Editing skill/ here is only half the job: skillset mirrors it at
skills/pi-extensions/, and that copy is what most consumers actually read --
each Mac's host-side ~/.agents/skills/pi-extensions symlinks into it, and a
workstation with only skillset cloned has no other copy. The refresh is a manual
cp in another repo and it has now been forgotten on two consecutive edits, so
the mirror drifted 4890 B behind, then 9579 B.
hooks/pre-push compares the PUSHED content (git show <sha>:skill/...) against the
mirror on disk and prints the exact cp/sed/commit sequence when they differ.
Pushed content rather than the worktree: uncommitted local edits are not what
this push publishes.
It warns and exits 0 rather than blocking, for two reasons that are not
squeamishness: the direction rule is "edit upstream, THEN refresh", so the
refresh legitimately comes after this push, and it is a commit in a different
repo that cannot be made from here. Enforcement belongs downstream and already
exists -- skillset's pre-commit gate refuses a commit that leaves the mirror
stale. This hook only shortens time-to-detection from "next skillset commit" to
"seconds, to the person who caused it".
Silent when the mirror already matches, when the push does not touch skill/, on
branch deletions, and when no skillset clone is on disk -- a reminder that cannot
be acted on is noise that trains people to skim hook output.
install.sh activates it (core.hooksPath=hooks, per-clone config that cannot be
tracked), preserves a foreign hooksPath rather than clobbering it, and does NOT
undo the activation on --uninstall: removing a safety gate as a side effect of
uninstalling extensions would be a surprise in the wrong direction.
Verified: all three activate_hooks branches in a throwaway repo, and five
pre-push scenarios driven through the real stdin protocol (stale -> warns,
in-sync -> silent, non-skill push -> silent, branch deletion -> silent, no
skillset clone -> silent).
