The traceability gate has failed on six commits in a row, every time for the
same reason: someone added a `TRACES:` tag and did not regenerate
docs/traceability.md. The gate is right to fail — a matrix that disagrees with
the tree is worse than none, because it is read as current — but it says so
after a push, on a commit that is otherwise fine, and by then the tag and the
matrix are two separate things to remember instead of one.
A pre-commit hook regenerates it and stages it, so the two travel together.
Enabled with `core.hooksPath`, which is a local setting: run
git config core.hooksPath .githooks
in a fresh clone, or the hook sits there doing nothing.
Only runs when something that can carry a tag is staged, and says nothing
unless it changed the matrix — a hook that prints on every commit is one people
start passing `--no-verify` to. If the report cannot run at all it leaves the
matrix alone and lets the commit through: refusing to commit because a build is
broken would be a worse failure than the one it prevents.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
