Try to fix background glitching over long periods of time

clients/apple/VoiceCat.iOS/IosAudioRouter.cs

@@ -18,6 +18,11 @@ internal sealed class IosAudioRouter
     internal static IosAudioRouter Shared { get; } = new();
     private readonly NSUserDefaults defaults = NSUserDefaults.StandardUserDefaults;
     private bool applying;
+    private System.Threading.Timer? watchdog;
+    private long lastRenderCallbacks = -1;
+    private int watchdogMisses;
+    private bool watchdogTicking;
+    private bool interrupted;
     internal event Action? Changed;
     internal IosAudioPreset Preset { get; private set; } = IosAudioPreset.VoiceChat;
     internal IosBluetoothMode BluetoothMode { get; private set; } = IosBluetoothMode.HfpVoice;
@@ -117,6 +122,7 @@ internal sealed class IosAudioRouter
                 $"preferred={session.PreferredInput?.PortName ?? "default"} dataSource={session.InputDataSource?.DataSourceName ?? "default"} " +
                 $"pattern={session.InputDataSource?.SelectedPolarPattern.ToString() ?? "default"}");
             session.OverrideOutputAudioPort(ForceSpeaker && BluetoothMode != IosBluetoothMode.BuiltInMicA2dp ? AVAudioSessionPortOverride.Speaker : AVAudioSessionPortOverride.None, out _); RefreshRoutes();
+            ResetWatchdog(); EnsureWatchdog();
         }
         finally { applying = false; }
     }
@@ -210,10 +216,14 @@ internal sealed class IosAudioRouter
     }
 
     private void Set(string key, string? value) { if (value is null) defaults.RemoveObject(key); else defaults.SetString(value, key); }
-    internal void Deactivate() => AVAudioSession.SharedInstance().SetActive(false, AVAudioSessionSetActiveOptions.NotifyOthersOnDeactivation, out _);
+    internal void Deactivate()
+    {
+        watchdog?.Dispose(); watchdog = null; ResetWatchdog();
+        AVAudioSession.SharedInstance().SetActive(false, AVAudioSessionSetActiveOptions.NotifyOthersOnDeactivation, out _);
+    }
     internal void EnsureAudio(string reason)
     {
-        if (!IosAudioEngine.Shared.IsConnected) return;
+        if (!IosAudioEngine.Shared.IsConnected || interrupted) return;
         try { IosAudioEngine.Shared.EnsureRunning(); }
         catch (Exception exception) { System.Diagnostics.Debug.WriteLine($"Audio recovery ({reason}) failed: {exception}"); }
     }
@@ -221,13 +231,47 @@ internal sealed class IosAudioRouter
     internal void Recover(string reason)
     {
         RefreshRoutes();
-        if (!IosAudioEngine.Shared.IsConnected) return;
+        if (!IosAudioEngine.Shared.IsConnected || interrupted) return;
         UIApplication.SharedApplication.BeginInvokeOnMainThread(() =>
         {
             try { IosAudioEngine.Shared.Reconfigure(); }
             catch (Exception exception) { System.Diagnostics.Debug.WriteLine($"Audio recovery ({reason}) failed: {exception}"); }
         });
     }
+
+    // The render callback is the only clock for the device-clocked pipeline, so a graph that
+    // stops while the app is backgrounded freezes capture, mix and send with no notification to
+    // recover from. Poll for that and rebuild; a failed rebuild is retried on the next tick.
+    private void EnsureWatchdog()
+    {
+        watchdog ??= new System.Threading.Timer(_ => UIApplication.SharedApplication.BeginInvokeOnMainThread(TickWatchdog),
+            null, TimeSpan.FromSeconds(1), TimeSpan.FromSeconds(1));
+    }
+
+    private void ResetWatchdog() { lastRenderCallbacks = -1; watchdogMisses = 0; }
+
+    // An interruption that ends while the app is suspended never delivers its Ended notification.
+    internal void ResumeForeground() { interrupted = false; ResetWatchdog(); Recover("foreground"); }
+
+    private void TickWatchdog()
+    {
+        if (watchdogTicking) return;
+        watchdogTicking = true;
+        try
+        {
+            if (!IosAudioEngine.Shared.IsConnected || interrupted || applying) { ResetWatchdog(); return; }
+            long callbacks = IosAudioEngine.Shared.RenderCallbacks;
+            bool stalled = !IosAudioEngine.Shared.IsRunning || callbacks == lastRenderCallbacks;
+            lastRenderCallbacks = callbacks;
+            if (!stalled) { watchdogMisses = 0; return; }
+            // One missed tick can be a route change already rebuilding the graph.
+            if (++watchdogMisses < 2) return;
+            ResetWatchdog();
+            try { IosAudioEngine.Shared.Reconfigure(); }
+            catch (Exception exception) { System.Diagnostics.Debug.WriteLine($"Audio watchdog rebuild failed: {exception}"); }
+        }
+        finally { watchdogTicking = false; }
+    }
     private void HandleRouteChange(NSNotification note)
     {
         NSNumber? value = note.UserInfo?[new NSString("AVAudioSessionRouteChangeReasonKey")] as NSNumber;
@@ -243,6 +287,10 @@ internal sealed class IosAudioRouter
     {
         NSNumber? type = note.UserInfo?[new NSString("AVAudioSessionInterruptionTypeKey")] as NSNumber;
         AVAudioSessionInterruptionType interruption = (AVAudioSessionInterruptionType)(type?.UInt32Value ?? 0);
-        if (interruption == AVAudioSessionInterruptionType.Ended) Recover("interruption ended");
+        // The system stops the graph on Began and SetActive fails until the interruption clears,
+        // so suppress recovery until Ended and let the watchdog retry if that rebuild fails.
+        if (interruption == AVAudioSessionInterruptionType.Began) { interrupted = true; ResetWatchdog(); return; }
+        if (interruption != AVAudioSessionInterruptionType.Ended) return;
+        interrupted = false; ResetWatchdog(); Recover("interruption ended");
     }
 }