fix: ensure toStore subscription correctly syncs latest value (#14015)

* fix: ensure toStore subscription correctly syncs latest value

* Update packages/svelte/src/store/index-client.js

---------

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>

.changeset/shaggy-frogs-fetch.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure toStore subscription correctly syncs latest value

packages/svelte/src/store/index-client.js

@@ -42,8 +42,11 @@ export { derived, get, readable, readonly, writable } from './shared/index.js';
  * @returns {Writable<V> | Readable<V>}
  */
 export function toStore(get, set) {
-	const store = writable(get(), (set) => {
-		let ran = false;
+	let init_value = get();
+	const store = writable(init_value, (set) => {
+		// If the value has changed before we call subscribe, then
+		// we need to treat the value as already having run
+		let ran = init_value !== get();
 
 		// TODO do we need a different implementation on the server?
 		const teardown = effect_root(() => {

packages/svelte/tests/runtime-runes/samples/toStore-subscribe/_config.js

@@ -0,0 +1,6 @@
+import { test } from '../../test';
+
+export default test({
+	html: `1`,
+	mode: ['client', 'hydrate']
+});

packages/svelte/tests/runtime-runes/samples/toStore-subscribe/main.svelte

@@ -0,0 +1,14 @@
+<script>
+	import { toStore } from 'svelte/store';
+
+	let count = $state(0);
+
+	const store = toStore(
+		() => count,
+		(v) => (count = v)
+	);
+
+	store.set(1);
+</script>
+
+{$store}