Checks

• I have updated to the lastest minor and patch version of Strands
• I have checked the documentation and this is not expected behavior
• I have searched ./issues and there are no duplicates of my issue

Strands Version

0.1.4

Python Version

3.13

Operating System

Windows and macOs

Installation Method

pip

Steps to Reproduce

1. Initiate any stdio_mcp_client with npx.

For example, use the npx example server for graph memory (anthropic)

`
from strands import Agent
from strands_tools import http_request
from strands.models import BedrockModel
from mcp import stdio_client, StdioServerParameters
from strands import Agent
from strands.tools.mcp import MCPClient
import logging

SYSTEM_PROMPT = """
You're great at remembering stuff from users
"""

stdio_mcp_client = MCPClient(lambda: stdio_client(
StdioServerParameters(command="npx", args=["-y", "@modelcontextprotocol/server-memory"])
))

with stdio_mcp_client:
# Get the tools from the MCP server
tools = stdio_mcp_client.list_tools_sync()

# Create an agent with these tools
agent = Agent(model=bedrock_model,tools=tools,system_prompt=SYSTEM_PROMPT)

Example usage

if name == "main":
print("\n📁 Memory Master Assistant Agent 📁\n")
print("How can I help you?")
print("Type 'exit' to quit.")

# Interactive loop
while True:
    try:
        user_input = input("\n> ")
        if user_input.lower() == "exit":
            print("\nGoodbye! 👋")
            break

        response = agent(
            user_input, 
        )
        
        # Extract and print only the relevant content from the specialized agent's response
        content = str(response)
        print(content)
        
    except KeyboardInterrupt:
        print("\n\nExecution interrupted. Exiting...")
        break
    except Exception as e:
        print(f"\nAn error occurred: {str(e)}")
        print("Please try with a different question.")`

2. Trigger a prompt to let the agent invoke the tool, for example:

I'm Ricardo, remember this

Expected Behavior

Invoke the tool without issues.

Actual Behavior

An exception is raised

File "/home/xxxx/desarrollo/strands2/.venv/lib/python3.13/site-packages/strands/tools/mcp/mcp_agent_tool.py", line 83, in invoke
return self.mcp_client.call_tool_sync(
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
tool_use_id=tool["toolUseId"], name=self.tool_name, arguments=tool["input"]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
)
^
File "/home/xxxx/desarrollo/strands2/.venv/lib/python3.13/site-packages/strands/tools/mcp/mcp_client.py", line 183, in call_tool_sync
raise MCPClientInitializationError("the client session is not running")
strands.types.exceptions.MCPClientInitializationError: the client session is not running

This happens with any MCP Server that is ran via npx.

Additional Context

No response

Possible Solution

No response

Related Issues

No response