fix(messages): stop skeleton sticking after full content replace

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/widget-system/message-center-contract.test.cjs

@@ -89,6 +89,12 @@ test('message centre shows a skeleton during the AJAX load-more cycle', () => {
   assert.match(script, /content\.querySelector\('\.messages-list > \.post_ajax_loader'\)/);
   assert.match(script, /skeleton\.classList\.add\('is-loading'\)/);
   assert.match(script, /loader\.classList\.remove\('is-loading'\)/);
+  // Teardown must sweep every loader, not just `.messages-list >` children:
+  // a loader stranded outside a list (empty view / detail) would stay open.
+  assert.match(script, /content\.querySelectorAll\('\.post_ajax_loader\.is-loading'\)/);
+  // Full replacement must not carry the old (still is-loading) node across.
+  assert.doesNotMatch(script, /list\.appendChild\(keep\)/);
+  assert.doesNotMatch(script, /content\.appendChild\(keep\)/);
   // Appended rows land before the skeleton so it stays flush under the list.
   assert.match(script, /currentList\.insertBefore\(item, skeleton\)/);