feat(safety-sell): dcy-017 워치독 소유권 가시화 — snapshot 상태 + 발동 로깅 (BAT-021)

전략 이탈로 슬롯이 내부 청산 루틴(워치독) 소유로 넘어간 상태가 무성이라
운영자가 인지할 수 없던 문제(issue #12)를 가시화한다.

거버넌스: 전부 change-req (신규 REQ 없음, dcy-017 OQ-3; Redis 미채택).
- REQ-034/021: WatchdogStore.last_seen + snapshot RPC 응답에 holding 슬롯
  워치독 상태(expired/last_seen) read-only 동봉(best-effort)
- REQ-032: trex-core slots 가 expired 슬롯을 WATCHDOG-OWNED(전략 이탈) 표시
- REQ-037/038/039: safety-sell 워치독 소유 진입(WARN)/이탈(INFO) + 발동
  (forced_close·stop_loss=WARN, take_profit·market_close=INFO) 로그 +
  in-process 카운터(SafetySellService.counters), 구조화 필드(slot_id/
  portfolio_id/reason/phase/instance_key). per-tick 스킵은 카운터만
- REQ-042: runtime-flows/interface-contract 정합

best-effort 격리(NFR-1): 모든 가시화는 예외 격리 — 워치독 판정·청산 불변.
dcy-016 억제 읽기로 관측이 워치독을 리셋하지 않음(비침습).

검증: 단위 335 passed/34 skipped, 인프라 게이트(PG+RabbitMQ) 369 passed, ruff clean.
신규 test_safety_sell_visibility(6) + snapshot watchdog(1) + CLI(1). BAT-021 rc.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

trex_core/application/messaging_handlers.py

@@ -168,6 +168,7 @@ def make_snapshot_rpc_handler(
     pause_store: Optional[PauseStore] = None,
     default_total_slots: int = 10,
     watchdog_store: Optional[WatchdogStore] = None,
+    watchdog_timeout_sec: int = 120,
     killswitch_store=None,
 ):
     """Build the RPC handler for `trex.snapshot.req` (REQ-028).
@@ -225,7 +226,9 @@ def make_snapshot_rpc_handler(
                 trading_date=day,
                 killswitch_store=killswitch_store,
             )
-            return RpcResponse(payload=envelope.to_dict())
+            payload = envelope.to_dict()
+            _attach_watchdog(payload, slot_repo, day, watchdog_store, watchdog_timeout_sec)
+            return RpcResponse(payload=payload)
 
         # --- BAT-007 legacy stub-shape path ---
         view_raw = str(body.get("view") or "all")
@@ -236,7 +239,7 @@ def make_snapshot_rpc_handler(
         if strategy_filter is not None:
             slots = [s for s in slots if s.strategy_id == strategy_filter]
         cap = slot_service.compute_slot_capacity(day, max(1, len(slot_repo.list_slots(day))))
-        return RpcResponse(payload={
+        payload = {
             "view": view_raw,
             "strategy_id": strategy_filter,
             "trading_date": day.isoformat(),
@@ -248,11 +251,40 @@ def make_snapshot_rpc_handler(
                 "total_slots": cap.total_slots,
                 "scarcity_ratio": cap.scarcity_ratio,
             },
-        })
+        }
+        _attach_watchdog(payload, slot_repo, day, watchdog_store, watchdog_timeout_sec)
+        return RpcResponse(payload=payload)
 
     return handler
 
 
+def _attach_watchdog(payload, slot_repo, day, watchdog_store, timeout_sec) -> None:
+    """Attach holding-slot watchdog state to a snapshot response (dcy-017/REQ-034).
+
+    `watchdog` = list of {slot_id, portfolio_id, symbol, expired, last_seen} for
+    holding slots — lets `trex-core slots` surface watchdog ownership (strategy
+    absence). Best-effort: any failure leaves the response unchanged (FR-4)."""
+    if watchdog_store is None:
+        return
+    try:
+        states = []
+        for s in slot_repo.list_slots(day):
+            if s.status is not SlotState.HOLDING:
+                continue
+            sid = str(s.slot_id)
+            last = watchdog_store.last_seen(sid)
+            states.append({
+                "slot_id": sid,
+                "portfolio_id": s.portfolio_id,
+                "symbol": s.symbol,
+                "expired": watchdog_store.is_expired(sid, timeout_sec),
+                "last_seen": last.isoformat() if last else None,
+            })
+        payload["watchdog"] = states
+    except Exception:  # noqa: BLE001 - visibility must never break the response
+        return
+
+
 # ---- pause/resume RPC handler (REQ-032 AC-4) --------------------------------
 
 def make_pause_rpc_handler(pause_store: PauseStore):