MeloTTS voice output, signal handling, auto pipeline

- melo_server.py subprocess (MeloTTS v3 EN-Newest, speed 1.3): line protocol
  stdin->stdout, model loaded once, warmup before READY
- src/melo.zig: lifecycle ownership (spawn/kill with inferon), line protocol
  client, reply sanitizer (newlines/markdown stripped before synthesis)
- SIGINT/SIGTERM handlers: async-signal-safe kill of whisper/melo/recorder,
  default disposition restored + re-raise for truthful exit status
- processUtterance: transcribe->infer->speak chains automatically after
  stop-click; mid-pipeline clicks are no-ops; back to idle after reply
- temp cleanup: recording WAV deleted after transcription, TTS WAV after
  playback
- whisper: pid() export for signal handler

👾 Generated with [Letta Code](https://letta.com)

Co-Authored-By: Letta Code <noreply@letta.com>

scripts/melo_server.py

@@ -0,0 +1,83 @@
+#!/usr/bin/env python3
+"""MeloTTS server for inferon.
+
+Long-running subprocess: loads the MeloTTS model once, then reads lines of
+text on stdin and writes "<wav-path> <duration-seconds>" per line on stdout.
+stderr passes through for logging.
+
+Protocol:
+    -> one line of text to synthesize
+    <- e.g. "/tmp/inferon/tts-1723.wav 3.42"
+
+Kill with SIGTERM — no cleanup needed, WAVs live in /tmp.
+"""
+
+import sys
+import os
+import time
+import signal
+import warnings
+
+warnings.filterwarnings("ignore")
+
+MELO_ROOT = os.path.expanduser("~/Projects/MeloTTS")
+CKPT = os.path.join(MELO_ROOT, "ckpt/MeloTTS-English-v3/checkpoint.pth")
+CONFIG = os.path.join(MELO_ROOT, "ckpt/MeloTTS-English-v3/config.json")
+OUT_DIR = "/tmp/inferon"
+SPEAKER = "EN-Newest"  # v3 English: single speaker (British-accented female)
+LANG = "EN"
+SPEED = 1.3  # speech rate; 1.0 = natural, higher = faster
+
+sys.path.insert(0, MELO_ROOT)
+
+
+def main() -> None:
+    signal.signal(signal.SIGTERM, lambda *_: sys.exit(0))
+    signal.signal(signal.SIGINT, lambda *_: sys.exit(0))
+
+    os.makedirs(OUT_DIR, exist_ok=True)
+
+    # Heavy imports inside main so signal handlers are installed first.
+    from melo.api import TTS
+
+    model = TTS(language=LANG, config_path=CONFIG, ckpt_path=CKPT)
+
+    speaker_ids = model.hps.data.spk2id
+    if SPEAKER not in speaker_ids:
+        # English v3 fallback: use the first speaker and say so on stderr.
+        fallback = next(iter(speaker_ids))
+        print(f"melo_server: speaker {SPEAKER!r} not in {list(speaker_ids)}; using {fallback!r}",
+              file=sys.stderr, flush=True)
+        speaker = fallback
+    else:
+        speaker = speaker_ids[SPEAKER]
+
+    # Warm up with a full sentence (longer text paths hit NLTK/num2words,
+    # which is where missing-data errors surface). Fail before READY.
+    warmup = "/tmp/inferon/tts-warmup.wav"
+    model.tts_to_file("Warmup sentence number twelve, spoken on the first of January.",
+                      speaker, warmup, speed=SPEED)
+    os.unlink(warmup)
+
+    # Ready marker — inferon waits for this before declaring the backend up.
+    print("READY", flush=True)
+
+    for line in sys.stdin:
+        text = line.strip()
+        if not text:
+            continue
+        text = text[:2000]  # protocol cap — extremely long replies get clipped
+
+        wav_path = os.path.join(OUT_DIR, f"tts-{time.time_ns()}.wav")
+        try:
+            start = time.monotonic()
+            model.tts_to_file(text, speaker, wav_path, speed=SPEED)
+            dur = time.monotonic() - start
+            print(f"{wav_path} {dur:.2f}", flush=True)
+        except Exception as e:  # noqa: BLE001 - protocol: report and survive
+            print(f"melo_server: synthesis failed: {e}", file=sys.stderr, flush=True)
+            print("ERROR", flush=True)
+
+
+if __name__ == "__main__":
+    main()