From 2b740e496e857ae9e53bd15f5d5d7a2d4398139b Mon Sep 17 00:00:00 2001
From: Nic Polumeyv <nicolas.polum@outlook.com>
Date: Tue, 25 Aug 2026 04:14:43 -0400
Subject: [PATCH 01/29] fix: commit a reaction's dependencies even when it
 throws (#18703)

Fixes #18414 and a second bug with the same cause.

`update_reaction` in `runtime.js` commits a reaction's dependencies
after `fn()` returns: it swaps in `new_deps`, removes stale reactions
and registers the reaction into each new dep's `reactions`. When `fn()`
throws, the whole block is skipped. Two things go wrong from that.

A derived that the run read for the first time was already set
`CONNECTED` in `get` and registered itself into its own deps'
`reactions` during `update_derived`, but the throwing reaction never
registers as its reader. It sits in its deps' `reactions` with
`reactions === null` of its own, `remove_reaction`'s disconnect cascade
can never reach it, and it retains its `ctx`, closures and DOM past
component destruction and `unmount()`.

A derived that throws during its own run ends up with no dependencies at
all. It is not in its sources' `reactions`, so a later change to them
never re-runs it, and for an unowned derived `update_derived` then marks
the error value CLEAN because the derived has no deps. Anything reading
it keeps getting the first error forever.

The commit block is now `update_dependencies` and the `catch` calls it
before `handle_error`, so a failing reaction keeps the deps it read up
to the throw. That subscribes it to the inputs that produced the error,
and lets the normal disconnect cascade clean up when it is destroyed
(`Boundary.#handle_error` destroys the failed effect).

Co-authored-by: Randy Murphy <randalmurphal@users.noreply.github.com>
---
 .changeset/quiet-deriveds-unwind.md           |  5 ++
 .../svelte/src/internal/client/runtime.js     | 76 +++++++++++--------
 packages/svelte/tests/signals/test.ts         | 70 +++++++++++++++++
 3 files changed, 119 insertions(+), 32 deletions(-)
 create mode 100644 .changeset/quiet-deriveds-unwind.md

diff --git a/.changeset/quiet-deriveds-unwind.md b/.changeset/quiet-deriveds-unwind.md
new file mode 100644
index 0000000000..8036bdb781
--- /dev/null
+++ b/.changeset/quiet-deriveds-unwind.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: keep the dependencies of a reaction that throws, so deriveds it read are neither leaked nor stuck in their error
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index e0914b8f70..a881403f58 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -258,37 +258,7 @@ export function update_reaction(reaction) {
 		var fn = /** @type {Function} */ (reaction.fn);
 		var result = fn();
 		reaction.f |= REACTION_RAN;
-		var deps = reaction.deps;
-
-		// Don't remove reactions during fork;
-		// they must remain for when fork is discarded
-		var is_fork = current_batch?.is_fork;
-
-		if (new_deps !== null) {
-			var i;
-
-			if (!is_fork) {
-				remove_reactions(reaction, skipped_deps);
-			}
-
-			if (deps !== null && skipped_deps > 0) {
-				deps.length = skipped_deps + new_deps.length;
-				for (i = 0; i < new_deps.length; i++) {
-					deps[skipped_deps + i] = new_deps[i];
-				}
-			} else {
-				reaction.deps = deps = new_deps;
-			}
-
-			if (effect_tracking() && (reaction.f & CONNECTED) !== 0) {
-				for (i = skipped_deps; i < deps.length; i++) {
-					(deps[i].reactions ??= []).push(reaction);
-				}
-			}
-		} else if (!is_fork && deps !== null && skipped_deps < deps.length) {
-			remove_reactions(reaction, skipped_deps);
-			deps.length = skipped_deps;
-		}
+		var deps = update_dependencies(reaction);
 
 		// If we're inside an effect and we have untracked writes, then we need to
 		// ensure that if any of those untracked writes result in re-invalidation
@@ -300,7 +270,7 @@ export function update_reaction(reaction) {
 			deps !== null &&
 			(reaction.f & (DERIVED | MAYBE_DIRTY | DIRTY)) === 0
 		) {
-			for (i = 0; i < /** @type {Source[]} */ (untracked_writes).length; i++) {
+			for (var i = 0; i < /** @type {Source[]} */ (untracked_writes).length; i++) {
 				schedule_possible_effect_self_invalidation(
 					untracked_writes[i],
 					/** @type {Effect} */ (reaction)
@@ -344,6 +314,9 @@ export function update_reaction(reaction) {
 
 		return result;
 	} catch (error) {
+		// still commit the deps read before the throw, otherwise deriveds connected by this run keep no reader and the reaction never re-runs when they change
+		update_dependencies(reaction);
+
 		return handle_error(error);
 	} finally {
 		reaction.f ^= REACTION_IS_UPDATING;
@@ -358,6 +331,45 @@ export function update_reaction(reaction) {
 	}
 }
 
+/**
+ * @param {Reaction} reaction
+ */
+function update_dependencies(reaction) {
+	var deps = reaction.deps;
+
+	// Don't remove reactions during fork;
+	// they must remain for when fork is discarded
+	var is_fork = current_batch?.is_fork;
+
+	if (new_deps !== null) {
+		var i;
+
+		if (!is_fork) {
+			remove_reactions(reaction, skipped_deps);
+		}
+
+		if (deps !== null && skipped_deps > 0) {
+			deps.length = skipped_deps + new_deps.length;
+			for (i = 0; i < new_deps.length; i++) {
+				deps[skipped_deps + i] = new_deps[i];
+			}
+		} else {
+			reaction.deps = deps = new_deps;
+		}
+
+		if (effect_tracking() && (reaction.f & CONNECTED) !== 0) {
+			for (i = skipped_deps; i < deps.length; i++) {
+				(deps[i].reactions ??= []).push(reaction);
+			}
+		}
+	} else if (!is_fork && deps !== null && skipped_deps < deps.length) {
+		remove_reactions(reaction, skipped_deps);
+		deps.length = skipped_deps;
+	}
+
+	return deps;
+}
+
 /**
  * @template V
  * @param {Reaction} signal
diff --git a/packages/svelte/tests/signals/test.ts b/packages/svelte/tests/signals/test.ts
index 07f79bd395..c1ebc3ec75 100644
--- a/packages/svelte/tests/signals/test.ts
+++ b/packages/svelte/tests/signals/test.ts
@@ -1521,4 +1521,74 @@ describe('signals', () => {
 			assert.equal(s.reactions, null);
 		};
 	});
+
+	// https://github.com/sveltejs/svelte/issues/18414
+	test('a reaction that throws after first-reading a fresh derived does not leak it', () => {
+		const src = state(0);
+		const pane = derived(() => $.get(src));
+		const base = derived(() => $.get(pane) + ':base');
+		const extra = derived(() => $.get(pane) + ':extra');
+		const flag = state(false);
+
+		const destroy = effect_root(() => {
+			render_effect(() => {
+				if ($.get(flag)) {
+					$.get(extra);
+					throw new Error('render boom');
+				} else {
+					$.get(base);
+				}
+			});
+		});
+
+		return () => {
+			try {
+				flushSync(() => set(flag, true));
+			} catch {}
+
+			destroy();
+
+			assert.equal(src.reactions, null);
+		};
+	});
+
+	test('a derived that throws on its first run re-runs when its dependencies change', () => {
+		const s = state(0);
+		const fn = () => {
+			if ($.get(s) === 0) throw new Error('boom');
+			return $.get(s);
+		};
+		const owned = derived(fn);
+		const previous_effect = $.active_effect;
+		$.set_active_effect(null);
+		const unowned = derived(fn);
+		$.set_active_effect(previous_effect);
+		const log: any[] = [];
+
+		const destroy = effect_root(() => {
+			render_effect(() => {
+				for (const d of [owned, unowned]) {
+					try {
+						log.push($.get(d));
+					} catch {
+						log.push('error');
+					}
+				}
+			});
+		});
+
+		return () => {
+			assert.notEqual(owned.parent, null);
+			assert.equal(unowned.parent, null);
+
+			flushSync();
+			assert.deepEqual(log, ['error', 'error']);
+
+			flushSync(() => set(s, 1));
+			assert.deepEqual(log, ['error', 'error', 1, 1]);
+
+			destroy();
+			assert.equal(s.reactions, null);
+		};
+	});
 });

From 1b02aa28c8d746280617f59d6126b8b60f6cd748 Mon Sep 17 00:00:00 2001
From: Jawad Ali <contact.jawaddd@gmail.com>
Date: Tue, 25 Aug 2026 13:28:46 +0500
Subject: [PATCH 02/29] fix: decode uppercase-X hex numeric character
 references (#18708)

uppercase X is also valid per the HTML spec
---
 .changeset/uppercase-hex-entities.md                         | 5 +++++
 packages/svelte/src/compiler/phases/1-parse/utils/html.js    | 4 ++--
 .../tests/runtime-legacy/samples/html-entities/_config.js    | 1 +
 .../tests/runtime-legacy/samples/html-entities/main.svelte   | 1 +
 4 files changed, 9 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/uppercase-hex-entities.md

diff --git a/.changeset/uppercase-hex-entities.md b/.changeset/uppercase-hex-entities.md
new file mode 100644
index 0000000000..e6e13d5df5
--- /dev/null
+++ b/.changeset/uppercase-hex-entities.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: decode uppercase-`X` hex numeric character references (`&#X...;`)
diff --git a/packages/svelte/src/compiler/phases/1-parse/utils/html.js b/packages/svelte/src/compiler/phases/1-parse/utils/html.js
index a0c2a5b06f..1d660298c7 100644
--- a/packages/svelte/src/compiler/phases/1-parse/utils/html.js
+++ b/packages/svelte/src/compiler/phases/1-parse/utils/html.js
@@ -20,7 +20,7 @@ function reg_exp_entity(entity_name, is_attribute_value) {
 
 /** @param {boolean} is_attribute_value */
 function get_entity_pattern(is_attribute_value) {
-	const reg_exp_num = '#(?:x[a-fA-F\\d]+|\\d+)(?:;)?';
+	const reg_exp_num = '#(?:[xX][a-fA-F\\d]+|\\d+)(?:;)?';
 	const reg_exp_entities = Object.keys(entities).map(
 		/** @param {any} entity_name */ (entity_name) => reg_exp_entity(entity_name, is_attribute_value)
 	);
@@ -50,7 +50,7 @@ export function decode_character_references(html, is_attribute_value) {
 			// Handle named entities
 			if (entity[0] !== '#') {
 				code = entities[entity];
-			} else if (entity[1] === 'x') {
+			} else if (entity[1] === 'x' || entity[1] === 'X') {
 				code = parseInt(entity.substring(2), 16);
 			} else {
 				code = parseInt(entity.substring(1), 10);
diff --git a/packages/svelte/tests/runtime-legacy/samples/html-entities/_config.js b/packages/svelte/tests/runtime-legacy/samples/html-entities/_config.js
index add763989e..82c87495c4 100644
--- a/packages/svelte/tests/runtime-legacy/samples/html-entities/_config.js
+++ b/packages/svelte/tests/runtime-legacy/samples/html-entities/_config.js
@@ -7,6 +7,7 @@ export default test({
 		<span>*</span>
 		<span>*</span>
 		<span>*</span>
+		<span>*</span>
 
 		<span></span>
 		<span>A</span>
diff --git a/packages/svelte/tests/runtime-legacy/samples/html-entities/main.svelte b/packages/svelte/tests/runtime-legacy/samples/html-entities/main.svelte
index 2d0d66c939..25a60cb930 100644
--- a/packages/svelte/tests/runtime-legacy/samples/html-entities/main.svelte
+++ b/packages/svelte/tests/runtime-legacy/samples/html-entities/main.svelte
@@ -2,6 +2,7 @@
 <span>&midast;</span>
 <span>&#x0002A;</span>
 <span>&#x0002A</span>
+<span>&#X0002A;</span>
 <span>&#42;</span>
 
 <span>&#10;</span>

From 6b16b7f73fe8223ad7ab8bc629c98ba6d581f5cf Mon Sep 17 00:00:00 2001
From: Nic Polumeyv <nicolas.polum@outlook.com>
Date: Tue, 25 Aug 2026 04:35:46 -0400
Subject: [PATCH 03/29] fix: keep defaultChecked on hydrated radio inputs with
 spread attributes (#18701)

radio buttons were missing in the type check - remove the check instead (aligns with how we do it in the compiler, see `has_default_value_attribute`). Strictly speaking not fully correct but pragmatic solution that doesn't have any impact in practise

Needed by sveltejs/kit#16926.
---
 .changeset/keep-radio-default-checked.md      |  5 ++++
 .../client/dom/elements/attributes.js         |  7 ++----
 .../_config.js                                | 23 +++++++++++++++++++
 .../main.svelte                               |  9 ++++++++
 4 files changed, 39 insertions(+), 5 deletions(-)
 create mode 100644 .changeset/keep-radio-default-checked.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/form-default-checked-radio-spread/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/form-default-checked-radio-spread/main.svelte

diff --git a/.changeset/keep-radio-default-checked.md b/.changeset/keep-radio-default-checked.md
new file mode 100644
index 0000000000..b3b32afda6
--- /dev/null
+++ b/.changeset/keep-radio-default-checked.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: keep `defaultChecked` on hydrated radio inputs with spread attributes
diff --git a/packages/svelte/src/internal/client/dom/elements/attributes.js b/packages/svelte/src/internal/client/dom/elements/attributes.js
index 3d71abcd10..69d4dd42a8 100644
--- a/packages/svelte/src/internal/client/dom/elements/attributes.js
+++ b/packages/svelte/src/internal/client/dom/elements/attributes.js
@@ -291,11 +291,8 @@ function set_attributes(
 	skip_warning = false
 ) {
 	if (hydrating && should_remove_defaults && element.nodeName === INPUT_TAG) {
-		var input = /** @type {HTMLInputElement} */ (element);
-		var attribute = input.type === 'checkbox' ? 'defaultChecked' : 'defaultValue';
-
-		if (!(attribute in next)) {
-			remove_input_defaults(input);
+		if (!('defaultValue' in next || 'defaultChecked' in next)) {
+			remove_input_defaults(/** @type {HTMLInputElement} */ (element));
 		}
 	}
 
diff --git a/packages/svelte/tests/runtime-runes/samples/form-default-checked-radio-spread/_config.js b/packages/svelte/tests/runtime-runes/samples/form-default-checked-radio-spread/_config.js
new file mode 100644
index 0000000000..3f3134ee7a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/form-default-checked-radio-spread/_config.js
@@ -0,0 +1,23 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['hydrate'],
+
+	async test({ assert, target }) {
+		const [a, b, reset] = target.querySelectorAll('input');
+
+		// let the deferred hydration cleanup run
+		await Promise.resolve();
+		flushSync();
+
+		b.checked = true;
+		reset.click();
+		await Promise.resolve();
+		flushSync();
+
+		assert.equal(a.defaultChecked, true);
+		assert.equal(a.checked, true);
+		assert.equal(b.checked, false);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/form-default-checked-radio-spread/main.svelte b/packages/svelte/tests/runtime-runes/samples/form-default-checked-radio-spread/main.svelte
new file mode 100644
index 0000000000..cb7ff0abd3
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/form-default-checked-radio-spread/main.svelte
@@ -0,0 +1,9 @@
+<script>
+	let spread = { defaultChecked: true, checked: true };
+</script>
+
+<form>
+	<input type="radio" name="option" value="a" {...spread} />
+	<input type="radio" name="option" value="b" />
+	<input type="reset" value="Reset" />
+</form>

From c894afd8c73e4f08a377909f29aa58177a256277 Mon Sep 17 00:00:00 2001
From: Jawad Ali <contact.jawaddd@gmail.com>
Date: Tue, 25 Aug 2026 13:37:34 +0500
Subject: [PATCH 04/29] fix: sync SvelteURL port when protocol setter clears it
 (#18705)

Per the WHATWG URL spec, assigning a new protocol can clear the URL's port when the current port equals the new scheme's default port. Therefore also `set` the port when the protocol is updated.
---
 .changeset/svelte-url-protocol-port.md     |  5 +++++
 packages/svelte/src/reactivity/url.js      |  2 ++
 packages/svelte/src/reactivity/url.test.ts | 22 ++++++++++++++++++++++
 3 files changed, 29 insertions(+)
 create mode 100644 .changeset/svelte-url-protocol-port.md

diff --git a/.changeset/svelte-url-protocol-port.md b/.changeset/svelte-url-protocol-port.md
new file mode 100644
index 0000000000..2c37fce4ab
--- /dev/null
+++ b/.changeset/svelte-url-protocol-port.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: sync `SvelteURL` port signal when the protocol setter clears the port
diff --git a/packages/svelte/src/reactivity/url.js b/packages/svelte/src/reactivity/url.js
index 549a20baa7..1e24e774ee 100644
--- a/packages/svelte/src/reactivity/url.js
+++ b/packages/svelte/src/reactivity/url.js
@@ -163,6 +163,8 @@ export class SvelteURL extends URL {
 	set protocol(value) {
 		super.protocol = value;
 		set(this.#protocol, super.protocol);
+		// changing the protocol can clear the port when it matches the new scheme's default
+		set(this.#port, super.port);
 	}
 
 	get search() {
diff --git a/packages/svelte/src/reactivity/url.test.ts b/packages/svelte/src/reactivity/url.test.ts
index d698116421..72518d730a 100644
--- a/packages/svelte/src/reactivity/url.test.ts
+++ b/packages/svelte/src/reactivity/url.test.ts
@@ -240,3 +240,25 @@ test('url.searchParams.forEach re-runs when the search string changes via the UR
 
 	cleanup();
 });
+
+test('url.port is updated when the protocol change clears the port', () => {
+	const url = new SvelteURL('http://example.com:443/');
+	const log: any = [];
+
+	const cleanup = effect_root(() => {
+		render_effect(() => {
+			log.push(url.port);
+		});
+	});
+
+	flushSync(() => {
+		// 443 is the default port for https, so it gets stripped
+		url.protocol = 'https:';
+	});
+
+	assert.equal(url.port, '');
+	assert.equal(url.href, 'https://example.com/');
+	assert.deepEqual(log, ['443', '']);
+
+	cleanup();
+});

From 135f1ec004352048454e732202c0bc8332816242 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Tue, 25 Aug 2026 11:24:45 +0200
Subject: [PATCH 05/29] fix: more robust rendering of Svelte custom element
 slots (#18710)

Instead of checking the given nodes at startup and only injecting those
into the inner Svelte component constructor, we are now detecting (via
the `$$host` property) whether or not the component is rendered as a
custom element, and in that case create all slots as real slots right
away.

Fixes #13638
Fixes #8997 (therefore closes #8999)
---
 .changeset/open-parents-stare.md              |  5 ++++
 .../src/internal/client/dom/blocks/slot.js    | 19 +++++++++++++
 .../$$slot-dynamic-content/_config.js         |  8 +++---
 .../html-slots/_config.js                     | 28 +++++++++++++++----
 .../no-shadow-dom/_config.js                  |  3 +-
 .../no-shadow-dom/main.svelte                 |  1 +
 6 files changed, 53 insertions(+), 11 deletions(-)
 create mode 100644 .changeset/open-parents-stare.md

diff --git a/.changeset/open-parents-stare.md b/.changeset/open-parents-stare.md
new file mode 100644
index 0000000000..cb94267ea0
--- /dev/null
+++ b/.changeset/open-parents-stare.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: more robust rendering of Svelte custom element slots
diff --git a/packages/svelte/src/internal/client/dom/blocks/slot.js b/packages/svelte/src/internal/client/dom/blocks/slot.js
index 10b2959582..491f04a5ea 100644
--- a/packages/svelte/src/internal/client/dom/blocks/slot.js
+++ b/packages/svelte/src/internal/client/dom/blocks/slot.js
@@ -1,4 +1,6 @@
 import { hydrate_next, hydrating } from '../hydration.js';
+import { create_element, create_text } from '../operations.js';
+import { append } from '../template.js';
 
 /**
  * @param {Comment} anchor
@@ -12,6 +14,23 @@ export function slot(anchor, $$props, name, slot_props, fallback_fn) {
 		hydrate_next();
 	}
 
+	// Custom element slots are native DOM slots.
+	// Use the stored reference because the shadow root may be closed.
+	if ($$props.$$host?.$$shadowRoot) {
+		const element = create_element('slot');
+		if (name !== 'default') element.name = name;
+
+		append(anchor, element);
+
+		if (fallback_fn !== null) {
+			const fallback_anchor = create_text();
+			element.append(fallback_anchor);
+			fallback_fn(fallback_anchor);
+		}
+
+		return;
+	}
+
 	var slot_fn = $$props.$$slots?.[name];
 	// Interop: Can use snippets to fill slots
 	var is_interop = false;
diff --git a/packages/svelte/tests/runtime-browser/custom-elements-samples/$$slot-dynamic-content/_config.js b/packages/svelte/tests/runtime-browser/custom-elements-samples/$$slot-dynamic-content/_config.js
index 8ade347a79..3fd5a09888 100644
--- a/packages/svelte/tests/runtime-browser/custom-elements-samples/$$slot-dynamic-content/_config.js
+++ b/packages/svelte/tests/runtime-browser/custom-elements-samples/$$slot-dynamic-content/_config.js
@@ -14,8 +14,8 @@ export default test({
 		assert.htmlEqual(
 			ce.shadowRoot.innerHTML,
 			`
-		<slot></slot>
-		<p>named fallback</p>
+		<slot>fallback</slot>
+		<slot name="named"><p>named fallback</p></slot>
 	`
 		);
 
@@ -23,8 +23,8 @@ export default test({
 		assert.htmlEqual(
 			ce.shadowRoot.innerHTML,
 			`
-		<slot></slot>
-		<p>named fallback</p>
+		<slot>fallback</slot>
+		<slot name="named"><p>named fallback</p></slot>
 	`
 		);
 	}
diff --git a/packages/svelte/tests/runtime-browser/custom-elements-samples/html-slots/_config.js b/packages/svelte/tests/runtime-browser/custom-elements-samples/html-slots/_config.js
index 287e2987b8..e3e8ce072b 100644
--- a/packages/svelte/tests/runtime-browser/custom-elements-samples/html-slots/_config.js
+++ b/packages/svelte/tests/runtime-browser/custom-elements-samples/html-slots/_config.js
@@ -3,10 +3,7 @@ const tick = () => Promise.resolve();
 
 export default test({
 	async test({ assert, target }) {
-		target.innerHTML = `
-		<custom-element>
-			<strong>slotted</strong>
-		</custom-element>`;
+		target.innerHTML = '<custom-element></custom-element>';
 		await tick();
 		await tick();
 
@@ -16,7 +13,26 @@ export default test({
 		const div = el.shadowRoot.children[0];
 		const [slot0, slot1] = div.children;
 
-		assert.equal(slot0.assignedNodes()[1], target.querySelector('strong'));
-		assert.equal(slot1.innerHTML, 'foo fallback content');
+		assert.equal(slot0.localName, 'slot');
+		assert.equal(slot0.assignedNodes().length, 0);
+		assert.equal(slot0.innerHTML, '<p>default fallback content</p>');
+		assert.equal(slot1.localName, 'slot');
+		assert.equal(slot1.name, 'foo');
+		assert.equal(slot1.assignedNodes().length, 0);
+		assert.equal(slot1.innerHTML, '<p>foo fallback content</p>');
+
+		const default_content = document.createElement('strong');
+		default_content.textContent = 'default content';
+		el.append(default_content);
+
+		const named_content = document.createElement('strong');
+		named_content.slot = 'foo';
+		named_content.textContent = 'named content';
+		el.append(named_content);
+
+		assert.equal(slot0.assignedNodes().length, 1);
+		assert.equal(slot0.assignedNodes()[0], default_content);
+		assert.equal(slot1.assignedNodes().length, 1);
+		assert.equal(slot1.assignedNodes()[0], named_content);
 	}
 });
diff --git a/packages/svelte/tests/runtime-browser/custom-elements-samples/no-shadow-dom/_config.js b/packages/svelte/tests/runtime-browser/custom-elements-samples/no-shadow-dom/_config.js
index cd8550120a..e83491418a 100644
--- a/packages/svelte/tests/runtime-browser/custom-elements-samples/no-shadow-dom/_config.js
+++ b/packages/svelte/tests/runtime-browser/custom-elements-samples/no-shadow-dom/_config.js
@@ -3,7 +3,7 @@ const tick = () => Promise.resolve();
 
 export default test({
 	async test({ assert, target }) {
-		target.innerHTML = '<custom-element name="world"></custom-element>';
+		target.innerHTML = '<custom-element name="world"><span>slotted</span></custom-element>';
 		await tick();
 		await tick();
 
@@ -15,5 +15,6 @@ export default test({
 		assert.equal(el.shadowRoot, null);
 		assert.equal(h1.innerHTML, 'Hello world!');
 		assert.equal(getComputedStyle(h1).color, 'rgb(255, 0, 0)');
+		assert.equal(el.querySelector('slot').innerHTML, '');
 	}
 });
diff --git a/packages/svelte/tests/runtime-browser/custom-elements-samples/no-shadow-dom/main.svelte b/packages/svelte/tests/runtime-browser/custom-elements-samples/no-shadow-dom/main.svelte
index 36fea3c43e..1c14fb98d8 100644
--- a/packages/svelte/tests/runtime-browser/custom-elements-samples/no-shadow-dom/main.svelte
+++ b/packages/svelte/tests/runtime-browser/custom-elements-samples/no-shadow-dom/main.svelte
@@ -5,6 +5,7 @@
 </script>
 
 <h1>Hello {name}!</h1>
+<slot>fallback</slot>
 
 <style>
 	h1 {

From 359413f5122bf866175e516141515c5387ad7743 Mon Sep 17 00:00:00 2001
From: Mathias Picker <48158184+MathiasWP@users.noreply.github.com>
Date: Tue, 25 Aug 2026 11:47:17 +0200
Subject: [PATCH 06/29] perf: treat `<img loading>` as a static element again
 (#18711)

Emits less code and skips two live DOM traversals per instance.

