QuestionSpec

A question exactly as it goes on the wire.

Closed and non-generic on purpose: the service defines these three shapes, so this is the protocol rather than an extension point. Callers who want a question that answers in their own type use Question[A], which pairs one of these with a decoder — see the typed question builders.

QuestionSpec.Raw exists only for forward compatibility: it lets a caller send a question shape a given release does not model yet, rather than wait for a library version.