From 19d84d2ffaff91ccb473491548399c046488195a Mon Sep 17 00:00:00 2001
From: svelte-triage-bot <team@svelte.com>
Date: Mon, 24 Aug 2026 10:29:05 +0000
Subject: [PATCH 1/2] fix: track SvelteDate snapshots in reactions

---
 .changeset/calm-dates-track.md                |  5 +++++
 packages/svelte/src/internal/shared/clone.js  |  2 ++
 .../state-snapshot-svelte-date/_config.js     | 19 +++++++++++++++++++
 .../state-snapshot-svelte-date/main.svelte    |  9 +++++++++
 4 files changed, 35 insertions(+)
 create mode 100644 .changeset/calm-dates-track.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/state-snapshot-svelte-date/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/state-snapshot-svelte-date/main.svelte

diff --git a/.changeset/calm-dates-track.md b/.changeset/calm-dates-track.md
new file mode 100644
index 000000000000..e7275ae55677
--- /dev/null
+++ b/.changeset/calm-dates-track.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: track SvelteDate snapshots in reactions
diff --git a/packages/svelte/src/internal/shared/clone.js b/packages/svelte/src/internal/shared/clone.js
index 1a83adf8c594..ba0c731047d6 100644
--- a/packages/svelte/src/internal/shared/clone.js
+++ b/packages/svelte/src/internal/shared/clone.js
@@ -105,6 +105,8 @@ function clone(value, cloned, path, paths, original = null, no_tojson = false) {
 		}
 
 		if (value instanceof Date) {
+			// Ensure SvelteDate snapshots are tracked
+			value.getTime();
 			return /** @type {Snapshot<T>} */ (structuredClone(value));
 		}
 
diff --git a/packages/svelte/tests/runtime-runes/samples/state-snapshot-svelte-date/_config.js b/packages/svelte/tests/runtime-runes/samples/state-snapshot-svelte-date/_config.js
new file mode 100644
index 000000000000..6e1c54de61a2
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/state-snapshot-svelte-date/_config.js
@@ -0,0 +1,19 @@
+import { test } from '../../test';
+import { tick } from 'svelte';
+
+export default test({
+	async test({ assert, target }) {
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>update</button><p>1970-01-01T00:00:00.000Z</p>'
+		);
+
+		target.querySelector('button').click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>update</button><p>1970-01-02T00:00:00.000Z</p>'
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/state-snapshot-svelte-date/main.svelte b/packages/svelte/tests/runtime-runes/samples/state-snapshot-svelte-date/main.svelte
new file mode 100644
index 000000000000..634a7ee3e812
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/state-snapshot-svelte-date/main.svelte
@@ -0,0 +1,9 @@
+<script>
+	import { SvelteDate } from 'svelte/reactivity';
+
+	const date = new SvelteDate(0);
+	const snapshot = $derived($state.snapshot(date));
+</script>
+
+<button onclick={() => date.setTime(86400000)}>update</button>
+<p>{snapshot.toISOString()}</p>

From fa9b4d12a1a212cb9f81025aad2116744c478bad Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Mon, 24 Aug 2026 14:03:23 +0200
Subject: [PATCH 2/2] format /fix

---
 .../samples/state-snapshot-svelte-date/_config.js    | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/packages/svelte/tests/runtime-runes/samples/state-snapshot-svelte-date/_config.js b/packages/svelte/tests/runtime-runes/samples/state-snapshot-svelte-date/_config.js
index 6e1c54de61a2..53d8e1d4fff6 100644
--- a/packages/svelte/tests/runtime-runes/samples/state-snapshot-svelte-date/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/state-snapshot-svelte-date/_config.js
@@ -3,17 +3,11 @@ import { tick } from 'svelte';
 
 export default test({
 	async test({ assert, target }) {
-		assert.htmlEqual(
-			target.innerHTML,
-			'<button>update</button><p>1970-01-01T00:00:00.000Z</p>'
-		);
+		assert.htmlEqual(target.innerHTML, '<button>update</button><p>1970-01-01T00:00:00.000Z</p>');
 
-		target.querySelector('button').click();
+		target.querySelector('button')?.click();
 		await tick();
 
-		assert.htmlEqual(
-			target.innerHTML,
-			'<button>update</button><p>1970-01-02T00:00:00.000Z</p>'
-		);
+		assert.htmlEqual(target.innerHTML, '<button>update</button><p>1970-01-02T00:00:00.000Z</p>');
 	}
 });