35,7 @@ export function suite<Test extends BaseTest>(fn: (config: Test, test_dir: string
 
 export function suite_with_variants<Test extends BaseTest, Variants extends string, Common>(
 	variants: Variants[],
-	should_skip_variant: (variant: Variants, config: Test) => boolean | 'no-test',
+	should_skip_variant: (variant: Variants, config: Test, test_name: string) => boolean | 'no-test',
 	common_setup: (config: Test, test_dir: string) => Promise<Common> | Common,
 	fn: (config: Test, test_dir: string, variant: Variants, common: Common) => void
 ) {
@@ -46,11 +46,11 @@ export function suite_with_variants<Test extends BaseTest, Variants extends stri
 				let called_common = false;
 				let common: any = undefined;
 				for (const variant of variants) {
-					if (should_skip_variant(variant, config) === 'no-test') {
+					if (should_skip_variant(variant, config, dir) === 'no-test') {
 						continue;
 					}
 					// TODO unify test interfaces
-					const skip = config.skip || should_skip_variant(variant, config);
+					const skip = config.skip || should_skip_variant(variant, config, dir);
 					const solo = config.solo;
 					let it_fn = skip ? it.skip : solo ? it.only : it;
 
diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index 432171ae0d..72eb871db6 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -434,6 +434,11 @@ declare module 'svelte' {
 	 * @deprecated Use [`$effect`](https://svelte.dev/docs/svelte/$effect) instead
 	 * */
 	export function afterUpdate(fn: () => void): void;
+	/**
+	 * Synchronously flush any pending updates.
+	 * Returns void if no callback is provided, otherwise returns the result of calling the callback.
+	 * */
+	export function flushSync<T = void>(fn?: (() => T) | undefined): T;
 	/**
 	 * Create a snippet programmatically
 	 * */
@@ -443,29 +448,6 @@ declare module 'svelte' {
 	}): Snippet<Params>;
 	/** Anything except a function */
 	type NotFunction<T> = T extends Function ? never : T;
-	/**
-	 * Synchronously flush any pending updates.
-	 * Returns void if no callback is provided, otherwise returns the result of calling the callback.
-	 * */
-	export function flushSync<T = void>(fn?: (() => T) | undefined): T;
-	/**
-	 * Returns a promise that resolves once any pending state changes have been applied.
-	 * */
-	export function tick(): Promise<void>;
-	/**
-	 * When used inside a [`$derived`](https://svelte.dev/docs/svelte/$derived) or [`$effect`](https://svelte.dev/docs/svelte/$effect),
-	 * any state read inside `fn` will not be treated as a dependency.
-	 *
-	 * ```ts
-	 * $effect(() => {
-	 *   // this will run when `data` changes, but not when `time` changes
-	 *   save(data, {
-	 *     timestamp: untrack(() => time)
-	 *   });
-	 * });
-	 * ```
-	 * */
-	export function untrack<T>(fn: () => T): T;
 	/**
 	 * Retrieves the context that belongs to the closest parent component with the specified `key`.
 	 * Must be called during component initialisation.
@@ -539,6 +521,29 @@ declare module 'svelte' {
 	export function unmount(component: Record<string, any>, options?: {
 		outro?: boolean;
 	} | undefined): Promise<void>;
+	/**
+	 * Returns a promise that resolves once any pending state changes have been applied.
+	 * */
+	export function tick(): Promise<void>;
+	/**
+	 * Returns a promise that resolves once any state changes, and asynchronous work resulting from them,
+	 * have resolved and the DOM has been updated
+	 * */
+	export function settled(): Promise<void>;
+	/**
+	 * When used inside a [`$derived`](https://svelte.dev/docs/svelte/$derived) or [`$effect`](https://svelte.dev/docs/svelte/$effect),
+	 * any state read inside `fn` will not be treated as a dependency.
+	 *
+	 * ```ts
+	 * $effect(() => {
+	 *   // this will run when `data` changes, but not when `time` changes
+	 *   save(data, {
+	 *     timestamp: untrack(() => time)
+	 *   });
+	 * });
+	 * ```
+	 * */
+	export function untrack<T>(fn: () => T): T;
 	type Getters<T> = {
 		[K in keyof T]: () => T[K];
 	};
@@ -1111,6 +1116,11 @@ declare module 'svelte/compiler' {
 		 * Use this to filter out warnings. Return `true` to keep the warning, `false` to discard it.
 		 */
 		warningFilter?: (warning: Warning) => boolean;
+		/** Experimental options */
+		experimental?: {
+			/** Allow `await` keyword in deriveds, template expressions, and the top level of components */
+			async?: boolean;
+		};
 	}
 	/**
 	 * - `html`    — the default, for e.g. `<div>` or `<span>`
@@ -3021,6 +3031,11 @@ declare module 'svelte/types/compiler/interfaces' {
 		 * Use this to filter out warnings. Return `true` to keep the warning, `false` to discard it.
 		 */
 		warningFilter?: (warning: Warning_1) => boolean;
+		/** Experimental options */
+		experimental?: {
+			/** Allow `await` keyword in deriveds, template expressions, and the top level of components */
+			async?: boolean;
+		};
 	}
 	/**
 	 * - `html`    — the default, for e.g. `<div>` or `<span>`
diff --git a/playgrounds/sandbox/index.html b/playgrounds/sandbox/index.html
index 845538abf0..d70409ffb6 100644
--- a/playgrounds/sandbox/index.html
+++ b/playgrounds/sandbox/index.html
@@ -14,6 +14,12 @@
 			import { mount, hydrate, unmount } from 'svelte';
 			import App from '/src/App.svelte';
 
+			globalThis.delayed = (v, ms = 1000) => {
+				return new Promise((f) => {
+					setTimeout(() => f(v), ms);
+				});
+			};
+
 			const root = document.getElementById('root');
 			const render = root.firstChild?.nextSibling ? hydrate : mount;
 
diff --git a/playgrounds/sandbox/run.js b/playgrounds/sandbox/run.js
index 2029937f52..639b755020 100644
--- a/playgrounds/sandbox/run.js
+++ b/playgrounds/sandbox/run.js
@@ -76,7 +76,10 @@ for (const generate of /** @type {const} */ (['client', 'server'])) {
 			dev: false,
 			filename: input,
 			generate,
-			runes: argv.values.runes
+			runes: argv.values.runes,
+			experimental: {
+				async: true
+			}
 		});
 
 		for (const warning of compiled.warnings) {
@@ -94,7 +97,10 @@ for (const generate of /** @type {const} */ (['client', 'server'])) {
 				filename: input,
 				generate,
 				runes: argv.values.runes,
-				fragments: 'tree'
+				fragments: 'tree',
+				experimental: {
+					async: true
+				}
 			});
 
 			const output_js = `${cwd}/output/${generate}/${file}.tree.js`;
@@ -116,7 +122,10 @@ for (const generate of /** @type {const} */ (['client', 'server'])) {
 		const compiled = compileModule(source, {
 			dev: false,
 			filename: input,
-			generate
+			generate,
+			experimental: {
+				async: true
+			}
 		});
 
 		const output_js = `${cwd}/output/${generate}/${file}`;
diff --git a/playgrounds/sandbox/ssr-common.js b/playgrounds/sandbox/ssr-common.js
new file mode 100644
index 0000000000..db3e085508
--- /dev/null
+++ b/playgrounds/sandbox/ssr-common.js
@@ -0,0 +1,17 @@
+Promise.withResolvers ??= () => {
+	let resolve;
+	let reject;
+
+	const promise = new Promise((f, r) => {
+		resolve = f;
+		reject = r;
+	});
+
+	return { promise, resolve, reject };
+};
+
+globalThis.delayed = (v, ms = 1000) => {
+	return new Promise((f) => {
+		setTimeout(() => f(v), ms);
+	});
+};
diff --git a/playgrounds/sandbox/ssr-dev.js b/playgrounds/sandbox/ssr-dev.js
index 01ce14e266..e019b234a6 100644
--- a/playgrounds/sandbox/ssr-dev.js
+++ b/playgrounds/sandbox/ssr-dev.js
@@ -5,6 +5,7 @@ import { fileURLToPath } from 'node:url';
 import polka from 'polka';
 import { createServer as createViteServer } from 'vite';
 import { render } from 'svelte/server';
+import './ssr-common.js';
 
 const PORT = process.env.PORT || '5173';
 
diff --git a/playgrounds/sandbox/ssr-prod.js b/playgrounds/sandbox/ssr-prod.js
index 1ed9435249..e8f74ee93a 100644
--- a/playgrounds/sandbox/ssr-prod.js
+++ b/playgrounds/sandbox/ssr-prod.js
@@ -3,6 +3,7 @@ import path from 'node:path';
 import polka from 'polka';
 import { render } from 'svelte/server';
 import App from './src/App.svelte';
+import './ssr-common.js';
 
 const { head, body } = render(App);
 
diff --git a/playgrounds/sandbox/svelte.config.js b/playgrounds/sandbox/svelte.config.js
index 65f739bdb6..68ac605385 100644
--- a/playgrounds/sandbox/svelte.config.js
+++ b/playgrounds/sandbox/svelte.config.js
@@ -1,5 +1,9 @@
 export default {
 	compilerOptions: {
-		hmr: true
+		hmr: false,
+
+		experimental: {
+			async: true
+		}
 	}
 };

From 63b5ebf36eea3fb1fab138068f3731b122228edb Mon Sep 17 00:00:00 2001
From: "Ahmad S." <navorite@gmail.com>
Date: Mon, 14 Jul 2025 23:02:25 +0300
Subject: [PATCH 058/148] fix: silence a11y warning for inert elements (#16339)

* fix: silence a11y warning for inert elements

* changeset

* handle `inert=""`

* oops

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
---
 .changeset/tall-avocados-repair.md                           | 5 +++++
 .../compiler/phases/2-analyze/visitors/shared/a11y/index.js  | 5 ++++-
 .../samples/a11y-consider-explicit-label/input.svelte        | 1 +
 3 files changed, 10 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/tall-avocados-repair.md

diff --git a/.changeset/tall-avocados-repair.md b/.changeset/tall-avocados-repair.md
new file mode 100644
index 0000000000..cf11fc9610
--- /dev/null
+++ b/.changeset/tall-avocados-repair.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: silence a11y warning for inert elements
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y/index.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y/index.js
index 5db31314d4..f45a6c9a80 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y/index.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y/index.js
@@ -387,7 +387,10 @@ export function check_element(node, context) {
 	switch (node.name) {
 		case 'a':
 		case 'button': {
-			const is_hidden = get_static_value(attribute_map.get('aria-hidden')) === 'true';
+			const is_hidden =
+				get_static_value(attribute_map.get('aria-hidden')) === 'true' ||
+				get_static_value(attribute_map.get('inert')) !== null;
+
 			if (!has_spread && !is_hidden && !is_labelled && !has_content(node)) {
 				w.a11y_consider_explicit_label(node);
 			}
diff --git a/packages/svelte/tests/validator/samples/a11y-consider-explicit-label/input.svelte b/packages/svelte/tests/validator/samples/a11y-consider-explicit-label/input.svelte
index 11dc007352..e97951065d 100644
--- a/packages/svelte/tests/validator/samples/a11y-consider-explicit-label/input.svelte
+++ b/packages/svelte/tests/validator/samples/a11y-consider-explicit-label/input.svelte
@@ -5,6 +5,7 @@
 <a href="/#" aria-label="Valid empty link"></a>
 
 <button aria-hidden='true'></button>
+<button inert></button>
 <a href="/#" aria-hidden='true'><b></b></a>
 
 <button>Click me</button>

From 616d29f5cd439b0854280927e3ce5b91753c3fa1 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Mon, 14 Jul 2025 16:05:11 -0400
Subject: [PATCH 059/148] Version Packages (#16364)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/eleven-weeks-dance.md   |  5 -----
 .changeset/tall-avocados-repair.md |  5 -----
 .changeset/warm-olives-applaud.md  |  5 -----
 packages/svelte/CHANGELOG.md       | 12 ++++++++++++
 packages/svelte/package.json       |  2 +-
 packages/svelte/src/version.js     |  2 +-
 6 files changed, 14 insertions(+), 17 deletions(-)
 delete mode 100644 .changeset/eleven-weeks-dance.md
 delete mode 100644 .changeset/tall-avocados-repair.md
 delete mode 100644 .changeset/warm-olives-applaud.md

diff --git a/.changeset/eleven-weeks-dance.md b/.changeset/eleven-weeks-dance.md
deleted file mode 100644
index 91245df0eb..0000000000
--- a/.changeset/eleven-weeks-dance.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': minor
----
-
-feat: support `await` in components when using the `experimental.async` compiler option
diff --git a/.changeset/tall-avocados-repair.md b/.changeset/tall-avocados-repair.md
deleted file mode 100644
index cf11fc9610..0000000000
--- a/.changeset/tall-avocados-repair.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: silence a11y warning for inert elements
diff --git a/.changeset/warm-olives-applaud.md b/.changeset/warm-olives-applaud.md
deleted file mode 100644
index 63a7803b99..0000000000
--- a/.changeset/warm-olives-applaud.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-chore: clean up a11y analysis code
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 7b822ee9b1..dfa3376e25 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,17 @@
 # svelte
 
+## 5.36.0
+
+### Minor Changes
+
+- feat: support `await` in components when using the `experimental.async` compiler option ([#15844](https://github.com/sveltejs/svelte/pull/15844))
+
+### Patch Changes
+
+- fix: silence a11y warning for inert elements ([#16339](https://github.com/sveltejs/svelte/pull/16339))
+
+- chore: clean up a11y analysis code ([#16345](https://github.com/sveltejs/svelte/pull/16345))
+
 ## 5.35.7
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 0dc8b20f98..a9fead571d 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.35.7",
+  "version": "5.36.0",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 0674d46652..248b1a3f11 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.35.7';
+export const VERSION = '5.36.0';
 export const PUBLIC_VERSION = '5';

From be0818552de9d282f5033bf8d1be3de34ce01794 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 14 Jul 2025 16:20:14 -0400
Subject: [PATCH 060/148] chore: squelch hydration warning in test suite
 (#16336)

---
 .../runtime-runes/samples/error-boundary-9/_config.js     | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-9/_config.js b/packages/svelte/tests/runtime-runes/samples/error-boundary-9/_config.js
index 9664c233b7..9bb12e768d 100644
--- a/packages/svelte/tests/runtime-runes/samples/error-boundary-9/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-9/_config.js
@@ -1,7 +1,13 @@
 import { test } from '../../test';
 
 export default test({
-	test({ assert, target, logs }) {
+	test({ assert, target, logs, warnings, variant }) {
+		if (variant === 'hydrate') {
+			assert.deepEqual(warnings, [
+				'Hydration failed because the initial UI does not match what was rendered on the server'
+			]);
+		}
+
 		assert.deepEqual(logs, ['error caught']);
 		assert.htmlEqual(target.innerHTML, `<div>Error!</div><button>Retry</button>`);
 	}

From 96ff125fcfa8d60af978e01e300224386d86ef01 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 14 Jul 2025 21:38:53 -0400
Subject: [PATCH 061/148] chore: fix error boundary test (#16368)

---
 .../runtime-runes/samples/error-boundary-9/_config.js     | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-9/_config.js b/packages/svelte/tests/runtime-runes/samples/error-boundary-9/_config.js
index 9bb12e768d..9664c233b7 100644
--- a/packages/svelte/tests/runtime-runes/samples/error-boundary-9/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-9/_config.js
@@ -1,13 +1,7 @@
 import { test } from '../../test';
 
 export default test({
-	test({ assert, target, logs, warnings, variant }) {
-		if (variant === 'hydrate') {
-			assert.deepEqual(warnings, [
-				'Hydration failed because the initial UI does not match what was rendered on the server'
-			]);
-		}
-
+	test({ assert, target, logs }) {
 		assert.deepEqual(logs, ['error caught']);
 		assert.htmlEqual(target.innerHTML, `<div>Error!</div><button>Retry</button>`);
 	}

From 2e49783afa5185dc8ccdfede9feee3fe15248294 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 14 Jul 2025 21:45:30 -0400
Subject: [PATCH 062/148] docs: fix code snippets (#16367)

---
 .../.generated/client-warnings.md             | 19 +++++++++++++++++++
 .../messages/client-warnings/warnings.md      | 19 +++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/documentation/docs/98-reference/.generated/client-warnings.md b/documentation/docs/98-reference/.generated/client-warnings.md
index 1c75faef53..7548428e97 100644
--- a/documentation/docs/98-reference/.generated/client-warnings.md
+++ b/documentation/docs/98-reference/.generated/client-warnings.md
@@ -43,6 +43,9 @@ Detected reactivity loss when reading `%name%`. This happens when state is read
 Svelte's signal-based reactivity works by tracking which bits of state are read when a template or `$derived(...)` expression executes. If an expression contains an `await`, Svelte transforms it such that any state _after_ the `await` is also tracked — in other words, in a case like this...
 
 ```js
+let a = Promise.resolve(1);
+let b = 2;
+// ---cut---
 let total = $derived(await a + b);
 ```
 
@@ -51,6 +54,9 @@ let total = $derived(await a + b);
 This does _not_ apply to an `await` that is not 'visible' inside the expression. In a case like this...
 
 ```js
+let a = Promise.resolve(1);
+let b = 2;
+// ---cut---
 async function sum() {
 	return await a + b;
 }
@@ -61,6 +67,13 @@ let total = $derived(await sum());
 ...`total` will depend on `a` (which is read immediately) but not `b` (which is not). The solution is to pass the values into the function:
 
 ```js
+let a = Promise.resolve(1);
+let b = 2;
+// ---cut---
+/**
+ * @param {Promise<number>} a
+ * @param {number} b
+ */
 async function sum(a, b) {
 	return await a + b;
 }
@@ -77,6 +90,9 @@ An async derived, `%name%` (%location%) was not read immediately after it resolv
 In a case like this...
 
 ```js
+async function one() { return 1 }
+async function two() { return 2 }
+// ---cut---
 let a = $derived(await one());
 let b = $derived(await two());
 ```
@@ -88,6 +104,9 @@ let b = $derived(await two());
 You can solve this by creating the promises first and _then_ awaiting them:
 
 ```js
+async function one() { return 1 }
+async function two() { return 2 }
+// ---cut---
 let aPromise = $derived(one());
 let bPromise = $derived(two());
 
diff --git a/packages/svelte/messages/client-warnings/warnings.md b/packages/svelte/messages/client-warnings/warnings.md
index 498c19a547..13d9bfcd3b 100644
--- a/packages/svelte/messages/client-warnings/warnings.md
+++ b/packages/svelte/messages/client-warnings/warnings.md
@@ -37,6 +37,9 @@ function add() {
 Svelte's signal-based reactivity works by tracking which bits of state are read when a template or `$derived(...)` expression executes. If an expression contains an `await`, Svelte transforms it such that any state _after_ the `await` is also tracked — in other words, in a case like this...
 
 ```js
+let a = Promise.resolve(1);
+let b = 2;
+// ---cut---
 let total = $derived(await a + b);
 ```
 
@@ -45,6 +48,9 @@ let total = $derived(await a + b);
 This does _not_ apply to an `await` that is not 'visible' inside the expression. In a case like this...
 
 ```js
+let a = Promise.resolve(1);
+let b = 2;
+// ---cut---
 async function sum() {
 	return await a + b;
 }
@@ -55,6 +61,13 @@ let total = $derived(await sum());
 ...`total` will depend on `a` (which is read immediately) but not `b` (which is not). The solution is to pass the values into the function:
 
 ```js
+let a = Promise.resolve(1);
+let b = 2;
+// ---cut---
+/**
+ * @param {Promise<number>} a
+ * @param {number} b
+ */
 async function sum(a, b) {
 	return await a + b;
 }
@@ -69,6 +82,9 @@ let total = $derived(await sum(a, b));
 In a case like this...
 
 ```js
+async function one() { return 1 }
+async function two() { return 2 }
+// ---cut---
 let a = $derived(await one());
 let b = $derived(await two());
 ```
@@ -80,6 +96,9 @@ let b = $derived(await two());
 You can solve this by creating the promises first and _then_ awaiting them:
 
 ```js
+async function one() { return 1 }
+async function two() { return 2 }
+// ---cut---
 let aPromise = $derived(one());
 let bPromise = $derived(two());
 

From 79904b711329db9ad1927df2d5bde7eeb2909815 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 14 Jul 2025 22:08:08 -0400
Subject: [PATCH 063/148] docs: tweak (#16369)

---
 documentation/docs/02-runes/02-$state.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/documentation/docs/02-runes/02-$state.md b/documentation/docs/02-runes/02-$state.md
index 7c4571e575..8d3510e50c 100644
--- a/documentation/docs/02-runes/02-$state.md
+++ b/documentation/docs/02-runes/02-$state.md
@@ -50,7 +50,7 @@ todos.push({
 });
 ```
 
-> [!NOTE] When you update properties of proxies, the original object is _not_ mutated. If you desire to use your own proxy handlers in a state proxy, [you should wrap the object _after_ wrapping it in `$state`](https://svelte.dev/playground/hello-world?version=latest#H4sIAAAAAAAACpWR3WoDIRCFX2UqhWyIJL3erAulL9C7XnQLMe5ksbUqOpsfln33YuyGFNJC8UKdc2bOhw7Myk9kJXsJ0nttO9jcR5KEG9AWJDwHdzwxznbaYGTl68Do5JM_FRifuh-9X8Y9Gkq1rYx4q66cJbQUWcmqqIL2VDe2IYMEbvuOikBADi-GJDSkXG-phId0G-frye2DO2psQYDFQ0Ys8gQO350dUkEydEg82T0GOs0nsSG9g2IqgxACZueo2ZUlpdvoDC6N64qsg1QKY8T2bpZp8gpIfbCQ85Zn50Ud82HkeY83uDjspenxv3jXcSDyjPWf9L1vJf0GH666J-jLu1ery4dV257IWXBWGa0-xFDMQdTTn2ScxWKsn86ROsLwQxqrVR5QM84Ij8TKFD2-cUZSm4O2LSt30kQcvwCgCmfZnAIAAA==).
+> [!NOTE] When you update properties of proxies, the original object is _not_ mutated. If you need to use your own proxy handlers in a state proxy, [you should wrap the object _after_ wrapping it in `$state`](https://svelte.dev/playground/hello-world?version=latest#H4sIAAAAAAAACpWR3WoDIRCFX2UqhWyIJL3erAulL9C7XnQLMe5ksbUqOpsfln33YuyGFNJC8UKdc2bOhw7Myk9kJXsJ0nttO9jcR5KEG9AWJDwHdzwxznbaYGTl68Do5JM_FRifuh-9X8Y9Gkq1rYx4q66cJbQUWcmqqIL2VDe2IYMEbvuOikBADi-GJDSkXG-phId0G-frye2DO2psQYDFQ0Ys8gQO350dUkEydEg82T0GOs0nsSG9g2IqgxACZueo2ZUlpdvoDC6N64qsg1QKY8T2bpZp8gpIfbCQ85Zn50Ud82HkeY83uDjspenxv3jXcSDyjPWf9L1vJf0GH666J-jLu1ery4dV257IWXBWGa0-xFDMQdTTn2ScxWKsn86ROsLwQxqrVR5QM84Ij8TKFD2-cUZSm4O2LSt30kQcvwCgCmfZnAIAAA==).
 
 Note that if you destructure a reactive value, the references are not reactive — as in normal JavaScript, they are evaluated at the point of destructuring:
 

From 1e4547b005d875aa1da0fa4f2f367a949700d93e Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 14 Jul 2025 22:24:39 -0400
Subject: [PATCH 064/148] chore: add `@since` tags for `settled` and
 `experimental.async` (#16371)

* chore: add `@since` tag for `settled`

* same for compiler options

* regenerate
---
 packages/svelte/src/compiler/types/index.d.ts | 10 ++++++--
 .../svelte/src/internal/client/runtime.js     |  1 +
 packages/svelte/types/index.d.ts              | 23 +++++++++++++++----
 3 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/packages/svelte/src/compiler/types/index.d.ts b/packages/svelte/src/compiler/types/index.d.ts
index c4f41b724a..6211e69bd3 100644
--- a/packages/svelte/src/compiler/types/index.d.ts
+++ b/packages/svelte/src/compiler/types/index.d.ts
@@ -224,9 +224,15 @@ export interface ModuleCompileOptions {
 	 * Use this to filter out warnings. Return `true` to keep the warning, `false` to discard it.
 	 */
 	warningFilter?: (warning: Warning) => boolean;
-	/** Experimental options */
+	/**
+	 * Experimental options
+	 * @since 5.36
+	 */
 	experimental?: {
-		/** Allow `await` keyword in deriveds, template expressions, and the top level of components */
+		/**
+		 * Allow `await` keyword in deriveds, template expressions, and the top level of components
+		 * @since 5.36
+		 */
 		async?: boolean;
 	};
 }
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index b5f6822207..9fdb87239b 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -526,6 +526,7 @@ export async function tick() {
  * Returns a promise that resolves once any state changes, and asynchronous work resulting from them,
  * have resolved and the DOM has been updated
  * @returns {Promise<void>}
+ * @since 5.36
  */
 export function settled() {
 	return Batch.ensure().settled();
diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index 72eb871db6..60795e6681 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -528,7 +528,8 @@ declare module 'svelte' {
 	/**
 	 * Returns a promise that resolves once any state changes, and asynchronous work resulting from them,
 	 * have resolved and the DOM has been updated
-	 * */
+	 * @since 5.36
+	 */
 	export function settled(): Promise<void>;
 	/**
 	 * When used inside a [`$derived`](https://svelte.dev/docs/svelte/$derived) or [`$effect`](https://svelte.dev/docs/svelte/$effect),
@@ -1116,9 +1117,15 @@ declare module 'svelte/compiler' {
 		 * Use this to filter out warnings. Return `true` to keep the warning, `false` to discard it.
 		 */
 		warningFilter?: (warning: Warning) => boolean;
-		/** Experimental options */
+		/**
+		 * Experimental options
+		 * @since 5.36
+		 */
 		experimental?: {
-			/** Allow `await` keyword in deriveds, template expressions, and the top level of components */
+			/**
+			 * Allow `await` keyword in deriveds, template expressions, and the top level of components
+			 * @since 5.36
+			 */
 			async?: boolean;
 		};
 	}
@@ -3031,9 +3038,15 @@ declare module 'svelte/types/compiler/interfaces' {
 		 * Use this to filter out warnings. Return `true` to keep the warning, `false` to discard it.
 		 */
 		warningFilter?: (warning: Warning_1) => boolean;
-		/** Experimental options */
+		/**
+		 * Experimental options
+		 * @since 5.36
+		 */
 		experimental?: {
-			/** Allow `await` keyword in deriveds, template expressions, and the top level of components */
+			/**
+			 * Allow `await` keyword in deriveds, template expressions, and the top level of components
+			 * @since 5.36
+			 */
 			async?: boolean;
 		};
 	}

From 9134caca242f29170125e1c9fcb71bd8e2473ae1 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 15 Jul 2025 11:55:30 -0400
Subject: [PATCH 065/148] fix: only skip updating bound `<input>` if the input
 was the source of the change (#16373)

* fix: only skip updating bound `<input>` if the input was the source of the change

* import Batch as type, not value
---
 .changeset/healthy-garlics-do.md              |  5 +++
 .../client/dom/elements/bindings/input.js     | 14 ++++++-
 .../binding-update-while-focused/_config.js   | 40 +++++++++++++++++++
 .../binding-update-while-focused/main.svelte  | 16 ++++++++
 4 files changed, 74 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/healthy-garlics-do.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/binding-update-while-focused/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/binding-update-while-focused/main.svelte

diff --git a/.changeset/healthy-garlics-do.md b/.changeset/healthy-garlics-do.md
new file mode 100644
index 0000000000..c27ace34de
--- /dev/null
+++ b/.changeset/healthy-garlics-do.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: only skip updating bound `<input>` if the input was the source of the change
diff --git a/packages/svelte/src/internal/client/dom/elements/bindings/input.js b/packages/svelte/src/internal/client/dom/elements/bindings/input.js
index 569d1179e6..7c1fccea0f 100644
--- a/packages/svelte/src/internal/client/dom/elements/bindings/input.js
+++ b/packages/svelte/src/internal/client/dom/elements/bindings/input.js
@@ -1,3 +1,4 @@
+/** @import { Batch } from '../../../reactivity/batch.js' */
 import { DEV } from 'esm-env';
 import { render_effect, teardown } from '../../../reactivity/effects.js';
 import { listen_to_event_and_reset_event } from './shared.js';
@@ -7,6 +8,7 @@ import { queue_micro_task } from '../../task.js';
 import { hydrating } from '../../hydration.js';
 import { untrack } from '../../../runtime.js';
 import { is_runes } from '../../../context.js';
+import { current_batch } from '../../../reactivity/batch.js';
 
 /**
  * @param {HTMLInputElement} input
@@ -17,6 +19,8 @@ import { is_runes } from '../../../context.js';
 export function bind_value(input, get, set = get) {
 	var runes = is_runes();
 
+	var batches = new WeakSet();
+
 	listen_to_event_and_reset_event(input, 'input', (is_reset) => {
 		if (DEV && input.type === 'checkbox') {
 			// TODO should this happen in prod too?
@@ -28,6 +32,10 @@ export function bind_value(input, get, set = get) {
 		value = is_numberlike_input(input) ? to_number(value) : value;
 		set(value);
 
+		if (current_batch !== null) {
+			batches.add(current_batch);
+		}
+
 		// In runes mode, respect any validation in accessors (doesn't apply in legacy mode,
 		// because we use mutable state which ensures the render effect always runs)
 		if (runes && value !== (value = get())) {
@@ -54,6 +62,10 @@ export function bind_value(input, get, set = get) {
 		(untrack(get) == null && input.value)
 	) {
 		set(is_numberlike_input(input) ? to_number(input.value) : input.value);
+
+		if (current_batch !== null) {
+			batches.add(current_batch);
+		}
 	}
 
 	render_effect(() => {
@@ -64,7 +76,7 @@ export function bind_value(input, get, set = get) {
 
 		var value = get();
 
-		if (input === document.activeElement) {
+		if (input === document.activeElement && batches.has(/** @type {Batch} */ (current_batch))) {
 			// Never rewrite the contents of a focused input. We can get here if, for example,
 			// an update is deferred because of async work depending on the input:
 			//
diff --git a/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused/_config.js b/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused/_config.js
new file mode 100644
index 0000000000..1d2e6dd470
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused/_config.js
@@ -0,0 +1,40 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client', 'hydrate'],
+
+	async test({ assert, target }) {
+		const [input] = target.querySelectorAll('input');
+
+		flushSync(() => {
+			input.focus();
+			input.dispatchEvent(new KeyboardEvent('keydown', { key: 'ArrowUp', bubbles: true }));
+		});
+		assert.equal(input.value, '2');
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<label>
+					<input /> arrow up/down
+				</label>
+				<p>value = 2</p>
+			`
+		);
+
+		flushSync(() => {
+			input.focus();
+			input.dispatchEvent(new KeyboardEvent('keydown', { key: 'ArrowDown', bubbles: true }));
+		});
+		assert.equal(input.value, '1');
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<label>
+					<input /> arrow up/down
+				</label>
+				<p>value = 1</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused/main.svelte b/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused/main.svelte
new file mode 100644
index 0000000000..4cc174e404
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused/main.svelte
@@ -0,0 +1,16 @@
+<script>
+	let value = $state('1');
+
+	function onkeydown (e) {
+		let _v = parseFloat(value);
+		if (e.key === 'ArrowUp') _v += 1;
+		else if (e.key === 'ArrowDown') _v -= 1;
+		value = _v.toString();
+	}
+</script>
+
+<label>
+	<input bind:value {onkeydown} /> arrow up/down
+</label>
+
+<p>value = {value}</p>

From b23f1e0a43a06263e52b07296de57a12e53da750 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Tue, 15 Jul 2025 11:57:52 -0400
Subject: [PATCH 066/148] Version Packages (#16374)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/healthy-garlics-do.md | 5 -----
 packages/svelte/CHANGELOG.md     | 6 ++++++
 packages/svelte/package.json     | 2 +-
 packages/svelte/src/version.js   | 2 +-
 4 files changed, 8 insertions(+), 7 deletions(-)
 delete mode 100644 .changeset/healthy-garlics-do.md

diff --git a/.changeset/healthy-garlics-do.md b/.changeset/healthy-garlics-do.md
deleted file mode 100644
index c27ace34de..0000000000
--- a/.changeset/healthy-garlics-do.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: only skip updating bound `<input>` if the input was the source of the change
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index dfa3376e25..d9f1a2629c 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,11 @@
 # svelte
 
+## 5.36.1
+
+### Patch Changes
+
+- fix: only skip updating bound `<input>` if the input was the source of the change ([#16373](https://github.com/sveltejs/svelte/pull/16373))
+
 ## 5.36.0
 
 ### Minor Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index a9fead571d..aa76abaae4 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.0",
+  "version": "5.36.1",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 248b1a3f11..f50b7d23cc 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.0';
+export const VERSION = '5.36.1';
 export const PUBLIC_VERSION = '5';

From 9f591223b1ee79fb7ec83567e22077bde912bfe7 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 15 Jul 2025 15:21:06 -0400
Subject: [PATCH 067/148] docs: async stuff (#16376)

* WIP async docs

* WIP

* docs

* update $effect namespace

* changeset

* oops

* typo

* fixes

* tweak

* missing link

* fix

* tweak

* Update documentation/docs/03-template-syntax/19-await-expressions.md

Co-authored-by: Conduitry <git@chor.date>

---------

Co-authored-by: Conduitry <git@chor.date>
---
 .changeset/long-drinks-reply.md               |   5 +
 documentation/docs/02-runes/02-$state.md      |   2 +-
 documentation/docs/02-runes/04-$effect.md     |  15 ++
 .../19-await-expressions.md                   | 144 ++++++++++++++++++
 .../05-special-elements/01-svelte-boundary.md |  32 +++-
 packages/svelte/src/ambient.d.ts              |   7 +
 packages/svelte/types/index.d.ts              |   7 +
 7 files changed, 206 insertions(+), 6 deletions(-)
 create mode 100644 .changeset/long-drinks-reply.md
 create mode 100644 documentation/docs/03-template-syntax/19-await-expressions.md

diff --git a/.changeset/long-drinks-reply.md b/.changeset/long-drinks-reply.md
new file mode 100644
index 0000000000..d46b22f493
--- /dev/null
+++ b/.changeset/long-drinks-reply.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: add `$effect.pending()` to types
diff --git a/documentation/docs/02-runes/02-$state.md b/documentation/docs/02-runes/02-$state.md
index 8d3510e50c..aea427a8ec 100644
--- a/documentation/docs/02-runes/02-$state.md
+++ b/documentation/docs/02-runes/02-$state.md
@@ -119,7 +119,7 @@ class Todo {
 }
 ```
 
-> Svelte provides reactive implementations of built-in classes like `Set` and `Map` that can be imported from [`svelte/reactivity`](svelte-reactivity).
+> [NOTE!] Svelte provides reactive implementations of built-in classes like `Set` and `Map` that can be imported from [`svelte/reactivity`](svelte-reactivity).
 
 ## `$state.raw`
 
diff --git a/documentation/docs/02-runes/04-$effect.md b/documentation/docs/02-runes/04-$effect.md
index 0e129973d5..5820e178a0 100644
--- a/documentation/docs/02-runes/04-$effect.md
+++ b/documentation/docs/02-runes/04-$effect.md
@@ -221,6 +221,21 @@ The `$effect.tracking` rune is an advanced feature that tells you whether or not
 
 It is used to implement abstractions like [`createSubscriber`](/docs/svelte/svelte-reactivity#createSubscriber), which will create listeners to update reactive values but _only_ if those values are being tracked (rather than, for example, read inside an event handler).
 
+## `$effect.pending`
+
+When using [`await`](await-expressions) in components, the `$effect.pending()` rune tells you how many promises are pending in the current [boundary](svelte-boundary), not including child boundaries ([demo](/playground/untitled#H4sIAAAAAAAAE3WRMU_DMBCF_8rJdHDUqilILGkaiY2RgY0yOPYZWbiOFV8IleX_jpMUEAIWS_7u-d27c2ROnJBV7B6t7WDsequAozKEqmAbpo3FwKqnyOjsJ90EMr-8uvN-G97Q0sRaEfAvLjtH6CjbsDrI3nhqju5IFgkEHGAVSBDy62L_SdtvejPTzEU4Owl6cJJM50AoxcUG2gLiVM31URgChyM89N3JBORcF3BoICA9mhN2A3G9gdvdrij2UJYgejLaSCMsKLTivNj0SEOf7WEN7ZwnHV1dfqd2dTsQ5QCdk9bI10PkcxexXqcmH3W51Jt_le2kbH8os9Y3UaTcNLYpDx-Xab6GTHXpZ128MhpWqDVK2np0yrgXXqQpaLa4APDLBkIF8bd2sYql0Sn_DeE7sYr6AdNzvgljR-MUq7SwAdMHeUtgHR4CAAA=)):
+
+```svelte
+<button onclick={() => a++}>a++</button>
+<button onclick={() => b++}>b++</button>
+
+<p>{a} + {b} = {await add(a, b)}</p>
+
+{#if $effect.pending()}
+	<p>pending promises: {$effect.pending()}</p>
+{/if}
+```
+
 ## `$effect.root`
 
 The `$effect.root` rune is an advanced feature that creates a non-tracked scope that doesn't auto-cleanup. This is useful for nested effects that you want to manually control. This rune also allows for the creation of effects outside of the component initialisation phase.
diff --git a/documentation/docs/03-template-syntax/19-await-expressions.md b/documentation/docs/03-template-syntax/19-await-expressions.md
new file mode 100644
index 0000000000..4e5ec28b26
--- /dev/null
+++ b/documentation/docs/03-template-syntax/19-await-expressions.md
@@ -0,0 +1,144 @@
+---
+title: await
+---
+
+As of Svelte 5.36, you can use the `await` keyword inside your components in three places where it was previously unavailable:
+
+- at the top level of your component's `<script>`
+- inside `$derived(...)` declarations
+- inside your markup
+
+This feature is currently experimental, and you must opt in by adding the `experimental.async` option wherever you [configure](/docs/kit/configuration) Svelte, usually `svelte.config.js`:
+
+```js
+/// file: svelte.config.js
+export default {
+	compilerOptions: {
+		experimental: {
+			async: true
+		}
+	}
+};
+```
+
+The experimental flag will be removed in Svelte 6.
+
+## Boundaries
+
+Currently, you can only use `await` inside a [`<svelte:boundary>`](svelte-boundary) with a `pending` snippet:
+
+```svelte
+<svelte:boundary>
+	<MyApp />
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
+```
+
+This restriction will be lifted once Svelte supports asynchronous server-side rendering (see [caveats](#Caveats)).
+
+> [!NOTE] In the [playground](/playground), your app is rendered inside a boundary with an empty pending snippet, so that you can use `await` without having to create one.
+
+## Synchronized updates
+
+When an `await` expression depends on a particular piece of state, changes to that state will not be reflected in the UI until the asynchronous work has completed, so that the UI is not left in an inconsistent state. In other words, in an example like [this](/playground/untitled#H4sIAAAAAAAAE42QsWrDQBBEf2VZUkhYRE4gjSwJ0qVMkS6XYk9awcFpJe5Wdoy4fw-ycdykSPt2dpiZFYVGxgrf2PsJTlPwPWTcO-U-xwIH5zli9bminudNtwEsbl-v8_wYj-x1Y5Yi_8W7SZRFI1ZYxy64WVsjRj0rEDTwEJWUs6f8cKP2Tp8vVIxSPEsHwyKdukmA-j6jAmwO63Y1SidyCsIneA_T6CJn2ZBD00Jk_XAjT4tmQwEv-32eH6AsgYK6wXWOPPTs6Xy1CaxLECDYgb3kSUbq8p5aaifzorCt0RiUZbQcDIJ10ldH8gs3K6X2Xzqbro5zu1KCHaw2QQPrtclvwVSXc2sEC1T-Vqw0LJy-ClRy_uSkx2ogHzn9ADZ1CubKAQAA)...
+
+```svelte
+<script>
+	let a = $state(1);
+	let b = $state(2);
+
+	async function add(a, b) {
+		await new Promise((f) => setTimeout(f, 500)); // artificial delay
+		return a + b;
+	}
+</script>
+
+<input type="number" bind:value={a}>
+<input type="number" bind:value={b}>
+
+<p>{a} + {b} = {await add(a, b)}</p>
+```
+
+...if you increment `a`, the contents of the `<p>` will _not_ immediately update to read this —
+
+```html
+<p>2 + 2 = 3</p>
+```
+
+— instead, the text will update to `2 + 2 = 4` when `add(a, b)` resolves.
+
+Updates can overlap — a fast update will be reflected in the UI while an earlier slow update is still ongoing.
+
+## Concurrency
+
+Svelte will do as much asynchronous work as it can in parallel. For example if you have two `await` expressions in your markup...
+
+```svelte
+<p>{await one()}</p>
+<p>{await two()}</p>
+```
+
+...both functions will run at the same time, as they are independent expressions, even though they are _visually_ sequential.
+
+This does not apply to sequential `await` expressions inside your `<script>` or inside async functions — these run like any other asynchronous JavaScript. An exception is that independent `$derived` expressions will update independently, even though they will run sequentially when they are first created:
+
+```js
+async function one() { return 1; }
+async function two() { return 2; }
+// ---cut---
+// these will run sequentially the first time,
+// but will update independently
+let a = $derived(await one());
+let b = $derived(await two());
+```
+
+> [!NOTE] If you write code like this, expect Svelte to give you an [`await_waterfall`](runtime-warnings#Client-warnings-await_waterfall) warning
+
+## Indicating loading states
+
+In addition to the nearest boundary's [`pending`](svelte-boundary#Properties-pending) snippet, you can indicate that asynchronous work is ongoing with [`$effect.pending()`]($effect#$effect.pending).
+
+You can also use [`settled()`](svelte#settled) to get a promise that resolves when the current update is complete:
+
+```js
+let color = 'red';
+let answer = -1;
+let updating = false;
+// ---cut---
+import { tick, settled } from 'svelte';
+
+async function onclick() {
+	updating = true;
+
+	// without this, the change to `updating` will be
+	// grouped with the other changes, meaning it
+	// won't be reflected in the UI
+	await tick();
+
+	color = 'octarine';
+	answer = 42;
+
+	await settled();
+
+	// any updates affected by `color` or `answer`
+	// have now been applied
+	updating = false;
+}
+```
+
+## Error handling
+
+Errors in `await` expressions will bubble to the nearest [error boundary](svelte-boundary).
+
+## Caveats
+
+As an experimental feature, the details of how `await` is handled (and related APIs like `$effect.pending()`) are subject to breaking changes outside of a semver major release, though we intend to keep such changes to a bare minimum.
+
+Currently, server-side rendering is synchronous. If a `<svelte:boundary>` with a `pending` snippet is encountered during SSR, only the `pending` snippet will be rendered.
+
+## Breaking changes
+
+Effects run in a slightly different order when the `experimental.async` option is `true`. Specifically, _block_ effects like `{#if ...}` and `{#each ...}` now run before an `$effect.pre` or `beforeUpdate` in the same component, which means that in [very rare situations](/playground/untitled?#H4sIAAAAAAAAE22R3VLDIBCFX2WLvUhnTHsf0zre-Q7WmfwtFV2BgU1rJ5N3F0jaOuoVcPbw7VkYhK4_URTiGYkMnIyjDjLsFGO3EvdCKkIvipdB8NlGXxSCPt96snbtj0gctab2-J_eGs2oOWBE6VunLO_2es-EDKZ5x5ZhC0vPNWM2gHXGouNzAex6hHH1cPHil_Lsb95YT9VQX6KUAbS2DrNsBdsdDFHe8_XSYjH1SrhELTe3MLpsemajweiWVPuxHSbKNd-8eQTdE0EBf4OOaSg2hwNhhE_ABB_ulJzjj9FULvIcqgm5vnAqUB7wWFMfhuugQWkcAr8hVD-mq8D12kOep24J_IszToOXdveGDsuNnZwbJUNlXsKnhJdhUcTo42s41YpOSneikDV5HL8BktM6yRcCAAA=) it is possible to update a block that should no longer exist, but only if you update state inside an effect, [which you should avoid]($effect#When-not-to-use-$effect).
diff --git a/documentation/docs/05-special-elements/01-svelte-boundary.md b/documentation/docs/05-special-elements/01-svelte-boundary.md
index f5439b4b83..3e91af5d83 100644
--- a/documentation/docs/05-special-elements/01-svelte-boundary.md
+++ b/documentation/docs/05-special-elements/01-svelte-boundary.md
@@ -9,19 +9,41 @@ title: <svelte:boundary>
 > [!NOTE]
 > This feature was added in 5.3.0
 
-Boundaries allow you to guard against errors in part of your app from breaking the app as a whole, and to recover from those errors.
+Boundaries allow you to 'wall off' parts of your app, so that you can:
 
-If an error occurs while rendering or updating the children of a `<svelte:boundary>`, or running any [`$effect`]($effect) functions contained therein, the contents will be removed.
+- provide UI that should be shown when [`await`](await-expressions) expressions are first resolving
+- handle errors that occur during rendering or while running effects, and provide UI that should be rendered when an error happens
 
-Errors occurring outside the rendering process (for example, in event handlers or after a `setTimeout` or async work) are _not_ caught by error boundaries.
+If a boundary handles an error (with a `failed` snippet or `onerror` handler, or both) its existing content will be removed.
+
+> [!NOTE] Errors occurring outside the rendering process (for example, in event handlers or after a `setTimeout` or async work) are _not_ caught by error boundaries.
 
