Pagination Config is insufficient because there is no way to get a Topological Token at the Historical Start

[pik]

Currently the only way to get the first message sent in a room is to parse backwards from a topological token returned by get_room_events_max_id - there is no sufficient Pagination Config to obtain the first message if the topological token for the first message is not known (I guess handcrafting a from_token from a presumed topological_ordering=1 might work, but is also subject to break at any time, being solely an internal detail ? )

[richvdh]

turning this into a spec issue; https://github.com/matrix-org/matrix-doc/issues/2480