chore: add regression test for issue #17277 (verified fixed)

packages/svelte/tests/runtime-runes/samples/boundary-array-binding/_config.js

@@ -0,0 +1,24 @@
+// @ts-nocheck
+export default {
+	compileOptions: {
+		dev: false
+	},
+	async test({ assert, target, window }) {
+		// 1. Wait for the async await block to resolve
+		await Promise.resolve();
+		await Promise.resolve();
+
+		const input = target.querySelector('input');
+		const p = target.querySelector('p');
+
+		// 2. Simulate user typing "updated"
+		input.value = 'updated';
+		input.dispatchEvent(new window.Event('input'));
+
+		// 3. Wait for reactivity
+		await Promise.resolve();
+
+		// 4. Assert
+		assert.equal(p.innerHTML, 'Value: updated');
+	}
+};

packages/svelte/tests/runtime-runes/samples/boundary-array-binding/main.svelte

@@ -0,0 +1,12 @@
+<script>
+	let items = $state(['initial']);
+</script>
+
+<svelte:boundary onerror={() => {}}>
+	{#await Promise.resolve()}
+		{:then}
+			<input bind:value={items[0]} />
+		{/await}
+</svelte:boundary>
+
+<p>Value: {items[0]}</p>