feat!: upgrade to next 16

apps/web/next-env.d.ts

@@ -1,6 +1,6 @@
 /// <reference types="next" />
 /// <reference types="next/image-types/global" />
-/// <reference path="./.next/types/routes.d.ts" />
+import "./.next/dev/types/routes.d.ts";
 
 // NOTE: This file should not be edited
 // see https://nextjs.org/docs/app/api-reference/config/typescript for more information.

apps/web/next.config.mjs

@@ -11,8 +11,8 @@ const nextConfig = {
     minimumCacheTTL: 3600,
     contentDispositionType: "inline",
   },
-  eslint: {
-    ignoreDuringBuilds: true,
+  experimental: {
+    turbopackFileSystemCacheForDev: true,
   },
   typescript: {
     ignoreBuildErrors: true,

apps/web/package.json

@@ -4,10 +4,10 @@
   "private": true,
   "type": "module",
   "scripts": {
-    "build": "next build --turbopack",
+    "build": "next build",
     "clean": "rm -rf .next",
     "codegen": "pnpm generate:importmap && pnpm generate:types",
-    "dev": "next dev --turbopack",
+    "dev": "next dev",
     "email": "email dev --dir src/emails",
     "generate:importmap": "payload generate:importMap",
     "generate:types": "payload generate:types",
@@ -20,12 +20,12 @@
   "dependencies": {
     "@apollo/client": "^4.1.2",
     "@date-fns/tz": "^1.4.1",
-    "@payloadcms/admin-bar": "^3.55.1",
-    "@payloadcms/db-mongodb": "^3.55.1",
-    "@payloadcms/next": "^3.55.1",
-    "@payloadcms/richtext-lexical": "^3.55.1",
-    "@payloadcms/storage-azure": "^3.55.1",
-    "@payloadcms/ui": "^3.55.1",
+    "@payloadcms/admin-bar": "^3.72.0",
+    "@payloadcms/db-mongodb": "^3.72.0",
+    "@payloadcms/next": "^3.72.0",
+    "@payloadcms/richtext-lexical": "^3.72.0",
+    "@payloadcms/storage-azure": "^3.72.0",
+    "@payloadcms/ui": "^3.72.0",
     "@react-email/components": "^1.0.6",
     "@tailwindcss/postcss": "catalog:",
     "@tietokilta/ilmomasiina-client": "2.0.0",
@@ -35,11 +35,11 @@
     "date-fns": "^4.1.0",
     "mailgun.js": "^12.7.0",
     "nanoid": "^5.1.6",
-    "next": "^15.5.9",
+    "next": "16.1.6",
     "next-intl": "^4.7.0",
     "nextjs-toploader": "^3.9.17",
     "papaparse": "^5.5.3",
-    "payload": "^3.55.1",
+    "payload": "^3.72.0",
     "payload-oauth2": "^1.0.20",
     "postcss": "catalog:",
     "qs": "^6.14.1",
@@ -63,7 +63,7 @@
     "zod": "^4.3.5"
   },
   "devDependencies": {
-    "@next/eslint-plugin-next": "^15.5.9",
+    "@next/eslint-plugin-next": "16.1.6",
     "@tailwindcss/typography": "catalog:",
     "@tietokilta/config-typescript": "workspace:*",
     "@tietokilta/eslint-config": "workspace:*",

apps/web/src/app/[locale]/(main)/events/[slug]/opengraph-image.tsx

@@ -23,6 +23,12 @@ interface PageProps {
 
 export async function generateImageMetadata(props: PageProps) {
   const { locale, slug } = await props.params;
+  // Next.js 16 calls generateImageMetadata with undefined params during the
+  // "collecting page data" build phase to probe the route structure. Return
+  // an empty array so the build doesn't fail with NEXT_HTTP_ERROR_FALLBACK.
+  if (!slug) {
+    return [];
+  }
   const event = await fetchEvent(slug, locale);
   if (!event.ok) {
     return notFound();

apps/web/src/middleware.ts → apps/web/src/proxy.ts

@@ -30,7 +30,7 @@ function migrateLegacyCookie(request: NextRequest, response: NextResponse) {
   }
 }
 
-export default function middleware(request: NextRequest) {
+export default function proxy(request: NextRequest) {
   const pathname = request.nextUrl.pathname;
 
   // Check if URL already has a valid locale prefix