fix

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

@@ -345,10 +345,14 @@ export function run(thunks) {
 		promises.push(promise);
 	}
 
-	promise.then(() => {
-		boundary.update_pending_count(-1);
-		batch.decrement(blocking);
-	});
+	promise
+		// wait one more tick, so that template effects are
+		// guaranteed to run before `$effect(...)`
+		.then(() => Promise.resolve())
+		.then(() => {
+			boundary.update_pending_count(-1);
+			batch.decrement(blocking);
+		});
 
 	return promises;
 }

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

@@ -68,8 +68,8 @@ export default test({
 		assert.deepEqual(logs, [
 			'outside boundary 1',
 			'$effect.pre 42 1',
-			'$effect 42 1',
 			'template 42 1',
+			'$effect 42 1',
 			'$effect.pre 84 2',
 			'template 84 2',
 			'outside boundary 2',

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

@@ -34,8 +34,8 @@ export default test({
 		assert.deepEqual(logs, [
 			'outside boundary 1',
 			'$effect.pre 1a 1',
-			'$effect 1a 1',
 			'template 1a 1',
+			'$effect 1a 1',
 			'$effect.pre 2a 2',
 			'template 2a 2',
 			'outside boundary 2',