docs(compass): design topic stale-post check for managers (RIG-1714)

docs/designs/compass/decisions/agent/DL-472.md

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+---
+id: DL-472
+decision: "Agent posts carry their view of the topic, a last-seen mark and a seen set of at most 50 ids, and the server refuses a post when another author has a message after the floor that is not in the seen set; the floor is the mark or, with no mark, the lowest seen message; no topic write lock, lock table, TTL or waiter queue"
+status: "Active (proposed, pending Matt, 2026-10-11)"
+record: ../../agent/compass-topic-write-locks/design.md#the-change
+---

docs/designs/compass/decisions/agent/DL-473.md

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+---
+id: DL-473
+decision: "The stale-post check is per topic: every insert takes the topic row lock `FOR NO KEY UPDATE` before it inserts under READ COMMITTED, view ids resolve only inside the target topic, and `AnswerAsk` locks topic before message and re-reads the ask's topic once after a merge"
+status: "Active (proposed, pending Matt, 2026-10-11)"
+record: ../../agent/compass-topic-write-locks/design.md#q1-granularity-is-the-topic
+---

docs/designs/compass/decisions/agent/DL-474.md

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+---
+id: DL-474
+decision: "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
+---

docs/designs/compass/decisions/agent/DL-475.md

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+---
+id: DL-475
+decision: "A stale post returns a `stale_post` arm on `PostMessageResponse` with the oldest 20 unseen messages; idempotent retries win first, a non-locking pre-check runs only where the cost gate would hold, a confirm re-sends the current view, the render is body-budgeted, refused ids are deduplicated against later delivery, and tools never auto-retry"
+status: "Active (proposed, pending Matt, 2026-10-11)"
+record: ../../agent/compass-topic-write-locks/design.md#q4-what-a-refused-post-returns
+---

docs/designs/compass/decisions/agent/DL-476.md

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+---
+id: DL-476
+decision: "Every agent's posts are checked, whatever its role; human clients never set the view fields, so humans are never checked or blocked, and the public `PostMessage` honors the fields on purpose"
+status: "Active (proposed, pending Matt, 2026-10-11)"
+record: ../../agent/compass-topic-write-locks/design.md#q5-who-is-checked
+---