Nextjs Guideline: DataFetching — Configure caching explicitly (Next.js 15+). Description: Next.js 15 changed defaults to uncached for fetch. Do: Explicitly set cache: 'force-cache' for static data. Don't: Assume default is cached (it's not in Next.js 15). Good Example: fetch(url { cache: 'force-cache' }). Bad Example: fetch(url) // Uncached in v15. Severity: High. Docs: https://nextjs.org/docs/app/building-your-application/upgrading/version-15.