feat(api): Memory compaction 管线与调度修复，同步环境变量示例

Memory compaction（近重复 chunk 软排除）
- 新增 compaction 调度：Redis debounce、scheduler gate、增量游标；任务结束时 finalize，避免 gate 长期占用并处理运行期新 trigger。
- Celery memory_compaction_run：debounce 未到点则 retry；用户级 Redis 锁；成功路径更新游标并 finalize；异常时释放 scheduler gate 并 self.retry，避免静默卡死调度与瞬时失败不重试。
- compaction_service：多层判定 + canonical 打分；无 embedding 时停止前移游标（awaiting_embeddings）；curation details 补全 trigger 等上下文。
- ingest_transcript_sync：同步路径尽力写入 embedding，与异步 ingest 行为对齐，避免 compaction 永远扫不到无向量 chunk。
- repo：新增 update_chunk_embedding_sync。
测试
- 扩展 test_memory_compaction：调度合并、finalize、ingest embedding、无向量游标、异常路径 gate+retry 等回归用

api/app/core/redis_lock.py

@@ -1,34 +1,49 @@
 """Small Redis lock helpers for background tasks."""
 
-from dataclasses import dataclass
+import threading
 import uuid
+from dataclasses import dataclass
 
 import redis
 
 from app.core.config import settings
 
+_redis_lock_client: redis.Redis | None = None
+_redis_lock_init_lock = threading.Lock()
+
+
+def _get_redis_lock_client() -> redis.Redis:
+    """进程内复用单个 Redis 客户端（decode_responses=False，与锁 token 字节一致）。"""
+    global _redis_lock_client
+    if _redis_lock_client is None:
+        with _redis_lock_init_lock:
+            if _redis_lock_client is None:
+                _redis_lock_client = redis.from_url(
+                    settings.redis_url, decode_responses=False
+                )
+    return _redis_lock_client
+
 
 @dataclass(frozen=True)
 class RedisLockHandle:
-    client: redis.Redis
     key: str
     token: bytes
 
 
 def acquire_redis_lock(key: str, *, ttl_seconds: int) -> RedisLockHandle | None:
     """Acquire a single-owner Redis lock or return None when unavailable."""
-    client = redis.from_url(settings.redis_url, decode_responses=False)
+    client = _get_redis_lock_client()
     token = uuid.uuid4().hex.encode("utf-8")
     if not client.set(key, token, nx=True, ex=ttl_seconds):
         return None
-    return RedisLockHandle(client=client, key=key, token=token)
+    return RedisLockHandle(key=key, token=token)
 
 
 def release_redis_lock(handle: RedisLockHandle | None) -> None:
     """Release the lock only if we still own it."""
     if handle is None:
         return
-    handle.client.eval(
+    _get_redis_lock_client().eval(
         """
         if redis.call("GET", KEYS[1]) == ARGV[1] then
             return redis.call("DEL", KEYS[1])