Follow-ups on top of the salvaged #97712 foundation:
- read_events() pages now include the room's authority stamp
(authority.gateway_id + authority.epoch), so a replicating participant
can persist lineage with every page and a future takeover layer can
fence stale authorities from replayed state alone.
- New regression test proves the replay page bound counts UTF-8 BYTES,
not characters: sabotaging LENGTH(CAST(.. AS BLOB)) back to
LENGTH(TEXT) and dropping the .encode('utf-8') guard fails the test;
the pre-existing multibyte test passed under that sabotage.
- _raise_room_not_found typed NoReturn so narrowing survives closures.
David Dudok de Wit