fix: hydrate each blocks inside element correctly

.changeset/chilly-bats-build.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: hydrate each blocks inside element correctly

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

@@ -99,7 +99,14 @@ export function process_children(nodes, initial, is_element, context) {
 
 			if (is_static_element(node, context.state)) {
 				skipped += 1;
-			} else if (node.type === 'EachBlock' && nodes.length === 1 && is_element) {
+			} else if (
+				node.type === 'EachBlock' &&
+				nodes.length === 1 &&
+				is_element &&
+				// In case it's wrapped in async the async logic will want to skip sibling nodes up until the end, hence we cannot make this controlled
+				// TODO switch this around and instead optimize for elements with a single block child and not require extra comments (neither for async nor normally)
+				!(node.body.metadata.has_await || node.metadata.expression.has_await)
+			) {
 				node.metadata.is_controlled = true;
 			} else {
 				const id = flush_node(false, node.type === 'RegularElement' ? node.name : 'node');

packages/svelte/tests/runtime-runes/samples/async-each-sibling/_config.js

@@ -0,0 +1,16 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['async-server', 'hydrate', 'client'],
+	ssrHtml: `<ul><li>1</li></ul> <button>add</button>`,
+
+	async test({ assert, target }) {
+		await tick();
+		const [add] = target.querySelectorAll('button');
+
+		add.click();
+		await tick();
+		assert.htmlEqual(target.innerHTML, `<ul><li>1</li><li>2</li></ul> <button>add</button>`);
+	}
+});

packages/svelte/tests/runtime-runes/samples/async-each-sibling/main.svelte

@@ -0,0 +1,11 @@
+<script>
+	let array = $state(Promise.resolve([1]));
+</script>
+
+<ul>
+{#each await array as item}
+	<li>{item}</li>
+{/each}
+</ul>
+
+<button onclick={() => array = Promise.resolve([1, 2])}>add</button>