TanStack Query v5 in Next.js 15 App Router — QueryClient + QueryClientProvider setup, prefetch in RSC + HydrationBoundary, mutations with optimistic updates, Server Actions interop, invalidation patterns, infinite queries, suspense queries, devtools. Use when you need rich client-side caching for server data, interactive lists with optimistic updates, infinite scroll, or when Server Components alone can't handle your interaction patterns.
