diff --git a/test-app/app/src/main/assets/app/tests/testMessaging.js b/test-app/app/src/main/assets/app/tests/testMessaging.js
index c06a46037..faa6cfe2d 100644
--- a/test-app/app/src/main/assets/app/tests/testMessaging.js
+++ b/test-app/app/src/main/assets/app/tests/testMessaging.js
@@ -155,10 +155,11 @@ describe("Messaging runtime edges", function () {
             var got = [];
             worker.on("message", function (value) {
                 got.push(value);
-                if (got.length === 3) {
+                if (got.length === 4) {
                     setTimeout(function () {
-                        // Three messages: the once() registration fires only
-                        // for the first, the on() one for all three.
+                        // Three messages: the on() registration fires for all
+                        // three, the once() one only for the first. The settle
+                        // window catches a fifth reply.
                         expect(got).toEqual([1, 2, 3, 4]);
                         worker.terminate();
                         done();
diff --git a/test-app/app/src/main/assets/app/tests/testRuntimeImplementedAPIs.js b/test-app/app/src/main/assets/app/tests/testRuntimeImplementedAPIs.js
index 27b784df2..c17807cb8 100644
--- a/test-app/app/src/main/assets/app/tests/testRuntimeImplementedAPIs.js
+++ b/test-app/app/src/main/assets/app/tests/testRuntimeImplementedAPIs.js
@@ -64,9 +64,12 @@ describe("DOMException canary", function () {
   });
 
   it("serializes through structuredClone on this runtime", function () {
-    var clone = structuredClone(new DOMException("x", "AbortError"));
+    var original = new DOMException("x", "AbortError");
+    original.stack = "DOMException stack sentinel";
+    var clone = structuredClone(original);
     expect(clone instanceof DOMException).toBe(true);
     expect(clone.name).toBe("AbortError");
+    expect(clone.stack).toBe("DOMException stack sentinel");
   });
 
   it("clones the isolate's first DOMException even when a getter creates it mid-clone", function (done) {
diff --git a/test-app/runtime/src/main/cpp/WorkerEvents.cpp b/test-app/runtime/src/main/cpp/WorkerEvents.cpp
index 978aeb014..7ed146b52 100644
--- a/test-app/runtime/src/main/cpp/WorkerEvents.cpp
+++ b/test-app/runtime/src/main/cpp/WorkerEvents.cpp
@@ -62,6 +62,9 @@ void WorkerEvents::Init(Local<Context> context) {
 
 void WorkerEvents::EmitMessage(Isolate* isolate, Local<Object> receiver,
                                const std::shared_ptr<worker::Message>& message) {
+    // Callers drain a whole batch under one scope; without this the handles of
+    // every message in the batch stay alive until the batch ends.
+    HandleScope handleScope(isolate);
     auto* state = RuntimeState::For<WorkerEventsState>(isolate);
     if (state == nullptr || state->emitMessage.IsEmpty()) {
         return;