fix: make ownership widening more robust to userland proxies (#13377)

Fixes #13376

.changeset/nice-brooms-battle.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: make ownership widening more robust to userland proxies

packages/svelte/src/internal/client/dev/ownership.js

@@ -170,14 +170,13 @@ function add_owner_to_object(object, owner, seen) {
 
 	if (metadata) {
 		// this is a state proxy, add owner directly, if not globally shared
-		if (metadata.owners !== null) {
+		if ('owners' in metadata && metadata.owners != null) {
 			metadata.owners.add(owner);
 		}
 	} else if (object && typeof object === 'object') {
 		if (seen.has(object)) return;
 		seen.add(object);
-
-		if (object[ADD_OWNER]) {
+		if (ADD_OWNER in object && object[ADD_OWNER]) {
 			// this is a class with state fields. we put this in a render effect
 			// so that if state is replaced (e.g. `instance.name = { first, last }`)
 			// the new state is also co-owned by the caller of `getContext`

packages/svelte/tests/runtime-runes/samples/ownership-with-proxy/_config.js

@@ -0,0 +1,7 @@
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true
+	}
+});

packages/svelte/tests/runtime-runes/samples/ownership-with-proxy/main.svelte

@@ -0,0 +1,11 @@
+<script>
+	import { setContext, getContext } from "svelte";
+
+	setContext("", new Proxy({}, {
+		get(){
+			return {}
+		}
+	}));
+
+	getContext("");
+</script>