feat(ai_trade): NAS Redis heartbeat (trader market_open/closed)

- ai_trade/heartbeat.py: build_trader_payload() + heartbeat_loop() 자체 미니 헬퍼
  (Windows 호스트 실행이라 _shared import 경로 달라 독립 구현, 계약은 동일)
- ai_trade/main.py: lifespan에 hb_task spawn + shutdown 시 cancel
  state_fn = scheduler._is_market_day & _is_polling_window(KST now) 조합
  signals = len(state.signals) 실시간 주입
- requirements.txt: redis>=5.0 추가
- ai_trade/tests/test_heartbeat.py: build_trader_payload 3케이스 TDD 검증

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

ai_trade/heartbeat.py

@@ -0,0 +1,57 @@
+"""ai_trade heartbeat — NAS Redis로 worker:ai_trade:heartbeat SET.
+
+Global Constraints 계약 1: kind=trader, state=market_open|market_closed.
+ai_trade는 Windows 호스트 실행이라 _shared import 경로가 달라 자체 미니 헬퍼로 둔다.
+"""
+from __future__ import annotations
+
+import asyncio
+import datetime as dt
+import json
+import logging
+import os
+
+import redis.asyncio as aioredis
+
+logger = logging.getLogger(__name__)
+
+REDIS_URL = os.getenv("REDIS_URL", "redis://192.168.45.54:6379")
+KEY = "worker:ai_trade:heartbeat"
+INTERVAL = int(os.getenv("HEARTBEAT_INTERVAL", "15"))
+TTL = int(os.getenv("HEARTBEAT_TTL", "45"))
+
+
+def build_trader_payload(state: str, signals: int = 0) -> str:
+    """JSON 문자열 반환. state: 'market_open' | 'market_closed'."""
+    return json.dumps({
+        "name": "ai_trade",
+        "kind": "trader",
+        "state": state,
+        "ts": dt.datetime.now(dt.timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ"),
+        "last_job_at": None,
+        "jobs_done": signals,
+        "jobs_failed": 0,
+    })
+
+
+async def heartbeat_loop(state_fn) -> None:
+    """Redis에 HEARTBEAT_INTERVAL마다 SET EX TTL.
+
+    Args:
+        state_fn: () -> (state: str, signals: int). 호출자가 폴링 윈도우 판정 주입.
+    """
+    redis = aioredis.from_url(REDIS_URL, decode_responses=False)
+    try:
+        while True:
+            try:
+                state, signals = state_fn()
+                payload = build_trader_payload(state, signals)
+                await redis.set(KEY, payload, ex=TTL)
+                logger.debug("ai_trade heartbeat sent: state=%s signals=%d", state, signals)
+            except asyncio.CancelledError:
+                raise
+            except Exception:
+                logger.exception("ai_trade heartbeat 실패 — 다음 주기에 재시도")
+            await asyncio.sleep(INTERVAL)
+    finally:
+        await redis.aclose()