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 1/5] 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 2/5] 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 3/5] 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 4/5] 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 5/5] 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>