`is_static_element` treats `<img>` with a `loading` attribute as
non-static. That was added in #14237 so `RegularElement` could emit
`$.handle_lazy_img(node_id)`, which needed a reference to the element.
#15272 deleted `handle_lazy_img` (replaced by `importNode`) and removed
the call site, but left this check behind.


---------

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
---
 .changeset/tidy-owls-repeat.md                               | 5 +++++
 .../phases/3-transform/client/visitors/shared/fragment.js    | 5 -----
 .../skip-static-subtree/_expected/client/index.svelte.js     | 5 +----
 3 files changed, 6 insertions(+), 9 deletions(-)
 create mode 100644 .changeset/tidy-owls-repeat.md

diff --git a/.changeset/tidy-owls-repeat.md b/.changeset/tidy-owls-repeat.md
new file mode 100644
index 0000000000..2ef02e2051
--- /dev/null
+++ b/.changeset/tidy-owls-repeat.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+perf: treat `<img loading>` as a static element again
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/fragment.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/fragment.js
index 38346e64b2..72104481ec 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/fragment.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/fragment.js
@@ -171,11 +171,6 @@ export function is_static_element(node) {
 			return false;
 		}
 
-		// We need to apply src and loading after appending the img to the DOM for lazy loading to work
-		if (node.name === 'img' && attribute.name === 'loading') {
-			return false;
-		}
-
 		if (attribute.value !== true && !is_text_attribute(attribute)) {
 			return false;
 		}
diff --git a/packages/svelte/tests/snapshot/samples/skip-static-subtree/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/skip-static-subtree/_expected/client/index.svelte.js
index 78147659ff..85f7601bd7 100644
--- a/packages/svelte/tests/snapshot/samples/skip-static-subtree/_expected/client/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/skip-static-subtree/_expected/client/index.svelte.js
@@ -40,10 +40,7 @@ export default function Skip_static_subtree($$anchor, $$props) {
 
 	option.value = option.__value = 'a';
 	$.reset(select);
-
-	var img = $.sibling(select, 2);
-
-	$.next(2);
+	$.next(4);
 	$.template_effect(() => $.set_text(text, $$props.title));
 	$.append($$anchor, fragment);
 }
\ No newline at end of file

From 8299cbf11b266a561c822a7212526f3fbbadc53e Mon Sep 17 00:00:00 2001
From: Mathias Picker <48158184+MathiasWP@users.noreply.github.com>
Date: Tue, 25 Aug 2026 13:25:40 +0200
Subject: [PATCH 07/29] perf: use `$.comment()` for single comment templates
 (#18714)

Move the "single comment, we can make this faster" optimization into `transform_template` so all usage locations can benefit (e.g. select/option elements)

---------

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
---
 .changeset/quiet-swans-invent.md              |  5 +++++
 .../client/transform-template/index.js        |  6 ++++++
 .../3-transform/client/visitors/Fragment.js   |  9 ++-------
 .../_expected/client/index.svelte.js          | 19 +++++++++----------
 4 files changed, 22 insertions(+), 17 deletions(-)
 create mode 100644 .changeset/quiet-swans-invent.md

diff --git a/.changeset/quiet-swans-invent.md b/.changeset/quiet-swans-invent.md
new file mode 100644
index 0000000000..3b35a933d5
--- /dev/null
+++ b/.changeset/quiet-swans-invent.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+perf: use `$.comment()` for single-comment templates
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/transform-template/index.js b/packages/svelte/src/compiler/phases/3-transform/client/transform-template/index.js
index 5fdc88844b..4c6d5f4ece 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/transform-template/index.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/transform-template/index.js
@@ -39,6 +39,12 @@ export function transform_template(state, name, flags = 0) {
 	const namespace = state.metadata.namespace;
 	const tree = state.options.fragments === 'tree';
 
+	const { nodes } = state.template;
+	const is_lone_anchor = nodes.length === 1 && nodes[0].type === 'comment';
+
+	// special case - `$.comment` creates the anchor more cheaply than cloning a template
+	if (is_lone_anchor) return b.id('$.comment');
+
 	const expression = tree ? state.template.as_tree() : state.template.as_html();
 
 	const key =
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 893b1db568..1272290c4a 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
@@ -141,14 +141,9 @@ export function Fragment(node, context) {
 				flags |= TEMPLATE_USE_IMPORT_NODE;
 			}
 
-			if (state.template.nodes.length === 1 && state.template.nodes[0].type === 'comment') {
-				// special case — we can use `$.comment` instead of creating a unique template
-				state.init.unshift(b.var(id, b.call('$.comment')));
-			} else {
-				const template_name = transform_template(state, 'root', flags);
+			const template_name = transform_template(state, 'root', flags);
 
-				state.init.unshift(b.var(id, b.call(template_name)));
-			}
+			state.init.unshift(b.var(id, b.call(template_name)));
 
 			close = b.stmt(b.call('$.append', b.id('$$anchor'), id));
 		}
diff --git a/packages/svelte/tests/snapshot/samples/select-with-rich-content/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/select-with-rich-content/_expected/client/index.svelte.js
index c8354fe67e..fbeecbafb3 100644
--- a/packages/svelte/tests/snapshot/samples/select-with-rich-content/_expected/client/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/select-with-rich-content/_expected/client/index.svelte.js
@@ -35,7 +35,6 @@ var option_content = $.from_html(`<span>Rich</span>`, 1);
 var root_4 = $.from_html(`<option> </option>`);
 var root_5 = $.from_html(`<option>Visible</option>`);
 var root_6 = $.from_html(`<option>Keyed</option>`);
-var select_content = $.from_html(`<!>`, 1);
 var option_content_1 = $.from_html(`<strong>Bold</strong>`, 1);
 var option_content_2 = $.from_html(`<em>Italic</em> text`, 1);
 var option_content_3 = $.from_html(`<span> </span>`, 1);
@@ -116,7 +115,7 @@ export default function Select_with_rich_content($$anchor) {
 
 	$.customizable_select(select_4, () => {
 		var anchor_1 = $.child(select_4);
-		var fragment_2 = select_content();
+		var fragment_2 = $.comment();
 		var node_2 = $.first_child(fragment_2);
 
 		opt(node_2);
@@ -291,7 +290,7 @@ export default function Select_with_rich_content($$anchor) {
 
 	$.customizable_select(select_13, () => {
 		var anchor_6 = $.child(select_13);
-		var fragment_8 = select_content();
+		var fragment_8 = $.comment();
 		var node_7 = $.first_child(fragment_8);
 
 		Option(node_7, {});
@@ -302,7 +301,7 @@ export default function Select_with_rich_content($$anchor) {
 
 	$.customizable_select(select_14, () => {
 		var anchor_7 = $.child(select_14);
-		var fragment_9 = select_content();
+		var fragment_9 = $.comment();
 		var node_8 = $.first_child(fragment_9);
 
 		option_snippet(node_8);
@@ -313,7 +312,7 @@ export default function Select_with_rich_content($$anchor) {
 
 	$.customizable_select(select_15, () => {
 		var anchor_8 = $.child(select_15);
-		var fragment_10 = select_content();
+		var fragment_10 = $.comment();
 		var node_9 = $.first_child(fragment_10);
 
 		$.html(node_9, () => html);
@@ -325,7 +324,7 @@ export default function Select_with_rich_content($$anchor) {
 
 	$.customizable_select(optgroup_2, () => {
 		var anchor_9 = $.child(optgroup_2);
-		var fragment_11 = select_content();
+		var fragment_11 = $.comment();
 		var node_10 = $.first_child(fragment_11);
 
 		Option(node_10, {});
@@ -339,7 +338,7 @@ export default function Select_with_rich_content($$anchor) {
 
 	$.customizable_select(optgroup_3, () => {
 		var anchor_10 = $.child(optgroup_3);
-		var fragment_12 = select_content();
+		var fragment_12 = $.comment();
 		var node_11 = $.first_child(fragment_12);
 
 		option_snippet2(node_11);
@@ -353,7 +352,7 @@ export default function Select_with_rich_content($$anchor) {
 
 	$.customizable_select(option_16, () => {
 		var anchor_11 = $.child(option_16);
-		var fragment_13 = select_content();
+		var fragment_13 = $.comment();
 		var node_12 = $.first_child(fragment_13);
 
 		$.html(node_12, () => '<strong>Bold HTML</strong>');
@@ -366,7 +365,7 @@ export default function Select_with_rich_content($$anchor) {
 
 	$.customizable_select(select_19, () => {
 		var anchor_12 = $.child(select_19);
-		var fragment_14 = select_content();
+		var fragment_14 = $.comment();
 		var node_13 = $.first_child(fragment_14);
 
 		$.each(node_13, 1, () => items, $.index, ($$anchor, item) => {
@@ -380,7 +379,7 @@ export default function Select_with_rich_content($$anchor) {
 
 	$.customizable_select(select_20, () => {
 		var anchor_13 = $.child(select_20);
-		var fragment_16 = select_content();
+		var fragment_16 = $.comment();
 		var node_14 = $.first_child(fragment_16);
 
 		{

From 6b99f9fb52ae8db0f1d7f28b4cbdbcc2f4187a34 Mon Sep 17 00:00:00 2001
From: Mathias Picker <48158184+MathiasWP@users.noreply.github.com>
Date: Tue, 25 Aug 2026 13:26:32 +0200
Subject: [PATCH 08/29] perf: reuse the cached value in the
 `<option>`/`<select>` value guard (#18713)

One fewer evaluation of the value expression per update.

---------

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
---
 .changeset/eighty-moons-happen.md             |  5 ++
 .../client/visitors/RegularElement.js         | 53 +++++++++++--------
 .../_expected/client/index.svelte.js          |  8 +--
 3 files changed, 40 insertions(+), 26 deletions(-)
 create mode 100644 .changeset/eighty-moons-happen.md

diff --git a/.changeset/eighty-moons-happen.md b/.changeset/eighty-moons-happen.md
new file mode 100644
index 0000000000..94fb3d313d
--- /dev/null
+++ b/.changeset/eighty-moons-happen.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+perf: reuse the cached value in the `<option>`/`<select>` value guard
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 de09d3ef60..ab15d55670 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
@@ -701,28 +701,32 @@ function build_element_special_value_attribute(
 	);
 
 	const evaluated = context.state.scope.evaluate(value);
-	const assignment = b.assignment('=', b.member(node_id, '__value'), value);
 
-	const set_value_assignment = b.assignment(
-		'=',
-		b.member(node_id, 'value'),
-		evaluated.is_defined ? assignment : b.logical('??', assignment, b.literal(''))
-	);
+	/** @param {Expression} value */
+	const build_update = (value) => {
+		const assignment = b.assignment('=', b.member(node_id, '__value'), value);
 
-	const update = b.stmt(
-		is_select_with_value
-			? b.sequence([
-					set_value_assignment,
-					// This ensures a one-way street to the DOM in case it's <select {value}>
-					// and not <select bind:value>. We need it in addition to $.init_select
-					// because the select value is not reflected as an attribute, so the
-					// mutation observer wouldn't notice.
-					b.call('$.select_option', node_id, value)
-				])
-			: synthetic
-				? assignment
-				: set_value_assignment
-	);
+		const set_value_assignment = b.assignment(
+			'=',
+			b.member(node_id, 'value'),
+			evaluated.is_defined ? assignment : b.logical('??', assignment, b.literal(''))
+		);
+
+		return b.stmt(
+			is_select_with_value
+				? b.sequence([
+						set_value_assignment,
+						// This ensures a one-way street to the DOM in case it's <select {value}>
+						// and not <select bind:value>. We need it in addition to $.init_select
+						// because the select value is not reflected as an attribute, so the
+						// mutation observer wouldn't notice.
+						b.call('$.select_option', node_id, value)
+					])
+				: synthetic
+					? assignment
+					: set_value_assignment
+		);
+	};
 
 	if (has_state) {
 		const id = b.id(state.scope.generate(`${node_id.name}_value`));
@@ -733,9 +737,14 @@ function build_element_special_value_attribute(
 		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])));
+
+		// the guard already evaluated `value` into `id`, so read that back rather than
+		// evaluating the same expression (and its signal reads) a second time
+		state.update.push(
+			b.if(b.binary('!==', id, b.assignment('=', id, value)), b.block([build_update(id)]))
+		);
 	} else {
-		state.init.push(update);
+		state.init.push(build_update(value));
 	}
 
 	if (is_select_with_value) {
diff --git a/packages/svelte/tests/snapshot/samples/select-with-rich-content/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/select-with-rich-content/_expected/client/index.svelte.js
index fbeecbafb3..f24736e931 100644
--- a/packages/svelte/tests/snapshot/samples/select-with-rich-content/_expected/client/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/select-with-rich-content/_expected/client/index.svelte.js
@@ -74,7 +74,7 @@ export default function Select_with_rich_content($$anchor) {
 			$.set_text(text, $.get(item));
 
 			if (option_5_value !== (option_5_value = $.get(item))) {
-				option_5.__value = $.get(item);
+				option_5.__value = option_5_value;
 			}
 		});
 
@@ -137,7 +137,7 @@ export default function Select_with_rich_content($$anchor) {
 			$.set_text(text_1, $.get(x));
 
 			if (option_8_value !== (option_8_value = $.get(x))) {
-				option_8.__value = $.get(x);
+				option_8.__value = option_8_value;
 			}
 		});
 
@@ -175,7 +175,7 @@ export default function Select_with_rich_content($$anchor) {
 			$.set_text(text_2, $.get(item));
 
 			if (option_10_value !== (option_10_value = $.get(item))) {
-				option_10.__value = $.get(item);
+				option_10.__value = option_10_value;
 			}
 		});
 
@@ -240,7 +240,7 @@ export default function Select_with_rich_content($$anchor) {
 					$.set_text(text_4, $.get(item));
 
 					if (option_13_value !== (option_13_value = $.get(item))) {
-						option_13.__value = $.get(item);
+						option_13.__value = option_13_value;
 					}
 				});
 

From 34489c10df97de6af941a1c21b0cadbc85bfd7cf Mon Sep 17 00:00:00 2001
From: Mathias Picker <48158184+MathiasWP@users.noreply.github.com>
Date: Tue, 25 Aug 2026 14:13:21 +0200
Subject: [PATCH 09/29] perf: emit `$.only_child` for elements with a single
 child (#18717)

`<p>{text}</p>` and friends compile to `var x = $.child(p, true);
$.reset(p);`. Across the 4,020 components in `packages/svelte/tests`,
that exact pair occurs 1,885 times, more than any other adjacent
statement pair.

`$.only_child` does both, reducing the number of statements in the compiled output
---
 .changeset/olive-pugs-shake.md                |  5 +++
 .../client/visitors/RegularElement.js         | 40 ++++++++++++++++++-
 .../src/internal/client/dom/operations.js     | 22 +++++++++-
 packages/svelte/src/internal/client/index.js  |  1 +
 .../_expected/client/index.svelte.js          |  3 +-
 .../_expected/client/index.svelte.js          |  3 +-
 .../_expected/client/index.svelte.js          |  5 +--
 .../_expected/client/index.svelte.js          |  5 +--
 .../_expected/client/index.svelte.js          | 23 +++--------
 .../_expected/client/index.svelte.js          |  5 +--
 .../_expected/client/index.svelte.js          |  3 +-
 11 files changed, 76 insertions(+), 39 deletions(-)
 create mode 100644 .changeset/olive-pugs-shake.md

diff --git a/.changeset/olive-pugs-shake.md b/.changeset/olive-pugs-shake.md
new file mode 100644
index 0000000000..abd0db2152
--- /dev/null
+++ b/.changeset/olive-pugs-shake.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+perf: emit `$.only_child` for elements with a single child
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 ab15d55670..4c1538c331 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
@@ -1,4 +1,4 @@
-/** @import { ArrayExpression, Expression, ExpressionStatement, Identifier, MemberExpression, ObjectExpression } from 'estree' */
+/** @import { ArrayExpression, Expression, ExpressionStatement, Identifier, MemberExpression, ObjectExpression, Statement } from 'estree' */
 /** @import { AST } from '#compiler' */
 /** @import { ComponentClientTransformState, ComponentContext } from '../types' */
 /** @import { Scope } from '../../../scope' */
@@ -432,7 +432,7 @@ export function RegularElement(node, context) {
 			state: child_state
 		});
 
-		if (needs_reset) {
+		if (needs_reset && !fold_reset_into_child(child_state.init, context.state.node)) {
 			child_state.init.push(b.stmt(b.call('$.reset', context.state.node)));
 		}
 	}
@@ -751,3 +751,39 @@ function build_element_special_value_attribute(
 		state.init.push(b.stmt(b.call('$.init_select', node_id)));
 	}
 }
+
+/**
+ * `<p>{text}</p>` and friends produce `var x = $.child(p, true); $.reset(p);`. That pair is
+ * by far the most common shape in compiled output, and `$.only_child` does both, so fold the
+ * two together when the `$.child(...)` is the last thing we emitted for this element.
+ * @param {Statement[]} init
+ * @param {Expression} node_id
+ * @returns {boolean} whether the reset was folded in
+ */
+function fold_reset_into_child(init, node_id) {
+	const last = init.at(-1);
+
+	if (
+		node_id?.type !== 'Identifier' ||
+		last?.type !== 'VariableDeclaration' ||
+		last.declarations.length !== 1
+	) {
+		return false;
+	}
+
+	const call = last.declarations[0].init;
+
+	if (
+		call?.type !== 'CallExpression' ||
+		call.callee.type !== 'Identifier' ||
+		call.callee.name !== '$.child' ||
+		call.arguments[0]?.type !== 'Identifier' ||
+		call.arguments[0].name !== node_id.name
+	) {
+		return false;
+	}
+
+	call.callee = b.id('$.only_child');
+
+	return true;
+}
diff --git a/packages/svelte/src/internal/client/dom/operations.js b/packages/svelte/src/internal/client/dom/operations.js
index bc12a0b07e..21b5ee4ecb 100644
--- a/packages/svelte/src/internal/client/dom/operations.js
+++ b/packages/svelte/src/internal/client/dom/operations.js
@@ -1,5 +1,5 @@
 /** @import { Effect, TemplateNode } from '#client' */
-import { hydrate_node, hydrating, set_hydrate_node } from './hydration.js';
+import { hydrate_node, hydrating, reset, 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';
@@ -165,6 +165,26 @@ export function first_child(node, is_text = false) {
 	return hydrate_node;
 }
 
+/**
+ * `child`, for the very common case of an element with exactly one child. Resetting the
+ * hydration cursor is part of the same step, so the compiler doesn't have to emit a
+ * separate `reset` call for every `<p>{text}</p>` in an app.
+ * Don't mark this as side-effect-free, hydration needs to walk all nodes
+ * @param {TemplateNode} node
+ * @param {boolean} [is_text]
+ * @returns {TemplateNode | null}
+ */
+export function only_child(node, is_text = false) {
+	if (!hydrating) {
+		return get_first_child(node);
+	}
+
+	var first = child(node, is_text);
+	reset(node);
+
+	return first;
+}
+
 /**
  * Don't mark this as side-effect-free, hydration needs to walk all nodes
  * @param {TemplateNode} node
diff --git a/packages/svelte/src/internal/client/index.js b/packages/svelte/src/internal/client/index.js
index 6cdf81c155..8c922b0b84 100644
--- a/packages/svelte/src/internal/client/index.js
+++ b/packages/svelte/src/internal/client/index.js
@@ -164,6 +164,7 @@ export { proxy } from './proxy.js';
 export { create_custom_element } from './dom/elements/custom-element.js';
 export {
 	child,
+	only_child,
 	first_child,
 	sibling,
 	$window as window,
diff --git a/packages/svelte/tests/snapshot/samples/async-const/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/async-const/_expected/client/index.svelte.js
index b3e9e87aca..41ab26212c 100644
--- a/packages/svelte/tests/snapshot/samples/async-const/_expected/client/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/async-const/_expected/client/index.svelte.js
@@ -31,9 +31,8 @@ export default function Async_const($$anchor) {
 			]);
 
 			var p = root();
-			var text = $.child(p, true);
+			var text = $.only_child(p, true);
 
-			$.reset(p);
 			$.template_effect(() => $.set_text(text, $.get(b)), void 0, void 0, [promises[1]]);
 			$.append($$anchor, p);
 		};
diff --git a/packages/svelte/tests/snapshot/samples/async-top-level-inspect-server/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/async-top-level-inspect-server/_expected/client/index.svelte.js
index 668c936e4e..c5b700ffec 100644
--- a/packages/svelte/tests/snapshot/samples/async-top-level-inspect-server/_expected/client/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/async-top-level-inspect-server/_expected/client/index.svelte.js
@@ -8,9 +8,8 @@ export default function Async_top_level_inspect_server($$anchor) {
 	var data;
 	var $$promises = $.run([async () => data = await Promise.resolve(42), () => void 0]);
 	var p = root();
-	var text = $.child(p, true);
+	var text = $.only_child(p, true);
 
-	$.reset(p);
 	$.template_effect(() => $.set_text(text, data), void 0, void 0, [$$promises[1]]);
 	$.append($$anchor, p);
 }
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/await-block-scope/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/await-block-scope/_expected/client/index.svelte.js
index e1b87d6280..7097ec24d9 100644
--- a/packages/svelte/tests/snapshot/samples/await-block-scope/_expected/client/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/await-block-scope/_expected/client/index.svelte.js
@@ -13,10 +13,7 @@ export default function Await_block_scope($$anchor) {
 
 	var fragment = root();
 	var button = $.first_child(fragment);
-	var text = $.child(button);
-
-	$.reset(button);
-
+	var text = $.only_child(button);
 	var node = $.sibling(button, 2);
 
 	$.await(node, () => $.get(promise), null, ($$anchor, counter) => {});
diff --git a/packages/svelte/tests/snapshot/samples/nullish-coallescence-omittance/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/nullish-coallescence-omittance/_expected/client/index.svelte.js
index 837a7cd65a..8fe9663290 100644
--- a/packages/svelte/tests/snapshot/samples/nullish-coallescence-omittance/_expected/client/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/nullish-coallescence-omittance/_expected/client/index.svelte.js
@@ -16,10 +16,7 @@ export default function Nullish_coallescence_omittance($$anchor, $$props) {
 	b.textContent = '123';
 
 	var button = $.sibling(b, 2);
-	var text = $.child(button);
-
-	$.reset(button);
-
+	var text = $.only_child(button);
 	var h1_1 = $.sibling(button, 2);
 
 	h1_1.textContent = 'Hello, world';
diff --git a/packages/svelte/tests/snapshot/samples/select-with-rich-content/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/select-with-rich-content/_expected/client/index.svelte.js
index f24736e931..36b774340b 100644
--- a/packages/svelte/tests/snapshot/samples/select-with-rich-content/_expected/client/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/select-with-rich-content/_expected/client/index.svelte.js
@@ -64,10 +64,7 @@ export default function Select_with_rich_content($$anchor) {
 
 	$.each(select_1, 5, () => items, $.index, ($$anchor, item) => {
 		var option_5 = root_4();
-		var text = $.child(option_5, true);
-
-		$.reset(option_5);
-
+		var text = $.only_child(option_5, true);
 		var option_5_value = {};
 
 		$.template_effect(() => {
@@ -127,10 +124,7 @@ export default function Select_with_rich_content($$anchor) {
 	$.each(select_5, 5, () => items, $.index, ($$anchor, item) => {
 		const x = $.derived_safe_equal(() => $.get(item) * 2);
 		var option_8 = root_4();
-		var text_1 = $.child(option_8, true);
-
-		$.reset(option_8);
-
+		var text_1 = $.only_child(option_8, true);
 		var option_8_value = {};
 
 		$.template_effect(() => {
@@ -165,10 +159,7 @@ export default function Select_with_rich_content($$anchor) {
 
 	$.each(optgroup_1, 5, () => items, $.index, ($$anchor, item) => {
 		var option_10 = root_4();
-		var text_2 = $.child(option_10, true);
-
-		$.reset(option_10);
-
+		var text_2 = $.only_child(option_10, true);
 		var option_10_value = {};
 
 		$.template_effect(() => {
@@ -208,9 +199,8 @@ export default function Select_with_rich_content($$anchor) {
 			var anchor_4 = $.child(option_12);
 			var fragment_5 = option_content_3();
 			var span = $.first_child(fragment_5);
-			var text_3 = $.child(span, true);
+			var text_3 = $.only_child(span, true);
 
-			$.reset(span);
 			$.template_effect(() => $.set_text(text_3, $.get(item)));
 			$.append(anchor_4, fragment_5);
 		});
@@ -230,10 +220,7 @@ export default function Select_with_rich_content($$anchor) {
 
 			$.each(node_4, 1, () => items, $.index, ($$anchor, item) => {
 				var option_13 = root_4();
-				var text_4 = $.child(option_13, true);
-
-				$.reset(option_13);
-
+				var text_4 = $.only_child(option_13, true);
 				var option_13_value = {};
 
 				$.template_effect(() => {
diff --git a/packages/svelte/tests/snapshot/samples/skip-static-subtree/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/skip-static-subtree/_expected/client/index.svelte.js
index 85f7601bd7..30976b40e6 100644
--- a/packages/svelte/tests/snapshot/samples/skip-static-subtree/_expected/client/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/skip-static-subtree/_expected/client/index.svelte.js
@@ -7,10 +7,7 @@ export default function Skip_static_subtree($$anchor, $$props) {
 	var fragment = root();
 	var main = $.sibling($.first_child(fragment), 2);
 	var h1 = $.child(main);
-	var text = $.child(h1, true);
-
-	$.reset(h1);
-
+	var text = $.only_child(h1, true);
 	var node = $.sibling(h1, 10);
 
