Dogfooding

Ship the first usable vertical slice, then improve it by using it as its intended user would.

Rules

Pick one meaningful end-to-end journey and defer unrelated features.
Treat prototype replacements as clean breaks. Update callers, tests, examples, and disposable state to the new model; add backward compatibility only when explicitly required.
Exercise the documented setup and public interface with realistic input. Builder-only shortcuts and workarounds are product defects.
Debug from the user-visible symptom. Capture expected versus observed behavior, reproduce it publicly, fix the cause, then replay the journey.
Use focused tests for diagnosis, but require an end-to-end or manual check of the actual user experience.
Prototype code is disposable; real user data, production state, and authorization boundaries are not.