refactor: simplify mqtt pipeline state and remove event table

backend/app/mqtt/repository.py

@@ -9,7 +9,6 @@ from sqlmodel import Session, col, select
 from app.models import (
     TerminalDeviceState,
     TerminalMessageRaw,
-    TerminalObservationEvent,
     get_datetime_utc,
 )
 
@@ -34,7 +33,6 @@ def insert_raw_message(
         payload_sha256=hashlib.sha256(payload).hexdigest(),
         qos=qos,
         retain=retain,
-        parse_status="pending",
         created_at=ts,
     )
     session.add(row)
@@ -48,7 +46,8 @@ def fetch_pending_rows_for_update(
 ) -> list[TerminalMessageRaw]:
     statement = (
         select(TerminalMessageRaw)
-        .where(TerminalMessageRaw.parse_status == "pending")
+        .where(col(TerminalMessageRaw.parsed_at).is_(None))
+        .where(col(TerminalMessageRaw.parse_error).is_(None))
         .order_by(col(TerminalMessageRaw.received_at))
         .limit(batch_size)
     )
@@ -61,17 +60,9 @@ def fetch_pending_rows_for_update(
     return list(rows)
 
 
-def mark_processing(*, session: Session, row: TerminalMessageRaw) -> None:
-    row.parse_status = "processing"
-    row.parse_attempts += 1
-    row.parse_error = None
-    session.add(row)
-
-
 def mark_succeeded(*, session: Session, row: TerminalMessageRaw) -> None:
-    row.parse_status = "succeeded"
+    row.parsed_at = get_datetime_utc()
     row.parse_error = None
-    row.next_retry_at = None
     session.add(row)
 
 
@@ -80,15 +71,13 @@ def mark_failed(
     session: Session,
     row: TerminalMessageRaw,
     parse_error: str,
-    next_retry_at: datetime | None,
 ) -> None:
-    row.parse_status = "failed"
+    row.parsed_at = get_datetime_utc()
     row.parse_error = parse_error[:1024]
-    row.next_retry_at = next_retry_at
     session.add(row)
 
 
-def write_events_and_update_state(
+def update_device_state_from_events(
     *,
     session: Session,
     row: TerminalMessageRaw,
@@ -110,14 +99,6 @@ def write_events_and_update_state(
     for event in events:
         payload = event.get("payload", {})
         event_type = str(event.get("event_type", "unknown"))
-        db_event = TerminalObservationEvent(
-            raw_id=row.id,
-            device_id=row.device_id,
-            event_time=row.received_at,
-            event_type=event_type,
-            payload_json=payload if isinstance(payload, dict) else {"value": payload},
-        )
-        session.add(db_event)
 
         if event_type == "nmea_gga":
             state.lat = payload.get("lat")