 	$.html(node, () => $$props.content);
diff --git a/packages/svelte/tests/snapshot/samples/text-nodes-deriveds/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/text-nodes-deriveds/_expected/client/index.svelte.js
index 4148a546c8..a6a38f475c 100644
--- a/packages/svelte/tests/snapshot/samples/text-nodes-deriveds/_expected/client/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/text-nodes-deriveds/_expected/client/index.svelte.js
@@ -16,9 +16,8 @@ export default function Text_nodes_deriveds($$anchor) {
 	}
 
 	var p = root();
-	var text = $.child(p);
+	var text = $.only_child(p);
 
-	$.reset(p);
 	$.template_effect(($0, $1) => $.set_text(text, `${$0 ?? ''}${$1 ?? ''}`), [() => text1(), () => text2()]);
 	$.append($$anchor, p);
 }
\ No newline at end of file

From b433f3cd878814d6d141be359e5dafa9959b5f9e Mon Sep 17 00:00:00 2001
From: Bao Nguyen <39545125+giaBaoJS@users.noreply.github.com>
Date: Tue, 25 Aug 2026 19:22:56 +0700
Subject: [PATCH 10/29] fix: preserve line feed character references in
 attribute values (#18691)

Fixes #15555

Pass on whether we're in an attribute to not replace the charcode with the whitespace charcode in that case
---
 .changeset/tricky-donkeys-clap.md             |  5 ++
 .../src/compiler/phases/1-parse/utils/html.js | 15 ++++--
 .../convert-entities-line-feed/input.svelte   |  1 +
 .../convert-entities-line-feed/output.json    | 53 +++++++++++++++++++
 .../html-entity-line-feed/Component.svelte    |  5 ++
 .../samples/html-entity-line-feed/_config.js  | 15 ++++++
 .../samples/html-entity-line-feed/main.svelte |  9 ++++
 7 files changed, 98 insertions(+), 5 deletions(-)
 create mode 100644 .changeset/tricky-donkeys-clap.md
 create mode 100644 packages/svelte/tests/parser-legacy/samples/convert-entities-line-feed/input.svelte
 create mode 100644 packages/svelte/tests/parser-legacy/samples/convert-entities-line-feed/output.json
 create mode 100644 packages/svelte/tests/runtime-runes/samples/html-entity-line-feed/Component.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/html-entity-line-feed/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/html-entity-line-feed/main.svelte

diff --git a/.changeset/tricky-donkeys-clap.md b/.changeset/tricky-donkeys-clap.md
new file mode 100644
index 0000000000..b363b4ff57
--- /dev/null
+++ b/.changeset/tricky-donkeys-clap.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: preserve line feed character references in attribute values
diff --git a/packages/svelte/src/compiler/phases/1-parse/utils/html.js b/packages/svelte/src/compiler/phases/1-parse/utils/html.js
index 1d660298c7..ccb2005054 100644
--- a/packages/svelte/src/compiler/phases/1-parse/utils/html.js
+++ b/packages/svelte/src/compiler/phases/1-parse/utils/html.js
@@ -60,7 +60,7 @@ export function decode_character_references(html, is_attribute_value) {
 				return match;
 			}
 
-			return String.fromCodePoint(validate_code(code));
+			return String.fromCodePoint(validate_code(code, is_attribute_value));
 		}
 	);
 }
@@ -75,10 +75,15 @@ const NUL = 0;
 // Also see: https://en.wikipedia.org/wiki/Plane_(Unicode)
 // Also see: https://html.spec.whatwg.org/multipage/parsing.html#preprocessing-the-input-stream
 
-/** @param {number} code */
-function validate_code(code) {
-	// line feed becomes generic whitespace
-	if (code === 10) {
+/**
+ * @param {number} code
+ * @param {boolean} is_attribute_value
+ */
+function validate_code(code, is_attribute_value) {
+	// line feed becomes generic whitespace, since it is collapsed along with the
+	// surrounding whitespace anyway. In an attribute value it is significant, so it
+	// is left alone there
+	if (code === 10 && !is_attribute_value) {
 		return 32;
 	}
 
diff --git a/packages/svelte/tests/parser-legacy/samples/convert-entities-line-feed/input.svelte b/packages/svelte/tests/parser-legacy/samples/convert-entities-line-feed/input.svelte
new file mode 100644
index 0000000000..3ce2c605d6
--- /dev/null
+++ b/packages/svelte/tests/parser-legacy/samples/convert-entities-line-feed/input.svelte
@@ -0,0 +1 @@
+<p title="A&#x0A;B">A&#x0A;B</p>
diff --git a/packages/svelte/tests/parser-legacy/samples/convert-entities-line-feed/output.json b/packages/svelte/tests/parser-legacy/samples/convert-entities-line-feed/output.json
new file mode 100644
index 0000000000..5d1127ccdc
--- /dev/null
+++ b/packages/svelte/tests/parser-legacy/samples/convert-entities-line-feed/output.json
@@ -0,0 +1,53 @@
+{
+	"html": {
+		"type": "Fragment",
+		"start": 0,
+		"end": 32,
+		"children": [
+			{
+				"type": "Element",
+				"start": 0,
+				"end": 32,
+				"name": "p",
+				"attributes": [
+					{
+						"type": "Attribute",
+						"start": 3,
+						"end": 19,
+						"name": "title",
+						"name_loc": {
+							"start": {
+								"line": 1,
+								"column": 3,
+								"character": 3
+							},
+							"end": {
+								"line": 1,
+								"column": 8,
+								"character": 8
+							}
+						},
+						"value": [
+							{
+								"start": 10,
+								"end": 18,
+								"type": "Text",
+								"raw": "A&#x0A;B",
+								"data": "A\nB"
+							}
+						]
+					}
+				],
+				"children": [
+					{
+						"type": "Text",
+						"start": 20,
+						"end": 28,
+						"raw": "A&#x0A;B",
+						"data": "A B"
+					}
+				]
+			}
+		]
+	}
+}
diff --git a/packages/svelte/tests/runtime-runes/samples/html-entity-line-feed/Component.svelte b/packages/svelte/tests/runtime-runes/samples/html-entity-line-feed/Component.svelte
new file mode 100644
index 0000000000..85b608c739
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/html-entity-line-feed/Component.svelte
@@ -0,0 +1,5 @@
+<script>
+	const { text } = $props();
+</script>
+
+<span id="prop">{text}</span>
diff --git a/packages/svelte/tests/runtime-runes/samples/html-entity-line-feed/_config.js b/packages/svelte/tests/runtime-runes/samples/html-entity-line-feed/_config.js
new file mode 100644
index 0000000000..f6befd7703
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/html-entity-line-feed/_config.js
@@ -0,0 +1,15 @@
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		// a line feed entity in an attribute value stays a line feed...
+		assert.equal(target.querySelector('#attr')?.getAttribute('title'), 'A\nB');
+		assert.equal(target.querySelector('#attr-decimal')?.getAttribute('title'), 'A\nB');
+
+		// ...including when the attribute is a prop passed to a component
+		assert.equal(target.querySelector('#prop')?.textContent, 'A\nB');
+
+		// other entities in attribute values still decode
+		assert.equal(target.querySelector('#attr-other-entity')?.getAttribute('title'), '©');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/html-entity-line-feed/main.svelte b/packages/svelte/tests/runtime-runes/samples/html-entity-line-feed/main.svelte
new file mode 100644
index 0000000000..d7f5684351
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/html-entity-line-feed/main.svelte
@@ -0,0 +1,9 @@
+<script>
+	import Component from './Component.svelte';
+</script>
+
+<span id="attr" title="A&#x0A;B"></span>
+<span id="attr-decimal" title="A&#10;B"></span>
+<span id="attr-other-entity" title="&copy;"></span>
+
+<Component text="A&#x0A;B" />

From c575b07bca37178cd8ce8c10389ece6dd33e8c96 Mon Sep 17 00:00:00 2001
From: Ion <ivanterescheenko@gmail.com>
Date: Tue, 25 Aug 2026 16:15:19 +0200
Subject: [PATCH 11/29] feat: support `defaultValue` on `<select>` (#18591)

Closes #18447

---------

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
Co-authored-by: Simon Holthausen <simon.holthausen@vercel.com>
---
 .changeset/tall-hounds-tap.md                 |  5 +
 .../docs/03-template-syntax/12-bind.md        | 13 +++
 packages/svelte/elements.d.ts                 |  3 +
 .../client/visitors/RegularElement.js         | 26 +++++
 .../client/visitors/shared/element.js         |  7 +-
 .../server/visitors/RegularElement.js         |  2 +-
 .../server/visitors/shared/element.js         |  4 +-
 .../client/dom/elements/attributes.js         | 50 +++++-----
 .../client/dom/elements/bindings/select.js    | 56 ++++++++++-
 packages/svelte/src/internal/client/index.js  |  9 +-
 .../svelte/src/internal/server/renderer.js    | 21 ++--
 .../form-default-value-select/_config.js      | 96 +++++++++++++++++++
 .../form-default-value-select/main.svelte     | 79 +++++++++++++++
 .../select-default-value/_expected.html       | 25 +++++
 .../samples/select-default-value/main.svelte  | 34 +++++++
 15 files changed, 393 insertions(+), 37 deletions(-)
 create mode 100644 .changeset/tall-hounds-tap.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/form-default-value-select/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/form-default-value-select/main.svelte
 create mode 100644 packages/svelte/tests/server-side-rendering/samples/select-default-value/_expected.html
 create mode 100644 packages/svelte/tests/server-side-rendering/samples/select-default-value/main.svelte

