A device posts when its sources were watching, idempotent on the coverage id

Carries the device header (X-Six-Minute-Device) with a person's session, or the daemon's own device credential (a device route); the body's device_id must be that device, and a row's own device_id is that device or null. Each row is answered with one outcome: applied (written), unchanged (the row did not move, so a replay is not an error) or refused with a sentence saying what to fix. The write is monotone and the first value wins: to_at and settled_at are taken when the row has none yet and kept once stored, whatever a later body carries, and from_at, source and device_id never change after the first post. A row another member posted is refused and left untouched. The author is the caller, from the token; the body cannot name one.