fix(voice): stop wake re-fire loop and empty-transcript error spam

Two bugs surfaced by the desktop wake conversation:

1. Runaway loop: wake -> voice -> resume -> wake fired again within
   ~200ms. openWakeWord keeps its rolling feature buffer across
   pause/resume, so on resume it immediately re-scored the "hey jarvis"
   captured before the pause and re-fired, reopening a session and
   restarting voice in a tight cycle. Reset the engine buffer on every
   detector (re)start so resume begins from clean audio.

2. Empty-transcript toast: a silent re-listen returns
   success:false / "… STT returned empty transcript", which the desktop
   transcribe endpoint turned into a 400 -> thrown error -> "Voice
   transcription failed" notification on every silent gap. Treat an empty
   transcript as no-speech: return {ok, transcript: ""} so the voice loop
   quietly re-listens. Real failures still 4xx/5xx.

hermes_cli/web_server.py

@@ -4417,10 +4417,15 @@ async def transcribe_audio_upload(payload: AudioTranscriptionRequest):
                 pass
 
     if not result.get("success"):
-        raise HTTPException(
-            status_code=400,
-            detail=result.get("error") or "Transcription failed",
-        )
+        err = result.get("error") or "Transcription failed"
+        # An empty transcript means no speech was detected — a normal outcome
+        # for VAD/continuous voice loops (e.g. a wake-word conversation
+        # re-listening on silence), not an error. Return an empty transcript so
+        # the client quietly re-listens instead of surfacing a "transcription
+        # failed" toast on every silent gap.
+        if "empty transcript" in err.lower():
+            return {"ok": True, "transcript": "", "provider": result.get("provider")}
+        raise HTTPException(status_code=400, detail=err)
 
     return {
         "ok": True,

tests/tools/test_wake_word.py

@@ -136,10 +136,14 @@ class _FakeEngine:
     def __init__(self, fire=True):
         self._fire = fire
         self.closed = False
+        self.resets = 0
 
     def process(self, frame):
         return self._fire
 
+    def reset(self):
+        self.resets += 1
+
     def close(self):
         self.closed = True
 
@@ -182,6 +186,21 @@ def test_detector_no_fire_when_engine_quiet(monkeypatch):
     assert calls == []
 
 
+def test_detector_resets_engine_on_each_start(monkeypatch):
+    # Clearing the engine buffer on (re)start is what stops a resume right after
+    # a voice turn from re-firing on stale audio (the runaway wake loop).
+    _fake_audio(monkeypatch)
+    eng = _FakeEngine(fire=False)
+    det = ww.WakeWordDetector(eng, lambda: None)
+    det.start()
+    time.sleep(0.05)
+    det.pause()
+    det.resume()
+    time.sleep(0.05)
+    det.stop()
+    assert eng.resets >= 2  # initial start + resume
+
+
 def test_detector_pause_resume(monkeypatch):
     _fake_audio(monkeypatch)
     det = ww.WakeWordDetector(_FakeEngine(fire=False), lambda: None)

tools/wake_word.py

@@ -140,6 +140,10 @@ class _Engine:
     def process(self, frame) -> bool:  # frame: 1-D int16 ndarray
         raise NotImplementedError
 
+    def reset(self) -> None:
+        """Clear any internal audio/feature buffer (called on every (re)start)."""
+        pass
+
     def close(self) -> None:
         pass
 
@@ -189,12 +193,17 @@ class _OpenWakeWordEngine(_Engine):
         scores = self._model.predict(frame)
         return any(score >= self._threshold for score in scores.values())
 
-    def close(self) -> None:
+    def reset(self) -> None:
+        # Clears openWakeWord's rolling feature/prediction buffer so stale audio
+        # captured before a pause can't re-fire the moment we resume.
         try:
             self._model.reset()
         except Exception:
             pass
 
+    def close(self) -> None:
+        self.reset()
+
 
 class _PorcupineEngine(_Engine):
     """Picovoice Porcupine — premium, on-device, needs an access key."""
@@ -356,6 +365,14 @@ class WakeWordDetector:
             logger.error("wake word: failed to open microphone: %s", e)
             return
 
+        # Drop any buffered audio/feature state so a resume right after a voice
+        # turn can't immediately re-fire on audio captured before the pause (the
+        # wake → voice → resume → wake runaway loop).
+        try:
+            self.engine.reset()
+        except Exception:
+            pass
+
         logger.info("wake word: listening (frame=%d, rate=%d)", frame_length, SAMPLE_RATE)
         try:
             while not self._stop.is_set():