diff --git a/.changeset/tall-hounds-tap.md b/.changeset/tall-hounds-tap.md
new file mode 100644
index 0000000000..3a9f7d79cb
--- /dev/null
+++ b/.changeset/tall-hounds-tap.md
@@ -0,0 +1,5 @@
+---
+'svelte': minor
+---
+
+feat: support `defaultValue` on `<select>`
diff --git a/documentation/docs/03-template-syntax/12-bind.md b/documentation/docs/03-template-syntax/12-bind.md
index b93f207e71..ee91d607f0 100644
--- a/documentation/docs/03-template-syntax/12-bind.md
+++ b/documentation/docs/03-template-syntax/12-bind.md
@@ -251,6 +251,19 @@ You can give the `<select>` a default value by adding a `selected` attribute to
 </select>
 ```
 
+Since 5.57.0, if a `<select>` has a `defaultValue` and is part of a form, it will revert to that value instead of the empty string when the form is reset. Note that for the initial render the value of the binding takes precedence unless it is `null` or `undefined`.
+
+```svelte
+<form>
+	<select bind:value defaultValue="b">
+		<option>a</option>
+		<option>b</option>
+		<option>c</option>
+	</select>
+	<input type="reset" value="Reset">
+</form>
+```
+
 ## `<audio>`
 
 `<audio>` elements have their own set of bindings — five two-way ones...
diff --git a/packages/svelte/elements.d.ts b/packages/svelte/elements.d.ts
index daa40635b6..15837f831a 100644
--- a/packages/svelte/elements.d.ts
+++ b/packages/svelte/elements.d.ts
@@ -1352,6 +1352,9 @@ export interface HTMLSelectAttributes extends HTMLAttributes<HTMLSelectElement>
 	required?: boolean | undefined | null;
 	size?: number | undefined | null;
 	value?: any;
+	// needs both casing variants because language tools does lowercase names of non-shorthand attributes
+	defaultValue?: any;
+	defaultvalue?: any;
 
 	'on:change'?: ChangeEventHandler<HTMLSelectElement> | undefined | null;
 	onchange?: ChangeEventHandler<HTMLSelectElement> | undefined | null;
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 4c1538c331..401891b41b 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
@@ -229,6 +229,12 @@ export function RegularElement(node, context) {
 				continue;
 			}
 
+			// `<select defaultValue>` needs the options to exist before it can mark one
+			// as selected, so it is handled after the children, alongside `value`
+			if (node.name === 'select' && get_attribute_name(node, attribute) === 'defaultValue') {
+				continue;
+			}
+
 			const name = get_attribute_name(node, attribute);
 
 			if (
@@ -511,6 +517,26 @@ export function RegularElement(node, context) {
 		}
 	}
 
+	// deferred from the attribute loop above, so that the options it selects from
+	// have been created and had their values assigned
+	if (!has_spread && name === 'select') {
+		for (const attribute of /** @type {AST.Attribute[]} */ (attributes)) {
+			if (get_attribute_name(node, attribute) === 'defaultValue') {
+				const { value, has_state } = build_attribute_value(attribute.value, context, (v, m) =>
+					context.state.memoizer.add(v, m)
+				);
+
+				const update = b.stmt(b.call('$.set_default_select_value', node_id, value));
+
+				(has_state ? context.state.update : context.state.init).push(update);
+				if (!bindings.has('value')) {
+					context.state.init.push(b.stmt(b.call('$.init_select', node_id)));
+				}
+				break;
+			}
+		}
+	}
+
 	context.state.template.pop_element();
 }
 
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 58ed88855f..ec0ca83cb4 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
@@ -30,6 +30,7 @@ export function build_attribute_effect(
 ) {
 	/** @type {ObjectExpression['properties']} */
 	const values = [];
+	const is_select = element.type === 'RegularElement' && element.name === 'select';
 
 	const memoizer = new Memoizer();
 
@@ -48,7 +49,11 @@ export function build_attribute_effect(
 				context.state.init.push(b.var(id, value));
 				values.push(b.init(attribute.name, b.id(id)));
 			} else {
-				values.push(b.init(attribute.name, value));
+				const name =
+					is_select && normalize_attribute(attribute.name) === 'defaultValue'
+						? 'defaultValue'
+						: attribute.name;
+				values.push(b.init(name, value));
 			}
 		} else {
 			let value = /** @type {Expression} */ (context.visit(attribute));
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/RegularElement.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/RegularElement.js
index 90c34d7035..f31de46378 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/visitors/RegularElement.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/visitors/RegularElement.js
@@ -46,7 +46,7 @@ export function RegularElement(node, context) {
 		node.attributes.some(
 			(attribute) =>
 				((attribute.type === 'Attribute' || attribute.type === 'BindDirective') &&
-					attribute.name === 'value') ||
+					(attribute.name === 'value' || attribute.name.toLowerCase() === 'defaultvalue')) ||
 				attribute.type === 'SpreadAttribute'
 		);
 	const is_option_special = name === 'option';
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/element.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/element.js
index 6440510b01..5081d12c80 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/element.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/element.js
@@ -306,12 +306,14 @@ function get_attribute_name(element, attribute) {
  * @param {(expression: Expression, metadata: ExpressionMetadata) => Expression} transform
  */
 export function build_spread_object(element, attributes, context, transform) {
+	const is_select = element.type === 'RegularElement' && element.name === 'select';
 	const object = b.object(
 		attributes.map((attribute) => {
 			if (attribute.type === 'transformed') {
 				return b.prop('init', b.key(attribute.name), attribute.expression);
 			} else if (attribute.type === 'Attribute') {
-				const name = get_attribute_name(element, attribute);
+				let name = get_attribute_name(element, attribute);
+				if (is_select && name === 'defaultvalue') name = 'defaultValue';
 				const value = build_attribute_value(
 					attribute.value,
 					context,
diff --git a/packages/svelte/src/internal/client/dom/elements/attributes.js b/packages/svelte/src/internal/client/dom/elements/attributes.js
index 69d4dd42a8..7439db56e9 100644
--- a/packages/svelte/src/internal/client/dom/elements/attributes.js
+++ b/packages/svelte/src/internal/client/dom/elements/attributes.js
@@ -26,7 +26,12 @@ import { set_class } from './class.js';
 import { set_style } from './style.js';
 import { ATTACHMENT_KEY, NAMESPACE_HTML, UNINITIALIZED } from '../../../../constants.js';
 import { branch, destroy_effect, effect, managed } from '../../reactivity/effects.js';
-import { init_select, select_option } from './bindings/select.js';
+import {
+	init_select,
+	select_option,
+	set_default_select_value,
+	set_selected
+} from './bindings/select.js';
 import { flatten } from '../../reactivity/async.js';
 
 export const CLASS = Symbol('class');
@@ -122,25 +127,6 @@ export function set_checked(element, checked) {
 	element.checked = checked;
 }
 
-/**
- * Sets the `selected` attribute on an `option` element.
- * Not set through the property because that doesn't reflect to the DOM,
- * which means it wouldn't be taken into account when a form is reset.
- * @param {HTMLOptionElement} element
- * @param {boolean} selected
- */
-export function set_selected(element, selected) {
-	if (selected) {
-		// The selected option could've changed via user selection, and
-		// setting the value without this check would set it back.
-		if (!element.hasAttribute('selected')) {
-			element.setAttribute('selected', '');
-		}
-	} else {
-		element.removeAttribute('selected');
-	}
-}
-
 /**
  * Applies the default checked property without influencing the current checked property.
  * @param {HTMLInputElement} element
@@ -310,6 +296,7 @@ function set_attributes(
 
 	var current = prev || {};
 	var is_option_element = element.nodeName === OPTION_TAG;
+	var is_select_element = element.nodeName === SELECT_TAG;
 
 	for (var key in prev) {
 		// don't null our internal $$onX listeners
@@ -446,6 +433,9 @@ function set_attributes(
 
 			var is_default = name === 'defaultValue' || name === 'defaultChecked';
 
+			// A select's default value is represented by selected options, not a property.
+			if (is_select_element && name === 'defaultValue') continue;
+
 			if (value == null && !is_custom_element && !is_default) {
 				attributes[key] = null;
 
@@ -531,8 +521,16 @@ export function attribute_effect(
 				skip_warning
 			);
 
-			if (inited && is_select && 'value' in next) {
-				select_option(/** @type {HTMLSelectElement} */ (element), next.value);
+			if (inited && is_select) {
+				var select = /** @type {HTMLSelectElement} */ (element);
+
+				if ('defaultValue' in next) {
+					set_default_select_value(select, next.defaultValue, false);
+				}
+
+				if ('value' in next) {
+					select_option(select, next.value);
+				}
 			}
 
 			for (let symbol of Object.getOwnPropertySymbols(effects)) {
@@ -557,7 +555,13 @@ export function attribute_effect(
 			var select = /** @type {HTMLSelectElement} */ (element);
 
 			effect(() => {
-				select_option(select, /** @type {Record<string | symbol, any>} */ (prev).value, true);
+				var attrs = /** @type {Record<string | symbol, any>} */ (prev);
+
+				if ('defaultValue' in attrs) {
+					set_default_select_value(select, attrs.defaultValue, true);
+				}
+
+				select_option(select, attrs.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 a408613104..fd1ebb92b8 100644
--- a/packages/svelte/src/internal/client/dom/elements/bindings/select.js
+++ b/packages/svelte/src/internal/client/dom/elements/bindings/select.js
@@ -6,6 +6,50 @@ import * as w from '../../../warnings.js';
 import { Batch, current_batch, previous_batch } from '../../../reactivity/batch.js';
 import { async_mode_flag } from '../../../../flags/index.js';
 
+/**
+ * Sets the `selected` attribute on an option so form reset can restore it.
+ * @param {HTMLOptionElement} option
+ * @param {boolean} selected
+ */
+export function set_selected(option, selected) {
+	if (selected) {
+		if (!option.hasAttribute('selected')) option.setAttribute('selected', '');
+	} else {
+		option.removeAttribute('selected');
+	}
+}
+
+/**
+ * Sets the options a form reset should restore without changing the current selection.
+ * The initial call is allowed to establish the current selection when no value exists.
+ * @param {HTMLSelectElement} select
+ * @param {any} value
+ * @param {boolean} [mounting]
+ */
+export function set_default_select_value(select, value, mounting = !('__defaultValue' in select)) {
+	// The DOM cannot recover unmatched, object or multiple defaults from selected options.
+	// Keep the requested value so option mutations can reapply it; property presence also
+	// distinguishes the initial application from later updates when the value is undefined.
+	// @ts-expect-error
+	select.__defaultValue = value;
+	var values = select.multiple ? (value == null ? [] : value) : null;
+
+	if (select.multiple && !is_array(values)) return;
+	var selected = !mounting || '__value' in select ? new Set(select.selectedOptions) : null;
+
+	for (var option of select.options) {
+		var option_value = get_option_value(option);
+		var is_selected = select.multiple
+			? /** @type {any[]} */ (values).includes(option_value)
+			: is(option_value, value);
+		set_selected(option, is_selected);
+	}
+
+	if (selected !== null) {
+		for (option of select.options) option.selected = selected.has(option);
+	}
+}
+
 /**
  * Selects the correct option(s) (depending on whether this is a multiple select)
  * @template V
@@ -60,9 +104,15 @@ export function init_select(select) {
 		// Reacting to them could revert a user-initiated selection change, because the
 		// records are delivered as soon as any listener returns (e.g. a delegated `input`
 		// handler), which can happen before the `change` handler has updated `__value`
-		if (entries.every(is_selectedcontent_mutation) || !('__value' in select)) return;
-		// @ts-ignore
-		select_option(select, select.__value);
+		if (entries.every(is_selectedcontent_mutation)) return;
+
+		if ('__defaultValue' in select) {
+			set_default_select_value(select, select.__defaultValue, false);
+		}
+
+		if ('__value' in select) {
+			select_option(select, select.__value);
+		}
 		// Deliberately don't update the potential binding value,
 		// the model should be preserved unless explicitly changed
 	});
diff --git a/packages/svelte/src/internal/client/index.js b/packages/svelte/src/internal/client/index.js
index 8c922b0b84..15e92aa255 100644
--- a/packages/svelte/src/internal/client/index.js
+++ b/packages/svelte/src/internal/client/index.js
@@ -33,7 +33,6 @@ export {
 	set_xlink_attribute,
 	set_value,
 	set_checked,
-	set_selected,
 	set_default_checked,
 	set_default_value,
 	CLASS,
@@ -62,7 +61,13 @@ export {
 } from './dom/elements/bindings/media.js';
 export { bind_online } from './dom/elements/bindings/navigator.js';
 export { bind_prop } from './dom/elements/bindings/props.js';
-export { bind_select_value, init_select, select_option } from './dom/elements/bindings/select.js';
+export {
+	bind_select_value,
+	init_select,
+	select_option,
+	set_selected,
+	set_default_select_value
+} from './dom/elements/bindings/select.js';
 export { bind_element_size, bind_resize_observer } from './dom/elements/bindings/size.js';
 export { bind_this } from './dom/elements/bindings/this.js';
 export {
diff --git a/packages/svelte/src/internal/server/renderer.js b/packages/svelte/src/internal/server/renderer.js
index 1a5199d18e..240a7aa686 100644
--- a/packages/svelte/src/internal/server/renderer.js
+++ b/packages/svelte/src/internal/server/renderer.js
@@ -13,7 +13,7 @@ import { attributes } from './index.js';
 import { get_render_context, with_render_context, init_render_context } from './render-context.js';
 import { sha256 } from './crypto.js';
 import * as devalue from 'devalue';
-import { has_own_property, noop } from '../shared/utils.js';
+import { has_own_property, is_array, noop } from '../shared/utils.js';
 import { escape_html } from '../../escaping.js';
 
 /** @typedef {'head' | 'body'} RendererType */
@@ -89,7 +89,7 @@ export class Renderer {
 	 * State that is local to the branch it is declared in.
 	 * It will be shallow-copied to all children.
 	 *
-	 * @type {{ select_value: string | undefined }}
+	 * @type {{ select_value: any, select_default_multiple: boolean }}
 	 */
 	local;
 
@@ -101,7 +101,9 @@ export class Renderer {
 		this.#parent = parent;
 
 		this.global = global;
-		this.local = parent ? { ...parent.local } : { select_value: undefined };
+		this.local = parent
+			? { ...parent.local }
+			: { select_value: undefined, select_default_multiple: false };
 		this.type = parent ? parent.type : 'body';
 	}
 
@@ -338,11 +340,14 @@ export class Renderer {
 	 * @returns {void}
 	 */
 	select(attrs, fn, css_hash, classes, styles, flags, is_rich) {
-		const { value, ...select_attrs } = attrs;
+		const { value, defaultValue, ...select_attrs } = attrs;
+		if (select_attrs.multiple === '') select_attrs.multiple = true;
 
 		this.push(`<select${attributes(select_attrs, css_hash, classes, styles, flags)}>`);
 		this.child((renderer) => {
-			renderer.local.select_value = value;
+			renderer.local.select_value = value === undefined ? defaultValue : value;
+			renderer.local.select_default_multiple =
+				value === undefined && Boolean(select_attrs.multiple);
 			fn(renderer);
 		});
 		this.push(`${is_rich ? '<!>' : ''}</select>`);
@@ -370,7 +375,11 @@ export class Renderer {
 				value = attrs.value;
 			}
 
-			if (value === this.local.select_value) {
+			if (
+				this.local.select_default_multiple
+					? is_array(this.local.select_value) && this.local.select_value.includes(value)
+					: value === this.local.select_value
+			) {
 				renderer.#out.push(' selected=""');
 			}
 
diff --git a/packages/svelte/tests/runtime-runes/samples/form-default-value-select/_config.js b/packages/svelte/tests/runtime-runes/samples/form-default-value-select/_config.js
new file mode 100644
index 0000000000..5d0c964969
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/form-default-value-select/_config.js
@@ -0,0 +1,96 @@
+import { test } from '../../test';
+import { flushSync } from 'svelte';
+
+export default test({
+	async test({ assert, target }) {
+		/** @param {HTMLSelectElement} select @param {boolean[]} expected */
+		function check(select, expected) {
+			assert.deepEqual(
+				[...select.options].map((option) => option.selected),
+				expected
+			);
+		}
+
+		/** @param {HTMLSelectElement} select @param {number[]} indexes */
+		function select(select, indexes) {
+			for (let i = 0; i < select.options.length; i++) {
+				select.options[i].selected = indexes.includes(i);
+			}
+			select.dispatchEvent(new Event('change', { bubbles: true }));
+		}
+
+		const selects = target.querySelectorAll('select');
+		const reset = /** @type {HTMLInputElement} */ (target.querySelector('input[type=reset]'));
+		/** @param {string} name */
+		const button = (name) => /** @type {HTMLButtonElement} */ (target.querySelector(`.${name}`));
+
+		check(selects[0], [false, true, false]);
+		check(selects[1], [false, false, true]);
+		check(selects[2], [false, true, false]);
+		check(selects[3], [true]);
+		check(selects[4], [false, true]);
+		check(selects[5], [false, true, false]);
+		check(selects[6], [true, false]);
+		check(selects[7], [true, false, true]);
+		check(selects[8], [false, false, true]);
+
+		select(selects[0], [2]);
+		select(selects[1], [0]);
+		select(selects[5], [2]);
+		select(selects[7], [1]);
+		flushSync();
+
+		reset.click();
+		await Promise.resolve();
+		flushSync();
+		check(selects[0], [false, true, false]);
+		check(selects[1], [false, true, false]);
+		check(selects[5], [false, true, false]);
+		check(selects[7], [true, false, true]);
+
+		select(selects[2], [2]);
+		select(selects[5], [2]);
+		button('update').click();
+		flushSync();
+		check(selects[2], [false, false, true]);
+		check(selects[5], [false, false, true]);
+		assert.deepEqual(
+			[...selects[5].options].map((option) => option.defaultSelected),
+			[true, false, false]
+		);
+
+		button('add').click();
+		flushSync();
+		await Promise.resolve();
+		check(selects[3], [true, false]);
+		assert.equal(selects[3].options[1].defaultSelected, true);
+
+		reset.click();
+		await Promise.resolve();
+		flushSync();
+		check(selects[0], [true, false, false]);
+		check(selects[2], [true, false, false]);
+		check(selects[3], [false, true]);
+		check(selects[5], [true, false, false]);
+
+		select(selects[5], [2]);
+		select(selects[7], [1]);
+		button('remove').click();
+		button('clear').click();
+		flushSync();
+		assert.equal(
+			[...selects[5].options].some((option) => option.defaultSelected),
+			false
+		);
+		assert.equal(
+			[...selects[7].options].some((option) => option.defaultSelected),
+			false
+		);
+
+		reset.click();
+		await Promise.resolve();
+		flushSync();
+		check(selects[5], [true, false, false]);
+		check(selects[7], [false, false, false]);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/form-default-value-select/main.svelte b/packages/svelte/tests/runtime-runes/samples/form-default-value-select/main.svelte
new file mode 100644
index 0000000000..daa1f9ceee
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/form-default-value-select/main.svelte
@@ -0,0 +1,79 @@
+<script>
+	let selected1 = $state();
+	let selected2 = $state('c');
+	let selected3 = $state();
+	let selected4 = $state(['c']);
+	let defaultValue = $state('b');
+	let multipleDefault = $state(/** @type {string[] | undefined} */ (['a', 'c']));
+	let options = $state(['a']);
+	let props = $state({ defaultValue: 'b' });
+</script>
+
+<form>
+	<select {defaultValue} bind:value={selected1}>
+		<option value="a">A</option>
+		<option value="b">B</option>
+		<option value="c">C</option>
+	</select>
+
+	<select {defaultValue} bind:value={selected2}>
+		<option value="a">A</option>
+		<option value="b">B</option>
+		<option value="c">C</option>
+	</select>
+
+	<select {defaultValue}>
+		<option value="a">A</option>
+		<option value="b">B</option>
+		<option value="c">C</option>
+	</select>
+
+	<select defaultValue="b">
+		{#each options as option}
+			<option value={option}>{option}</option>
+		{/each}
+	</select>
+
+	<select defaultvalue="b">
+		<option value="a">A</option>
+		<option value="b">B</option>
+	</select>
+
+	<select {...props} bind:value={selected3}>
+		<option value="a">A</option>
+		<option value="b">B</option>
+		<option value="c">C</option>
+	</select>
+
+	<select {...{ defaultValue: 'b' }} defaultValue="a">
+		<option value="a">A</option>
+		<option value="b">B</option>
+	</select>
+
+	<select multiple defaultValue={multipleDefault}>
+		<option value="a">A</option>
+		<option value="b">B</option>
+		<option value="c">C</option>
+	</select>
+
+	<select multiple defaultValue={multipleDefault} bind:value={selected4}>
+		<option value="a">A</option>
+		<option value="b">B</option>
+		<option value="c">C</option>
+	</select>
+
+	<input type="reset" value="Reset" />
+	<button
+		type="button"
+		class="update"
+		onclick={() => {
+			defaultValue = 'a';
+			props.defaultValue = 'a';
+		}}>Update defaults</button
+	>
+	<button type="button" class="add" onclick={() => options.push('b')}>Add option</button>
+	<button type="button" class="remove" onclick={() => delete props.defaultValue}>Remove default</button>
+	<button type="button" class="clear" onclick={() => (multipleDefault = undefined)}>Clear defaults</button>
+</form>
+
+<p>{selected1} {selected2} {selected3} {selected4.join(',')}</p>
diff --git a/packages/svelte/tests/server-side-rendering/samples/select-default-value/_expected.html b/packages/svelte/tests/server-side-rendering/samples/select-default-value/_expected.html
new file mode 100644
index 0000000000..482f4a9d4c
--- /dev/null
+++ b/packages/svelte/tests/server-side-rendering/samples/select-default-value/_expected.html
@@ -0,0 +1,25 @@
+<select>
+	<option value="a">A</option>
+	<option selected="" value="b">B</option>
+</select>
+<select>
+	<option value="a">A</option>
+	<option selected="" value="b">B</option>
+</select>
+<select>
+	<option selected="" value="a">A</option>
+	<option value="b">B</option>
+</select>
+<select multiple="">
+	<option selected="" value="a">A</option>
+	<option value="b">B</option>
+	<option selected="" value="c">C</option>
+</select>
+<select>
+	<option value="a">A</option>
+	<option selected="" value="b">B</option>
+</select>
+<select>
+	<option selected="" value="a">A</option>
+	<option value="b">B</option>
+</select>
diff --git a/packages/svelte/tests/server-side-rendering/samples/select-default-value/main.svelte b/packages/svelte/tests/server-side-rendering/samples/select-default-value/main.svelte
new file mode 100644
index 0000000000..fe5a858dd0
--- /dev/null
+++ b/packages/svelte/tests/server-side-rendering/samples/select-default-value/main.svelte
@@ -0,0 +1,34 @@
+<script>
+	const props = { defaultValue: 'b' };
+</script>
+
+<select defaultValue="b">
+	<option value="a">A</option>
+	<option value="b">B</option>
+</select>
+
+<select {...props}>
+	<option value="a">A</option>
+	<option value="b">B</option>
+</select>
+
+<select defaultValue="b" value="a">
+	<option value="a">A</option>
+	<option value="b">B</option>
+</select>
+
+<select multiple="" defaultValue={['a', 'c']}>
+	<option value="a">A</option>
+	<option value="b">B</option>
+	<option value="c">C</option>
+</select>
+
+<select defaultvalue="b">
+	<option value="a">A</option>
+	<option value="b">B</option>
+</select>
+
+<select {...{ defaultValue: 'b' }} defaultValue="a">
+	<option value="a">A</option>
+	<option value="b">B</option>
+</select>

From 14ec75c5fe88e4f54ab588fa8e7ca92493cd1116 Mon Sep 17 00:00:00 2001
From: Mathias Picker <48158184+MathiasWP@users.noreply.github.com>
Date: Tue, 25 Aug 2026 16:16:17 +0200
Subject: [PATCH 12/29] perf: fold SSR block-open markers into the branch's
 first push (#18712)

One fewer `$$renderer.push` per rendered branch
---
 .changeset/gold-moons-shave.md                |  5 ++
 .../3-transform/server/visitors/EachBlock.js  | 10 +++-
 .../3-transform/server/visitors/IfBlock.js    |  8 +--
 .../server/visitors/shared/utils.js           | 30 +++++++++++
 .../_expected/server/index.svelte.js          |  3 +-
 .../_expected/server/index.svelte.js          | 54 +++++++------------
 .../_expected/server/index.svelte.js          |  9 ++--
 .../_expected/server/index.svelte.js          |  3 +-
 8 files changed, 70 insertions(+), 52 deletions(-)
 create mode 100644 .changeset/gold-moons-shave.md

diff --git a/.changeset/gold-moons-shave.md b/.changeset/gold-moons-shave.md
new file mode 100644
index 0000000000..9ee98321b7
--- /dev/null
+++ b/.changeset/gold-moons-shave.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+perf: fold SSR block-open markers into the branch's first push
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 cb5a61d52f..923c4dd394 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
@@ -2,7 +2,13 @@
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext } from '../types.js' */
 import * as b from '#compiler/builders';
-import { block_close, block_open, block_open_else, create_child_block } from './shared/utils.js';
+import {
+	block_close,
+	block_open,
+	block_open_else,
+	create_child_block,
+	prepend_block_marker
+} from './shared/utils.js';
 
 /**
  * @param {AST.EachBlock} node
@@ -51,7 +57,7 @@ export function EachBlock(node, context) {
 
 		const fallback = /** @type {BlockStatement} */ (context.visit(node.fallback));
 
-		fallback.body.unshift(b.stmt(b.call(b.id('$$renderer.push'), block_open_else)));
+		prepend_block_marker(fallback, /** @type {string} */ (block_open_else.value));
 
 		statements.push(
 			b.if(
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 2d1a22605c..ea636e2064 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
@@ -2,7 +2,7 @@
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext } from '../types.js' */
 import * as b from '#compiler/builders';
-import { block_close, create_child_block } from './shared/utils.js';
+import { block_close, create_child_block, prepend_block_marker } from './shared/utils.js';
 
 /**
  * @param {AST.IfBlock} node
@@ -10,7 +10,7 @@ import { block_close, create_child_block } from './shared/utils.js';
  */
 export function IfBlock(node, context) {
 	const consequent = /** @type {BlockStatement} */ (context.visit(node.consequent));
-	consequent.body.unshift(b.stmt(b.call(b.id('$$renderer.push'), b.literal(`<!--[0-->`))));
+	prepend_block_marker(consequent, `<!--[0-->`);
 
 	/** @type {IfStatement} */
 	let if_statement = b.if(/** @type {Expression} */ (context.visit(node.test)), consequent);
@@ -22,7 +22,7 @@ export function IfBlock(node, context) {
 	// Walk the else-if chain, flattening branches
 	for (const elseif of node.metadata.flattened ?? []) {
 		const branch = /** @type {BlockStatement} */ (context.visit(elseif.consequent));
-		branch.body.unshift(b.stmt(b.call(b.id('$$renderer.push'), b.literal(`<!--[${index++}-->`))));
+		prepend_block_marker(branch, `<!--[${index++}-->`);
 
 		current_if = current_if.alternate = b.if(
 			/** @type {Expression} */ (context.visit(elseif.test)),
@@ -34,7 +34,7 @@ export function IfBlock(node, context) {
 	// Handle final else (or remaining async chain)
 	const final_alternate = alt ? /** @type {BlockStatement} */ (context.visit(alt)) : b.block([]);
 
-	final_alternate.body.unshift(b.stmt(b.call(b.id('$$renderer.push'), b.literal(`<!--[-1-->`))));
+	prepend_block_marker(final_alternate, `<!--[-1-->`);
 	current_if.alternate = final_alternate;
 
 	context.state.template.push(
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 28d2d762f9..f38ae6164c 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
@@ -180,6 +180,36 @@ export function build_template(template) {
 	return statements;
 }
 
+/**
+ * Prepends a hydration marker (e.g. `<!--[0-->`) to a branch. The branch has already been
+ * turned into statements by `build_template`, so if it happens to start with a static
+ * `$$renderer.push(...)` we fold the marker into that call rather than emitting a second one.
+ * @param {BlockStatement} block
+ * @param {string} marker
+ */
+export function prepend_block_marker(block, marker) {
+	const first = block.body[0];
+
+	if (
+		first?.type === 'ExpressionStatement' &&
+		first.expression.type === 'CallExpression' &&
+		first.expression.callee.type === 'Identifier' &&
+		first.expression.callee.name === '$$renderer.push' &&
+		first.expression.arguments.length === 1 &&
+		first.expression.arguments[0].type === 'TemplateLiteral'
+	) {
+		const quasi = first.expression.arguments[0].quasis[0];
+
+		// markers never contain characters that need escaping in a template literal
+		quasi.value.cooked = marker + quasi.value.cooked;
+		quasi.value.raw = marker + quasi.value.raw;
+
+		return;
+	}
+
+	block.body.unshift(b.stmt(b.call(b.id('$$renderer.push'), b.literal(marker))));
+}
+
 /**
  *
  * @param {AST.Attribute['value']} value
diff --git a/packages/svelte/tests/snapshot/samples/async-each-fallback-hoisting/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/async-each-fallback-hoisting/_expected/server/index.svelte.js
index b331875d04..71ccba4d59 100644
--- a/packages/svelte/tests/snapshot/samples/async-each-fallback-hoisting/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/async-each-fallback-hoisting/_expected/server/index.svelte.js
@@ -15,8 +15,7 @@ export default function Async_each_fallback_hoisting($$renderer) {
 				$$renderer.push(async () => $.escape(await Promise.reject('This should never be reached')));
 			}
 		} else {
-			$$renderer.push('<!--[!-->');
-			$$renderer.push(`<!---->`);
+			$$renderer.push(`<!--[!--><!---->`);
 			$$renderer.push(async () => $.escape(await Promise.resolve(4)));
 		}
 	});
diff --git a/packages/svelte/tests/snapshot/samples/async-if-chain/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/async-if-chain/_expected/server/index.svelte.js
index 3fc25288ad..466683b868 100644
--- a/packages/svelte/tests/snapshot/samples/async-if-chain/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/async-if-chain/_expected/server/index.svelte.js
@@ -12,14 +12,11 @@ export default function Async_if_chain($$renderer) {
 
 	$$renderer.async_block([$$promises[0]], ($$renderer) => {
 		if (foo) {
-			$$renderer.push('<!--[0-->');
-			$$renderer.push(`foo`);
+			$$renderer.push(`<!--[0-->foo`);
 		} else if (bar) {
-			$$renderer.push('<!--[1-->');
-			$$renderer.push(`bar`);
+			$$renderer.push(`<!--[1-->bar`);
 		} else {
-			$$renderer.push('<!--[-1-->');
-			$$renderer.push(`else`);
+			$$renderer.push(`<!--[-1-->else`);
 		}
 	});
 
@@ -27,21 +24,17 @@ export default function Async_if_chain($$renderer) {
 
 	$$renderer.async_block([$$promises[0]], async ($$renderer) => {
 		if ((await $.save(foo))()) {
-			$$renderer.push('<!--[0-->');
-			$$renderer.push(`foo`);
+			$$renderer.push(`<!--[0-->foo`);
 		} else if (bar) {
-			$$renderer.push('<!--[1-->');
-			$$renderer.push(`bar`);
+			$$renderer.push(`<!--[1-->bar`);
 		} else {
 			$$renderer.push('<!--[-1-->');
 
 			$$renderer.child_block(async ($$renderer) => {
 				if ((await $.save(baz))()) {
-					$$renderer.push('<!--[0-->');
-					$$renderer.push(`baz`);
+					$$renderer.push(`<!--[0-->baz`);
 				} else {
-					$$renderer.push('<!--[-1-->');
-					$$renderer.push(`else`);
+					$$renderer.push(`<!--[-1-->else`);
 				}
 			});
 
@@ -53,21 +46,17 @@ export default function Async_if_chain($$renderer) {
 
 	$$renderer.async_block([$$promises[0]], async ($$renderer) => {
 		if ((await $.save(foo))() > 10) {
-			$$renderer.push('<!--[0-->');
-			$$renderer.push(`foo`);
+			$$renderer.push(`<!--[0-->foo`);
 		} else if (bar) {
-			$$renderer.push('<!--[1-->');
-			$$renderer.push(`bar`);
+			$$renderer.push(`<!--[1-->bar`);
 		} else {
 			$$renderer.push('<!--[-1-->');
 
 			$$renderer.async_block([$$promises[0]], async ($$renderer) => {
 				if ((await $.save(foo))() > 5) {
-					$$renderer.push('<!--[0-->');
-					$$renderer.push(`baz`);
+					$$renderer.push(`<!--[0-->baz`);
 				} else {
-					$$renderer.push('<!--[-1-->');
-					$$renderer.push(`else`);
+					$$renderer.push(`<!--[-1-->else`);
 				}
 			});
 
