TanStack React Query expert for data fetching and mutations in React applications. Use when working with useQuery, useMutation, cache invalidation, optimistic updates, query keys, or integrating server actions with React Query via @saas4dev/core hooks (useServerActionQuery, useServerActionMutation, useServerActionInfiniteQuery). Triggers on requests involving API data fetching, server state management, cache strategies, or converting fetch/useEffect patterns to React Query.