Try to fix background glitching over long periods of time

clients/apple/VoiceCat.iOS/IosAudioEngine.cs

@@ -40,7 +40,12 @@ internal sealed class IosAudioEngine
     private bool inputProvided;
     private bool tapInstalled;
     private long captureCallbacks, capturedFrames, convertedFrames, rejectedFeeds, converterFailures, stereoFrames, stereoDifferentFrames;
+    private long renderCallbacks, lastRenderTimestamp;
     internal bool IsConnected { get; private set; }
+    internal bool IsRunning => engine?.Running == true;
+    // The watchdog compares this across ticks: a graph that stops calling back while it still
+    // reports Running leaves the whole device-clocked pipeline frozen until it is rebuilt.
+    internal long RenderCallbacks => Interlocked.Read(ref renderCallbacks);
     internal int BufferMilliseconds { get => playbackRing.BufferMilliseconds; set => playbackRing.BufferMilliseconds = value; }
 
     internal void StartListening(VoiceCatClient owner)
@@ -201,15 +206,24 @@ internal sealed class IosAudioEngine
         // This callback is the cadence iOS keeps exact while the app is backgrounded or the device
         // is locked, so it owns both managed 20 ms hands-offs: capture into the sender and one mix
         // cycle per 20 ms of render demand. Both run allocation-free and without locks or I/O.
+        Interlocked.Increment(ref renderCallbacks);
+        long now = System.Diagnostics.Stopwatch.GetTimestamp(), previous = lastRenderTimestamp;
+        lastRenderTimestamp = now;
         VoiceCatClient? owner = Volatile.Read(ref client);
         if (owner is null || !IsConnected) microphoneCredit = 0;
         else
         {
+            if (previous != 0 && (now - previous) * 1000.0 / System.Diagnostics.Stopwatch.Frequency > 100)
+            {
+                Volatile.Read(ref microphone)?.Ring.Resynchronize();
+                playbackRing.Resynchronize(); owner.Audio.ResynchronizeInputs(); microphoneCredit = 0;
+            }
             microphoneCredit += frames;
             while (microphoneCredit >= 960) { microphoneCredit -= 960; PumpMicrophoneChunk(owner); }
             // Top the mix ring up to cover this callback plus its configured target so the read
-            // below never starves and the buffer keeps its chosen buffering latency.
-            int deficit = frames + playbackRing.TargetFrames - playbackRing.CountFrames;
+            // below never starves and the buffer keeps its chosen buffering latency. Catch-up is
+            // capped at one extra cycle so a refill cannot overrun this callback's deadline.
+            int deficit = Math.Min(frames + playbackRing.TargetFrames - playbackRing.CountFrames, frames + 960);
             for (int produced = 0; produced < deficit; produced += 960) owner.Audio.RunCycle();
         }
         Span<short> input = renderScratch.AsSpan(0, requested);
@@ -245,7 +259,7 @@ internal sealed class IosAudioEngine
             if (tapInstalled) old.InputNode.RemoveTapOnBus(0);
             old.Stop(); if (source is not null) old.DetachNode(source); old.Dispose();
         }
-        tapInstalled = false; pendingInput = null; inputProvider = null;
+        tapInstalled = false; pendingInput = null; inputProvider = null; lastRenderTimestamp = 0; microphoneCredit = 0;
         convertedMicrophone?.Dispose(); convertedMicrophone = null;
         microphoneConverter?.Dispose(); microphoneConverter = null;
         microphoneFormat?.Dispose(); microphoneFormat = null;