@@ -78,31 +67,24 @@ export default function Async_if_chain($$renderer) {
 	$$renderer.push(`<!--]--> `);
 
 	if (simple1) {
-		$$renderer.push('<!--[0-->');
-		$$renderer.push(`foo`);
+		$$renderer.push(`<!--[0-->foo`);
 	} else if (simple2 > 10) {
-		$$renderer.push('<!--[1-->');
-		$$renderer.push(`bar`);
+		$$renderer.push(`<!--[1-->bar`);
 	} else if (complex1() * complex2 > 100) {
-		$$renderer.push('<!--[2-->');
-		$$renderer.push(`baz`);
+		$$renderer.push(`<!--[2-->baz`);
 	} else {
-		$$renderer.push('<!--[-1-->');
-		$$renderer.push(`else`);
+		$$renderer.push(`<!--[-1-->else`);
 	}
 
 	$$renderer.push(`<!--]--> `);
 
 	$$renderer.async_block([$$promises[0]], ($$renderer) => {
 		if (blocking() > 10) {
-			$$renderer.push('<!--[0-->');
-			$$renderer.push(`foo`);
+			$$renderer.push(`<!--[0-->foo`);
 		} else if (blocking() > 5) {
-			$$renderer.push('<!--[1-->');
-			$$renderer.push(`bar`);
+			$$renderer.push(`<!--[1-->bar`);
 		} else {
-			$$renderer.push('<!--[-1-->');
-			$$renderer.push(`else`);
+			$$renderer.push(`<!--[-1-->else`);
 		}
 	});
 
diff --git a/packages/svelte/tests/snapshot/samples/dedupe-templates/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/dedupe-templates/_expected/server/index.svelte.js
index 1f4a56779e..be305165cb 100644
--- a/packages/svelte/tests/snapshot/samples/dedupe-templates/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/dedupe-templates/_expected/server/index.svelte.js
@@ -4,18 +4,15 @@ export default function Dedupe_templates($$renderer, $$props) {
 	let { a, b } = $$props;
 
 	if (a) {
-		$$renderer.push('<!--[0-->');
-		$$renderer.push(`<p class="x">hello</p>`);
+		$$renderer.push(`<!--[0--><p class="x">hello</p>`);
 	} else {
-		$$renderer.push('<!--[-1-->');
-		$$renderer.push(`<p class="x">hello</p>`);
+		$$renderer.push(`<!--[-1--><p class="x">hello</p>`);
 	}
 
 	$$renderer.push(`<!--]--> `);
 
 	if (b) {
-		$$renderer.push('<!--[0-->');
-		$$renderer.push(`<p class="x">hello</p>`);
+		$$renderer.push(`<!--[0--><p class="x">hello</p>`);
 	} else {
 		$$renderer.push('<!--[-1-->');
 	}
diff --git a/packages/svelte/tests/snapshot/samples/select-with-rich-content/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/select-with-rich-content/_expected/server/index.svelte.js
index bc346b4b0a..de22dc2f96 100644
--- a/packages/svelte/tests/snapshot/samples/select-with-rich-content/_expected/server/index.svelte.js
+++ b/packages/svelte/tests/snapshot/samples/select-with-rich-content/_expected/server/index.svelte.js
@@ -148,8 +148,7 @@ export default function Select_with_rich_content($$renderer) {
 	$$renderer.push(`<!--]--></select> <select>`);
 
 	if (show) {
-		$$renderer.push('<!--[0-->');
-		$$renderer.push(`<!--[-->`);
+		$$renderer.push(`<!--[0--><!--[-->`);
 
 		const each_array_4 = $.ensure_array_like(items);
 

From 68e7c9b5218b613c2b58be98bc5910bfa0dbacd4 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Tue, 25 Aug 2026 16:24:46 +0200
Subject: [PATCH 13/29] fix: transform derived assignments and select function
 bindings correctly during server-side rendering (#18669)

follow-up to the fix in #18607 - there are a two more bugs related to
writeable deriveds in that area
---
 .changeset/slow-dots-smile.md                          |  5 +++++
 .../server/visitors/AssignmentExpression.js            |  2 +-
 .../3-transform/server/visitors/shared/element.js      |  5 ++---
 .../derived-forward-ref-leading-comments/_config.js    |  6 ------
 .../samples/derived-leading-comments/_config.js        |  6 ++++++
 .../main.svelte                                        | 10 ++++++++++
 .../samples/select-function-binding-derived/_config.js |  9 +++++++++
 .../select-function-binding-derived/main.svelte        |  9 +++++++++
 8 files changed, 42 insertions(+), 10 deletions(-)
 create mode 100644 .changeset/slow-dots-smile.md
 delete mode 100644 packages/svelte/tests/runtime-runes/samples/derived-forward-ref-leading-comments/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/derived-leading-comments/_config.js
 rename packages/svelte/tests/runtime-runes/samples/{derived-forward-ref-leading-comments => derived-leading-comments}/main.svelte (55%)
 create mode 100644 packages/svelte/tests/runtime-runes/samples/select-function-binding-derived/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/select-function-binding-derived/main.svelte

diff --git a/.changeset/slow-dots-smile.md b/.changeset/slow-dots-smile.md
new file mode 100644
index 0000000000..18d2517b6c
--- /dev/null
+++ b/.changeset/slow-dots-smile.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: transform derived assignments and select function bindings correctly during server-side rendering
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/AssignmentExpression.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/AssignmentExpression.js
index e6a1a86aa8..d555b6bb1d 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/visitors/AssignmentExpression.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/visitors/AssignmentExpression.js
@@ -110,7 +110,7 @@ function build_assignment(operator, left, right, context) {
 			context.visit(build_assignment_value(operator, left, right))
 		);
 
-		return b.call(binding.node, value);
+		return b.call(object, value);
 	}
 
 	return null;
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/element.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/element.js
index 5081d12c80..b4f4facb5d 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/element.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/element.js
@@ -324,10 +324,9 @@ export function build_spread_object(element, attributes, context, transform) {
 				return b.prop('init', b.key(name), value);
 			} else if (attribute.type === 'BindDirective') {
 				const name = get_attribute_name(element, attribute);
+				const expression = /** @type {Expression} */ (context.visit(attribute.expression));
 				const value =
-					attribute.expression.type === 'SequenceExpression'
-						? b.call(attribute.expression.expressions[0])
-						: /** @type {Expression} */ (context.visit(attribute.expression));
+					expression.type === 'SequenceExpression' ? b.call(expression.expressions[0]) : expression;
 
 				return b.prop('init', b.key(name), value);
 			}
diff --git a/packages/svelte/tests/runtime-runes/samples/derived-forward-ref-leading-comments/_config.js b/packages/svelte/tests/runtime-runes/samples/derived-forward-ref-leading-comments/_config.js
deleted file mode 100644
index 204581389d..0000000000
--- a/packages/svelte/tests/runtime-runes/samples/derived-forward-ref-leading-comments/_config.js
+++ /dev/null
@@ -1,6 +0,0 @@
-import { test } from '../../test';
-
-export default test({
-	ssrHtml: '<p>LATER</p> <input value="LATER">',
-	html: '<p>LATER</p> <input>'
-});
diff --git a/packages/svelte/tests/runtime-runes/samples/derived-leading-comments/_config.js b/packages/svelte/tests/runtime-runes/samples/derived-leading-comments/_config.js
new file mode 100644
index 0000000000..2048fbadf7
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/derived-leading-comments/_config.js
@@ -0,0 +1,6 @@
+import { test } from '../../test';
+
+export default test({
+	ssrHtml: '<p>y:y</p> <p>LATER</p> <input value="LATER">',
+	html: '<p>y:y</p> <p>LATER</p> <input>'
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/derived-forward-ref-leading-comments/main.svelte b/packages/svelte/tests/runtime-runes/samples/derived-leading-comments/main.svelte
similarity index 55%
rename from packages/svelte/tests/runtime-runes/samples/derived-forward-ref-leading-comments/main.svelte
rename to packages/svelte/tests/runtime-runes/samples/derived-leading-comments/main.svelte
index f9a1a1a6fb..0424d3fb15 100644
--- a/packages/svelte/tests/runtime-runes/samples/derived-forward-ref-leading-comments/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/derived-leading-comments/main.svelte
@@ -1,4 +1,13 @@
 <script>
+	function write(value) {
+		return foo = value;
+	}
+
+	// a leading comment on the declaration
+	// that spans more than one line
+	let foo = $derived('x');
+	let bar = write('y');
+
 	const ctx = {
 		get later() {
 			return later;
@@ -10,5 +19,6 @@
 	let later = $derived.by(() => 'LATER');
 </script>
 
+<p>{foo}:{bar}</p>
 <p>{ctx.later}</p>
 <input bind:value={later} />
diff --git a/packages/svelte/tests/runtime-runes/samples/select-function-binding-derived/_config.js b/packages/svelte/tests/runtime-runes/samples/select-function-binding-derived/_config.js
new file mode 100644
index 0000000000..13b7302cee
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/select-function-binding-derived/_config.js
@@ -0,0 +1,9 @@
+import { test } from '../../test';
+
+export default test({
+	ssrHtml: '<select><option value="a">a</option><option value="b" selected="">b</option></select>',
+	test({ assert, target }) {
+		const select = /** @type {HTMLSelectElement} */ (target.querySelector('select'));
+		assert.equal(select.value, 'b');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/select-function-binding-derived/main.svelte b/packages/svelte/tests/runtime-runes/samples/select-function-binding-derived/main.svelte
new file mode 100644
index 0000000000..2c14566193
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/select-function-binding-derived/main.svelte
@@ -0,0 +1,9 @@
+<script>
+	let source = $state('b');
+	let value = $derived(source);
+</script>
+
+<select bind:value={() => value, (next) => (value = next)}>
+	<option value="a">a</option>
+	<option value="b">b</option>
+</select>

From c7d8233a5ce70546971413ba84282ba0518a0828 Mon Sep 17 00:00:00 2001
From: "svelte-triage-bot[bot]"
 <316883489+svelte-triage-bot[bot]@users.noreply.github.com>
Date: Tue, 25 Aug 2026 16:47:30 +0200
Subject: [PATCH 14/29] fix: apply ownership mutation ignores to bindings
 (#18718)

Fixes #18715.

Copy ignore comment info to the generated assignment so it's recognized later

---------

Co-authored-by: svelte-triage-bot <team@svelte.com>
Co-authored-by: Simon Holthausen <simon.holthausen@vercel.com>
---
 .changeset/fix-binding-ownership-ignore.md    |  5 ++++
 .../client/visitors/BindDirective.js          | 23 ++++++++-----------
 .../Item.svelte                               |  6 +++++
 .../_config.js                                | 22 ++++++++++++++++++
 .../main.svelte                               |  8 +++++++
 5 files changed, 51 insertions(+), 13 deletions(-)
 create mode 100644 .changeset/fix-binding-ownership-ignore.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/ownership-invalid-mutation-binding-ignore/Item.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/ownership-invalid-mutation-binding-ignore/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/ownership-invalid-mutation-binding-ignore/main.svelte

diff --git a/.changeset/fix-binding-ownership-ignore.md b/.changeset/fix-binding-ownership-ignore.md
new file mode 100644
index 0000000000..13c9c797e3
--- /dev/null
+++ b/.changeset/fix-binding-ownership-ignore.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: apply ownership mutation ignores to binding assignments
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/BindDirective.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/BindDirective.js
index 6838e5006d..c7bf24b3f9 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/BindDirective.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/BindDirective.js
@@ -1,7 +1,7 @@
 /** @import { CallExpression, Expression, Pattern } from 'estree' */
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext } from '../types' */
-import { dev, is_ignored } from '../../../../state.js';
+import { dev, ignore_map, is_ignored } from '../../../../state.js';
 import { is_text_attribute } from '../../../../utils/ast.js';
 import * as b from '#compiler/builders';
 import { binding_properties } from '../../../bindings.js';
@@ -40,9 +40,15 @@ export function BindDirective(node, context) {
 			validate_binding(context.state, node, expression);
 		}
 
-		const assignment = /** @type {Expression} */ (
-			context.visit(b.assignment('=', /** @type {Pattern} */ (node.expression), b.id('$$value')))
+		const raw_assignment = b.assignment(
+			'=',
+			/** @type {Pattern} */ (node.expression),
+			b.id('$$value')
 		);
+		// The assignment is generated, so inherit any ignores attached to the binding
+		ignore_map.set(raw_assignment, ignore_map.get(node) ?? []);
+
+		const assignment = /** @type {Expression} */ (context.visit(raw_assignment));
 
 		if (dev) {
 			// in dev, create named functions, so that `$inspect(...)` delivers
@@ -58,16 +64,7 @@ export function BindDirective(node, context) {
 			get = b.thunk(expression);
 
 			/** @type {Expression | undefined} */
-			set = b.unthunk(
-				b.arrow(
-					[b.id('$$value')],
-					/** @type {Expression} */ (
-						context.visit(
-							b.assignment('=', /** @type {Pattern} */ (node.expression), b.id('$$value'))
-						)
-					)
-				)
-			);
+			set = b.unthunk(b.arrow([b.id('$$value')], assignment));
 
 			if (get === set) {
 				set = undefined;
diff --git a/packages/svelte/tests/runtime-runes/samples/ownership-invalid-mutation-binding-ignore/Item.svelte b/packages/svelte/tests/runtime-runes/samples/ownership-invalid-mutation-binding-ignore/Item.svelte
new file mode 100644
index 0000000000..7beabf6124
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/ownership-invalid-mutation-binding-ignore/Item.svelte
@@ -0,0 +1,6 @@
+<script>
+	let { item } = $props();
+</script>
+
+<!-- svelte-ignore ownership_invalid_mutation -->
+<input bind:value={item.heading} />
diff --git a/packages/svelte/tests/runtime-runes/samples/ownership-invalid-mutation-binding-ignore/_config.js b/packages/svelte/tests/runtime-runes/samples/ownership-invalid-mutation-binding-ignore/_config.js
new file mode 100644
index 0000000000..11229fd13e
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/ownership-invalid-mutation-binding-ignore/_config.js
@@ -0,0 +1,22 @@
+import { flushSync } from 'svelte';
+import { ok, test } from '../../test';
+
+export default test({
+	mode: ['client'],
+	compileOptions: {
+		dev: true
+	},
+	test({ assert, target, warnings }) {
+		const input = target.querySelector('input');
+		const output = target.querySelector('p');
+		ok(input);
+		ok(output);
+
+		input.value = 'renamed';
+		input.dispatchEvent(new Event('input', { bubbles: true }));
+		flushSync();
+
+		assert.equal(output.textContent, 'renamed');
+		assert.deepEqual(warnings, []);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/ownership-invalid-mutation-binding-ignore/main.svelte b/packages/svelte/tests/runtime-runes/samples/ownership-invalid-mutation-binding-ignore/main.svelte
new file mode 100644
index 0000000000..e5b926cb9c
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/ownership-invalid-mutation-binding-ignore/main.svelte
@@ -0,0 +1,8 @@
+<script>
+	import Item from './Item.svelte';
+
+	let item = $state({ heading: 'initial' });
+</script>
+
+<Item {item} />
+<p>{item.heading}</p>

From 955b701df2d4c44215844a07a6112462558c2a1e Mon Sep 17 00:00:00 2001
From: Khaled Waleed <foxilated@gmail.com>
Date: Tue, 25 Aug 2026 17:48:09 +0300
Subject: [PATCH 15/29] fix: measure nested transitions before applying their
 starting styles (#18647)

Fixes #18421 (regression from #16035, which re-broke the #4784
scenario).

Since #16035 the dummy delay animation runs with `fill: 'forwards'`, so
an intro's `t = 0` styles (for `slide`, `height: 0`) apply the moment
the transition is created and stay applied until the real animation
starts a frame later. Transition functions of other elements in the same
batch run after that and measure a collapsed DOM. With nested intros
(the TreeView from the issue), intro effects run deepest-first, so every
ancestor's `slide` captures a height where its children are pinned at 0.
On the issue's REPL every `<ul>` animates `0px -> 36px` (the height of a
single row) and then jumps to its real size when the animation finishes,
which is the "children pop out" behavior from #4784.

The fix waits one microtask before applying the initial styles and
creating the dummy, the same way deferred transitions (`crossfade`)
already work in `animate()`. Everything in the batch measures the DOM
first; the microtask still runs before the next paint, so elements never
render unstyled and the #14732 behavior is preserved. Verified in a real
browser that a delayed intro (`delay: 300`) stays held at `height: 0`
for the whole delay, including the first painted frame.

Most of the diff is the existing dummy/onfinish block moving into
`queue_micro_task`; hiding whitespace shows the actual change.
---
 .changeset/moody-lamps-slide.md               |   5 +
 .../client/dom/elements/transitions.js        | 149 ++++++++++--------
 .../transition-nested-measure/Nested.svelte   |  14 ++
 .../transition-nested-measure/_config.js      |  36 +++++
 .../transition-nested-measure/main.svelte     |  11 ++
 5 files changed, 147 insertions(+), 68 deletions(-)
 create mode 100644 .changeset/moody-lamps-slide.md
 create mode 100644 packages/svelte/tests/runtime-browser/samples/transition-nested-measure/Nested.svelte
 create mode 100644 packages/svelte/tests/runtime-browser/samples/transition-nested-measure/_config.js
 create mode 100644 packages/svelte/tests/runtime-browser/samples/transition-nested-measure/main.svelte

diff --git a/.changeset/moody-lamps-slide.md b/.changeset/moody-lamps-slide.md
new file mode 100644
index 0000000000..5832f12e42
--- /dev/null
+++ b/.changeset/moody-lamps-slide.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: measure nested transitions before applying their starting styles
diff --git a/packages/svelte/src/internal/client/dom/elements/transitions.js b/packages/svelte/src/internal/client/dom/elements/transitions.js
index 7c4d385807..67b177841a 100644
--- a/packages/svelte/src/internal/client/dom/elements/transitions.js
+++ b/packages/svelte/src/internal/client/dom/elements/transitions.js
@@ -337,6 +337,7 @@ export function transition(flags, element, get_fn, get_params) {
  */
 function animate(element, options, counterpart, t2, on_begin, on_finish) {
 	var is_intro = t2 === 1;
+	var aborted = false;
 
 	if (is_function(options)) {
 		// In the case of a deferred transition (such as `crossfade`), `option` will be
@@ -344,7 +345,6 @@ function animate(element, options, counterpart, t2, on_begin, on_finish) {
 		// once the DOM has been updated...
 		/** @type {Animation} */
 		var a;
-		var aborted = false;
 
 		queue_micro_task(() => {
 			if (aborted) return;
@@ -381,99 +381,112 @@ function animate(element, options, counterpart, t2, on_begin, on_finish) {
 
 	const { delay = 0, css, tick, easing = linear } = options;
 
-	var keyframes = [];
+	/** @type {globalThis.Animation} */
+	var animation;
 
-	if (is_intro && counterpart === undefined) {
-		if (tick) {
-			tick(0, 1); // TODO put in nested effect, to avoid interleaved reads/writes?
-		}
+	var get_t = () => 1 - t2;
 
-		if (css) {
-			var styles = css_to_keyframe(css(0, 1));
-			keyframes.push(styles, styles);
-		}
-	}
+	// wait a microtask before applying the initial styles and creating the dummy animation,
+	// so that transitions created in the same batch (e.g. on nested elements) all measure
+	// the DOM first (#18421). this still happens before the next paint, so the element
+	// won't be rendered without styles applied (#14732)
+	queue_micro_task(() => {
+		if (aborted) return;
 
-	var get_t = () => 1 - t2;
+		var keyframes = [];
 
-	// create a dummy animation that lasts as long as the delay (but with whatever devtools
-	// multiplier is in effect). in the common case that it is `0`, we keep it anyway so that
-	// the CSS keyframes aren't created until the DOM is updated
-	//
-	// fill forwards to prevent the element from rendering without styles applied
-	// see https://github.com/sveltejs/svelte/issues/14732
-	var animation = element.animate(keyframes, { duration: delay, fill: 'forwards' });
+		if (is_intro && counterpart === undefined) {
+			if (tick) {
+				tick(0, 1); // TODO put in nested effect, to avoid interleaved reads/writes?
+			}
 
-	animation.onfinish = () => {
-		// remove dummy animation from the stack to prevent conflict with main animation
-		animation.cancel();
+			if (css) {
+				var styles = css_to_keyframe(css(0, 1));
+				keyframes.push(styles, styles);
+			}
+		}
 
-		on_begin();
+		// create a dummy animation that lasts as long as the delay (but with whatever devtools
+		// multiplier is in effect). in the common case that it is `0`, we keep it anyway so that
+		// the CSS keyframes aren't created until the DOM is updated
+		//
+		// fill forwards to prevent the element from rendering without styles applied
+		// see https://github.com/sveltejs/svelte/issues/14732
+		animation = element.animate(keyframes, { duration: delay, fill: 'forwards' });
 
-		// for bidirectional transitions, we start from the current position,
-		// rather than doing a full intro/outro
-		var t1 = counterpart?.t() ?? 1 - t2;
-		counterpart?.abort();
+		animation.onfinish = () => {
+			// remove dummy animation from the stack to prevent conflict with main animation
+			animation.cancel();
 
-		var delta = t2 - t1;
-		var duration = /** @type {number} */ (options.duration) * Math.abs(delta);
-		var keyframes = [];
+			on_begin();
 
-		if (duration > 0) {
-			/**
-			 * Whether or not the CSS includes `overflow: hidden`, in which case we need to
-			 * add it as an inline style to work around a Safari <18 bug
-			 * TODO 6.0 remove this, if possible
-			 */
-			var needs_overflow_hidden = false;
+			// for bidirectional transitions, we start from the current position,
+			// rather than doing a full intro/outro
+			var t1 = counterpart?.t() ?? 1 - t2;
+			counterpart?.abort();
 
-			if (css) {
-				var n = Math.ceil(duration / (1000 / 60)); // `n` must be an integer, or we risk missing the `t2` value
+			var delta = t2 - t1;
+			var duration = /** @type {number} */ (options.duration) * Math.abs(delta);
+			var keyframes = [];
+
+			if (duration > 0) {
+				/**
+				 * Whether or not the CSS includes `overflow: hidden`, in which case we need to
+				 * add it as an inline style to work around a Safari <18 bug
+				 * TODO 6.0 remove this, if possible
+				 */
+				var needs_overflow_hidden = false;
 
-				for (var i = 0; i <= n; i += 1) {
-					var t = t1 + delta * easing(i / n);
-					var styles = css_to_keyframe(css(t, 1 - t));
-					keyframes.push(styles);
+				if (css) {
+					var n = Math.ceil(duration / (1000 / 60)); // `n` must be an integer, or we risk missing the `t2` value
 
-					needs_overflow_hidden ||= styles.overflow === 'hidden';
+					for (var i = 0; i <= n; i += 1) {
+						var t = t1 + delta * easing(i / n);
+						var styles = css_to_keyframe(css(t, 1 - t));
+						keyframes.push(styles);
+
+						needs_overflow_hidden ||= styles.overflow === 'hidden';
+					}
 				}
-			}
 
-			if (needs_overflow_hidden) {
-				/** @type {HTMLElement} */ (element).style.overflow = 'hidden';
-			}
+				if (needs_overflow_hidden) {
+					/** @type {HTMLElement} */ (element).style.overflow = 'hidden';
+				}
 
-			get_t = () => {
-				var time = /** @type {number} */ (
-					/** @type {globalThis.Animation} */ (animation).currentTime
-				);
+				get_t = () => {
+					var time = /** @type {number} */ (
+						/** @type {globalThis.Animation} */ (animation).currentTime
+					);
 
-				return t1 + delta * easing(time / duration);
-			};
+					return t1 + delta * easing(time / duration);
+				};
 
-			if (tick) {
-				loop(() => {
-					if (animation.playState !== 'running') return false;
+				if (tick) {
+					loop(() => {
+						if (animation.playState !== 'running') return false;
 
-					var t = get_t();
-					tick(t, 1 - t);
+						var t = get_t();
+						tick(t, 1 - t);
 
-					return true;
-				});
+						return true;
+					});
+				}
 			}
-		}
 
-		animation = element.animate(keyframes, { duration, fill: 'forwards' });
+			animation = element.animate(keyframes, { duration, fill: 'forwards' });
 
-		animation.onfinish = () => {
-			get_t = () => t2;
-			tick?.(t2, 1 - t2);
-			on_finish();
+			animation.onfinish = () => {
+				get_t = () => t2;
+				tick?.(t2, 1 - t2);
+				on_finish();
+			};
 		};
-	};
+	});
 
 	return {
 		abort: () => {
+			aborted = true;
+
 			if (animation) {
 				animation.cancel();
 				// This prevents memory leaks in Chromium
diff --git a/packages/svelte/tests/runtime-browser/samples/transition-nested-measure/Nested.svelte b/packages/svelte/tests/runtime-browser/samples/transition-nested-measure/Nested.svelte
new file mode 100644
index 0000000000..eeb325059f
--- /dev/null
+++ b/packages/svelte/tests/runtime-browser/samples/transition-nested-measure/Nested.svelte
@@ -0,0 +1,14 @@
+<script>
+	import Nested from './Nested.svelte';
+	import { slide } from 'svelte/transition';
+
+	let { depth } = $props();
+</script>
+
+<div class="level-{depth}" in:slide|global={{ duration: 100 }}>
+	{#if depth > 0}
+		<Nested depth={depth - 1} />
+	{:else}
+		<div style="height: 100px">leaf</div>
+	{/if}
+</div>
diff --git a/packages/svelte/tests/runtime-browser/samples/transition-nested-measure/_config.js b/packages/svelte/tests/runtime-browser/samples/transition-nested-measure/_config.js
new file mode 100644
index 0000000000..00e5cb02a2
--- /dev/null
+++ b/packages/svelte/tests/runtime-browser/samples/transition-nested-measure/_config.js
@@ -0,0 +1,36 @@
+import { test } from '../../assert';
+
+export default test({
+	async test({ assert, target }) {
+		const button = target.querySelector('button');
+		button?.click();
+
+		// wait for the transition's keyframes to be created
+		const animation = await new Promise((resolve, reject) => {
+			const start = performance.now();
+
+			function check() {
+				const outer = target.querySelector('.level-2');
+				const animation = outer
+					?.getAnimations()
+					.find((a) => a.effect?.getTiming().duration === 100);
+
+				if (animation) {
+					resolve(animation);
+				} else if (performance.now() - start > 2000) {
+					reject(new Error('timed out waiting for the transition to start'));
+				} else {
+					requestAnimationFrame(check);
+				}
+			}
+
+			check();
+		});
+
+		// the outermost `slide` must have measured the element with its
+		// descendants at their natural size, not collapsed to zero by their
+		// own starting styles (#18421)
+		const keyframes = animation.effect?.getKeyframes() ?? [];
+		assert.equal(keyframes[keyframes.length - 1].height, '100px');
+	}
+});
diff --git a/packages/svelte/tests/runtime-browser/samples/transition-nested-measure/main.svelte b/packages/svelte/tests/runtime-browser/samples/transition-nested-measure/main.svelte
new file mode 100644
index 0000000000..a64a0cd2f4
--- /dev/null
+++ b/packages/svelte/tests/runtime-browser/samples/transition-nested-measure/main.svelte
@@ -0,0 +1,11 @@
+<script>
+	import Nested from './Nested.svelte';
+
+	let visible = $state(false);
+</script>
+
+<button onclick={() => (visible = !visible)}>toggle</button>
+
+{#if visible}
+	<Nested depth={2} />
+{/if}

From 0f458d5abaafaeaaeb15009700e6f7747c8f4121 Mon Sep 17 00:00:00 2001
From: Bao Nguyen <39545125+giaBaoJS@users.noreply.github.com>
Date: Tue, 25 Aug 2026 22:43:16 +0700
Subject: [PATCH 16/29] fix: report `derived_invalid_export` for `export let x
 = $derived(...)` (#18692)

Fixes #15842

Run the more targeted validations first

---------

Co-authored-by: Simon Holthausen <simon.holthausen@vercel.com>
---
 .changeset/heavy-pumas-report.md              |  5 +++++
 .../visitors/ExportNamedDeclaration.js        | 20 +++++++++----------
 .../runes-export-let-derived/_config.js       |  9 +++++++++
 .../runes-export-let-derived/main.svelte      |  4 ++++
 4 files changed, 28 insertions(+), 10 deletions(-)
 create mode 100644 .changeset/heavy-pumas-report.md
 create mode 100644 packages/svelte/tests/compiler-errors/samples/runes-export-let-derived/_config.js
 create mode 100644 packages/svelte/tests/compiler-errors/samples/runes-export-let-derived/main.svelte

diff --git a/.changeset/heavy-pumas-report.md b/.changeset/heavy-pumas-report.md
new file mode 100644
index 0000000000..71a9422828
--- /dev/null
+++ b/.changeset/heavy-pumas-report.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: report `derived_invalid_export` for `export let x = $derived(...)` in runes mode
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 5b8d9ba053..dec6ebe2b4 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/ExportNamedDeclaration.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/ExportNamedDeclaration.js
@@ -1,4 +1,4 @@
-/** @import { ExportNamedDeclaration, Identifier } from 'estree' */
+/** @import { ExportNamedDeclaration, Identifier, VariableDeclaration } from 'estree' */
 /** @import { Context } from '../types' */
 import * as e from '../../../errors.js';
 import { extract_identifiers } from '../../../utils/ast.js';
@@ -23,15 +23,6 @@ export function ExportNamedDeclaration(node, context) {
 	}
 
 	if (node.declaration?.type === 'VariableDeclaration') {
-		// in runes mode, forbid `export let`
-		if (
-			context.state.analysis.runes &&
-			context.state.ast_type === 'instance' &&
-			node.declaration.kind === 'let'
-		) {
-			e.legacy_export_invalid(node);
-		}
-
 		for (const declarator of node.declaration.declarations) {
 			for (const id of extract_identifiers(declarator.id)) {
 				const binding = context.state.scope.get(id.name);
@@ -46,6 +37,15 @@ export function ExportNamedDeclaration(node, context) {
 				}
 			}
 		}
+
+		// in runes mode, forbid `export let`
+		if (
+			context.state.analysis.runes &&
+			context.state.ast_type === 'instance' &&
+			node.declaration.kind === 'let'
+		) {
+			e.legacy_export_invalid(node);
+		}
 	}
 
 	if (context.state.analysis.runes) {
diff --git a/packages/svelte/tests/compiler-errors/samples/runes-export-let-derived/_config.js b/packages/svelte/tests/compiler-errors/samples/runes-export-let-derived/_config.js
new file mode 100644
index 0000000000..852f56ebcc
--- /dev/null
+++ b/packages/svelte/tests/compiler-errors/samples/runes-export-let-derived/_config.js
@@ -0,0 +1,9 @@
+import { test } from '../../test';
+
+export default test({
+	error: {
+		code: 'derived_invalid_export',
+		message:
+			'Cannot export derived state from a module. To expose the current derived value, export a function returning its value'
+	}
+});
diff --git a/packages/svelte/tests/compiler-errors/samples/runes-export-let-derived/main.svelte b/packages/svelte/tests/compiler-errors/samples/runes-export-let-derived/main.svelte
new file mode 100644
index 0000000000..512caf75f8
--- /dev/null
+++ b/packages/svelte/tests/compiler-errors/samples/runes-export-let-derived/main.svelte
@@ -0,0 +1,4 @@
+<script>
+	let count = $state(0);
+	export let double = $derived(count * 2);
+</script>

From bfc9b65b3d3c929046ba3ff594d4ae4ac300ffea Mon Sep 17 00:00:00 2001
From: Sushanth012 <146400678+Sushanth012@users.noreply.github.com>
Date: Tue, 25 Aug 2026 08:48:20 -0700
Subject: [PATCH 17/29] docs: clarify mounting components with context (#18515)

Closes #18462.
---
 documentation/docs/06-runtime/02-context.md | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/documentation/docs/06-runtime/02-context.md b/documentation/docs/06-runtime/02-context.md
index 439272df8f..a1e0347b7b 100644
--- a/documentation/docs/06-runtime/02-context.md
+++ b/documentation/docs/06-runtime/02-context.md
@@ -165,9 +165,9 @@ Svelte will warn you if you get it wrong.
 
 Similarly, to pass primitive values through context, use functions as described in [Passing state into functions]($state#Passing-state-into-functions).
 
-## Component testing
+## Mounting components with context
 
-When writing [component tests](testing#Unit-and-component-tests-with-Vitest-Component-testing), it can be useful to create a wrapper component that sets the context in order to check the behaviour of a component that uses it. As of version 5.49, you can do this sort of thing:
+To mount a component with specific context, create a wrapper component that sets the context before rendering the component. This is useful for [component tests](testing#Unit-and-component-tests-with-Vitest-Component-testing), or any other scenario that needs to provide context through `mount`. As of version 5.49, you can do this sort of thing:
 
