feat：接入mongodb

app/services/persistence.py

@@ -0,0 +1,70 @@
+"""持久化装配：按配置选择 MongoDB 或进程内存，统一返回会话存储、检查点和关闭函数"""
+
+from collections.abc import Awaitable, Callable
+from dataclasses import dataclass
+
+from langgraph.checkpoint.base import BaseCheckpointSaver
+from loguru import logger
+
+from app.config import settings
+from app.services.conversation import ConversationStore, InMemoryConversationStore
+
+
+@dataclass
+class Persistence:
+    store: ConversationStore
+    # 为空时由图使用默认的内存检查点
+    checkpointer: BaseCheckpointSaver | None
+    close: Callable[[], Awaitable[None]]
+
+
+async def _close_nothing() -> None:
+    return None
+
+
+async def open_persistence() -> Persistence:
+    if not settings.mongodb_uri:
+        logger.warning(
+            "未配置 MONGODB_URI，会话记录和检查点仅保存在进程内存，重启后丢失"
+        )
+        return Persistence(InMemoryConversationStore(), None, _close_nothing)
+
+    # 依赖较重且只在启用 MongoDB 时使用，放到函数内导入
+    from langgraph.checkpoint.mongodb import MongoDBSaver
+    from pymongo import AsyncMongoClient, MongoClient
+
+    from app.processor.graph import build_checkpoint_serde
+    from app.services.conversation_mongo import MongoConversationStore
+
+    # 会话记录使用异步客户端；官方检查点基于同步客户端，异步方法由其放入线程池执行
+    async_client = AsyncMongoClient(settings.mongodb_uri, serverSelectionTimeoutMS=5000)
+    sync_client = MongoClient(settings.mongodb_uri, serverSelectionTimeoutMS=5000)
+
+    async def close() -> None:
+        try:
+            await async_client.close()
+        finally:
+            sync_client.close()
+
+    try:
+        # 启动时探测连接，配置错误尽早暴露；异常信息不包含连接串，避免泄露账号密码
+        try:
+            await async_client.admin.command("ping")
+        except Exception as exc:
+            raise RuntimeError(f"无法连接 MongoDB：{type(exc).__name__}") from None
+
+        store = MongoConversationStore(async_client[settings.mongodb_db])
+        await store.ensure_indexes()
+        # 与内存检查点共用同一份类型白名单，保证读回后仍是业务模型对象
+        checkpointer = MongoDBSaver(
+            sync_client,
+            settings.mongodb_db,
+            ttl=settings.mongodb_checkpoint_ttl or None,
+            serde=build_checkpoint_serde(),
+        )
+    except BaseException:
+        await close()
+        raise
+
+    logger.info("已启用 MongoDB 持久化，库名 {}", settings.mongodb_db)
+    return Persistence(store, checkpointer, close)