Fix MessagePort communication after transfer to Worker (#22638)

## Summary

Fixes #22635 - MessagePort communication fails after being transferred
to a Worker thread.
Fixes #22636

The issue was that `MessagePort::addEventListener()` only called
`start()` for attribute listeners (like `onmessage = ...`) but not for
regular event listeners added via `addEventListener()` or the Node.js
EventEmitter wrapper (`.on('message', ...)`).

## Changes

- Modified `MessagePort::addEventListener()` to call `start()` for all
message event listeners, not just attribute listeners
- Added regression test for issue #22635

## Test Plan

- [x] Regression test added and passing
- [x] Original reproduction case from issue #22635 now works correctly
- [x] Existing MessagePort tests still pass

🤖 Generated with [Claude Code](https://claude.ai/code)

---------

Co-authored-by: Claude Bot <[email protected]>
Co-authored-by: Claude <[email protected]>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Jarred Sumner <[email protected]>

Author: 5 people

src/bun.js/bindings/webcore/MessagePort.cpp

@@ -427,8 +427,7 @@ Ref<MessagePort> MessagePort::entangle(ScriptExecutionContext& context, Transfer
 bool MessagePort::addEventListener(const AtomString& eventType, Ref<EventListener>&& listener, const AddEventListenerOptions& options)
 {
     if (eventType == eventNames().messageEvent) {
-        if (listener->isAttribute())
-            start();
+        start();
         m_hasMessageEventListener = true;
     }
     return EventTarget::addEventListener(eventType, WTFMove(listener), options);

test/js/node/test/parallel/test-worker-message-port-infinite-message-loop.js

@@ -0,0 +1,62 @@
+import { expect, test } from "bun:test";
+import { MessageChannel, Worker } from "worker_threads";
+
+test("issue #22635 - MessagePort communication fails after transfer to worker", async () => {
+  // Create a MessageChannel
+  const { port1, port2 } = new MessageChannel();
+
+  // Create a simple worker that receives a port
+  const workerCode = `
+    const { parentPort } = require('worker_threads');
+
+    parentPort.on('message', (msg) => {
+      if (msg.ports && msg.ports[0]) {
+        const port = msg.ports[0];
+
+        // Listen for messages on the transferred port
+        port.on('message', (data) => {
+          // Reply back through the same port
+          port.postMessage({ reply: 'Got: ' + data.text });
+        });
+
+        // Notify that we're ready
+        parentPort.postMessage({ ready: true });
+      }
+    });
+  `;
+
+  // Create worker with the code
+  const worker = new Worker(workerCode, { eval: true });
+
+  // Wait for worker to be ready
+  const readyPromise = new Promise<void>(resolve => {
+    worker.once("message", msg => {
+      if (msg.ready) {
+        resolve();
+      }
+    });
+  });
+
+  // Transfer port2 to the worker
+  worker.postMessage({ ports: [port2] }, [port2]);
+
+  // Wait for worker to be ready
+  await readyPromise;
+
+  // Test communication through the transferred port
+  const responsePromise = new Promise<void>(resolve => {
+    port1.on("message", msg => {
+      expect(msg.reply).toBe("Got: Hello from main");
+      resolve();
+    });
+  });
+
+  // Send message through port1
+  port1.postMessage({ text: "Hello from main" });
+
+  // Wait for response
+  await responsePromise;
+
+  // Clean up
+  worker.terminate();
+}, 10000);