Memento pattern

A design in which an originator creates an opaque snapshot of its state, a caretaker retains it, and the originator can later restore it. Encapsulation prevents the caretaker from depending on internal state representation. A memento must freeze the relevant state: references to mutable objects can require a deep copy, while immutable values can safely be shared. Scala's access controls and path-dependent types can restrict snapshot construction and associate it with its originating instance.