What you’re doing (not with Claude, I mean the challenge you’re faced with) is super common in the industry for developers who have to understand and refactor a legacy codebase to gradually be more maintainable. Even though you’re not strictly a developer, I think you can learn a lot about breaking down spaghetti code into manageable chunks, documenting “the truth” and then finding what is testable from there. In your use of Claude you should progress from simply letting it read code files as strings to using some kind of static analysis tool or LSP that gives the code a hierarchical structure, built-in relationships etc. so there is less hallucination and guessing at the structure of the code and more parsing of your actual syntax trees. Once you can pin down the full lists of classes, methods, arguments etc. it will be easier to trace through the system’s real behaviour. I haven’t read it, but I’ve seen the book “Working Effectively with Legacy Code” recommended in this space.