From e65025be58c2e6ed67caf982e8c49a078e521496 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 30 Apr 2026 16:58:06 -0400
Subject: [PATCH 01/10] docs: fix testing docs (#18163)

extracted from https://github.com/sveltejs/svelte.dev/pull/1959
---
 documentation/docs/07-misc/02-testing.md | 36 ++++++++++++++++++++++--
 1 file changed, 33 insertions(+), 3 deletions(-)

diff --git a/documentation/docs/07-misc/02-testing.md b/documentation/docs/07-misc/02-testing.md
index c1bc69c1c2..0ad82a19b5 100644
--- a/documentation/docs/07-misc/02-testing.md
+++ b/documentation/docs/07-misc/02-testing.md
@@ -38,6 +38,21 @@ You can now write unit tests for code inside your `.js/.ts` files:
 
 ```js
 /// file: multiplier.svelte.test.js
+// @filename: multiplier.svelte.ts
+export function multiplier(initial: number, k: number) {
+	let count = $state(initial);
+
+	return {
+		get value() {
+			return count * k;
+		},
+		set: (c: number) => {
+			count = c;
+		}
+	};
+}
+// @filename: multiplier.svelte.test.js
+// ---cut---
 import { flushSync } from 'svelte';
 import { expect, test } from 'vitest';
 import { multiplier } from './multiplier.svelte.js';
@@ -80,6 +95,16 @@ Since Vitest processes your test files the same way as your source files, you ca
 
 ```js
 /// file: multiplier.svelte.test.js
+// @filename: multiplier.svelte.ts
+export function multiplier(getCount: () => number, k: number) {
+	return {
+		get value() {
+			return getCount() * k;
+		}
+	};
+}
+// @filename: multiplier.svelte.test.js
+// ---cut---
 import { flushSync } from 'svelte';
 import { expect, test } from 'vitest';
 import { multiplier } from './multiplier.svelte.js';
@@ -115,6 +140,10 @@ If the code being tested uses effects, you need to wrap the test inside `$effect
 
 ```js
 /// file: logger.svelte.test.js
+// @filename: logger.svelte.ts
+export function logger(fn: () => void) {}
+// @filename: logger.svelte.test.js
+// ---cut---
 import { flushSync } from 'svelte';
 import { expect, test } from 'vitest';
 import { logger } from './logger.svelte.js';
@@ -213,7 +242,7 @@ test('Component', () => {
 	expect(document.body.innerHTML).toBe('<button>0</button>');
 
 	// Click the button, then flush the changes so you can synchronously write expectations
-	document.body.querySelector('button').click();
+	document.body.querySelector('button')?.click();
 	flushSync();
 
 	expect(document.body.innerHTML).toBe('<button>1</button>');
@@ -226,6 +255,7 @@ test('Component', () => {
 While the process is very straightforward, it is also low level and somewhat brittle, as the precise structure of your component may change frequently. Tools like [@testing-library/svelte](https://testing-library.com/docs/svelte-testing-library/intro/) can help streamline your tests. The above test could be rewritten like this:
 
 ```js
+// @errors: 2339
 /// file: component.test.js
 import { render, screen } from '@testing-library/svelte';
 import userEvent from '@testing-library/user-event';
@@ -270,9 +300,9 @@ You can create stories for component variations and test interactions with the [
 		}
 	});
 </script>
- 
+
 <Story name="Empty Form" />
- 
+
 <Story
 	name="Filled Form"
 	play={async ({ args, canvas, userEvent }) => {

From dc5bd887b50c593033408b7faa079d56f38e74b9 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 1 May 2026 15:57:15 -0400
Subject: [PATCH 02/10] fix: resolve stale deriveds with latest value (#18167)

While looking into #18162 I found an adjacent bug. Currently, if an
async derived resolves in batch 2 before it resolves in batch 1, we
reject the promise belonging to batch 1 and by extension the batch
itself. This means that any other changes in batch 1 are silently
discarded, incorrectly.

The fix is almost comically simple: rather than rejecting the earlier
promise, we just resolve it with the latest value.

I have a hunch that this might also enable us to simplify the rebase
logic, though I haven't investigated that in this PR.

### Before submitting the PR, please make sure you do the following

- [x] It's really useful if your PR references an issue where it is
discussed ahead of time. In many cases, features are absent for a
reason. For large changes, please create an RFC:
https://github.com/sveltejs/rfcs
- [x] Prefix your PR title with `feat:`, `fix:`, `chore:`, or `docs:`.
- [x] This message body should clearly illustrate what problems it
solves.
- [x] Ideally, include a test that fails without this PR but passes with
it.
- [x] If this PR changes code within `packages/svelte/src`, add a
changeset (`npx changeset`).

### Tests and linting

- [x] Run the tests with `pnpm test` and lint the project with `pnpm
lint`
---
 .changeset/modern-tables-fetch.md             |  5 ++++
 .../internal/client/reactivity/deriveds.js    |  2 +-
 .../samples/async-stale-derived-3/_config.js  | 29 +++++++++++++++++++
 .../samples/async-stale-derived-3/main.svelte | 22 ++++++++++++++
 4 files changed, 57 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/modern-tables-fetch.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-stale-derived-3/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-stale-derived-3/main.svelte

diff --git a/.changeset/modern-tables-fetch.md b/.changeset/modern-tables-fetch.md
new file mode 100644
index 0000000000..89543910fa
--- /dev/null
+++ b/.changeset/modern-tables-fetch.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: resolve stale deriveds with latest value
diff --git a/packages/svelte/src/internal/client/reactivity/deriveds.js b/packages/svelte/src/internal/client/reactivity/deriveds.js
index 4ae49fecba..eb934d96ff 100644
--- a/packages/svelte/src/internal/client/reactivity/deriveds.js
+++ b/packages/svelte/src/internal/client/reactivity/deriveds.js
@@ -232,7 +232,7 @@ export function async_derived(fn, label, location) {
 				for (const [b, d] of deferreds) {
 					deferreds.delete(b);
 					if (b === batch) break;
-					d.reject(STALE_REACTION);
+					d.resolve(value);
 				}
 
 				if (DEV && location !== undefined) {
diff --git a/packages/svelte/tests/runtime-runes/samples/async-stale-derived-3/_config.js b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-3/_config.js
new file mode 100644
index 0000000000..ff03e0e28e
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-3/_config.js
@@ -0,0 +1,29 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+
+		const [increment, pop] = target.querySelectorAll('button');
+
+		increment.click();
+		await tick();
+
+		increment.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`<button>increment</button><button>pop</button><p>0 0 0</p>`
+		);
+
+		pop.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`<button>increment</button><button>pop</button><p>2 2 1</p>`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-stale-derived-3/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-3/main.svelte
new file mode 100644
index 0000000000..589ac9ea0e
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-3/main.svelte
@@ -0,0 +1,22 @@
+<script>
+	let count = $state(0);
+	let other = $state(0);
+
+	const queue = [];
+
+	function push(v) {
+		if (v === 0) return v;
+
+		return new Promise((fulfil) => {
+			queue.push(() => fulfil(v));
+		});
+	}
+</script>
+
+<button onclick={() => {
+	if (count === 0) other++;
+	count++;
+}}>increment</button>
+<button onclick={() => queue.pop()?.()}>pop</button>
+
+<p>{await push(count)} {count} {other}</p>

From 89b6a939fe40ac657f27219d29c601fa67202eed Mon Sep 17 00:00:00 2001
From: Paolo Ricciuti <ricciutipaolo@gmail.com>
Date: Tue, 5 May 2026 20:48:50 +0200
Subject: [PATCH 03/10] fix: wrap `Promise.all` in `save` during SSR (#18178)

Closes #18168

Not sure if there's a deeper issue in play because the error it's only
really there if you also add a title to the component. I think the issue
is that with multiple arguments the top level `Promise.all` is not
wrapped in `save` and that probably causes a race condition with `title`
that sets the context back to `null` in a `finally`.

