You don't need a single type to represent the entire program state.

We probably both agree that separate types for shipping methods, priorities, size, country makes sense.

The API can be designed to prevent illegal transitions between types to arrive at an invalid state. The exact implementation depends on the language.

> The idea of encoding all of this business logic into the datatype is a road to madness IMHO

The alternative is hoping that every developer remembers not to violate any of the implicit and unenforced rules.

If the system is too complicated to be represented in code, can a human realistically hold the entire state machine in their head as they make changes?