Fix preview wedge after flip: remount SkiaCamera on facing change and as watchdog recovery

Flip only reconfigured the CameraSession in place, leaving the Skia
offscreen-surface cache from the old lens wedged on this Xiaomi: after a
flip the preview banded then went black while the frame pipeline kept
delivering (heartbeat kept rising) and only a full app restart revived it.

- key <SkiaCamera> by facing + mount nonce so a flip fully unmounts and
  remounts the camera (lib clears its surface cache on unmount), i.e. a
  clean restart on every lens switch instead of an in-place reconfigure.
- watchdog now recovers by the same full remount instead of an isActive
  toggle (which never revives a wedged preview), budgeted to 3 restarts.
- bump a re-render on every onStarted: after a remount cameraActive never
  drops (no onStopped on unmount) so the reopen did not re-render and the
  new controller was never re-read, leaving the 1x-10x zoom chips hidden
  until the next touch.

Verified on device: 15+ flips with no wedge, chips visible immediately
after each flip, preview stays live (was ~5 min to black before).

src/components/Viewfinder.tsx

@@ -298,11 +298,20 @@ const Viewfinder = forwardRef<ViewfinderHandle, ViewfinderProps>(function Viewfi
   // flicker-free (preview EV is software matrix gain).
   const skiaCameraRef = useRef<SkiaCameraRef>(null);
   const [cameraActive, setCameraActive] = useState(false);
+  // Re-render kicker bumped on every onStarted. A flip remounts <SkiaCamera>
+  // (key change) while cameraActive never drops (unmount fires no onStopped),
+  // so the reopen would not re-render and controller-derived UI (zoom chips)
+  // stayed stuck hidden until the next touch — the new controller only becomes
+  // readable from the ref once the fresh session has started.
+  const [, bumpSessionStart] = useState(0);
   // Stable identities so React.memo(SkiaCameraImpl) does not re-render (and
   // re-run its frame-output setup) on every adjustments change during slider
   // drags — inline lambdas here used to break memo and stall the main thread.
   const handleCameraStarted = useCallback(() => {
+    startedOnceRef.current = true;
+    watchdogBudgetRef.current = 0;
     setCameraActive(true);
+    bumpSessionStart((n) => n + 1);
   }, []);
   const handleCameraStopped = useCallback(() => {
     setCameraActive(false);
@@ -310,6 +319,19 @@ const Viewfinder = forwardRef<ViewfinderHandle, ViewfinderProps>(function Viewfi
   // Camera session pauses when the app backgrounds; toggling isActive back on
   // resume restarts it. Without this the preview stayed black after unlock.
   const [appActive, setAppActive] = useState(AppState.currentState === 'active');
+  const startedOnceRef = useRef(false);
+  const cameraActiveRef = useRef(false);
+  cameraActiveRef.current = cameraActive;
+  const appActiveRef = useRef(appActive);
+  appActiveRef.current = appActive;
+  // Watchdog bookkeeping — see the camera-watchdog effect near handleFrame.
+  const bouncePendingRef = useRef(false);
+  const watchdogBudgetRef = useRef(0);
+  // Full SkiaCamera remount counter. Bumping unmounts <SkiaCamera> and mounts a
+  // fresh one (its unmount clears the lib's offscreen surface cache), the only
+  // reliable revive on this device — an isActive toggle or a plain session
+  // reconfigure (flip) does NOT clear the wedged Skia/EGL state.
+  const [cameraMountNonce, setCameraMountNonce] = useState(0);
   useEffect(() => {
     const sub = AppState.addEventListener('change', (s) => setAppActive(s === 'active'));
     return () => sub.remove();
@@ -561,6 +583,10 @@ const Viewfinder = forwardRef<ViewfinderHandle, ViewfinderProps>(function Viewfi
   // the preview flicker. All live values flow through the synchronizables.
   type SkiaCameraOnFrame = NonNullable<ComponentProps<typeof SkiaCamera>['onFrame']>;
   const toneFailLogged = useMemo(() => createSynchronizable<boolean>(false), []);
+  // Frame heartbeat for the camera watchdog: bumped in handleFrame on every
+  // delivered frame. When the whole pipeline dies the session still reports
+  // OPEN but frame delivery stops, so the heartbeat freezes.
+  const frameBeatSync = useMemo(() => createSynchronizable<number>(0), []);
   // Composition band fed to the frame worklet: [active, viewAspect, fx, fy,
   // fw, fh] where (fx,fy,fw,fh) is the photo-area rect (ratio band / polaroid
   // window / wall window) normalized to the view. While active the worklet
@@ -578,6 +604,7 @@ const Viewfinder = forwardRef<ViewfinderHandle, ViewfinderProps>(function Viewfi
   const handleFrame = useCallback<SkiaCameraOnFrame>(
     (frame, render) => {
       'worklet';
+      frameBeatSync.setBlocking(frameBeatSync.getDirty() + 1);
       render(({ canvas, frameTexture }) => {
         // Quick-EV drags write colorMatrixSync from JS on every tick; a torn
         // read can throw inside MakeMatrix (or yield NaN -> black surface) for
@@ -727,7 +754,7 @@ const Viewfinder = forwardRef<ViewfinderHandle, ViewfinderProps>(function Viewfi
       });
       frame.dispose();
     },
-    [colorMatrixSync, toneSync, cinemaSync, toneFailLogged, feedRectSync]
+    [colorMatrixSync, toneSync, cinemaSync, toneFailLogged, feedRectSync, frameBeatSync]
   );
 
