fix(browser): wait for panel surface before capture

packages/ui/src/components/browser/BrowserPane.tsx

@@ -339,6 +339,25 @@ const WebviewBrowser: React.FC<BrowserPaneProps> = ({ initialUrl, directory, tab
     }
 
     if (action === 'browser.capture') {
+      // A user may close the panel after browser.open. Chromium then removes
+      // the zero-width webview's composited surface and capturePage() fails
+      // with UnknownVizError. Reveal this existing browser tab again and let
+      // the layout paint before asking Electron for the image.
+      useUIStore.getState().openContextBrowser(directory, webview.getURL());
+      const surfaceDeadline = Date.now() + 1_200;
+      let previousWidth = 0;
+      let stableSamples = 0;
+      while (stableSamples < 2 && Date.now() < surfaceDeadline) {
+        const width = webview.getBoundingClientRect().width;
+        stableSamples = width >= 2 && Math.abs(width - previousWidth) < 0.5
+          ? stableSamples + 1
+          : 0;
+        previousWidth = width;
+        await new Promise((resolve) => setTimeout(resolve, 50));
+      }
+      await new Promise<void>((resolve) => {
+        requestAnimationFrame(() => requestAnimationFrame(() => resolve()));
+      });
       // Wait for a settled page first: a screenshot of a half-painted layout is
       // worse than none, because it looks like a finished one.
       await waitForIdle();
@@ -450,7 +469,7 @@ const WebviewBrowser: React.FC<BrowserPaneProps> = ({ initialUrl, directory, tab
       await waitForIdle();
     }
     return result;
-  }, [annotationHost, loadUrl, waitForIdle]);
+  }, [annotationHost, directory, loadUrl, waitForIdle]);
 
   React.useEffect(
     () => registerBrowserController({ run: runControlAction }),

packages/ui/src/components/layout/__tests__/issue-3175-browserCaptureRevealsPanel.test.ts

@@ -15,6 +15,7 @@ import { useUIStore } from '@/stores/useUIStore';
 
 const __dirname = dirname(fileURLToPath(import.meta.url));
 const contextPanelSource = readFileSync(join(__dirname, '..', 'ContextPanel.tsx'), 'utf-8');
+const browserPaneSource = readFileSync(join(__dirname, '..', '..', 'browser', 'BrowserPane.tsx'), 'utf-8');
 const DIRECTORY = '/path/to/repository';
 
 beforeEach(() => {
@@ -40,4 +41,10 @@ describe('issue #3175 browser capture while the context panel is closed', () =>
     expect(panel.tabs[0]?.mode).toBe('browser');
     expect(panel.tabs[0]?.targetPath).toBe('https://example.com');
   });
+
+  test('reveals the browser again if it was closed before capture', () => {
+    expect(browserPaneSource).toContain(
+      'openContextBrowser(directory, webview.getURL())',
+    );
+  });
 });