One issue is that now the generated code looks like this

```js
const [$$0, $$1] = (await $.save(Promise.all([
	(async () => (await $.save(user()))().name)(),
	(async () => (await $.save(user()))().image)()
])))();
```
which seems a bit redundant, but I'm not sure if we can get rid of the
inner `save` since they are indeed awaiting something.
---
 .changeset/tough-knives-smell.md                  |  5 +++++
 .../3-transform/server/visitors/shared/utils.js   |  4 ++--
 .../samples/async-multiple-attrs/_config.js       |  8 ++++++++
 .../samples/async-multiple-attrs/_expected.html   |  1 +
 .../async-multiple-attrs/_expected_head.html      |  1 +
 .../samples/async-multiple-attrs/main.svelte      | 15 +++++++++++++++
 6 files changed, 32 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/tough-knives-smell.md
 create mode 100644 packages/svelte/tests/server-side-rendering/samples/async-multiple-attrs/_config.js
 create mode 100644 packages/svelte/tests/server-side-rendering/samples/async-multiple-attrs/_expected.html
 create mode 100644 packages/svelte/tests/server-side-rendering/samples/async-multiple-attrs/_expected_head.html
 create mode 100644 packages/svelte/tests/server-side-rendering/samples/async-multiple-attrs/main.svelte

diff --git a/.changeset/tough-knives-smell.md b/.changeset/tough-knives-smell.md
new file mode 100644
index 0000000000..7687188c1a
--- /dev/null
+++ b/.changeset/tough-knives-smell.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: wrap `Promise.all` in `save` during SSR
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 a87642bc4c..9b3ac3ad78 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
@@ -12,7 +12,7 @@ import {
 import * as b from '#compiler/builders';
 import { sanitize_template_string } from '../../../../../utils/sanitize_template_string.js';
 import { regex_whitespaces_strict } from '../../../../patterns.js';
-import { has_await_expression } from '../../../../../utils/ast.js';
+import { has_await_expression, save } from '../../../../../utils/ast.js';
 import { ExpressionMetadata } from '../../../../nodes.js';
 
 /** Opens an if/each block, so that we can remove nodes in the case of a mismatch */
@@ -360,7 +360,7 @@ export class PromiseOptimiser {
 
 		return b.const(
 			b.array_pattern(this.expressions.map((_, i) => b.id(`$$${i}`))),
-			b.await(b.call('Promise.all', promises))
+			save(b.call('Promise.all', promises))
 		);
 	}
 
diff --git a/packages/svelte/tests/server-side-rendering/samples/async-multiple-attrs/_config.js b/packages/svelte/tests/server-side-rendering/samples/async-multiple-attrs/_config.js
new file mode 100644
index 0000000000..aaf40e7a52
--- /dev/null
+++ b/packages/svelte/tests/server-side-rendering/samples/async-multiple-attrs/_config.js
@@ -0,0 +1,8 @@
+import { test } from '../../test';
+
+export default test({
+	mode: ['async'],
+	compileOptions: {
+		dev: true
+	}
+});
diff --git a/packages/svelte/tests/server-side-rendering/samples/async-multiple-attrs/_expected.html b/packages/svelte/tests/server-side-rendering/samples/async-multiple-attrs/_expected.html
new file mode 100644
index 0000000000..93016d569c
--- /dev/null
+++ b/packages/svelte/tests/server-side-rendering/samples/async-multiple-attrs/_expected.html
@@ -0,0 +1 @@
+<!--[--><img alt="test" src=""/><!--]-->
\ No newline at end of file
diff --git a/packages/svelte/tests/server-side-rendering/samples/async-multiple-attrs/_expected_head.html b/packages/svelte/tests/server-side-rendering/samples/async-multiple-attrs/_expected_head.html
new file mode 100644
index 0000000000..96ba2bba28
--- /dev/null
+++ b/packages/svelte/tests/server-side-rendering/samples/async-multiple-attrs/_expected_head.html
@@ -0,0 +1 @@
+<!--1410iyz--><!----><title>Async multiple attributes</title>
\ No newline at end of file
diff --git a/packages/svelte/tests/server-side-rendering/samples/async-multiple-attrs/main.svelte b/packages/svelte/tests/server-side-rendering/samples/async-multiple-attrs/main.svelte
new file mode 100644
index 0000000000..f14ccd088b
--- /dev/null
+++ b/packages/svelte/tests/server-side-rendering/samples/async-multiple-attrs/main.svelte
@@ -0,0 +1,15 @@
+<script>
+	const user = $derived(Promise.resolve({ 
+		name: 'test',
+		image: '',
+	}))
+</script>
+
+<svelte:head>
+<title>Async multiple attributes</title>
+</svelte:head>
+
+<img
+	alt={(await user).name}
+	src={(await user).image}
+/>

From d4c5a917356a4ef0905681bdd98113c84707db42 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Wed, 6 May 2026 09:59:39 +0200
Subject: [PATCH 04/10] fix: rethrow error of failed iterable after calling
 `return()` (#18169)

The fix in #17966 wasn't quite right, because we gotta rethrow in case
the iterator stopped because of an error. Fixes part of the SvelteKit
`query.live` test failure.

---------

Co-authored-by: vercel[bot] <35613825+vercel[bot]@users.noreply.github.com>
Co-authored-by: Rich Harris <rich.harris@vercel.com>
---
 .changeset/fresh-stars-grin.md                |  5 +++
 .../src/internal/client/reactivity/async.js   | 25 ++++++++---
 .../_config.js                                | 24 ++++++++++
 .../main.svelte                               | 45 +++++++++++++++++++
 .../_config.js                                | 21 +++++++++
 .../main.svelte                               | 43 ++++++++++++++++++
 6 files changed, 157 insertions(+), 6 deletions(-)
 create mode 100644 .changeset/fresh-stars-grin.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-reactivity-loss-for-await-throws-1/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-reactivity-loss-for-await-throws-1/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-reactivity-loss-for-await-throws-2/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-reactivity-loss-for-await-throws-2/main.svelte

diff --git a/.changeset/fresh-stars-grin.md b/.changeset/fresh-stars-grin.md
new file mode 100644
index 0000000000..3d56792d1e
--- /dev/null
+++ b/.changeset/fresh-stars-grin.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: rethrow error of failed iterable after calling `return()`
diff --git a/packages/svelte/src/internal/client/reactivity/async.js b/packages/svelte/src/internal/client/reactivity/async.js
index 6aea790c36..61fff31f8a 100644
--- a/packages/svelte/src/internal/client/reactivity/async.js
+++ b/packages/svelte/src/internal/client/reactivity/async.js
@@ -213,22 +213,35 @@ export async function* for_await_track_reactivity_loss(iterable) {
 		throw new TypeError('value is not async iterable');
 	}
 