 ## Properties
 
-For the boundary to do anything, one or both of `failed` and `onerror` must be provided.
+For the boundary to do anything, one or more of the following must be provided.
+
+### `pending`
+
+As of Svelte 5.36, boundaries with a `pending` snippet can contain [`await`](await-expressions) expressions. This snippet will be shown when the boundary is first created, and will remain visible until all the `await` expressions inside the boundary have resolved ([demo](/playground/untitled#H4sIAAAAAAAAE21QQW6DQAz8ytY9BKQVpFdKkPqDHnorPWzAaSwt3tWugUaIv1eE0KpKD5as8YxnNBOw6RAKKOOAVrA4up5bEy6VGknOyiO3xJ8qMnmPAhpOZDFC8T6BXPyiXADQ258X77P1FWg4moj_4Y1jQZZ49W0CealqruXUcyPkWLVozQXbZDC2R606spYiNo7bqA7qab_fp2paFLUElD6wYhzVa3AdRUySgNHZAVN1qDZaLRHljTp0vSTJ9XJjrSbpX5f0eZXN6zLXXOa_QfmurIVU-moyoyH5ib87o7XuYZfOZe6vnGWmx1uZW7lJOq9upa-sMwuUZdkmmfIbfQ1xZwwaBL8ECgk9zh8axJAdiVsoTsZGnL8Bg4tX_OMBAAA=)):
+
+```svelte
+<svelte:boundary>
+	<p>{await delayed('hello!')}</p>
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
+```
+
+The `pending` snippet will _not_ be shown for subsequent async updates — for these, you can use [`$effect.pending()`]($effect#$effect.pending).
+
+> [!NOTE] In the [playground](/playground), your app is rendered inside a boundary with an empty pending snippet, so that you can use `await` without having to create one.
+
 
 ### `failed`
 
-If a `failed` snippet is provided, it will be rendered with the error that was thrown, and a `reset` function that recreates the contents ([demo](/playground/hello-world#H4sIAAAAAAAAE3VRy26DMBD8lS2tFCIh6JkAUlWp39Cq9EBg06CAbdlLArL87zWGKk8ORnhmd3ZnrD1WtOjFXqKO2BDGW96xqpBD5gXerm5QefG39mgQY9EIWHxueRMinLosti0UPsJLzggZKTeilLWgLGc51a3gkuCjKQ7DO7cXZotgJ3kLqzC6hmex1SZnSXTWYHcrj8LJjWTk0PHoZ8VqIdCOKayPykcpuQxAokJaG1dGybYj4gw4K5u6PKTasSbjXKgnIDlA8VvUdo-pzonraBY2bsH7HAl78mKSHZpgIcuHjq9jXSpZSLixRlveKYQUXhQVhL6GPobXAAb7BbNeyvNUs4qfRg3OnELLj5hqH9eQZqCnoBwR9lYcQxuVXeBzc8kMF8yXY4yNJ5oGiUzP_aaf_waTRGJib5_Ad3P_vbCuaYxzeNpbU0eUMPAOKh7Yw1YErgtoXyuYlPLzc10_xo_5A91zkQL_AgAA)):
+If a `failed` snippet is provided, it will be rendered when an error is thrown inside the boundary, with the `error` and a `reset` function that recreates the contents ([demo](/playground/hello-world#H4sIAAAAAAAAE3VRy26DMBD8lS2tFCIh6JkAUlWp39Cq9EBg06CAbdlLArL87zWGKk8ORnhmd3ZnrD1WtOjFXqKO2BDGW96xqpBD5gXerm5QefG39mgQY9EIWHxueRMinLosti0UPsJLzggZKTeilLWgLGc51a3gkuCjKQ7DO7cXZotgJ3kLqzC6hmex1SZnSXTWYHcrj8LJjWTk0PHoZ8VqIdCOKayPykcpuQxAokJaG1dGybYj4gw4K5u6PKTasSbjXKgnIDlA8VvUdo-pzonraBY2bsH7HAl78mKSHZpgIcuHjq9jXSpZSLixRlveKYQUXhQVhL6GPobXAAb7BbNeyvNUs4qfRg3OnELLj5hqH9eQZqCnoBwR9lYcQxuVXeBzc8kMF8yXY4yNJ5oGiUzP_aaf_waTRGJib5_Ad3P_vbCuaYxzeNpbU0eUMPAOKh7Yw1YErgtoXyuYlPLzc10_xo_5A91zkQL_AgAA)):
 
 ```svelte
 <svelte:boundary>
diff --git a/packages/svelte/src/ambient.d.ts b/packages/svelte/src/ambient.d.ts
index a1484718cc..7c3b941ed1 100644
--- a/packages/svelte/src/ambient.d.ts
+++ b/packages/svelte/src/ambient.d.ts
@@ -255,6 +255,13 @@ declare namespace $effect {
 	 */
 	export function pre(fn: () => void | (() => void)): void;
 
+	/**
+	 * Returns the number of promises that are pending in the current boundary, not including child boundaries.
+	 *
+	 * https://svelte.dev/docs/svelte/$effect#$effect.pending
+	 */
+	export function pending(): number;
+
 	/**
 	 * The `$effect.tracking` rune is an advanced feature that tells you whether or not the code is running inside a tracking context, such as an effect or inside your template.
 	 *
diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index 60795e6681..d356762a3f 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -3325,6 +3325,13 @@ declare namespace $effect {
 	 */
 	export function pre(fn: () => void | (() => void)): void;
 
+	/**
+	 * Returns the number of promises that are pending in the current boundary, not including child boundaries.
+	 *
+	 * https://svelte.dev/docs/svelte/$effect#$effect.pending
+	 */
+	export function pending(): number;
+
 	/**
 	 * The `$effect.tracking` rune is an advanced feature that tells you whether or not the code is running inside a tracking context, such as an effect or inside your template.
 	 *

From 886d566b93f4360fb927236fa41d941a16417ab6 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 15 Jul 2025 16:51:27 -0400
Subject: [PATCH 068/148] add async wrapper to sandbox (#16378)

* add async wrapper to sandbox

* bump pps
---
 package.json                       |  2 +-
 playgrounds/sandbox/Wrapper.svelte |  9 +++++++++
 playgrounds/sandbox/index.html     |  2 +-
 pnpm-lock.yaml                     | 10 +++++-----
 4 files changed, 16 insertions(+), 7 deletions(-)
 create mode 100644 playgrounds/sandbox/Wrapper.svelte

diff --git a/package.json b/package.json
index 62581782d7..3e609db87f 100644
--- a/package.json
+++ b/package.json
@@ -36,7 +36,7 @@
     "jsdom": "25.0.1",
     "playwright": "^1.46.1",
     "prettier": "^3.2.4",
-    "prettier-plugin-svelte": "^3.1.2",
+    "prettier-plugin-svelte": "^3.4.0",
     "svelte": "workspace:^",
     "typescript": "^5.5.4",
     "typescript-eslint": "^8.24.0",
diff --git a/playgrounds/sandbox/Wrapper.svelte b/playgrounds/sandbox/Wrapper.svelte
new file mode 100644
index 0000000000..1fe82c1716
--- /dev/null
+++ b/playgrounds/sandbox/Wrapper.svelte
@@ -0,0 +1,9 @@
+<script>
+	import App from './src/App.svelte';
+</script>
+
+<svelte:boundary>
+	<App />
+
+	{#snippet pending()}{/snippet}
+</svelte:boundary>
diff --git a/playgrounds/sandbox/index.html b/playgrounds/sandbox/index.html
index d70409ffb6..639409b877 100644
--- a/playgrounds/sandbox/index.html
+++ b/playgrounds/sandbox/index.html
@@ -12,7 +12,7 @@
 
 		<script type="module">
 			import { mount, hydrate, unmount } from 'svelte';
-			import App from '/src/App.svelte';
+			import App from '/Wrapper.svelte';
 
 			globalThis.delayed = (v, ms = 1000) => {
 				return new Promise((f) => {
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 87fb2b2667..d0982dc791 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -39,8 +39,8 @@ importers:
         specifier: ^3.2.4
         version: 3.2.4
       prettier-plugin-svelte:
-        specifier: ^3.1.2
-        version: 3.1.2(prettier@3.2.4)(svelte@packages+svelte)
+        specifier: ^3.4.0
+        version: 3.4.0(prettier@3.2.4)(svelte@packages+svelte)
       svelte:
         specifier: workspace:^
         version: link:packages/svelte
@@ -1906,8 +1906,8 @@ packages:
     resolution: {integrity: sha512-vkcDPrRZo1QZLbn5RLGPpg/WmIQ65qoWWhcGKf/b5eplkkarX0m9z8ppCat4mlOqUsWpyNuYgO3VRyrYHSzX5g==}
     engines: {node: '>= 0.8.0'}
 
-  prettier-plugin-svelte@3.1.2:
-    resolution: {integrity: sha512-7xfMZtwgAWHMT0iZc8jN4o65zgbAQ3+O32V6W7pXrqNvKnHnkoyQCGCbKeUyXKZLbYE0YhFRnamfxfkEGxm8qA==}
+  prettier-plugin-svelte@3.4.0:
+    resolution: {integrity: sha512-pn1ra/0mPObzqoIQn/vUTR3ZZI6UuZ0sHqMK5x2jMLGrs53h0sXhkVuDcrlssHwIMk7FYrMjHBPoUSyyEEDlBQ==}
     peerDependencies:
       prettier: ^3.0.0
       svelte: ^3.2.0 || ^4.0.0-next.0 || ^5.0.0-next.0
@@ -4226,7 +4226,7 @@ snapshots:
 
   prelude-ls@1.2.1: {}
 
-  prettier-plugin-svelte@3.1.2(prettier@3.2.4)(svelte@packages+svelte):
+  prettier-plugin-svelte@3.4.0(prettier@3.2.4)(svelte@packages+svelte):
     dependencies:
       prettier: 3.2.4
       svelte: link:packages/svelte

From eb23028d8f8b188ca8a963b27d05815977acd2af Mon Sep 17 00:00:00 2001
From: jjones315 <39281771+jjones315@users.noreply.github.com>
Date: Tue, 15 Jul 2025 16:49:06 -0500
Subject: [PATCH 069/148] fix: add pending snippet to  <svelte:boundary> types
 (#16379)

* add pending snippet to  <svelte:boundary> types

* Update .changeset/many-bats-juggle.md

---------

Co-authored-by: jayce jones <jayce.jones@trinityonline.com>
Co-authored-by: Rich Harris <hello@rich-harris.dev>
---
 .changeset/many-bats-juggle.md | 5 +++++
 packages/svelte/elements.d.ts  | 1 +
 2 files changed, 6 insertions(+)
 create mode 100644 .changeset/many-bats-juggle.md

diff --git a/.changeset/many-bats-juggle.md b/.changeset/many-bats-juggle.md
new file mode 100644
index 0000000000..e914c49087
--- /dev/null
+++ b/.changeset/many-bats-juggle.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: add `pending` snippet to `<svelte:boundary>` types
diff --git a/packages/svelte/elements.d.ts b/packages/svelte/elements.d.ts
index fe4078f56a..1492f77792 100644
--- a/packages/svelte/elements.d.ts
+++ b/packages/svelte/elements.d.ts
@@ -2080,6 +2080,7 @@ export interface SvelteHTMLElements {
 	'svelte:boundary': {
 		onerror?: (error: unknown, reset: () => void) => void;
 		failed?: import('svelte').Snippet<[error: unknown, reset: () => void]>;
+		pending?: import('svelte').Snippet;
 	};
 
 	[name: string]: { [name: string]: any };

From 3fa3dd78a1cbaa88a1571977b76bf6f02ed4231d Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Tue, 15 Jul 2025 17:55:37 -0400
Subject: [PATCH 070/148] Version Packages (#16377)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/long-drinks-reply.md | 5 -----
 .changeset/many-bats-juggle.md  | 5 -----
 packages/svelte/CHANGELOG.md    | 8 ++++++++
 packages/svelte/package.json    | 2 +-
 packages/svelte/src/version.js  | 2 +-
 5 files changed, 10 insertions(+), 12 deletions(-)
 delete mode 100644 .changeset/long-drinks-reply.md
 delete mode 100644 .changeset/many-bats-juggle.md

diff --git a/.changeset/long-drinks-reply.md b/.changeset/long-drinks-reply.md
deleted file mode 100644
index d46b22f493..0000000000
--- a/.changeset/long-drinks-reply.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: add `$effect.pending()` to types
diff --git a/.changeset/many-bats-juggle.md b/.changeset/many-bats-juggle.md
deleted file mode 100644
index e914c49087..0000000000
--- a/.changeset/many-bats-juggle.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: add `pending` snippet to `<svelte:boundary>` types
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index d9f1a2629c..8c0b21364d 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,13 @@
 # svelte
 
+## 5.36.2
+
+### Patch Changes
+
+- fix: add `$effect.pending()` to types ([#16376](https://github.com/sveltejs/svelte/pull/16376))
+
+- fix: add `pending` snippet to `<svelte:boundary>` types ([#16379](https://github.com/sveltejs/svelte/pull/16379))
+
 ## 5.36.1
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index aa76abaae4..6e000e2bbf 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.1",
+  "version": "5.36.2",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index f50b7d23cc..9ccd2ff0ce 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.1';
+export const VERSION = '5.36.2';
 export const PUBLIC_VERSION = '5';

From e01bd97befd8181b0c1050b156062abc5b98eeaa Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 15 Jul 2025 19:58:39 -0400
Subject: [PATCH 071/148] fix: update `$effect.pending()` immediately after a
 batch is removed (#16382)

* WIP sync effect pending updates

* fix

* changeset

* fix

* add test

* inline

* unused
---
 .changeset/popular-tips-lie.md                |  5 ++
 .../internal/client/dom/blocks/boundary.js    | 14 ++--
 .../src/internal/client/reactivity/batch.js   | 17 +++-
 .../samples/async-effect-pending/_config.js   | 81 +++++++++++++++++++
 .../samples/async-effect-pending/main.svelte  | 32 ++++++++
 5 files changed, 142 insertions(+), 7 deletions(-)
 create mode 100644 .changeset/popular-tips-lie.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-effect-pending/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-effect-pending/main.svelte

diff --git a/.changeset/popular-tips-lie.md b/.changeset/popular-tips-lie.md
new file mode 100644
index 0000000000..45bd3e23f3
--- /dev/null
+++ b/.changeset/popular-tips-lie.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: update `$effect.pending()` immediately after a batch is removed
diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 5ed0515210..5e678ab113 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -22,7 +22,7 @@ import { get_next_sibling } from '../operations.js';
 import { queue_micro_task } from '../task.js';
 import * as e from '../../errors.js';
 import { DEV } from 'esm-env';
-import { Batch } from '../../reactivity/batch.js';
+import { Batch, effect_pending_updates } from '../../reactivity/batch.js';
 import { internal_set, source } from '../../reactivity/sources.js';
 import { tag } from '../../dev/tracing.js';
 import { createSubscriber } from '../../../../reactivity/create-subscriber.js';
@@ -92,6 +92,12 @@ export class Boundary {
 	 */
 	#effect_pending = null;
 
+	#effect_pending_update = () => {
+		if (this.#effect_pending) {
+			internal_set(this.#effect_pending, this.#pending_count);
+		}
+	};
+
 	#effect_pending_subscriber = createSubscriber(() => {
 		this.#effect_pending = source(this.#pending_count);
 
@@ -238,11 +244,7 @@ export class Boundary {
 			this.parent.#update_pending_count(d);
 		}
 
-		queueMicrotask(() => {
-			if (this.#effect_pending) {
-				internal_set(this.#effect_pending, this.#pending_count);
-			}
-		});
+		effect_pending_updates.add(this.#effect_pending_update);
 	}
 
 	get_effect_pending() {
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index 1126946ce9..f881330e90 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -49,6 +49,9 @@ export let batch_deriveds = null;
 /** @type {Effect[]} Stack of effects, dev only */
 export let dev_effect_stack = [];
 
+/** @type {Set<() => void>} */
+export let effect_pending_updates = new Set();
+
 /** @type {Effect[]} */
 let queued_root_effects = [];
 
@@ -296,6 +299,16 @@ export class Batch {
 
 	deactivate() {
 		current_batch = null;
+
+		for (const update of effect_pending_updates) {
+			effect_pending_updates.delete(update);
+			update();
+
+			if (current_batch !== null) {
+				// only do one at a time
+				break;
+			}
+		}
 	}
 
 	neuter() {
@@ -319,7 +332,7 @@ export class Batch {
 			batches.delete(this);
 		}
 
-		current_batch = null;
+		this.deactivate();
 	}
 
 	flush_effects() {
@@ -389,6 +402,8 @@ export class Batch {
 			this.#effects = [];
 
 			this.flush();
+		} else {
+			this.deactivate();
 		}
 	}
 
diff --git a/packages/svelte/tests/runtime-runes/samples/async-effect-pending/_config.js b/packages/svelte/tests/runtime-runes/samples/async-effect-pending/_config.js
new file mode 100644
index 0000000000..9df3620798
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-effect-pending/_config.js
@@ -0,0 +1,81 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const [increment, shift] = target.querySelectorAll('button');
+
+		shift.click();
+		shift.click();
+		shift.click();
+
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<button>shift</button>
+				<p>0</p>
+				<p>0</p>
+				<p>0</p>
+				<p>pending: 0</p>
+			`
+		);
+
+		increment.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<button>shift</button>
+				<p>0</p>
+				<p>0</p>
+				<p>0</p>
+				<p>pending: 3</p>
+			`
+		);
+
+		shift.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<button>shift</button>
+				<p>0</p>
+				<p>0</p>
+				<p>0</p>
+				<p>pending: 2</p>
+			`
+		);
+
+		shift.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<button>shift</button>
+				<p>0</p>
+				<p>0</p>
+				<p>0</p>
+				<p>pending: 1</p>
+			`
+		);
+
+		shift.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<button>shift</button>
+				<p>1</p>
+				<p>1</p>
+				<p>1</p>
+				<p>pending: 0</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-effect-pending/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-effect-pending/main.svelte
new file mode 100644
index 0000000000..89cead2cc6
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-effect-pending/main.svelte
@@ -0,0 +1,32 @@
+<script>
+	let value = $state(0);
+	let deferreds = [];
+
+	function push(value) {
+		const deferred = Promise.withResolvers();
+		deferreds.push({ value, deferred });
+		return deferred.promise;
+	}
+
+	function shift() {
+		const d = deferreds.shift();
+		d?.deferred.resolve(d.value);
+	}
+</script>
+
+<button onclick={() => value++}>increment</button>
+<button onclick={() => shift()}>shift</button>
+
+<svelte:boundary>
+	<p>{await push(value)}</p>
+	<p>{await push(value)}</p>
+	<p>{await push(value)}</p>
+
+	<p>pending: {$effect.pending()}</p>
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
+
+

From 8e73fd4b0343cae992429b7e75812acf0ec6cb6c Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Wed, 16 Jul 2025 05:14:19 -0700
Subject: [PATCH 072/148] fix: don't log `await_reactivity_loss` warning when
 signal is read in `untrack` (#16385)

* fix: don't log `await_reactivity_loss` warning when signal is read in `untrack`

* add test

* fix
---
 .changeset/big-readers-lie.md                         |  5 +++++
 packages/svelte/src/internal/client/runtime.js        |  2 +-
 .../samples/async-reactivity-loss/_config.js          |  7 +++++--
 .../samples/async-reactivity-loss/main.svelte         | 11 +++++++----
 4 files changed, 18 insertions(+), 7 deletions(-)
 create mode 100644 .changeset/big-readers-lie.md

diff --git a/.changeset/big-readers-lie.md b/.changeset/big-readers-lie.md
new file mode 100644
index 0000000000..9f5dd166c1
--- /dev/null
+++ b/.changeset/big-readers-lie.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: don't log `await_reactivity_loss` warning when signal is read in `untrack`
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 9fdb87239b..6c4d92bbad 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -609,7 +609,7 @@ export function get(signal) {
 			var tracking = (current_async_effect.f & REACTION_IS_UPDATING) !== 0;
 			var was_read = current_async_effect.deps?.includes(signal);
 
-			if (!tracking && !was_read) {
+			if (!tracking && !untracking && !was_read) {
 				w.await_reactivity_loss(/** @type {string} */ (signal.label));
 
 				var trace = get_stack('TracedAt');
diff --git a/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss/_config.js b/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss/_config.js
index f8a7cfd479..16318a3b44 100644
--- a/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss/_config.js
@@ -6,11 +6,14 @@ export default test({
 		dev: true
 	},
 
-	html: `<button>a</button><button>b</button><p>pending</p>`,
+	html: `<button>a</button><button>b</button><button>c</button><p>pending</p>`,
 
 	async test({ assert, target, warnings }) {
 		await tick();
-		assert.htmlEqual(target.innerHTML, '<button>a</button><button>b</button><h1>3</h1><p>3</p>');
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>a</button><button>b</button><button>c</button><h1>6</h1><p>6</p>'
+		);
 
 		assert.equal(
 			warnings[0],
diff --git a/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss/main.svelte
index bdb1b095c9..03596ce051 100644
--- a/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss/main.svelte
@@ -1,18 +1,21 @@
 <script>
+	import { untrack } from 'svelte';
 	let a = $state(1);
 	let b = $state(2);
+	let c = $state(3);
 
-	async function a_plus_b() {
-		return await a + await b;
+	async function a_plus_b_plus_c() {
+		return await a + await b + await untrack(() => c);
 	}
 </script>
 
 <button onclick={() => a++}>a</button>
 <button onclick={() => b++}>b</button>
+<button onclick={() => c++}>c</button>
 
 <svelte:boundary>
-	<h1>{await a_plus_b()}</h1>
-	<p>{await a + await b}</p>
+	<h1>{await a_plus_b_plus_c()}</h1>
+	<p>{await a + await b + await c}</p>
 
 	{#snippet pending()}
 		<p>pending</p>

From 6cf3a193428f08a1c15b403dad681627425c0f1d Mon Sep 17 00:00:00 2001
From: 7nik <kifiranet@gmail.com>
Date: Wed, 16 Jul 2025 16:55:15 +0300
Subject: [PATCH 073/148] fix: better handle $inspect on array mutations
 (#16389)

* fix: better handle $inspect on array mutations

* increase stack trace limit, revert test change

* second changeset

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
---
 .changeset/curvy-houses-jog.md                |  5 ++
 .changeset/metal-coats-thank.md               |  5 ++
 packages/svelte/src/internal/client/proxy.js  | 60 +++++++++++++++----
 .../src/internal/client/reactivity/sources.js | 40 ++++++++-----
 .../samples/array-delete-item/_config.js      | 13 ++++
 .../samples/array-delete-item/main.svelte     |  8 +++
 .../samples/inspect-deep-array/_config.js     | 13 +---
 packages/svelte/tests/suite.ts                |  3 +
 8 files changed, 110 insertions(+), 37 deletions(-)
 create mode 100644 .changeset/curvy-houses-jog.md
 create mode 100644 .changeset/metal-coats-thank.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/array-delete-item/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/array-delete-item/main.svelte

diff --git a/.changeset/curvy-houses-jog.md b/.changeset/curvy-houses-jog.md
new file mode 100644
index 0000000000..0a2323d8e4
--- /dev/null
+++ b/.changeset/curvy-houses-jog.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: better handle $inspect on array mutations
diff --git a/.changeset/metal-coats-thank.md b/.changeset/metal-coats-thank.md
new file mode 100644
index 0000000000..b307fd3d45
--- /dev/null
+++ b/.changeset/metal-coats-thank.md
@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: leave proxied array `length` untouched when deleting properties
diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index 5da1b7e188..3ae4b87ed5 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -15,7 +15,13 @@ import {
 	is_array,
 	object_prototype
 } from '../shared/utils.js';
-import { state as source, set, increment } from './reactivity/sources.js';
+import {
+	state as source,
+	set,
+	increment,
+	flush_inspect_effects,
+	set_inspect_effects_deferred
+} from './reactivity/sources.js';
 import { PROXY_PATH_SYMBOL, STATE_SYMBOL } from '#client/constants';
 import { UNINITIALIZED } from '../../constants.js';
 import * as e from './errors.js';
@@ -80,6 +86,9 @@ export function proxy(value) {
 		// We need to create the length source eagerly to ensure that
 		// mutations to the array are properly synced with our proxy
 		sources.set('length', source(/** @type {any[]} */ (value).length, stack));
+		if (DEV) {
+			value = /** @type {any} */ (inspectable_array(/** @type {any[]} */ (value)));
+		}
 	}
 
 	/** Used in dev for $inspect.trace() */
@@ -142,16 +151,6 @@ export function proxy(value) {
 					}
 				}
 			} else {
-				// When working with arrays, we need to also ensure we update the length when removing
-				// an indexed property
-				if (is_proxied_array && typeof prop === 'string') {
-					var ls = /** @type {Source<number>} */ (sources.get('length'));
-					var n = Number(prop);
-
-					if (Number.isInteger(n) && n < ls.v) {
-						set(ls, n);
-					}
-				}
 				set(s, UNINITIALIZED);
 				increment(version);
 			}
@@ -388,3 +387,42 @@ export function get_proxied_value(value) {
 export function is(a, b) {
 	return Object.is(get_proxied_value(a), get_proxied_value(b));
 }
+
+const ARRAY_MUTATING_METHODS = new Set([
+	'copyWithin',
+	'fill',
+	'pop',
+	'push',
+	'reverse',
+	'shift',
+	'sort',
+	'splice',
+	'unshift'
+]);
+
+/**
+ * Wrap array mutating methods so $inspect is triggered only once and
+ * to prevent logging an array in intermediate state (e.g. with an empty slot)
+ * @param {any[]} array
+ */
+function inspectable_array(array) {
+	return new Proxy(array, {
+		get(target, prop, receiver) {
+			var value = Reflect.get(target, prop, receiver);
+			if (!ARRAY_MUTATING_METHODS.has(/** @type {string} */ (prop))) {
+				return value;
+			}
+
+			/**
+			 * @this {any[]}
+			 * @param {any[]} args
+			 */
+			return function (...args) {
+				set_inspect_effects_deferred();
+				var result = value.apply(this, args);
+				flush_inspect_effects();
+				return result;
+			};
+		}
+	});
+}
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index 29c657bdd0..bd55b9d935 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -49,6 +49,12 @@ export function set_inspect_effects(v) {
 	inspect_effects = v;
 }
 
+let inspect_effects_deferred = false;
+
+export function set_inspect_effects_deferred() {
+	inspect_effects_deferred = true;
+}
+
 /**
  * @template V
  * @param {V} v
@@ -213,26 +219,32 @@ export function internal_set(source, value) {
 			}
 		}
 
-		if (DEV && inspect_effects.size > 0) {
-			const inspects = Array.from(inspect_effects);
+		if (DEV && inspect_effects.size > 0 && !inspect_effects_deferred) {
+			flush_inspect_effects();
+		}
+	}
+
+	return value;
+}
 
-			for (const effect of inspects) {
-				// Mark clean inspect-effects as maybe dirty and then check their dirtiness
-				// instead of just updating the effects - this way we avoid overfiring.
-				if ((effect.f & CLEAN) !== 0) {
-					set_signal_status(effect, MAYBE_DIRTY);
-				}
+export function flush_inspect_effects() {
+	inspect_effects_deferred = false;
 
-				if (is_dirty(effect)) {
-					update_effect(effect);
-				}
-			}
+	const inspects = Array.from(inspect_effects);
 
-			inspect_effects.clear();
+	for (const effect of inspects) {
+		// Mark clean inspect-effects as maybe dirty and then check their dirtiness
+		// instead of just updating the effects - this way we avoid overfiring.
+		if ((effect.f & CLEAN) !== 0) {
+			set_signal_status(effect, MAYBE_DIRTY);
+		}
+
+		if (is_dirty(effect)) {
+			update_effect(effect);
 		}
 	}
 
-	return value;
+	inspect_effects.clear();
 }
 
 /**
diff --git a/packages/svelte/tests/runtime-runes/samples/array-delete-item/_config.js b/packages/svelte/tests/runtime-runes/samples/array-delete-item/_config.js
new file mode 100644
index 0000000000..7134117067
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/array-delete-item/_config.js
@@ -0,0 +1,13 @@
+import { ok, test } from '../../test';
+import { flushSync } from 'svelte';
+
+export default test({
+	mode: ['client'],
+	async test({ target, assert, logs }) {
+		const btn = target.querySelector('button');
+
+		flushSync(() => btn?.click());
+
+		assert.deepEqual(logs[0], [0, , 2]);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/array-delete-item/main.svelte b/packages/svelte/tests/runtime-runes/samples/array-delete-item/main.svelte
new file mode 100644
index 0000000000..ca00a85491
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/array-delete-item/main.svelte
@@ -0,0 +1,8 @@
+<script>
+	const arr = [0, 1, 2];
+</script>
+
+<button onclick={() => {
+	delete arr[1];
+	console.log(arr);
+}}>del</button>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/inspect-deep-array/_config.js b/packages/svelte/tests/runtime-runes/samples/inspect-deep-array/_config.js
index 0e6b12508b..49f1b5de41 100644
--- a/packages/svelte/tests/runtime-runes/samples/inspect-deep-array/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/inspect-deep-array/_config.js
@@ -13,17 +13,6 @@ export default test({
 			button?.click();
 		});
 
-		assert.deepEqual(logs, [
-			'init',
-			[1, 2, 3, 7],
-			'update',
-			[2, 2, 3, 7],
-			'update',
-			[2, 3, 3, 7],
-			'update',
-			[2, 3, 7, 7],
-			'update',
-			[2, 3, 7]
-		]);
+		assert.deepEqual(logs, ['init', [1, 2, 3, 7], 'update', [2, 3, 7]]);
 	}
 });
diff --git a/packages/svelte/tests/suite.ts b/packages/svelte/tests/suite.ts
index 6954b8b683..bbd252b8e1 100644
--- a/packages/svelte/tests/suite.ts
+++ b/packages/svelte/tests/suite.ts
@@ -20,6 +20,9 @@ const filter = process.env.FILTER
 		)
 	: /./;
 
+// this defaults to 10, which is too low for some of our tests
+Error.stackTraceLimit = 100;
+
 export function suite<Test extends BaseTest>(fn: (config: Test, test_dir: string) => void) {
 	return {
 		test: (config: Test) => config,

From be44f8b23ecf14bb5945c06dd775000bcc483eaf Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Wed, 16 Jul 2025 10:45:47 -0400
Subject: [PATCH 074/148] Version Packages (#16384)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/big-readers-lie.md   |  5 -----
 .changeset/curvy-houses-jog.md  |  5 -----
 .changeset/metal-coats-thank.md |  5 -----
 .changeset/popular-tips-lie.md  |  5 -----
 packages/svelte/CHANGELOG.md    | 12 ++++++++++++
 packages/svelte/package.json    |  2 +-
 packages/svelte/src/version.js  |  2 +-
 7 files changed, 14 insertions(+), 22 deletions(-)
 delete mode 100644 .changeset/big-readers-lie.md
 delete mode 100644 .changeset/curvy-houses-jog.md
 delete mode 100644 .changeset/metal-coats-thank.md
 delete mode 100644 .changeset/popular-tips-lie.md

diff --git a/.changeset/big-readers-lie.md b/.changeset/big-readers-lie.md
deleted file mode 100644
index 9f5dd166c1..0000000000
--- a/.changeset/big-readers-lie.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: don't log `await_reactivity_loss` warning when signal is read in `untrack`
diff --git a/.changeset/curvy-houses-jog.md b/.changeset/curvy-houses-jog.md
deleted file mode 100644
index 0a2323d8e4..0000000000
--- a/.changeset/curvy-houses-jog.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: better handle $inspect on array mutations
diff --git a/.changeset/metal-coats-thank.md b/.changeset/metal-coats-thank.md
deleted file mode 100644
index b307fd3d45..0000000000
--- a/.changeset/metal-coats-thank.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-"svelte": patch
----
-
-fix: leave proxied array `length` untouched when deleting properties
diff --git a/.changeset/popular-tips-lie.md b/.changeset/popular-tips-lie.md
deleted file mode 100644
index 45bd3e23f3..0000000000
--- a/.changeset/popular-tips-lie.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: update `$effect.pending()` immediately after a batch is removed
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 8c0b21364d..2ea2f58de8 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,17 @@
 # svelte
 
+## 5.36.3
+
+### Patch Changes
+
+- fix: don't log `await_reactivity_loss` warning when signal is read in `untrack` ([#16385](https://github.com/sveltejs/svelte/pull/16385))
+
+- fix: better handle $inspect on array mutations ([#16389](https://github.com/sveltejs/svelte/pull/16389))
+
+- fix: leave proxied array `length` untouched when deleting properties ([#16389](https://github.com/sveltejs/svelte/pull/16389))
+
+- fix: update `$effect.pending()` immediately after a batch is removed ([#16382](https://github.com/sveltejs/svelte/pull/16382))
+
 ## 5.36.2
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 6e000e2bbf..119c4142cf 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.2",
+  "version": "5.36.3",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 9ccd2ff0ce..e8b0e6f1ee 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.2';
+export const VERSION = '5.36.3';
 export const PUBLIC_VERSION = '5';

From 4947283fa5547691adcb129e145eed77c38f39fc Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 16 Jul 2025 12:08:45 -0400
Subject: [PATCH 075/148] fix: avoid microtask in flushSync (#16394)

* fix: avoid microtask in flushSync

* fix/simplify

* on second thoughts

* changeset
---
 .changeset/soft-moles-work.md                 |  5 +++++
 .../src/internal/client/reactivity/batch.js   | 20 ++++++++++---------
 2 files changed, 16 insertions(+), 9 deletions(-)
 create mode 100644 .changeset/soft-moles-work.md

diff --git a/.changeset/soft-moles-work.md b/.changeset/soft-moles-work.md
new file mode 100644
index 0000000000..c3573e4bc5
--- /dev/null
+++ b/.changeset/soft-moles-work.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: avoid microtask in flushSync
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index f881330e90..1d08b5c3d8 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -416,19 +416,21 @@ export class Batch {
 		return (this.#deferred ??= deferred()).promise;
 	}
 
-	static ensure() {
+	static ensure(autoflush = true) {
 		if (current_batch === null) {
 			const batch = (current_batch = new Batch());
 			batches.add(current_batch);
 
-			queueMicrotask(() => {
-				if (current_batch !== batch) {
-					// a flushSync happened in the meantime
-					return;
-				}
+			if (autoflush) {
+				queueMicrotask(() => {
+					if (current_batch !== batch) {
+						// a flushSync happened in the meantime
+						return;
+					}
 
-				batch.flush();
-			});
+					batch.flush();
+				});
+			}
 		}
 
 		return current_batch;
@@ -449,7 +451,7 @@ export function flushSync(fn) {
 
 	var result;
 
-	const batch = Batch.ensure();
+	const batch = Batch.ensure(false);
 
 	if (fn) {
 		batch.flush_effects();

From ee1ef6083ad9fad44c677192d3dafefb4d731f1e Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Wed, 16 Jul 2025 18:20:44 +0200
Subject: [PATCH 076/148] fix: ensure compiler state is reset before
 compilation (#16396)

#16268 introduced a slight regression where the state is not reset completely upon compilation. It did reset warnings but not other state, which meant if file A succeeds but file B fails in the parsing state (before the state was reset for real) it would get wrong filename info. This fixes it by setting the filename at the very beginning.
---
 .changeset/two-terms-draw.md                  |  5 +++
 packages/svelte/src/compiler/index.js         |  6 +--
 packages/svelte/src/compiler/migrate/index.js |  6 +--
 .../src/compiler/phases/2-analyze/index.js    |  8 ++--
 .../phases/2-analyze/visitors/SvelteSelf.js   |  6 +--
 packages/svelte/src/compiler/state.js         | 37 ++++++++++++-------
 .../src/compiler/utils/compile_diagnostic.js  |  2 +-
 packages/svelte/tests/compiler-errors/test.ts | 14 ++++++-
 8 files changed, 55 insertions(+), 29 deletions(-)
 create mode 100644 .changeset/two-terms-draw.md

diff --git a/.changeset/two-terms-draw.md b/.changeset/two-terms-draw.md
new file mode 100644
index 0000000000..88ef4be86e
--- /dev/null
+++ b/.changeset/two-terms-draw.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure compiler state is reset before compilation
diff --git a/packages/svelte/src/compiler/index.js b/packages/svelte/src/compiler/index.js
index 9ba23c1485..a378af34ee 100644
--- a/packages/svelte/src/compiler/index.js
+++ b/packages/svelte/src/compiler/index.js
@@ -20,7 +20,7 @@ export { default as preprocess } from './preprocess/index.js';
  */
 export function compile(source, options) {
 	source = remove_bom(source);
-	state.reset_warnings(options.warningFilter);
+	state.reset({ warning: options.warningFilter, filename: options.filename });
 	const validated = validate_component_options(options, '');
 
 	let parsed = _parse(source);
@@ -63,7 +63,7 @@ export function compile(source, options) {
  */
 export function compileModule(source, options) {
 	source = remove_bom(source);
-	state.reset_warnings(options.warningFilter);
+	state.reset({ warning: options.warningFilter, filename: options.filename });
 	const validated = validate_module_options(options, '');
 
 	const analysis = analyze_module(source, validated);
@@ -111,7 +111,7 @@ export function compileModule(source, options) {
  */
 export function parse(source, { modern, loose } = {}) {
 	source = remove_bom(source);
-	state.reset_warnings(() => false);
+	state.reset({ warning: () => false, filename: undefined });
 
 	const ast = _parse(source, loose);
 	return to_public_ast(source, ast, modern);
diff --git a/packages/svelte/src/compiler/migrate/index.js b/packages/svelte/src/compiler/migrate/index.js
index 0e2fe019ed..6b2e6cda70 100644
--- a/packages/svelte/src/compiler/migrate/index.js
+++ b/packages/svelte/src/compiler/migrate/index.js
@@ -9,7 +9,7 @@ import { parse } from '../phases/1-parse/index.js';
 import { regex_valid_component_name } from '../phases/1-parse/state/element.js';
 import { analyze_component } from '../phases/2-analyze/index.js';
 import { get_rune } from '../phases/scope.js';
-import { reset, reset_warnings } from '../state.js';
+import { reset, UNKNOWN_FILENAME } from '../state.js';
 import {
 	extract_identifiers,
 	extract_all_identifiers_from_expression,
@@ -134,7 +134,7 @@ export function migrate(source, { filename, use_ts } = {}) {
 			return start + style_placeholder + end;
 		});
 
-		reset_warnings(() => false);
+		reset({ warning: () => false, filename });
 
 		let parsed = parse(source);
 
@@ -145,7 +145,7 @@ export function migrate(source, { filename, use_ts } = {}) {
 			...validate_component_options({}, ''),
 			...parsed_options,
 			customElementOptions,
-			filename: filename ?? '(unknown)',
+			filename: filename ?? UNKNOWN_FILENAME,
 			experimental: {
 				async: true
 			}
diff --git a/packages/svelte/src/compiler/phases/2-analyze/index.js b/packages/svelte/src/compiler/phases/2-analyze/index.js
index 258b59018a..d407b44556 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/index.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/index.js
@@ -279,9 +279,8 @@ export function analyze_module(source, options) {
 		classes: new Map()
 	};
 
-	state.reset({
+	state.adjust({
 		dev: options.dev,
-		filename: options.filename,
 		rootDir: options.rootDir,
 		runes: true
 	});
@@ -531,12 +530,11 @@ export function analyze_component(root, source, options) {
 		async_deriveds: new Set()
 	};
 
-	state.reset({
+	state.adjust({
 		component_name: analysis.name,
 		dev: options.dev,
-		filename: options.filename,
 		rootDir: options.rootDir,
-		runes: true
+		runes
 	});
 
 	if (!runes) {
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteSelf.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteSelf.js
index b87f082de0..652a447165 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteSelf.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteSelf.js
@@ -3,7 +3,7 @@
 import { visit_component } from './shared/component.js';
 import * as e from '../../../errors.js';
 import * as w from '../../../warnings.js';
-import { filename } from '../../../state.js';
+import { filename, UNKNOWN_FILENAME } from '../../../state.js';
 
 /**
  * @param {AST.SvelteSelf} node
@@ -23,9 +23,9 @@ export function SvelteSelf(node, context) {
 	}
 
 	if (context.state.analysis.runes) {
-		const name = filename === '(unknown)' ? 'Self' : context.state.analysis.name;
+		const name = filename === UNKNOWN_FILENAME ? 'Self' : context.state.analysis.name;
 		const basename =
-			filename === '(unknown)'
+			filename === UNKNOWN_FILENAME
 				? 'Self.svelte'
 				: /** @type {string} */ (filename.split(/[/\\]/).pop());
 
diff --git a/packages/svelte/src/compiler/state.js b/packages/svelte/src/compiler/state.js
index 5eb25dd6bb..725d03b802 100644
--- a/packages/svelte/src/compiler/state.js
+++ b/packages/svelte/src/compiler/state.js
@@ -16,6 +16,11 @@ export let warnings = [];
  */
 export let filename;
 
+/**
+ * This is the fallback used when no filename is specified.
+ */
+export const UNKNOWN_FILENAME = '(unknown)';
+
 /**
  * The name of the component that is used in the `export default function ...` statement.
  */
@@ -80,15 +85,6 @@ export function pop_ignore() {
 	ignore_stack.pop();
 }
 
-/**
- *
- * @param {(warning: Warning) => boolean} fn
- */
-export function reset_warnings(fn = () => true) {
-	warning_filter = fn;
-	warnings = [];
-}
-
 /**
  * @param {AST.SvelteNode | NodeLike} node
  * @param {import('../constants.js').IGNORABLE_RUNTIME_WARNINGS[number]} code
@@ -99,21 +95,36 @@ export function is_ignored(node, code) {
 }
 
 /**
+ * Call this to reset the compiler state. Should be called before each compilation.
+ * @param {{ warning?: (warning: Warning) => boolean; filename: string | undefined }} state
+ */
+export function reset(state) {
+	dev = false;
+	runes = false;
+	component_name = UNKNOWN_FILENAME;
+	source = '';
+	locator = () => undefined;
+	filename = (state.filename ?? UNKNOWN_FILENAME).replace(/\\/g, '/');
+	warning_filter = state.warning ?? (() => true);
+	warnings = [];
+}
+
+/**
+ * Adjust the compiler state based on the provided state object.
+ * Call this after parsing and basic analysis happened.
  * @param {{
  *   dev: boolean;
- *   filename: string;
  *   component_name?: string;
  *   rootDir?: string;
  *   runes: boolean;
  * }} state
  */
-export function reset(state) {
+export function adjust(state) {
 	const root_dir = state.rootDir?.replace(/\\/g, '/');
-	filename = state.filename.replace(/\\/g, '/');
 
 	dev = state.dev;
 	runes = state.runes;
-	component_name = state.component_name ?? '(unknown)';
+	component_name = state.component_name ?? UNKNOWN_FILENAME;
 
 	if (typeof root_dir === 'string' && filename.startsWith(root_dir)) {
 		// make filename relative to rootDir
diff --git a/packages/svelte/src/compiler/utils/compile_diagnostic.js b/packages/svelte/src/compiler/utils/compile_diagnostic.js
index db938cf2bd..c5df49e01c 100644
--- a/packages/svelte/src/compiler/utils/compile_diagnostic.js
+++ b/packages/svelte/src/compiler/utils/compile_diagnostic.js
@@ -61,7 +61,7 @@ export class CompileDiagnostic {
 		this.code = code;
 		this.message = message;
 
-		if (state.filename) {
+		if (state.filename !== state.UNKNOWN_FILENAME) {
 			this.filename = state.filename;
 		}
 
diff --git a/packages/svelte/tests/compiler-errors/test.ts b/packages/svelte/tests/compiler-errors/test.ts
index 5e57a3a032..13b9280dde 100644
--- a/packages/svelte/tests/compiler-errors/test.ts
+++ b/packages/svelte/tests/compiler-errors/test.ts
@@ -1,5 +1,5 @@
 import * as fs from 'node:fs';
-import { assert, expect } from 'vitest';
+import { assert, expect, it } from 'vitest';
 import { compile, compileModule, type CompileError } from 'svelte/compiler';
 import { suite, type BaseTest } from '../suite';
 import { read_file } from '../helpers.js';
@@ -78,3 +78,15 @@ const { test, run } = suite<CompilerErrorTest>((config, cwd) => {
 export { test };
 
 await run(__dirname);
+
+it('resets the compiler state including filename', () => {
+	// start with something that succeeds
+	compile('<div>hello</div>', { filename: 'foo.svelte' });
+	// then try something that fails in the parsing stage
+	try {
+		compile('<p>hello<div>invalid</p>', { filename: 'bar.svelte' });
+		expect.fail('Expected an error');
+	} catch (e: any) {
+		expect(e.toString()).toContain('bar.svelte');
+	}
+});

From 58788db27b33f2c86a649d603bc328fa330e8f6b Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Wed, 16 Jul 2025 12:42:25 -0400
Subject: [PATCH 077/148] Version Packages (#16397)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/soft-moles-work.md  | 5 -----
 .changeset/two-terms-draw.md   | 5 -----
 packages/svelte/CHANGELOG.md   | 8 ++++++++
 packages/svelte/package.json   | 2 +-
 packages/svelte/src/version.js | 2 +-
 5 files changed, 10 insertions(+), 12 deletions(-)
 delete mode 100644 .changeset/soft-moles-work.md
 delete mode 100644 .changeset/two-terms-draw.md

diff --git a/.changeset/soft-moles-work.md b/.changeset/soft-moles-work.md
deleted file mode 100644
index c3573e4bc5..0000000000
--- a/.changeset/soft-moles-work.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: avoid microtask in flushSync
diff --git a/.changeset/two-terms-draw.md b/.changeset/two-terms-draw.md
deleted file mode 100644
index 88ef4be86e..0000000000
--- a/.changeset/two-terms-draw.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: ensure compiler state is reset before compilation
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 2ea2f58de8..6d4f31480d 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,13 @@
 # svelte
 
+## 5.36.4
+
+### Patch Changes
+
+- fix: avoid microtask in flushSync ([#16394](https://github.com/sveltejs/svelte/pull/16394))
+
+- fix: ensure compiler state is reset before compilation ([#16396](https://github.com/sveltejs/svelte/pull/16396))
+
 ## 5.36.3
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 119c4142cf..3e9022a091 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.3",
+  "version": "5.36.4",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index e8b0e6f1ee..f8d23b44b1 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.3';
+export const VERSION = '5.36.4';
 export const PUBLIC_VERSION = '5';

From c11c5ec0e381fc45f9f6ead1bce42f219eb8de61 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 16 Jul 2025 14:41:16 -0400
Subject: [PATCH 078/148] docs: tweak createSubscriber explanation (#16398)

* docs: tweak createSubscriber explanation

* regenerate
---
 packages/svelte/src/reactivity/create-subscriber.js | 10 +++++++---
 packages/svelte/types/index.d.ts                    | 10 +++++++---
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/packages/svelte/src/reactivity/create-subscriber.js b/packages/svelte/src/reactivity/create-subscriber.js
index afcea9c5b4..4dcac4e6f6 100644
--- a/packages/svelte/src/reactivity/create-subscriber.js
+++ b/packages/svelte/src/reactivity/create-subscriber.js
@@ -6,10 +6,13 @@ import { DEV } from 'esm-env';
 import { queue_micro_task } from '../internal/client/dom/task.js';
 
 /**
- * Returns a `subscribe` function that, if called in an effect (including expressions in the template),
- * calls its `start` callback with an `update` function. Whenever `update` is called, the effect re-runs.
+ * Returns a `subscribe` function that integrates external event-based systems with Svelte's reactivity.
+ * It's particularly useful for integrating with web APIs like `MediaQuery`, `IntersectionObserver`, or `WebSocket`.
  *
- * If `start` returns a function, it will be called when the effect is destroyed.
+ * If `subscribe` is called inside an effect (including indirectly, for example inside a getter),
+ * the `start` callback will be called with an `update` function. Whenever `update` is called, the effect re-runs.
+ *
+ * If `start` returns a cleanup function, it will be called when the effect is destroyed.
  *
  * If `subscribe` is called in multiple effects, `start` will only be called once as long as the effects
  * are active, and the returned teardown function will only be called when all effects are destroyed.
@@ -37,6 +40,7 @@ import { queue_micro_task } from '../internal/client/dom/task.js';
  * 	}
  *
  * 	get current() {
+ * 		// This makes the getter reactive, if read in an effect
  * 		this.#subscribe();
  *
  * 		// Return the current state of the query, whether or not we're in an effect
diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index d356762a3f..a8b769d6d4 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -2335,10 +2335,13 @@ declare module 'svelte/reactivity' {
 		constructor(query: string, fallback?: boolean | undefined);
 	}
 	/**
-	 * Returns a `subscribe` function that, if called in an effect (including expressions in the template),
-	 * calls its `start` callback with an `update` function. Whenever `update` is called, the effect re-runs.
+	 * Returns a `subscribe` function that integrates external event-based systems with Svelte's reactivity.
+	 * It's particularly useful for integrating with web APIs like `MediaQuery`, `IntersectionObserver`, or `WebSocket`.
 	 *
-	 * If `start` returns a function, it will be called when the effect is destroyed.
+	 * If `subscribe` is called inside an effect (including indirectly, for example inside a getter),
+	 * the `start` callback will be called with an `update` function. Whenever `update` is called, the effect re-runs.
+	 *
+	 * If `start` returns a cleanup function, it will be called when the effect is destroyed.
 	 *
 	 * If `subscribe` is called in multiple effects, `start` will only be called once as long as the effects
 	 * are active, and the returned teardown function will only be called when all effects are destroyed.
@@ -2366,6 +2369,7 @@ declare module 'svelte/reactivity' {
 	 * 	}
 	 *
 	 * 	get current() {
+	 * 		// This makes the getter reactive, if read in an effect
 	 * 		this.#subscribe();
 	 *
 	 * 		// Return the current state of the query, whether or not we're in an effect

From 45cd000890202aff68e4c8aeeead1203ee369c7b Mon Sep 17 00:00:00 2001
From: Ben McCann <322311+benmccann@users.noreply.github.com>
Date: Wed, 16 Jul 2025 14:44:03 -0700
Subject: [PATCH 079/148] chore: fix peer dependency warning (#16401)

---
 package.json   |  2 +-
 pnpm-lock.yaml | 26 +++++++++++++++-----------
 2 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/package.json b/package.json
index 3e609db87f..458bf34084 100644
--- a/package.json
+++ b/package.json
@@ -30,7 +30,7 @@
     "@sveltejs/eslint-config": "^8.1.0",
     "@svitejs/changesets-changelog-github-compact": "^1.1.0",
     "@types/node": "^20.11.5",
-    "@vitest/coverage-v8": "^2.0.5",
+    "@vitest/coverage-v8": "^2.1.9",
     "eslint": "^9.9.1",
     "eslint-plugin-lube": "^0.4.3",
     "jsdom": "25.0.1",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index d0982dc791..5f902186ef 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -21,8 +21,8 @@ importers:
         specifier: ^20.11.5
         version: 20.12.7
       '@vitest/coverage-v8':
-        specifier: ^2.0.5
-        version: 2.0.5(vitest@2.1.9(@types/node@20.12.7)(jsdom@25.0.1)(lightningcss@1.23.0)(sass@1.70.0)(terser@5.27.0))
+        specifier: ^2.1.9
+        version: 2.1.9(vitest@2.1.9(@types/node@20.12.7)(jsdom@25.0.1)(lightningcss@1.23.0)(sass@1.70.0)(terser@5.27.0))
       eslint:
         specifier: ^9.9.1
         version: 9.9.1
@@ -869,10 +869,14 @@ packages:
     resolution: {integrity: sha512-ar0tjQfObzhSaW3C3QNmTc5ofj0hDoNQ5XWrCy6zDyabdr0TWhCkClp+rywGNj/odAFBVzzJrK4tEq5M4Hmu4w==}
     engines: {node: ^18.18.0 || ^20.9.0 || >=21.1.0}
 
-  '@vitest/coverage-v8@2.0.5':
-    resolution: {integrity: sha512-qeFcySCg5FLO2bHHSa0tAZAOnAUbp4L6/A5JDuj9+bt53JREl8hpLjLHEWF0e/gWc8INVpJaqA7+Ene2rclpZg==}
+  '@vitest/coverage-v8@2.1.9':
+    resolution: {integrity: sha512-Z2cOr0ksM00MpEfyVE8KXIYPEcBFxdbLSs56L8PO0QQMxt/6bDj45uQfxoc96v05KW3clk7vvgP0qfDit9DmfQ==}
     peerDependencies:
-      vitest: 2.0.5
+      '@vitest/browser': 2.1.9
+      vitest: 2.1.9
+    peerDependenciesMeta:
+      '@vitest/browser':
+        optional: true
 
   '@vitest/expect@2.1.9':
     resolution: {integrity: sha512-UJCIkTBenHeKT1TTlKMJWy1laZewsRIzYighyYiJKZreqtdxSos/S1t+ktRMQWu2CKqaarrkeszJx1cgC5tGZw==}
@@ -1683,8 +1687,8 @@ packages:
   magic-string@0.30.17:
     resolution: {integrity: sha512-sNPKHvyjVf7gyjwS4xGTaW/mCnF8wnjtifKBEhxfZ7E/S8tQ0rssrwGNn6q8JH/ohItJfSQp9mBtQYuTlH5QnA==}
 
-  magicast@0.3.4:
-    resolution: {integrity: sha512-TyDF/Pn36bBji9rWKHlZe+PZb6Mx5V8IHCSxk7X4aljM4e/vyDvZZYwHewdVaqiA0nb3ghfHU/6AUpDxWoER2Q==}
+  magicast@0.3.5:
+    resolution: {integrity: sha512-L0WhttDl+2BOsybvEOLK7fW3UA0OQ0IQ2d6Zl2x/a6vVRs3bAY0ECOSHHeL5jD+SbOpOCUEi0y1DgHEn9Qn1AQ==}
 
   make-dir@4.0.0:
     resolution: {integrity: sha512-hXdUTZYIVOt1Ex//jAQi+wTZZpUpwBj/0QsOzqegb3rGMMeJiSEu5xLHnYfBrRV4RH2+OCSOO95Is/7x1WJ4bw==}
@@ -3173,7 +3177,7 @@ snapshots:
       '@typescript-eslint/types': 8.32.1
       eslint-visitor-keys: 4.2.0
 
-  '@vitest/coverage-v8@2.0.5(vitest@2.1.9(@types/node@20.12.7)(jsdom@25.0.1)(lightningcss@1.23.0)(sass@1.70.0)(terser@5.27.0))':
+  '@vitest/coverage-v8@2.1.9(vitest@2.1.9(@types/node@20.12.7)(jsdom@25.0.1)(lightningcss@1.23.0)(sass@1.70.0)(terser@5.27.0))':
     dependencies:
       '@ampproject/remapping': 2.3.0
       '@bcoe/v8-coverage': 0.2.3
@@ -3183,7 +3187,7 @@ snapshots:
       istanbul-lib-source-maps: 5.0.6
       istanbul-reports: 3.1.7
       magic-string: 0.30.17
-      magicast: 0.3.4
+      magicast: 0.3.5
       std-env: 3.8.0
       test-exclude: 7.0.1
       tinyrainbow: 1.2.0
@@ -4045,7 +4049,7 @@ snapshots:
     dependencies:
       '@jridgewell/sourcemap-codec': 1.5.0
 
-  magicast@0.3.4:
+  magicast@0.3.5:
     dependencies:
       '@babel/parser': 7.25.4
       '@babel/types': 7.25.4
@@ -4053,7 +4057,7 @@ snapshots:
 
   make-dir@4.0.0:
     dependencies:
-      semver: 7.7.1
+      semver: 7.7.2
 
   merge2@1.4.1: {}
 

From ead409120229a3c8677d357823b86242fa196dda Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 16 Jul 2025 18:54:45 -0400
Subject: [PATCH 080/148] docs: diligently describe destructured derived
 declarations (#16400)

---
 documentation/docs/02-runes/03-$derived.md | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/documentation/docs/02-runes/03-$derived.md b/documentation/docs/02-runes/03-$derived.md
index 2464aa9295..5f253cf6d1 100644
--- a/documentation/docs/02-runes/03-$derived.md
+++ b/documentation/docs/02-runes/03-$derived.md
@@ -94,6 +94,23 @@ let selected = $derived(items[index]);
 
 ...you can change (or `bind:` to) properties of `selected` and it will affect the underlying `items` array. If `items` was _not_ deeply reactive, mutating `selected` would have no effect.
 
+## Destructuring
+
+If you use destructuring with a `$derived` declaration, the resulting variables will all be reactive — this...
+
+```js
+let { a, b, c } = $derived(stuff());
+```
+
+...is roughly equivalent to this:
+
+```js
+let _stuff = $derived(stuff());
+let a = $derived(_stuff.a);
+let b = $derived(_stuff.b);
+let c = $derived(_stuff.c);
+```
+
 ## Update propagation
 
 Svelte uses something called _push-pull reactivity_ — when state is updated, everything that depends on the state (whether directly or indirectly) is immediately notified of the change (the 'push'), but derived values are not re-evaluated until they are actually read (the 'pull').

From 3edebd51035404c30c6c9f694c79037e2f93d433 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 16 Jul 2025 18:54:56 -0400
Subject: [PATCH 081/148] chore: update to new pnpm syntax (#16399)

---
 CONTRIBUTING.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 0e2628f84f..c2d3e45049 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -105,10 +105,10 @@ Test samples are kept in `/test/xxx/samples` folder.
    pnpm test validator
    ```
 
-1. To filter tests _within_ a test suite, use `pnpm test <suite-name> -- -t <test-name>`, for example:
+1. To filter tests _within_ a test suite, use `pnpm test <suite-name> -t <test-name>`, for example:
 
    ```bash
-   pnpm test validator -- -t a11y-alt-text
+   pnpm test validator -t a11y-alt-text
    ```
 
    (You can also do `FILTER=<test-name> pnpm test <suite-name>` which removes other tests rather than simply skipping them — this will result in faster and more compact test results, but it's non-idiomatic. Choose your fighter.)

From 09c9a3c16533d2223e17700684718b4829cda9c6 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 16 Jul 2025 18:55:24 -0400
Subject: [PATCH 082/148] fix: silence `$inspect` errors when the effect is
 about to be destroyed (#16391)

* fix: silence `$inspect` errors when the effect is about to be destroyed

* changeset
---
 .changeset/six-swans-rush.md                  |  5 ++
 .../svelte/src/internal/client/dev/inspect.js | 51 ++++++++++++-------
 .../samples/inspect-exception/_config.js      |  2 +-
 3 files changed, 39 insertions(+), 19 deletions(-)
 create mode 100644 .changeset/six-swans-rush.md

diff --git a/.changeset/six-swans-rush.md b/.changeset/six-swans-rush.md
new file mode 100644
index 0000000000..cfb5b97400
--- /dev/null
+++ b/.changeset/six-swans-rush.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: silence `$inspect` errors when the effect is about to be destroyed
diff --git a/packages/svelte/src/internal/client/dev/inspect.js b/packages/svelte/src/internal/client/dev/inspect.js
index e15c66901c..c593f2622c 100644
--- a/packages/svelte/src/internal/client/dev/inspect.js
+++ b/packages/svelte/src/internal/client/dev/inspect.js
@@ -1,6 +1,6 @@
 import { UNINITIALIZED } from '../../../constants.js';
 import { snapshot } from '../../shared/clone.js';
-import { inspect_effect, validate_effect } from '../reactivity/effects.js';
+import { inspect_effect, render_effect, validate_effect } from '../reactivity/effects.js';
 import { untrack } from '../runtime.js';
 
 /**
@@ -12,29 +12,44 @@ export function inspect(get_value, inspector = console.log) {
 	validate_effect('$inspect');
 
 	let initial = true;
+	let error = /** @type {any} */ (UNINITIALIZED);
 
+	// Inspect effects runs synchronously so that we can capture useful
+	// stack traces. As a consequence, reading the value might result
+	// in an error (an `$inspect(object.property)` will run before the
+	// `{#if object}...{/if}` that contains it)
 	inspect_effect(() => {
-		/** @type {any} */
-		var value = UNINITIALIZED;
-
-		// Capturing the value might result in an exception due to the inspect effect being
-		// sync and thus operating on stale data. In the case we encounter an exception we
-		// can bail-out of reporting the value. Instead we simply console.error the error
-		// so at least it's known that an error occured, but we don't stop execution
 		try {
-			value = get_value();
-		} catch (error) {
-			// eslint-disable-next-line no-console
-			console.error(error);
+			var value = get_value();
+		} catch (e) {
+			error = e;
+			return;
 		}
 
-		if (value !== UNINITIALIZED) {
-			var snap = snapshot(value, true);
-			untrack(() => {
-				inspector(initial ? 'init' : 'update', ...snap);
-			});
-		}
+		var snap = snapshot(value, true);
+		untrack(() => {
+			inspector(initial ? 'init' : 'update', ...snap);
+		});
 
 		initial = false;
 	});
+
+	// If an error occurs, we store it (along with its stack trace).
+	// If the render effect subsequently runs, we log the error,
+	// but if it doesn't run it's because the `$inspect` was
+	// destroyed, meaning we don't need to bother
+	render_effect(() => {
+		try {
+			// call `get_value` so that this runs alongside the inspect effect
+			get_value();
+		} catch {
+			// ignore
+		}
+
+		if (error !== UNINITIALIZED) {
+			// eslint-disable-next-line no-console
+			console.error(error);
+			error = UNINITIALIZED;
+		}
+	});
 }
diff --git a/packages/svelte/tests/runtime-runes/samples/inspect-exception/_config.js b/packages/svelte/tests/runtime-runes/samples/inspect-exception/_config.js
index e155ff236a..83e0eb9443 100644
--- a/packages/svelte/tests/runtime-runes/samples/inspect-exception/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/inspect-exception/_config.js
@@ -11,7 +11,7 @@ export default test({
 		b1?.click();
 		flushSync();
 
-		assert.ok(errors.length > 0);
+		assert.equal(errors.length, 0);
 		assert.deepEqual(logs, ['init', 'a', 'init', 'b']);
 	}
 });

From a67b5862f15ce763c0d3a038f88abbb4b08d2d80 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 16 Jul 2025 19:24:57 -0400
Subject: [PATCH 083/148] fix: more informative error when effects run in an
 infinite loop (#16405)

* update effect_update_depth_exceeded docs

* log update locations

* remove dev_effect_stack stuff, it's not very helpful

* tidy up

* test

* fix test

* changeset

* fix
---
 .changeset/slimy-doors-fetch.md               |  5 ++
 .../98-reference/.generated/client-errors.md  | 40 ++++++++++-
 .../svelte/messages/client-errors/errors.md   | 40 ++++++++++-
 .../svelte/src/internal/client/dev/tracing.js | 64 +++++++++--------
 packages/svelte/src/internal/client/errors.js |  4 +-
 .../src/internal/client/reactivity/batch.js   | 71 ++++++++-----------
 .../src/internal/client/reactivity/sources.js | 18 ++++-
 .../src/internal/client/reactivity/types.d.ts |  4 +-
 .../svelte/src/internal/client/runtime.js     | 12 +---
 .../samples/effect-loop-infinite/_config.js   | 21 ++++++
 .../samples/effect-loop-infinite/main.svelte  | 12 ++++
 .../samples/error-boundary-20/_config.js      |  4 +-
 12 files changed, 202 insertions(+), 93 deletions(-)
 create mode 100644 .changeset/slimy-doors-fetch.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/main.svelte

diff --git a/.changeset/slimy-doors-fetch.md b/.changeset/slimy-doors-fetch.md
new file mode 100644
index 0000000000..8dec24a98d
--- /dev/null
+++ b/.changeset/slimy-doors-fetch.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: more informative error when effects run in an infinite loop
diff --git a/documentation/docs/98-reference/.generated/client-errors.md b/documentation/docs/98-reference/.generated/client-errors.md
index c7d6ec8ac9..3b17ef9f9b 100644
--- a/documentation/docs/98-reference/.generated/client-errors.md
+++ b/documentation/docs/98-reference/.generated/client-errors.md
@@ -89,9 +89,47 @@ Effect cannot be created inside a `$derived` value that was not itself created i
 ### effect_update_depth_exceeded
 
