Function entry_path_in 

pub fn entry_path_in(
    cache_dir: &Path,
    project_root: &Path,
    phase: PhaseId,
) -> PathBuf

The deterministic per-registration entry file path for (project_root, phase). The digest is only a filename disambiguator — the authoritative project_root lives inside the file itself, and load_roots_in reads it from there, so a digest collision costs at most one shadowed entry and never a wrong path.