A bad or stale REPO_ROOT argument fell through to the "neither copy
present" no-op guard and exited 0 — the exact "clean result can mean
nothing was checked" anti-pattern this PR spent multiple review rounds
eliminating elsewhere. That guard exists for a repo that legitimately has
no kyberforge plugin installed, not for a typo'd path.
Only the documented manual-invocation mode was affected: the shipped
pre-push hook always calls this script with zero args, which resolves via
`git rev-parse --show-toplevel` and is always valid inside a repo.
Added a regression test asserting a nonexistent REPO_ROOT exits non-zero.
Refs: #85
Defame1297
cf5de2bd87