Engineering Notes

Building a money library is six design decisions, and 'don't use floats' is only the first. A walk through each one (fixed-point representation, the shortest-decimal parse boundary, rounding as configurable policy, conservation as a primitive, value-versus-object API, and verification via oracle plus invariants) using abakojs as the worked example, with the costs named and the alternatives (decimal.js, dinero, currency.js) placed in context.