The server-side data layer for a Next.js 16 site — fetch semantics (NOT cached by default anymore), the Cache Components model (the cacheComponents flag, the 'use cache' directive, cacheLife/cacheTag, revalidateTag with its cacheLife-profile second argument), streaming slow data behind Suspense with layout-true skeletons, parallel fetching with Promise.all, and when a route handler earns its place over a direct call.
