fix(mcp): report a dialog opened during navigation instead of timing out

packages/playwright-core/src/tools/backend/tab.ts

@@ -348,8 +348,16 @@ export class Tab extends EventEmitter<TabEventsInterface> {
     this._clearCollectedArtifacts();
 
     const { promise: downloadEvent, abort: abortDownloadEvent } = eventWaiter<playwright.Download>(this.page, 'download', 3000);
+    // A dialog that opens during the load blocks it, so report the dialog
+    // right away instead of waiting for the navigation timeout.
+    const modalStatePromise = new ManualPromise<void>();
+    const modalStateListener = () => modalStatePromise.resolve();
+    this.once(TabEvents.modalState, modalStateListener);
     try {
-      await this.page.goto(url, { waitUntil: 'domcontentloaded', ...this.navigationTimeoutOptions });
+      await Promise.race([
+        this.page.goto(url, { waitUntil: 'domcontentloaded', ...this.navigationTimeoutOptions }),
+        modalStatePromise,
+      ]);
       abortDownloadEvent();
     } catch (_e: unknown) {
       const e = _e as Error;
@@ -363,7 +371,11 @@ export class Tab extends EventEmitter<TabEventsInterface> {
       // Make sure other "download" listeners are notified first.
       await new Promise(resolve => setTimeout(resolve, 500));
       return;
+    } finally {
+      this.off(TabEvents.modalState, modalStateListener);
     }
+    if (modalStatePromise.isDone())
+      return;
 
     // Cap load event to 5 seconds, the page is operational at this point.
     await this.waitForLoadState('load', { timeout: 5000 });

tests/mcp/dialogs.spec.ts

@@ -293,3 +293,29 @@ test('alert dialog w/ race', async ({ client, server }) => {
 - Page Title: Title`),
   });
 });
+
+test('alert dialog during navigation', async ({ client, server }) => {
+  server.setContent('/', `<title>Title</title><script>alert('Alert')</script><button>Button</button>`, 'text/html');
+  expect(await client.callTool({
+    name: 'browser_navigate',
+    arguments: { url: server.PREFIX },
+  })).toHaveResponse({
+    modalState: expect.stringContaining(`- ["alert" dialog with message "Alert"]: can be handled by browser_handle_dialog`),
+  });
+
+  expect(await client.callTool({
+    name: 'browser_handle_dialog',
+    arguments: { accept: true },
+  })).toHaveResponse({
+    modalState: undefined,
+    page: expect.stringContaining(`- Page URL: ${server.PREFIX}/
+- Page Title: Title`),
+  });
+
+  expect(await client.callTool({
+    name: 'browser_snapshot',
+    arguments: {},
+  })).toHaveResponse({
+    inlineSnapshot: expect.stringContaining(`- button "Button"`),
+  });
+});