Yeah, this is something we tried!

And yea, from an IDE perspective, it seems like maybe a sensible default would be to run `mypy ${CURRENT_FILE}` on save or something -- I've tried this manually myself, and it's decent, but it's not good enough to use constantly. I don't remember specific issues since I haven't done this in a long time.

Pre-commits are painful (on purpose!), but preventing people from shipping seemed like the wrong call. So we ended up dropping them.