test: reproduce stale read from new dependency

packages/svelte/tests/runtime-runes/samples/async-stale-read-new-dependency/_config.js

@@ -0,0 +1,29 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client'],
+	async test({ assert, target }) {
+		await tick();
+		const [update, show, resolve] = target.querySelectorAll('button');
+
+		update.click();
+		await tick();
+
+		show.click();
+		await tick();
+
+		resolve.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>update</button>
+				<button>show</button>
+				<button>resolve</button>
+				<p>1</p>
+			`
+		);
+	}
+});

packages/svelte/tests/runtime-runes/samples/async-stale-read-new-dependency/main.svelte

@@ -0,0 +1,17 @@
+<script>
+	let value = $state();
+	let show = $state(false);
+	const deferred = Promise.withResolvers();
+
+	function wait(value) {
+		return value === undefined ? '' : deferred.promise;
+	}
+</script>
+
+<button onclick={() => (value = { x: 1 })}>update</button>
+<button onclick={() => (show = true)}>show</button>
+<button onclick={() => deferred.resolve('')}>resolve</button>
+
+{await wait(value)}
+
+<p>{show ? value.x : ''}</p>