   const grainOpacity = adjustments.grain / 20;
@@ -803,6 +830,62 @@ const Viewfinder = forwardRef<ViewfinderHandle, ViewfinderProps>(function Viewfi
         : [0, 0, 0, 0, 0, 0]
     );
   }, [cameraPhotoRect, vw, vh, feedRectSync]);
+
+  // Camera watchdog: the Xiaomi wedges the preview — horizontal banding then
+  // black, while the native session still logs OPEN (no error, no onStopped)
+  // and only a full app restart revives it (a flip = session reconfigure does
+  // NOT clear the wedged Skia state). Every 3s, while the app is foregrounded
+  // in camera mode and a session has started at least once: remount the whole
+  // SkiaCamera (unmount clears the lib surface cache, fresh mount == restart)
+  // when the session reports inactive, or when the frame heartbeat has not
+  // advanced for two ticks (~6s) — frame delivery is dead even though the
+  // session claims to be OPEN. Budgeted to 3 restarts per successful start so
+  // a genuinely broken session logs out instead of restart-looping forever.
+  const remountCameraSession = useCallback(() => {
+    if (bouncePendingRef.current) return;
+    bouncePendingRef.current = true;
+    setAppActive(false);
+    setTimeout(() => {
+      // Fresh mount while inactive, so the new instance starts clean and
+      // CLOSED; reopen below once it exists.
+      setCameraMountNonce((n) => n + 1);
+      setTimeout(() => {
+        bouncePendingRef.current = false;
+        // Never force the camera on while the app is backgrounded.
+        if (AppState.currentState === 'active') setAppActive(true);
+      }, 300);
+    }, 300);
+  }, []);
+  useEffect(() => {
+    if (mode !== 'camera') return;
+    let lastBeat = -1;
+    let stallTicks = 0;
+    const id = setInterval(() => {
+      const beat = frameBeatSync.getDirty();
+      if (beat === lastBeat) stallTicks++;
+      else {
+        lastBeat = beat;
+        stallTicks = 0;
+      }
+      // Backgrounding pauses the session on purpose — never watchdog that.
+      if (!startedOnceRef.current || !appActiveRef.current) return;
+      // Two stale ticks give an in-flight (flip/resume/remount) restart time
+      // to land.
+      if (stallTicks < 2) return;
+      const reason = cameraActiveRef.current ? 'no frames for ~6s' : 'session inactive';
+      if (watchdogBudgetRef.current >= 3) {
+        console.warn('[watchdog] camera looks dead (' + reason + ') — restart budget exhausted, giving up');
+        return;
+      }
+      watchdogBudgetRef.current++;
+      console.warn('[watchdog] remounting camera session: ' + reason);
+      lastBeat = -1;
+      stallTicks = 0;
+      remountCameraSession();
+    }, 3000);
+    return () => clearInterval(id);
+  }, [mode, frameBeatSync, remountCameraSession]);
+
   const onLibTouchStart = (e: any) => {
     const ts = e.nativeEvent.touches;
     if (ts.length >= 2) {
@@ -1120,6 +1203,7 @@ const Viewfinder = forwardRef<ViewfinderHandle, ViewfinderProps>(function Viewfi
     return (
       <View className="flex-1 relative overflow-hidden bg-black">
         <SkiaCamera
+          key={'cam-' + facing + '-' + cameraMountNonce}
           ref={skiaCameraRef}
           style={StyleSheet.absoluteFill}
           device={device}