federation.sx: a peer publishes a schedule; ev/federated-agenda merges local
(origin :local) with trusted peers' agendas, sorted by start, tagged with
:origin provenance. Trust is a peer-id set re-checked per merge; untrusted
peers contribute nothing. Real transport slots behind ev/peer-agenda.
209/209 green — all four plan phases implemented.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>