Structure and State

Organize by feature. Everything for one feature in one folder, genuinely shared things in a shared one. A change then happens in one place, and deleting a feature is deleting a folder.

Put state in the smallest component that needs it. Lifting everything to the top is the most common cause of a slow interface, and moving it down is free.

Build the states you designed in phase 2. All four, plus first-run. If you are using TypeScript, make them a discriminated union so an impossible combination cannot be constructed at all.

Keep a way to trigger each one by hand until the real requests work. An error state you cannot see on demand is an error state you have not actually designed.