fix(api): resolve db-only stale incidents

apps/api/src/services/incident_service.py

@@ -1168,12 +1168,14 @@ class IncidentService:
         from src.utils.timezone import now_taipei
 
         # 1. 從 Working Memory 讀取；Redis TTL 過期時退回 PostgreSQL。
+        hydrated_from_episodic = False
         incident = await self.get_from_working_memory(incident_id)
         if incident is None:
             incident = await self.get_from_episodic_memory(incident_id)
             if incident is None:
                 logger.warning("incident_not_found_for_resolve", incident_id=incident_id)
                 return None
+            hydrated_from_episodic = True
             logger.info(
                 "incident_resolve_hydrated_from_episodic_memory",
                 incident_id=incident_id,
@@ -1197,11 +1199,15 @@ class IncidentService:
         incident.resolved_at = now_taipei()
         incident.updated_at = now_taipei()
 
-        # 3. 寫入 Working Memory
-        redis_success = await self.save_to_working_memory(incident)
-        if not redis_success:
-            logger.error("resolve_redis_write_failed", incident_id=incident_id)
-            return None
+        # 3. 寫入 Working Memory。Redis TTL 已過的歷史 DB-only 事件只更新 DB，
+        # 不重新灌回 Redis working memory，避免舊事件回流成 active workload。
+        if hydrated_from_episodic:
+            logger.info("resolve_db_only_incident", incident_id=incident_id)
+        else:
+            redis_success = await self.save_to_working_memory(incident)
+            if not redis_success:
+                logger.error("resolve_redis_write_failed", incident_id=incident_id)
+                return None
 
         # 4. 同步到 Episodic Memory
         try: