What is tanstack-query?
TanStack Query v5 server state management for React. Covers query/mutation patterns, v4-to-v5 migration (object syntax, gcTime, isPending, keepPreviousData), optimistic updates via useMutationState, SSR/hydration with HydrationBoundary, infinite queries, offline/PWA support, error boundaries with throwOnError, and React 19 Suspense integration. Use when building data fetching, fixing migration errors, debugging hydration mismatches, implementing caching strategies, or configuring mutations. Source: oakoss/agent-skills.