-	/** Whether the completion of the iterator was "normal", meaning it wasn't ended via `break` or a similar method */
-	let normal_completion = false;
+	// eslint-disable-next-line no-useless-assignment
+	let invoke_return = true;
+
 	try {
 		while (true) {
 			const { done, value } = (await track_reactivity_loss(iterator.next()))();
 			if (done) {
-				normal_completion = true;
+				invoke_return = false;
 				break;
 			}
 			var prev = reactivity_loss_tracker;
-			yield value;
+			try {
+				yield value;
+			} catch (e) {
+				set_reactivity_loss_tracker(prev);
+				// If the yield throws, we need to call `return` but not return its value, instead rethrow
+				if (iterator.return !== undefined) {
+					(await track_reactivity_loss(iterator.return()))();
+				}
+				throw e;
+			}
 			set_reactivity_loss_tracker(prev);
 		}
+	} catch (error) {
+		invoke_return = false;
+		throw error;
 	} finally {
-		// If the iterator had an abrupt completion and `return` is defined on the iterator, call it and return the value
-		if (!normal_completion && iterator.return !== undefined) {
+		// If the iterator had an abrupt completion (break) and `return` is defined on the iterator, call it and return the value
+		if (invoke_return && iterator.return !== undefined) {
 			// eslint-disable-next-line no-unsafe-finally
 			return /** @type {TReturn} */ ((await track_reactivity_loss(iterator.return()))().value);
 		}
diff --git a/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss-for-await-throws-1/_config.js b/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss-for-await-throws-1/_config.js
new file mode 100644
index 0000000000..9785f639cb
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss-for-await-throws-1/_config.js
@@ -0,0 +1,24 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+import { normalise_trace_logs } from '../../../helpers.js';
+
+export default test({
+	compileOptions: {
+		dev: true
+	},
+	html: '<p>pending</p>',
+	async test({ assert, target, warnings }) {
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			'<h1>number -> number -> number -> return -> body failed -> ended</h1>'
+		);
+
+		assert.deepEqual(normalise_trace_logs(warnings), [
+			{
+				log: 'Detected reactivity loss when reading `values[1]`. This happens when state is read in an async function after an earlier `await`'
+			}
+		]);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss-for-await-throws-1/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss-for-await-throws-1/main.svelte
new file mode 100644
index 0000000000..da7c48642c
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss-for-await-throws-1/main.svelte
@@ -0,0 +1,45 @@
+<script>
+	let values = $state([0, 1, 2]);
+
+	async function get_result() {
+		const logs = [];
+
+		const iterator = {
+			index: 0,
+			async next() {
+				if (this.index > 2) { done: true }
+				return { done: false, value: values[this.index++] };
+			},
+			async return() {
+				logs.push('return');
+			},
+			[Symbol.asyncIterator]() {
+				return this;
+			}
+		};
+
+		try {
+			for await (const value of iterator) {
+				logs.push('number');
+				// Read reactive state after async iterator await.
+				if (values.length === 3 && value === 2) {
+					throw new Error('body failed');
+				}
+			}
+			logs.push('done');
+		} catch (error) {
+			logs.push(error.message);
+		}
+
+		logs.push('ended');
+		return logs.join(' -> ');
+	}
+</script>
+
+<svelte:boundary>
+	<h1>{await get_result()}</h1>
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss-for-await-throws-2/_config.js b/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss-for-await-throws-2/_config.js
new file mode 100644
index 0000000000..9e8a2d8def
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss-for-await-throws-2/_config.js
@@ -0,0 +1,21 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+import { normalise_trace_logs } from '../../../helpers.js';
+
+export default test({
+	compileOptions: {
+		dev: true
+	},
+	html: '<p>pending</p>',
+	async test({ assert, target, warnings }) {
+		await tick();
+
+		assert.htmlEqual(target.innerHTML, '<h1>number -> number -> next failed -> ended</h1>');
+
+		assert.deepEqual(normalise_trace_logs(warnings), [
+			{
+				log: 'Detected reactivity loss when reading `values[1]`. This happens when state is read in an async function after an earlier `await`'
+			}
+		]);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss-for-await-throws-2/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss-for-await-throws-2/main.svelte
new file mode 100644
index 0000000000..ffe2ef93c0
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-reactivity-loss-for-await-throws-2/main.svelte
@@ -0,0 +1,43 @@
+<script>
+	let values = $state([0, 1, 2]);
+
+	async function get_result() {
+		const logs = [];
+
+		const iterator = {
+			index: 0,
+			async next() {
+				if (this.index > 1) throw new Error('next failed');
+				return { done: false, value: values[this.index++] };
+			},
+			async return() {
+				logs.push('return');
+			},
+			[Symbol.asyncIterator]() {
+				return this;
+			}
+		};
+
+		try {
+			for await (const value of iterator) {
+				logs.push('number');
+				// Read reactive state after async iterator await.
+				values.length === value;
+			}
+			logs.push('done');
+		} catch (error) {
+			logs.push(error.message);
+		}
+
+		logs.push('ended');
+		return logs.join(' -> ');
+	}
+</script>
+
+<svelte:boundary>
+	<h1>{await get_result()}</h1>
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>

From 5e054574db2bd9f96176626a604046b6db13af09 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Wed, 6 May 2026 22:02:57 +0200
Subject: [PATCH 05/10] fix: don't override new current_batch (#18170)

This is a regression from #18117 - we moved `this.#commit()` higher up
but that means that `current_batch` could be nulled out / overridden
through `batch.activate/deactivate` / blocker runs inside `#commit()`.
Therefore restore the previous value afterwards. No changest because
#18117 is not released yet.
Fixes the other part of the failing SvelteKit `query.live` test.

