I was trying to create something like this too, because I need something that also work for mathematical writing. Let me push a version on github and update, it fixes a lot of issues.

Unfortunately it works on my own version of markdown, which is a subset of pandoc markdown, but I think one can get claude to update the parser to work for other things.

I'm curious when I see things more geared toward prose using CodeMirror instead of ProseMirror. Any comment on that decision?