separate suspend and capture from save

packages/svelte/src/internal/client/dom/blocks/async.js

@@ -1,7 +1,7 @@
 /** @import { TemplateNode, Value } from '#client' */
 
 import { async_derived } from '../../reactivity/deriveds.js';
-import { save } from './boundary.js';
+import { capture, suspend } from './boundary.js';
 
 /**
  * @param {TemplateNode} node
@@ -11,7 +11,12 @@ import { save } from './boundary.js';
 export function async(node, expressions, fn) {
 	// TODO handle hydration
 
-	save(Promise.all(expressions.map(async_derived))).then((result) => {
-		fn(node, ...result.restore());
+	var restore = capture();
+	var unsuspend = suspend();
+
+	Promise.all(expressions.map(async_derived)).then((result) => {
+		restore();
+		fn(node, ...result);
+		unsuspend();
 	});
 }

packages/svelte/src/internal/client/dom/blocks/boundary.js

@@ -268,6 +268,30 @@ export function capture() {
 	};
 }
 
+export function suspend() {
+	var boundary = active_effect;
+
+	while (boundary !== null) {
+		if ((boundary.f & BOUNDARY_EFFECT) !== 0) {
+			break;
+		}
+
+		boundary = boundary.parent;
+	}
+
+	if (boundary === null) {
+		e.await_outside_boundary();
+	}
+
+	// @ts-ignore
+	boundary?.fn(ASYNC_INCREMENT);
+
+	return function unsuspend() {
+		// @ts-ignore
+		boundary?.fn(ASYNC_DECREMENT);
+	};
+}
+
 /**
  * @template T
  * @param {Promise<T>} promise