Live sync cannot send work to a page the server no longer has, so the
unsaved mark never cleared and the page swap waited forever: the canvas
stayed on the deleted page with the sync button spinning, and switching
pages dropped the work without a word.

When the page on screen is gone and holds work the server never got, the
session now stops and asks: restore the page (re-created with everything
on screen, then synced from it) or discard the changes and move to a page
that exists. With nothing unsent, the stale unsaved mark is cleared and
the canvas moves on as before.

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