fix(plaza): use hero-generated thumbnails and portal cover URLs

Plaza posts now resolve cover_url to /u/{slug}/pages/{urlSlug}.thumbnail.png
instead of MindSpace workspace paths that fail on plaza.tkmind.cn. Public-html
and chat quick-plaza flows regenerate workspace thumbnails with force:true
after hero images are on disk so feed cards embed the generated art.

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

plaza-posts.test.mjs

@@ -53,6 +53,47 @@ test('resolvePlazaCoverUrl prefers explicit cover urls and falls back to publica
     plazaInternals.resolvePlazaCoverUrl('', '/u/john/pages/demo'),
     '/u/john/pages/demo.thumbnail.png',
   );
+  assert.equal(
+    plazaInternals.defaultPlazaCoverUrl('/MindSpace/user/public/page.html'),
+    '/MindSpace/user/public/page.thumbnail.png',
+  );
+  assert.equal(
+    plazaInternals.resolvePlazaCoverUrl(
+      'https://m.tkmind.cn/MindSpace/u/public/demo.html.thumbnail.png',
+      '/u/john/pages/demo',
+    ),
+    'https://m.tkmind.cn/MindSpace/u/public/demo.thumbnail.png',
+  );
+});
+
+test('resolvePlazaPublicationCoverUrl prefers portal publication thumbnail over MindSpace cover', () => {
+  assert.equal(
+    plazaInternals.resolvePlazaPublicationCoverUrl({
+      inputCoverUrl: '',
+      publicUrl: 'https://m.tkmind.cn/MindSpace/wx_ul610et8/public/demo.html',
+      publicationUrlSlug: 'plaza-batch-001',
+      userSlug: 'wx_ul610et8',
+    }),
+    '/u/wx_ul610et8/pages/plaza-batch-001.thumbnail.png',
+  );
+  assert.equal(
+    plazaInternals.resolvePlazaPublicationCoverUrl({
+      inputCoverUrl: 'https://m.tkmind.cn/MindSpace/wx_ul610et8/public/demo.html.thumbnail.png',
+      publicUrl: 'https://m.tkmind.cn/MindSpace/wx_ul610et8/public/demo.html',
+      publicationUrlSlug: 'plaza-batch-001',
+      userSlug: 'wx_ul610et8',
+    }),
+    '/u/wx_ul610et8/pages/plaza-batch-001.thumbnail.png',
+  );
+  assert.equal(
+    plazaInternals.resolvePlazaPublicationCoverUrl({
+      inputCoverUrl: 'https://cdn.example.com/cover.png',
+      publicUrl: '/u/john/pages/demo',
+      publicationUrlSlug: 'demo',
+      userSlug: 'john',
+    }),
+    'https://cdn.example.com/cover.png',
+  );
 });
 
 test('mapPlazaError maps documented API codes', () => {