Codex's re-review of c50788c found four gaps; a fifth turned up while
testing the teammate scenario.

- Landing identity (P1). A fresh landing got its own uuid, but the cloud
  projection keys each item by its link id and hydration makes that the
  landing id, so every landing id changed on the first rehydrate. Retained
  actions then pointed at a missing landing: undoing a link edit could
  leave a link whose landing projection dropped (an empty-items group the
  server stores), undoing a fresh lineup orphaned a landing, and reconcile
  discarded landing edits. A landing made for a link now takes the link's
  id, so projection and hydration agree. Nodes also exist only while a
  link uses them, so no undo can leave an orphan.
- Field-specific edits (P2). A LineUpEditAction records the target and
  only the field it changed (origin position, landing position, landing
  visibility, link details) and writes just that field onto the entry as
  it is now, so a teammate's weapon or anything else changed since is
  kept. Link edits never touch which origin and landing a link joins.
- Overlapping side toggles (P2). The op queue publishes an op only after
  its durable write, so a second all-pages toggle starting before the
  first finished read the older side. The requested side is recorded per
  page synchronously and cleared by the call that set it, unless a later
  call replaced it.
- Reconcile (P2). A lineup edit is kept while its target exists or any
  retained lineup addition or deletion, on either stack, can bring it
  back, so an edit made before a deletion stays undoable after the
  deletion lands.
- Stale overlays after rehydration. When acks arrive, _reconcileAcks
  refreshes; the refreshed snapshot starts a rehydrate, which marks the
  page unhydrated, so the syncLocalPage that clears satisfied overlays
  skipped the page. The leftover overlay kept painting the local version
  over later remote changes to that entity and would eventually write it
  back over a teammate's edit. markPageHydrated now drops a page's
  overlays that no queued, in-flight, successor, paused or attention op
  still carries.

Tests go through the real path: the editor places a lineup, live sync
authors ops from the projection, the fake queue drains them in one update
that publishes their acks, and the session reconciles and rehydrates from
what the server stored; page settings mark which revision is on screen.

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