DL-474

An agent’s topic mark moves only on observations contiguous from its view (a head page that reaches the mark, or with no mark holds every seen id); steers (on ASIDE_MESSAGE_COMMIT) and delivers (on the turn-start ack) join a per-topic seen set that never drops a markless topic’s first-seen id; tool-result observations apply at the next turn_start or agent_end; the view persists as a compass_topic_seen session entry and resets when the session id changes

Status: Active (proposed, pending Matt, 2026-10-11)

Record: ../../agent/compass-topic-write-locks/design.md#q3-what-counts-as-seen