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
---
 .../src/internal/client/reactivity/batch.js   | 13 ++++++--
 .../svelte/tests/runtime-legacy/shared.ts     |  6 ++--
 .../_config.js                                | 19 ++++++++++++
 .../main.svelte                               | 30 +++++++++++++++++++
 4 files changed, 63 insertions(+), 5 deletions(-)
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-commit-preserve-new-batch/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-commit-preserve-new-batch/main.svelte

diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index 4239cda04b..2801445ae7 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -92,6 +92,9 @@ let uid = 1;
 export class Batch {
 	id = uid++;
 
+	/** True as soon as `#process()` was called */
+	#started = false;
+
 	/**
 	 * The current values of any signals that are updated in this batch.
 	 * Tuple format: [value, is_derived] (note: is_derived is false for deriveds, too, if they were overridden via assignment)
@@ -255,6 +258,8 @@ export class Batch {
 	}
 
 	#process() {
+		this.#started = true;
+
 		if (flush_count++ > 1000) {
 			batches.delete(this);
 			infinite_loop_guard();
@@ -342,6 +347,8 @@ export class Batch {
 			this.#deferred?.resolve();
 		}
 
+		var next_batch = /** @type {Batch | null} */ (/** @type {unknown} */ (current_batch));
+
 		// Order matters here - we need to commit and THEN continue flushing new batches, not the other way around,
 		// else we could start flushing a new batch and then, if it has pending work, rebase it right afterwards, which is wrong.
 		// In sync mode flushSync can cause #commit to wrongfully think that there needs to be a rebase, so we only do it in async mode
@@ -350,8 +357,6 @@ export class Batch {
 			this.#commit();
 		}
 
-		var next_batch = /** @type {Batch | null} */ (/** @type {unknown} */ (current_batch));
-
 		// Edge case: During traversal new branches might create effects that run immediately and set state,
 		// causing an effect and therefore a root to be scheduled again. We need to traverse the current batch
 		// once more in that case - most of the time this will just clean up dirty branches.
@@ -537,6 +542,8 @@ export class Batch {
 				sources.push(source);
 			}
 
+			if (!batch.#started) continue;
+
 			// Re-run async/block effects that depend on distinct values changed in both batches
 			var others = [...batch.current.keys()].filter((s) => !this.current.has(s));
 
@@ -722,7 +729,7 @@ export class Batch {
 
 				if (!is_flushing_sync) {
 					queue_micro_task(() => {
-						if (!batches.has(batch) || batch.#pending.size > 0) {
+						if (batch.#started) {
 							// a flushSync happened in the meantime
 							return;
 						}
diff --git a/packages/svelte/tests/runtime-legacy/shared.ts b/packages/svelte/tests/runtime-legacy/shared.ts
index 454ae2f766..6f30fb5d98 100644
--- a/packages/svelte/tests/runtime-legacy/shared.ts
+++ b/packages/svelte/tests/runtime-legacy/shared.ts
@@ -60,6 +60,8 @@ export interface RuntimeTest<Props extends Record<string, any> = Record<string,
 	id_prefix?: string;
 	before_test?: () => void;
 	after_test?: () => void;
+	/** If true, flushSync() will not be called before invoking test() */
+	skip_initial_flushSync?: boolean;
 	test?: (args: {
 		variant: 'dom' | 'hydrate';
 		assert: Assert;
@@ -505,7 +507,7 @@ async function run_test_variant(
 
 			try {
 				if (config.test) {
-					flushSync();
+					if (!config.skip_initial_flushSync) flushSync();
 
 					if (variant === 'hydrate' && cwd.includes('async-')) {
 						// wait for pending boundaries to render
@@ -543,7 +545,7 @@ async function run_test_variant(
 				}
 			} finally {
 				if (runes) {
-					unmount(instance);
+					await unmount(instance);
 				} else {
 					instance.$destroy();
 				}
diff --git a/packages/svelte/tests/runtime-runes/samples/async-commit-preserve-new-batch/_config.js b/packages/svelte/tests/runtime-runes/samples/async-commit-preserve-new-batch/_config.js
new file mode 100644
index 0000000000..922feed515
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-commit-preserve-new-batch/_config.js
@@ -0,0 +1,19 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+// Tests that batch.#commit() does not null out a potentially new current_batch
+export default test({
+	skip_initial_flushSync: true, // test that the initial batch is flushed without an explicit flushSync() call
+	async test({ assert, target }) {
+		await tick();
+
+		const [button] = target.querySelectorAll('button');
+		const [updates] = target.querySelectorAll('p');
+
+		assert.htmlEqual(updates.innerHTML, 'false');
+
+		button.click();
+		await tick();
+		assert.htmlEqual(updates.innerHTML, 'true');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-commit-preserve-new-batch/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-commit-preserve-new-batch/main.svelte
new file mode 100644
index 0000000000..f7dae33b7e
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-commit-preserve-new-batch/main.svelte
@@ -0,0 +1,30 @@
+<script>
+	let count = $state(-1);
+	let payload = $state(false);
+	let updated = $state(false);
+
+	$effect(() => {
+		if (payload) {
+			updated = true;
+		}
+	});
+
+	function update() {
+		count = 0;
+		queueMicrotask(() => {
+			payload = true;
+		});
+	}
+</script>
+
+<button onclick={update}>update</button>
+
+<p>{updated}</p>
+
+<svelte:boundary>
+	{await new Promise(() => {})}
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>

From aeb6bd088b0f54d3847b244f7066333b28dead3f Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Wed, 6 May 2026 22:04:50 +0200
Subject: [PATCH 06/10] fix: reapply context after transforming error during
 SSR (#18099)

Don't have a test for it and no bug report but I stumbled upon this and
I'm very certain not restoring context here is wrong since it means the
failed snippet rendering gets the wrong context.

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
---
 .changeset/cruel-boxes-serve.md                 | 5 +++++
 packages/svelte/src/internal/server/renderer.js | 7 ++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/cruel-boxes-serve.md

diff --git a/.changeset/cruel-boxes-serve.md b/.changeset/cruel-boxes-serve.md
new file mode 100644
index 0000000000..592cec4d01
--- /dev/null
+++ b/.changeset/cruel-boxes-serve.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: reapply context after transforming error during SSR
diff --git a/packages/svelte/src/internal/server/renderer.js b/packages/svelte/src/internal/server/renderer.js
index d2ab35a1f2..35aac64721 100644
--- a/packages/svelte/src/internal/server/renderer.js
+++ b/packages/svelte/src/internal/server/renderer.js
@@ -715,7 +715,12 @@ export class Renderer {
 						const { context, failed, transformError } = item.#boundary;
 
 						set_ssr_context(context);
-						let transformed = await transformError(error);
+
+						let promise = transformError(error);
+						set_ssr_context(null);
+
+						let transformed = await promise;
+						set_ssr_context(context);
 
 						// Render the failed snippet instead of the partial children content
 						const failed_renderer = new Renderer(item.global, item);

From 91e1ead773c00eece56d49542c94670aabbc5902 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 6 May 2026 16:16:06 -0400
Subject: [PATCH 07/10] chore: remove unnecessary `increment_pending` calls
 (#18183)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

These might have been necessary at one point, but I'm confident they're
unnecessary now — `increment_pending` happens (if necessary) inside
`flatten`, which is called inside `async` and
`deferred_template_effect`, so there's no need to call it inside those
functions as well.
---
 .changeset/public-mammals-float.md                     |  5 +++++
 .../svelte/src/internal/client/dom/blocks/async.js     |  6 +-----
 .../svelte/src/internal/client/reactivity/effects.js   | 10 +---------
 3 files changed, 7 insertions(+), 14 deletions(-)
 create mode 100644 .changeset/public-mammals-float.md

diff --git a/.changeset/public-mammals-float.md b/.changeset/public-mammals-float.md
new file mode 100644
index 0000000000..d890c9e070
--- /dev/null
+++ b/.changeset/public-mammals-float.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: remove unnecessary `increment_pending` calls
diff --git a/packages/svelte/src/internal/client/dom/blocks/async.js b/packages/svelte/src/internal/client/dom/blocks/async.js
index 43af3d8dd3..170529a6b9 100644
--- a/packages/svelte/src/internal/client/dom/blocks/async.js
+++ b/packages/svelte/src/internal/client/dom/blocks/async.js
@@ -1,5 +1,5 @@
 /** @import { Blocker, TemplateNode, Value } from '#client' */
-import { flatten, increment_pending } from '../../reactivity/async.js';
+import { flatten } from '../../reactivity/async.js';
 import { get } from '../../runtime.js';
 import {
 	hydrate_next,
@@ -42,8 +42,6 @@ export function async(node, blockers = [], expressions = [], fn) {
 		return;
 	}
 
