AI hands it a string of Lisp, it runs inside live Emacs session, poking into it via emacsclient. Behaves like a REPL the LLM can drive - state persists between the calls.

Emacs is a Lisp machine. Buffers, files, network, subprocesses, games, major modes, the UI itself: every feature is already an elisp function. Hand an LLM a way to run arbitrary elisp and it inherits the entire Emacs API for free. No per-task glue code required.

The same MCP can drive Magit, Org, Eshell, Dired, eww, or anything else someone ever wrote in elisp. Tetris is just to make the point.