read_version required --- at byte 0 while skill-size-check accepts
leading blank lines, so a file one gate passed the other reported as
unversioned, and an unversioned merge-base side let an unbumped change
through. Match FRONTMATTER_RE, add case 39, and describe the main-tip
check and fail-closed cases in the hook entry.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>