feat: validate intentional post requests

src/features/posts/page.test.ts

@@ -0,0 +1,20 @@
+import { describe, expect, it } from 'vitest'
+import { flattenPostPages } from './page'
+import type { Post, PostPage } from './types'
+
+const post = (id: string): Post => ({
+  id,
+  text: `post-${id}`,
+  author: { username: `user-${id}`, name: `User ${id}` },
+})
+
+describe('flattenPostPages', () => {
+  it('preserves API order and removes duplicate IDs', () => {
+    const pages: PostPage[] = [
+      { tweets: [post('1'), post('2')], nextCursor: 'next' },
+      { tweets: [post('2'), post('3')] },
+    ]
+
+    expect(flattenPostPages(pages).map(({ id }) => id)).toEqual(['1', '2', '3'])
+  })
+})