camview: tell the client when the camera is unavailable

The server sends "camera unavailable" after 3 s without a frame and
"camera ok" when frames come; the app shows the notice instead of a
stale frame.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

lib/camview.dart

@@ -28,6 +28,9 @@ class CamView extends ChangeNotifier {
   final _delays = <double>[];
   String lastReply = '';
 
+  /// Whether the Orin has the camera: null until it says, then its last notice.
+  bool? available;
+
   final _window = <(int, int)>[]; // (arrival µs, bytes) over the last second
   final _clock = Stopwatch()..start();
 
@@ -55,6 +58,7 @@ class CamView extends ChangeNotifier {
           timeout: const Duration(seconds: 3),
         );
         _s = s;
+        available = null;
         status = 'connected';
         notifyListeners();
         await _read(s);
@@ -63,6 +67,7 @@ class CamView extends ChangeNotifier {
         status = '$e'.split('\n').first;
       }
       _s = null;
+      frame = null; // a frame from a closed connection is not live
       notifyListeners();
       if (_running) await Future<void>.delayed(const Duration(seconds: 1));
     }
@@ -92,7 +97,7 @@ class CamView extends ChangeNotifier {
         final bytes = Uint8List.sublistView(data, off + 16, off + 16 + body);
         off += 16 + body;
         if (len == 0) {
-          lastReply = utf8.decode(bytes);
+          _onText(utf8.decode(bytes));
         } else {
           _onFrame(Uint8List.fromList(bytes), sentAt);
         }
@@ -101,6 +106,16 @@ class CamView extends ChangeNotifier {
     }
   }
 
+  void _onText(String text) {
+    if (text == 'camera unavailable' || text == 'camera ok') {
+      available = text == 'camera ok';
+      if (available == false) frame = null; // never show a stale frame as live
+    } else {
+      lastReply = text;
+    }
+    notifyListeners();
+  }
+
   void _onFrame(Uint8List jpeg, double sentAt) {
     final now = _clock.elapsedMicroseconds;
     _window.add((now, jpeg.length));
@@ -163,7 +178,9 @@ class _CamViewPageState extends State<CamViewPage> {
                   child: f == null
                       ? Center(
                           child: Text(
-                            cam.status,
+                            cam.available == false
+                                ? 'Camera unavailable on the Orin'
+                                : cam.status,
                             style: const TextStyle(color: Colors.white70),
                           ),
                         )