feat: VAD ingestion buffer — Silero VAD, per-room accumulation

TDD: 3 tests covering silence passthrough, speech→silence segment emission,
and short-speech discard. Uses _speech_ms tracking (not total buffer length)
for accurate min_speech_ms enforcement. Silero VAD import is try/except'd
so tests run without torch via mocker.patch on vad_prob.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/pipeline/ingestion.py

@@ -0,0 +1,127 @@
+import numpy as np
+from datetime import datetime
+from typing import Optional
+
+# Silero VAD — docker-only; set to None when not available
+try:
+    import torch
+    _vad_model = None
+    _TORCH_AVAILABLE = True
+except ImportError:
+    _TORCH_AVAILABLE = False
+    _vad_model = None
+
+
+def _load_vad():
+    global _vad_model
+    if not _TORCH_AVAILABLE:
+        raise ImportError("torch not installed")
+    if _vad_model is None:
+        import torch
+        model, _ = torch.hub.load(
+            repo_or_dir="snakers4/silero-vad",
+            model="silero_vad",
+            force_reload=False,
+            trust_repo=True,
+        )
+        _vad_model = model
+    return _vad_model
+
+
+def vad_prob(chunk: bytes, sample_rate: int = 16000) -> float:
+    """Return speech probability (0-1) for a PCM int16 chunk."""
+    import torch
+    model = _load_vad()
+    audio = np.frombuffer(chunk, dtype=np.int16).astype(np.float32) / 32768.0
+    tensor = torch.FloatTensor(audio)
+    with torch.no_grad():
+        prob = model(tensor, sample_rate).item()
+    return prob
+
+
+class RoomVADBuffer:
+    """
+    Accumulates audio chunks for a single room.
+    Emits (audio_bytes, start_time) when a speech segment ends.
+    """
+
+    SPEECH_THRESHOLD = 0.5
+
+    def __init__(
+        self,
+        silence_threshold_ms: int = 600,
+        min_speech_ms: int = 500,
+        chunk_ms: int = 250,
+        sample_rate: int = 16000,
+    ):
+        self.silence_threshold_ms = silence_threshold_ms
+        self.min_speech_ms = min_speech_ms
+        self.chunk_ms = chunk_ms
+        self.sample_rate = sample_rate
+        self._buffer: list = []
+        self._speaking = False
+        self._silence_ms = 0
+        self._speech_ms = 0  # track pure speech duration
+        self._start_time: Optional[datetime] = None
+
+    def process_chunk(
+        self, chunk: bytes, timestamp: datetime
+    ) -> Optional[tuple]:
+        """
+        Returns (audio_bytes, start_time) when a complete speech segment is ready.
+        Returns None while accumulating or during silence.
+        """
+        prob = vad_prob(chunk)
+
+        if prob >= self.SPEECH_THRESHOLD:
+            if not self._speaking:
+                self._speaking = True
+                self._start_time = timestamp
+                self._buffer = []
+                self._speech_ms = 0
+            self._buffer.append(chunk)
+            self._silence_ms = 0
+            self._speech_ms += self.chunk_ms
+        elif self._speaking:
+            self._buffer.append(chunk)  # include trailing silence
+            self._silence_ms += self.chunk_ms
+            if self._silence_ms >= self.silence_threshold_ms:
+                audio = b"".join(self._buffer)
+                start = self._start_time
+                speech_ms = self._speech_ms
+                self._buffer = []
+                self._speaking = False
+                self._silence_ms = 0
+                self._speech_ms = 0
+                self._start_time = None
+                if speech_ms >= self.min_speech_ms:
+                    return audio, start
+
+        return None
+
+
+# Per-room registry: room_name -> {"buffer": RoomVADBuffer, "muted": bool}
+_rooms: dict = {}
+
+
+def get_or_create_room(room_id: str, silence_ms: int, min_speech_ms: int) -> dict:
+    if room_id not in _rooms:
+        _rooms[room_id] = {
+            "buffer": RoomVADBuffer(silence_threshold_ms=silence_ms, min_speech_ms=min_speech_ms),
+            "muted": False,
+        }
+    return _rooms[room_id]
+
+
+def mute_room(room_id: str) -> None:
+    if room_id in _rooms:
+        _rooms[room_id]["muted"] = True
+
+
+def unmute_room(room_id: str) -> None:
+    if room_id in _rooms:
+        _rooms[room_id]["muted"] = False
+
+
+def is_muted(room_id: str) -> bool:
+    return _rooms.get(room_id, {}).get("muted", False)