Something that contains Claude even more in this respect is if you explicitly gives it a directory that you tell it is entirely under its control, and tells it to write md files and other intermediate work products there (and this seems to work better than telling it where it isn't allowed to leave things).

That sounds like a good idea. When I have a one-off need for misc files I tell it to put them in the project’s ./tmp because that’s already in my global gitignore. That generally works, but I still run into surprise files it leaves in source dirs like a puppy leaves turds on a rug. I’ll try adding that to my instructions instead of doing it one-off.

I've often found that LLMs don't listen to "Don't do" commands with anywhere near the same gusto as "Do" commands.