fix: defer effects in pending boundary

packages/svelte/tests/runtime-runes/samples/async-boundary-coordination/_config.js

@@ -0,0 +1,46 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<p>hello from server</p>
+				<p>hello from server</p>
+				<p>hello from server</p>
+				<p>hello from server</p>
+			`
+		);
+
+		const [button1, button2] = target.querySelectorAll('button');
+
+		button1.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<p>hello from browser</p>
+				<p>hello from browser</p>
+				<p>hello from server</p>
+				<p>hello from server</p>
+			`
+		);
+
+		button2.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<p>hello from browser</p>
+				<p>hello from browser</p>
+				<p>hello from browser</p>
+				<p>hello from browser</p>
+			`
+		);
+	}
+});

packages/svelte/tests/runtime-runes/samples/async-boundary-coordination/main.svelte

@@ -0,0 +1,35 @@
+<script>
+	let browser = typeof window !== 'undefined';
+
+	let a = Promise.withResolvers();
+	let b = Promise.withResolvers();
+
+	if (!browser) {
+		a.resolve(true);
+		b.resolve(true);
+	}
+</script>
+
+<button onclick={() => a.resolve(true)}>
+	resolve a
+</button>
+
+<button onclick={() => b.resolve(true)}>
+	resolve b
+</button>
+
+<svelte:boundary>
+	{#if await a.promise}
+		<p>hello from {browser ? 'browser' : 'server'}</p>
+	{/if}
+
+	<p>hello from {browser ? 'browser' : 'server'}</p>
+</svelte:boundary>
+
+<svelte:boundary>
+	{#if await b.promise}
+		<p>hello from {browser ? 'browser' : 'server'}</p>
+	{/if}
+
+	<p>hello from {browser ? 'browser' : 'server'}</p>
+</svelte:boundary>

packages/svelte/tests/runtime-runes/samples/async-effect-after-await/Child.svelte

@@ -1,7 +1,11 @@
 <script>
+	$effect(() => {
+		console.log('before');
+	});
+
 	await 1;
 
 	$effect(() => {
-		console.log('hello');
+		console.log('after');
 	});
 </script>

packages/svelte/tests/runtime-runes/samples/async-effect-after-await/_config.js

@@ -3,7 +3,8 @@ import { test } from '../../test';
 
 export default test({
 	async test({ assert, logs }) {
+		assert.deepEqual(logs, []);
 		await tick();
-		assert.deepEqual(logs, ['hello']);
+		assert.deepEqual(logs, ['before', 'after']);
 	}
 });