Comment by setr

If you’ve massaged and normalized the data at entry, then the assumptions at core logic should be well defined — it’s whatever the rules of the normalized output are.

You don’t need to know all of the call chains because you’ve established a “narrow waist” where ideally all things have been made clear, and errors have been handled or scoped. So you only need to know the call chain from entry point to narrow waist, and separately narrow waist till end.