Fix iOS voice capture and screen sharing

clients/apple/VoiceCat.iOS/AppModel.cs

@@ -33,6 +33,7 @@ internal sealed class AppModel
     private bool restoreMuted;
     private bool restoreDeafened;
     private bool backgrounded;
+    private int diagnosticPolls;
 
     internal event Action? Changed;
     internal event Action<ServerIdentityChallenge>? IdentityRequested;
@@ -274,6 +275,13 @@ internal sealed class AppModel
     {
         VoiceCatClient? owner = client; uint stream = microphoneStream; if (owner is null || stream == 0) return;
         (float level, bool talking) = owner.Audio.GetLocalLevel(stream); MicrophoneLevel = level;
+        if (++diagnosticPolls >= 20)
+        {
+            diagnosticPolls = 0;
+            LocalAudioDiagnostics audio = owner.Audio.GetLocalDiagnostics(stream);
+            Console.Error.WriteLine($"VC_AUDIO {IosAudioEngine.Shared.CaptureDiagnostics()} cycles={audio.Cycles} starved={audio.StarvedCycles} " +
+                $"encoded={audio.EncodedPackets} packetDrops={audio.RejectedPackets} queued={audio.BufferedFrames}");
+        }
         if (talking != lastTalking) { lastTalking = talking; owner.PublishStreamState(stream, talking); feedback.Play(talking ? SoundEvent.VoiceStart : SoundEvent.VoiceStop); }
         UIApplication.SharedApplication.BeginInvokeOnMainThread(Notify);
     }
@@ -290,7 +298,17 @@ internal sealed class AppModel
 
     private void AddActivity(string text) { activity.Add(new(DateTime.Now, text)); if (activity.Count > 500) activity.RemoveAt(0); }
     private static string Name(VoiceCatClient owner, uint id) => owner.Users.FirstOrDefault(user => user.Id == id)?.Nickname ?? $"User {id}";
-    private void BroadcastChanged() => UIApplication.SharedApplication.BeginInvokeOnMainThread(Notify);
+    private void BroadcastChanged()
+    {
+        UIApplication.SharedApplication.BeginInvokeOnMainThread(() =>
+        {
+            // Presenting either system picker can replace or interrupt the app's audio session.
+            // Rebuild after the producer becomes active so playback and an existing mic tap are
+            // attached to the session that will remain in use for the broadcast.
+            if (ScreenSharing) IosAudioRouter.Shared.Recover("screen sharing started");
+            Notify();
+        });
+    }
 
     private void CaptureRestoreState(VoiceCatClient owner)
     {