Next.js 16

• Async params/cookies/headers; opt-in caching via "use cache"; Turbopack default.

Anti-patterns:

• ❌ Sync request APIs; ✅ await params, cookies(), and headers().
• ❌ Keep middleware.ts; ✅ use proxy.ts and export function proxy.
• ❌ revalidateTag("posts"); ✅ revalidateTag("posts", "max") or { expire: ... }.

References: references/migration-checklist.md, references/cache-components.md, references/turbopack.md