Aggregates per agent and per revision (annex 16 §3.6).
Offset-paged rather than keyset: the rows are groups, not table rows, so there is no
(created_at, id) to build a cursor from. page.cursor is therefore not accepted
here — a cursor this endpoint cannot honour would be silently ignored, which is the class
of bug annex 05 §1.3’s “an unknown filter is a 422” rule exists to stop.