fix(worker): open a handle scope per delivered message, and fix two messaging specs

NativeScript/runtime/Worker.mm

@@ -744,6 +744,9 @@ throw NativeScriptException(
 
 void Worker::OnMessageCallback(Isolate* isolate, Local<Object> receiver,
                                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);
   WorkerEventsState* state = Caches::StateFor<WorkerEventsState>(isolate);
   if (state == nullptr || state->emitMessage.IsEmpty()) {
     return;

TestRunner/app/tests/MessagingTests.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();

TestRunner/app/tests/RuntimeImplementedAPIs.js

@@ -83,9 +83,12 @@ describe("DOMException canary", () => {
   });
 
   it("serializes through structuredClone on this runtime", () => {
-    const clone = structuredClone(new DOMException("x", "AbortError"));
+    const original = new DOMException("x", "AbortError");
+    original.stack = "DOMException stack sentinel";
+    const clone = structuredClone(original);
     expect(clone instanceof DOMException).toBe(true);
     expect(clone.name).toBe("AbortError");
+    expect(clone.stack).toBe("DOMException stack sentinel");
   });
 
   // Once an isolate holds a DOMException the serializer claims host objects