Every source, and what rests on it
Every citation on both paths, gathered and de-duplicated. A source cited by nine entries appears once, with the nine underneath it — so a reader can go the other way round for once, starting from a document and finding everything in the record that stands on it.
This map isn't finished.
You are still holding the pen.
One day someone will ask what we did. Let this be part of the answer: we told the truth, and we kept a record of both halves of it.