The explicit, ONE-WAY "Mark Complete" action, distinct from Save. Save persists an in-progress draft privately; Mark Complete releases the authored content so it becomes visible to participants, coaches, and peer leaders (AC5). Readiness is now manual — content that merely meets the agenda field rule is NOT visible until this action runs (AC1, AC5).

Precondition (AC3): the PERSISTED agenda must meet the required-fields rule — at least one section, every section with a non-blank name and a duration. When it doesn't, the request is rejected 422 with a message describing what is missing; nothing is released. (The editor also disables the action client-side, but this is the authoritative guard.)

One-way: there is no un-mark. After release the CM can keep editing and Save; content stays complete and edits go live (AC8). Re-calling this endpoint is idempotent and preserves the original completed_at. Only the session_number_config release flag is touched — agenda section rows and their ids are untouched, so coach/peer Leader Notes and participant reflection answers keyed off those ids survive.