Review round 3:
- Leaving a page (a switch, or the replace a teammate's change waits on)
  checks for lost work itself, busy editor or not, and whatever the save
  flags say; only the automatic notice waits for a gesture to end.
- The user's own delete of the page, still on its way, is not a
  teammate's deletion and says nothing.
- A new queue operation, discardDeletedPage, drops every record of the
  page with its successor, so a paused edit with a successor no longer
  keeps the notice open for good.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>