crates/mcp (L5, engine only): JSON-RPC 2.0 over stdio with protocol version negotiation, a headless Session backend and a bridge to the app's control port, 14 tools (list_commands, execute, batch with rollback, inspect_design, measure, body_topology, set_parameter, screenshot as an image block, export, undo/redo, new_design/open/save) and tests. Co-Authored-By: Claude Opus 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL