Review round 1: the two existing safe_abs_path escape tests both pass even against
the classic buggy `str(path).startswith(str(root))` containment check, so a
regression to that bug would have shipped green. Add the one input that
distinguishes the correct `root not in path.parents` guard: a sibling dir whose name
prefixes the root (/root vs /rootx). Mutation-verified — swapping the guard to
startswith now fails this test. Also corrected the requirements-dev header (installed
by Dockerfile.test, not a nonexistent `dev` stage).
peter
4bae9113e4