 ```
-Maximum update depth exceeded. This can happen when a reactive block or effect repeatedly sets a new value. Svelte limits the number of nested updates to prevent infinite loops
+Maximum update depth exceeded. This typically indicates that an effect reads and writes the same piece of state
 ```
 
+If an effect updates some state that it also depends on, it will re-run, potentially in a loop:
+
+```js
+let count = $state(0);
+
+$effect(() => {
+	// this both reads and writes `count`,
+	// so will run in an infinite loop
+	count += 1;
+});
+```
+
+(Svelte intervenes before this can crash your browser tab.)
+
+The same applies to array mutations, since these both read and write to the array:
+
+```js
+let array = $state([]);
+
+$effect(() => {
+	array.push('hello');
+});
+```
+
+Note that it's fine for an effect to re-run itself as long as it 'settles':
+
+```js
+let array = ['a', 'b', 'c'];
+// ---cut---
+$effect(() => {
+	// this is okay, because sorting an already-sorted array
+	// won't result in a mutation
+	array.sort();
+});
+```
+
+Often when encountering this issue, the value in question shouldn't be state (for example, if you are pushing to a `logs` array in an effect, make `logs` a normal array rather than `$state([])`). In the rare cases where you really _do_ need to write to state in an effect — [which you should avoid]($effect#When-not-to-use-$effect) — you can read the state with [untrack](svelte#untrack) to avoid adding it as a dependency.
+
 ### flush_sync_in_effect
 
 ```
diff --git a/packages/svelte/messages/client-errors/errors.md b/packages/svelte/messages/client-errors/errors.md
index 2ce25dbd53..d6af859881 100644
--- a/packages/svelte/messages/client-errors/errors.md
+++ b/packages/svelte/messages/client-errors/errors.md
@@ -60,7 +60,45 @@ See the [migration guide](/docs/svelte/v5-migration-guide#Components-are-no-long
 
 ## effect_update_depth_exceeded
 
-> Maximum update depth exceeded. This can happen when a reactive block or effect repeatedly sets a new value. Svelte limits the number of nested updates to prevent infinite loops
+> Maximum update depth exceeded. This typically indicates that an effect reads and writes the same piece of state
+
+If an effect updates some state that it also depends on, it will re-run, potentially in a loop:
+
+```js
+let count = $state(0);
+
+$effect(() => {
+	// this both reads and writes `count`,
+	// so will run in an infinite loop
+	count += 1;
+});
+```
+
+(Svelte intervenes before this can crash your browser tab.)
+
+The same applies to array mutations, since these both read and write to the array:
+
+```js
+let array = $state([]);
+
+$effect(() => {
+	array.push('hello');
+});
+```
+
+Note that it's fine for an effect to re-run itself as long as it 'settles':
+
+```js
+let array = ['a', 'b', 'c'];
+// ---cut---
+$effect(() => {
+	// this is okay, because sorting an already-sorted array
+	// won't result in a mutation
+	array.sort();
+});
+```
+
+Often when encountering this issue, the value in question shouldn't be state (for example, if you are pushing to a `logs` array in an effect, make `logs` a normal array rather than `$state([])`). In the rare cases where you really _do_ need to write to state in an effect — [which you should avoid]($effect#When-not-to-use-$effect) — you can read the state with [untrack](svelte#untrack) to avoid adding it as a dependency.
 
 ## flush_sync_in_effect
 
diff --git a/packages/svelte/src/internal/client/dev/tracing.js b/packages/svelte/src/internal/client/dev/tracing.js
index 128942ceb2..b7a6a38548 100644
--- a/packages/svelte/src/internal/client/dev/tracing.js
+++ b/packages/svelte/src/internal/client/dev/tracing.js
@@ -56,8 +56,10 @@ function log_entry(signal, entry) {
 	}
 
 	if (dirty && signal.updated) {
-		// eslint-disable-next-line no-console
-		console.log(signal.updated);
+		for (const updated of signal.updated.values()) {
+			// eslint-disable-next-line no-console
+			console.log(updated.error);
+		}
 	}
 
 	if (entry) {
@@ -120,44 +122,46 @@ export function trace(label, fn) {
 
 /**
  * @param {string} label
+ * @returns {Error & { stack: string } | null}
  */
 export function get_stack(label) {
 	let error = Error();
 	const stack = error.stack;
 
-	if (stack) {
-		const lines = stack.split('\n');
-		const new_lines = ['\n'];
-
-		for (let i = 0; i < lines.length; i++) {
-			const line = lines[i];
-
-			if (line === 'Error') {
-				continue;
-			}
-			if (line.includes('validate_each_keys')) {
-				return null;
-			}
-			if (line.includes('svelte/src/internal')) {
-				continue;
-			}
-			new_lines.push(line);
-		}
+	if (!stack) return null;
 
-		if (new_lines.length === 1) {
+	const lines = stack.split('\n');
+	const new_lines = ['\n'];
+
+	for (let i = 0; i < lines.length; i++) {
+		const line = lines[i];
+
+		if (line === 'Error') {
+			continue;
+		}
+		if (line.includes('validate_each_keys')) {
 			return null;
 		}
+		if (line.includes('svelte/src/internal')) {
+			continue;
+		}
+		new_lines.push(line);
+	}
 
-		define_property(error, 'stack', {
-			value: new_lines.join('\n')
-		});
-
-		define_property(error, 'name', {
-			// 'Error' suffix is required for stack traces to be rendered properly
-			value: `${label}Error`
-		});
+	if (new_lines.length === 1) {
+		return null;
 	}
-	return error;
+
+	define_property(error, 'stack', {
+		value: new_lines.join('\n')
+	});
+
+	define_property(error, 'name', {
+		// 'Error' suffix is required for stack traces to be rendered properly
+		value: `${label}Error`
+	});
+
+	return /** @type {Error & { stack: string }} */ (error);
 }
 
 /**
diff --git a/packages/svelte/src/internal/client/errors.js b/packages/svelte/src/internal/client/errors.js
index a491dc683d..edd66a7400 100644
--- a/packages/svelte/src/internal/client/errors.js
+++ b/packages/svelte/src/internal/client/errors.js
@@ -214,12 +214,12 @@ export function effect_pending_outside_reaction() {
 }
 
 /**
- * Maximum update depth exceeded. This can happen when a reactive block or effect repeatedly sets a new value. Svelte limits the number of nested updates to prevent infinite loops
+ * Maximum update depth exceeded. This typically indicates that an effect reads and writes the same piece of state
  * @returns {never}
  */
 export function effect_update_depth_exceeded() {
 	if (DEV) {
-		const error = new Error(`effect_update_depth_exceeded\nMaximum update depth exceeded. This can happen when a reactive block or effect repeatedly sets a new value. Svelte limits the number of nested updates to prevent infinite loops\nhttps://svelte.dev/e/effect_update_depth_exceeded`);
+		const error = new Error(`effect_update_depth_exceeded\nMaximum update depth exceeded. This typically indicates that an effect reads and writes the same piece of state\nhttps://svelte.dev/e/effect_update_depth_exceeded`);
 
 		error.name = 'Svelte error';
 
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index 1d08b5c3d8..cdce971b18 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -46,9 +46,6 @@ export let current_batch = null;
  */
 export let batch_deriveds = null;
 
-/** @type {Effect[]} Stack of effects, dev only */
-export let dev_effect_stack = [];
-
 /** @type {Set<() => void>} */
 export let effect_pending_updates = new Set();
 
@@ -345,6 +342,28 @@ export class Batch {
 
 			while (queued_root_effects.length > 0) {
 				if (flush_count++ > 1000) {
+					if (DEV) {
+						var updates = new Map();
+
+						for (const source of this.#current.keys()) {
+							for (const [stack, update] of source.updated ?? []) {
+								var entry = updates.get(stack);
+
+								if (!entry) {
+									entry = { error: update.error, count: 0 };
+									updates.set(stack, entry);
+								}
+
+								entry.count += update.count;
+							}
+						}
+
+						for (const update of updates.values()) {
+							// eslint-disable-next-line no-console
+							console.error(update.error);
+						}
+					}
+
 					infinite_loop_guard();
 				}
 
@@ -356,9 +375,6 @@ export class Batch {
 			set_is_updating_effect(was_updating_effect);
 
 			last_scheduled_effect = null;
-			if (DEV) {
-				dev_effect_stack = [];
-			}
 		}
 	}
 
@@ -471,10 +487,6 @@ export function flushSync(fn) {
 			// we need to reset it here as well in case the first time there's 0 queued root effects
 			last_scheduled_effect = null;
 
-			if (DEV) {
-				dev_effect_stack = [];
-			}
-
 			return /** @type {T} */ (result);
 		}
 
@@ -482,45 +494,18 @@ export function flushSync(fn) {
 	}
 }
 
-function log_effect_stack() {
-	// eslint-disable-next-line no-console
-	console.error(
-		'Last ten effects were: ',
-		dev_effect_stack.slice(-10).map((d) => d.fn)
-	);
-	dev_effect_stack = [];
-}
-
 function infinite_loop_guard() {
 	try {
 		e.effect_update_depth_exceeded();
 	} catch (error) {
 		if (DEV) {
-			// stack is garbage, ignore. Instead add a console.error message.
-			define_property(error, 'stack', {
-				value: ''
-			});
-		}
-		// Try and handle the error so it can be caught at a boundary, that's
-		// if there's an effect available from when it was last scheduled
-		if (last_scheduled_effect !== null) {
-			if (DEV) {
-				try {
-					invoke_error_boundary(error, last_scheduled_effect);
-				} catch (e) {
-					// Only log the effect stack if the error is re-thrown
-					log_effect_stack();
-					throw e;
-				}
-			} else {
-				invoke_error_boundary(error, last_scheduled_effect);
-			}
-		} else {
-			if (DEV) {
-				log_effect_stack();
-			}
-			throw error;
+			// stack contains no useful information, replace it
+			define_property(error, 'stack', { value: '' });
 		}
+
+		// Best effort: invoke the boundary nearest the most recent
+		// effect and hope that it's relevant to the infinite loop
+		invoke_error_boundary(error, last_scheduled_effect);
 	}
 }
 
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index bd55b9d935..9b534d2d71 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -182,8 +182,22 @@ export function internal_set(source, value) {
 		const batch = Batch.ensure();
 		batch.capture(source, old_value);
 
-		if (DEV && tracing_mode_flag) {
-			source.updated = get_stack('UpdatedAt');
+		if (DEV) {
+			if (tracing_mode_flag || active_effect !== null) {
+				const error = get_stack('UpdatedAt');
+
+				if (error !== null) {
+					source.updated ??= new Map();
+					let entry = source.updated.get(error.stack);
+
+					if (!entry) {
+						entry = { error, count: 0 };
+						source.updated.set(error.stack, entry);
+					}
+
+					entry.count++;
+				}
+			}
 
 			if (active_effect !== null) {
 				source.set_during_effect = true;
diff --git a/packages/svelte/src/internal/client/reactivity/types.d.ts b/packages/svelte/src/internal/client/reactivity/types.d.ts
index 90f922df68..72187e84a7 100644
--- a/packages/svelte/src/internal/client/reactivity/types.d.ts
+++ b/packages/svelte/src/internal/client/reactivity/types.d.ts
@@ -29,8 +29,8 @@ export interface Value<V = unknown> extends Signal {
 	label?: string;
 	/** An error with a stack trace showing when the source was created */
 	created?: Error | null;
-	/** An error with a stack trace showing when the source was last updated */
-	updated?: Error | null;
+	/** An map of errors with stack traces showing when the source was updated, keyed by the stack trace */
+	updated?: Map<string, { error: Error; count: number }> | null;
 	/**
 	 * Whether or not the source was set while running an effect — if so, we need to
 	 * increment the write version so that it shows up as dirty when the effect re-runs
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 6c4d92bbad..306b9b9dd9 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -42,13 +42,7 @@ import {
 	set_dev_stack
 } from './context.js';
 import * as w from './warnings.js';
-import {
-	Batch,
-	batch_deriveds,
-	dev_effect_stack,
-	flushSync,
-	schedule_effect
-} from './reactivity/batch.js';
+import { Batch, batch_deriveds, flushSync, schedule_effect } from './reactivity/batch.js';
 import { handle_error } from './error-handling.js';
 import { UNINITIALIZED } from '../../constants.js';
 
@@ -491,10 +485,6 @@ export function update_effect(effect) {
 				}
 			}
 		}
-
-		if (DEV) {
-			dev_effect_stack.push(effect);
-		}
 	} finally {
 		is_updating_effect = was_updating_effect;
 		active_effect = previous_effect;
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/_config.js b/packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/_config.js
new file mode 100644
index 0000000000..400495050c
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/_config.js
@@ -0,0 +1,21 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client', 'hydrate'],
+
+	compileOptions: {
+		dev: true
+	},
+
+	test({ assert, errors }) {
+		const [button] = document.querySelectorAll('button');
+
+		try {
+			flushSync(() => button.click());
+		} catch (e) {
+			assert.equal(errors.length, 1); // for whatever reason we can't get the name which should be UpdatedAtError
+			assert.ok(/** @type {Error} */ (e).message.startsWith('effect_update_depth_exceeded'));
+		}
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/main.svelte b/packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/main.svelte
new file mode 100644
index 0000000000..ddb91a90ad
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/main.svelte
@@ -0,0 +1,12 @@
+<script>
+	let condition = $state(false);
+	let count = $state(0);
+
+	$effect(() => {
+		if (condition) {
+			count++;
+		}
+	});
+</script>
+
+<button onclick={() => condition = !condition}>toggle</button>
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-20/_config.js b/packages/svelte/tests/runtime-runes/samples/error-boundary-20/_config.js
index ccff614ade..e3a3b0c7d7 100644
--- a/packages/svelte/tests/runtime-runes/samples/error-boundary-20/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-20/_config.js
@@ -2,12 +2,14 @@ import { flushSync } from 'svelte';
 import { test } from '../../test';
 
 export default test({
-	test({ assert, target }) {
+	test({ assert, target, errors }) {
 		let btn = target.querySelector('button');
 
 		btn?.click();
 		flushSync();
 
+		assert.equal(errors.length, 1);
+
 		assert.htmlEqual(target.innerHTML, `<div class="error">An error occurred!</div>`);
 	}
 });

From fcfbc9cca0720d2d57cf6a594f099f568dedfe88 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Wed, 16 Jul 2025 20:01:58 -0400
Subject: [PATCH 084/148] Version Packages (#16406)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/six-swans-rush.md    | 5 -----
 .changeset/slimy-doors-fetch.md | 5 -----
 packages/svelte/CHANGELOG.md    | 8 ++++++++
 packages/svelte/package.json    | 2 +-
 packages/svelte/src/version.js  | 2 +-
 5 files changed, 10 insertions(+), 12 deletions(-)
 delete mode 100644 .changeset/six-swans-rush.md
 delete mode 100644 .changeset/slimy-doors-fetch.md

diff --git a/.changeset/six-swans-rush.md b/.changeset/six-swans-rush.md
deleted file mode 100644
index cfb5b97400..0000000000
--- a/.changeset/six-swans-rush.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: silence `$inspect` errors when the effect is about to be destroyed
diff --git a/.changeset/slimy-doors-fetch.md b/.changeset/slimy-doors-fetch.md
deleted file mode 100644
index 8dec24a98d..0000000000
--- a/.changeset/slimy-doors-fetch.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: more informative error when effects run in an infinite loop
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 6d4f31480d..56f91c395f 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,13 @@
 # svelte
 
+## 5.36.5
+
+### Patch Changes
+
+- fix: silence `$inspect` errors when the effect is about to be destroyed ([#16391](https://github.com/sveltejs/svelte/pull/16391))
+
+- fix: more informative error when effects run in an infinite loop ([#16405](https://github.com/sveltejs/svelte/pull/16405))
+
 ## 5.36.4
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 3e9022a091..2a1b3cf9e5 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.4",
+  "version": "5.36.5",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index f8d23b44b1..4d6811c409 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.4';
+export const VERSION = '5.36.5';
 export const PUBLIC_VERSION = '5';

From c56914d739d70c1ba444c2a4ac9df37db7a033cf Mon Sep 17 00:00:00 2001
From: Ben McCann <322311+benmccann@users.noreply.github.com>
Date: Wed, 16 Jul 2025 18:08:54 -0700
Subject: [PATCH 085/148] chore: upgrade to eslint-plugin-svelte 3 (#16407)

---
 eslint.config.js |   3 +-
 package.json     |   3 +-
 pnpm-lock.yaml   | 107 ++++++++++++++++++++++++-----------------------
 3 files changed, 58 insertions(+), 55 deletions(-)

diff --git a/eslint.config.js b/eslint.config.js
index 41d98fa428..b0f25bab03 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -80,7 +80,8 @@ export default [
 		files: ['packages/svelte/src/**/*'],
 		ignores: ['packages/svelte/src/compiler/**/*'],
 		rules: {
-			'custom/no_compiler_imports': 'error'
+			'custom/no_compiler_imports': 'error',
+			'svelte/no-svelte-internal': 'off'
 		}
 	},
 	{
diff --git a/package.json b/package.json
index 458bf34084..971bd020d1 100644
--- a/package.json
+++ b/package.json
@@ -27,12 +27,13 @@
   },
   "devDependencies": {
     "@changesets/cli": "^2.27.8",
-    "@sveltejs/eslint-config": "^8.1.0",
+    "@sveltejs/eslint-config": "^8.3.3",
     "@svitejs/changesets-changelog-github-compact": "^1.1.0",
     "@types/node": "^20.11.5",
     "@vitest/coverage-v8": "^2.1.9",
     "eslint": "^9.9.1",
     "eslint-plugin-lube": "^0.4.3",
+    "eslint-plugin-svelte": "^3.11.0",
     "jsdom": "25.0.1",
     "playwright": "^1.46.1",
     "prettier": "^3.2.4",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 5f902186ef..315d699e25 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -12,8 +12,8 @@ importers:
         specifier: ^2.27.8
         version: 2.27.8
       '@sveltejs/eslint-config':
-        specifier: ^8.1.0
-        version: 8.1.0(@stylistic/eslint-plugin-js@1.8.0(eslint@9.9.1))(eslint-config-prettier@9.1.0(eslint@9.9.1))(eslint-plugin-n@17.16.1(eslint@9.9.1)(typescript@5.5.4))(eslint-plugin-svelte@2.38.0(eslint@9.9.1)(svelte@packages+svelte))(eslint@9.9.1)(typescript-eslint@8.26.0(eslint@9.9.1)(typescript@5.5.4))(typescript@5.5.4)
+        specifier: ^8.3.3
+        version: 8.3.3(@stylistic/eslint-plugin-js@1.8.0(eslint@9.9.1))(eslint-config-prettier@9.1.0(eslint@9.9.1))(eslint-plugin-n@17.16.1(eslint@9.9.1)(typescript@5.5.4))(eslint-plugin-svelte@3.11.0(eslint@9.9.1)(svelte@packages+svelte))(eslint@9.9.1)(typescript-eslint@8.26.0(eslint@9.9.1)(typescript@5.5.4))(typescript@5.5.4)
       '@svitejs/changesets-changelog-github-compact':
         specifier: ^1.1.0
         version: 1.1.0
@@ -29,6 +29,9 @@ importers:
       eslint-plugin-lube:
         specifier: ^0.4.3
         version: 0.4.3
+      eslint-plugin-svelte:
+        specifier: ^3.11.0
+        version: 3.11.0(eslint@9.9.1)(svelte@packages+svelte)
       jsdom:
         specifier: 25.0.1
         version: 25.0.1
@@ -737,16 +740,16 @@ packages:
     peerDependencies:
       acorn: ^8.9.0
 
-  '@sveltejs/eslint-config@8.1.0':
-    resolution: {integrity: sha512-cfgp4lPREYBjNd4ZzaP/jA85ufm7vfXiaV7h9vILXNogne80IbZRNhRCQ8XoOqTAOY/pChIzWTBuR8aDNMbAEA==}
+  '@sveltejs/eslint-config@8.3.3':
+    resolution: {integrity: sha512-vkrQgEmhokFEOpuTo7NlVXJJMJJGNzxjmkQCTkHSwIOdzQSUukDIJ4038IjdcnIERSIlo4OpLAydWLx52BVyQA==}
     peerDependencies:
       '@stylistic/eslint-plugin-js': '>= 1'
       eslint: '>= 9'
       eslint-config-prettier: '>= 9'
       eslint-plugin-n: '>= 17'
-      eslint-plugin-svelte: '>= 2.36'
+      eslint-plugin-svelte: '>= 3'
       typescript: '>= 5'
-      typescript-eslint: '>= 7.5'
+      typescript-eslint: '>= 8'
 
   '@sveltejs/vite-plugin-svelte-inspector@3.0.0-next.2':
     resolution: {integrity: sha512-Yl9BWvEj+1j+8mICIAA04/Sx0wEHNL0n9pSIZFM8n4NWgLFmR3v41qX2k54J/r4LWE2YHTeNNH2WJqEUb3geEA==}
@@ -1209,24 +1212,24 @@ packages:
     peerDependencies:
       eslint: '>=8.23.0'
 
-  eslint-plugin-svelte@2.38.0:
-    resolution: {integrity: sha512-IwwxhHzitx3dr0/xo0z4jjDlb2AAHBPKt+juMyKKGTLlKi1rZfA4qixMwnveU20/JTHyipM6keX4Vr7LZFYc9g==}
-    engines: {node: ^14.17.0 || >=16.0.0}
+  eslint-plugin-svelte@3.11.0:
+    resolution: {integrity: sha512-KliWlkieHyEa65aQIkRwUFfHzT5Cn4u3BQQsu3KlkJOs7c1u7ryn84EWaOjEzilbKgttT4OfBURA8Uc4JBSQIw==}
+    engines: {node: ^18.18.0 || ^20.9.0 || >=21.1.0}
     peerDependencies:
-      eslint: ^7.0.0 || ^8.0.0-0 || ^9.0.0-0
-      svelte: ^3.37.0 || ^4.0.0 || ^5.0.0-next.112
+      eslint: ^8.57.1 || ^9.0.0
+      svelte: ^3.37.0 || ^4.0.0 || ^5.0.0
     peerDependenciesMeta:
       svelte:
         optional: true
 
-  eslint-scope@7.2.2:
-    resolution: {integrity: sha512-dOt21O7lTMhDM+X9mB4GX+DZrZtCUJPL/wlcTqxyrx5IvO0IYtILdtrQGQp+8n5S0gwSVmOf9NQrjMOgfQZlIg==}
-    engines: {node: ^12.22.0 || ^14.17.0 || >=16.0.0}
-
   eslint-scope@8.0.2:
     resolution: {integrity: sha512-6E4xmrTw5wtxnLA5wYL3WDfhZ/1bUBGOXV0zQvVRDOtrR8D0p6W7fs3JweNYhwRYeGvd/1CKX2se0/2s7Q/nJA==}
     engines: {node: ^18.18.0 || ^20.9.0 || >=21.1.0}
 
+  eslint-scope@8.4.0:
+    resolution: {integrity: sha512-sNXOfKCn74rt8RICKMvJS7XKV/Xk9kA7DyJr8mJik3S7Cwgy3qlkkmyS2uQB3jiJg6VNdZd/pDBJu0nvG2NlTg==}
+    engines: {node: ^18.18.0 || ^20.9.0 || >=21.1.0}
+
   eslint-visitor-keys@3.4.3:
     resolution: {integrity: sha512-wpc+LXeiyiisxPlEkUzU6svyS1frIO3Mgxj1fdy7Pm8Ygzguax2N3Fa/D/ag1WqbOprdI+uY6wMUl8/a2G+iag==}
     engines: {node: ^12.22.0 || ^14.17.0 || >=16.0.0}
@@ -1400,14 +1403,14 @@ packages:
     resolution: {integrity: sha512-oahGvuMGQlPw/ivIYBjVSrWAfWLBeku5tpPE2fOPLi+WHffIWbuh2tCjhyQhTBPMf5E9jDEH4FOmTYgYwbKwtQ==}
     engines: {node: '>=18'}
 
-  globals@15.14.0:
-    resolution: {integrity: sha512-OkToC372DtlQeje9/zHIo5CT8lRP/FUgEOKBEhU4e0abL7J7CD24fD9ohiLN5hagG/kWCYj4K5oaxxtj2Z0Dig==}
-    engines: {node: '>=18'}
-
   globals@15.15.0:
     resolution: {integrity: sha512-7ACyT3wmyp3I61S4fG682L0VA2RGD9otkqGJIwNUMF1SWUombIIk+af1unuDYgMm082aHYwD+mzJvv9Iu8dsgg==}
     engines: {node: '>=18'}
 
+  globals@16.3.0:
+    resolution: {integrity: sha512-bqWEnJ1Nt3neqx2q5SFfGS8r/ahumIakg3HcwtNlrVlwXIeNumWn/c7Pn/wKzGhf6SaW6H6uWXLqC30STCMchQ==}
+    engines: {node: '>=18'}
+
   globby@11.1.0:
     resolution: {integrity: sha512-jhIXaOzy1sb8IyocaruWSn1TjmnBVs8Ayhcy83rmxNJ8q2uWKCAj3CnJY+KpGSXCueAPc0i05kVvVKtP1t9S3g==}
     engines: {node: '>=10'}
@@ -1589,8 +1592,8 @@ packages:
     resolution: {integrity: sha512-o+NO+8WrRiQEE4/7nwRJhN1HWpVmJm511pBHUxPLtp0BUISzlBplORYSmTclCnJvQq2tKu/sgl3xVpkc7ZWuQQ==}
     engines: {node: '>=6'}
 
-  known-css-properties@0.30.0:
-    resolution: {integrity: sha512-VSWXYUnsPu9+WYKkfmJyLKtIvaRJi1kXUqVmBACORXZQxT5oZDsoZ2vQP+bQFDnWtpI/4eq3MLoRMjI2fnLzTQ==}
+  known-css-properties@0.37.0:
+    resolution: {integrity: sha512-JCDrsP4Z1Sb9JwG0aJ8Eo2r7k4Ou5MwmThS/6lcIe1ICyb7UBJKGRIUUdqc2ASdE/42lgz6zFUnzAIhtXnBVrQ==}
 
   levn@0.4.1:
     resolution: {integrity: sha512-+bT2uH4E5LGE7h/n3evcS/sQlJXCpIp6ym8OWJ5eV6+67Dsql/LaaT7qJBAt2rzfoa/5QBGBhxDix1dMt2kQKQ==}
@@ -1886,11 +1889,11 @@ packages:
       ts-node:
         optional: true
 
-  postcss-safe-parser@6.0.0:
-    resolution: {integrity: sha512-FARHN8pwH+WiS2OPCxJI8FuRJpTVnn6ZNFiqAM2aeW2LwTHWWmWgIyKC6cUo0L8aeKiF/14MNvnpls6R2PBeMQ==}
-    engines: {node: '>=12.0'}
+  postcss-safe-parser@7.0.1:
+    resolution: {integrity: sha512-0AioNCJZ2DPYz5ABT6bddIqlhgwhpHZ/l65YAYo0BCIn0xiDpsnTHz0gnoTGk0OXZW0JRs+cDwL8u/teRdz+8A==}
+    engines: {node: '>=18.0'}
     peerDependencies:
-      postcss: ^8.3.3
+      postcss: ^8.4.31
 
   postcss-scss@4.0.9:
     resolution: {integrity: sha512-AjKOeiwAitL/MXxQW2DliT28EKukvvbEWx3LBmJIRN8KfBGZbRTxNYW0kSqi1COiTZ57nZ9NW06S6ux//N1c9A==}
@@ -1898,8 +1901,8 @@ packages:
     peerDependencies:
       postcss: ^8.4.29
 
-  postcss-selector-parser@6.1.2:
-    resolution: {integrity: sha512-Q8qQfPiZ+THO/3ZrOrO0cJJKfpYCagtMUkXbnEfmgUjwXg6z/WBeOyS9APBBPCTSiDV+s4SwQGu8yFsiMRIudg==}
+  postcss-selector-parser@7.1.0:
+    resolution: {integrity: sha512-8sLjZwK0R+JlxlYcTuVnyT2v+htpdrjDOKuMcOVdYjt52Lh8hWRYpxBPoKx/Zg+bcjc3wx6fmQevMmUztS/ccA==}
     engines: {node: '>=4'}
 
   postcss@8.5.3:
@@ -2121,9 +2124,9 @@ packages:
     resolution: {integrity: sha512-ot0WnXS9fgdkgIcePe6RHNk1WA8+muPa6cSjeR3V8K27q9BB1rTE3R1p7Hv0z1ZyAc8s6Vvv8DIyWf681MAt0w==}
     engines: {node: '>= 0.4'}
 
-  svelte-eslint-parser@0.43.0:
-    resolution: {integrity: sha512-GpU52uPKKcVnh8tKN5P4UZpJ/fUDndmq7wfsvoVXsyP+aY0anol7Yqo01fyrlaWGMFfm4av5DyrjlaXdLRJvGA==}
-    engines: {node: ^12.22.0 || ^14.17.0 || >=16.0.0}
+  svelte-eslint-parser@1.3.0:
+    resolution: {integrity: sha512-VCgMHKV7UtOGcGLGNFSbmdm6kEKjtzo5nnpGU/mnx4OsFY6bZ7QwRF5DUx+Hokw5Lvdyo8dpk8B1m8mliomrNg==}
+    engines: {node: ^18.18.0 || ^20.9.0 || >=21.1.0}
     peerDependencies:
       svelte: ^3.37.0 || ^4.0.0 || ^5.0.0
     peerDependenciesMeta:
@@ -2998,14 +3001,14 @@ snapshots:
     dependencies:
       acorn: 8.14.0
 
-  '@sveltejs/eslint-config@8.1.0(@stylistic/eslint-plugin-js@1.8.0(eslint@9.9.1))(eslint-config-prettier@9.1.0(eslint@9.9.1))(eslint-plugin-n@17.16.1(eslint@9.9.1)(typescript@5.5.4))(eslint-plugin-svelte@2.38.0(eslint@9.9.1)(svelte@packages+svelte))(eslint@9.9.1)(typescript-eslint@8.26.0(eslint@9.9.1)(typescript@5.5.4))(typescript@5.5.4)':
+  '@sveltejs/eslint-config@8.3.3(@stylistic/eslint-plugin-js@1.8.0(eslint@9.9.1))(eslint-config-prettier@9.1.0(eslint@9.9.1))(eslint-plugin-n@17.16.1(eslint@9.9.1)(typescript@5.5.4))(eslint-plugin-svelte@3.11.0(eslint@9.9.1)(svelte@packages+svelte))(eslint@9.9.1)(typescript-eslint@8.26.0(eslint@9.9.1)(typescript@5.5.4))(typescript@5.5.4)':
     dependencies:
       '@stylistic/eslint-plugin-js': 1.8.0(eslint@9.9.1)
       eslint: 9.9.1
       eslint-config-prettier: 9.1.0(eslint@9.9.1)
       eslint-plugin-n: 17.16.1(eslint@9.9.1)(typescript@5.5.4)
-      eslint-plugin-svelte: 2.38.0(eslint@9.9.1)(svelte@packages+svelte)
-      globals: 15.14.0
+      eslint-plugin-svelte: 3.11.0(eslint@9.9.1)(svelte@packages+svelte)
+      globals: 15.15.0
       typescript: 5.5.4
       typescript-eslint: 8.26.0(eslint@9.9.1)(typescript@5.5.4)
 
@@ -3125,7 +3128,7 @@ snapshots:
       fast-glob: 3.3.2
       is-glob: 4.0.3
       minimatch: 9.0.5
-      semver: 7.7.1
+      semver: 7.7.2
       ts-api-utils: 2.0.1(typescript@5.5.4)
       typescript: 5.5.4
     transitivePeerDependencies:
@@ -3532,33 +3535,30 @@ snapshots:
       - supports-color
       - typescript
 
-  eslint-plugin-svelte@2.38.0(eslint@9.9.1)(svelte@packages+svelte):
+  eslint-plugin-svelte@3.11.0(eslint@9.9.1)(svelte@packages+svelte):
     dependencies:
       '@eslint-community/eslint-utils': 4.7.0(eslint@9.9.1)
       '@jridgewell/sourcemap-codec': 1.5.0
-      debug: 4.4.0
       eslint: 9.9.1
-      eslint-compat-utils: 0.5.1(eslint@9.9.1)
       esutils: 2.0.3
-      known-css-properties: 0.30.0
+      globals: 16.3.0
+      known-css-properties: 0.37.0
       postcss: 8.5.3
       postcss-load-config: 3.1.4(postcss@8.5.3)
-      postcss-safe-parser: 6.0.0(postcss@8.5.3)
-      postcss-selector-parser: 6.1.2
+      postcss-safe-parser: 7.0.1(postcss@8.5.3)
       semver: 7.7.2
-      svelte-eslint-parser: 0.43.0(svelte@packages+svelte)
+      svelte-eslint-parser: 1.3.0(svelte@packages+svelte)
     optionalDependencies:
       svelte: link:packages/svelte
     transitivePeerDependencies:
-      - supports-color
       - ts-node
 
-  eslint-scope@7.2.2:
+  eslint-scope@8.0.2:
     dependencies:
       esrecurse: 4.3.0
       estraverse: 5.3.0
 
-  eslint-scope@8.0.2:
+  eslint-scope@8.4.0:
     dependencies:
       esrecurse: 4.3.0
       estraverse: 5.3.0
@@ -3769,10 +3769,10 @@ snapshots:
 
   globals@14.0.0: {}
 
-  globals@15.14.0: {}
-
   globals@15.15.0: {}
 
+  globals@16.3.0: {}
+
   globby@11.1.0:
     dependencies:
       array-union: 2.1.0
@@ -3971,7 +3971,7 @@ snapshots:
 
   kleur@4.1.5: {}
 
-  known-css-properties@0.30.0: {}
+  known-css-properties@0.37.0: {}
 
   levn@0.4.1:
     dependencies:
@@ -4209,7 +4209,7 @@ snapshots:
     optionalDependencies:
       postcss: 8.5.3
 
-  postcss-safe-parser@6.0.0(postcss@8.5.3):
+  postcss-safe-parser@7.0.1(postcss@8.5.3):
     dependencies:
       postcss: 8.5.3
 
@@ -4217,7 +4217,7 @@ snapshots:
     dependencies:
       postcss: 8.5.3
 
-  postcss-selector-parser@6.1.2:
+  postcss-selector-parser@7.1.0:
     dependencies:
       cssesc: 3.0.0
       util-deprecate: 1.0.2
@@ -4442,13 +4442,14 @@ snapshots:
 
   supports-preserve-symlinks-flag@1.0.0: {}
 
-  svelte-eslint-parser@0.43.0(svelte@packages+svelte):
+  svelte-eslint-parser@1.3.0(svelte@packages+svelte):
     dependencies:
-      eslint-scope: 7.2.2
-      eslint-visitor-keys: 3.4.3
-      espree: 9.6.1
+      eslint-scope: 8.4.0
+      eslint-visitor-keys: 4.2.0
+      espree: 10.1.0
       postcss: 8.5.3
       postcss-scss: 4.0.9(postcss@8.5.3)
+      postcss-selector-parser: 7.1.0
     optionalDependencies:
       svelte: link:packages/svelte
 

From b17557cd91a223a060041300a4761574d7f94e6e Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 16 Jul 2025 21:14:55 -0400
Subject: [PATCH 086/148] docs: fix typo (#16408)

---
 documentation/docs/02-runes/02-$state.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/documentation/docs/02-runes/02-$state.md b/documentation/docs/02-runes/02-$state.md
index aea427a8ec..e67206b535 100644
--- a/documentation/docs/02-runes/02-$state.md
+++ b/documentation/docs/02-runes/02-$state.md
@@ -119,7 +119,7 @@ class Todo {
 }
 ```
 
-> [NOTE!] Svelte provides reactive implementations of built-in classes like `Set` and `Map` that can be imported from [`svelte/reactivity`](svelte-reactivity).
+> [!NOTE] Svelte provides reactive implementations of built-in classes like `Set` and `Map` that can be imported from [`svelte/reactivity`](svelte-reactivity).
 
 ## `$state.raw`
 

From e5e6c0cd129c30bd2f02dabf5c1ab3edaae9bb8f Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 16 Jul 2025 21:53:40 -0400
Subject: [PATCH 087/148] fix docs (#16409)

* fix docs

* oops

* another

* gah
---
 documentation/docs/02-runes/03-$derived.md                  | 4 ++++
 documentation/docs/98-reference/.generated/client-errors.md | 4 ++--
 packages/svelte/messages/client-errors/errors.md            | 4 ++--
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/documentation/docs/02-runes/03-$derived.md b/documentation/docs/02-runes/03-$derived.md
index 5f253cf6d1..0123868c4e 100644
--- a/documentation/docs/02-runes/03-$derived.md
+++ b/documentation/docs/02-runes/03-$derived.md
@@ -99,12 +99,16 @@ let selected = $derived(items[index]);
 If you use destructuring with a `$derived` declaration, the resulting variables will all be reactive — this...
 
 ```js
+function stuff() { return { a: 1, b: 2, c: 3 } }
+// ---cut---
 let { a, b, c } = $derived(stuff());
 ```
 
 ...is roughly equivalent to this:
 
 ```js
+function stuff() { return { a: 1, b: 2, c: 3 } }
+// ---cut---
 let _stuff = $derived(stuff());
 let a = $derived(_stuff.a);
 let b = $derived(_stuff.b);
diff --git a/documentation/docs/98-reference/.generated/client-errors.md b/documentation/docs/98-reference/.generated/client-errors.md
index 3b17ef9f9b..4d1de435fe 100644
--- a/documentation/docs/98-reference/.generated/client-errors.md
+++ b/documentation/docs/98-reference/.generated/client-errors.md
@@ -109,10 +109,10 @@ $effect(() => {
 The same applies to array mutations, since these both read and write to the array:
 
 ```js
-let array = $state([]);
+let array = $state(['hello']);
 
 $effect(() => {
-	array.push('hello');
+	array.push('goodbye');
 });
 ```
 
diff --git a/packages/svelte/messages/client-errors/errors.md b/packages/svelte/messages/client-errors/errors.md
index d6af859881..a30bdd7593 100644
--- a/packages/svelte/messages/client-errors/errors.md
+++ b/packages/svelte/messages/client-errors/errors.md
@@ -79,10 +79,10 @@ $effect(() => {
 The same applies to array mutations, since these both read and write to the array:
 
 ```js
-let array = $state([]);
+let array = $state(['hello']);
 
 $effect(() => {
-	array.push('hello');
+	array.push('goodbye');
 });
 ```
 

From b8b662a1ad74d54891fd854962e92d5aa3d72fe3 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 16 Jul 2025 22:02:02 -0400
Subject: [PATCH 088/148] docs: make link to svelte/reactivity more prominent
 (#16410)

---
 documentation/docs/02-runes/02-$state.md | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/documentation/docs/02-runes/02-$state.md b/documentation/docs/02-runes/02-$state.md
index e67206b535..741e24fde0 100644
--- a/documentation/docs/02-runes/02-$state.md
+++ b/documentation/docs/02-runes/02-$state.md
@@ -119,7 +119,9 @@ class Todo {
 }
 ```
 
-> [!NOTE] Svelte provides reactive implementations of built-in classes like `Set` and `Map` that can be imported from [`svelte/reactivity`](svelte-reactivity).
+### Built-in classes
+
+Svelte provides reactive implementations of built-in classes like `Set`, `Map`, `Date` and `URL` that can be imported from [`svelte/reactivity`](svelte-reactivity).
 
 ## `$state.raw`
 

From 9e1e7139fb406e6ac94cf5fda99d04e6642aa522 Mon Sep 17 00:00:00 2001
From: Ray Thurn Void <53383860+raythurnvoid@users.noreply.github.com>
Date: Thu, 17 Jul 2025 09:41:21 +0100
Subject: [PATCH 089/148] fix: robustify reset calls in error boundaries
 (#16171)

Fixes #16134

* Add a warning when the misuse of `reset` in an `error:boundary` causes an error to be thrown when flushing the boundary content

* Prevent uncaught errors to make test fails when they are expected and are fired during template effects flush

* reset should just be a noop after the first call

* correctly handle errors inside boundary during reset

* handle errors in the correct boundary

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
---
 .changeset/new-dogs-obey.md                   |  5 ++
 .changeset/polite-toys-report.md              |  5 ++
 .../98-reference/.generated/client-errors.md  | 20 +++++
 .../.generated/client-warnings.md             | 26 +++++++
 .../svelte/messages/client-errors/errors.md   | 18 +++++
 .../messages/client-warnings/warnings.md      | 24 ++++++
 .../internal/client/dom/blocks/boundary.js    | 73 +++++++++++++------
 .../src/internal/client/error-handling.js     |  4 +-
 packages/svelte/src/internal/client/errors.js | 16 ++++
 .../svelte/src/internal/client/warnings.js    | 11 +++
 .../svelte/tests/runtime-legacy/shared.ts     |  7 +-
 .../error-boundary-reset-onerror/_config.js   | 15 ++++
 .../error-boundary-reset-onerror/main.svelte  | 17 +++++
 .../error-boundary-reset-premature/_config.js | 28 +++++++
 .../main.svelte                               | 26 +++++++
 .../_config.js                                | 27 +++++++
 .../main.svelte                               | 20 +++++
 17 files changed, 315 insertions(+), 27 deletions(-)
 create mode 100644 .changeset/new-dogs-obey.md
 create mode 100644 .changeset/polite-toys-report.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/error-boundary-reset-onerror/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/error-boundary-reset-onerror/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/error-boundary-reset-premature/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/error-boundary-reset-premature/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/error-boundary-reset-with-error/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/error-boundary-reset-with-error/main.svelte

diff --git a/.changeset/new-dogs-obey.md b/.changeset/new-dogs-obey.md
new file mode 100644
index 0000000000..aa9a3d73b9
--- /dev/null
+++ b/.changeset/new-dogs-obey.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: handle error in correct boundary after reset
diff --git a/.changeset/polite-toys-report.md b/.changeset/polite-toys-report.md
new file mode 100644
index 0000000000..bf5386e069
--- /dev/null
+++ b/.changeset/polite-toys-report.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: make `<svelte:boundary>` reset function a noop after the first call
diff --git a/documentation/docs/98-reference/.generated/client-errors.md b/documentation/docs/98-reference/.generated/client-errors.md
index 4d1de435fe..8fdb7770aa 100644
--- a/documentation/docs/98-reference/.generated/client-errors.md
+++ b/documentation/docs/98-reference/.generated/client-errors.md
@@ -238,3 +238,23 @@ let odd = $derived(!even);
 ```
 
 If side-effects are unavoidable, use [`$effect`]($effect) instead.
+
+### svelte_boundary_reset_onerror
+
+```
+A `<svelte:boundary>` `reset` function cannot be called while an error is still being handled
+```
+
+If a [`<svelte:boundary>`](https://svelte.dev/docs/svelte/svelte-boundary) has an `onerror` function, it must not call the provided `reset` function synchronously since the boundary is still in a broken state. Typically, `reset()` is called later, once the error has been resolved.
+
+If it's possible to resolve the error inside the `onerror` callback, you must at least wait for the boundary to settle before calling `reset()`, for example using [`tick`](https://svelte.dev/docs/svelte/lifecycle-hooks#tick):
+
+```svelte
+<svelte:boundary onerror={async (error, reset) => {
+	fixTheError();
+	+++await tick();+++
+	reset();
+}}>
+
+</svelte:boundary>
+```
diff --git a/documentation/docs/98-reference/.generated/client-warnings.md b/documentation/docs/98-reference/.generated/client-warnings.md
index 7548428e97..6f1d677fe9 100644
--- a/documentation/docs/98-reference/.generated/client-warnings.md
+++ b/documentation/docs/98-reference/.generated/client-warnings.md
@@ -312,6 +312,32 @@ Reactive `$state(...)` proxies and the values they proxy have different identiti
 
 To resolve this, ensure you're comparing values where both values were created with `$state(...)`, or neither were. Note that `$state.raw(...)` will _not_ create a state proxy.
 
+### svelte_boundary_reset_noop
+
+```
+A `<svelte:boundary>` `reset` function only resets the boundary the first time it is called
+```
+
+When an error occurs while rendering the contents of a [`<svelte:boundary>`](https://svelte.dev/docs/svelte/svelte-boundary), the `onerror` handler is called with the error plus a `reset` function that attempts to re-render the contents.
+
+This `reset` function should only be called once. After that, it has no effect — in a case like this, where a reference to `reset` is stored outside the boundary, clicking the button while `<Contents />` is rendered will _not_ cause the contents to be rendered again.
+
+```svelte
+<script>
+	let reset;
+</script>
+
+<button onclick={reset}>reset</button>
+
+<svelte:boundary onerror={(e, r) => (reset = r)}>
+	<!-- contents -->
+
+	{#snippet failed(e)}
+		<p>oops! {e.message}</p>
+	{/snippet}
+</svelte:boundary>
+```
+
 ### transition_slide_display
 
 ```
diff --git a/packages/svelte/messages/client-errors/errors.md b/packages/svelte/messages/client-errors/errors.md
index a30bdd7593..57ecca0489 100644
--- a/packages/svelte/messages/client-errors/errors.md
+++ b/packages/svelte/messages/client-errors/errors.md
@@ -184,3 +184,21 @@ let odd = $derived(!even);
 ```
 
 If side-effects are unavoidable, use [`$effect`]($effect) instead.
+
+## svelte_boundary_reset_onerror
+
+> A `<svelte:boundary>` `reset` function cannot be called while an error is still being handled
+
+If a [`<svelte:boundary>`](https://svelte.dev/docs/svelte/svelte-boundary) has an `onerror` function, it must not call the provided `reset` function synchronously since the boundary is still in a broken state. Typically, `reset()` is called later, once the error has been resolved.
+
+If it's possible to resolve the error inside the `onerror` callback, you must at least wait for the boundary to settle before calling `reset()`, for example using [`tick`](https://svelte.dev/docs/svelte/lifecycle-hooks#tick):
+
+```svelte
+<svelte:boundary onerror={async (error, reset) => {
+	fixTheError();
+	+++await tick();+++
+	reset();
+}}>
+
+</svelte:boundary>
+```
diff --git a/packages/svelte/messages/client-warnings/warnings.md b/packages/svelte/messages/client-warnings/warnings.md
index 13d9bfcd3b..123c6833e6 100644
--- a/packages/svelte/messages/client-warnings/warnings.md
+++ b/packages/svelte/messages/client-warnings/warnings.md
@@ -272,6 +272,30 @@ To silence the warning, ensure that `value`:
 
 To resolve this, ensure you're comparing values where both values were created with `$state(...)`, or neither were. Note that `$state.raw(...)` will _not_ create a state proxy.
 
+## svelte_boundary_reset_noop
+
+> A `<svelte:boundary>` `reset` function only resets the boundary the first time it is called
+
+When an error occurs while rendering the contents of a [`<svelte:boundary>`](https://svelte.dev/docs/svelte/svelte-boundary), the `onerror` handler is called with the error plus a `reset` function that attempts to re-render the contents.
+
+This `reset` function should only be called once. After that, it has no effect — in a case like this, where a reference to `reset` is stored outside the boundary, clicking the button while `<Contents />` is rendered will _not_ cause the contents to be rendered again.
+
+```svelte
+<script>
+	let reset;
+</script>
+
+<button onclick={reset}>reset</button>
+
+<svelte:boundary onerror={(e, r) => (reset = r)}>
+	<!-- contents -->
+
+	{#snippet failed(e)}
+		<p>oops! {e.message}</p>
+	{/snippet}
+</svelte:boundary>
+```
+
 ## transition_slide_display
 
 > The `slide` transition does not work correctly for elements with `display: %value%`
diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 5e678ab113..4ea137bfa8 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -1,7 +1,12 @@
 /** @import { Effect, Source, TemplateNode, } from '#client' */
-import { BOUNDARY_EFFECT, EFFECT_PRESERVED, EFFECT_TRANSPARENT } from '#client/constants';
+import {
+	BOUNDARY_EFFECT,
+	EFFECT_PRESERVED,
+	EFFECT_RAN,
+	EFFECT_TRANSPARENT
+} from '#client/constants';
 import { component_context, set_component_context } from '../../context.js';
-import { invoke_error_boundary } from '../../error-handling.js';
+import { handle_error, invoke_error_boundary } from '../../error-handling.js';
 import { block, branch, destroy_effect, pause_effect } from '../../reactivity/effects.js';
 import {
 	active_effect,
@@ -21,6 +26,7 @@ import {
 import { get_next_sibling } from '../operations.js';
 import { queue_micro_task } from '../task.js';
 import * as e from '../../errors.js';
+import * as w from '../../warnings.js';
 import { DEV } from 'esm-env';
 import { Batch, effect_pending_updates } from '../../reactivity/batch.js';
 import { internal_set, source } from '../../reactivity/sources.js';
@@ -196,6 +202,9 @@ export class Boundary {
 
 		try {
 			return fn();
+		} catch (e) {
+			handle_error(e);
+			return null;
 		} finally {
 			set_active_effect(previous_effect);
 			set_active_reaction(previous_reaction);
@@ -257,7 +266,42 @@ export class Boundary {
 		var onerror = this.#props.onerror;
 		let failed = this.#props.failed;
 
+		if (this.#main_effect) {
+			destroy_effect(this.#main_effect);
+			this.#main_effect = null;
+		}
+
+		if (this.#pending_effect) {
+			destroy_effect(this.#pending_effect);
+			this.#pending_effect = null;
+		}
+
+		if (this.#failed_effect) {
+			destroy_effect(this.#failed_effect);
+			this.#failed_effect = null;
+		}
+
+		if (hydrating) {
+			set_hydrate_node(this.#hydrate_open);
+			next();
+			set_hydrate_node(remove_nodes());
+		}
+
+		var did_reset = false;
+		var calling_on_error = false;
+
 		const reset = () => {
+			if (did_reset) {
+				w.svelte_boundary_reset_noop();
+				return;
+			}
+
+			did_reset = true;
+
+			if (calling_on_error) {
+				e.svelte_boundary_reset_onerror();
+			}
+
 			this.#pending_count = 0;
 
 			if (this.#failed_effect !== null) {
@@ -290,32 +334,15 @@ export class Boundary {
 
 		try {
 			set_active_reaction(null);
+			calling_on_error = true;
 			onerror?.(error, reset);
+			calling_on_error = false;
+		} catch (error) {
+			invoke_error_boundary(error, this.#effect && this.#effect.parent);
 		} finally {
 			set_active_reaction(previous_reaction);
 		}
 
-		if (this.#main_effect) {
-			destroy_effect(this.#main_effect);
-			this.#main_effect = null;
-		}
-
-		if (this.#pending_effect) {
-			destroy_effect(this.#pending_effect);
-			this.#pending_effect = null;
-		}
-
-		if (this.#failed_effect) {
-			destroy_effect(this.#failed_effect);
-			this.#failed_effect = null;
-		}
-
-		if (hydrating) {
-			set_hydrate_node(this.#hydrate_open);
-			next();
-			set_hydrate_node(remove_nodes());
-		}
-
 		if (failed) {
 			queue_micro_task(() => {
 				this.#failed_effect = this.#run(() => {
diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index a512839181..6c83a453d5 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -53,7 +53,9 @@ export function invoke_error_boundary(error, effect) {
 			try {
 				/** @type {Boundary} */ (effect.b).error(error);
 				return;
-			} catch {}
+			} catch (e) {
+				error = e;
+			}
 		}
 
 		effect = effect.parent;
diff --git a/packages/svelte/src/internal/client/errors.js b/packages/svelte/src/internal/client/errors.js
index edd66a7400..937971da5e 100644
--- a/packages/svelte/src/internal/client/errors.js
+++ b/packages/svelte/src/internal/client/errors.js
@@ -423,4 +423,20 @@ export function state_unsafe_mutation() {
 	} else {
 		throw new Error(`https://svelte.dev/e/state_unsafe_mutation`);
 	}
+}
+
+/**
+ * A `<svelte:boundary>` `reset` function cannot be called while an error is still being handled
+ * @returns {never}
+ */
+export function svelte_boundary_reset_onerror() {
+	if (DEV) {
+		const error = new Error(`svelte_boundary_reset_onerror\nA \`<svelte:boundary>\` \`reset\` function cannot be called while an error is still being handled\nhttps://svelte.dev/e/svelte_boundary_reset_onerror`);
+
+		error.name = 'Svelte error';
+
+		throw error;
+	} else {
+		throw new Error(`https://svelte.dev/e/svelte_boundary_reset_onerror`);
+	}
 }
\ No newline at end of file
diff --git a/packages/svelte/src/internal/client/warnings.js b/packages/svelte/src/internal/client/warnings.js
index dfd50a8722..dfa2a3752e 100644
--- a/packages/svelte/src/internal/client/warnings.js
+++ b/packages/svelte/src/internal/client/warnings.js
@@ -224,6 +224,17 @@ export function state_proxy_equality_mismatch(operator) {
 	}
 }
 
+/**
+ * A `<svelte:boundary>` `reset` function only resets the boundary the first time it is called
+ */
+export function svelte_boundary_reset_noop() {
+	if (DEV) {
+		console.warn(`%c[svelte] svelte_boundary_reset_noop\n%cA \`<svelte:boundary>\` \`reset\` function only resets the boundary the first time it is called\nhttps://svelte.dev/e/svelte_boundary_reset_noop`, bold, normal);
+	} else {
+		console.warn(`https://svelte.dev/e/svelte_boundary_reset_noop`);
+	}
+}
+
 /**
  * The `slide` transition does not work correctly for elements with `display: %value%`
  * @param {string} value
diff --git a/packages/svelte/tests/runtime-legacy/shared.ts b/packages/svelte/tests/runtime-legacy/shared.ts
index 8d7b3544bc..05c1a982ec 100644
--- a/packages/svelte/tests/runtime-legacy/shared.ts
+++ b/packages/svelte/tests/runtime-legacy/shared.ts
@@ -489,10 +489,11 @@ async function run_test_variant(
 					'Expected component to unmount and leave nothing behind after it was destroyed'
 				);
 
-				// TODO: This seems useless, unhandledRejection is only triggered on the next task
-				// by which time the test has already finished and the next test resets it to null above
+				// uncaught errors like during template effects flush
 				if (unhandled_rejection) {
-					throw unhandled_rejection; // eslint-disable-line no-unsafe-finally
+					if (!config.expect_unhandled_rejections) {
+						throw unhandled_rejection; // eslint-disable-line no-unsafe-finally
+					}
 				}
 			}
 		}
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-onerror/_config.js b/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-onerror/_config.js
new file mode 100644
index 0000000000..092d7ad37d
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-onerror/_config.js
@@ -0,0 +1,15 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	test({ assert, target }) {
+		const btn = target.querySelector('button');
+
+		btn?.click();
+
+		assert.throws(flushSync, 'svelte_boundary_reset_onerror');
+
+		// boundary content empty; only button remains
+		assert.htmlEqual(target.innerHTML, `<button>trigger throw</button>`);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-onerror/main.svelte b/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-onerror/main.svelte
new file mode 100644
index 0000000000..f91048a9e7
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-onerror/main.svelte
@@ -0,0 +1,17 @@
+<script>
+	let must_throw = $state(false);
+
+	function throw_error() {
+		throw new Error("error on template render");
+	}
+</script>
+
+<svelte:boundary onerror={(_, reset) => reset()}>
+	{must_throw ? throw_error() : 'normal content'}
+
+	{#snippet failed()}
+		<div>err</div>
+	{/snippet}
+</svelte:boundary>
+
+<button onclick={() => must_throw = true}>trigger throw</button>
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-premature/_config.js b/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-premature/_config.js
new file mode 100644
index 0000000000..687961e721
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-premature/_config.js
@@ -0,0 +1,28 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `
+		normal content
+		<button>toggle</button>
+	`,
+
+	async test({ assert, target, warnings }) {
+		const [btn] = target.querySelectorAll('button');
+
+		flushSync(() => btn.click());
+		assert.htmlEqual(target.innerHTML, `<div>err</div><button>toggle</button>`);
+		assert.deepEqual(warnings, []);
+
+		flushSync(() => btn.click());
+		assert.htmlEqual(target.innerHTML, `normal content <button>toggle</button>`);
+		assert.deepEqual(warnings, []);
+
+		flushSync(() => btn.click());
+		assert.htmlEqual(target.innerHTML, `<div>err</div><button>toggle</button>`);
+
+		assert.deepEqual(warnings, [
+			'A `<svelte:boundary>` `reset` function only resets the boundary the first time it is called'
+		]);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-premature/main.svelte b/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-premature/main.svelte
new file mode 100644
index 0000000000..c1462eaf09
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-premature/main.svelte
@@ -0,0 +1,26 @@
+<script>
+	let must_throw = $state(false);
+	let reset = $state(null);
+
+	function throw_error() {
+		throw new Error("error on template render");
+	}
+</script>
+
+<svelte:boundary onerror={console.error}>
+	<svelte:boundary onerror={(_, fn) => (reset = fn)}>
+		{must_throw ? throw_error() : 'normal content'}
+
+		{#snippet failed()}
+			<div>err</div>
+		{/snippet}
+	</svelte:boundary>
+</svelte:boundary>
+
+<button
+	onclick={() => {
+		must_throw = !must_throw;
+		if (reset) reset();
+	}}>
+	toggle
+</button>
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-with-error/_config.js b/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-with-error/_config.js
new file mode 100644
index 0000000000..844e6981bd
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-with-error/_config.js
@@ -0,0 +1,27 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	test({ assert, target, warnings }) {
+		const [toggle] = target.querySelectorAll('button');
+
+		flushSync(() => toggle.click());
+		assert.htmlEqual(
+			target.innerHTML,
+			`<button>toggle</button><p>yikes!</p><button>reset</button>`
+		);
+
+		const [, reset] = target.querySelectorAll('button');
+		flushSync(() => reset.click());
+		assert.htmlEqual(
+			target.innerHTML,
+			`<button>toggle</button><p>yikes!</p><button>reset</button>`
+		);
+
+		flushSync(() => toggle.click());
+
+		const [, reset2] = target.querySelectorAll('button');
+		flushSync(() => reset2.click());
+		assert.htmlEqual(target.innerHTML, `<button>toggle</button><p>hello!</p>`);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-with-error/main.svelte b/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-with-error/main.svelte
new file mode 100644
index 0000000000..91479a631a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-reset-with-error/main.svelte
@@ -0,0 +1,20 @@
+<script>
+	let must_throw = $state(false);
+
+	function throw_error() {
+		throw new Error('yikes!');
+	}
+</script>
+
+<button onclick={() => must_throw = !must_throw}>toggle</button>
+
+<svelte:boundary>
+	<p>{must_throw ? throw_error() : 'hello!'}</p>
+
+	{#snippet failed(error, reset)}
+		<p>{error.message}</p>
+		<button onclick={reset}>reset</button>
+	{/snippet}
+</svelte:boundary>
+
+

From f3431709279df1311f591c1a6b47e4c0caa9b45e Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Thu, 17 Jul 2025 01:56:24 -0700
Subject: [PATCH 090/148] docs: fix `$effect.root` jsdoc formatting (#16411)

---
 packages/svelte/src/ambient.d.ts | 12 ++++++------
 packages/svelte/types/index.d.ts | 12 ++++++------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/packages/svelte/src/ambient.d.ts b/packages/svelte/src/ambient.d.ts
index 7c3b941ed1..ad32eaa56f 100644
--- a/packages/svelte/src/ambient.d.ts
+++ b/packages/svelte/src/ambient.d.ts
@@ -295,13 +295,13 @@ declare namespace $effect {
 	 *   let count = $state(0);
 	 *
 	 *   const cleanup = $effect.root(() => {
-	 *	    $effect(() => {
-	 *				console.log(count);
-	 *			})
+	 *     $effect(() => {
+	 *       console.log(count);
+	 *     })
 	 *
-	 *      return () => {
-	 *        console.log('effect root cleanup');
-	 * 			}
+	 *     return () => {
+	 *       console.log('effect root cleanup');
+	 *     }
 	 *   });
 	 * </script>
 	 *
diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index a8b769d6d4..9ea45af7e6 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -3369,13 +3369,13 @@ declare namespace $effect {
 	 *   let count = $state(0);
 	 *
 	 *   const cleanup = $effect.root(() => {
-	 *	    $effect(() => {
-	 *				console.log(count);
-	 *			})
+	 *     $effect(() => {
+	 *       console.log(count);
+	 *     })
 	 *
-	 *      return () => {
-	 *        console.log('effect root cleanup');
-	 * 			}
+	 *     return () => {
+	 *       console.log('effect root cleanup');
+	 *     }
 	 *   });
 	 * </script>
 	 *

From bdf6adb411cd5fd4f227778d87c116dd16c533d2 Mon Sep 17 00:00:00 2001
From: Paolo Ricciuti <ricciutipaolo@gmail.com>
Date: Thu, 17 Jul 2025 11:03:53 +0200
Subject: [PATCH 091/148] fix: delegate functions with shadowed variables if
 declared locally (#16417)

---
 .changeset/fast-parrots-draw.md               |  5 ++++
 .../phases/2-analyze/visitors/Attribute.js    |  9 ++++--
 .../_expected/client/index.svelte.js          | 28 +++++++++++++++++++
 .../_expected/server/index.svelte.js          | 13 +++++++++
 .../index.svelte                              | 12 ++++++++
 5 files changed, 65 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/fast-parrots-draw.md
 create mode 100644 packages/svelte/tests/snapshot/samples/delegated-locally-declared-shadowed/_expected/client/index.svelte.js
 create mode 100644 packages/svelte/tests/snapshot/samples/delegated-locally-declared-shadowed/_expected/server/index.svelte.js
 create mode 100644 packages/svelte/tests/snapshot/samples/delegated-locally-declared-shadowed/index.svelte

diff --git a/.changeset/fast-parrots-draw.md b/.changeset/fast-parrots-draw.md
new file mode 100644
index 0000000000..e56a35ff9b
--- /dev/null
+++ b/.changeset/fast-parrots-draw.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: delegate functions with shadowed variables if declared locally
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/Attribute.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/Attribute.js
index 773aa59744..b13f3f89b6 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/Attribute.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/Attribute.js
@@ -192,8 +192,13 @@ function get_delegated_event(event_name, handler, context) {
 			return unhoisted;
 		}
 
-		// If we are referencing a binding that is shadowed in another scope then bail out.
-		if (local_binding !== null && binding !== null && local_binding.node !== binding.node) {
+		// If we are referencing a binding that is shadowed in another scope then bail out (unless it's declared within the function).
+		if (
+			local_binding !== null &&
+			binding !== null &&
+			local_binding.node !== binding.node &&
+			scope.declarations.get(reference) !== binding
+		) {
 			return unhoisted;
 		}
 
diff --git a/packages/svelte/tests/snapshot/samples/delegated-locally-declared-shadowed/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/delegated-locally-declared-shadowed/_expected/client/index.svelte.js
new file mode 100644
index 0000000000..0d95d8d335
--- /dev/null
+++ b/packages/svelte/tests/snapshot/samples/delegated-locally-declared-shadowed/_expected/client/index.svelte.js
@@ -0,0 +1,28 @@
+import 'svelte/internal/disclose-version';
+import 'svelte/internal/flags/legacy';
+import * as $ from 'svelte/internal/client';
+
+var on_click = (e) => {
+	const index = Number(e.currentTarget.dataset.index);
+
+	console.log(index);
+};
+
+var root_1 = $.from_html(`<button type="button">B</button>`);
+
+export default function Delegated_locally_declared_shadowed($$anchor) {
+	var fragment = $.comment();
+	var node = $.first_child(fragment);
+
+	$.each(node, 0, () => ({ length: 1 }), $.index, ($$anchor, $$item, index) => {
+		var button = root_1();
+
+		$.set_attribute(button, 'data-index', index);
+		button.__click = [on_click];
+		$.append($$anchor, button);
+	});
+
+	$.append($$anchor, fragment);
+}
+
+$.delegate(['click']);
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/delegated-locally-declared-shadowed/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/delegated-locally-declared-shadowed/_expected/server/index.svelte.js
new file mode 100644
index 0000000000..e465af6f8b
--- /dev/null
+++ b/packages/svelte/tests/snapshot/samples/delegated-locally-declared-shadowed/_expected/server/index.svelte.js
@@ -0,0 +1,13 @@
+import * as $ from 'svelte/internal/server';
+
+export default function Delegated_locally_declared_shadowed($$payload) {
+	const each_array = $.ensure_array_like({ length: 1 });
+
+	$$payload.out += `<!--[-->`;
+
+	for (let index = 0, $$length = each_array.length; index < $$length; index++) {
+		$$payload.out += `<button type="button"${$.attr('data-index', index)}>B</button>`;
+	}
+
+	$$payload.out += `<!--]-->`;
+}
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/delegated-locally-declared-shadowed/index.svelte b/packages/svelte/tests/snapshot/samples/delegated-locally-declared-shadowed/index.svelte
new file mode 100644
index 0000000000..d870a6b270
--- /dev/null
+++ b/packages/svelte/tests/snapshot/samples/delegated-locally-declared-shadowed/index.svelte
@@ -0,0 +1,12 @@
+<script lang="ts"></script>
+
+{#each { length: 1 }, index}
+	<button
+		type="button"
+		data-index={index}
+		onclick={(e) => {
+			const index = Number(e.currentTarget.dataset.index)!;
+			console.log(index);
+		}}>B</button
+	>
+{/each}

From 65e524929661fefcdeaadfa8aa79cc06b26d9a76 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Thu, 17 Jul 2025 13:24:21 +0200
Subject: [PATCH 092/148] docs: remove mention of deprecated way to enhance
 typings (#16416)

Since #9070 it's prefered to use the "enhance svelte elements" way of doing things. That's so long ago that we can now remove the other option from the docs, and eventually remove the backwards compatibility that still allows the old way of doing things.
---
 documentation/docs/07-misc/03-typescript.md | 33 +++++++--------------
 packages/svelte/svelte-html.d.ts            |  1 +
 2 files changed, 11 insertions(+), 23 deletions(-)

diff --git a/documentation/docs/07-misc/03-typescript.md b/documentation/docs/07-misc/03-typescript.md
index ff33885fb8..49ecd8adb5 100644
--- a/documentation/docs/07-misc/03-typescript.md
+++ b/documentation/docs/07-misc/03-typescript.md
@@ -254,39 +254,24 @@ To declare that a variable expects the constructor or instance type of a compone
 
 Svelte provides a best effort of all the HTML DOM types that exist. Sometimes you may want to use experimental attributes or custom events coming from an action. In these cases, TypeScript will throw a type error, saying that it does not know these types. If it's a non-experimental standard attribute/event, this may very well be a missing typing from our [HTML typings](https://github.com/sveltejs/svelte/blob/main/packages/svelte/elements.d.ts). In that case, you are welcome to open an issue and/or a PR fixing it.
 
-In case this is a custom or experimental attribute/event, you can enhance the typings like this:
-
-```ts
-/// file: additional-svelte-typings.d.ts
-declare namespace svelteHTML {
-	// enhance elements
-	interface IntrinsicElements {
-		'my-custom-element': { someattribute: string; 'on:event': (e: CustomEvent<any>) => void };
-	}
-	// enhance attributes
-	interface HTMLAttributes<T> {
-		// If you want to use the beforeinstallprompt event
-		onbeforeinstallprompt?: (event: any) => any;
-		// If you want to use myCustomAttribute={..} (note: all lowercase)
-		mycustomattribute?: any; // You can replace any with something more specific if you like
-	}
-}
-```
-
-Then make sure that `d.ts` file is referenced in your `tsconfig.json`. If it reads something like `"include": ["src/**/*"]` and your `d.ts` file is inside `src`, it should work. You may need to reload for the changes to take effect.
-
-You can also declare the typings by augmenting the `svelte/elements` module like this:
+In case this is a custom or experimental attribute/event, you can enhance the typings by augmenting the `svelte/elements` module like this:
 
 ```ts
 /// file: additional-svelte-typings.d.ts
 import { HTMLButtonAttributes } from 'svelte/elements';
 
 declare module 'svelte/elements' {
+	// add a new element
 	export interface SvelteHTMLElements {
 		'custom-button': HTMLButtonAttributes;
 	}
 
-	// allows for more granular control over what element to add the typings to
+	// add a new global attribute that is available on all html elements
+	export interface HTMLAttributes<T> {
+		globalattribute?: string;
+	}
+
+	// add a new attribute for button elements
 	export interface HTMLButtonAttributes {
 		veryexperimentalattribute?: string;
 	}
@@ -294,3 +279,5 @@ declare module 'svelte/elements' {
 
 export {}; // ensure this is not an ambient module, else types will be overridden instead of augmented
 ```
+
+Then make sure that the `d.ts` file is referenced in your `tsconfig.json`. If it reads something like `"include": ["src/**/*"]` and your `d.ts` file is inside `src`, it should work. You may need to reload for the changes to take effect.
diff --git a/packages/svelte/svelte-html.d.ts b/packages/svelte/svelte-html.d.ts
index 5042eaa4b8..476b24e275 100644
--- a/packages/svelte/svelte-html.d.ts
+++ b/packages/svelte/svelte-html.d.ts
@@ -50,6 +50,7 @@ declare global {
 				? SVGElementTagNameMap[Key]
 				: any;
 
+		// TODO remove HTMLAttributes/SVGAttributes/IntrinsicElements in Svelte 6
 		// For backwards-compatibility and ease-of-use, in case someone enhanced the typings from import('svelte/elements').HTMLAttributes/SVGAttributes
 		// eslint-disable-next-line @typescript-eslint/no-unused-vars
 		interface HTMLAttributes<T extends EventTarget = any> {}

From 0ae1d5afffae954d6691b19b71531e0e287c5fa3 Mon Sep 17 00:00:00 2001
From: "Ahmad S." <navorite@gmail.com>
Date: Thu, 17 Jul 2025 14:25:01 +0300
Subject: [PATCH 093/148] chore: cleanup obselete stuff (#16412)

* Update vitest.config.js

* Update vitest.config.js

* cleanup

* woops

* Update eslint.config.js

---------

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
---
 .prettierignore       | 9 ---------
 .prettierrc           | 6 ------
 .vscode/settings.json | 3 ---
 eslint.config.js      | 6 +-----
 vitest.config.js      | 2 +-
 5 files changed, 2 insertions(+), 24 deletions(-)

diff --git a/.prettierignore b/.prettierignore
index 72cd10aca8..5e1d9b1aa7 100644
--- a/.prettierignore
+++ b/.prettierignore
@@ -28,15 +28,6 @@ packages/svelte/types
 packages/svelte/compiler/index.js
 playgrounds/sandbox/src/*
 
-# sites/svelte.dev
-sites/svelte.dev/static/svelte-app.json
-sites/svelte.dev/scripts/svelte-app/
-sites/svelte.dev/src/routes/_components/Supporters/contributors.jpg
-sites/svelte.dev/src/routes/_components/Supporters/contributors.js
-sites/svelte.dev/src/routes/_components/Supporters/donors.jpg
-sites/svelte.dev/src/routes/_components/Supporters/donors.js
-sites/svelte.dev/src/lib/generated
-
 **/node_modules
 **/.svelte-kit
 **/.vercel
diff --git a/.prettierrc b/.prettierrc
index c4fd5d9f2f..c2d09a4289 100644
--- a/.prettierrc
+++ b/.prettierrc
@@ -17,12 +17,6 @@
 				"useTabs": false,
 				"tabWidth": 2
 			}
-		},
-		{
-			"files": ["sites/svelte-5-preview/src/routes/docs/content/**/*.md"],
-			"options": {
-				"printWidth": 60
-			}
 		}
 	]
 }
diff --git a/.vscode/settings.json b/.vscode/settings.json
index 21a2a11c84..4d360cbc8a 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -1,6 +1,3 @@
 {
-	"search.exclude": {
-		"sites/svelte-5-preview/static/*": true
-	},
 	"typescript.tsdk": "node_modules/typescript/lib"
 }
diff --git a/eslint.config.js b/eslint.config.js
index b0f25bab03..5241cb43a6 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -103,11 +103,7 @@ export default [
 			'*.config.js',
 			// documentation can contain invalid examples
 			'documentation',
-			// contains a fork of the REPL which doesn't adhere to eslint rules
-			'sites/svelte-5-preview/**',
-			'tmp/**',
-			// wasn't checked previously, reenable at some point
-			'sites/svelte.dev/**'
+			'tmp/**'
 		]
 	}
 ];
diff --git a/vitest.config.js b/vitest.config.js
index caeda27e30..ba1edb355b 100644
--- a/vitest.config.js
+++ b/vitest.config.js
@@ -39,7 +39,7 @@ export default defineConfig({
 			provider: 'v8',
 			reporter: ['lcov', 'html'],
 			include: ['packages/svelte/src/**'],
-			reportsDirectory: 'sites/svelte-5-preview/static/coverage',
+			reportsDirectory: 'coverage',
 			reportOnFailure: true
 		}
 	}

From 6c9717a91f2f6ae10641d1cf502ba13d227fbe45 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Thu, 17 Jul 2025 07:26:50 -0400
Subject: [PATCH 094/148] Version Packages (#16418)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/fast-parrots-draw.md  |  5 -----
 .changeset/new-dogs-obey.md      |  5 -----
 .changeset/polite-toys-report.md |  5 -----
 packages/svelte/CHANGELOG.md     | 10 ++++++++++
 packages/svelte/package.json     |  2 +-
 packages/svelte/src/version.js   |  2 +-
 6 files changed, 12 insertions(+), 17 deletions(-)
 delete mode 100644 .changeset/fast-parrots-draw.md
 delete mode 100644 .changeset/new-dogs-obey.md
 delete mode 100644 .changeset/polite-toys-report.md

diff --git a/.changeset/fast-parrots-draw.md b/.changeset/fast-parrots-draw.md
deleted file mode 100644
index e56a35ff9b..0000000000
--- a/.changeset/fast-parrots-draw.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: delegate functions with shadowed variables if declared locally
diff --git a/.changeset/new-dogs-obey.md b/.changeset/new-dogs-obey.md
deleted file mode 100644
index aa9a3d73b9..0000000000
--- a/.changeset/new-dogs-obey.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: handle error in correct boundary after reset
diff --git a/.changeset/polite-toys-report.md b/.changeset/polite-toys-report.md
deleted file mode 100644
index bf5386e069..0000000000
--- a/.changeset/polite-toys-report.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: make `<svelte:boundary>` reset function a noop after the first call
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 56f91c395f..f78255e7fe 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,15 @@
 # svelte
 
+## 5.36.6
+
+### Patch Changes
+
+- fix: delegate functions with shadowed variables if declared locally ([#16417](https://github.com/sveltejs/svelte/pull/16417))
+
+- fix: handle error in correct boundary after reset ([#16171](https://github.com/sveltejs/svelte/pull/16171))
+
+- fix: make `<svelte:boundary>` reset function a noop after the first call ([#16171](https://github.com/sveltejs/svelte/pull/16171))
+
 ## 5.36.5
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 2a1b3cf9e5..aec8a34478 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.5",
+  "version": "5.36.6",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 4d6811c409..b0e4ebbab8 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.5';
+export const VERSION = '5.36.6';
 export const PUBLIC_VERSION = '5';

From 98fb1b1f8b95352c9882b653b45b230609fc95cf Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 17 Jul 2025 12:14:03 -0400
Subject: [PATCH 095/148] fix: allow instrinsic `<svelte:...>` elements to
 inherit from `SvelteHTMLElements` (#16424)

---
 .changeset/funny-masks-build.md  |  5 +++++
 packages/svelte/svelte-html.d.ts | 12 ------------
 2 files changed, 5 insertions(+), 12 deletions(-)
 create mode 100644 .changeset/funny-masks-build.md

diff --git a/.changeset/funny-masks-build.md b/.changeset/funny-masks-build.md
new file mode 100644
index 0000000000..07658e2540
--- /dev/null
+++ b/.changeset/funny-masks-build.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: allow instrinsic `<svelte:...>` elements to inherit from `SvelteHTMLElements`
diff --git a/packages/svelte/svelte-html.d.ts b/packages/svelte/svelte-html.d.ts
index 476b24e275..ebd58c8cc0 100644
--- a/packages/svelte/svelte-html.d.ts
+++ b/packages/svelte/svelte-html.d.ts
@@ -239,18 +239,6 @@ declare global {
 			use: HTMLProps<'use', SVGAttributes>;
 			view: HTMLProps<'view', SVGAttributes>;
 
-			// Svelte specific
-			'svelte:window': HTMLProps<'svelte:window', HTMLAttributes>;
-			'svelte:body': HTMLProps<'svelte:body', HTMLAttributes>;
-			'svelte:document': HTMLProps<'svelte:document', HTMLAttributes>;
-			'svelte:fragment': { slot?: string };
-			'svelte:head': { [name: string]: any };
-			'svelte:boundary': {
-				onerror?: (error: unknown, reset: () => void) => void;
-				failed?: import('svelte').Snippet<[error: unknown, reset: () => void]>;
-			};
-			// don't type svelte:options, it would override the types in svelte/elements and it isn't extendable anyway
-
 			[name: string]: { [name: string]: any };
 		}
 	}

From 93a8a495d2365c28588f2858da6bc197f40c3d4a Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Thu, 17 Jul 2025 12:21:43 -0400
Subject: [PATCH 096/148] Version Packages (#16426)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/funny-masks-build.md | 5 -----
 packages/svelte/CHANGELOG.md    | 6 ++++++
 packages/svelte/package.json    | 2 +-
 packages/svelte/src/version.js  | 2 +-
 4 files changed, 8 insertions(+), 7 deletions(-)
 delete mode 100644 .changeset/funny-masks-build.md

diff --git a/.changeset/funny-masks-build.md b/.changeset/funny-masks-build.md
deleted file mode 100644
index 07658e2540..0000000000
--- a/.changeset/funny-masks-build.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: allow instrinsic `<svelte:...>` elements to inherit from `SvelteHTMLElements`
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index f78255e7fe..a82d9ddefe 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,11 @@
 # svelte
 
+## 5.36.7
+
+### Patch Changes
+
+- fix: allow instrinsic `<svelte:...>` elements to inherit from `SvelteHTMLElements` ([#16424](https://github.com/sveltejs/svelte/pull/16424))
+
 ## 5.36.6
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index aec8a34478..83567a6123 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.6",
+  "version": "5.36.7",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index b0e4ebbab8..88cdc069a0 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.6';
+export const VERSION = '5.36.7';
 export const PUBLIC_VERSION = '5';

From c2da1ebb85d65ef044766d3f920cb935df65e359 Mon Sep 17 00:00:00 2001
From: Paolo Ricciuti <ricciutipaolo@gmail.com>
Date: Fri, 18 Jul 2025 18:07:06 +0200
Subject: [PATCH 097/148] fix: keep effect in the graph if it has an abort
 controller (#16430)

---
 .changeset/four-kings-drum.md                        |  5 +++++
 .../svelte/src/internal/client/reactivity/batch.js   |  4 +++-
 .../dependencyless-abort-signal/Component.svelte     |  8 ++++++++
 .../samples/dependencyless-abort-signal/_config.js   | 12 ++++++++++++
 .../samples/dependencyless-abort-signal/main.svelte  | 10 ++++++++++
 5 files changed, 38 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/four-kings-drum.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/dependencyless-abort-signal/Component.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/dependencyless-abort-signal/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/dependencyless-abort-signal/main.svelte

diff --git a/.changeset/four-kings-drum.md b/.changeset/four-kings-drum.md
new file mode 100644
index 0000000000..8c7343145e
--- /dev/null
+++ b/.changeset/four-kings-drum.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: keep effect in the graph if it has an abort controller
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index cdce971b18..ed82af94ed 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -532,7 +532,9 @@ function flush_queued_effects(effects) {
 				// here (rather than in `update_effect`) allows us to skip the work for
 				// immediate effects.
 				if (effect.deps === null && effect.first === null && effect.nodes_start === null) {
-					if (effect.teardown === null) {
+					// if there's no teardown or abort controller we completely unlink
+					// the effect from the graph
+					if (effect.teardown === null && effect.ac === null) {
 						// remove this effect from the graph
 						unlink_effect(effect);
 					} else {
diff --git a/packages/svelte/tests/runtime-runes/samples/dependencyless-abort-signal/Component.svelte b/packages/svelte/tests/runtime-runes/samples/dependencyless-abort-signal/Component.svelte
new file mode 100644
index 0000000000..b184e0e9b3
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/dependencyless-abort-signal/Component.svelte
@@ -0,0 +1,8 @@
+<script>
+	import { getAbortSignal } from 'svelte';
+
+	$effect(() => {
+		const signal = getAbortSignal()
+		signal.addEventListener('abort', () => console.log('abort'))
+	})
+</script>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/dependencyless-abort-signal/_config.js b/packages/svelte/tests/runtime-runes/samples/dependencyless-abort-signal/_config.js
new file mode 100644
index 0000000000..6eb4b06712
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/dependencyless-abort-signal/_config.js
@@ -0,0 +1,12 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target, logs }) {
+		const btn = target.querySelector('button');
+		flushSync(() => {
+			btn?.click();
+		});
+		assert.deepEqual(logs, ['abort']);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/dependencyless-abort-signal/main.svelte b/packages/svelte/tests/runtime-runes/samples/dependencyless-abort-signal/main.svelte
new file mode 100644
index 0000000000..99ea3fabb4
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/dependencyless-abort-signal/main.svelte
@@ -0,0 +1,10 @@
+<script>
+	import Component from './Component.svelte'
+
+	let show = $state(true)
+</script>
+
+<button onclick={() => (show = !show)}>click</button>
+{#if show}
+	<Component />
+{/if}

From f5db130e2d233564437d64430a9e54b8b8b6c52a Mon Sep 17 00:00:00 2001
From: Elliott Johnson <sejohnson@torchcloudconsulting.com>
Date: Fri, 18 Jul 2025 10:09:10 -0600
Subject: [PATCH 098/148] chore: Switch `payload.out` to an array (#16428)

* chore: Switch `payload.out` to an array

* Apply suggestions from code review

* changeset
---
 .changeset/old-dots-sin.md                    |  5 ++
 .../3-transform/server/visitors/EachBlock.js  |  4 +-
 .../3-transform/server/visitors/IfBlock.js    |  6 ++-
 .../server/visitors/shared/utils.js           | 38 +++++++++-----
 .../src/internal/server/blocks/snippet.js     |  8 +--
 packages/svelte/src/internal/server/dev.js    |  2 +-
 packages/svelte/src/internal/server/index.js  | 51 ++++++++++---------
 .../svelte/src/internal/server/payload.js     | 14 ++---
 .../_expected/server/index.svelte.js          |  4 +-
 .../_expected/server/index.svelte.js          |  4 +-
 .../_expected/server/index.svelte.js          |  6 +--
 .../_expected/server/main.svelte.js           |  2 +-
 .../_expected/server/index.svelte.js          |  6 +--
 .../_expected/server/index.svelte.js          |  6 +--
 .../_expected/server/index.svelte.js          |  2 +-
 .../_expected/server/index.svelte.js          |  2 +-
 .../_expected/server/index.svelte.js          |  2 +-
 .../hmr/_expected/server/index.svelte.js      |  2 +-
 .../_expected/server/index.svelte.js          |  2 +-
 .../purity/_expected/server/index.svelte.js   |  4 +-
 .../_expected/server/index.svelte.js          |  2 +-
 .../_expected/server/index.svelte.js          |  2 +-
 .../_expected/server/index.svelte.js          |  2 +-
 23 files changed, 103 insertions(+), 73 deletions(-)
 create mode 100644 .changeset/old-dots-sin.md

diff --git a/.changeset/old-dots-sin.md b/.changeset/old-dots-sin.md
new file mode 100644
index 0000000000..f7e2933897
--- /dev/null
+++ b/.changeset/old-dots-sin.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: Switch `payload.out` to an array
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/EachBlock.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/EachBlock.js
index ac6c9891a7..ee0086de2e 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/visitors/EachBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/visitors/EachBlock.js
@@ -44,12 +44,12 @@ export function EachBlock(node, context) {
 	);
 
 	if (node.fallback) {
-		const open = b.stmt(b.assignment('+=', b.id('$$payload.out'), block_open));
+		const open = b.stmt(b.call(b.member(b.id('$$payload.out'), b.id('push')), block_open));
 
 		const fallback = /** @type {BlockStatement} */ (context.visit(node.fallback));
 
 		fallback.body.unshift(
-			b.stmt(b.assignment('+=', b.id('$$payload.out'), b.literal(BLOCK_OPEN_ELSE)))
+			b.stmt(b.call(b.member(b.id('$$payload.out'), b.id('push')), b.literal(BLOCK_OPEN_ELSE)))
 		);
 
 		state.template.push(
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/IfBlock.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/IfBlock.js
index 508dcc0fdd..8c082f38d5 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/visitors/IfBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/visitors/IfBlock.js
@@ -17,10 +17,12 @@ export function IfBlock(node, context) {
 		? /** @type {BlockStatement} */ (context.visit(node.alternate))
 		: b.block([]);
 
-	consequent.body.unshift(b.stmt(b.assignment('+=', b.id('$$payload.out'), block_open)));
+	consequent.body.unshift(
+		b.stmt(b.call(b.member(b.id('$$payload.out'), b.id('push')), block_open))
+	);
 
 	alternate.body.unshift(
-		b.stmt(b.assignment('+=', b.id('$$payload.out'), b.literal(BLOCK_OPEN_ELSE)))
+		b.stmt(b.call(b.member(b.id('$$payload.out'), b.id('push')), b.literal(BLOCK_OPEN_ELSE)))
 	);
 
 	context.state.template.push(b.if(test, consequent, alternate), block_close);
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/utils.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/utils.js
index 8fcf8efa68..8a8633dd1a 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/utils.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/utils.js
@@ -96,10 +96,10 @@ function is_statement(node) {
 /**
  * @param {Array<Statement | Expression>} template
  * @param {Identifier} out
- * @param {AssignmentOperator} operator
+ * @param {AssignmentOperator | 'push'} operator
  * @returns {Statement[]}
  */
-export function build_template(template, out = b.id('$$payload.out'), operator = '+=') {
+export function build_template(template, out = b.id('$$payload.out'), operator = 'push') {
 	/** @type {string[]} */
 	let strings = [];
 
@@ -110,18 +110,32 @@ export function build_template(template, out = b.id('$$payload.out'), operator =
 	const statements = [];
 
 	const flush = () => {
-		statements.push(
-			b.stmt(
-				b.assignment(
-					operator,
-					out,
-					b.template(
-						strings.map((cooked, i) => b.quasi(cooked, i === strings.length - 1)),
-						expressions
+		if (operator === 'push') {
+			statements.push(
+				b.stmt(
+					b.call(
+						b.member(out, b.id('push')),
+						b.template(
+							strings.map((cooked, i) => b.quasi(cooked, i === strings.length - 1)),
+							expressions
+						)
 					)
 				)
-			)
-		);
+			);
+		} else {
+			statements.push(
+				b.stmt(
+					b.assignment(
+						operator,
+						out,
+						b.template(
+							strings.map((cooked, i) => b.quasi(cooked, i === strings.length - 1)),
+							expressions
+						)
+					)
+				)
+			);
+		}
 		strings = [];
 		expressions = [];
 	};
diff --git a/packages/svelte/src/internal/server/blocks/snippet.js b/packages/svelte/src/internal/server/blocks/snippet.js
index 9e96ae3430..bb82ca97d0 100644
--- a/packages/svelte/src/internal/server/blocks/snippet.js
+++ b/packages/svelte/src/internal/server/blocks/snippet.js
@@ -15,8 +15,10 @@ export function createRawSnippet(fn) {
 	// @ts-expect-error the types are a lie
 	return (/** @type {Payload} */ payload, /** @type {Params} */ ...args) => {
 		var getters = /** @type {Getters<Params>} */ (args.map((value) => () => value));
-		payload.out += fn(...getters)
-			.render()
-			.trim();
+		payload.out.push(
+			fn(...getters)
+				.render()
+				.trim()
+		);
 	};
 }
diff --git a/packages/svelte/src/internal/server/dev.js b/packages/svelte/src/internal/server/dev.js
index 3c320f9698..2a0cb057a3 100644
--- a/packages/svelte/src/internal/server/dev.js
+++ b/packages/svelte/src/internal/server/dev.js
@@ -40,7 +40,7 @@ function print_error(payload, message) {
 