-	const decrement_pending = increment_pending();
-
 	if (was_hydrating) {
 		var previous_hydrate_node = hydrate_node;
 		set_hydrate_node(end);
@@ -64,8 +62,6 @@ export function async(node, blockers = [], expressions = [], fn) {
 			if (was_hydrating) {
 				set_hydrating(false);
 			}
-
-			decrement_pending();
 		}
 	});
 }
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index 0fad074e6f..5bdba037b1 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -43,7 +43,7 @@ import { define_property } from '../../shared/utils.js';
 import { get_next_sibling } from '../dom/operations.js';
 import { component_context, dev_current_component_function, dev_stack } from '../context.js';
 import { Batch, collected_effects, current_batch } from './batch.js';
-import { flatten, increment_pending } from './async.js';
+import { flatten } from './async.js';
 import { without_reactive_context } from '../dom/elements/bindings/shared.js';
 import { set_signal_status } from './status.js';
 
@@ -396,16 +396,8 @@ export function template_effect(fn, sync = [], async = [], blockers = []) {
  * @param {Blocker[]} blockers
  */
 export function deferred_template_effect(fn, sync = [], async = [], blockers = []) {
-	if (async.length > 0 || blockers.length > 0) {
-		var decrement_pending = increment_pending();
-	}
-
 	flatten(blockers, sync, async, (values) => {
 		create_effect(EFFECT, () => fn(...values.map(get)));
-
-		if (decrement_pending) {
-			decrement_pending();
-		}
 	});
 }
 

From 1c150a460fdb67703aeba9eb515c0a30e2348ccb Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Wed, 6 May 2026 22:37:46 +0200
Subject: [PATCH 08/10] fix: abort running obsolete async branches (#18118)

We shouldn't continue executing async work where we know the surrounding
branch is destroyed already, it can leave to noisy "derived inter"
warnings or even runtime errors ("cannot stringify symbol" when running
a template effect with an uninitialized source). Neither should we warn
about waterfalls on an already-destroyed async effect.

Fixes #18097 (though strictly speaking that particular instance is also
fixed by #18117 which fixes the underlying cause for the reruns; this
one is necessary in itself though, as shown by the new test)

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
---
 .changeset/stupid-baboons-fall.md             |  5 +++
 .../src/internal/client/reactivity/async.js   |  8 +++--
 .../internal/client/reactivity/deriveds.js    |  2 +-
 .../Child.svelte                              |  6 ++++
 .../_config.js                                | 27 ++++++++++++++++
 .../main.svelte                               | 31 +++++++++++++++++++
 6 files changed, 75 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/stupid-baboons-fall.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/Child.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/main.svelte

diff --git a/.changeset/stupid-baboons-fall.md b/.changeset/stupid-baboons-fall.md
new file mode 100644
index 0000000000..66895ad015
--- /dev/null
+++ b/.changeset/stupid-baboons-fall.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: abort running obsolete async branches
diff --git a/packages/svelte/src/internal/client/reactivity/async.js b/packages/svelte/src/internal/client/reactivity/async.js
index 61fff31f8a..5e418d81a1 100644
--- a/packages/svelte/src/internal/client/reactivity/async.js
+++ b/packages/svelte/src/internal/client/reactivity/async.js
@@ -55,14 +55,16 @@ export function flatten(blockers, sync, async, fn) {
 
 	/** @param {Value[]} values */
 	function finish(values) {
+		if ((parent.f & DESTROYED) !== 0) {
+			return;
+		}
+
 		restore();
 
 		try {
 			fn(values);
 		} catch (error) {
-			if ((parent.f & DESTROYED) === 0) {
-				invoke_error_boundary(error, parent);
-			}
+			invoke_error_boundary(error, parent);
 		}
 
 		unset_context();
diff --git a/packages/svelte/src/internal/client/reactivity/deriveds.js b/packages/svelte/src/internal/client/reactivity/deriveds.js
index eb934d96ff..070dfc8ff3 100644
--- a/packages/svelte/src/internal/client/reactivity/deriveds.js
+++ b/packages/svelte/src/internal/client/reactivity/deriveds.js
@@ -239,7 +239,7 @@ export function async_derived(fn, label, location) {
 					recent_async_deriveds.add(signal);
 
 					setTimeout(() => {
-						if (recent_async_deriveds.has(signal)) {
+						if (recent_async_deriveds.has(signal) && (effect.f & DESTROYED) === 0) {
 							w.await_waterfall(/** @type {string} */ (signal.label), location);
 							recent_async_deriveds.delete(signal);
 						}
diff --git a/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/Child.svelte
new file mode 100644
index 0000000000..1d9bdfada2
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/Child.svelte
@@ -0,0 +1,6 @@
+<script>
+	let { count } = $props();
+	let double = $derived(count * 2);
+
+	$effect.pre(() => console.log(count, double));
+</script>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/_config.js b/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/_config.js
new file mode 100644
index 0000000000..83364706e5
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/_config.js
@@ -0,0 +1,27 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target, logs, warnings }) {
+		const [increment, resolve] = target.querySelectorAll('button');
+
+		increment.click();
+		await tick();
+		assert.deepEqual(logs, []);
+
+		resolve.click();
+		await tick();
+		assert.deepEqual(logs, []);
+
+		resolve.click();
+		await tick();
+		assert.deepEqual(logs, []);
+
+		resolve.click();
+		await tick();
+		assert.deepEqual(logs, [1, 2]);
+
+		// no await waterfall / inert derived warnings
+		assert.deepEqual(warnings, []);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/main.svelte
new file mode 100644
index 0000000000..fe01ae457e
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/main.svelte
@@ -0,0 +1,31 @@
+<script>
+	import Child from "./Child.svelte";
+	let count = $state(0);
+
+	let deferreds = [];
+
+	function push(v) {
+		return new Promise((resolve, reject) => {
+			deferreds.push({ resolve: () => resolve(v), reject });
+		});
+	}
+</script>
+
+<button onclick={() => count += 1}>increment</button>
+<button onclick={() => deferreds.shift()?.resolve()}>resolve</button>
+
+<svelte:boundary>
+	{#if count % 2 === 0}
+		{@const double = count * 2}
+		<p>true</p>
+		{await push(count)} {double}
+		<Child count={await push(count)} />
+	{:else}
+		<p>false</p>
+		<Child count={await push(count)} />
+	{/if}
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>

