A local MCP server driving AutoCAD over COM, tried on a real 42-sheet drawing set. Write tools require an expected_document and return DOCUMENT_CHANGED without writing if the user switched tabs. Writes run once, never retried, and a timeout mid-call returns UNKNOWN_COMMIT. The author says they studied three community AutoCAD MCP servers for the design. People are now building the "did that write land, and where" guard by hand.