 	// eslint-disable-next-line no-console
 	console.error(message);
-	payload.head.out += `<script>console.error(${JSON.stringify(message)})</script>`;
+	payload.head.out.push(`<script>console.error(${JSON.stringify(message)})</script>`);
 }
 
 export function reset_elements() {
diff --git a/packages/svelte/src/internal/server/index.js b/packages/svelte/src/internal/server/index.js
index 9942882d26..62ee22d6fc 100644
--- a/packages/svelte/src/internal/server/index.js
+++ b/packages/svelte/src/internal/server/index.js
@@ -33,23 +33,23 @@ const INVALID_ATTR_NAME_CHAR_REGEX =
  * @returns {void}
  */
 export function element(payload, tag, attributes_fn = noop, children_fn = noop) {
-	payload.out += '<!---->';
+	payload.out.push('<!---->');
 
 	if (tag) {
-		payload.out += `<${tag}`;
+		payload.out.push(`<${tag}`);
 		attributes_fn();
-		payload.out += `>`;
+		payload.out.push(`>`);
 
 		if (!is_void(tag)) {
 			children_fn();
 			if (!is_raw_text_element(tag)) {
-				payload.out += EMPTY_COMMENT;
+				payload.out.push(EMPTY_COMMENT);
 			}
-			payload.out += `</${tag}>`;
+			payload.out.push(`</${tag}>`);
 		}
 	}
 
-	payload.out += '<!---->';
+	payload.out.push('<!---->');
 }
 
 /**
@@ -72,7 +72,7 @@ export function render(component, options = {}) {
 
 		const prev_on_destroy = on_destroy;
 		on_destroy = [];
-		payload.out += BLOCK_OPEN;
+		payload.out.push(BLOCK_OPEN);
 
 		let reset_reset_element;
 
@@ -97,20 +97,22 @@ export function render(component, options = {}) {
 			reset_reset_element();
 		}
 
-		payload.out += BLOCK_CLOSE;
+		payload.out.push(BLOCK_CLOSE);
 		for (const cleanup of on_destroy) cleanup();
 		on_destroy = prev_on_destroy;
 
-		let head = payload.head.out + payload.head.title;
+		let head = payload.head.out.join('') + payload.head.title;
 
 		for (const { hash, code } of payload.css) {
 			head += `<style id="${hash}">${code}</style>`;
 		}
 
+		const body = payload.out.join('');
+
 		return {
 			head,
-			html: payload.out,
-			body: payload.out
+			html: body,
+			body: body
 		};
 	} finally {
 		abort();
@@ -124,9 +126,9 @@ export function render(component, options = {}) {
  */
 export function head(payload, fn) {
 	const head_payload = payload.head;
-	head_payload.out += BLOCK_OPEN;
+	head_payload.out.push(BLOCK_OPEN);
 	fn(head_payload);
-	head_payload.out += BLOCK_CLOSE;
+	head_payload.out.push(BLOCK_CLOSE);
 }
 
 /**
@@ -141,21 +143,21 @@ export function css_props(payload, is_html, props, component, dynamic = false) {
 	const styles = style_object_to_string(props);
 
 	if (is_html) {
-		payload.out += `<svelte-css-wrapper style="display: contents; ${styles}">`;
+		payload.out.push(`<svelte-css-wrapper style="display: contents; ${styles}">`);
 	} else {
-		payload.out += `<g style="${styles}">`;
+		payload.out.push(`<g style="${styles}">`);
 	}
 
 	if (dynamic) {
-		payload.out += '<!---->';
+		payload.out.push('<!---->');
 	}
 
 	component();
 
 	if (is_html) {
-		payload.out += `<!----></svelte-css-wrapper>`;
+		payload.out.push(`<!----></svelte-css-wrapper>`);
 	} else {
-		payload.out += `<!----></g>`;
+		payload.out.push(`<!----></g>`);
 	}
 }
 
@@ -440,13 +442,13 @@ export function bind_props(props_parent, props_now) {
  */
 function await_block(payload, promise, pending_fn, then_fn) {
 	if (is_promise(promise)) {
-		payload.out += BLOCK_OPEN;
+		payload.out.push(BLOCK_OPEN);
 		promise.then(null, noop);
 		if (pending_fn !== null) {
 			pending_fn();
 		}
 	} else if (then_fn !== null) {
-		payload.out += BLOCK_OPEN_ELSE;
+		payload.out.push(BLOCK_OPEN_ELSE);
 		then_fn(promise);
 	}
 }
@@ -493,7 +495,7 @@ export function once(get_value) {
  */
 export function props_id(payload) {
 	const uid = payload.uid();
-	payload.out += '<!--#' + uid + '-->';
+	payload.out.push('<!--#' + uid + '-->');
 	return uid;
 }
 
@@ -562,10 +564,13 @@ export function valueless_option(payload, children) {
 
 	children();
 
-	var body = payload.out.slice(i);
+	var body = payload.out.slice(i).join('');
 
 	if (body.replace(/<!---->/g, '') === payload.select_value) {
 		// replace '>' with ' selected>' (closing tag will be added later)
-		payload.out = payload.out.slice(0, i - 1) + ' selected>' + body;
+		var last_item = payload.out[i - 1];
+		payload.out[i - 1] = last_item.slice(0, -1) + ' selected>';
+		// Remove the old items after position i and add the body as a single item
+		payload.out.splice(i, payload.out.length - i, body);
 	}
 }
diff --git a/packages/svelte/src/internal/server/payload.js b/packages/svelte/src/internal/server/payload.js
index a31120ae16..195488e061 100644
--- a/packages/svelte/src/internal/server/payload.js
+++ b/packages/svelte/src/internal/server/payload.js
@@ -1,11 +1,12 @@
 export class HeadPayload {
 	/** @type {Set<{ hash: string; code: string }>} */
 	css = new Set();
-	out = '';
+	/** @type {string[]} */
+	out = [];
 	uid = () => '';
 	title = '';
 
-	constructor(css = new Set(), out = '', title = '', uid = () => '') {
+	constructor(css = new Set(), /** @type {string[]} */ out = [], title = '', uid = () => '') {
 		this.css = css;
 		this.out = out;
 		this.title = title;
@@ -16,7 +17,8 @@ export class HeadPayload {
 export class Payload {
 	/** @type {Set<{ hash: string; code: string }>} */
 	css = new Set();
-	out = '';
+	/** @type {string[]} */
+	out = [];
 	uid = () => '';
 	select_value = undefined;
 
@@ -36,12 +38,12 @@ export class Payload {
 export function copy_payload({ out, css, head, uid }) {
 	const payload = new Payload();
 
-	payload.out = out;
+	payload.out = [...out];
 	payload.css = new Set(css);
 	payload.uid = uid;
 
 	payload.head = new HeadPayload();
-	payload.head.out = head.out;
+	payload.head.out = [...head.out];
 	payload.head.css = new Set(head.css);
 	payload.head.title = head.title;
 	payload.head.uid = head.uid;
@@ -56,7 +58,7 @@ export function copy_payload({ out, css, head, uid }) {
  * @returns {void}
  */
 export function assign_payload(p1, p2) {
-	p1.out = p2.out;
+	p1.out = [...p2.out];
 	p1.css = p2.css;
 	p1.head = p2.head;
 	p1.uid = p2.uid;
diff --git a/packages/svelte/tests/snapshot/samples/await-block-scope/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/await-block-scope/_expected/server/index.svelte.js
index 4b6e32d58e..cc2628c852 100644
--- a/packages/svelte/tests/snapshot/samples/await-block-scope/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/await-block-scope/_expected/server/index.svelte.js
@@ -8,7 +8,7 @@ export default function Await_block_scope($$payload) {
 		counter.count += 1;
 	}
 
-	$$payload.out += `<button>clicks: ${$.escape(counter.count)}</button> `;
+	$$payload.out.push(`<button>clicks: ${$.escape(counter.count)}</button> `);
 	$.await($$payload, promise, () => {}, (counter) => {});
-	$$payload.out += `<!--]--> ${$.escape(counter.count)}`;
+	$$payload.out.push(`<!--]--> ${$.escape(counter.count)}`);
 }
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/bind-component-snippet/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/bind-component-snippet/_expected/server/index.svelte.js
index e2c0ee29a5..c0db7d2fd5 100644
--- a/packages/svelte/tests/snapshot/samples/bind-component-snippet/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/bind-component-snippet/_expected/server/index.svelte.js
@@ -2,7 +2,7 @@ import * as $ from 'svelte/internal/server';
 import TextInput from './Child.svelte';
 
 function snippet($$payload) {
-	$$payload.out += `<!---->Something`;
+	$$payload.out.push(`<!---->Something`);
 }
 
 export default function Bind_component_snippet($$payload) {
@@ -23,7 +23,7 @@ export default function Bind_component_snippet($$payload) {
 			}
 		});
 
-		$$payload.out += `<!----> value: ${$.escape(value)}`;
+		$$payload.out.push(`<!----> value: ${$.escape(value)}`);
 	}
 
 	do {
diff --git a/packages/svelte/tests/snapshot/samples/delegated-locally-declared-shadowed/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/delegated-locally-declared-shadowed/_expected/server/index.svelte.js
index e465af6f8b..ac3dfcd2cb 100644
--- a/packages/svelte/tests/snapshot/samples/delegated-locally-declared-shadowed/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/delegated-locally-declared-shadowed/_expected/server/index.svelte.js
@@ -3,11 +3,11 @@ import * as $ from 'svelte/internal/server';
 export default function Delegated_locally_declared_shadowed($$payload) {
 	const each_array = $.ensure_array_like({ length: 1 });
 
-	$$payload.out += `<!--[-->`;
+	$$payload.out.push(`<!--[-->`);
 
 	for (let index = 0, $$length = each_array.length; index < $$length; index++) {
-		$$payload.out += `<button type="button"${$.attr('data-index', index)}>B</button>`;
+		$$payload.out.push(`<button type="button"${$.attr('data-index', index)}>B</button>`);
 	}
 
-	$$payload.out += `<!--]-->`;
+	$$payload.out.push(`<!--]-->`);
 }
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/dynamic-attributes-casing/_expected/server/main.svelte.js b/packages/svelte/tests/snapshot/samples/dynamic-attributes-casing/_expected/server/main.svelte.js
index cf731d8187..9c837d4e1d 100644
--- a/packages/svelte/tests/snapshot/samples/dynamic-attributes-casing/_expected/server/main.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/dynamic-attributes-casing/_expected/server/main.svelte.js
@@ -6,5 +6,5 @@ export default function Main($$payload) {
 
 	let y = () => 'test';
 
-	$$payload.out += `<div${$.attr('foobar', x)}></div> <svg${$.attr('viewBox', x)}></svg> <custom-element${$.attr('foobar', x)}></custom-element> <div${$.attr('foobar', y())}></div> <svg${$.attr('viewBox', y())}></svg> <custom-element${$.attr('foobar', y())}></custom-element>`;
+	$$payload.out.push(`<div${$.attr('foobar', x)}></div> <svg${$.attr('viewBox', x)}></svg> <custom-element${$.attr('foobar', x)}></custom-element> <div${$.attr('foobar', y())}></div> <svg${$.attr('viewBox', y())}></svg> <custom-element${$.attr('foobar', y())}></custom-element>`);
 }
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/each-index-non-null/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/each-index-non-null/_expected/server/index.svelte.js
index 3431e36833..8fa0c5f28c 100644
--- a/packages/svelte/tests/snapshot/samples/each-index-non-null/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/each-index-non-null/_expected/server/index.svelte.js
@@ -3,11 +3,11 @@ import * as $ from 'svelte/internal/server';
 export default function Each_index_non_null($$payload) {
 	const each_array = $.ensure_array_like(Array(10));
 
-	$$payload.out += `<!--[-->`;
+	$$payload.out.push(`<!--[-->`);
 
 	for (let i = 0, $$length = each_array.length; i < $$length; i++) {
-		$$payload.out += `<p>index: ${$.escape(i)}</p>`;
+		$$payload.out.push(`<p>index: ${$.escape(i)}</p>`);
 	}
 
-	$$payload.out += `<!--]-->`;
+	$$payload.out.push(`<!--]-->`);
 }
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/each-string-template/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/each-string-template/_expected/server/index.svelte.js
index 4386c22ebe..6dbe8130da 100644
--- a/packages/svelte/tests/snapshot/samples/each-string-template/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/each-string-template/_expected/server/index.svelte.js
@@ -3,13 +3,13 @@ import * as $ from 'svelte/internal/server';
 export default function Each_string_template($$payload) {
 	const each_array = $.ensure_array_like(['foo', 'bar', 'baz']);
 
-	$$payload.out += `<!--[-->`;
+	$$payload.out.push(`<!--[-->`);
 
 	for (let $$index = 0, $$length = each_array.length; $$index < $$length; $$index++) {
 		let thing = each_array[$$index];
 
-		$$payload.out += `<!---->${$.escape(thing)}, `;
+		$$payload.out.push(`<!---->${$.escape(thing)}, `);
 	}
 
-	$$payload.out += `<!--]-->`;
+	$$payload.out.push(`<!--]-->`);
 }
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/function-prop-no-getter/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/function-prop-no-getter/_expected/server/index.svelte.js
index 7d37abd97b..ce4f09ed1d 100644
--- a/packages/svelte/tests/snapshot/samples/function-prop-no-getter/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/function-prop-no-getter/_expected/server/index.svelte.js
@@ -15,7 +15,7 @@ export default function Function_prop_no_getter($$payload) {
 		onmouseenter: () => count = plusOne(count),
 
 		children: ($$payload) => {
-			$$payload.out += `<!---->clicks: ${$.escape(count)}`;
+			$$payload.out.push(`<!---->clicks: ${$.escape(count)}`);
 		},
 
 		$$slots: { default: true }
diff --git a/packages/svelte/tests/snapshot/samples/functional-templating/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/functional-templating/_expected/server/index.svelte.js
index dc49c0c213..b1a0a5f9e6 100644
--- a/packages/svelte/tests/snapshot/samples/functional-templating/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/functional-templating/_expected/server/index.svelte.js
@@ -1,5 +1,5 @@
 import * as $ from 'svelte/internal/server';
 
 export default function Functional_templating($$payload) {
-	$$payload.out += `<h1>hello</h1> <div class="potato"><p>child element</p> <p>another child element</p></div>`;
+	$$payload.out.push(`<h1>hello</h1> <div class="potato"><p>child element</p> <p>another child element</p></div>`);
 }
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/hello-world/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/hello-world/_expected/server/index.svelte.js
index 8766fb1300..30f6d6b74a 100644
--- a/packages/svelte/tests/snapshot/samples/hello-world/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/hello-world/_expected/server/index.svelte.js
@@ -1,5 +1,5 @@
 import * as $ from 'svelte/internal/server';
 
 export default function Hello_world($$payload) {
-	$$payload.out += `<h1>hello world</h1>`;
+	$$payload.out.push(`<h1>hello world</h1>`);
 }
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/hmr/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/hmr/_expected/server/index.svelte.js
index 959e0a403e..ea1d12c83b 100644
--- a/packages/svelte/tests/snapshot/samples/hmr/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/hmr/_expected/server/index.svelte.js
@@ -1,5 +1,5 @@
 import * as $ from 'svelte/internal/server';
 
 export default function Hmr($$payload) {
-	$$payload.out += `<h1>hello world</h1>`;
+	$$payload.out.push(`<h1>hello world</h1>`);
 }
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/nullish-coallescence-omittance/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/nullish-coallescence-omittance/_expected/server/index.svelte.js
index 3b23befcd4..18e01b4f72 100644
--- a/packages/svelte/tests/snapshot/samples/nullish-coallescence-omittance/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/nullish-coallescence-omittance/_expected/server/index.svelte.js
@@ -4,5 +4,5 @@ export default function Nullish_coallescence_omittance($$payload) {
 	let name = 'world';
 	let count = 0;
 
-	$$payload.out += `<h1>Hello, world!</h1> <b>123</b> <button>Count is ${$.escape(count)}</button> <h1>Hello, world</h1>`;
+	$$payload.out.push(`<h1>Hello, world!</h1> <b>123</b> <button>Count is ${$.escape(count)}</button> <h1>Hello, world</h1>`);
 }
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/purity/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/purity/_expected/server/index.svelte.js
index 9457378c0d..29b0d0d594 100644
--- a/packages/svelte/tests/snapshot/samples/purity/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/purity/_expected/server/index.svelte.js
@@ -1,7 +1,7 @@
 import * as $ from 'svelte/internal/server';
 
 export default function Purity($$payload) {
-	$$payload.out += `<p>0</p> <p>${$.escape(location.href)}</p> `;
+	$$payload.out.push(`<p>0</p> <p>${$.escape(location.href)}</p> `);
 	Child($$payload, { prop: encodeURIComponent('hello') });
-	$$payload.out += `<!---->`;
+	$$payload.out.push(`<!---->`);
 }
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/skip-static-subtree/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/skip-static-subtree/_expected/server/index.svelte.js
index 0532ec5aa9..bad475ec86 100644
--- a/packages/svelte/tests/snapshot/samples/skip-static-subtree/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/skip-static-subtree/_expected/server/index.svelte.js
@@ -3,5 +3,5 @@ import * as $ from 'svelte/internal/server';
 export default function Skip_static_subtree($$payload, $$props) {
 	let { title, content } = $$props;
 
-	$$payload.out += `<header><nav><a href="/">Home</a> <a href="/away">Away</a></nav></header> <main><h1>${$.escape(title)}</h1> <div class="static"><p>we don't need to traverse these nodes</p></div> <p>or</p> <p>these</p> <p>ones</p> ${$.html(content)} <p>these</p> <p>trailing</p> <p>nodes</p> <p>can</p> <p>be</p> <p>completely</p> <p>ignored</p></main> <cant-skip><custom-elements with="attributes"></custom-elements></cant-skip> <div><input autofocus/></div> <div><source muted/></div> <select><option value="a"${$.maybe_selected($$payload, 'a')}>a</option></select> <img src="..." alt="" loading="lazy"/> <div><img src="..." alt="" loading="lazy"/></div>`;
+	$$payload.out.push(`<header><nav><a href="/">Home</a> <a href="/away">Away</a></nav></header> <main><h1>${$.escape(title)}</h1> <div class="static"><p>we don't need to traverse these nodes</p></div> <p>or</p> <p>these</p> <p>ones</p> ${$.html(content)} <p>these</p> <p>trailing</p> <p>nodes</p> <p>can</p> <p>be</p> <p>completely</p> <p>ignored</p></main> <cant-skip><custom-elements with="attributes"></custom-elements></cant-skip> <div><input autofocus/></div> <div><source muted/></div> <select><option value="a"${$.maybe_selected($$payload, 'a')}>a</option></select> <img src="..." alt="" loading="lazy"/> <div><img src="..." alt="" loading="lazy"/></div>`);
 }
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/state-proxy-literal/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/state-proxy-literal/_expected/server/index.svelte.js
index f814dd4f84..c2736b0f43 100644
--- a/packages/svelte/tests/snapshot/samples/state-proxy-literal/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/state-proxy-literal/_expected/server/index.svelte.js
@@ -11,5 +11,5 @@ export default function State_proxy_literal($$payload) {
 		tpl = ``;
 	}
 
-	$$payload.out += `<input${$.attr('value', str)}/> <input${$.attr('value', tpl)}/> <button>reset</button>`;
+	$$payload.out.push(`<input${$.attr('value', str)}/> <input${$.attr('value', tpl)}/> <button>reset</button>`);
 }
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/text-nodes-deriveds/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/text-nodes-deriveds/_expected/server/index.svelte.js
index 6f019647f5..f7dc586026 100644
--- a/packages/svelte/tests/snapshot/samples/text-nodes-deriveds/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/text-nodes-deriveds/_expected/server/index.svelte.js
@@ -12,5 +12,5 @@ export default function Text_nodes_deriveds($$payload) {
 		return count2;
 	}
 
-	$$payload.out += `<p>${$.escape(text1())}${$.escape(text2())}</p>`;
+	$$payload.out.push(`<p>${$.escape(text1())}${$.escape(text2())}</p>`);
 }
\ No newline at end of file

From 05f6436445d54a689ca12cced4bd359d15fc2e4c Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Fri, 18 Jul 2025 12:35:20 -0400
Subject: [PATCH 099/148] Version Packages (#16435)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/four-kings-drum.md  | 5 -----
 .changeset/old-dots-sin.md     | 5 -----
 packages/svelte/CHANGELOG.md   | 8 ++++++++
 packages/svelte/package.json   | 2 +-
 packages/svelte/src/version.js | 2 +-
 5 files changed, 10 insertions(+), 12 deletions(-)
 delete mode 100644 .changeset/four-kings-drum.md
 delete mode 100644 .changeset/old-dots-sin.md

diff --git a/.changeset/four-kings-drum.md b/.changeset/four-kings-drum.md
deleted file mode 100644
index 8c7343145e..0000000000
--- a/.changeset/four-kings-drum.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: keep effect in the graph if it has an abort controller
diff --git a/.changeset/old-dots-sin.md b/.changeset/old-dots-sin.md
deleted file mode 100644
index f7e2933897..0000000000
--- a/.changeset/old-dots-sin.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-chore: Switch `payload.out` to an array
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index a82d9ddefe..6f6b824174 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,13 @@
 # svelte
 
+## 5.36.8
+
+### Patch Changes
+
+- fix: keep effect in the graph if it has an abort controller ([#16430](https://github.com/sveltejs/svelte/pull/16430))
+
+- chore: Switch `payload.out` to an array ([#16428](https://github.com/sveltejs/svelte/pull/16428))
+
 ## 5.36.7
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 83567a6123..df53b69e93 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.7",
+  "version": "5.36.8",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 88cdc069a0..005a06dc19 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.7';
+export const VERSION = '5.36.8';
 export const PUBLIC_VERSION = '5';

From 27c90dfa8322c9f225e22a730a776c4f4cbd2c5e Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Sat, 19 Jul 2025 08:23:27 +0200
Subject: [PATCH 100/148] fix: don't reexecute derived with no dependencies on
 teardown (#16438)

The prior logic was wrong because it reexecuted when something was clean, but we want to when it's not. The remaining fix was to also check the reactions: If an effect is destroyed and it was the last reaction of a derived then the derived is set to `MAYBE_DIRTY`. We therefore also need to check if the derived still has anyone listening to it, and only then reexecute it.

Fixes #16363
---
 .changeset/clever-toys-decide.md              |  5 ++++
 .../svelte/src/internal/client/runtime.js     |  8 +++--
 .../props-derived-teardown/Teardown.svelte    | 11 +++++++
 .../samples/props-derived-teardown/_config.js | 30 +++++++++++++++++++
 .../props-derived-teardown/main.svelte        | 25 ++++++++++++++++
 5 files changed, 77 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/clever-toys-decide.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/props-derived-teardown/Teardown.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/props-derived-teardown/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/props-derived-teardown/main.svelte

diff --git a/.changeset/clever-toys-decide.md b/.changeset/clever-toys-decide.md
new file mode 100644
index 0000000000..57eb2b0058
--- /dev/null
+++ b/.changeset/clever-toys-decide.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: don't reexecute derived with no dependencies on teardown
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 306b9b9dd9..3d3c89975c 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -653,8 +653,12 @@ export function get(signal) {
 
 			var value = derived.v;
 
-			// if the derived is dirty, or depends on the values that just changed, re-execute
-			if ((derived.f & CLEAN) !== 0 || depends_on_old_values(derived)) {
+			// if the derived is dirty and has reactions, or depends on the values that just changed, re-execute
+			// (a derived can be maybe_dirty due to the effect destroy removing its last reaction)
+			if (
+				((derived.f & CLEAN) === 0 && derived.reactions !== null) ||
+				depends_on_old_values(derived)
+			) {
 				value = execute_derived(derived);
 			}
 
diff --git a/packages/svelte/tests/runtime-runes/samples/props-derived-teardown/Teardown.svelte b/packages/svelte/tests/runtime-runes/samples/props-derived-teardown/Teardown.svelte
new file mode 100644
index 0000000000..f71890d31e
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/props-derived-teardown/Teardown.svelte
@@ -0,0 +1,11 @@
+<script>
+	import { onDestroy } from 'svelte'
+	
+	const { callback } = $props()
+	
+	onDestroy(() => {
+		callback()
+	})
+</script>
+
+<div>teardown</div>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/props-derived-teardown/_config.js b/packages/svelte/tests/runtime-runes/samples/props-derived-teardown/_config.js
new file mode 100644
index 0000000000..c4e7d1307b
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/props-derived-teardown/_config.js
@@ -0,0 +1,30 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>click</button>
+				<div>teardown</div>
+				<div>1</div>
+				<div>2</div>
+				<div>3</div>
+			`
+		);
+		const [increment] = target.querySelectorAll('button');
+
+		increment.click();
+		flushSync();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>click</button>
+				<div>1</div>
+				<div>3</div>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/props-derived-teardown/main.svelte b/packages/svelte/tests/runtime-runes/samples/props-derived-teardown/main.svelte
new file mode 100644
index 0000000000..ff9e19b2c6
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/props-derived-teardown/main.svelte
@@ -0,0 +1,25 @@
+<script>
+	import { SvelteSet } from 'svelte/reactivity'
+	import Teardown from './Teardown.svelte'
+
+	class Test {
+		originalIds = $state.raw([1, 2, 3])
+		ids = $derived(new SvelteSet(this.originalIds))
+	}
+
+	let show = $state(true)
+	const test = new Test()
+
+	function callback() {
+		test.ids.delete(2)
+	}
+</script>
+
+
+<button onclick={() => (show = !show)}>click</button>
+{#if show}
+	<Teardown {callback} />
+{/if}
+{#each test.ids as id}
+	<div>{id}</div>
+{/each}

From 63cbe2108ac35204ffc99d16e5a520502ec7ade7 Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Sat, 19 Jul 2025 11:35:43 -0700
Subject: [PATCH 101/148] fix: disallow `export { foo as default }` in `<script
 module>` (#16447)

* fix: disallow `export { foo as default }` in `<script module>`

* add test

* fix test
---
 .changeset/curly-buttons-burn.md                   |  5 +++++
 .../2-analyze/visitors/ExportNamedDeclaration.js   | 11 +++++++++++
 .../samples/default-export-indirect/errors.json    | 14 ++++++++++++++
 .../samples/default-export-indirect/input.svelte   |  4 ++++
 4 files changed, 34 insertions(+)
 create mode 100644 .changeset/curly-buttons-burn.md
 create mode 100644 packages/svelte/tests/validator/samples/default-export-indirect/errors.json
 create mode 100644 packages/svelte/tests/validator/samples/default-export-indirect/input.svelte

diff --git a/.changeset/curly-buttons-burn.md b/.changeset/curly-buttons-burn.md
new file mode 100644
index 0000000000..f5d45256fa
--- /dev/null
+++ b/.changeset/curly-buttons-burn.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: disallow `export { foo as default }` in `<script module>`
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/ExportNamedDeclaration.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/ExportNamedDeclaration.js
index 4b85894e52..5b8d9ba053 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/ExportNamedDeclaration.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/ExportNamedDeclaration.js
@@ -11,6 +11,17 @@ export function ExportNamedDeclaration(node, context) {
 	// visit children, so bindings are correctly initialised
 	context.next();
 
+	if (
+		context.state.ast_type &&
+		node.specifiers.some((specifier) =>
+			specifier.exported.type === 'Identifier'
+				? specifier.exported.name === 'default'
+				: specifier.exported.value === 'default'
+		)
+	) {
+		e.module_illegal_default_export(node);
+	}
+
 	if (node.declaration?.type === 'VariableDeclaration') {
 		// in runes mode, forbid `export let`
 		if (
diff --git a/packages/svelte/tests/validator/samples/default-export-indirect/errors.json b/packages/svelte/tests/validator/samples/default-export-indirect/errors.json
new file mode 100644
index 0000000000..6a8b2b3c13
--- /dev/null
+++ b/packages/svelte/tests/validator/samples/default-export-indirect/errors.json
@@ -0,0 +1,14 @@
+[
+	{
+		"code": "module_illegal_default_export",
+		"message": "A component cannot have a default export",
+		"start": {
+			"line": 3,
+			"column": 4
+		},
+		"end": {
+			"line": 3,
+			"column": 32
+		}
+	}
+]
diff --git a/packages/svelte/tests/validator/samples/default-export-indirect/input.svelte b/packages/svelte/tests/validator/samples/default-export-indirect/input.svelte
new file mode 100644
index 0000000000..72150edab1
--- /dev/null
+++ b/packages/svelte/tests/validator/samples/default-export-indirect/input.svelte
@@ -0,0 +1,4 @@
+<script module>
+    let answer = 42;
+    export { answer as default};
+</script>
\ No newline at end of file

From ad0b58ee9606dd89038b055536e09c2b01112a0a Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Sat, 19 Jul 2025 14:21:25 -0700
Subject: [PATCH 102/148] fix: move ownership validation into async component
 body (#16449)

* fix: move ownership validation into async component body

* add test

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
---
 .changeset/healthy-carpets-deny.md            |  5 +++++
 .../3-transform/client/transform-client.js    | 12 +++++-----
 .../async-ownership-validation/Child.svelte   |  7 ++++++
 .../async-ownership-validation/_config.js     | 22 +++++++++++++++++++
 .../async-ownership-validation/main.svelte    | 13 +++++++++++
 5 files changed, 53 insertions(+), 6 deletions(-)
 create mode 100644 .changeset/healthy-carpets-deny.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-ownership-validation/Child.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-ownership-validation/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-ownership-validation/main.svelte

diff --git a/.changeset/healthy-carpets-deny.md b/.changeset/healthy-carpets-deny.md
new file mode 100644
index 0000000000..94ee865fe7
--- /dev/null
+++ b/.changeset/healthy-carpets-deny.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: move ownership validation into async component body
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js b/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
index c42d1b95d8..7f25e6c0d2 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
@@ -364,6 +364,12 @@ export function client_component(analysis, options) {
 			: b.stmt(b.call('$.init', analysis.immutable ? b.true : undefined))
 	]);
 
+	if (analysis.needs_mutation_validation) {
+		component_block.body.unshift(
+			b.var('$$ownership_validator', b.call('$.create_ownership_validator', b.id('$$props')))
+		);
+	}
+
 	const should_inject_context =
 		dev ||
 		analysis.needs_context ||
@@ -434,12 +440,6 @@ export function client_component(analysis, options) {
 		);
 	}
 
-	if (analysis.needs_mutation_validation) {
-		component_block.body.unshift(
-			b.var('$$ownership_validator', b.call('$.create_ownership_validator', b.id('$$props')))
-		);
-	}
-
 	// we want the cleanup function for the stores to run as the very last thing
 	// so that it can effectively clean up the store subscription even after the user effects runs
 	if (should_inject_context) {
diff --git a/packages/svelte/tests/runtime-runes/samples/async-ownership-validation/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-ownership-validation/Child.svelte
new file mode 100644
index 0000000000..d4d5cf7554
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-ownership-validation/Child.svelte
@@ -0,0 +1,7 @@
+<script>
+	let { object } = $props();
+
+	await 1;
+</script>
+
+<button onclick={() => object.count++}>clicks: {object.count}</button>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-ownership-validation/_config.js b/packages/svelte/tests/runtime-runes/samples/async-ownership-validation/_config.js
new file mode 100644
index 0000000000..167eee8488
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-ownership-validation/_config.js
@@ -0,0 +1,22 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true
+	},
+
+	async test({ assert, target, warnings }) {
+		await tick();
+
+		const [button] = target.querySelectorAll('button');
+
+		button.click();
+		await tick();
+
+		assert.htmlEqual(target.innerHTML, '<button>clicks: 1</button>');
+		assert.deepEqual(warnings, [
+			'Mutating unbound props (`object`, at Child.svelte:7:23) is strongly discouraged. Consider using `bind:object={...}` in main.svelte (or using a callback) instead'
+		]);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-ownership-validation/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-ownership-validation/main.svelte
new file mode 100644
index 0000000000..ae6b43cbb1
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-ownership-validation/main.svelte
@@ -0,0 +1,13 @@
+<script>
+	import Child from './Child.svelte';
+
+	let object = $state({ count: 0 });
+</script>
+
+<svelte:boundary>
+	<Child {object} />
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>

From 307ec228ffc70502b6c13c56c8e62f1abebeb73b Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Sat, 19 Jul 2025 14:24:47 -0700
Subject: [PATCH 103/148] fix: move store setup/cleanup outside of async
 component body (#16443)

---
 .changeset/new-fireants-bake.md               |  5 +++++
 .../3-transform/client/transform-client.js    | 21 ++++++++++++++-----
 2 files changed, 21 insertions(+), 5 deletions(-)
 create mode 100644 .changeset/new-fireants-bake.md

diff --git a/.changeset/new-fireants-bake.md b/.changeset/new-fireants-bake.md
new file mode 100644
index 0000000000..81bd596e43
--- /dev/null
+++ b/.changeset/new-fireants-bake.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: move store setup/cleanup outside of async component body
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js b/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
index 7f25e6c0d2..124438a9da 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
@@ -209,7 +209,8 @@ export function client_component(analysis, options) {
 
 	/** @type {ESTree.Statement[]} */
 	const store_setup = [];
-
+	/** @type {ESTree.Statement} */
+	let store_init = b.empty;
 	/** @type {ESTree.VariableDeclaration[]} */
 	const legacy_reactive_declarations = [];
 
@@ -227,8 +228,9 @@ export function client_component(analysis, options) {
 		if (binding.kind === 'store_sub') {
 			if (store_setup.length === 0) {
 				needs_store_cleanup = true;
-				store_setup.push(
-					b.const(b.array_pattern([b.id('$$stores'), b.id('$$cleanup')]), b.call('$.setup_stores'))
+				store_init = b.const(
+					b.array_pattern([b.id('$$stores'), b.id('$$cleanup')]),
+					b.call('$.setup_stores')
 				);
 			}
 
@@ -385,9 +387,16 @@ export function client_component(analysis, options) {
 		analysis.slot_names.size > 0;
 
 	if (analysis.instance.has_await) {
+		const params = [b.id('$$anchor')];
+		if (should_inject_props) {
+			params.push(b.id('$$props'));
+		}
+		if (store_setup.length > 0) {
+			params.push(b.id('$$stores'));
+		}
 		const body = b.function_declaration(
 			b.id('$$body'),
-			should_inject_props ? [b.id('$$anchor'), b.id('$$props')] : [b.id('$$anchor')],
+			params,
 			b.block([
 				b.var('$$unsuspend', b.call('$.suspend')),
 				...component_block.body,
@@ -403,10 +412,12 @@ export function client_component(analysis, options) {
 		component_block = b.block([
 			b.var('fragment', b.call('$.comment')),
 			b.var('node', b.call('$.first_child', b.id('fragment'))),
-			b.stmt(b.call(body.id, b.id('node'), should_inject_props && b.id('$$props'))),
+			store_init,
+			b.stmt(b.call(body.id, b.id('node'), ...params.slice(1))),
 			b.stmt(b.call('$.append', b.id('$$anchor'), b.id('fragment')))
 		]);
 	} else {
+		component_block.body.unshift(store_init);
 		component_block.body.push(.../** @type {ESTree.Statement[]} */ (template.body));
 	}
 

From e1e7a75d719ab6826238ddaef4571ac6f6d22732 Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Sat, 19 Jul 2025 14:26:31 -0700
Subject: [PATCH 104/148] fix: allow async destructured deriveds (#16444)

* fix: allow async destructured deriveds

* add test

* tweak

* tweak

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
---
 .changeset/mighty-balloons-rush.md            |  5 ++
 .../client/visitors/VariableDeclaration.js    | 55 ++++++++++++++-----
 .../async-derived-destructured/Child.svelte   | 13 +++++
 .../async-derived-destructured/_config.js     | 31 +++++++++++
 .../async-derived-destructured/main.svelte    | 11 ++++
 svelte.config.js                              |  8 +++
 6 files changed, 108 insertions(+), 15 deletions(-)
 create mode 100644 .changeset/mighty-balloons-rush.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-derived-destructured/Child.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-derived-destructured/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-derived-destructured/main.svelte
 create mode 100644 svelte.config.js

diff --git a/.changeset/mighty-balloons-rush.md b/.changeset/mighty-balloons-rush.md
new file mode 100644
index 0000000000..ce8c09ca55
--- /dev/null
+++ b/.changeset/mighty-balloons-rush.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: allow async destructured deriveds
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
index 19a7de5715..0998dc4778 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
@@ -171,11 +171,14 @@ export function VariableDeclaration(node, context) {
 							context.state.transform[id.name] = { read: get_value };
 
 							const expression = /** @type {Expression} */ (context.visit(b.thunk(value)));
-							const call = b.call('$.derived', expression);
-							return b.declarator(
-								id,
-								dev ? b.call('$.tag', call, b.literal('[$state iterable]')) : call
-							);
+							let call = b.call('$.derived', expression);
+
+							if (dev) {
+								const label = `[$state ${declarator.id.type === 'ArrayPattern' ? 'iterable' : 'object'}]`;
+								call = b.call('$.tag', call, b.literal(label));
+							}
+
+							return b.declarator(id, call);
 						}),
 						...paths.map((path) => {
 							const value = /** @type {Expression} */ (context.visit(path.expression));
@@ -228,19 +231,37 @@ export function VariableDeclaration(node, context) {
 					}
 				} else {
 					const init = /** @type {CallExpression} */ (declarator.init);
+					let expression = /** @type {Expression} */ (
+						context.visit(value, {
+							...context.state,
+							in_derived: rune === '$derived'
+						})
+					);
 
 					let rhs = value;
 
 					if (rune !== '$derived' || init.arguments[0].type !== 'Identifier') {
 						const id = b.id(context.state.scope.generate('$$d'));
+						let call = b.call('$.derived', rune === '$derived' ? b.thunk(expression) : expression);
+
 						rhs = b.call('$.get', id);
 
-						let expression = /** @type {Expression} */ (context.visit(value));
-						if (rune === '$derived') expression = b.thunk(expression);
-						const call = b.call('$.derived', expression);
-						declarations.push(
-							b.declarator(id, dev ? b.call('$.tag', call, b.literal('[$derived iterable]')) : call)
-						);
+						if (is_async) {
+							const location = dev && !is_ignored(init, 'await_waterfall') && locate_node(init);
+							call = b.call(
+								'$.async_derived',
+								b.thunk(expression, true),
+								location ? b.literal(location) : undefined
+							);
+							call = b.call(b.await(b.call('$.save', call)));
+						}
+
+						if (dev) {
+							const label = `[$derived ${declarator.id.type === 'ArrayPattern' ? 'iterable' : 'object'}]`;
+							call = b.call('$.tag', call, b.literal(label));
+						}
+
+						declarations.push(b.declarator(id, call));
 					}
 
 					const { inserts, paths } = extract_paths(declarator.id, rhs);
@@ -250,10 +271,14 @@ export function VariableDeclaration(node, context) {
 						context.state.transform[id.name] = { read: get_value };
 
 						const expression = /** @type {Expression} */ (context.visit(b.thunk(value)));
-						const call = b.call('$.derived', expression);
-						declarations.push(
-							b.declarator(id, dev ? b.call('$.tag', call, b.literal('[$derived iterable]')) : call)
-						);
+						let call = b.call('$.derived', expression);
+
+						if (dev) {
+							const label = `[$derived ${declarator.id.type === 'ArrayPattern' ? 'iterable' : 'object'}]`;
+							call = b.call('$.tag', call, b.literal(label));
+						}
+
+						declarations.push(b.declarator(id, call));
 					}
 
 					for (const path of paths) {
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-destructured/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-derived-destructured/Child.svelte
new file mode 100644
index 0000000000..39112b12a7
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-destructured/Child.svelte
@@ -0,0 +1,13 @@
+<script>
+	let count = $state(1);
+
+	let { squared, cubed } = $derived(await {
+		squared: count ** 2,
+		cubed: count ** 3
+	});
+</script>
+
+<button onclick={() => count++}>increment</button>
+
+<p>{count} ** 2 = {squared}</p>
+<p>{count} ** 3 = {cubed}</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-destructured/_config.js b/packages/svelte/tests/runtime-runes/samples/async-derived-destructured/_config.js
new file mode 100644
index 0000000000..d444e8e1d9
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-destructured/_config.js
@@ -0,0 +1,31 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+
+		const [increment] = target.querySelectorAll('button');
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<p>1 ** 2 = 1</p>
+				<p>1 ** 3 = 1</p>
+			`
+		);
+
+		increment.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<p>2 ** 2 = 4</p>
+				<p>2 ** 3 = 8</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-destructured/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-derived-destructured/main.svelte
new file mode 100644
index 0000000000..c5d8a12a78
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-destructured/main.svelte
@@ -0,0 +1,11 @@
+<script>
+	import Child from './Child.svelte';
+</script>
+
+<svelte:boundary>
+	<Child />
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/svelte.config.js b/svelte.config.js
new file mode 100644
index 0000000000..442cd7892c
--- /dev/null
+++ b/svelte.config.js
@@ -0,0 +1,8 @@
+// we need this so the VS Code extension doesn't yell at us
+export default {
+	compilerOptions: {
+		experimental: {
+			async: true
+		}
+	}
+};

From cc05cbcf5ccd1b19a42417dd374471c4cecb7776 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Sat, 19 Jul 2025 14:30:38 -0700
Subject: [PATCH 105/148] Version Packages (#16445)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/clever-toys-decide.md   |  5 -----
 .changeset/curly-buttons-burn.md   |  5 -----
 .changeset/healthy-carpets-deny.md |  5 -----
 .changeset/mighty-balloons-rush.md |  5 -----
 .changeset/new-fireants-bake.md    |  5 -----
 packages/svelte/CHANGELOG.md       | 14 ++++++++++++++
 packages/svelte/package.json       |  2 +-
 packages/svelte/src/version.js     |  2 +-
 8 files changed, 16 insertions(+), 27 deletions(-)
 delete mode 100644 .changeset/clever-toys-decide.md
 delete mode 100644 .changeset/curly-buttons-burn.md
 delete mode 100644 .changeset/healthy-carpets-deny.md
 delete mode 100644 .changeset/mighty-balloons-rush.md
 delete mode 100644 .changeset/new-fireants-bake.md

diff --git a/.changeset/clever-toys-decide.md b/.changeset/clever-toys-decide.md
deleted file mode 100644
index 57eb2b0058..0000000000
--- a/.changeset/clever-toys-decide.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: don't reexecute derived with no dependencies on teardown
diff --git a/.changeset/curly-buttons-burn.md b/.changeset/curly-buttons-burn.md
deleted file mode 100644
index f5d45256fa..0000000000
--- a/.changeset/curly-buttons-burn.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: disallow `export { foo as default }` in `<script module>`
diff --git a/.changeset/healthy-carpets-deny.md b/.changeset/healthy-carpets-deny.md
deleted file mode 100644
index 94ee865fe7..0000000000
--- a/.changeset/healthy-carpets-deny.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: move ownership validation into async component body
diff --git a/.changeset/mighty-balloons-rush.md b/.changeset/mighty-balloons-rush.md
deleted file mode 100644
index ce8c09ca55..0000000000
--- a/.changeset/mighty-balloons-rush.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: allow async destructured deriveds
diff --git a/.changeset/new-fireants-bake.md b/.changeset/new-fireants-bake.md
deleted file mode 100644
index 81bd596e43..0000000000
--- a/.changeset/new-fireants-bake.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: move store setup/cleanup outside of async component body
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 6f6b824174..59d88437e4 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,19 @@
 # svelte
 
+## 5.36.9
+
+### Patch Changes
+
+- fix: don't reexecute derived with no dependencies on teardown ([#16438](https://github.com/sveltejs/svelte/pull/16438))
+
+- fix: disallow `export { foo as default }` in `<script module>` ([#16447](https://github.com/sveltejs/svelte/pull/16447))
+
+- fix: move ownership validation into async component body ([#16449](https://github.com/sveltejs/svelte/pull/16449))
+
+- fix: allow async destructured deriveds ([#16444](https://github.com/sveltejs/svelte/pull/16444))
+
+- fix: move store setup/cleanup outside of async component body ([#16443](https://github.com/sveltejs/svelte/pull/16443))
+
 ## 5.36.8
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index df53b69e93..3c6c419bdc 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.8",
+  "version": "5.36.9",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 005a06dc19..2df5873aa9 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.8';
+export const VERSION = '5.36.9';
 export const PUBLIC_VERSION = '5';

From 9a52007785dd44c978ea56e2766e207e138401d1 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Sat, 19 Jul 2025 17:37:53 -0400
Subject: [PATCH 106/148] fix: prevent batches from getting intertwined
 (#16446)

* ensure batches are kept separate

* changeset

* activate batch before decrementing
---
 .changeset/fresh-birds-jam.md                 |  5 ++++
 .../internal/client/dom/blocks/boundary.js    |  2 +-
 .../src/internal/client/reactivity/batch.js   | 30 +++++++++++++++++--
 3 files changed, 34 insertions(+), 3 deletions(-)
 create mode 100644 .changeset/fresh-birds-jam.md

diff --git a/.changeset/fresh-birds-jam.md b/.changeset/fresh-birds-jam.md
new file mode 100644
index 0000000000..41d62d5366
--- /dev/null
+++ b/.changeset/fresh-birds-jam.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: prevent batches from getting intertwined
diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 4ea137bfa8..1866931ef2 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -148,7 +148,7 @@ export class Boundary {
 				// need to use hydration boundary comments to report whether
 				// the pending or main block was rendered for a given
 				// boundary, and hydrate accordingly
-				queueMicrotask(() => {
+				Batch.enqueue(() => {
 					this.#main_effect = this.#run(() => {
 						Batch.ensure();
 						return branch(() => this.#children(this.#anchor));
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index ed82af94ed..ec082bb595 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -49,6 +49,19 @@ export let batch_deriveds = null;
 /** @type {Set<() => void>} */
 export let effect_pending_updates = new Set();
 
+/** @type {Array<() => void>} */
+let tasks = [];
+
+function dequeue() {
+	const task = /** @type {() => void} */ (tasks.shift());
+
+	if (tasks.length > 0) {
+		queueMicrotask(dequeue);
+	}
+
+	task();
+}
+
 /** @type {Effect[]} */
 let queued_root_effects = [];
 
@@ -438,7 +451,7 @@ export class Batch {
 			batches.add(current_batch);
 
 			if (autoflush) {
-				queueMicrotask(() => {
+				Batch.enqueue(() => {
 					if (current_batch !== batch) {
 						// a flushSync happened in the meantime
 						return;
@@ -451,6 +464,15 @@ export class Batch {
 
 		return current_batch;
 	}
+
+	/** @param {() => void} task */
+	static enqueue(task) {
+		if (tasks.length === 0) {
+			queueMicrotask(dequeue);
+		}
+
+		tasks.unshift(task);
+	}
 }
 
 /**
@@ -593,7 +615,11 @@ export function suspend() {
 
 	return function unsuspend() {
 		boundary.update_pending_count(-1);
-		if (!pending) batch.decrement();
+
+		if (!pending) {
+			batch.activate();
+			batch.decrement();
+		}
 
 		unset_context();
 	};

From dd55de3b75e4448c7fd80bcae0fb4db442890daa Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Sat, 19 Jul 2025 18:05:29 -0400
Subject: [PATCH 107/148] Version Packages (#16450)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/fresh-birds-jam.md  | 5 -----
 packages/svelte/CHANGELOG.md   | 6 ++++++
 packages/svelte/package.json   | 2 +-
 packages/svelte/src/version.js | 2 +-
 4 files changed, 8 insertions(+), 7 deletions(-)
 delete mode 100644 .changeset/fresh-birds-jam.md

diff --git a/.changeset/fresh-birds-jam.md b/.changeset/fresh-birds-jam.md
deleted file mode 100644
index 41d62d5366..0000000000
--- a/.changeset/fresh-birds-jam.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: prevent batches from getting intertwined
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 59d88437e4..c20618af11 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,11 @@
 # svelte
 
+## 5.36.10
+
+### Patch Changes
+
+- fix: prevent batches from getting intertwined ([#16446](https://github.com/sveltejs/svelte/pull/16446))
+
 ## 5.36.9
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 3c6c419bdc..28ccb2884a 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.9",
+  "version": "5.36.10",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 2df5873aa9..8c59098e0c 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.9';
+export const VERSION = '5.36.10';
 export const PUBLIC_VERSION = '5';

From 5033c8e965c39b903b2b0858c591926c9026f3bf Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Sat, 19 Jul 2025 20:35:28 -0400
Subject: [PATCH 108/148] fix: tag stores for `$inspect.trace()` (#16452)

---
 .changeset/silent-rockets-tease.md            |  5 ++++
 .../svelte/src/internal/client/dev/tracing.js | 11 ++++++-
 .../src/internal/client/reactivity/store.js   |  5 ++++
 .../samples/inspect-trace-store/_config.js    | 30 +++++++++++++++++++
 .../samples/inspect-trace-store/main.svelte   | 14 +++++++++
 5 files changed, 64 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/silent-rockets-tease.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/inspect-trace-store/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/inspect-trace-store/main.svelte

diff --git a/.changeset/silent-rockets-tease.md b/.changeset/silent-rockets-tease.md
new file mode 100644
index 0000000000..1a708c1d69
--- /dev/null
+++ b/.changeset/silent-rockets-tease.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: tag stores for `$inspect.trace()`
diff --git a/packages/svelte/src/internal/client/dev/tracing.js b/packages/svelte/src/internal/client/dev/tracing.js
index b7a6a38548..1b26c702fb 100644
--- a/packages/svelte/src/internal/client/dev/tracing.js
+++ b/packages/svelte/src/internal/client/dev/tracing.js
@@ -26,7 +26,7 @@ function log_entry(signal, entry) {
 		return;
 	}
 
-	const type = (signal.f & (DERIVED | ASYNC)) !== 0 ? '$derived' : '$state';
+	const type = get_type(signal);
 	const current_reaction = /** @type {Reaction} */ (active_reaction);
 	const dirty = signal.wv > current_reaction.wv || current_reaction.wv === 0;
 	const style = dirty
@@ -73,6 +73,15 @@ function log_entry(signal, entry) {
 	console.groupEnd();
 }
 
