Idiomatic React 18/19 patterns for building robust, accessible, performant component trees. - Writing or modifying React function components, custom hooks, or component trees - Reviewing JSX/TSX files - Designing state shape or component composition - Migrating class components or older `forwardRef`/`useEffect`-heavy code - Choosing between local state, lifted state, context, and external stores - Working with Server Components / Client Components (Next.js App Router, RSC) - Implementing forms with React 19 actions or controlled inputs - Wiring data fetching with TanStack Query / SWR / RSC