Pagination Contract Audit

Audit a pagination contract for the ways it loses or repeats rows. The central finding is the one almost every paginated API has at first: a sort on a non-unique field with no unique tiebreaker, so rows that compare equal have no defined order and a caller walking the pages can get one row twice and never get its neighbour, with nothing failing. Also reports offset pagination over a mutable sort, an unbounded page size, contradictory bounds, and a cursor contract that also takes an offset.