+/**
+ * @param {Value} signal
+ * @returns {'$state' | '$derived' | 'store'}
+ */
+function get_type(signal) {
+	if ((signal.f & (DERIVED | ASYNC)) !== 0) return '$derived';
+	return signal.label?.startsWith('$') ? 'store' : '$state';
+}
+
 /**
  * @template T
  * @param {() => string} label
diff --git a/packages/svelte/src/internal/client/reactivity/store.js b/packages/svelte/src/internal/client/reactivity/store.js
index e7a92ee052..ce082866ce 100644
--- a/packages/svelte/src/internal/client/reactivity/store.js
+++ b/packages/svelte/src/internal/client/reactivity/store.js
@@ -6,6 +6,7 @@ import { define_property, noop } from '../../shared/utils.js';
 import { get } from '../runtime.js';
 import { teardown } from './effects.js';
 import { mutable_source, set } from './sources.js';
+import { DEV } from 'esm-env';
 
 /**
  * Whether or not the prop currently being read is a store binding, as in
@@ -33,6 +34,10 @@ export function store_get(store, store_name, stores) {
 		unsubscribe: noop
 	});
 
+	if (DEV) {
+		entry.source.label = store_name;
+	}
+
 	// if the component that setup this is already unmounted we don't want to register a subscription
 	if (entry.store !== store && !(IS_UNMOUNTED in stores)) {
 		entry.unsubscribe();
diff --git a/packages/svelte/tests/runtime-runes/samples/inspect-trace-store/_config.js b/packages/svelte/tests/runtime-runes/samples/inspect-trace-store/_config.js
new file mode 100644
index 0000000000..4e16c0cf2a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/inspect-trace-store/_config.js
@@ -0,0 +1,30 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+import { normalise_trace_logs } from '../../../helpers.js';
+
+export default test({
+	compileOptions: {
+		dev: true
+	},
+
+	test({ assert, target, logs }) {
+		assert.deepEqual(normalise_trace_logs(logs), [
+			{ log: 'effect' },
+			{ log: 'store', highlighted: true },
+			{ log: '$count', highlighted: false },
+			{ log: 0 }
+		]);
+
+		logs.length = 0;
+
+		const [button] = target.querySelectorAll('button');
+		flushSync(() => button.click());
+
+		assert.deepEqual(normalise_trace_logs(logs), [
+			{ log: 'effect' },
+			{ log: 'store', highlighted: true },
+			{ log: '$count', highlighted: false },
+			{ log: 1 }
+		]);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/inspect-trace-store/main.svelte b/packages/svelte/tests/runtime-runes/samples/inspect-trace-store/main.svelte
new file mode 100644
index 0000000000..af57513365
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/inspect-trace-store/main.svelte
@@ -0,0 +1,14 @@
+<script>
+	import { writable } from 'svelte/store';
+
+	const count = writable(0);
+
+	$effect(() => {
+		$inspect.trace('effect');
+		$count;
+	});
+</script>
+
+<button onclick={() => $count += 1}>
+	clicks: {$count}
+</button>

From 0a2a2e213ab183dc5b038e4fa4eb4913dd7761a4 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Sat, 19 Jul 2025 22:17:14 -0400
Subject: [PATCH 109/148] fix: add labels to `@const` tags and props (#16454)

* fix: add labels to `@const` tags and props

* changeset
---
 .changeset/four-spiders-type.md                  |  5 +++++
 .../3-transform/client/visitors/ConstTag.js      | 16 ++++++++++++++--
 .../src/internal/client/reactivity/props.js      |  4 ++++
 3 files changed, 23 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/four-spiders-type.md

diff --git a/.changeset/four-spiders-type.md b/.changeset/four-spiders-type.md
new file mode 100644
index 0000000000..9a4056c50a
--- /dev/null
+++ b/.changeset/four-spiders-type.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: add labels to `@const` tags and props
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/ConstTag.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/ConstTag.js
index c1be1e3220..34acdd6bb9 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/ConstTag.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/ConstTag.js
@@ -17,7 +17,13 @@ export function ConstTag(node, context) {
 	// TODO we can almost certainly share some code with $derived(...)
 	if (declaration.id.type === 'Identifier') {
 		const init = build_expression(context, declaration.init, node.metadata.expression);
-		context.state.init.push(b.const(declaration.id, create_derived(context.state, b.thunk(init))));
+		let expression = create_derived(context.state, b.thunk(init));
+
+		if (dev) {
+			expression = b.call('$.tag', expression, b.literal(declaration.id.name));
+		}
+
+		context.state.init.push(b.const(declaration.id, expression));
 
 		context.state.transform[declaration.id.name] = { read: get_value };
 
@@ -55,7 +61,13 @@ export function ConstTag(node, context) {
 			])
 		);
 
-		context.state.init.push(b.const(tmp, create_derived(context.state, fn)));
+		let expression = create_derived(context.state, fn);
+
+		if (dev) {
+			expression = b.call('$.tag', expression, b.literal('[@const]'));
+		}
+
+		context.state.init.push(b.const(tmp, expression));
 
 		// we need to eagerly evaluate the expression in order to hit any
 		// 'Cannot access x before initialization' errors
diff --git a/packages/svelte/src/internal/client/reactivity/props.js b/packages/svelte/src/internal/client/reactivity/props.js
index f39d45bb04..28bfa88d96 100644
--- a/packages/svelte/src/internal/client/reactivity/props.js
+++ b/packages/svelte/src/internal/client/reactivity/props.js
@@ -393,6 +393,10 @@ export function prop(props, key, flags, fallback) {
 		return getter();
 	});
 
+	if (DEV) {
+		d.label = key;
+	}
+
 	// Capture the initial value if it's bindable
 	if (bindable) get(d);
 

From 53fdd0f93abee0dc89418c7338363e9b298d0900 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Sat, 19 Jul 2025 22:18:50 -0400
Subject: [PATCH 110/148] chore: remove some unused code (#16455)

---
 packages/svelte/src/internal/client/reactivity/props.js | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/packages/svelte/src/internal/client/reactivity/props.js b/packages/svelte/src/internal/client/reactivity/props.js
index 28bfa88d96..05b747a1c4 100644
--- a/packages/svelte/src/internal/client/reactivity/props.js
+++ b/packages/svelte/src/internal/client/reactivity/props.js
@@ -1,13 +1,11 @@
-/** @import { ComponentContext } from '#client' */
-/** @import { Derived, Effect, Source } from './types.js' */
+/** @import { Effect, Source } from './types.js' */
 import { DEV } from 'esm-env';
 import {
 	PROPS_IS_BINDABLE,
 	PROPS_IS_IMMUTABLE,
 	PROPS_IS_LAZY_INITIAL,
 	PROPS_IS_RUNES,
-	PROPS_IS_UPDATED,
-	UNINITIALIZED
+	PROPS_IS_UPDATED
 } from '../../../constants.js';
 import { get_descriptor, is_function } from '../../shared/utils.js';
 import { set, source, update } from './sources.js';

From d3a01bd5a7d09384e29a599834d9b554a7a973ee Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Sun, 20 Jul 2025 17:19:56 -0400
Subject: [PATCH 111/148] fix: always mark reactions of deriveds (#16457)

* tweak

* fix

* test

* changeset
---
 .changeset/angry-hornets-hug.md               |  5 ++
 .../internal/client/reactivity/deriveds.js    |  4 +-
 .../src/internal/client/reactivity/sources.js | 19 +++----
 .../async-time-travelling-derived/_config.js  | 56 +++++++++++++++++++
 .../async-time-travelling-derived/main.svelte | 26 +++++++++
 5 files changed, 98 insertions(+), 12 deletions(-)
 create mode 100644 .changeset/angry-hornets-hug.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-time-travelling-derived/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-time-travelling-derived/main.svelte

diff --git a/.changeset/angry-hornets-hug.md b/.changeset/angry-hornets-hug.md
new file mode 100644
index 0000000000..ffe59db100
--- /dev/null
+++ b/.changeset/angry-hornets-hug.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: always mark reactions of deriveds
diff --git a/packages/svelte/src/internal/client/reactivity/deriveds.js b/packages/svelte/src/internal/client/reactivity/deriveds.js
index fa6a9e02a1..7f730e365e 100644
--- a/packages/svelte/src/internal/client/reactivity/deriveds.js
+++ b/packages/svelte/src/internal/client/reactivity/deriveds.js
@@ -337,7 +337,9 @@ export function update_derived(derived) {
 
 	// don't mark derived clean if we're reading it inside a
 	// cleanup function, or it will cache a stale value
-	if (is_destroying_effect) return;
+	if (is_destroying_effect) {
+		return;
+	}
 
 	if (batch_deriveds !== null) {
 		batch_deriveds.set(derived, derived.v);
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index 9b534d2d71..f6b14f3360 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -314,9 +314,6 @@ function mark_reactions(signal, status) {
 		var reaction = reactions[i];
 		var flags = reaction.f;
 
-		// Skip any effects that are already dirty
-		if ((flags & DIRTY) !== 0) continue;
-
 		// In legacy mode, skip the current effect to prevent infinite loops
 		if (!runes && reaction === active_effect) continue;
 
@@ -326,15 +323,15 @@ function mark_reactions(signal, status) {
 			continue;
 		}
 
-		set_signal_status(reaction, status);
+		// don't set a DIRTY reaction to MAYBE_DIRTY
+		if ((flags & DIRTY) === 0) {
+			set_signal_status(reaction, status);
+		}
 
-		// If the signal a) was previously clean or b) is an unowned derived, then mark it
-		if ((flags & (CLEAN | UNOWNED)) !== 0) {
-			if ((flags & DERIVED) !== 0) {
-				mark_reactions(/** @type {Derived} */ (reaction), MAYBE_DIRTY);
-			} else {
-				schedule_effect(/** @type {Effect} */ (reaction));
-			}
+		if ((flags & DERIVED) !== 0) {
+			mark_reactions(/** @type {Derived} */ (reaction), MAYBE_DIRTY);
+		} else if ((flags & DIRTY) === 0) {
+			schedule_effect(/** @type {Effect} */ (reaction));
 		}
 	}
 }
diff --git a/packages/svelte/tests/runtime-runes/samples/async-time-travelling-derived/_config.js b/packages/svelte/tests/runtime-runes/samples/async-time-travelling-derived/_config.js
new file mode 100644
index 0000000000..06437d2e31
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-time-travelling-derived/_config.js
@@ -0,0 +1,56 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+
+		const [a, b, update] = target.querySelectorAll('button');
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>a</button>
+				<button>b</button>
+				<button>0</button>
+				<h1>a</h1>
+			`
+		);
+
+		b.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>a</button>
+				<button>b</button>
+				<button>0</button>
+				<h1>b</h1>
+			`
+		);
+
+		update.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>a</button>
+				<button>b</button>
+				<button>1</button>
+				<h1>b</h1>
+			`
+		);
+
+		a.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>a</button>
+				<button>b</button>
+				<button>1</button>
+				<h1>a</h1>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-time-travelling-derived/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-time-travelling-derived/main.svelte
new file mode 100644
index 0000000000..5fca286a78
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-time-travelling-derived/main.svelte
@@ -0,0 +1,26 @@
+<script>
+	let object = $state(null);
+	let count = $state(0);
+
+	const condition = $derived(object === null);
+</script>
+
+<svelte:boundary>
+	<button onclick={() => (object = null)}>a</button>
+	<button onclick={() => (object = {})}>b</button>
+
+	<button onclick={async () => {
+		count++;
+		await Promise.resolve();
+		object = {};
+	}}>{await count}</button>
+
+	{#if condition}
+		<h1>a</h1>
+	{:else}
+		<h1>b</h1>
+	{/if}
+
+	{#snippet pending()}{/snippet}
+</svelte:boundary>
+

From 1f99914a16e03209cb7c0aac8ce9d3d72bb32f15 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Sun, 20 Jul 2025 17:22:01 -0400
Subject: [PATCH 112/148] chore: move `capture_signals` to legacy module
 (#16456)

---
 .changeset/swift-cherries-know.md             |  5 ++
 .../svelte/src/internal/client/dev/tracing.js |  2 +-
 packages/svelte/src/internal/client/index.js  |  2 +-
 packages/svelte/src/internal/client/legacy.js | 46 ++++++++++++++++
 .../svelte/src/internal/client/runtime.js     | 54 ++-----------------
 5 files changed, 56 insertions(+), 53 deletions(-)
 create mode 100644 .changeset/swift-cherries-know.md
 create mode 100644 packages/svelte/src/internal/client/legacy.js

diff --git a/.changeset/swift-cherries-know.md b/.changeset/swift-cherries-know.md
new file mode 100644
index 0000000000..d8bbb1256a
--- /dev/null
+++ b/.changeset/swift-cherries-know.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: move `capture_signals` to legacy module
diff --git a/packages/svelte/src/internal/client/dev/tracing.js b/packages/svelte/src/internal/client/dev/tracing.js
index 1b26c702fb..673a710fac 100644
--- a/packages/svelte/src/internal/client/dev/tracing.js
+++ b/packages/svelte/src/internal/client/dev/tracing.js
@@ -4,7 +4,7 @@ import { snapshot } from '../../shared/clone.js';
 import { define_property } from '../../shared/utils.js';
 import { DERIVED, ASYNC, PROXY_PATH_SYMBOL, STATE_SYMBOL } from '#client/constants';
 import { effect_tracking } from '../reactivity/effects.js';
-import { active_reaction, captured_signals, set_captured_signals, untrack } from '../runtime.js';
+import { active_reaction, untrack } from '../runtime.js';
 
 /**
  * @typedef {{
diff --git a/packages/svelte/src/internal/client/index.js b/packages/svelte/src/internal/client/index.js
index cddb432a98..90f0f9baac 100644
--- a/packages/svelte/src/internal/client/index.js
+++ b/packages/svelte/src/internal/client/index.js
@@ -138,11 +138,11 @@ export {
 	mark_store_binding
 } from './reactivity/store.js';
 export { boundary, pending } from './dom/blocks/boundary.js';
+export { invalidate_inner_signals } from './legacy.js';
 export { set_text } from './render.js';
 export {
 	get,
 	safe_get,
-	invalidate_inner_signals,
 	tick,
 	untrack,
 	exclude_from_object,
diff --git a/packages/svelte/src/internal/client/legacy.js b/packages/svelte/src/internal/client/legacy.js
new file mode 100644
index 0000000000..97ad7244c0
--- /dev/null
+++ b/packages/svelte/src/internal/client/legacy.js
@@ -0,0 +1,46 @@
+/** @import { Value } from '#client' */
+import { internal_set } from './reactivity/sources.js';
+import { untrack } from './runtime.js';
+
+/**
+ * @type {Set<Value> | null}
+ * @deprecated
+ */
+export let captured_signals = null;
+
+/**
+ * Capture an array of all the signals that are read when `fn` is called
+ * @template T
+ * @param {() => T} fn
+ */
+function capture_signals(fn) {
+	var previous_captured_signals = captured_signals;
+
+	try {
+		captured_signals = new Set();
+
+		untrack(fn);
+
+		if (previous_captured_signals !== null) {
+			for (var signal of captured_signals) {
+				previous_captured_signals.add(signal);
+			}
+		}
+
+		return captured_signals;
+	} finally {
+		captured_signals = previous_captured_signals;
+	}
+}
+
+/**
+ * Invokes a function and captures all signals that are read during the invocation,
+ * then invalidates them.
+ * @param {() => any} fn
+ * @deprecated
+ */
+export function invalidate_inner_signals(fn) {
+	for (var signal of capture_signals(fn)) {
+		internal_set(signal, signal.v);
+	}
+}
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 3d3c89975c..e86866af2a 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -22,7 +22,7 @@ import {
 	STALE_REACTION,
 	ERROR_VALUE
 } from './constants.js';
-import { internal_set, old_values } from './reactivity/sources.js';
+import { old_values } from './reactivity/sources.js';
 import {
 	destroy_derived_effects,
 	execute_derived,
@@ -45,6 +45,7 @@ import * as w from './warnings.js';
 import { Batch, batch_deriveds, flushSync, schedule_effect } from './reactivity/batch.js';
 import { handle_error } from './error-handling.js';
 import { UNINITIALIZED } from '../../constants.js';
+import { captured_signals } from './legacy.js';
 
 export let is_updating_effect = false;
 
@@ -137,14 +138,6 @@ export function set_update_version(value) {
 // If we are working with a get() chain that has no active container,
 // to prevent memory leaks, we skip adding the reaction.
 export let skip_reaction = false;
-// Handle collecting all signals which are read during a specific time frame
-/** @type {Set<Value> | null} */
-export let captured_signals = null;
-
-/** @param {Set<Value> | null} value */
-export function set_captured_signals(value) {
-	captured_signals = value;
-}
 
 export function increment_write_version() {
 	return ++write_version;
@@ -531,9 +524,7 @@ export function get(signal) {
 	var flags = signal.f;
 	var is_derived = (flags & DERIVED) !== 0;
 
-	if (captured_signals !== null) {
-		captured_signals.add(signal);
-	}
+	captured_signals?.add(signal);
 
 	// Register the dependency on the current reaction signal.
 	if (active_reaction !== null && !untracking) {
@@ -713,45 +704,6 @@ export function safe_get(signal) {
 	return signal && get(signal);
 }
 
-/**
- * Capture an array of all the signals that are read when `fn` is called
- * @template T
- * @param {() => T} fn
- */
-function capture_signals(fn) {
-	var previous_captured_signals = captured_signals;
-	captured_signals = new Set();
-
-	var captured = captured_signals;
-	var signal;
-
-	try {
-		untrack(fn);
-		if (previous_captured_signals !== null) {
-			for (signal of captured_signals) {
-				previous_captured_signals.add(signal);
-			}
-		}
-	} finally {
-		captured_signals = previous_captured_signals;
-	}
-
-	return captured;
-}
-
-/**
- * Invokes a function and captures all signals that are read during the invocation,
- * then invalidates them.
- * @param {() => any} fn
- */
-export function invalidate_inner_signals(fn) {
-	var captured = capture_signals(() => untrack(fn));
-
-	for (var signal of captured) {
-		internal_set(signal, signal.v);
-	}
-}
-
 /**
  * When used inside a [`$derived`](https://svelte.dev/docs/svelte/$derived) or [`$effect`](https://svelte.dev/docs/svelte/$effect),
  * any state read inside `fn` will not be treated as a dependency.

From 8afe5ec0c5a2e38b9b3a55b0dec94b99aa10447c Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Sun, 20 Jul 2025 17:23:10 -0400
Subject: [PATCH 113/148] Version Packages (#16453)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/angry-hornets-hug.md    |  5 -----
 .changeset/four-spiders-type.md    |  5 -----
 .changeset/silent-rockets-tease.md |  5 -----
 packages/svelte/CHANGELOG.md       | 10 ++++++++++
 packages/svelte/package.json       |  2 +-
 packages/svelte/src/version.js     |  2 +-
 6 files changed, 12 insertions(+), 17 deletions(-)
 delete mode 100644 .changeset/angry-hornets-hug.md
 delete mode 100644 .changeset/four-spiders-type.md
 delete mode 100644 .changeset/silent-rockets-tease.md

diff --git a/.changeset/angry-hornets-hug.md b/.changeset/angry-hornets-hug.md
deleted file mode 100644
index ffe59db100..0000000000
--- a/.changeset/angry-hornets-hug.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: always mark reactions of deriveds
diff --git a/.changeset/four-spiders-type.md b/.changeset/four-spiders-type.md
deleted file mode 100644
index 9a4056c50a..0000000000
--- a/.changeset/four-spiders-type.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: add labels to `@const` tags and props
diff --git a/.changeset/silent-rockets-tease.md b/.changeset/silent-rockets-tease.md
deleted file mode 100644
index 1a708c1d69..0000000000
--- a/.changeset/silent-rockets-tease.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: tag stores for `$inspect.trace()`
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index c20618af11..472a2b4a98 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,15 @@
 # svelte
 
+## 5.36.11
+
+### Patch Changes
+
+- fix: always mark reactions of deriveds ([#16457](https://github.com/sveltejs/svelte/pull/16457))
+
+- fix: add labels to `@const` tags and props ([#16454](https://github.com/sveltejs/svelte/pull/16454))
+
+- fix: tag stores for `$inspect.trace()` ([#16452](https://github.com/sveltejs/svelte/pull/16452))
+
 ## 5.36.10
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 28ccb2884a..4b22911e6e 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.10",
+  "version": "5.36.11",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 8c59098e0c..07cf3cdf4d 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.10';
+export const VERSION = '5.36.11';
 export const PUBLIC_VERSION = '5';

From ce4a99ed6d0b4b53c7abb7a8763e8e4bc4de5431 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Sun, 20 Jul 2025 18:11:26 -0400
Subject: [PATCH 114/148] Version Packages (#16459)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/swift-cherries-know.md | 5 -----
 packages/svelte/CHANGELOG.md      | 6 ++++++
 packages/svelte/package.json      | 2 +-
 packages/svelte/src/version.js    | 2 +-
 4 files changed, 8 insertions(+), 7 deletions(-)
 delete mode 100644 .changeset/swift-cherries-know.md

diff --git a/.changeset/swift-cherries-know.md b/.changeset/swift-cherries-know.md
deleted file mode 100644
index d8bbb1256a..0000000000
--- a/.changeset/swift-cherries-know.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-chore: move `capture_signals` to legacy module
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 472a2b4a98..1234efa0d5 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,11 @@
 # svelte
 
+## 5.36.12
+
+### Patch Changes
+
+- chore: move `capture_signals` to legacy module ([#16456](https://github.com/sveltejs/svelte/pull/16456))
+
 ## 5.36.11
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 4b22911e6e..629ec99af8 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.11",
+  "version": "5.36.12",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 07cf3cdf4d..465bd73f0f 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.11';
+export const VERSION = '5.36.12';
 export const PUBLIC_VERSION = '5';

From aabd333d89a4c9241bc3ed57752cb2616dd66b7c Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Mon, 21 Jul 2025 15:22:13 +0200
Subject: [PATCH 115/148] fix: ensure subscriptions are picked up correctly by
 deriveds (#16466)

Increment the version to ensure any dependent deriveds are marked dirty when the subscription is picked up again later. If we didn't do this then the comparison of write versions would determine that the derived has a later version than the subscriber, and it would not be re-run.

Fixes #16311
Fixes #15888
---
 .changeset/fresh-penguins-impress.md          |  5 +++
 .../src/reactivity/create-subscriber.js       |  4 ++
 .../samples/store-inside-derived/_config.js   | 45 +++++++++++++++++++
 .../samples/store-inside-derived/main.svelte  | 36 +++++++++++++++
 4 files changed, 90 insertions(+)
 create mode 100644 .changeset/fresh-penguins-impress.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/store-inside-derived/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/store-inside-derived/main.svelte

diff --git a/.changeset/fresh-penguins-impress.md b/.changeset/fresh-penguins-impress.md
new file mode 100644
index 0000000000..35ff4f0aaa
--- /dev/null
+++ b/.changeset/fresh-penguins-impress.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure subscriptions are picked up correctly by deriveds
diff --git a/packages/svelte/src/reactivity/create-subscriber.js b/packages/svelte/src/reactivity/create-subscriber.js
index 4dcac4e6f6..6f9313eb0a 100644
--- a/packages/svelte/src/reactivity/create-subscriber.js
+++ b/packages/svelte/src/reactivity/create-subscriber.js
@@ -82,6 +82,10 @@ export function createSubscriber(start) {
 						if (subscribers === 0) {
 							stop?.();
 							stop = undefined;
+							// Increment the version to ensure any dependent deriveds are marked dirty when the subscription is picked up again later.
+							// If we didn't do this then the comparison of write versions would determine that the derived has a later version than
+							// the subscriber, and it would not be re-run.
+							increment(version);
 						}
 					});
 				};
diff --git a/packages/svelte/tests/runtime-runes/samples/store-inside-derived/_config.js b/packages/svelte/tests/runtime-runes/samples/store-inside-derived/_config.js
new file mode 100644
index 0000000000..de078b1e75
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/store-inside-derived/_config.js
@@ -0,0 +1,45 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	test: ({ assert, target }) => {
+		const [loading, increment] = target.querySelectorAll('button');
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<div>$value: 0</div>
+				<div>valueFromStore.current: 0</div>
+				<div>valueDerivedCurrent: 0</div>
+				<button>Loading</button>
+				<button>Increment</button>
+			`
+		);
+
+		loading.click();
+		flushSync();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<div>$value: Loading...</div>
+				<div>valueFromStore.current: Loading...</div>
+				<div>valueDerivedCurrent: Loading...</div>
+				<button>Loading</button>
+				<button>Increment</button>
+			`
+		);
+
+		increment.click();
+		flushSync();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<div>$value: 1</div>
+				<div>valueFromStore.current: 1</div>
+				<div>valueDerivedCurrent: 1</div>
+				<button>Loading</button>
+				<button>Increment</button>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/store-inside-derived/main.svelte b/packages/svelte/tests/runtime-runes/samples/store-inside-derived/main.svelte
new file mode 100644
index 0000000000..06d0a0d4b4
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/store-inside-derived/main.svelte
@@ -0,0 +1,36 @@
+<script>
+  import { fromStore, writable } from 'svelte/store';
+	
+  let isLoading = $state(false);
+
+  const value = writable(0);
+  const valueFromStore = fromStore(value);
+  const valueDerivedCurrent = $derived(valueFromStore.current);
+</script>
+
+<div>
+	$value: {isLoading ? 'Loading...' : $value}
+</div>
+
+<div>
+	valueFromStore.current: {isLoading ? 'Loading...' : valueFromStore.current}
+</div>
+
+<div>
+	valueDerivedCurrent: {isLoading ? 'Loading...' : valueDerivedCurrent}
+</div>
+
+<button
+	onclick={() => {
+		isLoading = true;
+	}}>
+	Loading
+</button>
+
+<button
+	onclick={() => {
+		$value++;
+		isLoading = false;
+	}}>
+	Increment
+</button>

From 28403beaeb360fd7b4096fe7c8ef98e43d0676c2 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Mon, 21 Jul 2025 13:32:47 -0400
Subject: [PATCH 116/148] Version Packages (#16467)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/fresh-penguins-impress.md | 5 -----
 packages/svelte/CHANGELOG.md         | 6 ++++++
 packages/svelte/package.json         | 2 +-
 packages/svelte/src/version.js       | 2 +-
 4 files changed, 8 insertions(+), 7 deletions(-)
 delete mode 100644 .changeset/fresh-penguins-impress.md

diff --git a/.changeset/fresh-penguins-impress.md b/.changeset/fresh-penguins-impress.md
deleted file mode 100644
index 35ff4f0aaa..0000000000
--- a/.changeset/fresh-penguins-impress.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: ensure subscriptions are picked up correctly by deriveds
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 1234efa0d5..5a5e532a08 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,11 @@
 # svelte
 
+## 5.36.13
+
+### Patch Changes
+
+- fix: ensure subscriptions are picked up correctly by deriveds ([#16466](https://github.com/sveltejs/svelte/pull/16466))
+
 ## 5.36.12
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 629ec99af8..4bf9a5df22 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.12",
+  "version": "5.36.13",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 465bd73f0f..7d47fbc5f1 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.12';
+export const VERSION = '5.36.13';
 export const PUBLIC_VERSION = '5';

From 9412c5861c365610d7c6c0e4ecd3572ac3fe5860 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 21 Jul 2025 22:17:25 -0400
Subject: [PATCH 117/148] chore: log effect functions in log_effect_tree
 (#16468)

---
 packages/svelte/src/internal/client/dev/debug.js | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/packages/svelte/src/internal/client/dev/debug.js b/packages/svelte/src/internal/client/dev/debug.js
index c47080ed2f..2714a3af1f 100644
--- a/packages/svelte/src/internal/client/dev/debug.js
+++ b/packages/svelte/src/internal/client/dev/debug.js
@@ -63,6 +63,13 @@ export function log_effect_tree(effect, depth = 0) {
 
 		// eslint-disable-next-line no-console
 		console.log(callsite);
+	} else {
+		// eslint-disable-next-line no-console
+		console.groupCollapsed(`%cfn`, `font-weight: normal`);
+		// eslint-disable-next-line no-console
+		console.log(effect.fn);
+		// eslint-disable-next-line no-console
+		console.groupEnd();
 	}
 
 	if (effect.deps !== null) {

From 1deb31082a383fb5f4f9ae86f1ff12657823bcd7 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 22 Jul 2025 12:56:32 -0400
Subject: [PATCH 118/148] fix: abort and reschedule `$effect.pre` when
 necessary (#16335)

* unskip failing test

* fix

* tidy up

* skip_no_async

* add comment
---
 .../runtime-runes/samples/effect-order-7/_config.js  | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/packages/svelte/tests/runtime-runes/samples/effect-order-7/_config.js b/packages/svelte/tests/runtime-runes/samples/effect-order-7/_config.js
index 29c33c7b18..f0a9c2e867 100644
--- a/packages/svelte/tests/runtime-runes/samples/effect-order-7/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/effect-order-7/_config.js
@@ -2,14 +2,18 @@ import { flushSync } from 'svelte';
 import { test } from '../../test';
 
 export default test({
-	skip: true,
+	// For this to work in non-async mode, we would need to abort
+	// inside `#traverse_effect_tree`, which would be very
+	// complicated and annoying. Since this hasn't been
+	// a real issue (AFAICT), we ignore it
+	skip_no_async: true,
 
-	async test({ assert, target, logs }) {
+	async test({ target }) {
 		const [open, close] = target.querySelectorAll('button');
 
 		flushSync(() => open.click());
-		flushSync(() => close.click());
 
-		assert.deepEqual(logs, [true]);
+		// if the effect queue isn't aborted after the state change, this will throw
+		flushSync(() => close.click());
 	}
 });

From 68372460e999e48ac09b1c2bd4935ceaea8c33e9 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 22 Jul 2025 13:29:15 -0400
Subject: [PATCH 119/148] chore: small tidy up (#16476)

---
 .../src/internal/client/reactivity/batch.js   | 66 +++++++++----------
 1 file changed, 33 insertions(+), 33 deletions(-)

diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index ec082bb595..c452211894 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -193,6 +193,8 @@ export class Batch {
 		// if we didn't start any new async work, and no async work
 		// is outstanding from a previous flush, commit
 		if (this.#async_effects.length === 0 && this.#pending === 0) {
+			this.#commit();
+
 			var render_effects = this.#render_effects;
 			var effects = this.#effects;
 
@@ -200,8 +202,6 @@ export class Batch {
 			this.#effects = [];
 			this.#block_effects = [];
 
-			this.#commit();
-
 			flush_queued_effects(render_effects);
 			flush_queued_effects(effects);
 
@@ -539,43 +539,43 @@ function flush_queued_effects(effects) {
 	var length = effects.length;
 	if (length === 0) return;
 
-	for (var i = 0; i < length; i++) {
-		var effect = effects[i];
-
-		if ((effect.f & (DESTROYED | INERT)) === 0) {
-			if (is_dirty(effect)) {
-				var wv = write_version;
-
-				update_effect(effect);
-
-				// Effects with no dependencies or teardown do not get added to the effect tree.
-				// Deferred effects (e.g. `$effect(...)`) _are_ added to the tree because we
-				// don't know if we need to keep them until they are executed. Doing the check
-				// here (rather than in `update_effect`) allows us to skip the work for
-				// immediate effects.
-				if (effect.deps === null && effect.first === null && effect.nodes_start === null) {
-					// if there's no teardown or abort controller we completely unlink
-					// the effect from the graph
-					if (effect.teardown === null && effect.ac === null) {
-						// remove this effect from the graph
-						unlink_effect(effect);
-					} else {
-						// keep the effect in the graph, but free up some memory
-						effect.fn = null;
-					}
-				}
+	var i = 0;
 
-				// if state is written in a user effect, abort and re-schedule, lest we run
-				// effects that should be removed as a result of the state change
-				if (write_version > wv && (effect.f & USER_EFFECT) !== 0) {
-					break;
+	while (i < length) {
+		var effect = effects[i++];
+
+		if ((effect.f & (DESTROYED | INERT)) === 0 && is_dirty(effect)) {
+			var wv = write_version;
+
+			update_effect(effect);
+
+			// Effects with no dependencies or teardown do not get added to the effect tree.
+			// Deferred effects (e.g. `$effect(...)`) _are_ added to the tree because we
+			// don't know if we need to keep them until they are executed. Doing the check
+			// here (rather than in `update_effect`) allows us to skip the work for
+			// immediate effects.
+			if (effect.deps === null && effect.first === null && effect.nodes_start === null) {
+				// if there's no teardown or abort controller we completely unlink
+				// the effect from the graph
+				if (effect.teardown === null && effect.ac === null) {
+					// remove this effect from the graph
+					unlink_effect(effect);
+				} else {
+					// keep the effect in the graph, but free up some memory
+					effect.fn = null;
 				}
 			}
+
+			// if state is written in a user effect, abort and re-schedule, lest we run
+			// effects that should be removed as a result of the state change
+			if (write_version > wv && (effect.f & USER_EFFECT) !== 0) {
+				break;
+			}
 		}
 	}
 
-	for (; i < length; i += 1) {
-		schedule_effect(effects[i]);
+	while (i < length) {
+		schedule_effect(effects[i++]);
 	}
 }
 

From 8e2f4b51c50a2e10bc482fac6d900be921dd8b74 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 23 Jul 2025 07:55:51 -0400
Subject: [PATCH 120/148] fix: unset batch before flushing queued effects
 (#16482)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

* - add state changes resulting from an $effect to a separate new batch
- schedule rerunning effects based on the sources that are dirty, not just rerunning them all blindly (excempting async effects which will have run by that time already)

* test

* better fix

* tests

* this fixes the last test somehow

* fix #16477

* typo

* copy over changeset from #16477

* copy over changeset from #16464

* changeset

* dedupe

* move flushing_sync check inside Batch.ensure

* unused

* flushing_sync -> is_flushing_sync

* remove flush_effects method

* dedupe declaration

* tweak

* tweak

* update comment — it _does_ feel slightly wrong, but no wronger than the rest of this cursed function

---------

Co-authored-by: Simon Holthausen <simon.holthausen@vercel.com>
---
 .changeset/grumpy-boats-beg.md                |   5 +
 .changeset/shiny-walls-fix.md                 |   5 +
 .changeset/thick-mice-kick.md                 |   5 +
 .../src/internal/client/reactivity/batch.js   | 190 ++++++++++--------
 .../src/internal/client/reactivity/sources.js |  11 +-
 .../Component.svelte                          |   7 +
 .../1000-reading-derived-effects/_config.js   |   5 +
 .../1000-reading-derived-effects/main.svelte  |   8 +
 .../_config.js                                |  26 +++
 .../main.svelte                               |  27 +++
 .../async-effect-triggers-await/_config.js    |  32 +++
 .../async-effect-triggers-await/main.svelte   |  24 +++
 .../binding-update-while-focused-2/_config.js |  24 +++
 .../main.svelte                               |  21 ++
 14 files changed, 298 insertions(+), 92 deletions(-)
 create mode 100644 .changeset/grumpy-boats-beg.md
 create mode 100644 .changeset/shiny-walls-fix.md
 create mode 100644 .changeset/thick-mice-kick.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/1000-reading-derived-effects/Component.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/1000-reading-derived-effects/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/1000-reading-derived-effects/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-binding-update-while-focused/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-binding-update-while-focused/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-effect-triggers-await/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-effect-triggers-await/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/binding-update-while-focused-2/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/binding-update-while-focused-2/main.svelte

diff --git a/.changeset/grumpy-boats-beg.md b/.changeset/grumpy-boats-beg.md
new file mode 100644
index 0000000000..f677743def
--- /dev/null
+++ b/.changeset/grumpy-boats-beg.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: keep input in sync when binding updated via effect
diff --git a/.changeset/shiny-walls-fix.md b/.changeset/shiny-walls-fix.md
new file mode 100644
index 0000000000..91ed548728
--- /dev/null
+++ b/.changeset/shiny-walls-fix.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: prevent infinite async loop
diff --git a/.changeset/thick-mice-kick.md b/.changeset/thick-mice-kick.md
new file mode 100644
index 0000000000..eec55b77ee
--- /dev/null
+++ b/.changeset/thick-mice-kick.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: exclude derived writes from effect abort and rescheduling
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index c452211894..ce413fa1e1 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -21,14 +21,13 @@ import {
 	is_updating_effect,
 	set_is_updating_effect,
 	set_signal_status,
-	update_effect,
-	write_version
+	update_effect
 } from '../runtime.js';
 import * as e from '../errors.js';
 import { flush_tasks } from '../dom/task.js';
 import { DEV } from 'esm-env';
 import { invoke_error_boundary } from '../error-handling.js';
-import { old_values } from './sources.js';
+import { mark_reactions, old_values } from './sources.js';
 import { unlink_effect } from './effects.js';
 import { unset_context } from './async.js';
 
@@ -70,13 +69,15 @@ let last_scheduled_effect = null;
 
 let is_flushing = false;
 
+let is_flushing_sync = false;
+
 export class Batch {
 	/**
 	 * The current values of any sources that are updated in this batch
 	 * They keys of this map are identical to `this.#previous`
 	 * @type {Map<Source, any>}
 	 */
-	#current = new Map();
+	current = new Map();
 
 	/**
 	 * The values of any sources that are updated in this batch _before_ those updates took place.
@@ -156,7 +157,7 @@ export class Batch {
 	 *
 	 * @param {Effect[]} root_effects
 	 */
-	#process(root_effects) {
+	process(root_effects) {
 		queued_root_effects = [];
 
 		/** @type {Map<Source, { v: unknown, wv: number }> | null} */
@@ -169,7 +170,7 @@ export class Batch {
 			current_values = new Map();
 			batch_deriveds = new Map();
 
-			for (const [source, current] of this.#current) {
+			for (const [source, current] of this.current) {
 				current_values.set(source, { v: source.v, wv: source.wv });
 				source.v = current;
 			}
@@ -202,9 +203,22 @@ export class Batch {
 			this.#effects = [];
 			this.#block_effects = [];
 
+			// If sources are written to, then work needs to happen in a separate batch, else prior sources would be mixed with
+			// newly updated sources, which could lead to infinite loops when effects run over and over again.
+			current_batch = null;
+
 			flush_queued_effects(render_effects);
 			flush_queued_effects(effects);
 
+			// Reinstate the current batch if there was no new one created, as `process()` runs in a loop in `flush_effects()`.
+			// That method expects `current_batch` to be set, and could run the loop again if effects result in new effects
+			// being scheduled but without writes happening in which case no new batch is created.
+			if (current_batch === null) {
+				current_batch = this;
+			} else {
+				batches.delete(this);
+			}
+
 			this.#deferred?.resolve();
 		} else {
 			// otherwise mark effects clean so they get scheduled on the next run
@@ -300,7 +314,7 @@ export class Batch {
 			this.#previous.set(source, value);
 		}
 
-		this.#current.set(source, source.v);
+		this.current.set(source, source.v);
 	}
 
 	activate() {
@@ -327,13 +341,13 @@ export class Batch {
 
 	flush() {
 		if (queued_root_effects.length > 0) {
-			this.flush_effects();
+			flush_effects();
 		} else {
 			this.#commit();
 		}
 
 		if (current_batch !== this) {
-			// this can happen if a `flushSync` occurred during `this.flush_effects()`,
+			// this can happen if a `flushSync` occurred during `flush_effects()`,
 			// which is permitted in legacy mode despite being a terrible idea
 			return;
 		}
@@ -345,52 +359,6 @@ export class Batch {
 		this.deactivate();
 	}
 
-	flush_effects() {
-		var was_updating_effect = is_updating_effect;
-		is_flushing = true;
-
-		try {
-			var flush_count = 0;
-			set_is_updating_effect(true);
-
-			while (queued_root_effects.length > 0) {
-				if (flush_count++ > 1000) {
-					if (DEV) {
-						var updates = new Map();
-
-						for (const source of this.#current.keys()) {
-							for (const [stack, update] of source.updated ?? []) {
-								var entry = updates.get(stack);
-
-								if (!entry) {
-									entry = { error: update.error, count: 0 };
-									updates.set(stack, entry);
-								}
-
-								entry.count += update.count;
-							}
-						}
-
-						for (const update of updates.values()) {
-							// eslint-disable-next-line no-console
-							console.error(update.error);
-						}
-					}
-
-					infinite_loop_guard();
-				}
-
-				this.#process(queued_root_effects);
-				old_values.clear();
-			}
-		} finally {
-			is_flushing = false;
-			set_is_updating_effect(was_updating_effect);
-
-			last_scheduled_effect = null;
-		}
-	}
-
 	/**
 	 * Append and remove branches to/from the DOM
 	 */
@@ -412,19 +380,8 @@ export class Batch {
 		this.#pending -= 1;
 
 		if (this.#pending === 0) {
-			for (const e of this.#render_effects) {
-				set_signal_status(e, DIRTY);
-				schedule_effect(e);
-			}
-
-			for (const e of this.#effects) {
-				set_signal_status(e, DIRTY);
-				schedule_effect(e);
-			}
-
-			for (const e of this.#block_effects) {
-				set_signal_status(e, DIRTY);
-				schedule_effect(e);
+			for (const source of this.current.keys()) {
+				mark_reactions(source, DIRTY, false);
 			}
 
 			this.#render_effects = [];
@@ -445,12 +402,12 @@ export class Batch {
 		return (this.#deferred ??= deferred()).promise;
 	}
 
-	static ensure(autoflush = true) {
+	static ensure() {
 		if (current_batch === null) {
 			const batch = (current_batch = new Batch());
 			batches.add(current_batch);
 
-			if (autoflush) {
+			if (!is_flushing_sync) {
 				Batch.enqueue(() => {
 					if (current_batch !== batch) {
 						// a flushSync happened in the meantime
@@ -487,32 +444,85 @@ export function flushSync(fn) {
 		e.flush_sync_in_effect();
 	}
 
-	var result;
+	var was_flushing_sync = is_flushing_sync;
+	is_flushing_sync = true;
 
-	const batch = Batch.ensure(false);
+	try {
+		var result;
 
-	if (fn) {
-		batch.flush_effects();
+		if (fn) {
+			flush_effects();
+			result = fn();
+		}
 
-		result = fn();
-	}
+		while (true) {
+			flush_tasks();
 
-	while (true) {
-		flush_tasks();
+			if (queued_root_effects.length === 0) {
+				current_batch?.flush();
 
-		if (queued_root_effects.length === 0) {
-			if (batch === current_batch) {
-				batch.flush();
+				// we need to check again, in case we just updated an `$effect.pending()`
+				if (queued_root_effects.length === 0) {
+					// this would be reset in `flush_effects()` but since we are early returning here,
+					// we need to reset it here as well in case the first time there's 0 queued root effects
+					last_scheduled_effect = null;
+
+					return /** @type {T} */ (result);
+				}
 			}
 
-			// this would be reset in `batch.flush_effects()` but since we are early returning here,
-			// we need to reset it here as well in case the first time there's 0 queued root effects
-			last_scheduled_effect = null;
+			flush_effects();
+		}
+	} finally {
+		is_flushing_sync = was_flushing_sync;
+	}
+}
+
+function flush_effects() {
+	var was_updating_effect = is_updating_effect;
+	is_flushing = true;
+
+	try {
+		var flush_count = 0;
+		set_is_updating_effect(true);
+
+		while (queued_root_effects.length > 0) {
+			var batch = Batch.ensure();
+
+			if (flush_count++ > 1000) {
+				if (DEV) {
+					var updates = new Map();
+
+					for (const source of batch.current.keys()) {
+						for (const [stack, update] of source.updated ?? []) {
+							var entry = updates.get(stack);
+
+							if (!entry) {
+								entry = { error: update.error, count: 0 };
+								updates.set(stack, entry);
+							}
+
+							entry.count += update.count;
+						}
+					}
+
+					for (const update of updates.values()) {
+						// eslint-disable-next-line no-console
+						console.error(update.error);
+					}
+				}
+
+				infinite_loop_guard();
+			}
 
-			return /** @type {T} */ (result);
+			batch.process(queued_root_effects);
+			old_values.clear();
 		}
+	} finally {
+		is_flushing = false;
+		set_is_updating_effect(was_updating_effect);
 
-		batch.flush_effects();
+		last_scheduled_effect = null;
 	}
 }
 
@@ -545,7 +555,7 @@ function flush_queued_effects(effects) {
 		var effect = effects[i++];
 
 		if ((effect.f & (DESTROYED | INERT)) === 0 && is_dirty(effect)) {
-			var wv = write_version;
+			var n = current_batch ? current_batch.current.size : 0;
 
 			update_effect(effect);
 
@@ -568,7 +578,11 @@ function flush_queued_effects(effects) {
 
 			// if state is written in a user effect, abort and re-schedule, lest we run
 			// effects that should be removed as a result of the state change
-			if (write_version > wv && (effect.f & USER_EFFECT) !== 0) {
+			if (
+				current_batch !== null &&
+				current_batch.current.size > n &&
+				(effect.f & USER_EFFECT) !== 0
+			) {
 				break;
 			}
 		}
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index f6b14f3360..3b28c8fdce 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -179,7 +179,7 @@ export function internal_set(source, value) {
 
 		source.v = value;
 
-		const batch = Batch.ensure();
+		var batch = Batch.ensure();
 		batch.capture(source, old_value);
 
 		if (DEV) {
@@ -301,9 +301,10 @@ export function increment(source) {
 /**
  * @param {Value} signal
  * @param {number} status should be DIRTY or MAYBE_DIRTY
+ * @param {boolean} schedule_async
  * @returns {void}
  */
-function mark_reactions(signal, status) {
+export function mark_reactions(signal, status, schedule_async = true) {
 	var reactions = signal.reactions;
 	if (reactions === null) return;
 
@@ -323,14 +324,16 @@ function mark_reactions(signal, status) {
 			continue;
 		}
 
+		var should_schedule = (flags & DIRTY) === 0 && (schedule_async || (flags & ASYNC) === 0);
+
 		// don't set a DIRTY reaction to MAYBE_DIRTY
-		if ((flags & DIRTY) === 0) {
+		if (should_schedule) {
 			set_signal_status(reaction, status);
 		}
 
 		if ((flags & DERIVED) !== 0) {
 			mark_reactions(/** @type {Derived} */ (reaction), MAYBE_DIRTY);
-		} else if ((flags & DIRTY) === 0) {
+		} else if (should_schedule) {
 			schedule_effect(/** @type {Effect} */ (reaction));
 		}
 	}
diff --git a/packages/svelte/tests/runtime-runes/samples/1000-reading-derived-effects/Component.svelte b/packages/svelte/tests/runtime-runes/samples/1000-reading-derived-effects/Component.svelte
new file mode 100644
index 0000000000..7a54323cb9
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/1000-reading-derived-effects/Component.svelte
@@ -0,0 +1,7 @@
+<script>
+	const der = $derived(false);
+
+	$effect(() => {
+		der
+	});
+</script>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/1000-reading-derived-effects/_config.js b/packages/svelte/tests/runtime-runes/samples/1000-reading-derived-effects/_config.js
new file mode 100644
index 0000000000..2e4a27cf09
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/1000-reading-derived-effects/_config.js
@@ -0,0 +1,5 @@
+import { test } from '../../test';
+
+export default test({
+	async test() {}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/1000-reading-derived-effects/main.svelte b/packages/svelte/tests/runtime-runes/samples/1000-reading-derived-effects/main.svelte
new file mode 100644
index 0000000000..bd326edfb9
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/1000-reading-derived-effects/main.svelte
@@ -0,0 +1,8 @@
+<script>
+	import Component from './Component.svelte';
+	const arr = Array.from({length: 10001});
+</script>
+
+{#each arr}
+	<Component />
+{/each}
diff --git a/packages/svelte/tests/runtime-runes/samples/async-binding-update-while-focused/_config.js b/packages/svelte/tests/runtime-runes/samples/async-binding-update-while-focused/_config.js
new file mode 100644
index 0000000000..782ae945f9
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-binding-update-while-focused/_config.js
@@ -0,0 +1,26 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+
+		const [input] = target.querySelectorAll('input');
+
+		input.focus();
+		input.value = '3';
+		input.dispatchEvent(new InputEvent('input', { bubbles: true }));
+		await tick();
+
+		assert.equal(input.value, '3');
+		assert.htmlEqual(target.innerHTML, `<p>3</p> <input type="number" />`);
+
+		input.focus();
+		input.value = '1';
+		input.dispatchEvent(new InputEvent('input', { bubbles: true }));
+		await tick();
+
+		assert.equal(input.value, '2');
+		assert.htmlEqual(target.innerHTML, `<p>2</p> <input type="number" />`);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-binding-update-while-focused/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-binding-update-while-focused/main.svelte
new file mode 100644
index 0000000000..763ce6ebf0
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-binding-update-while-focused/main.svelte
@@ -0,0 +1,27 @@
+<script>
+	let value = $state(0)
+	const min = 2
+	const max = 5
+
+	$effect(() => {
+		setValue()
+	})
+
+	function setValue() {
+		if (value < min) {
+			value = min
+		}
+		if (value > max) {
+			value = max
+		}
+	}
+</script>
+
+<svelte:boundary>
+	<p>{await value}</p>
+	<input type="number" bind:value />
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-effect-triggers-await/_config.js b/packages/svelte/tests/runtime-runes/samples/async-effect-triggers-await/_config.js
new file mode 100644
index 0000000000..c551cc6b8c
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-effect-triggers-await/_config.js
@@ -0,0 +1,32 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+
+		const [increment] = target.querySelectorAll('button');
+
+		increment.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<p>1</p>
+				<p>1</p>
+			`
+		);
+
+		increment.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<p>2</p>
+				<p>2</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-effect-triggers-await/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-effect-triggers-await/main.svelte
new file mode 100644
index 0000000000..153fe03f0d
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-effect-triggers-await/main.svelte
@@ -0,0 +1,24 @@
+<script lang="ts">
+	let data = $state(Promise.resolve(0));
+
+	let count = $state(0);
+	let unrelated = $state(0);
+
+	$effect(() => {
+		data = Promise.resolve(count)
+		unrelated = count;
+	});
+</script>
+
+<svelte:boundary>
+	<button onclick={() => count += 1}>increment</button>
+	<p>{JSON.stringify((await data), null, 2)}</p>
+	{#if true}
+		<!-- inside if block to force it into a different render effect -->
+		<p>{unrelated}</p>
+	{/if}
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused-2/_config.js b/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused-2/_config.js
new file mode 100644
index 0000000000..7a56c79d71
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused-2/_config.js
@@ -0,0 +1,24 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	test({ assert, target }) {
+		const [input] = target.querySelectorAll('input');
+
+		input.focus();
+		input.value = '3';
+		input.dispatchEvent(new InputEvent('input', { bubbles: true }));
+		flushSync();
+
+		assert.equal(input.value, '3');
+		assert.htmlEqual(target.innerHTML, `<p>3</p> <input type="number" />`);
+
+		input.focus();
+		input.value = '1';
+		input.dispatchEvent(new InputEvent('input', { bubbles: true }));
+		flushSync();
+
+		assert.equal(input.value, '2');
+		assert.htmlEqual(target.innerHTML, `<p>2</p> <input type="number" />`);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused-2/main.svelte b/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused-2/main.svelte
new file mode 100644
index 0000000000..b0597c223b
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused-2/main.svelte
@@ -0,0 +1,21 @@
+<script>
+	let value = $state(0)
+	const min = 2
+	const max = 5
+
+	$effect(() => {
+		setValue()
+	})
+
+	function setValue() {
+		if (value < min) {
+			value = min
+		}
+		if (value > max) {
+			value = max
+		}
+	}
+</script>
+
+<p>{value}</p>
+<input type="number" bind:value />

