principle-model-the-domain

Identify what the code must never allow and how the data gets read, then pick a structure that encodes exactly that, such as a state machine, discriminated union, or lookup table. The goal is making invalid states unrepresentable and deleting branches rather than adding abstraction.

Use a state machine when lifecycle checks, phases, or multiple booleans must stay in sync with each other. A second boolean that must mirror the first is the classic sign that a state machine would remove the coordination burden.

Skip it when the current shape is already clear, local, and unlikely to grow. Be skeptical of any abstraction that adds indirection without removing branches, duplicated rules, invalid states, or lifecycle risk; boring code is preferred in those cases.

Temporal decomposition is organizing modules by execution order, such as load, validate, transform, and save, instead of by domain knowledge. It repeats the same domain rules across steps, so the Skill recommends organizing modules around one body of domain knowledge instead.

It returns a HOLD naming the missing input, such as the situation object or trigger evidence, instead of guessing. A HOLD is a return value, not a delay before producing a polished guess.