 ```js
 import { mount, unmount } from 'svelte';
@@ -193,6 +193,8 @@ test('MyComponent', () => {
 
 This approach also works with [`hydrate`](imperative-component-api#hydrate) and [`render`](imperative-component-api#render).
 
+The context set by the wrapper only applies to that mounted component tree. Each call to `mount`, `hydrate` or `render` creates a separate wrapper instance, so the context does not leak into other mounted components.
+
 ## Replacing global state
 
 When you have state shared by many different components, you might be tempted to put it in its own module and just import it wherever it's needed:

From aadc97ce1be06e3dad4b98469ac385a07f34fd06 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 25 Aug 2026 12:06:14 -0400
Subject: [PATCH 18/29] fix: simplify boundary error handling and handle
 hydration errors correctly (#18539)

remove the `catch` clause in `this.#run` - in two locations there's already a catch, and in the hydration-location we have to add special handling for hydration errors.

---------

Co-authored-by: Simon Holthausen <simon.holthausen@vercel.com>
---
 .../internal/client/dom/blocks/boundary.js    | 33 ++++++++++++-------
 .../async-error-boundary-5/Child.svelte       |  7 ++++
 .../samples/async-error-boundary-5/_config.js | 14 ++++++++
 .../async-error-boundary-5/main.svelte        | 24 ++++++++++++++
 4 files changed, 66 insertions(+), 12 deletions(-)
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-error-boundary-5/Child.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-error-boundary-5/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-error-boundary-5/main.svelte

diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 4f655a3695..fd6bbdf5b4 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -1,14 +1,8 @@
 /** @import { Effect, Source, TemplateNode, } from '#client' */
-import {
-	BOUNDARY_EFFECT,
-	DIRTY,
-	EFFECT_PRESERVED,
-	EFFECT_TRANSPARENT,
-	MAYBE_DIRTY
-} from '#client/constants';
+import { BOUNDARY_EFFECT, EFFECT_PRESERVED, EFFECT_TRANSPARENT } from '#client/constants';
 import { HYDRATION_START_ELSE, HYDRATION_START_FAILED } from '../../../../constants.js';
 import { component_context, set_component_context } from '../../context.js';
-import { handle_error, invoke_error_boundary } from '../../error-handling.js';
+import { invoke_error_boundary } from '../../error-handling.js';
 import {
 	block,
 	branch,
@@ -271,13 +265,31 @@ export class Boundary {
 		queue_micro_task(() => {
 			var fragment = (this.#offscreen_fragment = document.createDocumentFragment());
 			var anchor = create_text();
+			var handled = false;
 
 			fragment.append(anchor);
 
 			this.#main_effect = this.#run(() => {
-				return branch(() => this.#children(anchor));
+				try {
+					return branch(() => this.#children(anchor));
+				} catch (error) {
+					try {
+						this.error(error);
+						handled = true;
+					} catch (error) {
+						invoke_error_boundary(error, this.#effect.parent);
+					}
+
+					return null;
+				}
 			});
 
+			if (this.#main_effect === null) {
+				this.#offscreen_fragment = null;
+				if (handled) this.#resolve(/** @type {Batch} */ (current_batch));
+				return;
+			}
+
 			if (this.#pending_count === 0) {
 				this.#anchor.before(fragment);
 				this.#offscreen_fragment = null;
@@ -362,9 +374,6 @@ export class Boundary {
 		try {
 			Batch.ensure();
 			return fn();
-		} catch (e) {
-			handle_error(e);
-			return null;
 		} finally {
 			set_active_effect(previous_effect);
 			set_active_reaction(previous_reaction);
diff --git a/packages/svelte/tests/runtime-runes/samples/async-error-boundary-5/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-error-boundary-5/Child.svelte
new file mode 100644
index 0000000000..a49033a8cc
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-error-boundary-5/Child.svelte
@@ -0,0 +1,7 @@
+<script>
+	const { environment } = $props();
+
+	if (environment === 'client') {
+		throw new Error('oops');
+	}
+</script>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-error-boundary-5/_config.js b/packages/svelte/tests/runtime-runes/samples/async-error-boundary-5/_config.js
new file mode 100644
index 0000000000..29e470e46f
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-error-boundary-5/_config.js
@@ -0,0 +1,14 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['hydrate'],
+	server_props: { environment: 'server' },
+	props: { environment: 'client' },
+	ssrHtml: 'loading inner loading nested',
+
+	async test({ assert, target }) {
+		await tick();
+		assert.htmlEqual(target.innerHTML, 'inner failed: oops outer failed: oops');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-error-boundary-5/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-error-boundary-5/main.svelte
new file mode 100644
index 0000000000..16a54630d0
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-error-boundary-5/main.svelte
@@ -0,0 +1,24 @@
+<script>
+	import Child from './Child.svelte';
+
+	const { environment } = $props();
+</script>
+
+<svelte:boundary>
+	<Child {environment} />
+	{await new Promise(() => {})}
+
+	{#snippet pending()}loading inner{/snippet}
+	{#snippet failed(error)}inner failed: {error.message}{/snippet}
+</svelte:boundary>
+
+<svelte:boundary>
+	<svelte:boundary>
+		<Child {environment} />
+		{await new Promise(() => {})}
+
+		{#snippet pending()}loading nested{/snippet}
+	</svelte:boundary>
+
+	{#snippet failed(error)}outer failed: {error.message}{/snippet}
+</svelte:boundary>

From 4d5139552dac8593c5e020846fa7ce8e96ea97b7 Mon Sep 17 00:00:00 2001
From: Nic Polumeyv <nicolas.polum@outlook.com>
Date: Tue, 25 Aug 2026 15:51:14 -0400
Subject: [PATCH 19/29] fix: block declaration tags on async values read inside
 closures (#18533)

Fixes #18469

Declaration tags collect blockers from `metadata.expression.dependencies`, which only sees eager reads, so a `$derived` reading an async declaration inside a closure gets no blocker and evaluates while the value is still `undefined`. Align with template expressions which already collect blockers from `references`

---------

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
Co-authored-by: Simon Holthausen <simon.holthausen@vercel.com>
---
 .changeset/thick-plums-wave.md                  |  5 +++++
 .../phases/2-analyze/visitors/DeclarationTag.js |  3 ++-
 .../client/visitors/DeclarationTag.js           |  2 +-
 .../server/visitors/DeclarationTag.js           |  2 +-
 packages/svelte/tests/runtime-legacy/shared.ts  |  6 +++---
 .../samples/async-const-closure-read/_config.js | 10 ++++++++++
 .../async-const-closure-read/main.svelte        | 12 ++++++++++++
 .../async-declaration-closure-read/_config.js   | 11 +++++++++++
 .../async-declaration-closure-read/main.svelte  | 17 +++++++++++++++++
 9 files changed, 62 insertions(+), 6 deletions(-)
 create mode 100644 .changeset/thick-plums-wave.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-const-closure-read/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-const-closure-read/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-declaration-closure-read/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-declaration-closure-read/main.svelte

diff --git a/.changeset/thick-plums-wave.md b/.changeset/thick-plums-wave.md
new file mode 100644
index 0000000000..d8b454bb90
--- /dev/null
+++ b/.changeset/thick-plums-wave.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: block declaration tags and `{@const}` on async values read inside closures
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/DeclarationTag.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/DeclarationTag.js
index 52e9480838..2f72b16c72 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/DeclarationTag.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/DeclarationTag.js
@@ -43,7 +43,8 @@ export function DeclarationTag(node, context) {
  */
 export function mark_async_declaration(context, metadata, declarations) {
 	const has_await = metadata.expression.has_await;
-	const blockers = [...metadata.expression.dependencies]
+	// reads inside closures must block too, like they do in template expressions
+	const blockers = [...metadata.expression.references]
 		.map((dep) => dep.blocker)
 		.filter((b) => b !== null && b.object !== context.state.async_consts?.id);
 
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/DeclarationTag.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/DeclarationTag.js
index 3f78b53c90..ceb81a468d 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/DeclarationTag.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/DeclarationTag.js
@@ -71,7 +71,7 @@ export function add_async_declaration(context, metadata, ids, assignments, kind
 		context.state.consts.push(kind === 'var' ? b.var(id.name) : b.let(id.name));
 	}
 
-	const blockers = [...metadata.expression.dependencies]
+	const blockers = [...metadata.expression.references]
 		.map((dep) => dep.blocker)
 		.filter((b) => b !== null && b.object !== context.state.async_consts?.id);
 
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/DeclarationTag.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/DeclarationTag.js
index 8338700c0b..3fbff7167b 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/visitors/DeclarationTag.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/visitors/DeclarationTag.js
@@ -66,7 +66,7 @@ export function add_async_declaration(context, metadata, ids, assignments, kind
 		context.state.init.push(kind === 'var' ? b.var(id.name) : b.let(id.name));
 	}
 
-	const blockers = [...metadata.expression.dependencies]
+	const blockers = [...metadata.expression.references]
 		.map((dep) => dep.blocker)
 		.filter((b) => b !== null && b.object !== context.state.async_consts?.id);
 
diff --git a/packages/svelte/tests/runtime-legacy/shared.ts b/packages/svelte/tests/runtime-legacy/shared.ts
index 5c2d0dfe1c..de6749c0e7 100644
--- a/packages/svelte/tests/runtime-legacy/shared.ts
+++ b/packages/svelte/tests/runtime-legacy/shared.ts
@@ -177,11 +177,11 @@ export function runtime_suite(runes: boolean) {
 		['dom', 'hydrate', 'ssr', 'async-ssr'],
 		(variant, config, test_name) => {
 			if (!async_mode && (config.skip_no_async || test_name.startsWith('async-'))) {
-				return true;
+				return 'no-test';
 			}
 
 			if (async_mode && config.skip_async) {
-				return true;
+				return 'no-test';
 			}
 
 			if (variant === 'hydrate') {
@@ -195,9 +195,9 @@ export function runtime_suite(runes: boolean) {
 			) {
 				return 'no-test';
 			}
-
 			if (variant === 'ssr') {
 				if (
+					(test_name.startsWith('async-') && !config.mode?.includes('server')) ||
 					(config.mode && !config.mode.includes('server')) ||
 					(!config.test_ssr &&
 						config.html === undefined &&
diff --git a/packages/svelte/tests/runtime-runes/samples/async-const-closure-read/_config.js b/packages/svelte/tests/runtime-runes/samples/async-const-closure-read/_config.js
new file mode 100644
index 0000000000..be0e3c7f40
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-const-closure-read/_config.js
@@ -0,0 +1,10 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+// #18469 — a @const in a nested snippet reading an async declaration through a closure must block on it
+export default test({
+	async test({ assert, target }) {
+		await tick();
+		assert.htmlEqual(target.innerHTML, '<p>true</p> <p>false</p>');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-const-closure-read/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-const-closure-read/main.svelte
new file mode 100644
index 0000000000..881455ec27
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-const-closure-read/main.svelte
@@ -0,0 +1,12 @@
+<script>
+	async function getValue() {
+		return new Set(['a', 'b', 'c']);
+	}
+
+	const value = await getValue();
+</script>
+
+{#each [['a', 'b'], ['a', 'x']] as keys}
+	{@const all_present = keys.every((k) => value.has(k))}
+	<p>{all_present}</p>
+{/each}
diff --git a/packages/svelte/tests/runtime-runes/samples/async-declaration-closure-read/_config.js b/packages/svelte/tests/runtime-runes/samples/async-declaration-closure-read/_config.js
new file mode 100644
index 0000000000..6a10f6928a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-declaration-closure-read/_config.js
@@ -0,0 +1,11 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+// #18469 — a sync $derived in a nested snippet reading an async declaration through a closure must block on it
+export default test({
+	ssrHtml: '<p>true</p> <p>false</p>',
+	async test({ assert, target }) {
+		await tick();
+		assert.htmlEqual(target.innerHTML, '<p>true</p> <p>false</p>');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-declaration-closure-read/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-declaration-closure-read/main.svelte
new file mode 100644
index 0000000000..ddd9a10b04
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-declaration-closure-read/main.svelte
@@ -0,0 +1,17 @@
+<script>
+	async function getValue() {
+		return new Set(['a', 'b', 'c']);
+	}
+</script>
+
+{#snippet outer()}
+	{const value = $derived(await getValue())}
+	{#snippet inner(keys)}
+		{const all_present = $derived(keys.every((k) => value.has(k)))}
+		<p>{all_present}</p>
+	{/snippet}
+	{@render inner(['a', 'b'])}
+	{@render inner(['a', 'x'])}
+{/snippet}
+
+{@render outer()}

From 864de81bb67372af9783081b039d946dcdb5aabf Mon Sep 17 00:00:00 2001
From: Nic Polumeyv <nicolas.polum@outlook.com>
Date: Wed, 26 Aug 2026 04:10:48 -0400
Subject: [PATCH 20/29] fix: keep the current selection of a `<select>` when
 its `defaultValue` is applied (#18719)

Also ensure init_select isn't called multiple times

Follow-up to #18591.
---
 .../client/visitors/RegularElement.js         | 36 ++++++-----
 .../client/dom/elements/attributes.js         |  4 +-
 .../client/dom/elements/bindings/select.js    | 64 ++++++++++++-------
 .../form-default-value-select/_config.js      |  2 +-
 .../_config.js                                | 52 +++++++++++++++
 .../main.svelte                               | 37 +++++++++++
 .../_config.js                                | 30 +++++++++
 .../main.svelte                               | 21 ++++++
 8 files changed, 204 insertions(+), 42 deletions(-)
 create mode 100644 packages/svelte/tests/runtime-runes/samples/select-default-value-preserve-selection/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/select-default-value-preserve-selection/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/select-default-value-single-observer/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/select-default-value-single-observer/main.svelte

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 401891b41b..adc9ec72dd 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
@@ -520,20 +520,28 @@ export function RegularElement(node, context) {
 	// deferred from the attribute loop above, so that the options it selects from
 	// have been created and had their values assigned
 	if (!has_spread && name === 'select') {
-		for (const attribute of /** @type {AST.Attribute[]} */ (attributes)) {
-			if (get_attribute_name(node, attribute) === 'defaultValue') {
-				const { value, has_state } = build_attribute_value(attribute.value, context, (v, m) =>
-					context.state.memoizer.add(v, m)
-				);
+		const default_value = /** @type {AST.Attribute[]} */ (attributes).find(
+			(attribute) => get_attribute_name(node, attribute) === 'defaultValue'
+		);
 
-				const update = b.stmt(b.call('$.set_default_select_value', node_id, value));
+		if (default_value) {
+			const { value, has_state } = build_attribute_value(default_value.value, context, (v, m) =>
+				context.state.memoizer.add(v, m)
+			);
 
-				(has_state ? context.state.update : context.state.init).push(update);
-				if (!bindings.has('value')) {
-					context.state.init.push(b.stmt(b.call('$.init_select', node_id)));
-				}
-				break;
-			}
+			(has_state ? context.state.update : context.state.init).push(
+				b.stmt(b.call('$.set_default_select_value', node_id, value))
+			);
+		}
+
+		const value_attribute = lookup.get('value');
+		const dynamic_value =
+			value_attribute !== undefined &&
+			value_attribute.value !== true &&
+			!is_text_attribute(value_attribute);
+
+		if (default_value || dynamic_value || bindings.has('value')) {
+			context.state.init.push(b.stmt(b.call('$.init_select', node_id)));
 		}
 	}
 
@@ -772,10 +780,6 @@ function build_element_special_value_attribute(
 	} else {
 		state.init.push(build_update(value));
 	}
-
-	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 7439db56e9..0fe1b8b2d3 100644
--- a/packages/svelte/src/internal/client/dom/elements/attributes.js
+++ b/packages/svelte/src/internal/client/dom/elements/attributes.js
@@ -525,7 +525,7 @@ export function attribute_effect(
 				var select = /** @type {HTMLSelectElement} */ (element);
 
 				if ('defaultValue' in next) {
-					set_default_select_value(select, next.defaultValue, false);
+					set_default_select_value(select, next.defaultValue);
 				}
 
 				if ('value' in next) {
@@ -558,7 +558,7 @@ export function attribute_effect(
 				var attrs = /** @type {Record<string | symbol, any>} */ (prev);
 
 				if ('defaultValue' in attrs) {
-					set_default_select_value(select, attrs.defaultValue, true);
+					set_default_select_value(select, attrs.defaultValue);
 				}
 
 				select_option(select, attrs.value, 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 fd1ebb92b8..cac7531ed2 100644
--- a/packages/svelte/src/internal/client/dom/elements/bindings/select.js
+++ b/packages/svelte/src/internal/client/dom/elements/bindings/select.js
@@ -20,33 +20,54 @@ export function set_selected(option, selected) {
 }
 
 /**
- * Sets the options a form reset should restore without changing the current selection.
- * The initial call is allowed to establish the current selection when no value exists.
+ * Sets the options a form reset should restore. The first call selects
+ * them if nothing has set a value, later calls leave the current selection alone.
  * @param {HTMLSelectElement} select
  * @param {any} value
- * @param {boolean} [mounting]
  */
-export function set_default_select_value(select, value, mounting = !('__defaultValue' in select)) {
-	// The DOM cannot recover unmatched, object or multiple defaults from selected options.
-	// Keep the requested value so option mutations can reapply it; property presence also
-	// distinguishes the initial application from later updates when the value is undefined.
+export function set_default_select_value(select, value) {
+	var mounting = !('__defaultValue' in select);
+	// @ts-expect-error
+	if (!mounting && select.__defaultValue === value) return;
 	// @ts-expect-error
 	select.__defaultValue = value;
-	var values = select.multiple ? (value == null ? [] : value) : null;
+	apply_default_select_value(select, !mounting || '__value' in select);
+}
 
-	if (select.multiple && !is_array(values)) return;
-	var selected = !mounting || '__value' in select ? new Set(select.selectedOptions) : null;
+/**
+ * Marks the options matching `__defaultValue` as selected. Without `preserve`
+ * a newly matching option gets selected, as an inserted `<option selected>` would.
+ * @param {HTMLSelectElement} select
+ * @param {boolean} preserve
+ */
+function apply_default_select_value(select, preserve) {
+	// @ts-expect-error
+	var value = select.__defaultValue;
+	var multiple = select.multiple;
+	var values = multiple ? value ?? [] : null;
+
+	if (multiple && !is_array(values)) return;
+
+	var index = select.selectedIndex;
+	var selected = preserve && multiple ? new Set(select.selectedOptions) : null;
 
 	for (var option of select.options) {
 		var option_value = get_option_value(option);
-		var is_selected = select.multiple
-			? /** @type {any[]} */ (values).includes(option_value)
-			: is(option_value, value);
-		set_selected(option, is_selected);
+		set_selected(
+			option,
+			multiple ? /** @type {any[]} */ (values).includes(option_value) : is(option_value, value)
+		);
 	}
 
+	if (!preserve) return;
+
 	if (selected !== null) {
-		for (option of select.options) option.selected = selected.has(option);
+		for (option of select.options) {
+			var was_selected = selected.has(option);
+			if (option.selected !== was_selected) option.selected = was_selected;
+		}
+	} else if (select.selectedIndex !== index) {
+		select.selectedIndex = index;
 	}
 }
 
@@ -91,11 +112,10 @@ export function select_option(select, value, mounting = false) {
 }
 
 /**
- * Selects the correct option(s) if `value` is given,
- * and then sets up a mutation observer to sync the
- * current selection to the dom when it changes. Such
- * changes could for example occur when options are
- * inside an `#each` block.
+ * Sets up a mutation observer to sync the current selection
+ * and default to the dom when the options change, for example
+ * when they are inside an `#each` block. Called once per `<select>`,
+ * by the compiled output or by `attribute_effect` for spreads.
  * @param {HTMLSelectElement} select
  */
 export function init_select(select) {
@@ -107,7 +127,7 @@ export function init_select(select) {
 		if (entries.every(is_selectedcontent_mutation)) return;
 
 		if ('__defaultValue' in select) {
-			set_default_select_value(select, select.__defaultValue, false);
+			apply_default_select_value(select, false);
 		}
 
 		if ('__value' in select) {
@@ -204,8 +224,6 @@ export function bind_select_value(select, get, set = get) {
 		select.__value = value;
 		mounting = false;
 	});
-
-	init_select(select);
 }
 
 /** @param {HTMLOptionElement} option */
diff --git a/packages/svelte/tests/runtime-runes/samples/form-default-value-select/_config.js b/packages/svelte/tests/runtime-runes/samples/form-default-value-select/_config.js
index 5d0c964969..784d20a0ce 100644
--- a/packages/svelte/tests/runtime-runes/samples/form-default-value-select/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/form-default-value-select/_config.js
@@ -62,7 +62,7 @@ export default test({
 		button('add').click();
 		flushSync();
 		await Promise.resolve();
-		check(selects[3], [true, false]);
+		check(selects[3], [false, true]);
 		assert.equal(selects[3].options[1].defaultSelected, true);
 
 		reset.click();
diff --git a/packages/svelte/tests/runtime-runes/samples/select-default-value-preserve-selection/_config.js b/packages/svelte/tests/runtime-runes/samples/select-default-value-preserve-selection/_config.js
new file mode 100644
index 0000000000..d409732ab8
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/select-default-value-preserve-selection/_config.js
@@ -0,0 +1,52 @@
+import { flushSync } from 'svelte';
+import { ok, test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const [nothing, unmatched, spread, late, touched] = target.querySelectorAll('select');
+		const [change_default, change_spread, load, add] = target.querySelectorAll('button');
+		const p = target.querySelector('p');
+		ok(p);
+
+		assert.equal(nothing.selectedIndex, -1);
+		assert.equal(unmatched.selectedIndex, -1);
+		assert.equal(spread.selectedIndex, -1);
+		assert.equal(late.selectedIndex, -1);
+		assert.equal(touched.value, 'b');
+
+		change_default.click();
+		change_spread.click();
+		flushSync();
+
+		assert.equal(nothing.selectedIndex, -1);
+		assert.equal(unmatched.selectedIndex, -1);
+		assert.equal(spread.selectedIndex, -1);
+		assert.equal(spread.className, 'two');
+		assert.htmlEqual(p.innerHTML, 'zzz null');
+		assert.deepEqual(
+			[...nothing.options].map((option) => option.defaultSelected),
+			[true, false]
+		);
+
+		// a default change never moves the current selection
+		assert.equal(touched.value, 'b');
+
+		// a default whose option arrives later selects it
+		load.click();
+		flushSync();
+		await Promise.resolve();
+		assert.equal(late.value, 'b');
+
+		// a user selection survives option mutations and default changes
+		touched.options[2].selected = true;
+		touched.dispatchEvent(new Event('change', { bubbles: true }));
+		add.click();
+		flushSync();
+		await Promise.resolve();
+		assert.equal(touched.value, 'c');
+		assert.deepEqual(
+			[...touched.options].map((option) => option.defaultSelected),
+			[true, false, false, false]
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/select-default-value-preserve-selection/main.svelte b/packages/svelte/tests/runtime-runes/samples/select-default-value-preserve-selection/main.svelte
new file mode 100644
index 0000000000..c7fdea482c
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/select-default-value-preserve-selection/main.svelte
@@ -0,0 +1,37 @@
+<script>
+	let unmatched = $state('zzz');
+	let nothing = $state(null);
+	let defaultValue = $state('b');
+	let props = $state({ defaultValue: 'b', class: 'one' });
+	let late = $state([]);
+	let options = $state(['a', 'b', 'c']);
+</script>
+
+<select value={null} {defaultValue}>
+	<option value="a">A</option>
+	<option value="b">B</option>
+</select>
+
+<select bind:value={unmatched} {defaultValue}>
+	<option value="a">A</option>
+	<option value="b">B</option>
+</select>
+
+<select {...props} bind:value={nothing}>
+	<option value="a">A</option>
+	<option value="b">B</option>
+</select>
+
+<select defaultValue="b">
+	{#each late as option}<option value={option}>{option}</option>{/each}
+</select>
+
+<select {defaultValue}>
+	{#each options as option}<option value={option}>{option}</option>{/each}
+</select>
+
+<button onclick={() => (defaultValue = 'a')}>change default</button>
+<button onclick={() => (props.class = 'two')}>change class</button>
+<button onclick={() => (late = ['a', 'b', 'c'])}>load options</button>
+<button onclick={() => options.push('d')}>add option</button>
+<p>{unmatched} {String(nothing)}</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/select-default-value-single-observer/_config.js b/packages/svelte/tests/runtime-runes/samples/select-default-value-single-observer/_config.js
new file mode 100644
index 0000000000..411a7868f7
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/select-default-value-single-observer/_config.js
@@ -0,0 +1,30 @@
+import { test } from '../../test';
+
+let observers = 0;
+const MutationObserver = globalThis.MutationObserver;
+
+export default test({
+	before_test() {
+		observers = 0;
+		globalThis.MutationObserver = class extends MutationObserver {
+			/** @param {MutationCallback} callback */
+			constructor(callback) {
+				super(callback);
+				observers++;
+			}
+		};
+	},
+
+	after_test() {
+		globalThis.MutationObserver = MutationObserver;
+	},
+
+	test({ assert, target }) {
+		const selects = target.querySelectorAll('select');
+		for (const select of selects) {
+			assert.equal(select.selectedIndex, 0);
+			assert.equal(select.options[1].defaultSelected, true);
+		}
+		assert.equal(observers, selects.length);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/select-default-value-single-observer/main.svelte b/packages/svelte/tests/runtime-runes/samples/select-default-value-single-observer/main.svelte
new file mode 100644
index 0000000000..7754b3c6fd
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/select-default-value-single-observer/main.svelte
@@ -0,0 +1,21 @@
+<script>
+	let value = $state('a');
+	let bound = $state('a');
+	let spread = $state('a');
+	let props = { defaultValue: 'b' };
+</script>
+
+<select {value} defaultValue="b">
+	<option value="a">A</option>
+	<option value="b">B</option>
+</select>
+
+<select bind:value={bound} defaultValue="b">
+	<option value="a">A</option>
+	<option value="b">B</option>
+</select>
+
+<select {...props} bind:value={spread}>
+	<option value="a">A</option>
+	<option value="b">B</option>
+</select>

From 2e8b57bc580b47004e4c48bf7dce11d4696ac785 Mon Sep 17 00:00:00 2001
From: Nic Polumeyv <nicolas.polum@outlook.com>
Date: Wed, 26 Aug 2026 04:11:35 -0400
Subject: [PATCH 21/29] fix: render `selected` options for `<select multiple>`
 with an array `value` on the server (#18720)

Follow-up to #18591.

