fix(music-render): F6 ReliableQueue 적용 (F6 part 3)

- worker.py: poll_once 신설, BLPOP → ReliableQueue.dequeue/ack/fail + startup recovery
- 12 job_type dispatch table 보존 (기존 13 tests 그대로 PASS)
- Dockerfile: build context=services/, _shared 포함, PYTHONPATH=/app
- docker-compose.yml: music-render build context 갱신

dispatch 자체 unhandled exception 발생 시 fail(raw, payload)로 retry/dead-letter.
provider 함수가 webhook("failed")를 잡고 있는 정상 케이스는 ack (멱등 webhook).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

services/music-render/worker.py

@@ -1,4 +1,4 @@
-"""Redis BLPOP worker — queue:music-render → job_type 디스패치 → NAS webhook.
+"""Redis ReliableQueue worker — F6 신뢰성 패턴 (BLMOVE + ack/fail + recovery).
 
 queue:paused 가 set이면 대기 (task-watcher가 박재오 활동 감지 시 set).
 """
@@ -20,6 +20,7 @@ from providers.suno import (
     run_add_instrumental, run_video_generate,
 )
 from providers.local import run_local_generation
+from _shared.reliable_queue import ReliableQueue
 
 logger = logging.getLogger(__name__)
 
@@ -67,26 +68,44 @@ def _dispatch(payload: dict) -> None:
     fn(task_id, params)
 
 
+async def poll_once(queue: ReliableQueue) -> bool:
+    """F6 — 1 cycle: dequeue → _dispatch → ack/fail. Returns True if a job handled."""
+    result = await queue.dequeue(timeout=5)
+    if result is None:
+        return False
+    payload, raw = result
+    try:
+        # sync provider 함수 — thread로 실행해서 이벤트 루프 블로킹 방지
+        await asyncio.to_thread(_dispatch, payload)
+    except Exception:
+        logger.exception("dispatch unhandled exception task_id=%s",
+                         payload.get("task_id"))
+        await queue.fail(raw, payload)
+        return True
+    await queue.ack(raw)
+    return True
+
+
 async def worker_loop():
     redis = aioredis.from_url(REDIS_URL, decode_responses=False)
-    logger.info("music-render worker started (queue=%s)", QUEUE_KEY)
+    queue = ReliableQueue(redis, queue_key=QUEUE_KEY)
+    logger.info("music-render worker started worker_id=%s queue=%s",
+                queue.worker_id, QUEUE_KEY)
+    # F6: startup recovery
+    try:
+        recovered = await queue.recover()
+        if recovered:
+            logger.info("recovered %d orphaned items at startup", recovered)
+    except Exception:
+        logger.exception("startup recover failed")
+
     while True:
         try:
             paused = await redis.get(PAUSED_KEY)
             if paused == b"1":
                 await asyncio.sleep(10)
                 continue
-            item = await redis.blpop(QUEUE_KEY, timeout=1)
-            if item is None:
-                continue
-            _, raw = item
-            try:
-                payload = json.loads(raw)
-            except json.JSONDecodeError:
-                logger.error("invalid queue payload: %r", raw[:200])
-                continue
-            # sync provider 함수 — thread로 실행해서 이벤트 루프 블로킹 방지
-            await asyncio.to_thread(_dispatch, payload)
+            await poll_once(queue)
         except asyncio.CancelledError:
             logger.info("worker_loop cancelled")
             raise