Fix iOS stereo microphone capture

clients/apple/VoiceCat.iOS/IosAudioEngine.cs

@@ -55,7 +55,7 @@ internal sealed class IosAudioEngine
 
     internal void StartMicrophone(uint streamId, int channels)
     {
-        Volatile.Write(ref microphone, new(streamId, Math.Clamp(channels, 1, 2))); Rebuild();
+        Volatile.Write(ref microphone, CreateMicrophoneRoute(streamId, channels)); Rebuild();
     }
 
     internal void StopMicrophone() { Volatile.Write(ref microphone, null); Rebuild(); }
@@ -70,10 +70,21 @@ internal sealed class IosAudioEngine
             // an in-flight callback could interpret its old converter buffer using the new width.
             DestroyGraph();
             if (current.Channels != channels) client!.Audio.SetCaptureChannels(current.StreamId, channels);
-            Volatile.Write(ref microphone, new(current.StreamId, channels));
+            Volatile.Write(ref microphone, CreateMicrophoneRoute(current.StreamId, channels));
         }
         Rebuild();
     }
+
+    private static MicrophoneRoute CreateMicrophoneRoute(uint streamId, int channels)
+    {
+        var route = new MicrophoneRoute(streamId, Math.Clamp(channels, 1, 2));
+        // Physical RemoteIO capture is commonly delivered in 100 ms bursts. Starting its 20 ms
+        // pacer with only the VPIO-oriented 60 ms cushion guarantees several underruns after every
+        // mono/stereo rebuild before the adaptive path catches up. Prime one full burst plus one
+        // frame for non-VPIO routes; VPIO remains at the proven low-latency three-frame cushion.
+        route.TargetFrames = IosAudioRouter.Shared.UsesVoiceProcessing ? 3 : 6;
+        return route;
+    }
     internal bool EnsureRunning()
     {
         if (!IsConnected || engine?.Running == true) return true;