chore: import upstream snapshot with attribution

showcase/shell/next.config.ts

@@ -0,0 +1,38 @@
+import type { NextConfig } from "next";
+import path from "path";
+import { fileURLToPath } from "url";
+// Logic lives in src/lib so vitest can cover it (missing-file warning,
+// TCP-port validation) — see src/lib/local-backends-env.test.ts.
+import { localBackendsEnv } from "./src/lib/local-backends-env";
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+
+const LOCAL_PORTS_PATH = path.resolve(
+  __dirname,
+  "..",
+  "shared",
+  "local-ports.json",
+);
+
+// NOTE: the docs-host 308s (/docs, /ag-ui, /reference and the
+// /<framework-slug> routes) intentionally do NOT live here. A
+// next.config `redirects()` table is baked into the build artifact, so
+// the destination host would freeze to whatever was current at Docker
+// build (staging shells 301'd to the PROD docs host). They are issued
+// by src/middleware.ts instead, resolving the docs host from runtime
+// config (DOCS_HOST env var) on every request — see
+// src/lib/docs-redirects.ts.
+
+const nextConfig: NextConfig = {
+  env: {
+    // NEXT_PUBLIC_BASE_URL intentionally NOT listed here: it must be
+    // read at request time via runtime-config (otherwise `next build`
+    // re-bakes the build-time value into every chunk). NEXT_PUBLIC_LOCAL_BACKENDS
+    // is fine to bake because it is computed from `shared/local-ports.json`
+    // (a JSON file on disk, not an env var) and only used in local-dev.
+    NEXT_PUBLIC_LOCAL_BACKENDS: localBackendsEnv(LOCAL_PORTS_PATH),
+  },
+  serverExternalPackages: ["@copilotkit/runtime"],
+};
+
+export default nextConfig;