feat: inactivity watchdog for sockets

lib/core/services/persistent_streaming_service.dart

@@ -333,7 +333,9 @@ class PersistentStreamingService with WidgetsBindingObserver {
     final lastUpdate = metadata['lastUpdate'] as DateTime?;
     if (lastUpdate != null) {
       final timeSinceUpdate = DateTime.now().difference(lastUpdate);
-      return timeSinceUpdate > const Duration(minutes: 1);
+      // Align with app-side watchdogs: be less aggressive than UI guard
+      // but still attempt recovery before server timeouts become likely.
+      return timeSinceUpdate > const Duration(minutes: 2);
     }
 
     return false;

lib/core/utils/inactivity_watchdog.dart

@@ -0,0 +1,83 @@
+import 'dart:async';
+
+/// A simple activity-based watchdog.
+///
+/// Call [ping] whenever activity occurs. If no activity happens
+/// within [window], [onTimeout] fires. Optionally, an [absoluteCap]
+/// enforces a maximum total duration regardless of activity.
+class InactivityWatchdog {
+  InactivityWatchdog({
+    required Duration window,
+    required this.onTimeout,
+    Duration? absoluteCap,
+  })  : _window = window,
+        _absoluteCap = absoluteCap;
+
+  final void Function() onTimeout;
+
+  Duration _window;
+  Duration? _absoluteCap;
+  Timer? _timer;
+  Timer? _absoluteTimer;
+  bool _started = false;
+
+  Duration get window => _window;
+
+  void setWindow(Duration newWindow) {
+    _window = newWindow;
+    if (_started) {
+      // Restart timer with new window
+      _restart();
+    }
+  }
+
+  void setAbsoluteCap(Duration? cap) {
+    _absoluteCap = cap;
+    if (_started) {
+      _absoluteTimer?.cancel();
+      if (_absoluteCap != null) {
+        _absoluteTimer = Timer(_absoluteCap!, _fire);
+      }
+    }
+  }
+
+  void start() {
+    if (_started) return;
+    _started = true;
+    _restart();
+    if (_absoluteCap != null) {
+      _absoluteTimer = Timer(_absoluteCap!, _fire);
+    }
+  }
+
+  void ping() {
+    if (!_started) {
+      start();
+      return;
+    }
+    _restart();
+  }
+
+  void stop() {
+    _timer?.cancel();
+    _timer = null;
+    _absoluteTimer?.cancel();
+    _absoluteTimer = null;
+    _started = false;
+  }
+
+  void dispose() => stop();
+
+  void _restart() {
+    _timer?.cancel();
+    _timer = Timer(_window, _fire);
+  }
+
+  void _fire() {
+    stop();
+    try {
+      onTimeout();
+    } catch (_) {}
+  }
+}
+