I am completely confused by any discussion of "unilateral exit" or "self-custodial" when it comes to Spark. I completely don't understand why that matters, or what those concepts even mean, in the context of an API controlled by one company (actually one family, in this case.) They can just turn off the API at any time and then nobody can exit! If their servers go down, nobody can exit! It's 100% permissioned, right?