Use per-deploy preview hosts under the site root domain.

Build hosts as <userPrefix>-<deploymentNumber>-preview.<rootDomain> from FRONTEND_URL, wire them through ingress/TLS, and open them from the preview API.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/src/config/configuration.ts

@@ -1,3 +1,49 @@
+function resolvePlatformDomainFromEnv(): string {
+  const frontendUrl = process.env.FRONTEND_URL;
+  if (frontendUrl) {
+    try {
+      const url = new URL(frontendUrl);
+      if (url.hostname && !/^\d+\.\d+\.\d+\.\d+$/.test(url.hostname)) {
+        return url.hostname;
+      }
+    } catch {
+      // ignore parse errors and fall back to PLATFORM_DOMAIN
+    }
+  }
+  return process.env.PLATFORM_DOMAIN || 'apps.cloudhost.local';
+}
+
+function stripLeadingSubdomain(hostname: string): string {
+  const h = (hostname || '').toLowerCase();
+  if (!h) return h;
+  // If it looks like an IP (IPv4 or IPv6), don't try to strip labels.
+  if (h.includes(':') || /^\d+\.\d+\.\d+\.\d+$/.test(h)) {
+    return h;
+  }
+  const parts = h.split('.').filter(Boolean);
+  if (parts.length >= 3) {
+    return parts.slice(1).join('.');
+  }
+  return h;
+}
+
+function resolvePreviewRootDomainFromEnv(): string {
+  const frontendUrl = process.env.FRONTEND_URL;
+  if (frontendUrl) {
+    try {
+      const url = new URL(frontendUrl);
+      if (url.hostname) {
+        return stripLeadingSubdomain(url.hostname);
+      }
+    } catch {
+      // ignore and fall back
+    }
+  }
+
+  // Fallback: strip from PLATFORM_DOMAIN if it's already a subdomain host.
+  return stripLeadingSubdomain(process.env.PLATFORM_DOMAIN || 'apps.cloudhost.local');
+}
+
 export default () => ({
   nodeEnv: process.env.NODE_ENV || 'development',
   port: parseInt(process.env.PORT || '4000', 10),
@@ -60,7 +106,8 @@ export default () => ({
   },
 
   platform: {
-    domain: process.env.PLATFORM_DOMAIN || 'apps.cloudhost.local',
+    domain: resolvePlatformDomainFromEnv(),
+    previewRootDomain: resolvePreviewRootDomainFromEnv(),
     uploadDir: process.env.UPLOAD_DIR || './uploads',
     /** StorageClass for new PVCs; must support allowVolumeExpansion for disk resize */
     storageClass: process.env.PLATFORM_STORAGE_CLASS || 'cloudhost-expandable',