--check fetches and prints current|behind <installed> -> <remote> (<n>
commits); the default fast-forwards to the remote default branch tip and
reinstalls (bin/gstack-capy-install on a Capy install, else ./setup
--refresh-registered), completing a pending reinstall on the next run. It
refuses (UPGRADE_REFUSED, exit 3, nothing changed) a dirty tracked byte, a
diverged commit, a pinned checkout, the incoming Bun floor and a held
.setup-lock; never stashes or resets; an unreachable remote is
UPGRADE_FETCH_FAILED. Fetches are receipted (fail-open). The unattended
skill-end UPGRADE_AVAILABLE line is followed by UPGRADE_COMMAND naming it.
Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>
