I love emacs. I used emacs for 20 years. But I haven't used it as much since moving to codex/claude. Even with vterm, can't really use TUIs that well inside IMO. Or at least, had way too many issues where emacs/vterm was the culprit
In emacs, everything is available, everything is a primitive function, everything can be inspected, the documentation (ie, contextual food for agents) is built-in, and emacs itself can be piloted entirely through function calls. This means that agents can fully control an emacs instance and run that closed loop (write, test, evaluate, repeat) with almost complete information - which makes the [given prompt] : [results conforming to spec] relationship much tighter than in most environments.