WIP

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

@@ -140,7 +140,7 @@ export class Boundary {
 				// the pending or main block was rendered for a given
 				// boundary, and hydrate accordingly
 				queueMicrotask(() => {
-					destroy_effect(/** @type {Effect} */ (this.#pending_effect));
+					// destroy_effect(/** @type {Effect} */ (this.#pending_effect));
 
 					this.#main_effect = this.#run(() => {
 						return branch(() => this.#children(this.#anchor));

packages/svelte/src/internal/client/reactivity/deriveds.js

@@ -105,6 +105,12 @@ export function async_derived(fn, location) {
 	// only suspend in async deriveds created on initialisation
 	var should_suspend = !active_reaction;
 
+	var boundary = /** @type {Effect} */ (active_effect).b;
+
+	while (boundary !== null && !boundary.has_pending_snippet()) {
+		boundary = boundary.parent;
+	}
+
 	render_effect(() => {
 		if (DEV) from_async_derived = active_effect;
 		promise = fn();
@@ -115,8 +121,16 @@ export function async_derived(fn, location) {
 		var fork = active_fork;
 
 		if (should_suspend) {
-			// TODO if nearest pending boundary is not ready, attach to the boundary
+			if (fork !== null) {
-			fork?.increment();
+				fork.increment();
+			} else {
+				if (boundary === null) {
+					throw new Error('TODO');
+				}
+
+				// if nearest pending boundary is not ready, attach to the boundary
+				boundary.increment();
+			}
 		}
 
 		promise.then(
@@ -129,7 +143,15 @@ export function async_derived(fn, location) {
 				from_async_derived = null;
 
 				if (should_suspend) {
-					fork?.decrement();
+					if (fork !== null) {
+						fork.decrement();
+					} else {
+						if (boundary === null) {
+							throw new Error('TODO');
+						}
+
+						boundary.decrement();
+					}
 				}
 
 				if (fork !== null) {

packages/svelte/tests/runtime-runes/samples/async-derived-module/_config.js

@@ -26,6 +26,7 @@ export default test({
 		await Promise.resolve();
 		await Promise.resolve();
 		await Promise.resolve();
+		await Promise.resolve();
 		flushSync();
 		await tick();
 		assert.htmlEqual(target.innerHTML, '<p>42</p>');