refactor(mcp): 移除全局MCP客户端缓存并优化工具加载逻辑

移除全局MCP客户端缓存，改为每次调用时创建新客户端实例
优化工具加载逻辑，添加服务器名称校验并改进错误处理
清理未使用的导入和冗余代码

src/agents/chatbot/graph.py

@@ -1,10 +1,8 @@
 import os
 import uuid
-from typing import Any, cast, Annotated
+from typing import Any, cast
 from pathlib import Path
-from datetime import datetime, timezone
 
-from dataclasses import dataclass, field, fields
 from langchain_core.messages import AIMessage, ToolMessage
 from langgraph.graph import StateGraph, START, END
 from langgraph.runtime import Runtime
@@ -14,7 +12,6 @@ from langgraph.checkpoint.memory import InMemorySaver
 
 from src import config as sys_config
 from src.utils import logger
-from src.agents.common.utils import get_cur_time_with_utc
 from src.agents.common.base import BaseAgent
 from src.agents.common.models import load_chat_model
 from src.agents.common.mcp import get_mcp_tools

src/agents/common/mcp.py

@@ -11,8 +11,7 @@ from langchain_mcp_adapters.client import (  # type: ignore[import-untyped]
 
 from src.utils import logger
 
-# Global MCP client and tools cache
-_mcp_client: MultiServerMCPClient | None = None
+# Global MCP tools cache
 _mcp_tools_cache: dict[str, list[Callable[..., Any]]] = {}
 
 # MCP Server configurations
@@ -30,25 +29,22 @@ MCP_SERVERS = {
         "command": "uvx",
         "args": ["mcp-server-time"],
         "transport": "stdio",
-    }
+    },
 }
 
 
 async def get_mcp_client(
     server_configs: dict[str, Any] | None = None,
 ) -> MultiServerMCPClient | None:
-    """Get or initialize the global MCP client with given server configurations."""
-    global _mcp_client
-
-    if _mcp_client is None:
-        configs = server_configs or MCP_SERVERS
-        try:
-            _mcp_client = MultiServerMCPClient(configs)  # pyright: ignore[reportArgumentType]
-            logger.info(f"Initialized MCP client with servers: {list(configs.keys())}")
-        except Exception as e:
-            logger.error("Failed to initialize MCP client: %s", e)
-            return None
-    return _mcp_client
+    """Initializes an MCP client with the given server configurations."""
+    configs = server_configs or MCP_SERVERS
+    try:
+        client = MultiServerMCPClient(configs)  # pyright: ignore[reportArgumentType]
+        logger.info(f"Initialized MCP client with servers: {list(configs.keys())}")
+        return client
+    except Exception as e:
+        logger.error("Failed to initialize MCP client: %s", e)
+        return None
 
 
 async def get_mcp_tools(server_name: str) -> list[Callable[..., Any]]:
@@ -60,9 +56,9 @@ async def get_mcp_tools(server_name: str) -> list[Callable[..., Any]]:
         return _mcp_tools_cache[server_name]
 
     try:
+        assert server_name in MCP_SERVERS, f"Server {server_name} not found in MCP_SERVERS"
         client = await get_mcp_client({server_name: MCP_SERVERS[server_name]})
         if client is None:
-            _mcp_tools_cache[server_name] = []
             return []
 
         # Get all tools and filter by server (if tools have server metadata)
@@ -72,9 +68,11 @@ async def get_mcp_tools(server_name: str) -> list[Callable[..., Any]]:
         _mcp_tools_cache[server_name] = tools
         logger.info(f"Loaded {len(tools)} tools from MCP server '{server_name}'")
         return tools
-    except Exception as e:
-        logger.warning(f"Failed to load tools from MCP server '{server_name}': %s\n{traceback.format_exc()}", e)
-        _mcp_tools_cache[server_name] = []
+    except AssertionError as e:
+        logger.warning(f"Failed to load tools from MCP server '{server_name}': {e}")
+        return []
+    except Exception:
+        logger.opt(exception=True).warning(f"Failed to load tools from MCP server '{server_name}'")
         return []
 
 async def get_all_mcp_tools() -> list[Callable[..., Any]]:
@@ -94,7 +92,6 @@ def add_mcp_server(name: str, config: dict[str, Any]) -> None:
 
 
 def clear_mcp_cache() -> None:
-    """Clear the MCP client and tools cache (useful for testing)."""
-    global _mcp_client, _mcp_tools_cache
-    _mcp_client = None
+    """Clear the MCP tools cache (useful for testing)."""
+    global _mcp_tools_cache
     _mcp_tools_cache = {}