fix(checkpoint): act on landed chunks and shrink chunks a slow link cannot land

Commit

peyton-altyesterday

The pre-push commits the captured sync remote and warns about an ignored checkpoint_remote whenever refs landed, even if a later chunk failed.
The chunk size adapts: a chunk the budget cuts before anything lands quarters the next one (remembered per clone), a clean flush doubles it back. A budget cut mid-chunk ends the flush and rotates that chunk instead of retrying refs on a spent budget.

Co-Authored-By: Claude Opus 5.5 noreply@anthropic.com Entire-Checkpoint: 01M6M74P60V6SSAQEFN0GB8BDF