Fix Vercel ESM runtime error by removing "type": "module" from backend

apps/backend/package.json

@@ -14,7 +14,7 @@
     "dev": "BACKEND_PORT=${STACK_DEV_FALLBACK_BACKEND:+${NEXT_PUBLIC_STACK_PORT_PREFIX:-81}10} && BACKEND_PORT=${BACKEND_PORT:-${NEXT_PUBLIC_STACK_PORT_PREFIX:-81}02} && concurrently -n \"dev,codegen,prisma-studio,email-queue,cron-jobs,bulldozer-studio\" -k \"STACK_DISABLE_REACT_ASYNC_DEBUG_INFO=${STACK_DISABLE_REACT_ASYNC_DEBUG_INFO:-true} next dev --port $BACKEND_PORT ${STACK_BACKEND_DEV_EXTRA_ARGS:-}\" \"pnpm run codegen:watch\" \"pnpm run prisma-studio\" \"pnpm run run-email-queue\" \"pnpm run run-cron-jobs\" \"pnpm run run-bulldozer-studio\"",
     "dev:inspect": "STACK_BACKEND_DEV_EXTRA_ARGS=\"--inspect\" pnpm run dev",
     "dev:profile": "STACK_BACKEND_DEV_EXTRA_ARGS=\"--experimental-cpu-prof\" pnpm run dev",
-    "build": "pnpm run codegen && next build",
+    "build": "pnpm run codegen && next build && node scripts/patch-required-server-files.mjs",
     "docker-build": "pnpm run codegen && next build --experimental-build-mode compile",
     "build-self-host-migration-script": "tsdown --config scripts/db-migrations.tsdown.config.ts",
     "analyze-bundle": "next experimental-analyze",

apps/backend/scripts/patch-required-server-files.mjs

@@ -0,0 +1,36 @@
+/**
+ * Workaround for https://github.com/vercel/next.js/issues/91661
+ *
+ * Next.js 16.2 doesn't include `.next/package.json` (the CJS boundary marker)
+ * in the `required-server-files.json` manifest. Without it, Vercel's serverless
+ * functions inherit `"type": "module"` from the project's package.json, causing
+ * `require is not defined` at runtime.
+ *
+ * The upstream fix landed in vercel/next.js#93612 (canary only as of 16.2.6).
+ * This script patches the manifest after `next build` to include the file.
+ *
+ * Remove this script once we upgrade to a stable Next.js release containing the fix.
+ */
+
+import { readFileSync, writeFileSync, existsSync } from 'fs';
+import { join } from 'path';
+
+const distDir = '.next';
+const manifestPath = join(distDir, 'required-server-files.json');
+
+if (!existsSync(manifestPath)) {
+  // Not all build modes produce this manifest (e.g. compile-only docker builds)
+  process.exit(0);
+}
+
+const manifest = JSON.parse(readFileSync(manifestPath, 'utf8'));
+
+const packageJsonEntry = join(distDir, 'package.json');
+
+if (!manifest.files.includes(packageJsonEntry)) {
+  manifest.files.push(packageJsonEntry);
+  writeFileSync(manifestPath, JSON.stringify(manifest));
+  console.log(`Patched ${manifestPath}: added ${packageJsonEntry} to files array`);
+} else {
+  console.log(`${manifestPath} already includes ${packageJsonEntry}, no patch needed`);
+}