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/application/messaging_handlers.py

@@ -168,6 +168,17 @@ def _handle_update_thresholds(
 
 # ---- slots RPC handler (REQ-073/074) ----------------------------------------
 
+# Maps a `trex.slots.req` filter token to the set of slot status values it
+# selects (issue #25 — pushed to the repository via list_slots status_filter).
+# "all" and unrecognized tokens map to None (no filter — REQ-073 AC-2).
+_FILTER_STATUS: dict[str, set[str]] = {
+    "inactive": {"inactive"},
+    "pending": {"pending_buy", "pending_sell"},
+    "holding": {"holding"},
+    "error": {"error"},
+}
+
+
 def make_slots_rpc_handler(
     slot_repo: SlotRepository,
     *,
@@ -196,21 +207,21 @@ def make_slots_rpc_handler(
         filter_val = str(body.get("filter") or "all").lower()
         spy = bool(body.get("spy", False))
 
-        # Retrieve and filter slots by status
-        slots = slot_repo.list_slots(instance_key)
-        if filter_val == "inactive":
-            slots = [s for s in slots if s.status.value == "inactive"]
-        elif filter_val == "pending":
-            slots = [s for s in slots if s.status.value in ("pending_buy", "pending_sell")]
-        elif filter_val == "holding":
-            slots = [s for s in slots if s.status.value == "holding"]
-        elif filter_val == "error":
-            slots = [s for s in slots if s.status.value == "error"]
-        # "all" or unrecognized → no filter (REQ-073 AC-2)
+        # issue #25: filter by status at the DB (REQ-002/006 list_slots
+        # status_filter) instead of fetching every row and filtering in Python.
+        # "all"/unrecognized → None (no filter, REQ-073 AC-2).
+        status_filter = _FILTER_STATUS.get(filter_val)
+        slots = slot_repo.list_slots(instance_key, status_filter=status_filter)
 
-        # REQ-034 CHG-01: update watchdog for holding slots unless spy=True
+        # REQ-034 CHG-01: update watchdog for holding slots unless spy=True.
+        # When the fetched set already contains every holding slot (filter "all"
+        # or "holding"), reuse it and skip the second connection (issue #25 (2)).
         if not spy and watchdog_store is not None:
-            for s in slot_repo.list_holding_slots(instance_key):
+            if status_filter is None or filter_val == "holding":
+                holding_slots = [s for s in slots if s.status.value == "holding"]
+            else:
+                holding_slots = slot_repo.list_holding_slots(instance_key)
+            for s in holding_slots:
                 watchdog_store.update(str(s.slot_id))
 
         # Build merged slot rows (REQ-074)