Function relocate 

pub(crate) fn relocate(
    src: &Path,
    dest_config_dir: &str,
    cwd: &str,
    sid: &str,
    owner_uid: &str,
) -> Result<Relocated, String>

Copy src in as session sid for cwd under dest_config_dir, marked as owner_uid’s. Refuses when the destination already exists: an existing file with the head’s id is never overwritten (spec §4.3 (5)).