From 179f66b297a1cfd943ad31dcd575587d629c412c Mon Sep 17 00:00:00 2001
From: jarrednorris <58517737+jarrednorrisdev@users.noreply.github.com>
Date: Tue, 6 Oct 2026 10:50:59 +0100
Subject: [PATCH] fix: don't create async deriveds for a component destroyed
 while waiting for its top-level `await` (#18931)

Fixes #18930

---------

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
---
 .changeset/brave-owls-wait.md                 |  5 +++
 .../src/internal/client/reactivity/async.js   |  5 +++
 .../Child.svelte                              |  7 +++++
 .../_config.js                                | 31 +++++++++++++++++++
 .../main.svelte                               | 20 ++++++++++++
 5 files changed, 68 insertions(+)
 create mode 100644 .changeset/brave-owls-wait.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-destroyed-before-blockers-settle/Child.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-destroyed-before-blockers-settle/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-destroyed-before-blockers-settle/main.svelte

diff --git a/.changeset/brave-owls-wait.md b/.changeset/brave-owls-wait.md
new file mode 100644
index 0000000000..827868b8c3
--- /dev/null
+++ b/.changeset/brave-owls-wait.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: don't create async deriveds for a component destroyed while waiting for its top-level `await`
diff --git a/packages/svelte/src/internal/client/reactivity/async.js b/packages/svelte/src/internal/client/reactivity/async.js
index a75f97a54f..efdfe6625c 100644
--- a/packages/svelte/src/internal/client/reactivity/async.js
+++ b/packages/svelte/src/internal/client/reactivity/async.js
@@ -103,6 +103,11 @@ export function flatten(blockers, sync, async, fn) {
 
 	if (blocker_promise) {
 		blocker_promise.then(() => {
+			if ((parent.f & DESTROYED) !== 0) {
+				decrement_pending();
+				return;
+			}
+
 			restore();
 			run();
 			unset_context();
diff --git a/packages/svelte/tests/runtime-runes/samples/async-destroyed-before-blockers-settle/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-destroyed-before-blockers-settle/Child.svelte
new file mode 100644
index 0000000000..63a16dde43
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-destroyed-before-blockers-settle/Child.svelte
@@ -0,0 +1,7 @@
+<script>
+	let { promise } = $props();
+
+	const value = await promise;
+</script>
+
+<p>{await Promise.resolve(value)}</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-destroyed-before-blockers-settle/_config.js b/packages/svelte/tests/runtime-runes/samples/async-destroyed-before-blockers-settle/_config.js
new file mode 100644
index 0000000000..096f90e2df
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-destroyed-before-blockers-settle/_config.js
@@ -0,0 +1,31 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const [hide, resolve] = target.querySelectorAll('button');
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>hide</button>
+				<button>resolve</button>
+				<p>loading...</p>
+			`
+		);
+
+		hide.click();
+		await tick();
+
+		resolve.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>hide</button>
+				<button>resolve</button>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-destroyed-before-blockers-settle/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-destroyed-before-blockers-settle/main.svelte
new file mode 100644
index 0000000000..3bc50e5d24
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-destroyed-before-blockers-settle/main.svelte
@@ -0,0 +1,20 @@
+<script>
+	import Child from './Child.svelte';
+
+	const deferred = Promise.withResolvers();
+
+	let show = $state(true);
+</script>
+
+<button onclick={() => (show = false)}>hide</button>
+<button onclick={() => deferred.resolve(1)}>resolve</button>
+
+<svelte:boundary>
+	{#if show}
+		<Child promise={deferred.promise} />
+	{/if}
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>