I'm testing it and seems to be very broken, typing things around and things jumps everywhere.

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.

Nice work! It seems like selection highlighting(?) doesn't work but the interaction feels good otherwise.

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

That looks pretty good, but it isn't quite there yet, for me. If you try to delete the opening fence, the closing fence turns into a closing fence, and the abstraction leaks in tables.