fix(chat_router): 修复流式消息处理中未正确累积内容的问题 Question: 上下文比较长时，回答速度很慢，CPU只吃了单核，一直占满资源

Fixes #410

确保在流式处理过程中正确累积消息内容，并在各种中断情况下（如敏感内容检测、错误处理等）保存已累积的内容。同时添加对用户会话的权限检查

server/routers/chat_router.py

@@ -5,7 +5,7 @@ import uuid
 
 from fastapi import APIRouter, Body, Depends, HTTPException, Query, UploadFile, File
 from fastapi.responses import StreamingResponse
-from langchain.messages import AIMessageChunk, HumanMessage
+from langchain.messages import AIMessageChunk, HumanMessage, AIMessage
 from langgraph.types import Command
 from pydantic import BaseModel
 from sqlalchemy.ext.asyncio import AsyncSession
@@ -577,13 +577,16 @@ async def chat_agent(
                     input_context["attachments"] = []
 
                 full_msg = None
+                accumulated_content = []
                 langgraph_config = {"configurable": input_context}
                 async for msg, metadata in agent.stream_messages(messages, input_context=input_context):
                     if isinstance(msg, AIMessageChunk):
-                        full_msg = msg if not full_msg else full_msg + msg
-                        content_for_check = full_msg.content[-20:]
+                        accumulated_content.append(msg.content)
+
+                        content_for_check = "".join(accumulated_content[-10:])
                         if conf.enable_content_guard and await content_guard.check_with_keywords(content_for_check):
                             logger.warning("Sensitive content detected in stream")
+                            full_msg = AIMessage(content="".join(accumulated_content))
                             await save_partial_message(conv_manager, thread_id, full_msg, "content_guard_blocked")
                             meta["time_cost"] = asyncio.get_event_loop().time() - start_time
                             yield make_chunk(status="interrupted", message="检测到敏感内容，已中断输出", meta=meta)
@@ -606,6 +609,9 @@ async def chat_agent(
                             logger.error(f"Error processing tool message: {e}")
                             pass
 
+                if not full_msg and accumulated_content:
+                    full_msg = AIMessage(content="".join(accumulated_content))
+
                 if (
                     conf.enable_content_guard
                     and hasattr(full_msg, "content")
@@ -650,6 +656,10 @@ async def chat_agent(
 
             # Run save in a separate task to avoid cancellation
             async def save_cleanup():
+                nonlocal full_msg
+                if not full_msg and accumulated_content:
+                    full_msg = AIMessage(content="".join(accumulated_content))
+
                 async with db_manager.get_async_session_context() as new_db:
                     new_conv_manager = ConversationManager(new_db)
                     await save_partial_message(
@@ -679,6 +689,9 @@ async def chat_agent(
             error_msg = f"Error streaming messages: {e}"
             error_type = "unexpected_error"
 
+            if not full_msg and accumulated_content:
+                full_msg = AIMessage(content="".join(accumulated_content))
+
             # 保存错误消息到数据库
             async with db_manager.get_async_session_context() as new_db:
                 new_conv_manager = ConversationManager(new_db)
@@ -888,6 +901,7 @@ async def get_agent_history(
 
         # Use new storage system ONLY
         conv_manager = ConversationManager(db)
+        await _require_user_conversation(conv_manager, thread_id, str(current_user.id))
         messages = await conv_manager.get_messages_by_thread_id(thread_id)
 
         # 当前用户ID - 用于过滤反馈