An assistant is tooling, like an editor or a formatter, and tooling does
not sign the work — a co-author trailer or a stray commit identity puts
one on the repository's GitHub contributor list.
Both guards are git's own, so they need no editor-specific directory in
the tree. .mailmap folds a tool identity into the author who owns the
work, which git honours in log and shortlog and GitHub honours when it
builds the contributor list. The commit-msg hook strips the trailers if
one is written anyway; CLAUDE.md says so in words and names the one-time
config that turns the hook on.