MCP's Python SDK wires BlockBuster into its test suite to catch event-loop blocking in the SDK itself
GitHub·medium signal
PR #3510, merged 2026-09-16, adds BlockBuster to detect blocking calls originating from the mcp and mcp_types packages during tests, exempting coverage internals, jsonschema lazy imports and synchronous media conversion. It also moves Windows executable resolution off the event loop. This is a structural guard rather than a single fix: async MCP servers built on the Python SDK now get a test-time tripwire for the class of stall that only shows up under concurrent tool calls.