Add disable_seo config to keep preview deployments out of search engines

Co-Authored-By: Claude Opus 5.5 <[email protected]>

dist/commands/sitemap/index.js

@@ -18,6 +18,10 @@ export default function () {
         const { ROOT_DIR, PUBLIC_DIR } = grabDirNames();
         global.BUNEXT_CONFIG = (await grabConfig()) || {};
         global.BUNEXT_CONSTANTS = grabConstants();
+        if (global.BUNEXT_CONFIG.disable_seo) {
+            log.warn(`\`disable_seo\` is set: the server blocks all crawlers at ` +
+                `/robots.txt, so the generated robots.txt is not served.`);
+        }
         const { output, chunk_size, chunks_dir, ...sitemap_config } = global.BUNEXT_CONFIG.sitemap || {};
         if (!existsSync(grabPageLastmodFile(sitemap_config.lastmod_file))) {
             log.warn(`No page lastmod record found. Run \`bunext build\` first ` +