How do sitemap.ts and robots.ts work in Next.js?

// app/sitemap.ts
import type { MetadataRoute } from 'next';
export default async function sitemap(): Promise<MetadataRoute.Sitemap> {
  const posts = await getAllPosts();
  return posts.map((p) => ({ url: `https://site.com/blog/${p.slug}`, lastModified: p.updatedAt }));
}

// app/robots.ts
export default function robots(): MetadataRoute.Robots {
  return { rules: { userAgent: '*', allow: '/', disallow: '/admin' },
           sitemap: 'https://site.com/sitemap.xml' };
}