From c26365bdda1a13e98a2e75f17da655e08ff4f8bc Mon Sep 17 00:00:00 2001
From: Hyunbin Seo <47051820+hyunbinseo@users.noreply.github.com>
Date: Wed, 23 Jul 2025 21:02:28 +0900
Subject: [PATCH 121/148] chore: rename form `accept-charset` attribute
 (#16478)

* chore: rename form accept-charset attribute

* chore: utf-8 to lowercase

Co-authored-by: Rich Harris <hello@rich-harris.dev>

* Update .changeset/healthy-carpets-deny.md

---------

Co-authored-by: Rich Harris <hello@rich-harris.dev>
---
 .changeset/healthy-carpets-deny.md | 5 +++++
 packages/svelte/elements.d.ts      | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/healthy-carpets-deny.md

diff --git a/.changeset/healthy-carpets-deny.md b/.changeset/healthy-carpets-deny.md
new file mode 100644
index 0000000000..8f8db7fa9c
--- /dev/null
+++ b/.changeset/healthy-carpets-deny.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: rename form accept-charset attribute
diff --git a/packages/svelte/elements.d.ts b/packages/svelte/elements.d.ts
index 1492f77792..604241592a 100644
--- a/packages/svelte/elements.d.ts
+++ b/packages/svelte/elements.d.ts
@@ -996,7 +996,7 @@ export interface HTMLFieldsetAttributes extends HTMLAttributes<HTMLFieldSetEleme
 }
 
 export interface HTMLFormAttributes extends HTMLAttributes<HTMLFormElement> {
-	acceptcharset?: string | undefined | null;
+	'accept-charset'?: 'utf-8' | (string & {}) | undefined | null;
 	action?: string | undefined | null;
 	autocomplete?: AutoFillBase | undefined | null;
 	enctype?:

From f8820956d2591288de53927c5e173242a13f125a Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Wed, 23 Jul 2025 11:23:52 -0400
Subject: [PATCH 122/148] Version Packages (#16484)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/grumpy-boats-beg.md     |  5 -----
 .changeset/healthy-carpets-deny.md |  5 -----
 .changeset/shiny-walls-fix.md      |  5 -----
 .changeset/thick-mice-kick.md      |  5 -----
 packages/svelte/CHANGELOG.md       | 12 ++++++++++++
 packages/svelte/package.json       |  2 +-
 packages/svelte/src/version.js     |  2 +-
 7 files changed, 14 insertions(+), 22 deletions(-)
 delete mode 100644 .changeset/grumpy-boats-beg.md
 delete mode 100644 .changeset/healthy-carpets-deny.md
 delete mode 100644 .changeset/shiny-walls-fix.md
 delete mode 100644 .changeset/thick-mice-kick.md

diff --git a/.changeset/grumpy-boats-beg.md b/.changeset/grumpy-boats-beg.md
deleted file mode 100644
index f677743def..0000000000
--- a/.changeset/grumpy-boats-beg.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: keep input in sync when binding updated via effect
diff --git a/.changeset/healthy-carpets-deny.md b/.changeset/healthy-carpets-deny.md
deleted file mode 100644
index 8f8db7fa9c..0000000000
--- a/.changeset/healthy-carpets-deny.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: rename form accept-charset attribute
diff --git a/.changeset/shiny-walls-fix.md b/.changeset/shiny-walls-fix.md
deleted file mode 100644
index 91ed548728..0000000000
--- a/.changeset/shiny-walls-fix.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: prevent infinite async loop
diff --git a/.changeset/thick-mice-kick.md b/.changeset/thick-mice-kick.md
deleted file mode 100644
index eec55b77ee..0000000000
--- a/.changeset/thick-mice-kick.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: exclude derived writes from effect abort and rescheduling
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 5a5e532a08..8cd3850460 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,17 @@
 # svelte
 
+## 5.36.14
+
+### Patch Changes
+
+- fix: keep input in sync when binding updated via effect ([#16482](https://github.com/sveltejs/svelte/pull/16482))
+
+- fix: rename form accept-charset attribute ([#16478](https://github.com/sveltejs/svelte/pull/16478))
+
+- fix: prevent infinite async loop ([#16482](https://github.com/sveltejs/svelte/pull/16482))
+
+- fix: exclude derived writes from effect abort and rescheduling ([#16482](https://github.com/sveltejs/svelte/pull/16482))
+
 ## 5.36.13
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 4bf9a5df22..7fe1d161f2 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.13",
+  "version": "5.36.14",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 7d47fbc5f1..cd9d8b459c 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.13';
+export const VERSION = '5.36.14';
 export const PUBLIC_VERSION = '5';

From 53417ea8f785f2ec884b095ac1bacd08aa30da86 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 24 Jul 2025 01:48:32 -0400
Subject: [PATCH 123/148] fix: preserve dirty status of deferred effects
 (#16487)

* don't mark_reactions inside decrement, it can cause infinite loops

* revert mark_reactions changes

* preserve DIRTY/MAYBE_DIRTY status of deferred effects

* changeset

* tweak
---
 .changeset/cool-insects-argue.md              |  5 ++
 .../src/internal/client/reactivity/batch.js   | 63 ++++++++++++++-----
 .../src/internal/client/reactivity/sources.js |  9 +--
 .../async-effect-conservative/_config.js      | 28 +++++++++
 .../async-effect-conservative/main.svelte     | 17 +++++
 5 files changed, 101 insertions(+), 21 deletions(-)
 create mode 100644 .changeset/cool-insects-argue.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-effect-conservative/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-effect-conservative/main.svelte

diff --git a/.changeset/cool-insects-argue.md b/.changeset/cool-insects-argue.md
new file mode 100644
index 0000000000..ff1c520b7b
--- /dev/null
+++ b/.changeset/cool-insects-argue.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: preserve dirty status of deferred effects
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index ce413fa1e1..89bad947c7 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -10,7 +10,8 @@ import {
 	INERT,
 	RENDER_EFFECT,
 	ROOT_EFFECT,
-	USER_EFFECT
+	USER_EFFECT,
+	MAYBE_DIRTY
 } from '#client/constants';
 import { async_mode_flag } from '../../flags/index.js';
 import { deferred, define_property } from '../../shared/utils.js';
@@ -27,7 +28,7 @@ import * as e from '../errors.js';
 import { flush_tasks } from '../dom/task.js';
 import { DEV } from 'esm-env';
 import { invoke_error_boundary } from '../error-handling.js';
-import { mark_reactions, old_values } from './sources.js';
+import { old_values } from './sources.js';
 import { unlink_effect } from './effects.js';
 import { unset_context } from './async.js';
 
@@ -146,6 +147,18 @@ export class Batch {
 	 */
 	#block_effects = [];
 
+	/**
+	 * Deferred effects (which run after async work has completed) that are DIRTY
+	 * @type {Effect[]}
+	 */
+	#dirty_effects = [];
+
+	/**
+	 * Deferred effects that are MAYBE_DIRTY
+	 * @type {Effect[]}
+	 */
+	#maybe_dirty_effects = [];
+
 	/**
 	 * A set of branches that still exist, but will be destroyed when this batch
 	 * is committed — we skip over these during `process`
@@ -221,10 +234,9 @@ export class Batch {
 
 			this.#deferred?.resolve();
 		} else {
-			// otherwise mark effects clean so they get scheduled on the next run
-			for (const e of this.#render_effects) set_signal_status(e, CLEAN);
-			for (const e of this.#effects) set_signal_status(e, CLEAN);
-			for (const e of this.#block_effects) set_signal_status(e, CLEAN);
+			this.#defer_effects(this.#render_effects);
+			this.#defer_effects(this.#effects);
+			this.#defer_effects(this.#block_effects);
 		}
 
 		if (current_values) {
@@ -271,15 +283,15 @@ export class Batch {
 			if (!skip && effect.fn !== null) {
 				if (is_branch) {
 					effect.f ^= CLEAN;
-				} else if ((flags & EFFECT) !== 0) {
-					this.#effects.push(effect);
-				} else if (async_mode_flag && (flags & RENDER_EFFECT) !== 0) {
-					this.#render_effects.push(effect);
-				} else if (is_dirty(effect)) {
-					if ((flags & ASYNC) !== 0) {
+				} else if ((flags & CLEAN) === 0) {
+					if ((flags & EFFECT) !== 0) {
+						this.#effects.push(effect);
+					} else if (async_mode_flag && (flags & RENDER_EFFECT) !== 0) {
+						this.#render_effects.push(effect);
+					} else if ((flags & ASYNC) !== 0) {
 						var effects = effect.b?.pending ? this.#boundary_async_effects : this.#async_effects;
 						effects.push(effect);
-					} else {
+					} else if (is_dirty(effect)) {
 						if ((effect.f & BLOCK_EFFECT) !== 0) this.#block_effects.push(effect);
 						update_effect(effect);
 					}
@@ -303,6 +315,21 @@ export class Batch {
 		}
 	}
 
+	/**
+	 * @param {Effect[]} effects
+	 */
+	#defer_effects(effects) {
+		for (const e of effects) {
+			const target = (e.f & DIRTY) !== 0 ? this.#dirty_effects : this.#maybe_dirty_effects;
+			target.push(e);
+
+			// mark as clean so they get scheduled if they depend on pending async state
+			set_signal_status(e, CLEAN);
+		}
+
+		effects.length = 0;
+	}
+
 	/**
 	 * Associate a change to a given source with the current
 	 * batch, noting its previous and current values
@@ -380,8 +407,14 @@ export class Batch {
 		this.#pending -= 1;
 
 		if (this.#pending === 0) {
-			for (const source of this.current.keys()) {
-				mark_reactions(source, DIRTY, false);
+			for (const e of this.#dirty_effects) {
+				set_signal_status(e, DIRTY);
+				schedule_effect(e);
+			}
+
+			for (const e of this.#maybe_dirty_effects) {
+				set_signal_status(e, MAYBE_DIRTY);
+				schedule_effect(e);
 			}
 
 			this.#render_effects = [];
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index 3b28c8fdce..7b5198542a 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -301,10 +301,9 @@ export function increment(source) {
 /**
  * @param {Value} signal
  * @param {number} status should be DIRTY or MAYBE_DIRTY
- * @param {boolean} schedule_async
  * @returns {void}
  */
-export function mark_reactions(signal, status, schedule_async = true) {
+function mark_reactions(signal, status) {
 	var reactions = signal.reactions;
 	if (reactions === null) return;
 
@@ -324,16 +323,14 @@ export function mark_reactions(signal, status, schedule_async = true) {
 			continue;
 		}
 
-		var should_schedule = (flags & DIRTY) === 0 && (schedule_async || (flags & ASYNC) === 0);
-
 		// don't set a DIRTY reaction to MAYBE_DIRTY
-		if (should_schedule) {
+		if ((flags & DIRTY) === 0) {
 			set_signal_status(reaction, status);
 		}
 
 		if ((flags & DERIVED) !== 0) {
 			mark_reactions(/** @type {Derived} */ (reaction), MAYBE_DIRTY);
-		} else if (should_schedule) {
+		} else {
 			schedule_effect(/** @type {Effect} */ (reaction));
 		}
 	}
diff --git a/packages/svelte/tests/runtime-runes/samples/async-effect-conservative/_config.js b/packages/svelte/tests/runtime-runes/samples/async-effect-conservative/_config.js
new file mode 100644
index 0000000000..bab06a203d
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-effect-conservative/_config.js
@@ -0,0 +1,28 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target, logs }) {
+		await tick();
+
+		const [increment] = target.querySelectorAll('button');
+
+		assert.deepEqual(logs, [false]);
+		assert.htmlEqual(target.innerHTML, '<button>increment</button><p>0</p>');
+
+		increment.click();
+		await tick();
+		assert.deepEqual(logs, [false]);
+		assert.htmlEqual(target.innerHTML, '<button>increment</button><p>1</p>');
+
+		increment.click();
+		await tick();
+		assert.deepEqual(logs, [false, true]);
+		assert.htmlEqual(target.innerHTML, '<button>increment</button><p>2</p>');
+
+		increment.click();
+		await tick();
+		assert.deepEqual(logs, [false, true]);
+		assert.htmlEqual(target.innerHTML, '<button>increment</button><p>3</p>');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-effect-conservative/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-effect-conservative/main.svelte
new file mode 100644
index 0000000000..5305067a5a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-effect-conservative/main.svelte
@@ -0,0 +1,17 @@
+<script lang="ts">
+	let count = $state(0);
+	let two_or_larger = $derived(count >= 2);
+
+	$effect(() => {
+		console.log(two_or_larger);
+	});
+</script>
+
+<svelte:boundary>
+	<button onclick={() => count += 1}>increment</button>
+	<p>{await count}</p>
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>

From 46d3261ed9a7d6acb9908f52e989013795555a56 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Thu, 24 Jul 2025 11:39:54 +0200
Subject: [PATCH 124/148] chore: don't do effect scheduling unnecessarily
 (#16489)

mini-cleanup post #16487 - we don't need to do the work of scheduling an effect that's already dirty which means it already scheduled its root effect to run
---
 packages/svelte/src/internal/client/reactivity/sources.js | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index 7b5198542a..3b2087d56b 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -323,14 +323,16 @@ function mark_reactions(signal, status) {
 			continue;
 		}
 
+		var not_dirty = (flags & DIRTY) === 0;
+
 		// don't set a DIRTY reaction to MAYBE_DIRTY
-		if ((flags & DIRTY) === 0) {
+		if (not_dirty) {
 			set_signal_status(reaction, status);
 		}
 
 		if ((flags & DERIVED) !== 0) {
 			mark_reactions(/** @type {Derived} */ (reaction), MAYBE_DIRTY);
-		} else {
+		} else if (not_dirty) {
 			schedule_effect(/** @type {Effect} */ (reaction));
 		}
 	}

From 4e74cd35fedf55e65b60c957041f79ca94dfc197 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Thu, 24 Jul 2025 11:43:28 +0200
Subject: [PATCH 125/148] Version Packages (#16488)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/cool-insects-argue.md | 5 -----
 packages/svelte/CHANGELOG.md     | 6 ++++++
 packages/svelte/package.json     | 2 +-
 packages/svelte/src/version.js   | 2 +-
 4 files changed, 8 insertions(+), 7 deletions(-)
 delete mode 100644 .changeset/cool-insects-argue.md

diff --git a/.changeset/cool-insects-argue.md b/.changeset/cool-insects-argue.md
deleted file mode 100644
index ff1c520b7b..0000000000
--- a/.changeset/cool-insects-argue.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: preserve dirty status of deferred effects
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 8cd3850460..5bffa5f70e 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,11 @@
 # svelte
 
+## 5.36.15
+
+### Patch Changes
+
+- fix: preserve dirty status of deferred effects ([#16487](https://github.com/sveltejs/svelte/pull/16487))
+
 ## 5.36.14
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 7fe1d161f2..051f82ec3a 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.14",
+  "version": "5.36.15",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index cd9d8b459c..1d469f29b0 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.14';
+export const VERSION = '5.36.15';
 export const PUBLIC_VERSION = '5';

From 7eb11e0e247d9da4edb88dc5652101ceb55fc530 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Thu, 24 Jul 2025 16:00:43 +0200
Subject: [PATCH 126/148] fix: don't destroy effect roots created inside of
 deriveds (#16492)

We were wrongfully adding effect roots to `derived.effects`, too, which meant those were destroyed when the derived reran.
---
 .changeset/lemon-weeks-call.md                |  5 ++
 .../src/internal/client/reactivity/effects.js |  6 ++-
 .../src/internal/client/reactivity/types.d.ts |  2 +-
 packages/svelte/tests/signals/test.ts         | 51 +++++++++++++++++++
 4 files changed, 62 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/lemon-weeks-call.md

diff --git a/.changeset/lemon-weeks-call.md b/.changeset/lemon-weeks-call.md
new file mode 100644
index 0000000000..ae62305630
--- /dev/null
+++ b/.changeset/lemon-weeks-call.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: don't destroy effect roots created inside of deriveds
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index c4edd2bf8d..f44efa32f1 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -148,7 +148,11 @@ function create_effect(type, fn, sync, push = true) {
 		}
 
 		// if we're in a derived, add the effect there too
-		if (active_reaction !== null && (active_reaction.f & DERIVED) !== 0) {
+		if (
+			active_reaction !== null &&
+			(active_reaction.f & DERIVED) !== 0 &&
+			(type & ROOT_EFFECT) === 0
+		) {
 			var derived = /** @type {Derived} */ (active_reaction);
 			(derived.effects ??= []).push(effect);
 		}
diff --git a/packages/svelte/src/internal/client/reactivity/types.d.ts b/packages/svelte/src/internal/client/reactivity/types.d.ts
index 72187e84a7..81f7197b80 100644
--- a/packages/svelte/src/internal/client/reactivity/types.d.ts
+++ b/packages/svelte/src/internal/client/reactivity/types.d.ts
@@ -54,7 +54,7 @@ export interface Reaction extends Signal {
 export interface Derived<V = unknown> extends Value<V>, Reaction {
 	/** The derived function */
 	fn: () => V;
-	/** Effects created inside this signal */
+	/** Effects created inside this signal. Used to destroy those effects when the derived reruns or is cleaned up */
 	effects: null | Effect[];
 	/** Parent effect or derived */
 	parent: Effect | Derived | null;
diff --git a/packages/svelte/tests/signals/test.ts b/packages/svelte/tests/signals/test.ts
index 937324727b..eff6d6166a 100644
--- a/packages/svelte/tests/signals/test.ts
+++ b/packages/svelte/tests/signals/test.ts
@@ -1390,4 +1390,55 @@ describe('signals', () => {
 			destroy();
 		};
 	});
+
+	test('$effect.root inside deriveds stay alive independently', () => {
+		const log: any[] = [];
+		const c = state(0);
+		const cleanup: any[] = [];
+		const inner_states: any[] = [];
+
+		const d = derived(() => {
+			const destroy = effect_root(() => {
+				const x = state(0);
+				inner_states.push(x);
+
+				effect(() => {
+					log.push('inner ' + $.get(x));
+					return () => {
+						log.push('inner destroyed');
+					};
+				});
+			});
+
+			cleanup.push(destroy);
+
+			return $.get(c);
+		});
+
+		return () => {
+			log.push($.get(d));
+			flushSync();
+
+			assert.deepEqual(log, [0, 'inner 0']);
+			log.length = 0;
+
+			set(inner_states[0], 1);
+			flushSync();
+
+			assert.deepEqual(log, ['inner destroyed', 'inner 1']);
+			log.length = 0;
+
+			set(c, 1);
+			log.push($.get(d));
+			flushSync();
+
+			assert.deepEqual(log, [1, 'inner 0']);
+			log.length = 0;
+
+			cleanup.forEach((fn) => fn());
+			flushSync();
+
+			assert.deepEqual(log, ['inner destroyed', 'inner destroyed']);
+		};
+	});
 });

From dc043fb2d3c87619e1c26315f600acd4fe19dfa4 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 24 Jul 2025 10:16:15 -0400
Subject: [PATCH 127/148] fix: don't update a focused input with values from
 its own past (#16491)

* fix: don't update a focused input with values from its own past

* remove

* fix
---
 .changeset/fast-mails-fail.md                 |  5 +++
 .../client/dom/elements/bindings/input.js     | 11 ++++--
 .../src/internal/client/reactivity/batch.js   | 12 +++++-
 .../_config.js                                | 37 +++++++++++++++++++
 .../main.svelte                               | 25 +++++++++++++
 5 files changed, 86 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/fast-mails-fail.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-binding-update-while-focused-2/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-binding-update-while-focused-2/main.svelte

diff --git a/.changeset/fast-mails-fail.md b/.changeset/fast-mails-fail.md
new file mode 100644
index 0000000000..027cb01548
--- /dev/null
+++ b/.changeset/fast-mails-fail.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: don't update a focused input with values from its own past
diff --git a/packages/svelte/src/internal/client/dom/elements/bindings/input.js b/packages/svelte/src/internal/client/dom/elements/bindings/input.js
index 7c1fccea0f..7c73280dd6 100644
--- a/packages/svelte/src/internal/client/dom/elements/bindings/input.js
+++ b/packages/svelte/src/internal/client/dom/elements/bindings/input.js
@@ -8,7 +8,7 @@ import { queue_micro_task } from '../../task.js';
 import { hydrating } from '../../hydration.js';
 import { untrack } from '../../../runtime.js';
 import { is_runes } from '../../../context.js';
-import { current_batch } from '../../../reactivity/batch.js';
+import { current_batch, previous_batch } from '../../../reactivity/batch.js';
 
 /**
  * @param {HTMLInputElement} input
@@ -76,13 +76,18 @@ export function bind_value(input, get, set = get) {
 
 		var value = get();
 
-		if (input === document.activeElement && batches.has(/** @type {Batch} */ (current_batch))) {
+		if (input === document.activeElement) {
+			// we need both, because in non-async mode, render effects run before previous_batch is set
+			var batch = /** @type {Batch} */ (previous_batch ?? current_batch);
+
 			// Never rewrite the contents of a focused input. We can get here if, for example,
 			// an update is deferred because of async work depending on the input:
 			//
 			// <input bind:value={query}>
 			// <p>{await find(query)}</p>
-			return;
+			if (batches.has(batch)) {
+				return;
+			}
 		}
 
 		if (is_numberlike_input(input) && value === to_number(input.value)) {
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index 89bad947c7..123bc95d16 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -38,6 +38,13 @@ const batches = new Set();
 /** @type {Batch | null} */
 export let current_batch = null;
 
+/**
+ * This is needed to avoid overwriting inputs in non-async mode
+ * TODO 6.0 remove this, as non-async mode will go away
+ * @type {Batch | null}
+ */
+export let previous_batch = null;
+
 /**
  * When time travelling, we re-evaluate deriveds based on the temporary
  * values of their dependencies rather than their actual values, and cache
@@ -71,7 +78,6 @@ let last_scheduled_effect = null;
 let is_flushing = false;
 
 let is_flushing_sync = false;
-
 export class Batch {
 	/**
 	 * The current values of any sources that are updated in this batch
@@ -173,6 +179,8 @@ export class Batch {
 	process(root_effects) {
 		queued_root_effects = [];
 
+		previous_batch = null;
+
 		/** @type {Map<Source, { v: unknown, wv: number }> | null} */
 		var current_values = null;
 
@@ -218,6 +226,7 @@ export class Batch {
 
 			// If sources are written to, then work needs to happen in a separate batch, else prior sources would be mixed with
 			// newly updated sources, which could lead to infinite loops when effects run over and over again.
+			previous_batch = current_batch;
 			current_batch = null;
 
 			flush_queued_effects(render_effects);
@@ -350,6 +359,7 @@ export class Batch {
 
 	deactivate() {
 		current_batch = null;
+		previous_batch = null;
 
 		for (const update of effect_pending_updates) {
 			effect_pending_updates.delete(update);
diff --git a/packages/svelte/tests/runtime-runes/samples/async-binding-update-while-focused-2/_config.js b/packages/svelte/tests/runtime-runes/samples/async-binding-update-while-focused-2/_config.js
new file mode 100644
index 0000000000..b0772ad3c0
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-binding-update-while-focused-2/_config.js
@@ -0,0 +1,37 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target, instance }) {
+		instance.shift();
+		await tick();
+
+		const [input] = target.querySelectorAll('input');
+
+		input.focus();
+		input.value = '1';
+		input.dispatchEvent(new InputEvent('input', { bubbles: true }));
+		await tick();
+
+		assert.htmlEqual(target.innerHTML, `<input type="number" /> <p>0</p>`);
+		assert.equal(input.value, '1');
+
+		input.focus();
+		input.value = '2';
+		input.dispatchEvent(new InputEvent('input', { bubbles: true }));
+		await tick();
+
+		assert.htmlEqual(target.innerHTML, `<input type="number" /> <p>0</p>`);
+		assert.equal(input.value, '2');
+
+		instance.shift();
+		await tick();
+		assert.htmlEqual(target.innerHTML, `<input type="number" /> <p>1</p>`);
+		assert.equal(input.value, '2');
+
+		instance.shift();
+		await tick();
+		assert.htmlEqual(target.innerHTML, `<input type="number" /> <p>2</p>`);
+		assert.equal(input.value, '2');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-binding-update-while-focused-2/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-binding-update-while-focused-2/main.svelte
new file mode 100644
index 0000000000..2fc898e654
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-binding-update-while-focused-2/main.svelte
@@ -0,0 +1,25 @@
+<script lang="ts">
+	let count = $state(0);
+
+	let deferreds = [];
+
+	export function shift() {
+		const d = deferreds.shift();
+		d.d.resolve(d.v);
+	}
+
+	function push(v) {
+		const d = Promise.withResolvers();
+		deferreds.push({ d, v });
+		return d.promise;
+	}
+</script>
+
+<svelte:boundary>
+	<input type="number" bind:value={count} />
+	<p>{await push(count)}</p>
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>

From 8ad02e4a8c920823034051e5e2a13df58f25ebd5 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Thu, 24 Jul 2025 16:22:30 +0200
Subject: [PATCH 128/148] Version Packages (#16493)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/fast-mails-fail.md  | 5 -----
 .changeset/lemon-weeks-call.md | 5 -----
 packages/svelte/CHANGELOG.md   | 8 ++++++++
 packages/svelte/package.json   | 2 +-
 packages/svelte/src/version.js | 2 +-
 5 files changed, 10 insertions(+), 12 deletions(-)
 delete mode 100644 .changeset/fast-mails-fail.md
 delete mode 100644 .changeset/lemon-weeks-call.md

diff --git a/.changeset/fast-mails-fail.md b/.changeset/fast-mails-fail.md
deleted file mode 100644
index 027cb01548..0000000000
--- a/.changeset/fast-mails-fail.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: don't update a focused input with values from its own past
diff --git a/.changeset/lemon-weeks-call.md b/.changeset/lemon-weeks-call.md
deleted file mode 100644
index ae62305630..0000000000
--- a/.changeset/lemon-weeks-call.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: don't destroy effect roots created inside of deriveds
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 5bffa5f70e..450ecde53b 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,13 @@
 # svelte
 
+## 5.36.16
+
+### Patch Changes
+
+- fix: don't update a focused input with values from its own past ([#16491](https://github.com/sveltejs/svelte/pull/16491))
+
+- fix: don't destroy effect roots created inside of deriveds ([#16492](https://github.com/sveltejs/svelte/pull/16492))
+
 ## 5.36.15
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 051f82ec3a..07954026b5 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.15",
+  "version": "5.36.16",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 1d469f29b0..5d76fc3f29 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.15';
+export const VERSION = '5.36.16';
 export const PUBLIC_VERSION = '5';

From 0bba84cc203c7cab945527cc3928597d3612a37d Mon Sep 17 00:00:00 2001
From: Bladesheng <keadr23@gmail.com>
Date: Fri, 25 Jul 2025 14:43:41 +0200
Subject: [PATCH 129/148] fix: add types for `part` attribute to svg attributes
 (#16499)

---
 .changeset/seven-colts-obey.md | 5 +++++
 packages/svelte/elements.d.ts  | 1 +
 2 files changed, 6 insertions(+)
 create mode 100644 .changeset/seven-colts-obey.md

diff --git a/.changeset/seven-colts-obey.md b/.changeset/seven-colts-obey.md
new file mode 100644
index 0000000000..b41216f649
--- /dev/null
+++ b/.changeset/seven-colts-obey.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: add types for `part` attribute to svg attributes
diff --git a/packages/svelte/elements.d.ts b/packages/svelte/elements.d.ts
index 604241592a..2e1042dfd6 100644
--- a/packages/svelte/elements.d.ts
+++ b/packages/svelte/elements.d.ts
@@ -1553,6 +1553,7 @@ export interface SVGAttributes<T extends EventTarget> extends AriaAttributes, DO
 	height?: number | string | undefined | null;
 	id?: string | undefined | null;
 	lang?: string | undefined | null;
+	part?: string | undefined | null;
 	max?: number | string | undefined | null;
 	media?: string | undefined | null;
 	// On the `textPath` element

From b0f9ea3ae62cfb9eb4437898bf8a6b90e0531657 Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Fri, 25 Jul 2025 15:57:32 -0700
Subject: [PATCH 130/148] fix: throw on duplicate class field declarations
 (#16502)

* fix: throw on duplicate class field declarations

* doh

* handle assignment in constructor

* fix

* apply suggestion from review

* fix

* fix failing test
---
 .changeset/odd-phones-taste.md                |  5 ++
 .../98-reference/.generated/compile-errors.md |  6 +++
 .../svelte/messages/compile-errors/script.md  |  4 ++
 packages/svelte/src/compiler/errors.js        | 10 ++++
 .../phases/2-analyze/visitors/ClassBody.js    | 53 ++++++++++++++++++-
 .../class-state-constructor-9/errors.json     | 12 ++---
 6 files changed, 82 insertions(+), 8 deletions(-)
 create mode 100644 .changeset/odd-phones-taste.md

diff --git a/.changeset/odd-phones-taste.md b/.changeset/odd-phones-taste.md
new file mode 100644
index 0000000000..ec9534b741
--- /dev/null
+++ b/.changeset/odd-phones-taste.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: throw on duplicate class field declarations
diff --git a/documentation/docs/98-reference/.generated/compile-errors.md b/documentation/docs/98-reference/.generated/compile-errors.md
index 20f57770d1..957a9f67c7 100644
--- a/documentation/docs/98-reference/.generated/compile-errors.md
+++ b/documentation/docs/98-reference/.generated/compile-errors.md
@@ -364,6 +364,12 @@ The $ name is reserved, and cannot be used for variables and imports
 The $ prefix is reserved, and cannot be used for variables and imports
 ```
 
+### duplicate_class_field
+
+```
+`%name%` has already been declared
+```
+
 ### each_item_invalid_assignment
 
 ```
diff --git a/packages/svelte/messages/compile-errors/script.md b/packages/svelte/messages/compile-errors/script.md
index 2b0c5eafdf..5c1080aced 100644
--- a/packages/svelte/messages/compile-errors/script.md
+++ b/packages/svelte/messages/compile-errors/script.md
@@ -30,6 +30,10 @@
 
 > The $ prefix is reserved, and cannot be used for variables and imports
 
+## duplicate_class_field
+
+> `%name%` has already been declared
+
 ## each_item_invalid_assignment
 
 > Cannot reassign or bind to each block argument in runes mode. Use the array and index variables instead (e.g. `array[i] = value` instead of `entry = value`, or `bind:value={array[i]}` instead of `bind:value={entry}`)
diff --git a/packages/svelte/src/compiler/errors.js b/packages/svelte/src/compiler/errors.js
index 599d3e8248..e763a6e073 100644
--- a/packages/svelte/src/compiler/errors.js
+++ b/packages/svelte/src/compiler/errors.js
@@ -152,6 +152,16 @@ export function dollar_prefix_invalid(node) {
 	e(node, 'dollar_prefix_invalid', `The $ prefix is reserved, and cannot be used for variables and imports\nhttps://svelte.dev/e/dollar_prefix_invalid`);
 }
 
+/**
+ * `%name%` has already been declared
+ * @param {null | number | NodeLike} node
+ * @param {string} name
+ * @returns {never}
+ */
+export function duplicate_class_field(node, name) {
+	e(node, 'duplicate_class_field', `\`${name}\` has already been declared\nhttps://svelte.dev/e/duplicate_class_field`);
+}
+
 /**
  * Cannot reassign or bind to each block argument in runes mode. Use the array and index variables instead (e.g. `array[i] = value` instead of `entry = value`, or `bind:value={array[i]}` instead of `bind:value={entry}`)
  * @param {null | number | NodeLike} node
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/ClassBody.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/ClassBody.js
index ffc39ac00d..2bfc1dbce3 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/ClassBody.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/ClassBody.js
@@ -33,6 +33,9 @@ export function ClassBody(node, context) {
 	/** @type {Map<string, StateField>} */
 	const state_fields = new Map();
 
+	/** @type {Map<string, Array<MethodDefinition['kind'] | 'prop' | 'assigned_prop'>>} */
+	const fields = new Map();
+
 	context.state.analysis.classes.set(node, state_fields);
 
 	/** @type {MethodDefinition | null} */
@@ -54,6 +57,14 @@ export function ClassBody(node, context) {
 				e.state_field_duplicate(node, name);
 			}
 
+			const _key = (key.type === 'PrivateIdentifier' ? '#' : '') + name;
+			const field = fields.get(_key);
+
+			// if there's already a method or assigned field, error
+			if (field && !(field.length === 1 && field[0] === 'prop')) {
+				e.duplicate_class_field(node, _key);
+			}
+
 			state_fields.set(name, {
 				node,
 				type: rune,
@@ -67,10 +78,48 @@ export function ClassBody(node, context) {
 	for (const child of node.body) {
 		if (child.type === 'PropertyDefinition' && !child.computed && !child.static) {
 			handle(child, child.key, child.value);
+			const key = (child.key.type === 'PrivateIdentifier' ? '#' : '') + get_name(child.key);
+			const field = fields.get(key);
+			if (!field) {
+				fields.set(key, [child.value ? 'assigned_prop' : 'prop']);
+				continue;
+			}
+			e.duplicate_class_field(child, key);
 		}
 
-		if (child.type === 'MethodDefinition' && child.kind === 'constructor') {
-			constructor = child;
+		if (child.type === 'MethodDefinition') {
+			if (child.kind === 'constructor') {
+				constructor = child;
+			} else if (!child.computed) {
+				const key = (child.key.type === 'PrivateIdentifier' ? '#' : '') + get_name(child.key);
+				const field = fields.get(key);
+				if (!field) {
+					fields.set(key, [child.kind]);
+					continue;
+				}
+				if (
+					field.includes(child.kind) ||
+					field.includes('prop') ||
+					field.includes('assigned_prop')
+				) {
+					e.duplicate_class_field(child, key);
+				}
+				if (child.kind === 'get') {
+					if (field.length === 1 && field[0] === 'set') {
+						field.push('get');
+						continue;
+					}
+				} else if (child.kind === 'set') {
+					if (field.length === 1 && field[0] === 'get') {
+						field.push('set');
+						continue;
+					}
+				} else {
+					field.push(child.kind);
+					continue;
+				}
+				e.duplicate_class_field(child, key);
+			}
 		}
 	}
 
diff --git a/packages/svelte/tests/validator/samples/class-state-constructor-9/errors.json b/packages/svelte/tests/validator/samples/class-state-constructor-9/errors.json
index b7dd4c8ed4..94b5f191c2 100644
--- a/packages/svelte/tests/validator/samples/class-state-constructor-9/errors.json
+++ b/packages/svelte/tests/validator/samples/class-state-constructor-9/errors.json
@@ -1,14 +1,14 @@
 [
 	{
-		"code": "state_field_invalid_assignment",
-		"message": "Cannot assign to a state field before its declaration",
+		"code": "duplicate_class_field",
+		"message": "`count` has already been declared",
 		"start": {
-			"line": 2,
-			"column": 1
+			"line": 5,
+			"column": 2
 		},
 		"end": {
-			"line": 2,
-			"column": 12
+			"line": 5,
+			"column": 24
 		}
 	}
 ]

From d0ebd42986c4d3e4db0420f1aaebd337afdb230f Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Fri, 25 Jul 2025 16:46:12 -0700
Subject: [PATCH 131/148] Version Packages (#16500)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/odd-phones-taste.md | 5 -----
 .changeset/seven-colts-obey.md | 5 -----
 packages/svelte/CHANGELOG.md   | 8 ++++++++
 packages/svelte/package.json   | 2 +-
 packages/svelte/src/version.js | 2 +-
 5 files changed, 10 insertions(+), 12 deletions(-)
 delete mode 100644 .changeset/odd-phones-taste.md
 delete mode 100644 .changeset/seven-colts-obey.md

diff --git a/.changeset/odd-phones-taste.md b/.changeset/odd-phones-taste.md
deleted file mode 100644
index ec9534b741..0000000000
--- a/.changeset/odd-phones-taste.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: throw on duplicate class field declarations
diff --git a/.changeset/seven-colts-obey.md b/.changeset/seven-colts-obey.md
deleted file mode 100644
index b41216f649..0000000000
--- a/.changeset/seven-colts-obey.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: add types for `part` attribute to svg attributes
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 450ecde53b..766c83763a 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,13 @@
 # svelte
 
+## 5.36.17
+
+### Patch Changes
+
+- fix: throw on duplicate class field declarations ([#16502](https://github.com/sveltejs/svelte/pull/16502))
+
+- fix: add types for `part` attribute to svg attributes ([#16499](https://github.com/sveltejs/svelte/pull/16499))
+
 ## 5.36.16
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 07954026b5..22bc8cc8fa 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.16",
+  "version": "5.36.17",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 5d76fc3f29..d2992a3dcd 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.16';
+export const VERSION = '5.36.17';
 export const PUBLIC_VERSION = '5';

From c7851789d71cc3d0b5d89ce9c759a39be6caa51a Mon Sep 17 00:00:00 2001
From: 7nik <kifiranet@gmail.com>
Date: Sat, 26 Jul 2025 21:27:22 +0300
Subject: [PATCH 132/148] fix: always mark props as stateful (#16504)

---
 .changeset/gorgeous-jeans-begin.md                |  5 +++++
 .../phases/2-analyze/visitors/Identifier.js       |  5 ++++-
 .../props-default-value-function/_config.js       | 15 +++++++++++++++
 .../props-default-value-function/inner.svelte     |  4 ++++
 .../props-default-value-function/main.svelte      | 14 ++++++++++++++
 .../props-default-value-function/wrapper.svelte   |  7 +++++++
 .../props-default-value-function/wrapper2.svelte  |  7 +++++++
 7 files changed, 56 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/gorgeous-jeans-begin.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/props-default-value-function/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/props-default-value-function/inner.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/props-default-value-function/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/props-default-value-function/wrapper.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/props-default-value-function/wrapper2.svelte

diff --git a/.changeset/gorgeous-jeans-begin.md b/.changeset/gorgeous-jeans-begin.md
new file mode 100644
index 0000000000..586c4d8a57
--- /dev/null
+++ b/.changeset/gorgeous-jeans-begin.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: always mark props as stateful
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/Identifier.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/Identifier.js
index cced326f9b..4dfdfe5af1 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/Identifier.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/Identifier.js
@@ -93,7 +93,10 @@ export function Identifier(node, context) {
 			context.state.expression.references.add(binding);
 			context.state.expression.has_state ||=
 				binding.kind !== 'static' &&
-				!binding.is_function() &&
+				(binding.kind === 'prop' ||
+					binding.kind === 'bindable_prop' ||
+					binding.kind === 'rest_prop' ||
+					!binding.is_function()) &&
 				!context.state.scope.evaluate(node).is_known;
 		}
 
diff --git a/packages/svelte/tests/runtime-runes/samples/props-default-value-function/_config.js b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/_config.js
new file mode 100644
index 0000000000..6b281f04f0
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/_config.js
@@ -0,0 +1,15 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client'],
+
+	test({ assert, target }) {
+		const btn = target.querySelector('button');
+
+		assert.htmlEqual(target.innerHTML, `<button>inc</button> Inner: 0 Inner: 0`);
+		btn?.click();
+		flushSync();
+		assert.htmlEqual(target.innerHTML, `<button>inc</button> Inner: 1 Inner: 1`);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/props-default-value-function/inner.svelte b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/inner.svelte
new file mode 100644
index 0000000000..6bde0a15a8
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/inner.svelte
@@ -0,0 +1,4 @@
+<script>
+	let { getter } = $props()
+</script>
+Inner: {getter()}
diff --git a/packages/svelte/tests/runtime-runes/samples/props-default-value-function/main.svelte b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/main.svelte
new file mode 100644
index 0000000000..2cb2f67b82
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/main.svelte
@@ -0,0 +1,14 @@
+<script>
+	import Wrapper1 from "./wrapper.svelte"
+	import Wrapper2 from "./wrapper2.svelte"
+	let count = $state(0);
+
+	let getter = $derived.by(() => {
+		const copy = count;
+		return () => copy;
+	});
+</script>
+
+<button onclick={() => count++}>inc</button>
+<Wrapper1 {getter}/>
+<Wrapper2 {getter}/>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/props-default-value-function/wrapper.svelte b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/wrapper.svelte
new file mode 100644
index 0000000000..525494ddfb
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/wrapper.svelte
@@ -0,0 +1,7 @@
+<script >
+  import Inner from "./inner.svelte";
+
+  const { getter = () => -1} = $props();
+</script>
+
+<Inner {getter} />
diff --git a/packages/svelte/tests/runtime-runes/samples/props-default-value-function/wrapper2.svelte b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/wrapper2.svelte
new file mode 100644
index 0000000000..9498f432d8
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/props-default-value-function/wrapper2.svelte
@@ -0,0 +1,7 @@
+<script >
+  import Inner from "./inner.svelte";
+
+  const { getter = $bindable(() => -1)} = $props();
+</script>
+
+<Inner {getter} />

From 7cc4d56263f724c4d76ab6140af4d117cbb41f1d Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Sat, 26 Jul 2025 22:16:40 -0400
Subject: [PATCH 133/148] feat: ignore component options in `compileModule`
 (#16362)

---
 .changeset/violet-ways-sleep.md               |   5 +
 .../svelte/src/compiler/validate-options.js   | 172 +++++++++---------
 2 files changed, 96 insertions(+), 81 deletions(-)
 create mode 100644 .changeset/violet-ways-sleep.md

diff --git a/.changeset/violet-ways-sleep.md b/.changeset/violet-ways-sleep.md
new file mode 100644
index 0000000000..749ecb1719
--- /dev/null
+++ b/.changeset/violet-ways-sleep.md
@@ -0,0 +1,5 @@
+---
+'svelte': minor
+---
+
+feat: ignore component options in `compileModule`
diff --git a/packages/svelte/src/compiler/validate-options.js b/packages/svelte/src/compiler/validate-options.js
index ed83375d22..2b727ad093 100644
--- a/packages/svelte/src/compiler/validate-options.js
+++ b/packages/svelte/src/compiler/validate-options.js
@@ -8,7 +8,7 @@ import * as w from './warnings.js';
  * @typedef {(input: Input, keypath: string) => Required<Output>} Validator
  */
 
-const common = {
+const common_options = {
 	filename: string('(unknown)'),
 
 	// default to process.cwd() where it exists to replicate svelte4 behavior (and make Deno work with this as well)
@@ -48,110 +48,120 @@ const common = {
 	})
 };
 
-export const validate_module_options =
-	/** @type {Validator<ModuleCompileOptions, ValidatedModuleCompileOptions>} */ (
-		object({
-			...common
-		})
-	);
+const component_options = {
+	accessors: deprecate(w.options_deprecated_accessors, boolean(false)),
 
-export const validate_component_options =
-	/** @type {Validator<CompileOptions, ValidatedCompileOptions>} */ (
-		object({
-			...common,
+	css: validator('external', (input) => {
+		if (input === true || input === false) {
+			throw_error(
+				'The boolean options have been removed from the css option. Use "external" instead of false and "injected" instead of true'
+			);
+		}
+		if (input === 'none') {
+			throw_error(
+				'css: "none" is no longer a valid option. If this was crucial for you, please open an issue on GitHub with your use case.'
+			);
+		}
 
-			accessors: deprecate(w.options_deprecated_accessors, boolean(false)),
+		if (input !== 'external' && input !== 'injected') {
+			throw_error(`css should be either "external" (default, recommended) or "injected"`);
+		}
 
-			css: validator('external', (input) => {
-				if (input === true || input === false) {
-					throw_error(
-						'The boolean options have been removed from the css option. Use "external" instead of false and "injected" instead of true'
-					);
-				}
-				if (input === 'none') {
-					throw_error(
-						'css: "none" is no longer a valid option. If this was crucial for you, please open an issue on GitHub with your use case.'
-					);
-				}
+		return input;
+	}),
 
-				if (input !== 'external' && input !== 'injected') {
-					throw_error(`css should be either "external" (default, recommended) or "injected"`);
-				}
+	cssHash: fun(({ css, hash }) => {
+		return `svelte-${hash(css)}`;
+	}),
+
+	// TODO this is a sourcemap option, would be good to put under a sourcemap namespace
+	cssOutputFilename: string(undefined),
+
+	customElement: boolean(false),
+
+	discloseVersion: boolean(true),
 
-				return input;
-			}),
+	immutable: deprecate(w.options_deprecated_immutable, boolean(false)),
 
-			cssHash: fun(({ css, hash }) => {
-				return `svelte-${hash(css)}`;
-			}),
+	legacy: removed(
+		'The legacy option has been removed. If you are using this because of legacy.componentApi, use compatibility.componentApi instead'
+	),
+
+	compatibility: object({
+		componentApi: list([4, 5], 5)
+	}),
+
+	loopGuardTimeout: warn_removed(w.options_removed_loop_guard_timeout),
+
+	name: string(undefined),
 
-			// TODO this is a sourcemap option, would be good to put under a sourcemap namespace
-			cssOutputFilename: string(undefined),
+	namespace: list(['html', 'mathml', 'svg']),
 
-			customElement: boolean(false),
+	modernAst: boolean(false),
 
-			discloseVersion: boolean(true),
+	outputFilename: string(undefined),
 
-			immutable: deprecate(w.options_deprecated_immutable, boolean(false)),
+	preserveComments: boolean(false),
 
-			legacy: removed(
-				'The legacy option has been removed. If you are using this because of legacy.componentApi, use compatibility.componentApi instead'
-			),
+	fragments: list(['html', 'tree']),
 
-			compatibility: object({
-				componentApi: list([4, 5], 5)
-			}),
+	preserveWhitespace: boolean(false),
 
-			loopGuardTimeout: warn_removed(w.options_removed_loop_guard_timeout),
+	runes: boolean(undefined),
 
-			name: string(undefined),
+	hmr: boolean(false),
 
-			namespace: list(['html', 'mathml', 'svg']),
+	sourcemap: validator(undefined, (input) => {
+		// Source maps can take on a variety of values, including string, JSON, map objects from magic-string and source-map,
+		// so there's no good way to check type validity here
+		return input;
+	}),
 
-			modernAst: boolean(false),
+	enableSourcemap: warn_removed(w.options_removed_enable_sourcemap),
 
-			outputFilename: string(undefined),
+	hydratable: warn_removed(w.options_removed_hydratable),
 
-			preserveComments: boolean(false),
+	format: removed(
+		'The format option has been removed in Svelte 4, the compiler only outputs ESM now. Remove "format" from your compiler options. ' +
+			'If you did not set this yourself, bump the version of your bundler plugin (vite-plugin-svelte/rollup-plugin-svelte/svelte-loader)'
+	),
 
-			fragments: list(['html', 'tree']),
+	tag: removed(
+		'The tag option has been removed in Svelte 5. Use `<svelte:options customElement="tag-name" />` inside the component instead. ' +
+			'If that does not solve your use case, please open an issue on GitHub with details.'
+	),
 
-			preserveWhitespace: boolean(false),
+	sveltePath: removed(
+		'The sveltePath option has been removed in Svelte 5. ' +
+			'If this option was crucial for you, please open an issue on GitHub with your use case.'
+	),
 
-			runes: boolean(undefined),
+	// These two were primarily created for svelte-preprocess (https://github.com/sveltejs/svelte/pull/6194),
+	// but with new TypeScript compilation modes strictly separating types it's not necessary anymore
+	errorMode: removed(
+		'The errorMode option has been removed. If you are using this through svelte-preprocess with TypeScript, ' +
+			'use the https://www.typescriptlang.org/tsconfig#verbatimModuleSyntax setting instead'
+	),
 
-			hmr: boolean(false),
+	varsReport: removed(
+		'The vars option has been removed. If you are using this through svelte-preprocess with TypeScript, ' +
+			'use the https://www.typescriptlang.org/tsconfig#verbatimModuleSyntax setting instead'
+	)
+};
 
-			sourcemap: validator(undefined, (input) => {
-				// Source maps can take on a variety of values, including string, JSON, map objects from magic-string and source-map,
-				// so there's no good way to check type validity here
-				return input;
-			}),
+export const validate_module_options =
+	/** @type {Validator<ModuleCompileOptions, ValidatedModuleCompileOptions>} */ (
+		object({
+			...common_options,
+			...Object.fromEntries(Object.keys(component_options).map((key) => [key, () => {}]))
+		})
+	);
 
