Test 3: scale playback timeout to buffer length (was hardcoded 2 s)

FireAndForgetPlayback's cleanup task had the same 2 s done.Wait timeout
as the beep cleanup. Beep is 200 ms so 2 s is generous; recording
playback is 5 s so the timeout fired mid-playback, cleanup ran
stream.Stop(), and the audio cut at ~2.2 s. Timeout is now
recording-duration + 2 s.

tests/03-full-cycle-cs/Program.cs

@@ -347,10 +347,14 @@ static void FireAndForgetPlayback(int device, short[] recordBuf, PlaybackDoneFla
         done.Dispose();
         throw;
     }
+    // Timeout = playback wall-clock + 2 s safety margin. Test 2's beep cleanup uses
+    // a flat 2 s because beep is 200 ms; for a 5 s recording the same value would
+    // fire mid-playback, Stop the stream, and cut the audio.
+    double expectedSeconds = recordBuf.Length / (double)WakewordModel.SampleRate;
+    var waitTimeout = TimeSpan.FromSeconds(expectedSeconds + 2.0);
     Task.Run(() =>
     {
-        // Same 2 s safety timeout as the beep cleanup.
+        if (!done.Wait(waitTimeout))
-        if (!done.Wait(TimeSpan.FromSeconds(2)))
             Console.Error.WriteLine("[error] recording playback timed out — callback may have faulted");
         Thread.Sleep(200);
         stream.Stop();