Fix Browser viewer input after stream restarts

Notify screencast consumers when a stream is stopped so the WebSocket frame supervisor restarts after viewport-driven screencast resets.

Keep the active canvas as the frame/input surface and avoid replacing live screencasts with click snapshots, preserving hover, click, and wheel feedback.

Tested: conda run -n a0 pytest tests/test_browser_agent_regressions.py -q

plugins/_browser/helpers/runtime.py

@@ -411,8 +411,11 @@ class _BrowserScreencast:
     async def stop(self) -> None:
         if self._closed:
             return
+        was_stopped = self.stopped
         self._closed = True
         self.stopped = True
+        if not was_stopped:
+            self._notify_stopped()
         self._drop_queued_frames()
         with contextlib.suppress(asyncio.QueueFull):
             self.queue.put_nowait(None)

plugins/_browser/webui/browser-store.js

@@ -1412,8 +1412,15 @@ const model = {
     this._frameCanvas = canvas || null;
   },
 
+  currentFrameCanvas() {
+    const stageCanvas = this._stageElement?.querySelector?.(".browser-frame-canvas");
+    if (stageCanvas?.isConnected) return stageCanvas;
+    if (this._frameCanvas?.isConnected) return this._frameCanvas;
+    return null;
+  },
+
   canUseCanvasFrames() {
-    return Boolean(BROWSER_CANVAS_FRAMES_SUPPORTED && this._frameCanvas?.getContext);
+    return Boolean(BROWSER_CANVAS_FRAMES_SUPPORTED && this.currentFrameCanvas()?.getContext);
   },
 
   hasFrame() {
@@ -1421,7 +1428,7 @@ const model = {
   },
 
   paintFrameBitmap(bitmap) {
-    const canvas = this._frameCanvas;
+    const canvas = this.currentFrameCanvas();
     if (!canvas || !bitmap?.width || !bitmap?.height) return false;
     if (canvas.width !== bitmap.width) canvas.width = bitmap.width;
     if (canvas.height !== bitmap.height) canvas.height = bitmap.height;
@@ -1433,7 +1440,7 @@ const model = {
   },
 
   clearFrameCanvas() {
-    const canvas = this._frameCanvas;
+    const canvas = this.currentFrameCanvas();
     if (canvas?.width && canvas?.height) {
       canvas.getContext("2d")?.clearRect(0, 0, canvas.width, canvas.height);
     }
@@ -1441,9 +1448,10 @@ const model = {
   },
 
   freezeCanvasFrameToImage() {
-    if (!this.frameCanvasReady || !this._frameCanvas) return;
+    const canvas = this.currentFrameCanvas();
+    if (!this.frameCanvasReady || !canvas) return;
     try {
-      this.frameSrc = this._frameCanvas.toDataURL("image/jpeg", 0.86);
+      this.frameSrc = canvas.toDataURL("image/jpeg", 0.86);
     } catch {
       this.frameSrc = "";
     }
@@ -1451,8 +1459,9 @@ const model = {
   },
 
   frameElement() {
-    if (this.frameCanvasReady && this._frameCanvas) {
-      return this._frameCanvas;
+    if (this.frameCanvasReady) {
+      const canvas = this.currentFrameCanvas();
+      if (canvas) return canvas;
     }
     return this._stageElement?.querySelector?.(".browser-frame-image") || null;
   },
@@ -2616,7 +2625,9 @@ const model = {
 	        const response = await websocket.request("browser_viewer_input", payload, { timeoutMs: 10000 });
 	        const data = firstOk(response);
 	        this.applyActiveFrameState(data.state);
-	        this.applySnapshot(data.snapshot);
+	        if (!this.frameCanvasReady || !this.usesScreencastTransport()) {
+	          this.applySnapshot(data.snapshot);
+	        }
 	      } catch (error) {
         this.error = error instanceof Error ? error.message : String(error);
       }

tests/test_browser_agent_regressions.py

@@ -1218,7 +1218,9 @@ def test_browser_viewer_defaults_to_live_screencast_with_snapshot_fallback():
     assert "paintFrameBitmap(bitmap)" in browser_store
     assert "if (canvas.width !== bitmap.width) canvas.width = bitmap.width;" in browser_store
     assert "freezeCanvasFrameToImage()" in browser_store
-    assert 'this._frameCanvas.toDataURL("image/jpeg", 0.86)' in browser_store
+    assert "currentFrameCanvas()" in browser_store
+    assert 'this._stageElement?.querySelector?.(".browser-frame-canvas")' in browser_store
+    assert 'canvas.toDataURL("image/jpeg", 0.86)' in browser_store
     assert "this.frameSrc = frameSrc;" in browser_store
     assert "hasFrame()" in browser_store
     assert "frameCanvasReady: false" in browser_store
@@ -1246,6 +1248,7 @@ def test_browser_viewer_defaults_to_live_screencast_with_snapshot_fallback():
     assert "shouldAcceptMismatchedFrame(dimensions = null)" in browser_store
     assert "requestViewportSyncAfterRejectedFrame()" in browser_store
     assert "this.applySnapshot(data.snapshot);" in browser_store
+    assert "if (!this.frameCanvasReady || !this.usesScreencastTransport())" in browser_store
     assert "else if (!data.state)" in browser_store
     assert '"snapshot": snapshot' in ws_browser
     assert '"binary_frames": binary_frames' in ws_browser
@@ -1755,6 +1758,40 @@ async def test_browser_screencast_notifies_consumer_when_frame_task_stops_before
     assert session.detached is True
 
 
+@pytest.mark.anyio
+async def test_browser_screencast_stop_notifies_consumer_once():
+    class FakeSession:
+        def __init__(self):
+            self.handlers = {}
+            self.sent = []
+
+        def on(self, event, handler):
+            self.handlers[event] = handler
+
+        async def send(self, method, params=None):
+            self.sent.append((method, params or {}))
+
+        async def detach(self):
+            pass
+
+    session = FakeSession()
+    stopped = []
+    screencast = _BrowserScreencast(
+        stream_id="stream",
+        browser_id=7,
+        session=session,
+        mime="image/jpeg",
+    )
+
+    await screencast.start(quality=92, every_nth_frame=1, viewport={"width": 640, "height": 480})
+    await screencast.attach_consumer(lambda frame: None, lambda: stopped.append(True))
+    await screencast.stop()
+    await screencast.stop()
+
+    assert stopped == [True]
+    assert ("Page.stopScreencast", {}) in session.sent
+
+
 @pytest.mark.anyio
 async def test_browser_screencast_attach_consumer_flushes_queued_frame():
     class FakeSession: