fix: add sitemap index route at /sitemap.xml for Next.js 16 generateSitemaps

app/sitemap.xml/route.ts

@@ -0,0 +1,27 @@
+import { generateSitemaps } from "@/app/sitemap"
+import { getBaseUrl } from "@/lib/sitemap-utils"
+
+export const revalidate = 3600
+
+export async function GET() {
+  const baseUrl = getBaseUrl()
+  const sitemaps = await generateSitemaps()
+
+  const entries = sitemaps
+    .map(({ id }) => `  <sitemap>\n    <loc>${baseUrl}/sitemap/${id}.xml</loc>\n  </sitemap>`)
+    .join("\n")
+
+  const xml = [
+    `<?xml version="1.0" encoding="UTF-8"?>`,
+    `<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">`,
+    entries,
+    `</sitemapindex>`,
+  ].join("\n")
+
+  return new Response(xml, {
+    headers: {
+      "Content-Type": "application/xml",
+      "Cache-Control": "public, max-age=3600, s-maxage=3600, stale-while-revalidate=86400",
+    },
+  })
+}