fn relative_workdir(abs: &str, agents_root: &Path) -> Option<String>Expand description
Express abs as a path relative to agents_root. Returns None
when abs is empty, not under agents_root, or after stripping
resolves to an empty path. Anchors against the resolved shared
root (passed in by the caller) — never scans for a path segment
named “agents”, which would match unrelated user directories like
/home/me/projects/agents/foo.