feat：新增对话历史列表

app/services/conversation_mongo.py

@@ -8,7 +8,8 @@ from pymongo import ASCENDING, DESCENDING
 from pymongo.asynchronous.database import AsyncDatabase
 
 from app.config import settings
-from app.schemas.conversation import Turn
+from app.schemas.conversation import ConversationSummary, Turn
+from app.services.conversation import make_title
 
 # 单次清理的空会话上限，避免积压时一次请求扫描过多
 PURGE_BATCH = 200
@@ -119,3 +120,42 @@ class MongoConversationStore:
             {"$set": data, "$setOnInsert": {"created_at": created_at}},
             upsert=True,
         )
+
+    async def list_by_user(
+        self, user_id: int, limit: int, offset: int
+    ) -> list[ConversationSummary]:
+        # $unwind 会丢弃没有任何轮次的空会话
+        pipeline = [
+            {"$match": {"user_id": user_id}},
+            {
+                "$lookup": {
+                    "from": self._turns.name,
+                    "localField": "_id",
+                    "foreignField": "conversation_id",
+                    "pipeline": [
+                        {"$sort": {"created_at": 1, "_id": 1}},
+                        {
+                            "$group": {
+                                "_id": None,
+                                "first_prompt": {"$first": "$prompt"},
+                                "updated_at": {"$last": "$created_at"},
+                            }
+                        },
+                    ],
+                    "as": "stats",
+                }
+            },
+            {"$unwind": "$stats"},
+            {"$sort": {"stats.updated_at": -1, "_id": -1}},
+            {"$skip": offset},
+            {"$limit": limit},
+        ]
+        cursor = await self._conversations.aggregate(pipeline)
+        return [
+            ConversationSummary(
+                conversation_id=item["_id"],
+                title=make_title(item["stats"]["first_prompt"]),
+                updated_at=item["stats"]["updated_at"],
+            )
+            for item in await cursor.to_list()
+        ]