> but the AI doesn't need this

That's not true. The LLM performance will degrade as the codebase gets messier as well. You get to a point where every fix breaks something else and you can't really make forward progress.

Yes, you might be able to get a bit further with a messy codebase just because the LLM won't complain and will just grind through fixing things, but eventually it will just start disabling failing tests instead of actually fixing things.

The token cost to fix might surpass what a human would cost to just do it.