Value types

Price and Quantity: exact, fixed-precision integers.

Rule

Price and Quantity are a 128-bit integer raw value plus a decimal precision from 0 to 9. The only text entry point is an exact decimal string and the only numeric entry point is a raw integer. There is deliberately no constructor from a floating-point number.

Arithmetic

Checked. Mismatched precisions and overflow are errors, never silent rounding or wrapping.