Review (MEDIUM): `git push ... 2>&1` did not check exit code, so a silent push
failure (auth-token expiry, network blip, non-fast-forward) would proceed to the
report step and declare success — silently reproducing the exact #2138 defect.
Add a fallback warning naming the rerun command so a failed push is visible
(best-effort: the PR already exists, so we still report it rather than abort).
Recaptures goldens + size baseline.
924ff6822e