I think you’re describing Aider.chat. There are 2 Emacs packages for it, one official and a very recent fork. Aider is a cli so it works great with vim as well.
In Emacs I’ve had good experience with gptel as well but I prefer aider for the coding workflow
Yep, I've particularly been enjoying the recent "watchfiles" feature where a comment can be added to the source file, and ending it with "ai?" or "ai!" triggers use of said comment as a prompt to ask about or change that section upon save.
In Emacs I’ve had good experience with gptel as well but I prefer aider for the coding workflow