-			enableSourcemap: warn_removed(w.options_removed_enable_sourcemap),
-			hydratable: warn_removed(w.options_removed_hydratable),
-			format: removed(
-				'The format option has been removed in Svelte 4, the compiler only outputs ESM now. Remove "format" from your compiler options. ' +
-					'If you did not set this yourself, bump the version of your bundler plugin (vite-plugin-svelte/rollup-plugin-svelte/svelte-loader)'
-			),
-			tag: removed(
-				'The tag option has been removed in Svelte 5. Use `<svelte:options customElement="tag-name" />` inside the component instead. ' +
-					'If that does not solve your use case, please open an issue on GitHub with details.'
-			),
-			sveltePath: removed(
-				'The sveltePath option has been removed in Svelte 5. ' +
-					'If this option was crucial for you, please open an issue on GitHub with your use case.'
-			),
-			// These two were primarily created for svelte-preprocess (https://github.com/sveltejs/svelte/pull/6194),
-			// but with new TypeScript compilation modes strictly separating types it's not necessary anymore
-			errorMode: removed(
-				'The errorMode option has been removed. If you are using this through svelte-preprocess with TypeScript, ' +
-					'use the https://www.typescriptlang.org/tsconfig#verbatimModuleSyntax setting instead'
-			),
-			varsReport: removed(
-				'The vars option has been removed. If you are using this through svelte-preprocess with TypeScript, ' +
-					'use the https://www.typescriptlang.org/tsconfig#verbatimModuleSyntax setting instead'
-			)
+export const validate_component_options =
+	/** @type {Validator<CompileOptions, ValidatedCompileOptions>} */ (
+		object({
+			...common_options,
+			...component_options
 		})
 	);
 

From 39ee7cf4c247965ebacdd16fc365a31f00506026 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Sat, 26 Jul 2025 22:22:14 -0700
Subject: [PATCH 134/148] Version Packages (#16505)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/gorgeous-jeans-begin.md |  5 -----
 .changeset/violet-ways-sleep.md    |  5 -----
 packages/svelte/CHANGELOG.md       | 10 ++++++++++
 packages/svelte/package.json       |  2 +-
 packages/svelte/src/version.js     |  2 +-
 5 files changed, 12 insertions(+), 12 deletions(-)
 delete mode 100644 .changeset/gorgeous-jeans-begin.md
 delete mode 100644 .changeset/violet-ways-sleep.md

diff --git a/.changeset/gorgeous-jeans-begin.md b/.changeset/gorgeous-jeans-begin.md
deleted file mode 100644
index 586c4d8a57..0000000000
--- a/.changeset/gorgeous-jeans-begin.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: always mark props as stateful
diff --git a/.changeset/violet-ways-sleep.md b/.changeset/violet-ways-sleep.md
deleted file mode 100644
index 749ecb1719..0000000000
--- a/.changeset/violet-ways-sleep.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': minor
----
-
-feat: ignore component options in `compileModule`
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 766c83763a..f939f69d28 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,15 @@
 # svelte
 
+## 5.37.0
+
+### Minor Changes
+
+- feat: ignore component options in `compileModule` ([#16362](https://github.com/sveltejs/svelte/pull/16362))
+
+### Patch Changes
+
+- fix: always mark props as stateful ([#16504](https://github.com/sveltejs/svelte/pull/16504))
+
 ## 5.36.17
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 22bc8cc8fa..c781eda8c8 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.17",
+  "version": "5.37.0",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index d2992a3dcd..e83ba6fb30 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.17';
+export const VERSION = '5.37.0';
 export const PUBLIC_VERSION = '5';

From 1773df94845bc53d55a1c9e9eb033d08056c845a Mon Sep 17 00:00:00 2001
From: fkobi <fkobi@pm.me>
Date: Sun, 27 Jul 2025 14:17:50 +0000
Subject: [PATCH 135/148] docs: use sh instead of bash in source blocks
 (#16506)

* use sh instead of bash in source blocks

no bash-specific functionality is used

* regenerate

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
---
 CONTRIBUTING.md                                               | 4 ++--
 documentation/docs/01-introduction/02-getting-started.md      | 2 +-
 documentation/docs/07-misc/02-testing.md                      | 4 ++--
 .../docs/98-reference/.generated/compile-warnings.md          | 2 +-
 packages/svelte/README.md                                     | 2 +-
 packages/svelte/messages/compile-warnings/template.md         | 2 +-
 6 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index c2d3e45049..0653b08b76 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -101,13 +101,13 @@ Test samples are kept in `/test/xxx/samples` folder.
 1. To run test, run `pnpm test`.
 1. To run a particular test suite, use `pnpm test <suite-name>`, for example:
 
-   ```bash
+   ```sh
    pnpm test validator
    ```
 
 1. To filter tests _within_ a test suite, use `pnpm test <suite-name> -t <test-name>`, for example:
 
-   ```bash
+   ```sh
    pnpm test validator -t a11y-alt-text
    ```
 
diff --git a/documentation/docs/01-introduction/02-getting-started.md b/documentation/docs/01-introduction/02-getting-started.md
index c7351729ff..e97a46ad34 100644
--- a/documentation/docs/01-introduction/02-getting-started.md
+++ b/documentation/docs/01-introduction/02-getting-started.md
@@ -4,7 +4,7 @@ title: Getting started
 
 We recommend using [SvelteKit](../kit), which lets you [build almost anything](../kit/project-types). It's the official application framework from the Svelte team and powered by [Vite](https://vite.dev/). Create a new project with:
 
-```bash
+```sh
 npx sv create myapp
 cd myapp
 npm install
diff --git a/documentation/docs/07-misc/02-testing.md b/documentation/docs/07-misc/02-testing.md
index db99b70770..bcec4db0a3 100644
--- a/documentation/docs/07-misc/02-testing.md
+++ b/documentation/docs/07-misc/02-testing.md
@@ -10,7 +10,7 @@ Unit tests allow you to test small isolated parts of your code. Integration test
 
 To setup Vitest manually, first install it:
 
-```bash
+```sh
 npm install -D vitest
 ```
 
@@ -166,7 +166,7 @@ It is possible to test your components in isolation using Vitest.
 
 To get started, install jsdom (a library that shims DOM APIs):
 
-```bash
+```sh
 npm install -D jsdom
 ```
 
diff --git a/documentation/docs/98-reference/.generated/compile-warnings.md b/documentation/docs/98-reference/.generated/compile-warnings.md
index 2af9021a6a..01003f30c5 100644
--- a/documentation/docs/98-reference/.generated/compile-warnings.md
+++ b/documentation/docs/98-reference/.generated/compile-warnings.md
@@ -683,7 +683,7 @@ Some templating languages (including Svelte) will 'fix' HTML by turning `<span /
 
 To automate this, run the dedicated migration:
 
-```bash
+```sh
 npx sv migrate self-closing-tags
 ```
 
diff --git a/packages/svelte/README.md b/packages/svelte/README.md
index c37617da30..03e4db5db0 100644
--- a/packages/svelte/README.md
+++ b/packages/svelte/README.md
@@ -19,7 +19,7 @@ You can play around with Svelte in the [tutorial](https://svelte.dev/tutorial),
 
 When you're ready to build a full-fledge application, we recommend using [SvelteKit](https://svelte.dev/docs/kit):
 
-```bash
+```sh
 npx sv create my-app
 cd my-app
 npm install
diff --git a/packages/svelte/messages/compile-warnings/template.md b/packages/svelte/messages/compile-warnings/template.md
index d61a61d950..8af5aa2b98 100644
--- a/packages/svelte/messages/compile-warnings/template.md
+++ b/packages/svelte/messages/compile-warnings/template.md
@@ -71,7 +71,7 @@ Some templating languages (including Svelte) will 'fix' HTML by turning `<span /
 
 To automate this, run the dedicated migration:
 
-```bash
+```sh
 npx sv migrate self-closing-tags
 ```
 

From 99452053af5d3280caa9773ac45f9c7cc6b9ad5d Mon Sep 17 00:00:00 2001
From: Paolo Ricciuti <ricciutipaolo@gmail.com>
Date: Sun, 27 Jul 2025 19:50:22 +0200
Subject: [PATCH 136/148] fix: `append_styles` in an effect to make them
 available on mount (#16509)

Co-authored-by: Rich Harris <rich.harris@vercel.com>
---
 .changeset/shaggy-comics-fail.md              |  5 +++++
 .changeset/wise-hairs-pay.md                  |  5 +++++
 .../src/compiler/phases/2-analyze/index.js    | 16 +++++++-------
 .../3-transform/client/transform-client.js    |  5 +++--
 .../svelte/src/internal/client/dom/css.js     |  4 ++--
 .../host-rune-access-injected-css/_config.js  | 21 +++++++++++++++++++
 .../host-rune-access-injected-css/main.svelte | 16 ++++++++++++++
 .../Thing.svelte                              |  9 ++++++++
 .../custom-element-injected-styles/_config.js | 15 +++++++++++++
 .../main.svelte                               |  5 +++++
 10 files changed, 90 insertions(+), 11 deletions(-)
 create mode 100644 .changeset/shaggy-comics-fail.md
 create mode 100644 .changeset/wise-hairs-pay.md
 create mode 100644 packages/svelte/tests/runtime-browser/custom-elements-samples/host-rune-access-injected-css/_config.js
 create mode 100644 packages/svelte/tests/runtime-browser/custom-elements-samples/host-rune-access-injected-css/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/custom-element-injected-styles/Thing.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/custom-element-injected-styles/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/custom-element-injected-styles/main.svelte

diff --git a/.changeset/shaggy-comics-fail.md b/.changeset/shaggy-comics-fail.md
new file mode 100644
index 0000000000..981a25c978
--- /dev/null
+++ b/.changeset/shaggy-comics-fail.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: `append_styles` in an effect to make them available on mount
diff --git a/.changeset/wise-hairs-pay.md b/.changeset/wise-hairs-pay.md
new file mode 100644
index 0000000000..7d96c1daab
--- /dev/null
+++ b/.changeset/wise-hairs-pay.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: always inject styles when compiling as a custom element
diff --git a/packages/svelte/src/compiler/phases/2-analyze/index.js b/packages/svelte/src/compiler/phases/2-analyze/index.js
index d407b44556..cd44fd998a 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/index.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/index.js
@@ -451,6 +451,8 @@ export function analyze_component(root, source, options) {
 		}
 	}
 
+	const is_custom_element = !!options.customElementOptions || options.customElement;
+
 	// TODO remove all the ?? stuff, we don't need it now that we're validating the config
 	/** @type {ComponentAnalysis} */
 	const analysis = {
@@ -500,13 +502,13 @@ export function analyze_component(root, source, options) {
 		needs_props: false,
 		event_directive_node: null,
 		uses_event_attributes: false,
-		custom_element: options.customElementOptions ?? options.customElement,
-		inject_styles: options.css === 'injected' || options.customElement,
-		accessors: options.customElement
-			? true
-			: (runes ? false : !!options.accessors) ||
-				// because $set method needs accessors
-				options.compatibility?.componentApi === 4,
+		custom_element: is_custom_element,
+		inject_styles: options.css === 'injected' || is_custom_element,
+		accessors:
+			is_custom_element ||
+			(runes ? false : !!options.accessors) ||
+			// because $set method needs accessors
+			options.compatibility?.componentApi === 4,
 		reactive_statements: new Map(),
 		binding_groups: new Map(),
 		slot_names: new Map(),
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js b/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
index 124438a9da..a56aca9c5f 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
@@ -621,8 +621,9 @@ export function client_component(analysis, options) {
 		);
 	}
 
-	if (analysis.custom_element) {
-		const ce = analysis.custom_element;
+	const ce = options.customElementOptions ?? options.customElement;
+
+	if (ce) {
 		const ce_props = typeof ce === 'boolean' ? {} : ce.props || {};
 
 		/** @type {ESTree.Property[]} */
diff --git a/packages/svelte/src/internal/client/dom/css.js b/packages/svelte/src/internal/client/dom/css.js
index 52be36aa1f..8e6faa0e32 100644
--- a/packages/svelte/src/internal/client/dom/css.js
+++ b/packages/svelte/src/internal/client/dom/css.js
@@ -1,6 +1,6 @@
 import { DEV } from 'esm-env';
-import { queue_micro_task } from './task.js';
 import { register_style } from '../dev/css.js';
+import { effect } from '../reactivity/effects.js';
 
 /**
  * @param {Node} anchor
@@ -8,7 +8,7 @@ import { register_style } from '../dev/css.js';
  */
 export function append_styles(anchor, css) {
 	// Use `queue_micro_task` to ensure `anchor` is in the DOM, otherwise getRootNode() will yield wrong results
-	queue_micro_task(() => {
+	effect(() => {
 		var root = anchor.getRootNode();
 
 		var target = /** @type {ShadowRoot} */ (root).host
diff --git a/packages/svelte/tests/runtime-browser/custom-elements-samples/host-rune-access-injected-css/_config.js b/packages/svelte/tests/runtime-browser/custom-elements-samples/host-rune-access-injected-css/_config.js
new file mode 100644
index 0000000000..99a223492b
--- /dev/null
+++ b/packages/svelte/tests/runtime-browser/custom-elements-samples/host-rune-access-injected-css/_config.js
@@ -0,0 +1,21 @@
+import { test } from '../../assert';
+const tick = () => Promise.resolve();
+
+export default test({
+	async test({ assert, target }) {
+		target.innerHTML = '<custom-element></custom-element>';
+		/** @type {any} */
+		const el = target.querySelector('custom-element');
+
+		/** @type {string} */
+		let html = '';
+		const handle_evt = (e) => (html = e.detail);
+		el.addEventListener('html', handle_evt);
+
+		await tick();
+		await tick();
+		await tick();
+
+		assert.ok(html.includes('<style'));
+	}
+});
diff --git a/packages/svelte/tests/runtime-browser/custom-elements-samples/host-rune-access-injected-css/main.svelte b/packages/svelte/tests/runtime-browser/custom-elements-samples/host-rune-access-injected-css/main.svelte
new file mode 100644
index 0000000000..ad8027f4d2
--- /dev/null
+++ b/packages/svelte/tests/runtime-browser/custom-elements-samples/host-rune-access-injected-css/main.svelte
@@ -0,0 +1,16 @@
+<svelte:options css="injected" customElement="custom-element"/>
+
+<script lang="ts">
+  $effect(() => {
+    $host().dispatchEvent(new CustomEvent("html", { detail: $host().shadowRoot?.innerHTML }));
+  })
+</script>
+
+<button class="btn">btn</button>
+
+<style >
+  .btn {
+    width: 123px;
+    height: 123px;
+  }
+</style>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/custom-element-injected-styles/Thing.svelte b/packages/svelte/tests/runtime-runes/samples/custom-element-injected-styles/Thing.svelte
new file mode 100644
index 0000000000..0a2b139274
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/custom-element-injected-styles/Thing.svelte
@@ -0,0 +1,9 @@
+<svelte:options customElement={{ tag: 'my-thing' }} />
+
+<h1>hello</h1>
+
+<style>
+	h1 {
+		color: red;
+	}
+</style>
diff --git a/packages/svelte/tests/runtime-runes/samples/custom-element-injected-styles/_config.js b/packages/svelte/tests/runtime-runes/samples/custom-element-injected-styles/_config.js
new file mode 100644
index 0000000000..74597504bd
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/custom-element-injected-styles/_config.js
@@ -0,0 +1,15 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client'],
+	async test({ assert, target }) {
+		const thing = /** @type HTMLElement & { object: { test: true }; } */ (
+			target.querySelector('my-thing')
+		);
+
+		await tick();
+
+		assert.include(thing.shadowRoot?.innerHTML, 'red');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/custom-element-injected-styles/main.svelte b/packages/svelte/tests/runtime-runes/samples/custom-element-injected-styles/main.svelte
new file mode 100644
index 0000000000..ba5b788da9
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/custom-element-injected-styles/main.svelte
@@ -0,0 +1,5 @@
+<script>
+	import './Thing.svelte';
+</script>
+
+<my-thing></my-thing>

From 51771447c6cf941da7a07733435a5b18a91ddd28 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Sun, 27 Jul 2025 16:59:29 -0400
Subject: [PATCH 137/148] chore: remove `parser.template_untrimmed` (#16511)

---
 .changeset/shiny-berries-call.md                          | 5 +++++
 packages/svelte/src/compiler/phases/1-parse/index.js      | 7 -------
 .../svelte/src/compiler/phases/1-parse/state/element.js   | 8 --------
 3 files changed, 5 insertions(+), 15 deletions(-)
 create mode 100644 .changeset/shiny-berries-call.md

diff --git a/.changeset/shiny-berries-call.md b/.changeset/shiny-berries-call.md
new file mode 100644
index 0000000000..adc62b3cd0
--- /dev/null
+++ b/.changeset/shiny-berries-call.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: remove `parser.template_untrimmed`
diff --git a/packages/svelte/src/compiler/phases/1-parse/index.js b/packages/svelte/src/compiler/phases/1-parse/index.js
index 77cc2bf3fa..f5e0693b31 100644
--- a/packages/svelte/src/compiler/phases/1-parse/index.js
+++ b/packages/svelte/src/compiler/phases/1-parse/index.js
@@ -23,12 +23,6 @@ export class Parser {
 	 */
 	template;
 
-	/**
-	 * @readonly
-	 * @type {string}
-	 */
-	template_untrimmed;
-
 	/**
 	 * Whether or not we're in loose parsing mode, in which
 	 * case we try to continue parsing as much as possible
@@ -67,7 +61,6 @@ export class Parser {
 		}
 
 		this.loose = loose;
-		this.template_untrimmed = template;
 		this.template = template.trimEnd();
 
 		let match_lang;
diff --git a/packages/svelte/src/compiler/phases/1-parse/state/element.js b/packages/svelte/src/compiler/phases/1-parse/state/element.js
index 87332f647d..ed1b047d55 100644
--- a/packages/svelte/src/compiler/phases/1-parse/state/element.js
+++ b/packages/svelte/src/compiler/phases/1-parse/state/element.js
@@ -370,14 +370,6 @@ export default function element(parser) {
 				// ... or we're followed by whitespace, for example near the end of the template,
 				// which we want to take in so that language tools has more room to work with
 				parser.allow_whitespace();
-				if (parser.index === parser.template.length) {
-					while (
-						parser.index < parser.template_untrimmed.length &&
-						regex_whitespace.test(parser.template_untrimmed[parser.index])
-					) {
-						parser.index++;
-					}
-				}
 			}
 		}
 	}

From 03f2e44757925d0ca53f4e563965c3135ef81f16 Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Mon, 28 Jul 2025 11:56:41 -0700
Subject: [PATCH 138/148] chore: remove some todos (#16515)

* chore: remove some todos

* fix

* fix

* doh

* convert `TemplateComment` back to `Comment`

* `Evaluation.has_unknown`
---
 .changeset/happy-countries-dance.md                  |  5 +++++
 packages/svelte/src/compiler/migrate/index.js        |  4 ++--
 packages/svelte/src/compiler/phases/1-parse/index.js |  1 -
 .../3-transform/client/visitors/CallExpression.js    |  4 +++-
 .../3-transform/client/visitors/OnDirective.js       |  4 ++--
 packages/svelte/src/compiler/phases/scope.js         | 11 +++++++++++
 packages/svelte/src/compiler/types/template.d.ts     | 12 +++++++++++-
 packages/svelte/types/index.d.ts                     | 12 +++++++++++-
 8 files changed, 45 insertions(+), 8 deletions(-)
 create mode 100644 .changeset/happy-countries-dance.md

diff --git a/.changeset/happy-countries-dance.md b/.changeset/happy-countries-dance.md
new file mode 100644
index 0000000000..641cf21fd8
--- /dev/null
+++ b/.changeset/happy-countries-dance.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: remove some todos
diff --git a/packages/svelte/src/compiler/migrate/index.js b/packages/svelte/src/compiler/migrate/index.js
index 6b2e6cda70..eb0e4eff8c 100644
--- a/packages/svelte/src/compiler/migrate/index.js
+++ b/packages/svelte/src/compiler/migrate/index.js
@@ -1707,14 +1707,14 @@ function extract_type_and_comment(declarator, state, path) {
 }
 
 // Ensure modifiers are applied in the same order as Svelte 4
-const modifier_order = [
+const modifier_order = /** @type {const} */ ([
 	'preventDefault',
 	'stopPropagation',
 	'stopImmediatePropagation',
 	'self',
 	'trusted',
 	'once'
-];
+]);
 
 /**
  * @param {AST.RegularElement | AST.SvelteElement | AST.SvelteWindow | AST.SvelteDocument | AST.SvelteBody} element
diff --git a/packages/svelte/src/compiler/phases/1-parse/index.js b/packages/svelte/src/compiler/phases/1-parse/index.js
index f5e0693b31..8f7ef76be5 100644
--- a/packages/svelte/src/compiler/phases/1-parse/index.js
+++ b/packages/svelte/src/compiler/phases/1-parse/index.js
@@ -1,5 +1,4 @@
 /** @import { AST } from '#compiler' */
-/** @import { Comment } from 'estree' */
 // @ts-expect-error acorn type definitions are borked in the release we use
 import { isIdentifierStart, isIdentifierChar } from 'acorn';
 import fragment from './state/fragment.js';
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/CallExpression.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/CallExpression.js
index 3e2f1414e6..c126742d3c 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/CallExpression.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/CallExpression.js
@@ -82,7 +82,9 @@ export function CallExpression(node, context) {
 		['debug', 'dir', 'error', 'group', 'groupCollapsed', 'info', 'log', 'trace', 'warn'].includes(
 			node.callee.property.name
 		) &&
-		node.arguments.some((arg) => arg.type !== 'Literal') // TODO more cases?
+		node.arguments.some(
+			(arg) => arg.type === 'SpreadElement' || context.state.scope.evaluate(arg).has_unknown
+		)
 	) {
 		return b.call(
 			node.callee,
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/OnDirective.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/OnDirective.js
index 7a66a8ecbb..0ee3b0fb10 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/OnDirective.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/OnDirective.js
@@ -3,14 +3,14 @@
 import * as b from '#compiler/builders';
 import { build_event, build_event_handler } from './shared/events.js';
 
-const modifiers = [
+const modifiers = /** @type {const} */ ([
 	'stopPropagation',
 	'stopImmediatePropagation',
 	'preventDefault',
 	'self',
 	'trusted',
 	'once'
-];
+]);
 
 /**
  * @param {AST.OnDirective} node
diff --git a/packages/svelte/src/compiler/phases/scope.js b/packages/svelte/src/compiler/phases/scope.js
index 700e098e45..eaacf5dda9 100644
--- a/packages/svelte/src/compiler/phases/scope.js
+++ b/packages/svelte/src/compiler/phases/scope.js
@@ -180,6 +180,13 @@ class Evaluation {
 	 */
 	is_known = true;
 
+	/**
+	 * True if the possible values contains `UNKNOWN`
+	 * @readonly
+	 * @type {boolean}
+	 */
+	has_unknown = false;
+
 	/**
 	 * True if the value is known to not be null/undefined
 	 * @readonly
@@ -540,6 +547,10 @@ class Evaluation {
 			if (value == null || value === UNKNOWN) {
 				this.is_defined = false;
 			}
+
+			if (value === UNKNOWN) {
+				this.has_unknown = true;
+			}
 		}
 
 		if (this.values.size > 1 || typeof this.value === 'symbol') {
diff --git a/packages/svelte/src/compiler/types/template.d.ts b/packages/svelte/src/compiler/types/template.d.ts
index de06a41469..058a1a8e66 100644
--- a/packages/svelte/src/compiler/types/template.d.ts
+++ b/packages/svelte/src/compiler/types/template.d.ts
@@ -247,7 +247,17 @@ export namespace AST {
 		name: string;
 		/** The 'y' in `on:x={y}` */
 		expression: null | Expression;
-		modifiers: string[]; // TODO specify
+		modifiers: Array<
+			| 'capture'
+			| 'nonpassive'
+			| 'once'
+			| 'passive'
+			| 'preventDefault'
+			| 'self'
+			| 'stopImmediatePropagation'
+			| 'stopPropagation'
+			| 'trusted'
+		>;
 		/** @internal */
 		metadata: {
 			expression: ExpressionMetadata;
diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index 9ea45af7e6..64aa9e23ba 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -1296,7 +1296,17 @@ declare module 'svelte/compiler' {
 			name: string;
 			/** The 'y' in `on:x={y}` */
 			expression: null | Expression;
-			modifiers: string[];
+			modifiers: Array<
+				| 'capture'
+				| 'nonpassive'
+				| 'once'
+				| 'passive'
+				| 'preventDefault'
+				| 'self'
+				| 'stopImmediatePropagation'
+				| 'stopPropagation'
+				| 'trusted'
+			>;
 		}
 
 		/** A `style:` directive */

From 48f2fa22c0c941ac6e550151212845adc628b3de Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Mon, 28 Jul 2025 12:04:06 -0700
Subject: [PATCH 139/148] fix: allow await expressions inside `{#await ...}`
 argument (#16514)

* fix: allow await expressions inside `{#await ...}` argument

* add test

* apply suggestion from review

---------

Co-authored-by: 7nik <kifiranet@gmail.com>
---
 .changeset/long-roses-train.md                |  5 +++
 .../3-transform/client/visitors/AwaitBlock.js |  7 ++-
 .../samples/async-await/_config.js            | 43 +++++++++++++++++++
 .../samples/async-await/main.svelte           | 22 ++++++++++
 4 files changed, 75 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/long-roses-train.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-await/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-await/main.svelte

diff --git a/.changeset/long-roses-train.md b/.changeset/long-roses-train.md
new file mode 100644
index 0000000000..10920ac5c4
--- /dev/null
+++ b/.changeset/long-roses-train.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: allow await expressions inside `{#await ...}` argument
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitBlock.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitBlock.js
index c550c8e17b..4246091bcf 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitBlock.js
@@ -1,7 +1,7 @@
 /** @import { BlockStatement, Pattern, Statement } from 'estree' */
 /** @import { AST } from '#compiler' */
 /** @import { ComponentClientTransformState, ComponentContext } from '../types' */
-import { extract_identifiers } from '../../../../utils/ast.js';
+import { extract_identifiers, is_expression_async } from '../../../../utils/ast.js';
 import * as b from '#compiler/builders';
 import { create_derived } from '../utils.js';
 import { get_value } from './shared/declarations.js';
@@ -15,7 +15,10 @@ export function AwaitBlock(node, context) {
 	context.state.template.push_comment();
 
 	// Visit {#await <expression>} first to ensure that scopes are in the correct order
-	const expression = b.thunk(build_expression(context, node.expression, node.metadata.expression));
+	const expression = b.thunk(
+		build_expression(context, node.expression, node.metadata.expression),
+		node.metadata.expression.has_await
+	);
 
 	let then_block;
 	let catch_block;
diff --git a/packages/svelte/tests/runtime-runes/samples/async-await/_config.js b/packages/svelte/tests/runtime-runes/samples/async-await/_config.js
new file mode 100644
index 0000000000..dda6a7a895
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-await/_config.js
@@ -0,0 +1,43 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const [reset, one, two, reject] = target.querySelectorAll('button');
+
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>reset</button><button>one</button><button>two</button><button>reject</button> waiting'
+		);
+
+		one.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>reset</button><button>one</button><button>two</button><button>reject</button> one_res'
+		);
+
+		reset.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>reset</button><button>one</button><button>two</button><button>reject</button> waiting'
+		);
+
+		two.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>reset</button><button>one</button><button>two</button><button>reject</button> two_res'
+		);
+
+		reset.click();
+		reject.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>reset</button><button>one</button><button>two</button><button>reject</button> reject_catch'
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-await/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-await/main.svelte
new file mode 100644
index 0000000000..8673e45414
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-await/main.svelte
@@ -0,0 +1,22 @@
+<script>
+	let deferred = $state(Promise.withResolvers());
+</script>
+
+<button onclick={() => deferred = Promise.withResolvers()}>reset</button>
+<button onclick={() => deferred.resolve("one")}>one</button>
+<button onclick={() => deferred.resolve("two")}>two</button>
+<button onclick={() => deferred.reject("reject")}>reject</button>
+
+<svelte:boundary>
+	{#await await deferred.promise + "_res"}
+		waiting
+	{:then res}
+		{res}
+	{:catch err}
+		{err}_catch
+	{/await}
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>

From d82edf6b1dfaac8af70462b1009f3b9da47a701a Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Mon, 28 Jul 2025 12:07:57 -0700
Subject: [PATCH 140/148] Version Packages (#16513)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/happy-countries-dance.md |  5 -----
 .changeset/long-roses-train.md      |  5 -----
 .changeset/shaggy-comics-fail.md    |  5 -----
 .changeset/shiny-berries-call.md    |  5 -----
 .changeset/wise-hairs-pay.md        |  5 -----
 packages/svelte/CHANGELOG.md        | 14 ++++++++++++++
 packages/svelte/package.json        |  2 +-
 packages/svelte/src/version.js      |  2 +-
 8 files changed, 16 insertions(+), 27 deletions(-)
 delete mode 100644 .changeset/happy-countries-dance.md
 delete mode 100644 .changeset/long-roses-train.md
 delete mode 100644 .changeset/shaggy-comics-fail.md
 delete mode 100644 .changeset/shiny-berries-call.md
 delete mode 100644 .changeset/wise-hairs-pay.md

diff --git a/.changeset/happy-countries-dance.md b/.changeset/happy-countries-dance.md
deleted file mode 100644
index 641cf21fd8..0000000000
--- a/.changeset/happy-countries-dance.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-chore: remove some todos
diff --git a/.changeset/long-roses-train.md b/.changeset/long-roses-train.md
deleted file mode 100644
index 10920ac5c4..0000000000
--- a/.changeset/long-roses-train.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: allow await expressions inside `{#await ...}` argument
diff --git a/.changeset/shaggy-comics-fail.md b/.changeset/shaggy-comics-fail.md
deleted file mode 100644
index 981a25c978..0000000000
--- a/.changeset/shaggy-comics-fail.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: `append_styles` in an effect to make them available on mount
diff --git a/.changeset/shiny-berries-call.md b/.changeset/shiny-berries-call.md
deleted file mode 100644
index adc62b3cd0..0000000000
--- a/.changeset/shiny-berries-call.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-chore: remove `parser.template_untrimmed`
diff --git a/.changeset/wise-hairs-pay.md b/.changeset/wise-hairs-pay.md
deleted file mode 100644
index 7d96c1daab..0000000000
--- a/.changeset/wise-hairs-pay.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: always inject styles when compiling as a custom element
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index f939f69d28..59c44dd4f9 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,19 @@
 # svelte
 
+## 5.37.1
+
+### Patch Changes
+
+- chore: remove some todos ([#16515](https://github.com/sveltejs/svelte/pull/16515))
+
+- fix: allow await expressions inside `{#await ...}` argument ([#16514](https://github.com/sveltejs/svelte/pull/16514))
+
+- fix: `append_styles` in an effect to make them available on mount ([#16509](https://github.com/sveltejs/svelte/pull/16509))
+
+- chore: remove `parser.template_untrimmed` ([#16511](https://github.com/sveltejs/svelte/pull/16511))
+
+- fix: always inject styles when compiling as a custom element ([#16509](https://github.com/sveltejs/svelte/pull/16509))
+
 ## 5.37.0
 
 ### Minor Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index c781eda8c8..826850ea60 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.37.0",
+  "version": "5.37.1",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index e83ba6fb30..2d5083a2a5 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.37.0';
+export const VERSION = '5.37.1';
 export const PUBLIC_VERSION = '5';

From a91e0154d4bc4b0a3209956647f868e518d0acba Mon Sep 17 00:00:00 2001
From: Laszlo Korte <laszlokorte@users.noreply.github.com>
Date: Thu, 31 Jul 2025 09:45:52 +0200
Subject: [PATCH 141/148] fix: double event processing in Firefox (#16522)
 (#16527)

* Fix double event processing (#16522)

Firefox seems to garbage collect event objects during event propagation if no global reference to the event object is kept.
That discards the __root marker set on the event object to early,
leading to duplicate processing.

* minor tweaks

---------

Co-authored-by: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
---
 .changeset/chilly-bananas-train.md                       | 5 +++++
 .../svelte/src/internal/client/dom/elements/events.js    | 9 +++++++++
 2 files changed, 14 insertions(+)
 create mode 100644 .changeset/chilly-bananas-train.md

diff --git a/.changeset/chilly-bananas-train.md b/.changeset/chilly-bananas-train.md
new file mode 100644
index 0000000000..b0305f9e61
--- /dev/null
+++ b/.changeset/chilly-bananas-train.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: double event processing in firefox due to event object being garbage collected
diff --git a/packages/svelte/src/internal/client/dom/elements/events.js b/packages/svelte/src/internal/client/dom/elements/events.js
index fa3bf0b021..19bd1cfa18 100644
--- a/packages/svelte/src/internal/client/dom/elements/events.js
+++ b/packages/svelte/src/internal/client/dom/elements/events.js
@@ -141,6 +141,13 @@ export function delegate(events) {
 	}
 }
 
+// used to store the reference to the currently propagated event
+// to prevent garbage collection between microtasks in Firefox
+// If the event object is GCed too early, the expando __root property
+// set on the event object is lost, causing the event delegation
+// to process the event twice
+let last_propagated_event = null;
+
 /**
  * @this {EventTarget}
  * @param {Event} event
@@ -153,6 +160,8 @@ export function handle_event_propagation(event) {
 	var path = event.composedPath?.() || [];
 	var current_target = /** @type {null | Element} */ (path[0] || event.target);
 
+	last_propagated_event = event;
+
 	// composedPath contains list of nodes the event has propagated through.
 	// We check __root to skip all nodes below it in case this is a
 	// parent of the __root node, which indicates that there's nested

From f5950f866c51d9325a432ebfd5362bcf2647763a Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Thu, 31 Jul 2025 02:11:52 -0700
Subject: [PATCH 142/148] fix: correctly differentiate static fields before
 emitting `duplicate_class_field` (#16526)

* fix: correctly differentiate static fields before emitting `duplicate_class_field`

* remove unnecessary `#` concatenation

* add test
---
 .changeset/nine-cups-film.md                                | 5 +++++
 .../src/compiler/phases/2-analyze/visitors/ClassBody.js     | 6 +++---
 .../samples/class-state-constructor-9/input.svelte.js       | 2 +-
 3 files changed, 9 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/nine-cups-film.md

diff --git a/.changeset/nine-cups-film.md b/.changeset/nine-cups-film.md
new file mode 100644
index 0000000000..ba72337dac
--- /dev/null
+++ b/.changeset/nine-cups-film.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: correctly differentiate static fields before emitting `duplicate_class_field`
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/ClassBody.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/ClassBody.js
index 2bfc1dbce3..dd21637174 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/ClassBody.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/ClassBody.js
@@ -57,7 +57,7 @@ export function ClassBody(node, context) {
 				e.state_field_duplicate(node, name);
 			}
 
-			const _key = (key.type === 'PrivateIdentifier' ? '#' : '') + name;
+			const _key = (node.type === 'AssignmentExpression' || !node.static ? '' : '@') + name;
 			const field = fields.get(_key);
 
 			// if there's already a method or assigned field, error
@@ -78,7 +78,7 @@ export function ClassBody(node, context) {
 	for (const child of node.body) {
 		if (child.type === 'PropertyDefinition' && !child.computed && !child.static) {
 			handle(child, child.key, child.value);
-			const key = (child.key.type === 'PrivateIdentifier' ? '#' : '') + get_name(child.key);
+			const key = /** @type {string} */ (get_name(child.key));
 			const field = fields.get(key);
 			if (!field) {
 				fields.set(key, [child.value ? 'assigned_prop' : 'prop']);
@@ -91,7 +91,7 @@ export function ClassBody(node, context) {
 			if (child.kind === 'constructor') {
 				constructor = child;
 			} else if (!child.computed) {
-				const key = (child.key.type === 'PrivateIdentifier' ? '#' : '') + get_name(child.key);
+				const key = (child.static ? '@' : '') + get_name(child.key);
 				const field = fields.get(key);
 				if (!field) {
 					fields.set(key, [child.kind]);
diff --git a/packages/svelte/tests/validator/samples/class-state-constructor-9/input.svelte.js b/packages/svelte/tests/validator/samples/class-state-constructor-9/input.svelte.js
index a8469e13af..3806046f3f 100644
--- a/packages/svelte/tests/validator/samples/class-state-constructor-9/input.svelte.js
+++ b/packages/svelte/tests/validator/samples/class-state-constructor-9/input.svelte.js
@@ -1,6 +1,6 @@
 export class Counter {
 	count = -1;
-
+	static count() {}
 	constructor() {
 		this.count = $state(0);
 	}

From 72e46d31c075eeea232a1cc320efc272f5ef87d7 Mon Sep 17 00:00:00 2001
From: Elliot Bentley <mail@elliotbentley.com>
Date: Thu, 31 Jul 2025 11:34:28 +0100
Subject: [PATCH 143/148] fix: add types for SVG bindable attributes (#16525)

* fix: types for SVG bind: attributes

* add changeset and tweak

---------

Co-authored-by: 7nik <kifiranet@gmail.com>
---
 .changeset/cuddly-feet-doubt.md |  5 +++++
 packages/svelte/elements.d.ts   | 14 ++++++++------
 2 files changed, 13 insertions(+), 6 deletions(-)
 create mode 100644 .changeset/cuddly-feet-doubt.md

diff --git a/.changeset/cuddly-feet-doubt.md b/.changeset/cuddly-feet-doubt.md
new file mode 100644
index 0000000000..8d7d955daa
--- /dev/null
+++ b/.changeset/cuddly-feet-doubt.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: add bindable dimension attributes types to SVG and MathML elements
diff --git a/packages/svelte/elements.d.ts b/packages/svelte/elements.d.ts
index 2e1042dfd6..b3d44d9ed6 100644
--- a/packages/svelte/elements.d.ts
+++ b/packages/svelte/elements.d.ts
@@ -464,6 +464,14 @@ export interface DOMAttributes<T extends EventTarget> {
 	onfullscreenerror?: EventHandler<Event, T> | undefined | null;
 	onfullscreenerrorcapture?: EventHandler<Event, T> | undefined | null;
 
+	// Dimensions
+	readonly 'bind:contentRect'?: DOMRectReadOnly | undefined | null;
+	readonly 'bind:contentBoxSize'?: Array<ResizeObserverSize> | undefined | null;
+	readonly 'bind:borderBoxSize'?: Array<ResizeObserverSize> | undefined | null;
+	readonly 'bind:devicePixelContentBoxSize'?: Array<ResizeObserverSize> | undefined | null;
+	readonly 'bind:clientWidth'?: number | undefined | null;
+	readonly 'bind:clientHeight'?: number | undefined | null;
+
 	xmlns?: string | undefined | null;
 }
 
@@ -839,13 +847,7 @@ export interface HTMLAttributes<T extends EventTarget> extends AriaAttributes, D
 	 */
 	'bind:innerText'?: string | undefined | null;
 
-	readonly 'bind:contentRect'?: DOMRectReadOnly | undefined | null;
-	readonly 'bind:contentBoxSize'?: Array<ResizeObserverSize> | undefined | null;
-	readonly 'bind:borderBoxSize'?: Array<ResizeObserverSize> | undefined | null;
-	readonly 'bind:devicePixelContentBoxSize'?: Array<ResizeObserverSize> | undefined | null;
 	readonly 'bind:focused'?: boolean | undefined | null;
-	readonly 'bind:clientWidth'?: number | undefined | null;
-	readonly 'bind:clientHeight'?: number | undefined | null;
 	readonly 'bind:offsetWidth'?: number | undefined | null;
 	readonly 'bind:offsetHeight'?: number | undefined | null;
 

From c04975d3db74e59f8612ffd0f64d3b3bb3133ef1 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 31 Jul 2025 18:28:01 -0400
Subject: [PATCH 144/148] fix: prevent last_propagated_event from being DCE'd
 (#16538)

* fix: prevent last_propagated_event from being DCE'd

* changeset
---
 .changeset/serious-cars-hear.md                            | 5 +++++
 packages/svelte/src/internal/client/dom/elements/events.js | 5 ++++-
 2 files changed, 9 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/serious-cars-hear.md

diff --git a/.changeset/serious-cars-hear.md b/.changeset/serious-cars-hear.md
new file mode 100644
index 0000000000..4647e89ed9
--- /dev/null
+++ b/.changeset/serious-cars-hear.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: prevent last_propagated_event from being DCE'd
diff --git a/packages/svelte/src/internal/client/dom/elements/events.js b/packages/svelte/src/internal/client/dom/elements/events.js
index 19bd1cfa18..15544d7426 100644
--- a/packages/svelte/src/internal/client/dom/elements/events.js
+++ b/packages/svelte/src/internal/client/dom/elements/events.js
@@ -168,8 +168,11 @@ export function handle_event_propagation(event) {
 	// mounted apps. In this case we don't want to trigger events multiple times.
 	var path_idx = 0;
 
+	// the `last_propagated_event === event` check is redundant, but
+	// without it the variable will be DCE'd and things will
+	// fail mysteriously in Firefox
 	// @ts-expect-error is added below
-	var handled_at = event.__root;
+	var handled_at = last_propagated_event === event && event.__root;
 
 	if (handled_at) {
 		var at_idx = path.indexOf(handled_at);

From 9134856fece750608ba81da45c4a330b3d8ebb1e Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Thu, 31 Jul 2025 19:15:45 -0400
Subject: [PATCH 145/148] Version Packages (#16529)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/chilly-bananas-train.md |  5 -----
 .changeset/cuddly-feet-doubt.md    |  5 -----
 .changeset/nine-cups-film.md       |  5 -----
 .changeset/serious-cars-hear.md    |  5 -----
 packages/svelte/CHANGELOG.md       | 12 ++++++++++++
 packages/svelte/package.json       |  2 +-
 packages/svelte/src/version.js     |  2 +-
 7 files changed, 14 insertions(+), 22 deletions(-)
 delete mode 100644 .changeset/chilly-bananas-train.md
 delete mode 100644 .changeset/cuddly-feet-doubt.md
 delete mode 100644 .changeset/nine-cups-film.md
 delete mode 100644 .changeset/serious-cars-hear.md

diff --git a/.changeset/chilly-bananas-train.md b/.changeset/chilly-bananas-train.md
deleted file mode 100644
index b0305f9e61..0000000000
--- a/.changeset/chilly-bananas-train.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: double event processing in firefox due to event object being garbage collected
diff --git a/.changeset/cuddly-feet-doubt.md b/.changeset/cuddly-feet-doubt.md
deleted file mode 100644
index 8d7d955daa..0000000000
--- a/.changeset/cuddly-feet-doubt.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: add bindable dimension attributes types to SVG and MathML elements
diff --git a/.changeset/nine-cups-film.md b/.changeset/nine-cups-film.md
deleted file mode 100644
index ba72337dac..0000000000
--- a/.changeset/nine-cups-film.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: correctly differentiate static fields before emitting `duplicate_class_field`
diff --git a/.changeset/serious-cars-hear.md b/.changeset/serious-cars-hear.md
deleted file mode 100644
index 4647e89ed9..0000000000
--- a/.changeset/serious-cars-hear.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: prevent last_propagated_event from being DCE'd
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 59c44dd4f9..6e0a199ddc 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,17 @@
 # svelte
 
+## 5.37.2
+
+### Patch Changes
+
+- fix: double event processing in firefox due to event object being garbage collected ([#16527](https://github.com/sveltejs/svelte/pull/16527))
+
+- fix: add bindable dimension attributes types to SVG and MathML elements ([#16525](https://github.com/sveltejs/svelte/pull/16525))
+
+- fix: correctly differentiate static fields before emitting `duplicate_class_field` ([#16526](https://github.com/sveltejs/svelte/pull/16526))
+
+- fix: prevent last_propagated_event from being DCE'd ([#16538](https://github.com/sveltejs/svelte/pull/16538))
+
 ## 5.37.1
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 826850ea60..8536135ca8 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.37.1",
+  "version": "5.37.2",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 2d5083a2a5..b8f3bcfdd5 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.37.1';
+export const VERSION = '5.37.2';
 export const PUBLIC_VERSION = '5';

From 80678411706e99c0224b8bf995959c2d4e7fd4db Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Thu, 31 Jul 2025 16:16:47 -0700
Subject: [PATCH 146/148] docs: add note about attachments to `svelte/action`
 docs (#16537)

---
 documentation/docs/98-reference/21-svelte-action.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/documentation/docs/98-reference/21-svelte-action.md b/documentation/docs/98-reference/21-svelte-action.md
index 53423ec409..ef3ebfbf70 100644
--- a/documentation/docs/98-reference/21-svelte-action.md
+++ b/documentation/docs/98-reference/21-svelte-action.md
@@ -2,4 +2,6 @@
 title: svelte/action
 ---
 
+This module provides types for [actions](use), which have been superseded by [attachments](@attach).
+
 > MODULE: svelte/action

From 540f1b19ec56a69dde85f24471f25d9d465937e4 Mon Sep 17 00:00:00 2001
From: 7nik <kifiranet@gmail.com>
Date: Sat, 2 Aug 2025 22:29:10 +0300
Subject: [PATCH 147/148] fix: reset attribute cache after setting
 corresponding property (#16543)

---
 .changeset/afraid-carrots-study.md            |  5 +++++
 .../client/dom/elements/attributes.js         |  4 +++-
 .../attribute-after-property/_config.js       | 19 +++++++++++++++++++
 .../attribute-after-property/main.svelte      |  6 ++++++
 4 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/afraid-carrots-study.md
 create mode 100644 packages/svelte/tests/runtime-legacy/samples/attribute-after-property/_config.js
 create mode 100644 packages/svelte/tests/runtime-legacy/samples/attribute-after-property/main.svelte

diff --git a/.changeset/afraid-carrots-study.md b/.changeset/afraid-carrots-study.md
new file mode 100644
index 0000000000..71f4232edb
--- /dev/null
+++ b/.changeset/afraid-carrots-study.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: reset attribute cache after setting corresponding property
diff --git a/packages/svelte/src/internal/client/dom/elements/attributes.js b/packages/svelte/src/internal/client/dom/elements/attributes.js
index 22e532f5e4..2fa5d4541c 100644
--- a/packages/svelte/src/internal/client/dom/elements/attributes.js
+++ b/packages/svelte/src/internal/client/dom/elements/attributes.js
@@ -19,7 +19,7 @@ import { attach } from './attachments.js';
 import { clsx } from '../../../shared/attributes.js';
 import { set_class } from './class.js';
 import { set_style } from './style.js';
-import { ATTACHMENT_KEY, NAMESPACE_HTML } from '../../../../constants.js';
+import { ATTACHMENT_KEY, NAMESPACE_HTML, UNINITIALIZED } from '../../../../constants.js';
 import { block, branch, destroy_effect, effect } from '../../reactivity/effects.js';
 import { init_select, select_option } from './bindings/select.js';
 import { flatten } from '../../reactivity/async.js';
@@ -446,6 +446,8 @@ export function set_attributes(element, prev, next, css_hash, skip_warning = fal
 			) {
 				// @ts-ignore
 				element[name] = value;
+				// remove it from attributes's cache
+				if (name in attributes) attributes[name] = UNINITIALIZED;
 			} else if (typeof value !== 'function') {
 				set_attribute(element, name, value, skip_warning);
 			}
diff --git a/packages/svelte/tests/runtime-legacy/samples/attribute-after-property/_config.js b/packages/svelte/tests/runtime-legacy/samples/attribute-after-property/_config.js
new file mode 100644
index 0000000000..f6a98b1797
--- /dev/null
+++ b/packages/svelte/tests/runtime-legacy/samples/attribute-after-property/_config.js
@@ -0,0 +1,19 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	test({ target, assert }) {
+		const input = target.querySelector('input');
+		const button = target.querySelector('button');
+
+		assert.equal(input?.step, 'any');
+
+		button?.click();
+		flushSync();
+		assert.equal(input?.step, '10');
+
+		button?.click();
+		flushSync();
+		assert.equal(input?.step, 'any');
+	}
+});
diff --git a/packages/svelte/tests/runtime-legacy/samples/attribute-after-property/main.svelte b/packages/svelte/tests/runtime-legacy/samples/attribute-after-property/main.svelte
new file mode 100644
index 0000000000..2921e4e241
--- /dev/null
+++ b/packages/svelte/tests/runtime-legacy/samples/attribute-after-property/main.svelte
@@ -0,0 +1,6 @@
+<script>
+    let step = "any";
+</script>
+
+<input type="range" {...{step}} />
+<button onclick={() => step = step === "any" ? 10 : "any"}>change step</button>
\ No newline at end of file

From 0cbb5becf6d62ae3334b78606a76d21a91eda32b Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Sat, 2 Aug 2025 21:17:58 -0700
Subject: [PATCH 148/148] Version Packages (#16544)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/afraid-carrots-study.md | 5 -----
 packages/svelte/CHANGELOG.md       | 6 ++++++
 packages/svelte/package.json       | 2 +-
 packages/svelte/src/version.js     | 2 +-
 4 files changed, 8 insertions(+), 7 deletions(-)
 delete mode 100644 .changeset/afraid-carrots-study.md

diff --git a/.changeset/afraid-carrots-study.md b/.changeset/afraid-carrots-study.md
deleted file mode 100644
index 71f4232edb..0000000000
--- a/.changeset/afraid-carrots-study.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: reset attribute cache after setting corresponding property
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 6e0a199ddc..9766e3f06b 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,11 @@
 # svelte
 
+## 5.37.3
+
+### Patch Changes
+
+- fix: reset attribute cache after setting corresponding property ([#16543](https://github.com/sveltejs/svelte/pull/16543))
+
 ## 5.37.2
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 8536135ca8..e8927fcf56 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.37.2",
+  "version": "5.37.3",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index b8f3bcfdd5..127b43e205 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.37.2';
+export const VERSION = '5.37.3';
 export const PUBLIC_VERSION = '5';