Product from scratch

Decide what a person will see and do before code constrains it: the user, the outcome, the journey, the interactions, the states, the failures, and the recovery. When implementation exposes a real constraint, reopen the decision that owns it instead of redesigning around the code.

Cost rules

1. Design effort stays proportionate to consequence and unresolved uncertainty. For an ordinary change it costs materially less than implementing the change twice.
2. Every artifact and every field must force a distinct decision or improve verification. Remove one that repeatedly does neither.
3. Reuse existing canon before authoring anything. Touching the interface does not earn a new document.

When work grows without resolving a decision or reducing a plausible risk, cut process. A process defect is never fixed with another process layer: no manifests, hashes, computed statuses, approval records, evidence taxonomies, reviewer machinery, or artifact quotas. Document lint proves mechanics; it never approves a design.