next.config and Build Configuration

// next.config.js
/** @type {import('next').NextConfig} */
module.exports = {
  reactStrictMode: true,

  images: {
    remotePatterns: [
      { protocol: 'https', hostname: '**.supabase.co', pathname: '/storage/**' },
    ],
    formats: ['image/avif', 'image/webp'],
  },

  async redirects() {
    return [
      // moved 2026-08 — keep until the old links stop appearing in logs
      { source: '/old-problems', destination: '/dsa/problems', permanent: true },
    ]
  },

  async headers() {
    return [{ source: '/:path*', headers: SECURITY_HEADERS }]
  },

  async rewrites() {
    // proxy the API so cookies stay first-party
    return [{ source: '/api/:path*', destination: `${process.env.API_URL}/:path*` }]
  },

  // Trim large barrel-file libraries
  experimental: { optimizePackageImports: ['lucide-react', 'date-fns'] },
}

// redirect  — the URL changes, the browser sees the new one (301/308)
// rewrite   — the URL stays, different content is served (a proxy)

// Never ship these:
typescript: { ignoreBuildErrors: true }
eslint: { ignoreDuringBuilds: true }
// They convert a build-time failure into a runtime one. If the build
// is slow, run tsc and eslint as separate CI steps — do not silence.

// Experimental flags change real behaviour. Each one is a decision:
experimental: {
  ppr: 'incremental',              // changes how routes render
  staleTimes: { dynamic: 30 },     // changes client cache freshness
  serverActions: { bodySizeLimit: '2mb' },
}
// Write down why each is enabled. A flag nobody can explain is a flag
// that will be blamed for the next unexplained bug.

// trailingSlash changes every URL you have — decide once, early:
trailingSlash: false               // /problems  (the default)
// Changing it later means redirecting every indexed URL.

// basePath, if the app is served under a subpath — it affects every
// link, asset and API route:
basePath: '/app'

// And keep business logic out. A redirect that depends on the user
// belongs in middleware; one that depends on data belongs in a page.

const isProd = process.env.NODE_ENV === 'production'
const isPreview = process.env.VERCEL_ENV === 'preview'

module.exports = {
  // keep source maps for the error tracker but do not serve them
  productionBrowserSourceMaps: false,

  // block preview deployments from search engines
  async headers() {
    return isPreview
      ? [{ source: '/:path*', headers: [{ key: 'X-Robots-Tag', value: 'noindex' }] }]
      : [{ source: '/:path*', headers: SECURITY_HEADERS }]
  },

  compiler: {
    removeConsole: isProd ? { exclude: ['error', 'warn'] } : false,
  },
}
// The noindex on previews matters: a preview URL indexed by Google
// competes with production for the same content.

// The config runs at BUILD time, so process.env here is the build
// environment — not the runtime one. A value read here is frozen into
// the build, exactly like NEXT_PUBLIC_.

// Changing this file requires a rebuild and a redeploy. Anything that
// must change without one belongs in a server-read environment
// variable or a database row.