---------

Co-authored-by: Simon Holthausen <simon.holthausen@vercel.com>
---
 .../svelte/src/internal/server/renderer.js    | 19 ++++++-----
 .../binding-select-multiple/_config.js        | 33 +++++++++++++------
 .../select-multiple-value/_expected.html      |  5 +++
 .../samples/select-multiple-value/main.svelte |  5 +++
 4 files changed, 43 insertions(+), 19 deletions(-)
 create mode 100644 packages/svelte/tests/server-side-rendering/samples/select-multiple-value/_expected.html
 create mode 100644 packages/svelte/tests/server-side-rendering/samples/select-multiple-value/main.svelte

diff --git a/packages/svelte/src/internal/server/renderer.js b/packages/svelte/src/internal/server/renderer.js
index 240a7aa686..a30c302693 100644
--- a/packages/svelte/src/internal/server/renderer.js
+++ b/packages/svelte/src/internal/server/renderer.js
@@ -89,7 +89,7 @@ export class Renderer {
 	 * State that is local to the branch it is declared in.
 	 * It will be shallow-copied to all children.
 	 *
-	 * @type {{ select_value: any, select_default_multiple: boolean }}
+	 * @type {{ select_value: any, multiple: boolean }}
 	 */
 	local;
 
@@ -101,9 +101,7 @@ export class Renderer {
 		this.#parent = parent;
 
 		this.global = global;
-		this.local = parent
-			? { ...parent.local }
-			: { select_value: undefined, select_default_multiple: false };
+		this.local = parent ? { ...parent.local } : { select_value: undefined, multiple: false };
 		this.type = parent ? parent.type : 'body';
 	}
 
@@ -346,8 +344,7 @@ export class Renderer {
 		this.push(`<select${attributes(select_attrs, css_hash, classes, styles, flags)}>`);
 		this.child((renderer) => {
 			renderer.local.select_value = value === undefined ? defaultValue : value;
-			renderer.local.select_default_multiple =
-				value === undefined && Boolean(select_attrs.multiple);
+			renderer.local.multiple = !!select_attrs.multiple;
 			fn(renderer);
 		});
 		this.push(`${is_rich ? '<!>' : ''}</select>`);
@@ -375,10 +372,14 @@ export class Renderer {
 				value = attrs.value;
 			}
 
+			var select_value = this.local.select_value;
+
 			if (
-				this.local.select_default_multiple
-					? is_array(this.local.select_value) && this.local.select_value.includes(value)
-					: value === this.local.select_value
+				// Super edge-case, but theoretically someone could use arrays with non-multiple selects,
+				// so we gotta check for the multiple attribute presence, too.
+				this.local.multiple && is_array(select_value)
+					? select_value.includes(value)
+					: value === select_value
 			) {
 				renderer.#out.push(' selected=""');
 			}
diff --git a/packages/svelte/tests/runtime-legacy/samples/binding-select-multiple/_config.js b/packages/svelte/tests/runtime-legacy/samples/binding-select-multiple/_config.js
index 42c0e018e5..d7c1b8d339 100644
--- a/packages/svelte/tests/runtime-legacy/samples/binding-select-multiple/_config.js
+++ b/packages/svelte/tests/runtime-legacy/samples/binding-select-multiple/_config.js
@@ -6,17 +6,30 @@ export default test({
 		return { selected: ['two', 'three'] };
 	},
 
-	html: `
+	ssrHtml: `
 		<select multiple>
 			<option>one</option>
-			<option>two</option>
-			<option>three</option>
+			<option selected>two</option>
+			<option selected>three</option>
 		</select>
 
 		<p>selected: two, three</p>
 	`,
 
-	test({ assert, component, target, window }) {
+	test({ assert, component, target, window, variant }) {
+		const selected = variant === 'hydrate' ? ' selected' : '';
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+			<select multiple>
+				<option>one</option>
+				<option${selected}>two</option>
+				<option${selected}>three</option>
+			</select>
+
+			<p>selected: two, three</p>
+		`
+		);
 		const select = target.querySelector('select');
 		ok(select);
 		const options = [...target.querySelectorAll('option')];
@@ -33,8 +46,8 @@ export default test({
 			`
 			<select multiple>
 				<option>one</option>
-				<option>two</option>
-				<option>three</option>
+				<option${selected}>two</option>
+				<option${selected}>three</option>
 			</select>
 
 			<p>selected: three</p>
@@ -51,8 +64,8 @@ export default test({
 			`
 			<select multiple>
 				<option>one</option>
-				<option>two</option>
-				<option>three</option>
+				<option${selected}>two</option>
+				<option${selected}>three</option>
 			</select>
 
 			<p>selected: one, three</p>
@@ -70,8 +83,8 @@ export default test({
 			`
 			<select multiple>
 				<option>one</option>
-				<option>two</option>
-				<option>three</option>
+				<option${selected}>two</option>
+				<option${selected}>three</option>
 			</select>
 
 			<p>selected: one, two</p>
diff --git a/packages/svelte/tests/server-side-rendering/samples/select-multiple-value/_expected.html b/packages/svelte/tests/server-side-rendering/samples/select-multiple-value/_expected.html
new file mode 100644
index 0000000000..c0ab4a082e
--- /dev/null
+++ b/packages/svelte/tests/server-side-rendering/samples/select-multiple-value/_expected.html
@@ -0,0 +1,5 @@
+<select multiple="">
+	<option selected="" value="a">A</option>
+	<option value="b">B</option>
+	<option selected="" value="c">C</option>
+</select>
diff --git a/packages/svelte/tests/server-side-rendering/samples/select-multiple-value/main.svelte b/packages/svelte/tests/server-side-rendering/samples/select-multiple-value/main.svelte
new file mode 100644
index 0000000000..6bde3f597a
--- /dev/null
+++ b/packages/svelte/tests/server-side-rendering/samples/select-multiple-value/main.svelte
@@ -0,0 +1,5 @@
+<select multiple value={['a', 'c']}>
+	<option value="a">A</option>
+	<option value="b">B</option>
+	<option value="c">C</option>
+</select>

From 7c6f36aa924700baca30f8fb0f03dde4d46a1d21 Mon Sep 17 00:00:00 2001
From: Nic Polumeyv <nicolas.polum@outlook.com>
Date: Wed, 26 Aug 2026 04:19:59 -0400
Subject: [PATCH 22/29] fix: keep boolean attributes with an empty string value
 when rendering attribute objects on the server (#18721)

`<input disabled="" {...props}>` and any other boolean attribute written as `""` now renders on the server the way it does on the client and in plain markup.
---
 .changeset/ssr-empty-boolean-attribute.md              |  5 +++++
 packages/svelte/src/internal/shared/attributes.js      |  3 ++-
 .../empty-boolean-attribute-object/_expected.html      |  6 ++++++
 .../samples/empty-boolean-attribute-object/main.svelte | 10 ++++++++++
 4 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/ssr-empty-boolean-attribute.md
 create mode 100644 packages/svelte/tests/server-side-rendering/samples/empty-boolean-attribute-object/_expected.html
 create mode 100644 packages/svelte/tests/server-side-rendering/samples/empty-boolean-attribute-object/main.svelte

diff --git a/.changeset/ssr-empty-boolean-attribute.md b/.changeset/ssr-empty-boolean-attribute.md
new file mode 100644
index 0000000000..dbf5465014
--- /dev/null
+++ b/.changeset/ssr-empty-boolean-attribute.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: keep boolean attributes with an empty string value when rendering attribute objects on the server
diff --git a/packages/svelte/src/internal/shared/attributes.js b/packages/svelte/src/internal/shared/attributes.js
index bb1abf22c1..68994bf85e 100644
--- a/packages/svelte/src/internal/shared/attributes.js
+++ b/packages/svelte/src/internal/shared/attributes.js
@@ -27,7 +27,8 @@ export function attr(name, value, is_boolean = false) {
 	if (name === 'hidden' && value !== 'until-found') {
 		is_boolean = true;
 	}
-	if (value == null || (!value && is_boolean)) return '';
+	// `''` is a present boolean attribute, as it is in markup and on the client
+	if (value == null || (is_boolean && !value && value !== '')) return '';
 	const normalized =
 		(has_own_property.call(replacements, name) && replacements[name].get(value)) || value;
 	const assignment = is_boolean ? `=""` : `="${escape_html(normalized, true)}"`;
diff --git a/packages/svelte/tests/server-side-rendering/samples/empty-boolean-attribute-object/_expected.html b/packages/svelte/tests/server-side-rendering/samples/empty-boolean-attribute-object/_expected.html
new file mode 100644
index 0000000000..0c9cc0cd8c
--- /dev/null
+++ b/packages/svelte/tests/server-side-rendering/samples/empty-boolean-attribute-object/_expected.html
@@ -0,0 +1,6 @@
+<input disabled="">
+<input hidden="">
+<input>
+<select multiple="">
+	<option selected="" value="a">A</option>
+</select>
diff --git a/packages/svelte/tests/server-side-rendering/samples/empty-boolean-attribute-object/main.svelte b/packages/svelte/tests/server-side-rendering/samples/empty-boolean-attribute-object/main.svelte
new file mode 100644
index 0000000000..25af2b774d
--- /dev/null
+++ b/packages/svelte/tests/server-side-rendering/samples/empty-boolean-attribute-object/main.svelte
@@ -0,0 +1,10 @@
+<script>
+	const props = {};
+</script>
+
+<input disabled="" {...props} />
+<input hidden="" {...props} />
+<input disabled={false} {...props} />
+<select multiple="" value="a">
+	<option value="a">A</option>
+</select>

From 08c2a72907838f8466bfff91f1deff2dc1bccd57 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Wed, 26 Aug 2026 11:29:50 +0200
Subject: [PATCH 23/29] chore: set Vitest reporter for github actions (#18722)

test failures show up really bad now, minimal is way better for github actions
---
 vitest.config.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/vitest.config.js b/vitest.config.js
index 116dfae9d8..faabcfbea4 100644
--- a/vitest.config.js
+++ b/vitest.config.js
@@ -28,7 +28,7 @@ export default defineConfig({
 	},
 	test: {
 		dir: '.',
-		reporters: ['dot'],
+		reporters: process.env.GITHUB_ACTIONS === 'true' ? ['minimal'] : ['dot'],
 		// A handful of dev-mode tests trigger Svelte's `effect_update_depth_exceeded`
 		// guard, which involves ~1000 Error objects per flush for stack tracking —
 		// slow enough under vitest 4's deeper async stacks (and CI's slower workers)

From 05b69164d11aa241f16c9d3904d91fb4aa357970 Mon Sep 17 00:00:00 2001
From: Xia Chao <shapirolutts@gmail.com>
Date: Thu, 27 Aug 2026 21:44:40 +0800
Subject: [PATCH 24/29] fix: omit bind:focused from SSR output (#18724)

---------

Co-authored-by: Xia Chao <236466140+bun-unsafe@users.noreply.github.com>
Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
---
 .changeset/omit-bind-focused-ssr.md             | 5 +++++
 packages/svelte/src/compiler/phases/bindings.js | 4 +++-
 2 files changed, 8 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/omit-bind-focused-ssr.md

diff --git a/.changeset/omit-bind-focused-ssr.md b/.changeset/omit-bind-focused-ssr.md
new file mode 100644
index 0000000000..80200808aa
--- /dev/null
+++ b/.changeset/omit-bind-focused-ssr.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: omit `bind:focused` from SSR output (it has no HTML attribute)
diff --git a/packages/svelte/src/compiler/phases/bindings.js b/packages/svelte/src/compiler/phases/bindings.js
index 6714a6e77d..dfe78da98c 100644
--- a/packages/svelte/src/compiler/phases/bindings.js
+++ b/packages/svelte/src/compiler/phases/bindings.js
@@ -23,7 +23,9 @@ export const binding_properties = {
 		event: 'durationchange',
 		omit_in_ssr: true
 	},
-	focused: {},
+	focused: {
+		omit_in_ssr: true // no corresponding HTML attribute
+	},
 	paused: {
 		valid_elements: ['audio', 'video'],
 		omit_in_ssr: true,

From edbe11ebc93c26410867748a34c4ed311d128de0 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Thu, 27 Aug 2026 16:27:08 +0200
Subject: [PATCH 25/29] fix: properly apply static textarea value attribute
 during CSR (#18727)

Fixes #18574
Simpler alternative to #18627 - we just special-case this in the "should
this be treated as a dynamic attribute" branches so `$.set_value(...)`
is always generated. Given how edge-case-y this is (why would you not
just write it into the body of the textarea?) this is fine.
---
 .changeset/polite-zoos-melt.md                  |  5 +++++
 .../client/visitors/RegularElement.js           |  1 +
 .../samples/textarea-value/_config.js           | 17 +++++++++++------
 .../samples/textarea-value/main.svelte          |  3 ++-
 4 files changed, 19 insertions(+), 7 deletions(-)
 create mode 100644 .changeset/polite-zoos-melt.md

diff --git a/.changeset/polite-zoos-melt.md b/.changeset/polite-zoos-melt.md
new file mode 100644
index 0000000000..cfff0e82e4
--- /dev/null
+++ b/.changeset/polite-zoos-melt.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: properly apply static textarea value attribute during CSR
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 adc9ec72dd..0a32e0dd53 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
@@ -240,6 +240,7 @@ export function RegularElement(node, context) {
 			if (
 				!is_custom_element &&
 				!cannot_be_set_statically(attribute.name) &&
+				(name !== 'value' || node.name !== 'textarea') &&
 				(attribute.value === true || is_text_attribute(attribute)) &&
 				(name !== 'class' || class_directives.length === 0) &&
 				(name !== 'style' || style_directives.length === 0)
diff --git a/packages/svelte/tests/runtime-legacy/samples/textarea-value/_config.js b/packages/svelte/tests/runtime-legacy/samples/textarea-value/_config.js
index 06264b653b..30e2633154 100644
--- a/packages/svelte/tests/runtime-legacy/samples/textarea-value/_config.js
+++ b/packages/svelte/tests/runtime-legacy/samples/textarea-value/_config.js
@@ -5,14 +5,19 @@ export default test({
 		return { foo: 42 };
 	},
 
-	html: '<textarea></textarea>',
-	ssrHtml: '<textarea>42</textarea>',
+	ssrHtml: '<textarea>42</textarea> <textarea>static</textarea>',
 
-	test({ assert, component, target }) {
-		const textarea = /** @type {HTMLTextAreaElement} */ (target.querySelector('textarea'));
-		assert.strictEqual(textarea.value, '42');
+	test({ assert, component, target, variant }) {
+		assert.htmlEqual(
+			target.innerHTML,
+			`<textarea></textarea> <textarea>${variant === 'hydrate' ? 'static' : ''}</textarea>`
+		);
+
+		const [textarea1, textarea2] = target.querySelectorAll('textarea');
+		assert.strictEqual(textarea1.value, '42');
+		assert.strictEqual(textarea2.value, 'static');
 
 		component.foo = 43;
-		assert.strictEqual(textarea.value, '43');
+		assert.strictEqual(textarea1.value, '43');
 	}
 });
diff --git a/packages/svelte/tests/runtime-legacy/samples/textarea-value/main.svelte b/packages/svelte/tests/runtime-legacy/samples/textarea-value/main.svelte
index 7eaf783f7f..203a3ed039 100644
--- a/packages/svelte/tests/runtime-legacy/samples/textarea-value/main.svelte
+++ b/packages/svelte/tests/runtime-legacy/samples/textarea-value/main.svelte
@@ -2,4 +2,5 @@
 	export let foo;
 </script>
 
-<textarea value='{foo}'/>
\ No newline at end of file
+<textarea value='{foo}'/>
+<textarea value="static"></textarea>

From 74197ccbe1d84cab76c1eefbf3def43903661691 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Thu, 27 Aug 2026 17:05:23 +0200
Subject: [PATCH 26/29] feat: add getOrInsert/getOrInsertComputed to SvelteMap
 (#18728)

Closes #18014
---
 .changeset/tasty-years-hammer.md           |  5 ++
 packages/svelte/src/reactivity/map.js      | 22 ++++++
 packages/svelte/src/reactivity/map.test.ts | 79 ++++++++++++++++++++++
 packages/svelte/types/index.d.ts           |  4 ++
 4 files changed, 110 insertions(+)
 create mode 100644 .changeset/tasty-years-hammer.md

diff --git a/.changeset/tasty-years-hammer.md b/.changeset/tasty-years-hammer.md
new file mode 100644
index 0000000000..42b559ac9f
--- /dev/null
+++ b/.changeset/tasty-years-hammer.md
@@ -0,0 +1,5 @@
+---
+'svelte': minor
+---
+
+feat: add getOrInsert/getOrInsertComputed to SvelteMap
diff --git a/packages/svelte/src/reactivity/map.js b/packages/svelte/src/reactivity/map.js
index 48d06a05a7..935db8fcb1 100644
--- a/packages/svelte/src/reactivity/map.js
+++ b/packages/svelte/src/reactivity/map.js
@@ -153,6 +153,28 @@ export class SvelteMap extends Map {
 		return super.get(key);
 	}
 
+	/**
+	 * @param {K} key
+	 * @param {V} value
+	 * */
+	getOrInsert(key, value) {
+		if (!super.has(key)) {
+			this.set(key, value);
+		}
+		return /** @type {V} */ (this.get(key));
+	}
+
+	/**
+	 * @param {K} key
+	 * @param {(key: K) => V} callbackFn
+	 */
+	getOrInsertComputed(key, callbackFn) {
+		if (!super.has(key)) {
+			this.set(key, callbackFn(key));
+		}
+		return /** @type {V} */ (this.get(key));
+	}
+
 	/**
 	 * @param {K} key
 	 * @param {V} value
diff --git a/packages/svelte/src/reactivity/map.test.ts b/packages/svelte/src/reactivity/map.test.ts
index 8bb6f72f7b..f5cbb21923 100644
--- a/packages/svelte/src/reactivity/map.test.ts
+++ b/packages/svelte/src/reactivity/map.test.ts
@@ -100,6 +100,85 @@ test('map.get(...)', () => {
 	cleanup();
 });
 
+test('map.getOrInsert(...)', () => {
+	const map = new SvelteMap([
+		[2, 2],
+		[3, 3]
+	]);
+
+	const log: any = [];
+
+	const cleanup = effect_root(() => {
+		render_effect(() => {
+			log.push('get 1', map.getOrInsert(1, 1));
+		});
+
+		render_effect(() => {
+			log.push('get 2', map.getOrInsert(2, 2));
+		});
+
+		render_effect(() => {
+			log.push('get 3', map.getOrInsert(3, 4));
+		});
+	});
+
+	flushSync(() => {
+		map.delete(2);
+	});
+
+	flushSync(() => {
+		map.set(2, 2);
+	});
+
+	assert.deepEqual(log, ['get 1', 1, 'get 2', 2, 'get 3', 3, 'get 2', 2]);
+
+	cleanup();
+});
+
+test('map.getOrInsertComputed(...)', () => {
+	const map = new SvelteMap([
+		[2, 2],
+		[3, 3]
+	]);
+
+	const log: any = [];
+
+	const cleanup = effect_root(() => {
+		render_effect(() => {
+			log.push(
+				'get 1',
+				map.getOrInsertComputed(1, (k) => k)
+			);
+		});
+
+		render_effect(() => {
+			log.push(
+				'get 2',
+				map.getOrInsertComputed(2, (k) => k)
+			);
+		});
+
+		render_effect(() => {
+			log.push(
+				'get 3',
+				map.getOrInsertComputed(3, () => 4)
+			);
+		});
+	});
+
+	flushSync(() => {
+		map.delete(2);
+	});
+
+	flushSync(() => {
+		map.set(2, 2);
+	});
+
+	assert.deepEqual(log, ['get 1', 1, 'get 2', 2, 'get 3', 3, 'get 2', 2]);
+
+	cleanup();
+});
+
 test('map.has(...)', () => {
 	const map = new SvelteMap([
 		[1, 1],
diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index dcc6dc5914..9e69796691 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -2466,6 +2466,10 @@ declare module 'svelte/reactivity' {
 		
 		constructor(value?: Iterable<readonly [K, V]> | null | undefined);
 		
+		getOrInsert(key: K, value: V): V;
+		
+		getOrInsertComputed(key: K, callbackFn: (key: K) => V): V;
+		
 		set(key: K, value: V): this;
 		#private;
 	}

From 5034b59e9e6cff42451d9136650f5fbde4c25260 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Thu, 27 Aug 2026 22:38:50 +0200
Subject: [PATCH 27/29] chore: bump playwright (#18729)

supports later ubuntu versions
---
 package.json                 |  2 +-
 packages/svelte/package.json |  2 +-
 pnpm-lock.yaml               | 66 ++++++++++++++++++++++++++----------
 3 files changed, 50 insertions(+), 20 deletions(-)

diff --git a/package.json b/package.json
index 16fc26bc32..8004698dd1 100644
--- a/package.json
+++ b/package.json
@@ -37,7 +37,7 @@
     "eslint-plugin-lube": "^0.5.1",
     "eslint-plugin-svelte": "^3.15.0",
     "jsdom": "25.0.1",
-    "playwright": "^1.60.0",
+    "playwright": "^1.62.0",
     "prettier": "^3.2.4",
     "prettier-plugin-svelte": "^3.4.0",
     "svelte": "workspace:^",
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 2da4ee428d..1f85001520 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -152,7 +152,7 @@
   },
   "devDependencies": {
     "@jridgewell/trace-mapping": "^0.3.25",
-    "@playwright/test": "^1.60.0",
+    "@playwright/test": "^1.62.0",
     "@rollup/plugin-commonjs": "^28.0.1",
     "@rollup/plugin-node-resolve": "^15.3.0",
     "@rollup/plugin-terser": "^0.4.4",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 70dcf70e5b..9224650e7d 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -42,8 +42,8 @@ importers:
         specifier: 25.0.1
         version: 25.0.1
       playwright:
-        specifier: ^1.60.0
-        version: 1.60.0
+        specifier: ^1.62.0
+        version: 1.62.1
       prettier:
         specifier: ^3.2.4
         version: 3.2.4
@@ -121,8 +121,8 @@ importers:
         specifier: ^0.3.25
         version: 0.3.31
       '@playwright/test':
-        specifier: ^1.60.0
-        version: 1.60.0
+        specifier: ^1.62.0
+        version: 1.62.1
       '@rollup/plugin-commonjs':
         specifier: ^28.0.1
         version: 28.0.1(rollup@4.60.1)
@@ -723,9 +723,9 @@ packages:
     resolution: {integrity: sha512-oGB+UxlgWcgQkgwo8GcEGwemoTFt3FIO9ababBmaGwXIoBKZ+GTy0pP185beGg7Llih/NSHSV2XAs1lnznocSg==}
     engines: {node: '>= 8'}
 
-  '@playwright/test@1.60.0':
-    resolution: {integrity: sha512-O71yZIbAh/PxDMNGns37GHBIfrVkEVyn+AXyIa5dOTfb4/xNvRWV+Vv/NMbNCtODB/pO7vLlF2OTmMVLhmr7Ag==}
-    engines: {node: '>=18'}
+  '@playwright/test@1.62.1':
+    resolution: {integrity: sha512-DTcUc8qii+cpHvtOwggMtBRMjKZHXYWdw8syRYu2vtzuq4Wxphqq4NfCs5Zt44L6mA8rfDfj+PHnxFc/FeK6mQ==}
+    engines: {node: '>=20'}
     hasBin: true
 
   '@polka/url@1.0.0-next.25':
@@ -840,131 +840,157 @@ packages:
     resolution: {integrity: sha512-L+34Qqil+v5uC0zEubW7uByo78WOCIrBvci69E7sFASRl0X7b/MB6Cqd1lky/CtcSVTydWa2WZwFuWexjS5o6g==}
     cpu: [arm]
     os: [linux]
+    libc: [glibc]
 
   '@rollup/rollup-linux-arm-gnueabihf@4.62.2':
     resolution: {integrity: sha512-n1GJHPOvpIfhi3TmrCeh6S6URt9BFCt0KQE3qvexyGCTAKpR4Lg+eWvNZEqu7epxwus/8ElT3hacYEucm49SZg==}
     cpu: [arm]
     os: [linux]
+    libc: [glibc]
 
   '@rollup/rollup-linux-arm-musleabihf@4.60.1':
     resolution: {integrity: sha512-n83O8rt4v34hgFzlkb1ycniJh7IR5RCIqt6mz1VRJD6pmhRi0CXdmfnLu9dIUS6buzh60IvACM842Ffb3xd6Gg==}
     cpu: [arm]
     os: [linux]
+    libc: [musl]
 
   '@rollup/rollup-linux-arm-musleabihf@4.62.2':
     resolution: {integrity: sha512-JqgflS8wEB+UXV/vS1RpRbifGBeN4D5lz8D8oOFbFZw4vedvdOgCFAjfBmIMdW3yL10XpQQ0Ambepw6MXrhOnA==}
     cpu: [arm]
     os: [linux]
+    libc: [musl]
 
   '@rollup/rollup-linux-arm64-gnu@4.60.1':
     resolution: {integrity: sha512-Nql7sTeAzhTAja3QXeAI48+/+GjBJ+QmAH13snn0AJSNL50JsDqotyudHyMbO2RbJkskbMbFJfIJKWA6R1LCJQ==}
     cpu: [arm64]
     os: [linux]
+    libc: [glibc]
 
   '@rollup/rollup-linux-arm64-gnu@4.62.2':
     resolution: {integrity: sha512-wnFJkogWvN4jm/hQRF2UBaeUmk20j5+DmHvoyWii2b8HJDyvz1MF2OU/6ynXt2KR63rbZLWkFpoytpdc/yBuSA==}
     cpu: [arm64]
     os: [linux]
+    libc: [glibc]
 
   '@rollup/rollup-linux-arm64-musl@4.60.1':
     resolution: {integrity: sha512-+pUymDhd0ys9GcKZPPWlFiZ67sTWV5UU6zOJat02M1+PiuSGDziyRuI/pPue3hoUwm2uGfxdL+trT6Z9rxnlMA==}
     cpu: [arm64]
     os: [linux]
+    libc: [musl]
 
   '@rollup/rollup-linux-arm64-musl@4.62.2':
     resolution: {integrity: sha512-HVu2bp0zhvJ8xHEV9+UUs7S90VadmBSY3LcIMvozbPo4AuMGDWlz3ymHLHZPX4hR67TKTt8Qp5PJ5RBg/i+RMQ==}
     cpu: [arm64]
     os: [linux]
+    libc: [musl]
 
   '@rollup/rollup-linux-loong64-gnu@4.60.1':
     resolution: {integrity: sha512-VSvgvQeIcsEvY4bKDHEDWcpW4Yw7BtlKG1GUT4FzBUlEKQK0rWHYBqQt6Fm2taXS+1bXvJT6kICu5ZwqKCnvlQ==}
     cpu: [loong64]
     os: [linux]
+    libc: [glibc]
 
