def _create_default_branch_id(repo_url: str, default_branch_ref_id: str) -> str:
    """
    Return a unique node id for a repo's defaultBranchId using the given repo_url and default_branch_ref_id.
    This ensures that default branches for each GitHub repo are unique nodes in the graph.
    """
    return f"{repo_url}:{default_branch_ref_id}"