Fail-closed compatibility lane between legacy LocalMap and canonical projection.
@spec authority( term(), keyword() ) :: {:ok, module(), map()} | {:error, atom()}
@spec backfill(keyword(), keyword()) :: {:ok, map()} | {:error, atom()}
@spec compare( term(), keyword() ) :: {:ok, map()} | {:error, atom()}
@spec enable( term(), keyword() ) :: :ok | {:error, atom()}
@spec rollback(keyword()) :: :ok
@spec validate_clean_window(keyword()) :: {:ok, map()} | {:error, :invalid_clean_window}