fix(agent-office): node_monitor 루프 예외 방어 + 테스트 보강 (B2 리뷰)

- per-worker 루프 전체를 try/except로 감싸 Redis 예외 시 redis_ok=False+break (Blocker)
- heartbeat 파싱 except에 UnicodeDecodeError 추가 (Important)
- hb.get('ts') or '' 로 null ts 안전 처리 (Minor)
- 테스트 3개 추가: paused 폴백·processing 집계·llen 예외 회귀

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019LV86jBozkNhSFXJA412fq

agent-office/app/node_monitor.py

@@ -55,29 +55,34 @@ async def collect_status(redis=None) -> dict:
         return out
 
     for w in WORKER_REGISTRY:
-        info = {"name": w["name"], "kind": w["kind"], "alive": False, "state": None,
-                "last_beat_age_s": None, "queue_depth": 0, "dead_letter": 0,
-                "processing": 0, "jobs_done": 0, "jobs_failed": 0, "last_job_at": None}
-        raw = await r.get(f"worker:{w['name']}:heartbeat")
-        if raw:
-            try:
-                hb = json.loads(raw)
-                info.update(alive=True, state=hb.get("state"),
-                            jobs_done=hb.get("jobs_done", 0), jobs_failed=hb.get("jobs_failed", 0),
-                            last_job_at=hb.get("last_job_at"),
-                            last_beat_age_s=_beat_age(hb.get("ts", ""), now))
-                if w["kind"] == "watcher" and hb.get("mode"):
-                    out["paused_reason"] = hb["mode"]
-            except json.JSONDecodeError:
-                logger.warning("heartbeat JSON 파싱 실패 name=%s", w["name"])
-        if w["queue"]:
-            info["queue_depth"] = await r.llen(w["queue"])
-            info["dead_letter"] = await r.llen(f"dead_letter:{w['queue']}")
-            proc = 0
-            async for key in r.scan_iter(match=f"processing:{w['queue']}:*"):
-                proc += await r.llen(key)
-            info["processing"] = proc
-        out["workers"].append(info)
+        try:
+            info = {"name": w["name"], "kind": w["kind"], "alive": False, "state": None,
+                    "last_beat_age_s": None, "queue_depth": 0, "dead_letter": 0,
+                    "processing": 0, "jobs_done": 0, "jobs_failed": 0, "last_job_at": None}
+            raw = await r.get(f"worker:{w['name']}:heartbeat")
+            if raw:
+                try:
+                    hb = json.loads(raw)
+                    info.update(alive=True, state=hb.get("state"),
+                                jobs_done=hb.get("jobs_done", 0), jobs_failed=hb.get("jobs_failed", 0),
+                                last_job_at=hb.get("last_job_at"),
+                                last_beat_age_s=_beat_age(hb.get("ts") or "", now))
+                    if w["kind"] == "watcher" and hb.get("mode"):
+                        out["paused_reason"] = hb["mode"]
+                except (json.JSONDecodeError, UnicodeDecodeError):
+                    logger.warning("heartbeat JSON 파싱 실패 name=%s", w["name"])
+            if w["queue"]:
+                info["queue_depth"] = await r.llen(w["queue"])
+                info["dead_letter"] = await r.llen(f"dead_letter:{w['queue']}")
+                proc = 0
+                async for key in r.scan_iter(match=f"processing:{w['queue']}:*"):
+                    proc += await r.llen(key)
+                info["processing"] = proc
+            out["workers"].append(info)
+        except Exception:
+            logger.exception("워커 상태 수집 실패 name=%s", w["name"])
+            out["redis_ok"] = False
+            break
 
     for w in out["workers"]:
         if w["kind"] == "trader":