Function materialization_path 

pub fn materialization_path(
    root: &StorageRoot,
    candidate: &AllocationCandidate,
) -> Result<PathBuf>

Construct the safe materialization path for a candidate.

The namespace is always one path component, followed by the candidate’s relative path. Absolute paths and parent-directory traversal are rejected.

Errors

Returns an error if the candidate path is empty, absolute, or traverses a parent directory.