> taking an old and badly-documented codebase and answering questions like "where does this variable come from, and what are its ultimate consumers?"

Why do you even need an LLM for this? Code is formal notation, it’s not magic. Unless the code is obfuscated, even bad code is pretty clean on what they’re doing and how various symbols are created and used. What is not clear is “why” and the answer is often a business or a technical decision.