perf(slots): BAT-040 — slots RPC DB-level status 필터 (REQ-002/006/073, issue #25)

REQ-002/006 change-req(CHG-20260612-01)→구현→confirm-req-implemented,
REQ-073 change-req(CHG-20260612-02, 관찰 계약 불변 Implemented 유지) 전체 delivery.

- repository.py/in_memory_repository.py: SlotRepository.list_slots(instance_key,
  status_filter=None) — status 값 집합 필터, None=전체(기존 호출자 불변).
- postgresql.py: list_slots DB-level WHERE status = ANY(%s) (full scan + Python
  필터 제거). 스키마/마이그레이션 변경 없음.
- messaging_handlers.py: _FILTER_STATUS 매핑으로 filter→status 집합 위임,
  watchdog 갱신용 holding 조회를 all/holding fetch 결과에서 재사용(2nd 커넥션 생략).
- 관찰 가능한 RPC 계약(REQ-073 AC-1~6) 불변 — 동작 보존 최적화.
- tests: in-memory status_filter 5종 + PG 게이트 1종. 439 passed (+5), ruff clean.

REQ-002·006 Approved→Implemented, REQ-073 Implemented 유지, BAT-040 release-candidate.
issue #25 close.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

trex_core/adapters/persistence/postgresql.py

@@ -66,13 +66,25 @@ class PostgreSQLSlotRepository:
                 conn.rollback()
                 raise
 
-    def list_slots(self, instance_key: str) -> list[Slot]:
+    def list_slots(
+        self, instance_key: str, status_filter: Optional[set[str]] = None
+    ) -> list[Slot]:
         with self._psycopg.connect(self._dsn) as conn:
             with conn.cursor() as cur:
-                cur.execute(
-                    f"SELECT {_SLOT_COLUMNS} FROM daily_slot WHERE instance_key = %s",
-                    (instance_key,),
-                )
+                if status_filter:
+                    # issue #25: filter by status at the DB instead of fetching
+                    # every row and filtering in Python. ANY(%s) binds the set
+                    # as a single PG array parameter.
+                    cur.execute(
+                        f"SELECT {_SLOT_COLUMNS} FROM daily_slot "
+                        "WHERE instance_key = %s AND status = ANY(%s)",
+                        (instance_key, list(status_filter)),
+                    )
+                else:
+                    cur.execute(
+                        f"SELECT {_SLOT_COLUMNS} FROM daily_slot WHERE instance_key = %s",
+                        (instance_key,),
+                    )
                 return [self._row_to_slot(r) for r in cur.fetchall()]
 
     def fetch_slot(self, slot_id: UUID) -> Optional[Slot]: