fix

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

@@ -18,13 +18,27 @@ export function async(node, expressions, fn) {
 
 	var restore = capture();
 
+	let boundary = effect.b;
+
+	while (boundary !== null && !boundary.has_pending_snippet()) {
+		boundary = boundary.parent;
+	}
+
+	if (boundary === null) {
+		throw new Error('TODO cannot create async derived outside a boundary with a pending snippet');
+	}
+
+	boundary.increment();
+
 	Promise.all(expressions.map((fn) => async_derived(fn))).then((result) => {
+		batch.run(() => {
 			restore();
 			fn(node, ...result);
 
 			// TODO is this necessary?
-		batch.run(() => {
 			schedule_effect(effect);
 		});
+
+		boundary.decrement();
 	});
 }

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

@@ -119,10 +119,13 @@ export class Boundary {
 						return branch(() => this.#children(this.#anchor));
 					});
 
-					if (this.#pending_count === 0) {
+					if (this.#pending_count > 0) {
+						this.#show_pending_snippet();
+					} else {
 						pause_effect(/** @type {Effect} */ (this.#pending_effect), () => {
 							this.#pending_effect = null;
 						});
+						this.ran = true;
 					}
 				});
 			} else {
@@ -130,14 +133,14 @@ export class Boundary {
 
 				if (this.#pending_count > 0) {
 					this.#show_pending_snippet();
+				} else {
+					this.ran = true;
 				}
 			}
 
 			reset_is_throwing_error();
 		}, flags);
 
-		this.ran = true;
-
 		if (hydrating) {
 			this.#anchor = hydrate_node;
 		}
@@ -189,6 +192,8 @@ export class Boundary {
 	}
 
 	commit() {
+		this.ran = true;
+
 		if (this.#pending_effect) {
 			pause_effect(this.#pending_effect, () => {
 				this.#pending_effect = null;
@@ -242,10 +247,10 @@ export class Boundary {
 				}
 			});
 
-			this.ran = true;
-
 			if (this.#pending_count > 0) {
 				this.#show_pending_snippet();
+			} else {
+				this.ran = true;
 			}
 		};