From 22e0adb75a07442015feb0465cee1d3a61729e90 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Thu, 16 Jul 2026 10:42:31 +0200
Subject: [PATCH] fix: rerun derived that had an abort controller on
 reconnection (#18551)

Follow-up to #18400 - we need to mark a derived with an abort signal
that is frozen as dirty so it is guaranteed to rerun when it
reconnects/is re-requested. Else you could return a stale value, or
worse, you returned a promise from the derived which you aborted, and
it's now in the rejected state until you update one of its dependencies.
---
 .changeset/lucky-dolls-yell.md                |  5 +++
 .../svelte/src/internal/client/runtime.js     |  2 ++
 .../_config.js                                | 32 +++++++++++++++++++
 .../main.svelte                               | 32 +++++++++++++++++++
 4 files changed, 71 insertions(+)
 create mode 100644 .changeset/lucky-dolls-yell.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/abort-signal-derived-rerun-on-reconnect/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/abort-signal-derived-rerun-on-reconnect/main.svelte

diff --git a/.changeset/lucky-dolls-yell.md b/.changeset/lucky-dolls-yell.md
new file mode 100644
index 0000000000..d158f376d1
--- /dev/null
+++ b/.changeset/lucky-dolls-yell.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: rerun derived that had an abort controller on reconnection
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 2ebce07916..4458595d35 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -413,6 +413,8 @@ function remove_reaction(signal, dependency) {
 			without_reactive_context(() => {
 				/** @type {AbortController} */ (derived.ac).abort(STALE_REACTION);
 				derived.ac = null;
+				// ensure it reruns right away next time instead of potentially returning a rejected promise as its value
+				set_signal_status(derived, DIRTY);
 			});
 		}
 
diff --git a/packages/svelte/tests/runtime-runes/samples/abort-signal-derived-rerun-on-reconnect/_config.js b/packages/svelte/tests/runtime-runes/samples/abort-signal-derived-rerun-on-reconnect/_config.js
new file mode 100644
index 0000000000..7caf765e3b
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/abort-signal-derived-rerun-on-reconnect/_config.js
@@ -0,0 +1,32 @@
+import { test } from '../../test';
+import { tick } from 'svelte';
+
+export default test({
+	async test({ assert, target }) {
+		const [increment, toggle, resolve] = target.querySelectorAll('button');
+		const [div] = target.querySelectorAll('div');
+
+		assert.htmlEqual(div.innerHTML, 'loading');
+		resolve.click();
+		await tick();
+		assert.htmlEqual(div.innerHTML, '0');
+
+		increment.click();
+		await tick();
+		assert.htmlEqual(div.innerHTML, 'loading');
+
+		toggle.click();
+		await tick();
+		assert.htmlEqual(div.innerHTML, '');
+
+		toggle.click();
+		await tick();
+		assert.htmlEqual(div.innerHTML, 'loading');
+
+		resolve.click(); // this one's for clearing the obsolete/aborted one from the queue
+		await tick();
+		resolve.click();
+		await tick();
+		assert.htmlEqual(div.innerHTML, '2');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/abort-signal-derived-rerun-on-reconnect/main.svelte b/packages/svelte/tests/runtime-runes/samples/abort-signal-derived-rerun-on-reconnect/main.svelte
new file mode 100644
index 0000000000..a047afdd44
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/abort-signal-derived-rerun-on-reconnect/main.svelte
@@ -0,0 +1,32 @@
+<script>
+	import { getAbortSignal } from 'svelte'
+	
+	let show = $state(true)
+	let count = $state(0);
+	let queued = [];
+
+	export function sleep(value, signal) {
+	  return new Promise((resolve, reject) => {
+	    signal.addEventListener('abort', reject, { once: true });
+		queued.push(() => resolve(value));
+	  });
+	}
+
+	const double = $derived(sleep(count * 2, getAbortSignal()));
+</script>
+
+<button onclick={() => count += 1}>clicks: {count}</button>
+<button onclick={() => show = !show}>toggle</button>
+<button onclick={() => queued.shift()?.()}>resolve</button>
+
+<div>
+	{#if show}
+		{#await double}
+			loading
+		{:then value}
+			{value}
+		{:catch}
+			error
+		{/await}
+	{/if}
+</div>