feat(voice): Whisper STT (robust to handset voice)

Switch the voice-loop STT from Kyutai to whisper.cpp large-v3-turbo
(subprocess, high-pass conditioned): it decodes the weak/noisy SLIC
handset captures Kyutai returned '' for. Filter whisper's silence/noise
hallucinations (sous-titrage, radio-canada, tipeurs, '...') so the NPC
never replies to a phantom line. Bump ESP32_ZACUS to 54022ed (VAD
recalibration for the quiet voice + bell stop on pickup).

tools/zacus-gateway/main.py

@@ -2004,6 +2004,52 @@ async def _transcribe_kyutai(http: httpx.AsyncClient, audio_wav: bytes) -> str:
     return (resp.json().get("text") or "").strip()
 
 
+# whisper.cpp (large-v3-turbo, CoreML) — far more robust to the weak/noisy SLIC
+# handset captures than Kyutai's streaming STT (decodes voice Kyutai returns ''
+# for). Used as the primary STT for the voice loop.
+_WHISPER_BIN = "/Users/electron/whisperx-server/whisper.cpp/build/bin/whisper-cli"
+_WHISPER_MODEL = "/Users/electron/whisperx-server/models/ggml-large-v3-turbo-q5_0.bin"
+_WHISPER_NOISE = re.compile(r"\[(?:_?BLANK_AUDIO_?|BLANK_AUDIO|silence|musique|music)\]|\(\s*\)", re.I)
+# whisper hallucinates these training-data artefacts on silence/noise — treat as empty.
+_WHISPER_HALLUC = re.compile(
+    r"sous-titr|société radio-canada|radio-canada|merci d'avoir regard|"
+    r"amara\.org|abonnez-vous|tipeur|souscripteur|merci à tous|"
+    r"n'oubliez pas de vous abonner|^\s*\.+\s*$",
+    re.I)
+
+
+def _strip_whisper_artefacts(txt: str) -> str:
+    """Drop whisper's silence/noise hallucinations so the NPC doesn't 'reply' to them."""
+    cleaned = _WHISPER_NOISE.sub("", txt or "").strip()
+    if not cleaned or _WHISPER_HALLUC.search(cleaned):
+        return ""
+    return cleaned
+
+
+def _transcribe_whisper_sync(audio_wav: bytes) -> str:
+    conditioned = _normalize_wav_for_stt(audio_wav)
+    with tempfile.NamedTemporaryFile(suffix=".wav", delete=False) as f:
+        f.write(conditioned)
+        path = f.name
+    try:
+        out = subprocess.run(
+            [_WHISPER_BIN, "-m", _WHISPER_MODEL, "-f", path,
+             "-l", "fr", "-nt", "-np"],
+            capture_output=True, text=True, timeout=30,
+        )
+        return _strip_whisper_artefacts(out.stdout or "")
+    finally:
+        try:
+            os.unlink(path)
+        except OSError:
+            pass
+
+
+async def _transcribe_whisper(audio_wav: bytes) -> str:
+    """Transcribe a WAV via whisper.cpp turbo (high-pass conditioned), off-thread."""
+    return await asyncio.to_thread(_transcribe_whisper_sync, audio_wav)
+
+
 def _ascii_header(s: str) -> str:
     """Make a string safe as an HTTP header value: ASCII-only AND no control
     characters (newlines/CR/tab break the HTTP framing)."""
@@ -2087,7 +2133,7 @@ async def voice_reply(
 
     try:
         audio_bytes = await audio.read()
-        heard = await _transcribe_kyutai(http, audio_bytes)
+        heard = await _transcribe_whisper(audio_bytes)
         logging.info("voice/reply[%s] HEARD: %r", number, heard)
         VOICE_SESSIONS.append(session_id, "user", heard or "(inaudible)")
         history = VOICE_SESSIONS.history(session_id)