Build It

Turn the design into a working prototype. The goal is not a sophisticated model but a reliable system: models, tools, data, and application logic integrated so that a run completes end to end, state is visible, and failures are handled rather than hidden. Use the simplest components that work. Keep the deterministic steps deterministic.

Expect the prototype to expose gaps in the design. That is what it is for. Update the design as you go so the two stay in step.