fix: address the release-prep review of #690

cleanup-state keeps the agent inbox of a removed record whose tmux session the multiplexer still lists (a detached pane the next boot re-adopts under the same id); test and architecture-invariants note added.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/architecture-invariants.md

@@ -700,7 +700,7 @@ Frontend `readmymind-ui.js`: header 🧠 marker-hidden (`btn-readmymind--hidden`
 
 ⚠️ **Caps refuse, they never drop.** 16 KiB per message (UTF-8 bytes), 512 KiB and 200 messages per inbox; a full inbox is 409 CONFLICT and nothing is stored. Dropping the oldest would lose exactly the message a slow receiver has not handled yet. TTL is 12 h from each message's own `createdAt`, swept lazily, and a restore keeps `createdAt`, so a restart does not restart the clock.
 
-⚠️ **Lifetime follows the session, not the pane.** `_doCleanupSession` drops the inbox only when `killMux` is set (a real delete); a detach or server shutdown keeps it, and `DELETE /api/sessions/:id` on a row that is no longer live (the persisted-only branch in `session-routes.ts`) drops what the detach kept. A detach also ends a parked read with `ended: true`, which is why `codeman agent inbox --wait` asks the session list before it exits 3. Persistence (`agentInboxPersistEnabled`, SYNCED, default OFF) writes `agent-inbox.json` via `dataPath()`, 0600 through tmp+rename, debounced and flushed on stop; off means no file, and switching it off deletes the snapshot while memory stays. It is never fed to `/api/search`, and `sensitive-path.ts` keeps the file viewer off it. Boot loads the snapshot before `restoreMuxSessions`, but prunes inboxes of sessions that no longer exist only in `finalizeRestoredState`'s SUCCESS path: a failed restore must not delete mail for sessions that are about to come back. The keep set is the live sessions, the records `state.json` still holds AND the sessions on the reboot-restore offer (`rebootRestoreRegistry`): `cleanupStaleSessions()` has already pruned an offered session's record by then, and a rebuild reuses its id, so leaving the offer out returned every rebuilt session with an empty inbox (the 12 h TTL bounds what is never rebuilt). `POST /api/cleanup-state` drops the inboxes of the records it removes, since it is a delete for a detached row. Tests: `test/agent-inbox.test.ts`, `test/agent-inbox-persistence.test.ts`, `test/routes/inbox-routes.test.ts`, `test/agent-inbox-server-wiring.test.ts`, the inbox block in `test/session-wait-registry.test.ts`.
+⚠️ **Lifetime follows the session, not the pane.** `_doCleanupSession` drops the inbox only when `killMux` is set (a real delete); a detach or server shutdown keeps it, and `DELETE /api/sessions/:id` on a row that is no longer live (the persisted-only branch in `session-routes.ts`) drops what the detach kept. A detach also ends a parked read with `ended: true`, which is why `codeman agent inbox --wait` asks the session list before it exits 3. Persistence (`agentInboxPersistEnabled`, SYNCED, default OFF) writes `agent-inbox.json` via `dataPath()`, 0600 through tmp+rename, debounced and flushed on stop; off means no file, and switching it off deletes the snapshot while memory stays. It is never fed to `/api/search`, and `sensitive-path.ts` keeps the file viewer off it. Boot loads the snapshot before `restoreMuxSessions`, but prunes inboxes of sessions that no longer exist only in `finalizeRestoredState`'s SUCCESS path: a failed restore must not delete mail for sessions that are about to come back. The keep set is the live sessions, the records `state.json` still holds AND the sessions on the reboot-restore offer (`rebootRestoreRegistry`): `cleanupStaleSessions()` has already pruned an offered session's record by then, and a rebuild reuses its id, so leaving the offer out returned every rebuilt session with an empty inbox (the 12 h TTL bounds what is never rebuilt). `POST /api/cleanup-state` drops the inboxes of the records it removes, since it is a delete for a detached row, except a record whose tmux session the multiplexer still lists (`mux.getSession`): a detach keeps that pane, and the next boot re-adopts it under the same id even without a `state.json` record. Tests: `test/agent-inbox.test.ts`, `test/agent-inbox-persistence.test.ts`, `test/routes/inbox-routes.test.ts`, `test/agent-inbox-server-wiring.test.ts`, the inbox block in `test/session-wait-registry.test.ts`.
 
 ### Voice dictation via Claude