Debug: Next.js build fails with dynamic server usage

Next.js build fails with 'Dynamic server usage' error when trying to statically generate a page that uses dynamic features like cookies, headers, or searchParams.

Diagnosis and fixes:

1. Identify the dynamic usage:

- cookies() or headers() in server components
- searchParams in page components
- fetch without cache option
- Route handlers without GET

1. Explicitly mark route as dynamic:

// app/page.tsx
export const dynamic = 'force-dynamic';
// or per-segment:
export const dynamicParams = true;

1. Move dynamic code to client components:

'use client'
// Use useSearchParams() instead of server-side searchParams

1. Use generateStaticParams for static paths:

export async function generateStaticParams() {
return posts.map(post => ({ slug: post.slug }));
}

1. Disable static generation for the whole route:

export const revalidate = 0; // No cache

1. Check middleware - it makes ALL routes dynamic:

// matcher in middleware.ts controls which routes
export const config = {
matcher: '/api/:path*', // Only apply to API routes
};