From 4d2b6c61e0259f497c14d5148fe80e16da684ef2 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 6 May 2026 18:24:23 -0400
Subject: [PATCH 09/10] chore: make `batch.#pending` a number rather than a map
 (#18184)

there's no reason for this to be a map
---
 .../src/internal/client/reactivity/batch.js    | 18 +++++-------------
 1 file changed, 5 insertions(+), 13 deletions(-)

diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index 2801445ae7..2d555bb34d 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -130,10 +130,9 @@ export class Batch {
 	#fork_commit_callbacks = new Set();
 
 	/**
-	 * Async effects that are currently in flight
-	 * @type {Map<Effect, number>}
+	 * The number of async effects that are currently in flight
 	 */
-	#pending = new Map();
+	#pending = 0;
 
 	/**
 	 * Async effects that are currently in flight, _not_ inside a pending boundary
@@ -327,7 +326,7 @@ export class Batch {
 				reset_branch(e, t);
 			}
 		} else {
-			if (this.#pending.size === 0) {
+			if (this.#pending === 0) {
 				batches.delete(this);
 			}
 
@@ -637,8 +636,7 @@ export class Batch {
 	 * @param {Effect} effect
 	 */
 	increment(blocking, effect) {
-		let pending_count = this.#pending.get(effect) ?? 0;
-		this.#pending.set(effect, pending_count + 1);
+		this.#pending += 1;
 
 		if (blocking) {
 			let blocking_pending_count = this.#blocking_pending.get(effect) ?? 0;
@@ -652,13 +650,7 @@ export class Batch {
 	 * @param {boolean} skip - whether to skip updates (because this is triggered by a stale reaction)
 	 */
 	decrement(blocking, effect, skip) {
-		let pending_count = this.#pending.get(effect) ?? 0;
-
-		if (pending_count === 1) {
-			this.#pending.delete(effect);
-		} else {
-			this.#pending.set(effect, pending_count - 1);
-		}
+		this.#pending -= 1;
 
 		if (blocking) {
 			let blocking_pending_count = this.#blocking_pending.get(effect) ?? 0;

From 908c9d031283955629f784a9a9cd523172c10353 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 7 May 2026 04:30:24 -0400
Subject: [PATCH 10/10] fix: leave stale promises to wait for a later
 resolution, instead of rejecting (#18180)

This incorporates some of the fixes and insights from #18177, but gets
rid of the `skip` logic.

Instead, we differentiate between _stale_ and _obsolete_ promises. A
promise is stale if it has been overtaken by a subsequent update, and
was rejected with `STALE_REACTION`:

```ts
async function search(query: string) {
  return fetch(`/search?q=${query}`, { signal: getAbortSignal() }).then((r) => r.json());
}
```

In this case, if we start typing `pot`, and then finish typing `potato`,
the first promise will eventually resolve with the results for
`/search?q=potato`, instead of the batch entering a weird limbo/zombie
state.

A promise is obsolete if it belongs to a now-destroyed effect, meaning
that toggling `show` doesn't result in an accumulation of
never-resolving batches:

```svelte
{#if show}
  {await neverResolves()}
{/if}
```

Fixes part of https://github.com/sveltejs/kit/issues/15431

---------

Co-authored-by: Simon Holthausen <simon.holthausen@vercel.com>
Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
---
 .changeset/big-webs-sing.md                   |  5 +++
 .../src/internal/client/reactivity/async.js   | 17 ++++---
 .../src/internal/client/reactivity/batch.js   | 19 ++++++--
 .../internal/client/reactivity/deriveds.js    | 43 ++++++++++--------
 .../samples/async-batch-order/_config.js      | 30 +++++++++++++
 .../samples/async-batch-order/main.svelte     | 21 +++++++++
 .../samples/async-stale-derived-4/_config.js  | 28 ++++++++++++
 .../samples/async-stale-derived-4/main.svelte | 21 +++++++++
 .../samples/async-stale-derived-5/_config.js  | 33 ++++++++++++++
 .../samples/async-stale-derived-5/main.svelte | 44 +++++++++++++++++++
 .../samples/async-stale-derived-6/_config.js  | 34 ++++++++++++++
 .../samples/async-stale-derived-6/main.svelte | 21 +++++++++
 .../samples/async-stale-derived-7/_config.js  | 34 ++++++++++++++
 .../samples/async-stale-derived-7/main.svelte | 22 ++++++++++
 14 files changed, 342 insertions(+), 30 deletions(-)
 create mode 100644 .changeset/big-webs-sing.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-batch-order/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-batch-order/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-stale-derived-4/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-stale-derived-4/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-stale-derived-5/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-stale-derived-5/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-stale-derived-6/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-stale-derived-6/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-stale-derived-7/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-stale-derived-7/main.svelte

diff --git a/.changeset/big-webs-sing.md b/.changeset/big-webs-sing.md
new file mode 100644
index 0000000000..946a41d881
--- /dev/null
+++ b/.changeset/big-webs-sing.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: leave stale promises to wait for a later resolution, instead of rejecting
diff --git a/packages/svelte/src/internal/client/reactivity/async.js b/packages/svelte/src/internal/client/reactivity/async.js
index 5e418d81a1..c1d4cbcd67 100644
--- a/packages/svelte/src/internal/client/reactivity/async.js
+++ b/packages/svelte/src/internal/client/reactivity/async.js
@@ -70,20 +70,23 @@ export function flatten(blockers, sync, async, fn) {
 		unset_context();
 	}
 
+	var decrement_pending = increment_pending();
+
 	// Fast path: blockers but no async expressions
 	if (async.length === 0) {
-		/** @type {Promise<any>} */ (blocker_promise).then(() => finish(sync.map(d)));
+		/** @type {Promise<any>} */ (blocker_promise)
+			.then(() => finish(sync.map(d)))
+			.finally(decrement_pending);
+
 		return;
 	}
 
-	var decrement_pending = increment_pending();
-
 	// Full path: has async expressions
 	function run() {
 		Promise.all(async.map((expression) => async_derived(expression)))
 			.then((result) => finish([...sync.map(d), ...result]))
 			.catch((error) => invoke_error_boundary(error, parent))
-			.finally(() => decrement_pending());
+			.finally(decrement_pending);
 	}
 
 	if (blocker_promise) {
@@ -325,7 +328,7 @@ export function run(thunks) {
 		// wait one more tick, so that template effects are
 		// guaranteed to run before `$effect(...)`
 		.then(() => Promise.resolve())
-		.finally(() => decrement_pending());
+		.finally(decrement_pending);
 
 	return blockers;
 }
@@ -349,8 +352,8 @@ export function increment_pending() {
 	boundary.update_pending_count(1, batch);
 	batch.increment(blocking, effect);
 
-	return (skip = false) => {
+	return () => {
 		boundary.update_pending_count(-1, batch);
-		batch.decrement(blocking, effect, skip);
+		batch.decrement(blocking, effect);
 	};
 }
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index 2d555bb34d..a106806721 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -110,6 +110,13 @@ export class Batch {
 	 */
 	previous = new Map();
 
