fix: prevent writable store value from becoming a proxy when reassigning using $-prefix (#15283)

fixes #15281

.changeset/lovely-chairs-compete.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: prevent writable store value from becoming a proxy when reassigning using $-prefix

packages/svelte/src/compiler/phases/3-transform/client/visitors/AssignmentExpression.js

@@ -118,6 +118,7 @@ function build_assignment(operator, left, right, context) {
 			binding.kind !== 'prop' &&
 			binding.kind !== 'bindable_prop' &&
 			binding.kind !== 'raw_state' &&
+			binding.kind !== 'store_sub' &&
 			context.state.analysis.runes &&
 			should_proxy(right, context.state.scope) &&
 			is_non_coercive_operator(operator)

packages/svelte/tests/runtime-runes/samples/store-reassign-object/_config.js

@@ -0,0 +1,7 @@
+import { test } from '../../test';
+
+export default test({
+	async test({ target, assert }) {
+		assert.htmlEqual(target.innerHTML, `<p>bar</p>`);
+	}
+});

packages/svelte/tests/runtime-runes/samples/store-reassign-object/main.svelte

@@ -0,0 +1,11 @@
+<script>
+	import { writable } from "svelte/store";
+
+	const obj = writable({ name: 'foo' });
+
+	$obj = { name: 'bar' };
+
+	const clone = structuredClone($obj);
+</script>
+
+<p>{clone.name}</p>