refactor: simplify mqtt pipeline state and remove event table

backend/app/mqtt/ingestor.py

@@ -1,24 +1,32 @@
 from __future__ import annotations
 
 import logging
+import re
+from typing import Any
 
-import paho.mqtt.client as mqtt  # type: ignore[import-not-found,import-untyped]
 from sqlmodel import Session
 
 from app.core.config import settings
 from app.core.db import engine
 from app.mqtt.repository import insert_raw_message
-from app.mqtt.topic import extract_device_id
 
 logger = logging.getLogger(__name__)
+TOPIC_PATTERN = re.compile(r"^terminal/(?P<device_id>[^/]+)/raw$")
+
+
+def extract_device_id(topic: str) -> str:
+    match = TOPIC_PATTERN.match(topic)
+    if match is None:
+        raise ValueError("topic must match terminal/{device_id}/raw")
+    return match.group("device_id")
 
 
 def _on_connect(
-    client: mqtt.Client,
+    client: Any,
     _userdata: object,
     _flags: dict[str, int],
     reason_code: int,
-    _properties: mqtt.Properties | None = None,
+    _properties: object | None = None,
 ) -> None:
     if reason_code != 0:
         logger.error("MQTT connect failed: rc=%s", reason_code)
@@ -31,9 +39,9 @@ def _on_connect(
 
 
 def _on_message(
-    _client: mqtt.Client,
+    _client: Any,
     _userdata: object,
-    message: mqtt.MQTTMessage,
+    message: Any,
 ) -> None:
     try:
         device_id = extract_device_id(message.topic)
@@ -52,7 +60,14 @@ def _on_message(
         )
 
 
-def create_client() -> mqtt.Client:
+def create_client() -> Any:
+    try:
+        import paho.mqtt.client as mqtt  # type: ignore[import-not-found,import-untyped]
+    except ModuleNotFoundError as exc:  # pragma: no cover - runtime guard
+        raise RuntimeError(
+            "paho-mqtt is required to run mqtt-ingestor. Install backend dependencies first."
+        ) from exc
+
     client = mqtt.Client(
         callback_api_version=mqtt.CallbackAPIVersion.VERSION2,
         client_id=settings.MQTT_CLIENT_ID,