+	/**
+	 * Async effects which this batch doesn't take into account anymore when calculating blockers,
+	 * as it has a value for it already.
+	 * @type {Set<Effect>}
+	 */
+	unblocked = new Set();
+
 	/**
 	 * When the batch is committed (and the DOM is updated), we need to remove old branches
 	 * and append new ones by calling the functions added inside (if/each/key/etc) blocks
@@ -200,6 +207,8 @@ export class Batch {
 	#is_blocked() {
 		for (const batch of this.#blockers) {
 			for (const effect of batch.#blocking_pending.keys()) {
+				if (this.unblocked.has(effect)) continue;
+
 				var skipped = false;
 				var e = effect;
 
@@ -647,9 +656,8 @@ export class Batch {
 	/**
 	 * @param {boolean} blocking
 	 * @param {Effect} effect
-	 * @param {boolean} skip - whether to skip updates (because this is triggered by a stale reaction)
 	 */
-	decrement(blocking, effect, skip) {
+	decrement(blocking, effect) {
 		this.#pending -= 1;
 
 		if (blocking) {
@@ -662,12 +670,15 @@ export class Batch {
 			}
 		}
 
-		if (this.#decrement_queued || skip) return;
+		if (this.#decrement_queued) return;
 		this.#decrement_queued = true;
 
 		queue_micro_task(() => {
 			this.#decrement_queued = false;
-			this.flush();
+
+			if (batches.has(this)) {
+				this.flush();
+			}
 		});
 	}
 
diff --git a/packages/svelte/src/internal/client/reactivity/deriveds.js b/packages/svelte/src/internal/client/reactivity/deriveds.js
index 070dfc8ff3..794da4f2b0 100644
--- a/packages/svelte/src/internal/client/reactivity/deriveds.js
+++ b/packages/svelte/src/internal/client/reactivity/deriveds.js
@@ -100,6 +100,8 @@ export function derived(fn) {
 	return signal;
 }
 
+const OBSOLETE = {};
+
 /**
  * @template V
  * @param {() => V | Promise<V>} fn
@@ -118,7 +120,7 @@ export function async_derived(fn, label, location) {
 	var promise = /** @type {Promise<V>} */ (/** @type {unknown} */ (undefined));
 	var signal = source(/** @type {V} */ (UNINITIALIZED));
 
-	if (DEV) signal.label = label;
+	if (DEV) signal.label = label ?? fn.toString();
 
 	// only suspend in async deriveds created on initialisation
 	var should_suspend = !active_reaction;
@@ -141,7 +143,13 @@ export function async_derived(fn, label, location) {
 			// If this code is changed at some point, make sure to still access the then property
 			// of fn() to read any signals it might access, so that we track them as dependencies.
 			// We call `unset_context` to undo any `save` calls that happen inside `fn()`
-			Promise.resolve(fn()).then(d.resolve, d.reject).finally(unset_context);
+			Promise.resolve(fn())
+				.then(d.resolve, (e) => {
+					// if the promise was rejected by the user, via `getAbortSignal`, then
+					// wait for a subsequent resolution instead of flushing the batch
+					if (e !== STALE_REACTION) d.reject(e);
+				})
+				.finally(unset_context);
 		} catch (error) {
 			d.reject(error);
 			unset_context();
@@ -180,15 +188,13 @@ export function async_derived(fn, label, location) {
 			}
 
 			if (/** @type {Boundary} */ (parent.b).is_rendered()) {
-				deferreds.get(batch)?.reject(STALE_REACTION);
-				deferreds.delete(batch); // delete to ensure correct order in Map iteration below
+				deferreds.get(batch)?.reject(OBSOLETE);
 			} else {
 				// While the boundary is still showing pending, a new run supersedes all older in-flight runs
 				// for this async expression. Cancel eagerly so resolution cannot commit stale values.
 				for (const d of deferreds.values()) {
-					d.reject(STALE_REACTION);
+					d.reject(OBSOLETE);
 				}
-				deferreds.clear();
 			}
 
 			deferreds.set(batch, d);
@@ -203,16 +209,10 @@ export function async_derived(fn, label, location) {
 				reactivity_loss_tracker = null;
 			}
 
-			if (decrement_pending) {
-				// don't trigger an update if we're only here because
-				// the promise was superseded before it could resolve
-				var skip = error === STALE_REACTION;
-				decrement_pending(skip);
-			}
+			decrement_pending?.();
+			deferreds.delete(batch);
 
-			if (error === STALE_REACTION || (effect.f & DESTROYED) !== 0) {
-				return;
-			}
+			if (error === OBSOLETE) return;
 
 			batch.activate();
 
@@ -230,9 +230,14 @@ export function async_derived(fn, label, location) {
 
 				// All prior async derived runs are now stale
 				for (const [b, d] of deferreds) {
-					deferreds.delete(b);
-					if (b === batch) break;
-					d.resolve(value);
+					if (b.id < batch.id) {
+						// Don't delete + resolve directly, instead only do that once
+						// the current batch commits. This way we avoid tearing when
+						// `b` is rendering through the early resolve while `batch` is
+						// still pending.
+						batch.unblocked.add(effect);
+						batch.oncommit(() => d.resolve(value));
+					}
 				}
 
 				if (DEV && location !== undefined) {
@@ -255,7 +260,7 @@ export function async_derived(fn, label, location) {
 
 	teardown(() => {
 		for (const d of deferreds.values()) {
-			d.reject(STALE_REACTION);
+			d.reject(OBSOLETE);
 		}
 	});
 
