Perhaps I missed where it was explained— but I don't see how rust enforces the type predicates (e.g. acquire vs wait state) there without typestate.

Say I have a protocol that transitions from A -> B -> C. Since the pipes compiler creates the only constructor for type B, there's no way for you to construct a value of type B (in the safe language) without giving up your one value of type A. The uniqueness typing system prevents you from copying your single value of A, and you must surrender all your references to it at the time you transition to state B.