fix: MCP node execution failed

Author: shaohuzhang1

apps/application/flow/step_node/mcp_node/impl/base_mcp_node.py

@@ -4,6 +4,7 @@
 from typing import List
 
 from langchain_mcp_adapters.client import MultiServerMCPClient
+from langchain_mcp_adapters.sessions import create_session
 
 from application.flow.i_step_node import NodeResult
 from application.flow.step_node.mcp_node.i_mcp_node import IMcpNode
@@ -22,12 +23,12 @@ def execute(self, mcp_servers, mcp_server, mcp_tool, tool_params, **kwargs) -> N
         params = json.loads(json.dumps(tool_params))
         params = self.handle_variables(params)
 
-        async def call_tool(s, session, t, a):
-            async with MultiServerMCPClient(s) as client:
-                s = await client.sessions[session].call_tool(t, a)
-                return s
+        async def call_tool(t, a):
+            client = MultiServerMCPClient(servers)
+            async with create_session(client.connections[mcp_server]) as s:
+                return await s.call_tool(t, a)
 
-        res = asyncio.run(call_tool(servers, mcp_server, mcp_tool, params))
+        res = asyncio.run(call_tool(mcp_tool, params))
         return NodeResult(
             {'result': [content.text for content in res.content], 'tool_params': params, 'mcp_tool': mcp_tool}, {})