diff --git a/packages/svelte/tests/runtime-runes/samples/async-batch-order/_config.js b/packages/svelte/tests/runtime-runes/samples/async-batch-order/_config.js
new file mode 100644
index 0000000000..53cceb9d54
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-batch-order/_config.js
@@ -0,0 +1,30 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+		const [increment, shift, middle] = target.querySelectorAll('button');
+		const [div] = target.querySelectorAll('div');
+
+		increment.click();
+		await tick();
+		increment.click();
+		await tick();
+		increment.click();
+		await tick();
+		middle.click(); // resolve the second increment which will make the if block go away and the first batch discarded
+		await tick();
+		assert.htmlEqual(div.innerHTML, '2 2');
+
+		shift.click();
+		await tick();
+		shift.click();
+		await tick();
+		shift.click();
+		await tick();
+		shift.click();
+		await tick();
+		assert.htmlEqual(div.innerHTML, '3 3');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-batch-order/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-batch-order/main.svelte
new file mode 100644
index 0000000000..0289380d78
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-batch-order/main.svelte
@@ -0,0 +1,21 @@
+<script>
+	let a = $state(0);
+
+	const deferred = [];
+
+	function delay(value) {
+		if (!value) return value;
+		return new Promise((resolve) => deferred.push(() => resolve(value)));
+	}
+</script>
+
+<div>
+	{a} {await delay(a)}
+	{#if a < 2}
+		{await delay(a)}
+	{/if}
+</div>
+
+<button onclick={() => {a++;}}>a++</button>
+<button onclick={() => deferred.shift()?.()}>shift</button>
+<button onclick={() => deferred[2]()}>middle</button>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-stale-derived-4/_config.js b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-4/_config.js
new file mode 100644
index 0000000000..e1555c0062
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-4/_config.js
@@ -0,0 +1,28 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+
+		const [increment, hide, pop] = target.querySelectorAll('button');
+
+		increment.click();
+		await tick();
+		pop.click();
+		await tick();
+		hide.click(); // hides the if block, which cancels the pending async inside, which means the batch can complete
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`<button>increment</button> <button>hide</button> <button>pop</button> 1`
+		);
+
+		pop.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`<button>increment</button> <button>hide</button> <button>pop</button> 1`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-stale-derived-4/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-4/main.svelte
new file mode 100644
index 0000000000..5ff3263d39
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-4/main.svelte
@@ -0,0 +1,21 @@
+<script>
+	let show = $state(true);
+	let count = $state(0);
+
+	const queue = [];
+
+	function push(value) {
+		if (!value) return value;
+		return new Promise(r => queue.push(() => r(value)));
+	}
+</script>
+
+<button onclick={() => count += 1}>increment</button>
+<button onclick={() => show = false}>hide</button>
+<!-- pop() so that the outer one resolves first, not the one inside the if block -->
+<button onclick={() => queue.pop()?.()}>pop</button>
+
+{await push(count)}
+{#if show}
+	{await push(count)}
+{/if}
diff --git a/packages/svelte/tests/runtime-runes/samples/async-stale-derived-5/_config.js b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-5/_config.js
new file mode 100644
index 0000000000..05d92e9df2
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-5/_config.js
@@ -0,0 +1,33 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+
+		const [increment, shift] = target.querySelectorAll('button');
+
+		increment.click();
+		await tick();
+		increment.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`<button>3</button><button>shift</button><p>1 = 1</p><p>fizz: true</p><p>buzz: true</p>`
+		);
+
+		shift.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`<button>3</button><button>shift</button><p>1 = 1</p><p>fizz: true</p><p>buzz: true</p>`
+		);
+
+		shift.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`<button>3</button><button>shift</button><p>3 = 3</p><p>fizz: true</p><p>buzz: false</p>`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-stale-derived-5/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-5/main.svelte
new file mode 100644
index 0000000000..b2a40e65b3
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-5/main.svelte
@@ -0,0 +1,44 @@
+<script>
+	import { getAbortSignal } from 'svelte';
+
+	const queue = [];
+
+	let n = $state(1);
+	let fizz = $state(true);
+	let buzz = $state(true);
+
+	function increment() {
+		n++;
+
+		fizz = n % 3 === 0;
+		buzz = n % 5 === 0;
+	}
+
+	function push(value) {
+		if (value === 1) return 1;
+		const d = Promise.withResolvers();
+
+		queue.push(() => d.resolve(value));
+
+		const signal = getAbortSignal();
+		signal.onabort = () => d.reject(signal.reason);
+
+		return d.promise;
+	}
+</script>
+
+<button onclick={increment}>
+	{$state.eager(n)}
+</button>
+
+<button onclick={() => queue.shift()?.()}>shift</button>
+
+<p>{n} = {await push(n)}</p>
+
+{#if true}
+	<p>fizz: {fizz}</p>
+{/if}
+
+{#if true}
+	<p>buzz: {buzz}</p>
+{/if}
diff --git a/packages/svelte/tests/runtime-runes/samples/async-stale-derived-6/_config.js b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-6/_config.js
new file mode 100644
index 0000000000..5b951d6c49
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-6/_config.js
@@ -0,0 +1,34 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+		const [button1, button2, pop, shift] = target.querySelectorAll('button');
+		const [p] = target.querySelectorAll('p');
+
+		button1.click();
+		await tick();
+		button2.click();
+		await tick();
+		assert.htmlEqual(p.innerHTML, `0 + 0 = 0 | 0 0`);
+
+		shift.click();
+		await tick();
+		assert.htmlEqual(p.innerHTML, `0 + 0 = 0 | 0 0`);
+
+		pop.click();
+		await tick();
+		assert.htmlEqual(p.innerHTML, `0 + 0 = 0 | 0 0`);
+
+		pop.click();
+		await tick();
+		assert.htmlEqual(p.innerHTML, `1 + 0 = 1 | 1 0`);
+
+		shift.click();
+		await tick();
+		pop.click();
+		await tick();
+		assert.htmlEqual(p.innerHTML, `1 + 2 = 3 | 1 1`);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-stale-derived-6/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-6/main.svelte
new file mode 100644
index 0000000000..4515e7a488
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-6/main.svelte
@@ -0,0 +1,21 @@
+<script>
+	const queue1 = [];
+	const queue2 = [];
+
+	let a = $state(0);
+	let b = $state(0);
+	let c = $state(0);
+	let d = $state(0)
+
+	function push(value, where = 1) {
+		if (!value) return value;
+		return new Promise(r => (where === 1 ? queue1 : queue2).push(() => r(value)));
+	}
+</script>
+
+<button onclick={() => {a++;c++}}>a / c</button>
+<button onclick={() => {b+=2;d++}}>b / d</button>
+<button onclick={() => queue1.pop()?.()}>pop 1</button>
+<button onclick={() => queue2.shift()?.()}>shift 2</button>
+
+<p>{a} + {b} = {await push(a + b)} | {await push(c, 2)} {await push(d, 2)}</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-stale-derived-7/_config.js b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-7/_config.js
new file mode 100644
index 0000000000..a6f1833d67
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-7/_config.js
@@ -0,0 +1,34 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+		const [button1, button2, shift_1, pop_1, shift_2] = target.querySelectorAll('button');
+		const [p] = target.querySelectorAll('p');
+
+		button1.click();
+		await tick();
+		button2.click();
+		await tick();
+		assert.htmlEqual(p.innerHTML, `0 + 0 = 0 | 0 0`);
+
+		pop_1.click();
+		await tick();
+		shift_2.click();
+		await tick();
+		assert.htmlEqual(p.innerHTML, `0 + 0 = 0 | 0 0`);
+
+		// Check that the first batch can still resolve before the second even if one of its async values
+		// is already superseeded (but the subsequent batch as a whole is still pending).
+		shift_1.click();
+		await tick();
+		assert.htmlEqual(p.innerHTML, `1 + 0 = 1 | 1 0`);
+
+		shift_1.click();
+		await tick();
+		shift_2.click();
+		await tick();
+		assert.htmlEqual(p.innerHTML, `1 + 2 = 3 | 1 1`);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-stale-derived-7/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-7/main.svelte
new file mode 100644
index 0000000000..fec684c257
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-stale-derived-7/main.svelte
@@ -0,0 +1,22 @@
+<script>
+	const queue1 = [];
+	const queue2 = [];
+
+	let a = $state(0);
+	let b = $state(0);
+	let c = $state(0);
+	let d = $state(0)
+
+	function push(value, where = 1) {
+		if (!value) return value;
+		return new Promise(r => (where === 1 ? queue1 : queue2).push(() => r(value)));
+	}
+</script>
+
+<button onclick={() => {a++;c++}}>a / c</button>
+<button onclick={() => {b+=2;d++}}>b / d</button>
+<button onclick={() => queue1.shift()?.()}>shift 1</button>
+<button onclick={() => queue1.pop()?.()}>pop 1</button>
+<button onclick={() => queue2.shift()?.()}>shift 2</button>
+
+<p>{a} + {b} = {await push(a + b)} | {await push(c, 2)} {await push(d, 2)}</p>