fix click: 5ms fade-out from last sample to zero before silence padding

Robovoice.App/AudioOutput.cs

@@ -8,6 +8,7 @@ internal sealed class AudioOutput : IDisposable
     private BufferedWaveProvider? _bufferProvider;
     private int _sampleRate;
     private string _deviceName = string.Empty;
+    private float _lastSample;
     private bool _disposed;
 
     public Action<string>? Log { get; set; }
@@ -18,6 +19,7 @@ internal sealed class AudioOutput : IDisposable
 
         _sampleRate = sampleRate;
         _deviceName = deviceName ?? string.Empty;
+        _lastSample = 0f;
 
         Stop();
 
@@ -42,6 +44,9 @@ internal sealed class AudioOutput : IDisposable
         ObjectDisposedException.ThrowIf(_disposed, this);
         if (_bufferProvider is null) return;
 
+        if (samples.Length > 0)
+            _lastSample = samples[^1];
+
         byte[] bytes = new byte[samples.Length * sizeof(float)];
         Buffer.BlockCopy(samples, 0, bytes, 0, bytes.Length);
         _bufferProvider.AddSamples(bytes, 0, bytes.Length);
@@ -52,8 +57,21 @@ internal sealed class AudioOutput : IDisposable
         ObjectDisposedException.ThrowIf(_disposed, this);
         if (_bufferProvider is null || _sampleRate == 0) return;
 
+        // Fade out from last sample to zero over 5ms to avoid click
+        int fadeSamples = (int)(_sampleRate * 0.005);
+        float[] fade = new float[fadeSamples];
+        for (int i = 0; i < fadeSamples; i++)
+        {
+            float t = (float)i / fadeSamples;
+            fade[i] = _lastSample * (1f - t);
+        }
+        WriteSamples(fade);
+
+        // Then 500ms of silence to let NAudio drain
         int padSamples = (int)(_sampleRate * 0.5);
         WriteSamples(new float[padSamples]);
+        
+        _lastSample = 0f;
     }
 
     private void OnPlaybackStopped(object? sender, StoppedEventArgs e)
@@ -71,6 +89,7 @@ internal sealed class AudioOutput : IDisposable
         }
         _bufferProvider?.ClearBuffer();
         _bufferProvider = null;
+        _lastSample = 0f;
     }
 
     private static int FindDevice(string? deviceName)