An empty $(mktemp) result silently disabled the redaction pass (redact-doc
resolver, ship pr-body) and made /gstack-upgrade's vendored path destructive:
clone lands at "/gstack", the swap mv fails, and rm -rf then deletes BOTH the
live install's backup and "". All three sites now guard the assignment with a
loud exit; the vendored block additionally restores the backup when the swap
fails (same failure class — backup deletion after a failed mv) and the GitLab
MR path sends the SCANNED file's bytes instead of re-rendering an unscanned
heredoc. bin/gstack-redact rejects an explicit empty --from-file path instead
of silently falling through to stdin.
Receipts: 6 of 8 new regression checks fail on a v1.77.0.0 scratch worktree.
Fixes#2679
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>