Type-system discipline

Let the checker carry the rules the code would otherwise test at runtime.

• Shape types so the checker rejects impossible states; define special cases out of existence instead of handling them.
• Handle every variant of a closed type so the checker reports a variant left unhandled.
• Give values that mean different things but share a primitive type their own types, validated once when created and trusted afterwards.
• Derive a type from the authoritative schema that owns its shape instead of hand-writing a parallel one.
• Where raw input becomes typed values is principle-boundary-discipline's rule.