I'm dealing with a situation right now where a critical mass of "messy" code means that nobody, human or LLM, can understand what it is trying to do or how a straightforward user-specified update should be applied to the underlying domain objects. Multiple proposed semantics have failed so far.

On the plus side.. AI is pretty good at creating (often excessive) tests around a given codebase in order to (re)implement the utility using different backends or structures. The one thing to look out for is that the agent does NOT try to change a failing test, where the test is valid, but the code isn't.