The commit message flags, matching upstream gitwatch byte for byte and
the macOS port decision for decision: -l/-L embed the diff via the
diff-lines rewrite with the 150-char cut and diffstat fallback, -c runs
a word-split command whose stdout becomes the message, -C feeds it the
changed file names on stdin, and -v is accepted and ignored.

The differential suite grows scenarios that compare whole commit-message
bodies against oracle/gitwatch.sh, including pins on upstream bugs kept
bug-for-bug: header-lookalike content lines are eaten, the 150-char cut
can split a colour escape, -L degrades on git > 2.39, and the -l diff is
repo-wide even for a file target.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>