Exactly. Failing early is the key part — especially before invalid state has a chance to propagate through the system. What I’ve found tricky in React apps is

Exactly. Failing early is the key part — especially before invalid state has a chance to propagate through the system. What I’ve found tricky in React apps is identifying where those invariants should live when the logic spans multiple async updates. Do you usually enforce them close to state updates, or at higher-level boundaries?