Test 1: add playback step — record-play loop complete

tests/01-record-play/main.py

@@ -1,9 +1,10 @@
 #!/usr/bin/env python3
-"""Record 5s from the USB Speaker Phone with a live RMS meter, save out.wav.
+"""Record 5s from the USB Speaker Phone with a live RMS meter, save out.wav, play it back.
 
-Pass criteria for the record stage:
+Pass criteria (per spec):
+- Playback is recognisable as what was said into the mic.
 - Level meter visibly responds to speech and to silence.
-- out.wav is written and non-empty.
+- No clipping, dropouts, or sustained PortAudio under/overrun warnings.
 """
 import os
 os.environ.setdefault("PA_ALSA_PLUGHW", "1")
@@ -73,11 +74,18 @@ def record(device: int) -> np.ndarray:
     return buf
 
 
+def play(device: int, audio: np.ndarray) -> None:
+    print(f"Playing back through device {device}")
+    sd.play(audio, samplerate=SAMPLE_RATE, device=device)
+    sd.wait()
+
+
 def main() -> int:
     device = find_usb_device()
     audio = record(device)
     sf.write(OUT_WAV, audio, SAMPLE_RATE)
     print(f"Wrote {OUT_WAV} ({audio.shape[0]} frames @ {SAMPLE_RATE} Hz)")
+    play(device, audio)
     return 0