Stage 4: honest health, explicit error policy, event-bus integrity

Engine mode is now explicit: USE_MOCK_SIP=true is the only way to get
the mock engine; an unconfigured trunk fails startup with guidance
instead of silently degrading. Root-caused why the engine always ran
mock: nested pydantic-settings never read .env (no env_file on the
sub-settings classes) — all 8 now declare it.

/health stops lying: reports engine mode (sippy|mock), a live DB
SELECT 1, trunk registration state with reason, and TTS/STT
availability from their last real request; "healthy" now requires
ready + db + sippy + registered trunk.

Error policy: leaf services (tts/transcription/llm_client) raise and
track availability; call-loop callers catch, publish EventType.ERROR
naming the failed service, and apply an explicit fallback. Persistence
writes get one bounded 3x exponential retry, then an ERROR log — no
more silent data loss.

Event bus: a full subscriber queue drops its oldest event (counted)
instead of silently evicting the subscription; subscribe(replay_last=N)
delivers the advertised history replay, used by /ws/events (25).

Receptionist correctness: a matched TAKE_MESSAGE rule beats the LLM;
voicemail polls for early hangup and stops/transcribes/hangs up in
finally; RecordingSession finally keeps its leg_ids so taps detach.

Dead code removed: models/contact.py + Contact table, dtmf_buffer,
transcribe_stream stub, SMS stub in notification.py.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

services/notification.py

@@ -67,7 +67,6 @@ class NotificationService:
         self._event_bus = event_bus
         self._settings = settings
         self._task: Optional[asyncio.Task] = None
-        self._sms_sender: Optional[Any] = None
 
         # Track what we've already notified (avoid spam)
         self._notified: dict[str, set[str]] = {}  # call_id -> set of event types
@@ -214,43 +213,3 @@ class NotificationService:
 
         # WebSocket notifications go through the event bus
         # (the WebSocket handler in the API reads from EventBus directly)
-
-        # SMS for critical notifications
-        if (
-            notification.priority == NotificationPriority.CRITICAL
-            and self._settings.notify_sms_number
-        ):
-            await self._send_sms(notification)
-
-    async def _send_sms(self, notification: Notification) -> None:
-        """
-        Send an SMS notification.
-
-        Uses a simple HTTP-based SMS gateway. In production,
-        this would use Twilio, AWS SNS, or similar.
-        """
-        phone = self._settings.notify_sms_number
-        if not phone:
-            return
-
-        try:
-            import httpx
-
-            # Generic webhook-based SMS (configure your provider)
-            # This is a placeholder — wire up your preferred SMS provider
-            logger.info(f"📱 SMS → {phone}: {notification.title}")
-
-            # Example: Twilio-style API
-            # async with httpx.AsyncClient() as client:
-            #     await client.post(
-            #         "https://api.twilio.com/2010-04-01/Accounts/.../Messages.json",
-            #         data={
-            #             "To": phone,
-            #             "From": self._settings.sip_trunk.did,
-            #             "Body": f"{notification.title}\n{notification.message}",
-            #         },
-            #         auth=(account_sid, auth_token),
-            #     )
-
-        except Exception as e:
-            logger.error(f"SMS send failed: {e}")