That is not the ideal that Your Party is set up on. Rules have not yet been agreed. We members get to look at the 4 founding documents and approve or change next week. So exact processes have not been agreed.
But we do know that the foundation is bottom up. Leaders do not get to make policy. Members do. He processes that control that are to be voted on in November. But the membership is clear. Unlike labour. Leaders taking over the party from the majority of the membership will be made impossible. No vote has happened on NATO. So ZSs comment are not in any way Your Party Policy. And no evidence I have seen so far indicates the majority of the membership would vote for leaving.