Clean partial editor mounts and failed refreshes

packages/block-editor/test/runtime.test.ts

@@ -9,6 +9,28 @@ const code = new Bun.Transpiler({ loader: "ts" })
   .replace(/^import .*;\s*$/gm, "")
   .replace("export function mountBlockEditor", "function mountBlockEditor");
 
+test("partial registration failure cleans the backend and live region on mount and refresh", () => {
+  for (const failingMount of [1, 2]) {
+    const window = new Window(), root = window.document.createElement("div");
+    window.document.body.append(root);
+    root.innerHTML = '<div data-block-id="a" data-block-parent="root" data-block-slot="content"></div><div data-block-id="b" data-block-parent="root" data-block-slot="content"></div>';
+    let mounts = 0, destroyed = 0, cleaned = 0;
+    const mount = new Function("createDndManager", code + ";return mountBlockEditor;")(() => {
+      const number = ++mounts; let registrations = 0;
+      return { registerSortable() { if (++registrations === 2 && number === failingMount) throw new Error("registration failed"); return () => { cleaned++; }; }, destroy() { destroyed++; } };
+    });
+    let editor: MountedEditor | undefined;
+    if (failingMount === 1) expect(() => mount(root, { onMove() {} })).toThrow("registration failed");
+    else { editor = mount(root, { onMove() {} }); expect(() => editor!.refresh()).toThrow("registration failed"); }
+    expect(root.querySelector('[role="status"]')).toBeNull();
+    expect(root.querySelectorAll('[data-block-id]')).toHaveLength(2);
+    expect(destroyed).toBe(failingMount);
+    expect(cleaned).toBe(failingMount === 1 ? 1 : 3);
+    editor?.destroy(); editor?.refresh();
+    expect(destroyed).toBe(failingMount);
+  }
+});
+
 function fixture(onMove: MountEditorOptions["onMove"] = () => false) {
   const window = new Window();
   const document = window.document;