   '@rollup/rollup-linux-loong64-gnu@4.62.2':
     resolution: {integrity: sha512-mQqqAV8QaoSgr9I2fKDLY2BAVvmKjWoGiu/cSYQonsLvtqwEn1E4QYfnCOcp5zoEqNhsDYin1s6jx/VJmrxlZg==}
     cpu: [loong64]
     os: [linux]
+    libc: [glibc]
 
   '@rollup/rollup-linux-loong64-musl@4.60.1':
     resolution: {integrity: sha512-4LqhUomJqwe641gsPp6xLfhqWMbQV04KtPp7/dIp0nzPxAkNY1AbwL5W0MQpcalLYk07vaW9Kp1PBhdpZYYcEw==}
     cpu: [loong64]
     os: [linux]
+    libc: [musl]
 
   '@rollup/rollup-linux-loong64-musl@4.62.2':
     resolution: {integrity: sha512-IxKLoxCQ2IWi6bT2akyDUBGsOImDKB+sPp4EsTmwFQ/fMwpCKm8uLSSgP/Kx/QYUgKis6SEZ5/Nlhup0DIA0PQ==}
     cpu: [loong64]
     os: [linux]
+    libc: [musl]
 
   '@rollup/rollup-linux-ppc64-gnu@4.60.1':
     resolution: {integrity: sha512-tLQQ9aPvkBxOc/EUT6j3pyeMD6Hb8QF2BTBnCQWP/uu1lhc9AIrIjKnLYMEroIz/JvtGYgI9dF3AxHZNaEH0rw==}
     cpu: [ppc64]
     os: [linux]
+    libc: [glibc]
 
   '@rollup/rollup-linux-ppc64-gnu@4.62.2':
     resolution: {integrity: sha512-Mk5ha2RQSgyFfmYYLkBpPnUk8D8FriBxesO1u9O75X0mHgXL1UQcH5Itl2lurWL2tj0RxV9b9tJgipac0hRY9A==}
     cpu: [ppc64]
     os: [linux]
+    libc: [glibc]
 
   '@rollup/rollup-linux-ppc64-musl@4.60.1':
     resolution: {integrity: sha512-RMxFhJwc9fSXP6PqmAz4cbv3kAyvD1etJFjTx4ONqFP9DkTkXsAMU4v3Vyc5BgzC+anz7nS/9tp4obsKfqkDHg==}
     cpu: [ppc64]
     os: [linux]
+    libc: [musl]
 
   '@rollup/rollup-linux-ppc64-musl@4.62.2':
     resolution: {integrity: sha512-CjvEnqJL/0/TQ3TXX3OPIJ/kmBellrWd4heXUmHeJlTnmwjKpSJzoehLaL6Xk0ZnMHBu9dZuFADNOrtjF4v+2w==}
     cpu: [ppc64]
     os: [linux]
+    libc: [musl]
 
   '@rollup/rollup-linux-riscv64-gnu@4.60.1':
     resolution: {integrity: sha512-QKgFl+Yc1eEk6MmOBfRHYF6lTxiiiV3/z/BRrbSiW2I7AFTXoBFvdMEyglohPj//2mZS4hDOqeB0H1ACh3sBbg==}
     cpu: [riscv64]
     os: [linux]
+    libc: [glibc]
 
   '@rollup/rollup-linux-riscv64-gnu@4.62.2':
     resolution: {integrity: sha512-1SiZbzwdkaDURsew/tSOrooKiYy7EQGT6m8ufavAi9NEyQb/6VuIxFXAL1fqa4iZe3g4NbNk4P7J32z2tw5Mgg==}
     cpu: [riscv64]
     os: [linux]
+    libc: [glibc]
 
   '@rollup/rollup-linux-riscv64-musl@4.60.1':
     resolution: {integrity: sha512-RAjXjP/8c6ZtzatZcA1RaQr6O1TRhzC+adn8YZDnChliZHviqIjmvFwHcxi4JKPSDAt6Uhf/7vqcBzQJy0PDJg==}
     cpu: [riscv64]
     os: [linux]
+    libc: [musl]
 
   '@rollup/rollup-linux-riscv64-musl@4.62.2':
     resolution: {integrity: sha512-nQts12zJ3NQRoE6uYljOH89v7szzLDvG2JD/vsX+vGXU8w/At1GowTZ5/7qeFQ8m7L55rpR8Okugnuo5bgjy2Q==}
     cpu: [riscv64]
     os: [linux]
+    libc: [musl]
 
   '@rollup/rollup-linux-s390x-gnu@4.60.1':
     resolution: {integrity: sha512-wcuocpaOlaL1COBYiA89O6yfjlp3RwKDeTIA0hM7OpmhR1Bjo9j31G1uQVpDlTvwxGn2nQs65fBFL5UFd76FcQ==}
     cpu: [s390x]
     os: [linux]
+    libc: [glibc]
 
   '@rollup/rollup-linux-s390x-gnu@4.62.2':
     resolution: {integrity: sha512-E9/ll019jhPIJgpzfZoIkBGhcz+kKNgVWYRY0zr9srBdPPFVpvOKW8VaJKUbeK+eZXyQF9ltME+Kk6affeaPgg==}
     cpu: [s390x]
     os: [linux]
+    libc: [glibc]
 
   '@rollup/rollup-linux-x64-gnu@4.60.1':
     resolution: {integrity: sha512-77PpsFQUCOiZR9+LQEFg9GClyfkNXj1MP6wRnzYs0EeWbPcHs02AXu4xuUbM1zhwn3wqaizle3AEYg5aeoohhg==}
     cpu: [x64]
     os: [linux]
+    libc: [glibc]
 
   '@rollup/rollup-linux-x64-gnu@4.62.2':
     resolution: {integrity: sha512-5BqxR/pshjey51iliyzTD5Xi3EN0aLmQ2lZ3lvefVV9c82BvrLo2/6OT55iifpWBufs6kdwWbuOKS841DrmK9A==}
     cpu: [x64]
     os: [linux]
+    libc: [glibc]
 
   '@rollup/rollup-linux-x64-musl@4.60.1':
     resolution: {integrity: sha512-5cIATbk5vynAjqqmyBjlciMJl1+R/CwX9oLk/EyiFXDWd95KpHdrOJT//rnUl4cUcskrd0jCCw3wpZnhIHdD9w==}
     cpu: [x64]
     os: [linux]
+    libc: [musl]
 
   '@rollup/rollup-linux-x64-musl@4.62.2':
     resolution: {integrity: sha512-uNN83XxQrRAh/w0/pmAfibcwyb6YWt4gP+dpnQKPVJshAloQ785ii8CT8ZCIxkGg9opVsvAlGhFitSm6D1Jjpg==}
     cpu: [x64]
     os: [linux]
+    libc: [musl]
 
   '@rollup/rollup-openbsd-x64@4.60.1':
     resolution: {integrity: sha512-cl0w09WsCi17mcmWqqglez9Gk8isgeWvoUZ3WiJFYSR3zjBQc2J5/ihSjpl+VLjPqjQ/1hJRcqBfLjssREQILw==}
@@ -1875,24 +1901,28 @@ packages:
     engines: {node: '>= 12.0.0'}
     cpu: [arm64]
     os: [linux]
+    libc: [glibc]
 
   lightningcss-linux-arm64-musl@1.23.0:
     resolution: {integrity: sha512-cU00LGb6GUXCwof6ACgSMKo3q7XYbsyTj0WsKHLi1nw7pV0NCq8nFTn6ZRBYLoKiV8t+jWl0Hv8KkgymmK5L5g==}
     engines: {node: '>= 12.0.0'}
     cpu: [arm64]
     os: [linux]
+    libc: [musl]
 
   lightningcss-linux-x64-gnu@1.23.0:
     resolution: {integrity: sha512-q4jdx5+5NfB0/qMbXbOmuC6oo7caPnFghJbIAV90cXZqgV8Am3miZhC4p+sQVdacqxfd+3nrle4C8icR3p1AYw==}
     engines: {node: '>= 12.0.0'}
     cpu: [x64]
     os: [linux]
+    libc: [glibc]
 
   lightningcss-linux-x64-musl@1.23.0:
     resolution: {integrity: sha512-G9Ri3qpmF4qef2CV/80dADHKXRAQeQXpQTLx7AiQrBYQHqBjB75oxqj06FCIe5g4hNCqLPnM9fsO4CyiT1sFSQ==}
     engines: {node: '>= 12.0.0'}
     cpu: [x64]
     os: [linux]
+    libc: [musl]
 
   lightningcss-win32-x64-msvc@1.23.0:
     resolution: {integrity: sha512-1rcBDJLU+obPPJM6qR5fgBUiCdZwZLafZM5f9kwjFLkb/UBNIzmae39uCSmh71nzPCTXZqHbvwu23OWnWEz+eg==}
@@ -2077,14 +2107,14 @@ packages:
     resolution: {integrity: sha512-uB80kBFb/tfd68bVleG9T5GGsGPjJrLAUpR5PZIrhBnIaRTQRjqdJSsIKkOP6OAIFbj7GOrcudc5pNjZ+geV2g==}
     engines: {node: '>=6'}
 
-  playwright-core@1.60.0:
-    resolution: {integrity: sha512-9bW6zvX/m0lEbgTKJ6YppOKx8H3VOPBMOCFh2irXFOT4BbHgrx5hPjwJYLT40Lu+4qtD36qKc/Hn56StUW57IA==}
-    engines: {node: '>=18'}
+  playwright-core@1.62.1:
+    resolution: {integrity: sha512-wPYSwEBJY9GHraISXqyqtx0na0LpO3XEX7jNDhntbex7tzUS7kLnZsOlFruFJB4Hi/rhDMjXGqHewDZ68nYZVw==}
+    engines: {node: '>=20'}
     hasBin: true
 
-  playwright@1.60.0:
-    resolution: {integrity: sha512-hheHdokM8cdqCb0lcE3s+zT4t4W+vvjpGxsZlDnikarzx8tSzMebh3UiFtgqwFwnTnjYQcsyMF8ei2mCO/tpeA==}
-    engines: {node: '>=18'}
+  playwright@1.62.1:
+    resolution: {integrity: sha512-0M+L3LAD8/nm554LOla9Ayx0j0tmFZ0FBcoQ7F1VuVHpM/XpiC8RcDzBQB8W5+hA8L22THxELzeF+2WcUzvcLg==}
+    engines: {node: '>=20'}
     hasBin: true
 
   polka@1.0.0-next.25:
@@ -3069,9 +3099,9 @@ snapshots:
       '@nodelib/fs.scandir': 2.1.5
       fastq: 1.16.0
 
-  '@playwright/test@1.60.0':
+  '@playwright/test@1.62.1':
     dependencies:
-      playwright: 1.60.0
+      playwright: 1.62.1
 
   '@polka/url@1.0.0-next.25': {}
 
@@ -4371,11 +4401,11 @@ snapshots:
 
   pify@4.0.1: {}
 
-  playwright-core@1.60.0: {}
+  playwright-core@1.62.1: {}
 
-  playwright@1.60.0:
+  playwright@1.62.1:
     dependencies:
-      playwright-core: 1.60.0
+      playwright-core: 1.62.1
     optionalDependencies:
       fsevents: 2.3.2
 

From 4ae5eb3f23df00de4d60bf40ff5a96580a0719dc Mon Sep 17 00:00:00 2001
From: Adnane Taghi <taghi.adnane@proton.me>
Date: Thu, 27 Aug 2026 21:58:40 +0100
Subject: [PATCH 28/29] feat: add has function to createContext (#18472)

closes #18471.

---------

Co-authored-by: Simon Holthausen <simon.holthausen@vercel.com>
---
 .changeset/short-feet-admire.md                    |  5 +++++
 documentation/docs/06-runtime/02-context.md        |  2 +-
 .../docs/98-reference/.generated/shared-errors.md  |  2 +-
 packages/svelte/messages/shared-errors/errors.md   |  2 +-
 packages/svelte/src/internal/client/context.js     |  6 +++---
 packages/svelte/src/internal/server/context.js     |  4 ++--
 packages/svelte/src/internal/shared/context.js     |  5 +++--
 .../create-context-programmatic/Child.svelte       |  8 +++++++-
 .../samples/create-context-programmatic/_config.js |  2 +-
 .../create-context-programmatic/main.svelte        | 14 +++++++++-----
 .../samples/create-context/Child.svelte            |  8 +++++++-
 .../samples/create-context/_config.js              |  2 +-
 .../samples/create-context/main.svelte             |  6 ++++--
 packages/svelte/types/index.d.ts                   |  4 ++--
 14 files changed, 47 insertions(+), 23 deletions(-)
 create mode 100644 .changeset/short-feet-admire.md

diff --git a/.changeset/short-feet-admire.md b/.changeset/short-feet-admire.md
new file mode 100644
index 0000000000..fdf56477c9
--- /dev/null
+++ b/.changeset/short-feet-admire.md
@@ -0,0 +1,5 @@
+---
+'svelte': minor
+---
+
+feat: add `has` function to `createContext`
diff --git a/documentation/docs/06-runtime/02-context.md b/documentation/docs/06-runtime/02-context.md
index a1e0347b7b..f67339c6cf 100644
--- a/documentation/docs/06-runtime/02-context.md
+++ b/documentation/docs/06-runtime/02-context.md
@@ -4,7 +4,7 @@ title: Context
 
 Context allows components to access values owned by parent components without passing them down as props (potentially through many layers of intermediate components, known as 'prop-drilling').
 
-By creating a `[get, set]` pair of functions with `createContext`, you can set the context in a parent component and get it in a child component:
+By creating a `[get, set, has]` triplet of functions with `createContext`, you can set the context in a parent component and get it in a child component:
 
 <!-- codeblock:start {"title":"Context","selected":"context.ts"} -->
 ```svelte
diff --git a/documentation/docs/98-reference/.generated/shared-errors.md b/documentation/docs/98-reference/.generated/shared-errors.md
index d7596fc068..44616d7c8d 100644
--- a/documentation/docs/98-reference/.generated/shared-errors.md
+++ b/documentation/docs/98-reference/.generated/shared-errors.md
@@ -78,7 +78,7 @@ Certain lifecycle methods can only be used during component initialisation. To f
 Context was not set in the current component or any of its ancestors
 ```
 
-The [`createContext()`](svelte#createContext) utility returns a `[get, set]` pair of functions. `get` will throw an error if `set` was not used to set the context in the current component or any of its ancestors.
+The [`createContext()`](svelte#createContext) utility returns a `[get, set, has]` triplet of functions. `get` will throw an error if `set` was not used to set the context in the current component or any of its ancestors.
 
 ### snippet_without_render_tag
 
diff --git a/packages/svelte/messages/shared-errors/errors.md b/packages/svelte/messages/shared-errors/errors.md
index 43dca57ac8..e005e34fc8 100644
--- a/packages/svelte/messages/shared-errors/errors.md
+++ b/packages/svelte/messages/shared-errors/errors.md
@@ -64,7 +64,7 @@ Certain lifecycle methods can only be used during component initialisation. To f
 
 > Context was not set in the current component or any of its ancestors
 
-The [`createContext()`](svelte#createContext) utility returns a `[get, set]` pair of functions. `get` will throw an error if `set` was not used to set the context in the current component or any of its ancestors.
+The [`createContext()`](svelte#createContext) utility returns a `[get, set, has]` triplet of functions. `get` will throw an error if `set` was not used to set the context in the current component or any of its ancestors.
 
 ## snippet_without_render_tag
 
diff --git a/packages/svelte/src/internal/client/context.js b/packages/svelte/src/internal/client/context.js
index e1571862ed..c3bb660e8c 100644
--- a/packages/svelte/src/internal/client/context.js
+++ b/packages/svelte/src/internal/client/context.js
@@ -72,17 +72,17 @@ export function set_dev_current_component_function(fn) {
 }
 
 /**
- * Returns a `[get, set]` pair of functions for working with context in a type-safe way.
+ * Returns a `[get, set, has]` triplet of functions for working with context in a type-safe way.
  *
  * `get` will throw an error if `set` has not yet been called in the current component or any of
  * its ancestors.
  *
  * @template T
- * @returns {[() => T, (context: T) => T]}
+ * @returns {[() => T, (context: T) => T, () => boolean]}
  * @since 5.40.0
  */
 export function createContext() {
-	return /** @type {[() => T, (context: T) => T]} */ (
+	return /** @type {[() => T, (context: T) => T, () => boolean]} */ (
 		create_context(getContext, setContext, hasContext)
 	);
 }
diff --git a/packages/svelte/src/internal/server/context.js b/packages/svelte/src/internal/server/context.js
index de11c11282..b204c4c138 100644
--- a/packages/svelte/src/internal/server/context.js
+++ b/packages/svelte/src/internal/server/context.js
@@ -12,11 +12,11 @@ export function set_ssr_context(v) {
 
 /**
  * @template T
- * @returns {[() => T, (context: T) => T]}
+ * @returns {[() => T, (context: T) => T, () => boolean]}
  * @since 5.40.0
  */
 export function createContext() {
-	return /** @type {[() => T, (context: T) => T]} */ (
+	return /** @type {[() => T, (context: T) => T, () => boolean]} */ (
 		create_context(getContext, setContext, hasContext)
 	);
 }
diff --git a/packages/svelte/src/internal/shared/context.js b/packages/svelte/src/internal/shared/context.js
index 943e15e415..005c009101 100644
--- a/packages/svelte/src/internal/shared/context.js
+++ b/packages/svelte/src/internal/shared/context.js
@@ -5,7 +5,7 @@ import { lifecycle_outside_component, missing_context } from './errors.js';
  * @param {(key: object) => T} get_context
  * @param {(key: object, context: T) => T} set_context
  * @param {(key: object) => boolean} has_context
- * @returns {[() => T, (context: T) => T]}
+ * @returns {[() => T, (context: T) => T, () => boolean]}
  */
 export function create_context(get_context, set_context, has_context) {
 	const key = {};
@@ -18,7 +18,8 @@ export function create_context(get_context, set_context, has_context) {
 
 			return get_context(key);
 		},
-		(context) => set_context(key, context)
+		(context) => set_context(key, context),
+		() => has_context(key)
 	];
 }
 
diff --git a/packages/svelte/tests/runtime-runes/samples/create-context-programmatic/Child.svelte b/packages/svelte/tests/runtime-runes/samples/create-context-programmatic/Child.svelte
index 3e39d5043e..0255132ad6 100644
--- a/packages/svelte/tests/runtime-runes/samples/create-context-programmatic/Child.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/create-context-programmatic/Child.svelte
@@ -1,7 +1,13 @@
 <script>
-	import { get } from './main.svelte';
+	import { get, has, has_unset } from './main.svelte';
 
 	const message = get();
 </script>
 
 <h1>{message}</h1>
+{#if has()}
+	<h2>it's me</h2>
+{/if}
+{#if !has_unset()}
+	<h2>or not</h2>
+{/if}
diff --git a/packages/svelte/tests/runtime-runes/samples/create-context-programmatic/_config.js b/packages/svelte/tests/runtime-runes/samples/create-context-programmatic/_config.js
index f4374c8759..c2eeca0de8 100644
--- a/packages/svelte/tests/runtime-runes/samples/create-context-programmatic/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/create-context-programmatic/_config.js
@@ -2,7 +2,7 @@ import { test } from '../../test';
 
 export default test({
 	ssrHtml: `<div></div>`,
-	html: `<div><h1>hello</h1></div>`,
+	html: `<div><h1>hello</h1><h2>it's me</h2><h2>or not</h2></div>`,
 
 	test() {}
 });
diff --git a/packages/svelte/tests/runtime-runes/samples/create-context-programmatic/main.svelte b/packages/svelte/tests/runtime-runes/samples/create-context-programmatic/main.svelte
index 3c42dbf180..8f4fb67d23 100644
--- a/packages/svelte/tests/runtime-runes/samples/create-context-programmatic/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/create-context-programmatic/main.svelte
@@ -3,9 +3,11 @@
 	import Child from './Child.svelte';
 
 	/** @type {ReturnType<typeof createContext<string>>} */
-	const [get, set] = createContext();
+	const [get, set, has] = createContext();
+	/** @type {ReturnType<typeof createContext<string>>} */
+	const [, , has_unset] = createContext();
 
-	export { get };
+	export { get, has, has_unset };
 
 	function Wrapper(Component) {
 		return (...args) => {
@@ -15,6 +17,8 @@
 	}
 </script>
 
-<div {@attach (target) => {
-	mount(Wrapper(Child), { target });
-}}></div>
+<div
+	{@attach (target) => {
+		mount(Wrapper(Child), { target });
+	}}
+></div>
diff --git a/packages/svelte/tests/runtime-runes/samples/create-context/Child.svelte b/packages/svelte/tests/runtime-runes/samples/create-context/Child.svelte
index 3e39d5043e..0255132ad6 100644
--- a/packages/svelte/tests/runtime-runes/samples/create-context/Child.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/create-context/Child.svelte
@@ -1,7 +1,13 @@
 <script>
-	import { get } from './main.svelte';
+	import { get, has, has_unset } from './main.svelte';
 
 	const message = get();
 </script>
 
 <h1>{message}</h1>
+{#if has()}
+	<h2>it's me</h2>
+{/if}
+{#if !has_unset()}
+	<h2>or not</h2>
+{/if}
diff --git a/packages/svelte/tests/runtime-runes/samples/create-context/_config.js b/packages/svelte/tests/runtime-runes/samples/create-context/_config.js
index 4ae28e68bd..fa782095de 100644
--- a/packages/svelte/tests/runtime-runes/samples/create-context/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/create-context/_config.js
@@ -1,5 +1,5 @@
 import { test } from '../../test';
 
 export default test({
-	html: `<h1>hello</h1>`
+	html: `<h1>hello</h1><h2>it's me</h2><h2>or not</h2>`
 });
diff --git a/packages/svelte/tests/runtime-runes/samples/create-context/main.svelte b/packages/svelte/tests/runtime-runes/samples/create-context/main.svelte
index 8d3c50ba55..35093f4c4e 100644
--- a/packages/svelte/tests/runtime-runes/samples/create-context/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/create-context/main.svelte
@@ -2,9 +2,11 @@
 	import { createContext } from 'svelte';
 
 	/** @type {ReturnType<typeof createContext<string>>} */
-	const [get, set] = createContext();
+	const [get, set, has] = createContext();
+	/** @type {ReturnType<typeof createContext<string>>} */
+	const [, , has_unset] = createContext();
 
-	export { get };
+	export { get, has, has_unset };
 </script>
 
 <script>
diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index 9e69796691..661b840354 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -492,14 +492,14 @@ declare module 'svelte' {
 	 */
 	export function fork(fn: () => void): Fork;
 	/**
-	 * Returns a `[get, set]` pair of functions for working with context in a type-safe way.
+	 * Returns a `[get, set, has]` triplet of functions for working with context in a type-safe way.
 	 *
 	 * `get` will throw an error if `set` has not yet been called in the current component or any of
 	 * its ancestors.
 	 *
 	 * @since 5.40.0
 	 */
-	export function createContext<T>(): [() => T, (context: T) => T];
+	export function createContext<T>(): [() => T, (context: T) => T, () => boolean];
 	/**
 	 * Retrieves the context set with the specified `key` in the current component or any of its
 	 * ancestors. If multiple components set the same key, the value from the closest one is returned.

From 6374a2a0db1cc2130e9ee69a233ce6d4c7334f82 Mon Sep 17 00:00:00 2001
From: Nic Polumeyv <nicolas.polum@outlook.com>
Date: Fri, 28 Aug 2026 04:52:34 -0400
Subject: [PATCH 29/29] chore: move `@types/trusted-types` to devDependencies
 (#18730)

Only referenced by a JSDoc `@import` in
`src/internal/client/dom/blocks/html.js`; nothing in the published
`types/index.d.ts` uses it, so consumers do not need it installed.
---
 .changeset/quiet-types-move.md | 5 +++++
 packages/svelte/package.json   | 2 +-
 pnpm-lock.yaml                 | 6 +++---
 3 files changed, 9 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/quiet-types-move.md

diff --git a/.changeset/quiet-types-move.md b/.changeset/quiet-types-move.md
new file mode 100644
index 0000000000..5c7180a01f
--- /dev/null
+++ b/.changeset/quiet-types-move.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: move `@types/trusted-types` to devDependencies
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 1f85001520..37489ac109 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -159,6 +159,7 @@
     "@rollup/plugin-virtual": "^3.0.2",
     "@types/aria-query": "^5.0.4",
     "@types/node": "^20.11.5",
+    "@types/trusted-types": "^2.0.7",
     "baseline-browser-mapping": "^2.10.32",
     "dts-buddy": "^0.5.5",
     "esbuild": "^0.28.1",
@@ -174,7 +175,6 @@
     "@jridgewell/sourcemap-codec": "^1.5.0",
     "@sveltejs/acorn-typescript": "^1.0.10",
     "@types/estree": "^1.0.5",
-    "@types/trusted-types": "^2.0.7",
     "acorn": "^8.12.1",
     "aria-query": "5.3.1",
     "axobject-query": "^4.1.0",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 9224650e7d..c51620fff5 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -80,9 +80,6 @@ importers:
       '@types/estree':
         specifier: ^1.0.5
         version: 1.0.8
-      '@types/trusted-types':
-        specifier: ^2.0.7
-        version: 2.0.7
       acorn:
         specifier: ^8.12.1
         version: 8.16.0
@@ -141,6 +138,9 @@ importers:
       '@types/node':
         specifier: ^20.11.5
         version: 20.19.17
+      '@types/trusted-types':
+        specifier: ^2.0.7
+        version: 2.0.7
       baseline-browser-mapping:
         specifier: ^2.10.32
         version: 2.10.32