fix: keep sitemap modification dates stable

src/app/sitemap.test.ts

@@ -0,0 +1,12 @@
+import { describe, expect, it } from 'vitest';
+import sitemap from './sitemap';
+
+describe('sitemap metadata', () => {
+  it('uses a stable content date instead of the current request time', () => {
+    const first = sitemap();
+    const second = sitemap();
+
+    expect(first).toEqual(second);
+    expect(first.every((entry) => entry.lastModified === '2026-08-20')).toBe(true);
+  });
+});

src/app/sitemap.ts

@@ -1,13 +1,15 @@
 import type { MetadataRoute } from 'next';
 
 const BASE_URL = process.env.NEXT_PUBLIC_APP_URL ?? 'http://localhost:3001';
+// Keep this stable between requests; update it when public page content changes.
+const LAST_MODIFIED = '2026-08-20';
 
 export default function sitemap(): MetadataRoute.Sitemap {
   const routes = ['', '/marketplace', '/login', '/register'];
 
   return routes.map((route) => ({
     url: `${BASE_URL}${route}`,
-    lastModified: new Date(),
+    lastModified: LAST_MODIFIED,
     changeFrequency: route === '' ? 'weekly' : 'monthly',
     priority: route === '' ? 1 : 0.6,
   }));