[lexical] Test: Use using for the #8563 regression editor

Manage the editor lifecycle with `using` and move root-element setup/teardown
into a test extension's register function (setRootElement + document.body
cleanup), matching the idiom used by the other reconciler repro tests. The
editor's dispose also calls setRootElement(null), so the whole fixture tears
down at end of scope without an afterEach.

https://claude.ai/code/session_01EAeZ6geVH74SpUrRhY6Z8h

Author: claude

packages/lexical/src/__tests__/unit/Issue8563Repro.test.ts

@@ -6,10 +6,26 @@
  *
  */
 
-import {buildEditorFromExtensions} from '@lexical/extension';
+import {buildEditorFromExtensions, defineExtension} from '@lexical/extension';
 import {RichTextExtension} from '@lexical/rich-text';
 import {$createParagraphNode, $createTextNode, $getRoot} from 'lexical';
-import {afterEach, describe, expect, test} from 'vitest';
+import {describe, expect, test} from 'vitest';
+
+// Attaches a root element so DOM reconciliation runs, and returns a dispose
+// that detaches it. `buildEditorFromExtensions` disposal calls both this
+// cleanup and `editor.setRootElement(null)`, so a `using` editor tears the
+// whole thing down at end of scope.
+const TestRootElementExtension = defineExtension({
+  name: 'issue-8563-root',
+  register(editor) {
+    const root = document.createElement('div');
+    document.body.appendChild(root);
+    editor.setRootElement(root);
+    return () => {
+      document.body.removeChild(root);
+    };
+  },
+});
 
 // Regression test for https://github.com/facebook/lexical/issues/8563
 //
@@ -24,39 +40,25 @@ import {afterEach, describe, expect, test} from 'vitest';
 // pointers and reached a key that only exists in the next state, throwing
 // `reconcileNode: prevNode or nextNode does not exist in nodeMap`.
 describe('Issue #8563: full reconcile with same-size child key swap', () => {
-  let cleanup: (() => void) | null = null;
-  afterEach(() => {
-    if (cleanup) {
-      cleanup();
-      cleanup = null;
-    }
-  });
-
   test('undo (setEditorState) does not crash when a child is replaced by a different-key child of equal count', () => {
     const errors: Error[] = [];
-    const editor = buildEditorFromExtensions({
-      dependencies: [RichTextExtension],
+    using editor = buildEditorFromExtensions({
+      dependencies: [RichTextExtension, TestRootElementExtension],
       name: 'issue-8563-repro',
       onError: e => {
         errors.push(e);
       },
     });
-    const root = document.createElement('div');
-    document.body.appendChild(root);
-    editor.setRootElement(root);
-    cleanup = () => {
-      editor.setRootElement(null);
-      document.body.removeChild(root);
-      editor.dispose();
-    };
 
     // State A: enough children to engage the fast path (>= 4).
     editor.update(
       () => {
-        const r = $getRoot();
-        r.clear();
+        const root = $getRoot();
+        root.clear();
         for (let i = 0; i < 5; i++) {
-          r.append($createParagraphNode().append($createTextNode(`line ${i}`)));
+          root.append(
+            $createParagraphNode().append($createTextNode(`line ${i}`)),
+          );
         }
       },
       {discrete: true},