Next.js Core (App Router) - Server Components by default; minimal . - Mutations in Server Actions (validate/authz; revalidate tags/paths). - Route handlers for APIs/webhooks; add loading/error boundaries. Anti-patterns: - ❌ Fetch initial data in . - ❌ Cache or revalidate too broadly. - ❌ Client-only authz. References: see (server actions, fetching, caching, routing, auth, testing). ---