Serve sitemap via a resource route and make the drift check fatal

Move sitemap generation from the buildEnd hook into a resource route
(app/routes/sitemap.tsx) whose loader returns renderSitemap() as
application/xml. It still prerenders to build/client/sitemap.xml and now also
serves live under `npm run dev`, at the cost of a sitemap.xml.data sidecar and
a tiny client chunk.

The prerender hook keeps the getStaticPaths() cross-check but now throws
instead of warning, so a prerendered page missing from both PAGES and the
exclude list fails the build. /sitemap.xml is added to the exclude list since
the resource route makes it a discovered path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Marv51

src/app/routes.ts

@@ -5,6 +5,7 @@ export default [
     route("/Project-Quick-Open/datenschutz.html", "routes/project-quick-privacy.tsx"),
     route("/SWR3App/datenschutz.html", "routes/swr3-app-privacy.tsx"),
     route("404", "routes/not-found.tsx", { "index": true}),
+    route("sitemap.xml", "routes/sitemap.tsx"),
     layout("routes/layout.tsx", [
         index("routes/home.tsx"),
         ...prefix("en", [

src/app/routes/sitemap.tsx

@@ -0,0 +1,9 @@
+import { renderSitemap } from "../seo-links";
+
+// Resource route (loader only, no component): prerendered to
+// build/client/sitemap.xml, and also served live under `npm run dev`.
+export function loader() {
+  return new Response(renderSitemap(), {
+    headers: { "Content-Type": "application/xml" },
+  });
+}

src/react-router.config.ts

@@ -1,38 +1,33 @@
 import type { Config } from "@react-router/dev/config";
-import { writeFile } from "node:fs/promises";
-import { join } from "node:path";
-import { renderSitemap, sitemapPaths } from "./app/seo-links";
+import { sitemapPaths } from "./app/seo-links";
 
-// Prerendered paths intentionally kept OUT of the sitemap: the error page and
-// the two standalone app privacy policies (not part of the bilingual site).
+// Prerendered paths intentionally kept OUT of the sitemap: the error page, the
+// sitemap resource route itself, and the two standalone app privacy policies
+// (not part of the bilingual site).
 const SITEMAP_EXCLUDED = new Set([
   "/404",
+  "/sitemap.xml",
   "/Project-Quick-Open/datenschutz.html",
   "/SWR3App/datenschutz.html",
 ]);
 
 export default {
   ssr: false,
   // Function form of `prerender` returns the same static paths as `true`, but
-  // also lets us cross-check route discovery against the sitemap so a new page
-  // can't silently go missing from it.
+  // also lets us cross-check route discovery against the sitemap. A prerendered
+  // page missing from both PAGES and the exclude list fails the build, so the
+  // sitemap can't silently fall out of sync with the routes.
   prerender: ({ getStaticPaths }) => {
     const discovered = getStaticPaths();
     const known = new Set([...sitemapPaths(), ...SITEMAP_EXCLUDED]);
     const unaccounted = discovered.filter((path) => !known.has(path));
     if (unaccounted.length > 0) {
-      console.warn(
+      throw new Error(
         `[sitemap] Prerendered path(s) missing from the sitemap and exclude ` +
           `list: ${unaccounted.join(", ")}. Add them to PAGES in ` +
           `app/seo-links.ts, or to SITEMAP_EXCLUDED in react-router.config.ts.`,
       );
     }
     return discovered;
   },
-  // Emit sitemap.xml into the prerendered output, derived from PAGES.
-  buildEnd: async ({ reactRouterConfig }) => {
-    const out = join(reactRouterConfig.buildDirectory, "client", "sitemap.xml");
-    await writeFile(out, renderSitemap(), "utf-8");
-    console.log(`[sitemap] wrote ${out}`);
-  },
 } satisfies Config;