I think it is the same with cleaning up a code base for human programmers.

For instance I picked up a typescript code base that was a real mess and if I tired to change anything I would get all these crazy error messages that made no sense to either me or the AI.

It took about two days going back and forth with the AI for me to understand that was going wrong and put the typescript into a good condition where, when it type checked, it typed check for the right reasons. As the code got better I was able to make changes easily and so was the agent. I haven't put a lot of effort into things like AGENTS.md files, I just write a lot of

  // documentation in comments