[BUG] MCP Instrumentation Wrapper Not Idempotent - Hits Python Recursion Limit

[mbutler-aws]

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

1.8.0

Python Version

3.11

Operating System

Windows (development), Linux (deployed)

Installation Method

pip

Steps to Reproduce

The mcp_instrumentation() function in strands/tools/mcp/mcp_instrumentation.py is non-idempotent, causing wrapper accumulation on BaseSession.send_request that eventually leads to RecursionError in production environments.

Environment

• Strands version: 1.8.0
• Python version: 3.11
• Use case: WebSocket server creating MCPClient per connection

Steps to Reproduce

from strands.tools.mcp import MCPClient
from mcp.client.streamable_http import streamablehttp_client

# Create ~1000 MCPClient instances
for i in range(1000):
    client = MCPClient(lambda: streamablehttp_client("http://localhost:8080/mcp"))
    client.start()
    # Each instantiation adds another wrapper layer

Expected Behavior

Telemetry instrumentation should be applied once per process, not per client instance.

Actual Behavior

mcp_instrumentation() unconditionally wraps BaseSession.send_request without checking if already wrapped, causing wrapper accumulation.

Observed Behavior

• Each MCPClient instantiation calls mcp_instrumentation() in __init__
• Each call adds a new wrap_function_wrapper() layer to BaseSession.send_request
• After a certain number of client creations, Python hits recursion limit
• Results in RecursionError and "client session is not running" errors

Additional Context

No response

Possible Solution

Make mcp_instrumentation() idempotent by:

1. Tracking if patches have been applied via module-level flag
2. Only applying instrumentation on first call
3. Skipping subsequent calls

Related Issues

No response

[Unshure]

Just merged the fix for this, will include on the next strands release.