I've noticed the cleaner the codebase, the better AI agents perform on it. They pick up on existing patterns and follow them. Throw them at a messy repo and they'll invent a new pattern every time.

It's basically like hiring a new developer for one task and letting them go right after. They don't know your conventions, your history, or why things are the way they are. The only thing they have is what they can see in the code. Your code quality is basically the prompt now.