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>

tests/test_receptionist.py

@@ -24,10 +24,27 @@ class TestReceptionistDecide:
         gw = _make_gateway()
         svc = ReceptionistService(gw)
         rule_action = RoutingAction(type=RoutingActionType.REJECT, message="nope")
-        decision = RoutingDecision(action=rule_action, reason="rule said so")
+        decision = RoutingDecision(
+            action=rule_action,
+            matched_rule_id="rule_1",
+            matched_rule_name="block",
+            reason="rule said so",
+        )
         chosen = svc._decide(decision, {"recommended_action": "ring"})
         assert chosen.type == RoutingActionType.REJECT
 
+    def test_matched_take_message_rule_beats_llm(self):
+        gw = _make_gateway()
+        svc = ReceptionistService(gw)
+        decision = RoutingDecision(
+            action=RoutingAction(type=RoutingActionType.TAKE_MESSAGE),
+            matched_rule_id="rule_2",
+            matched_rule_name="voicemail-hours",
+            reason="matched rule 'voicemail-hours'",
+        )
+        chosen = svc._decide(decision, {"recommended_action": "ring"})
+        assert chosen.type == RoutingActionType.TAKE_MESSAGE
+
     def test_falls_back_to_llm_when_rule_is_default_take_message(self):
         gw = _make_gateway()
         svc = ReceptionistService(gw)