> one that an unsupervised LLM rewrite is probably not even going to attempt.

Why not? A complete test suite exists, so it just boils down to "reimplement this code to reduce the number of 'unsafe' references, while keeping the tests passing" (the last part isn't even needed since Claude loves to run tests and linters anyway).

An LLM definitely can do that work, but LLMs have a tendency to follow the path of least resistance unless you force them to do things properly and carefully supervise them.