fix(mcp): handle downloads gracefully in extension mode

In extension mode, Browser.setDownloadBehavior is no-oped in the CDP
relay because it's a browser-level command that can't be forwarded
through the tab-level chrome.debugger session. This means download
events never fire, causing navigate() to throw "Download is starting"
even though Chrome downloads the file successfully.

Return gracefully when in extension mode instead of re-throwing.

Fixes #39253

Co-Authored-By: Claude Opus 4.6 <[email protected]>

Author: mickey-mikey

packages/playwright/src/mcp/browser/tab.ts

@@ -297,8 +297,11 @@ export class Tab extends EventEmitter<TabEventsInterface> {
         throw e;
       // on chromium, the download event is fired *after* page.goto rejects, so we wait a lil bit
       const download = await downloadEvent;
-      if (!download)
+      if (!download) {
+        if (this.context.config.extension)
+          return;
         throw e;
+      }
       // Make sure other "download" listeners are notified first.
       await new Promise(resolve => setTimeout(resolve, 500));
       return;