pub fn branch_files_stamp(root: &Path) -> Option<String>Expand description
A cheap fingerprint of the git state that decides which files a branch has
changed: the mtimes of .git/HEAD (commits, checkouts) and .git/index
(staging). Two stats, microseconds.
Deliberately not a complete invalidation signal — editing a tracked file
touches neither, so a caller must pair this with a freshness window rather
than trusting it alone. None when .git isn’t a plain directory, which
means “don’t cache this”.