Rebuild on a rotated epoch, and keep a blip from showing anywhere

A document rebuilt while a client was away is now rebuilt locally too,
rather than merged into, so edits made during a blip cannot fork it; the
person is told when unsent edits were dropped. Focus and visibility wake
the wire at most once a second and keep the backoff, and one attempt lands
inside the grace period. A send during a blip waits for the connection,
decision actions say when they failed for want of one, and Chat's
offline status matches the document header's.

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