@@ -0,0 +1,14 @@
+---
+'@object-ui/app-shell': patch
+---
+
+fix(app-shell): a locked metadata item's designer canvas is read-only
+
+Clause-②: no
+Metadata-protocol: none
+
+In Setup › All Metadata Types, a locked item (for example an object installed by a package, under the banner "This item is locked and cannot be edited or deleted.") still had a live designer canvas. On an object you could add a field, add a field to a section, move a section or remove one: the change showed in the canvas with an "Unsaved" chip, but the page offers no Save on a locked item, so the work was dropped without a word when you left.
+
+What changes: when the page cannot write the item (it is locked, or you lack the capability to author metadata), the designer canvas gets no edit callback, so it renders read-only for every designer type, the way the Studio canvas already does for a read-only package. The Description box was already disabled on a locked item. Writable items are unchanged.
+
+What to do: nothing.
@@ -0,0 +1,138 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * objectstack#26888 — a locked item's designer canvas is read-only.
+ *
+ * The page learns the lock from the layered read (`editable: false`) and keeps
+ * Save, the form and the inspectors read-only on it, but it handed the
+ * registered preview an `onPatch` unconditionally. The object canvas derives
+ * its read-only state from `onPatch` alone, so on a locked object it offered
+ * Add field, Add field to this section, Move section and Remove section: the
+ * edit landed in the draft, the inspector said "Unsaved", and no Save existed
+ * to keep it. The fix passes no `onPatch` when the page cannot write the item,
+ * the preview contract Studio already follows for a read-only package
+ * (objectui#11136).
+ *
+ * The unlocked case is the control: the same object, writable, still gets
+ * every control, so a red locked case is the defect and not a harness that
+ * never mounted the canvas.
+ */
+
+import '@testing-library/jest-dom/vitest';
+import * as React from 'react';
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { cleanup, render, screen } from '@testing-library/react';
+import { MemoryRouter } from 'react-router-dom';
+
+const OBJECT = {
+  name: 'crm_account',
+  label: 'Account',
+  fields: {
+    account_name: { type: 'text', label: 'Account Name', group: 'basics' },
+    website: { type: 'url', label: 'Website', group: 'basics' },
+    notes: { type: 'textarea', label: 'Notes', group: 'details' },
+  },
+  fieldGroups: [
+    { key: 'basics', label: 'Basics' },
+    { key: 'details', label: 'Details' },
+  ],
+};
+
+const layered = vi.hoisted(() => ({ editable: true }));
+
+const client = vi.hoisted(() => ({
+  list: async () => [],
+  listDrafts: async () => [],
+  get: async () => null,
+  getDraft: async () => null,
+  references: async () => [],
+  layered: async () => ({
+    code: OBJECT,
+    overlay: null,
+    overlayScope: null,
+    effective: OBJECT,
+    lock: layered.editable ? 'none' : 'full',
+    provenance: 'package',
+    packageId: 'app.objectstack.hotcrm',
+    editable: layered.editable,
+    deletable: layered.editable,
+  }),
+}));
+
+vi.mock('./useMetadata', async (importOriginal) => {
+  const mod = await importOriginal<typeof import('./useMetadata')>();
+  return {
+    ...mod,
+    useMetadataClient: () => client,
+    useMetadataTypes: () => ({
+      loading: false,
+      error: null,
+      entries: [
+        {
+          type: 'object',
+          name: 'object',
+          label: 'Object',
+          allowEnvironmentOverlay: true,
+          allowRuntimeCreate: true,
+          schema: { type: 'object', properties: { name: { type: 'string' }, label: { type: 'string' } } },
+        },
+      ],
+    }),
+  };
+});
+
+vi.stubGlobal(
+  'fetch',
+  vi.fn(async () => new Response('null', { status: 404, headers: { 'content-type': 'application/json' } })),
+);
+
+import { MetadataResourceEditPage } from './ResourceEditPage';
+import './register-builtins';
+// The built-in designers (the Object canvas among them), which the package
+// entry registers from a chunk it loads with a dynamic `import()`: called at
+// module scope so they are registered before the first render.
+import { registerBuiltinDesigners } from './register-builtin-designers';
+registerBuiltinDesigners();
+
+afterEach(() => {
+  cleanup();
+  layered.editable = true;
+});
+
+async function openObject(editable: boolean) {
+  layered.editable = editable;
+  render(
+    <MemoryRouter initialEntries={['/metadata/object/crm_account']}>
+      <MetadataResourceEditPage type="object" name="crm_account" />
+    </MemoryRouter>,
+  );
+  // The canvas is up once its first section header shows.
+  expect(await screen.findByText('Basics', {}, { timeout: 8000 })).toBeInTheDocument();
+}
+
+const CANVAS_WRITES = [
+  'Add field to this section',
+  'Move section up',
+  'Move section down',
+  'Remove section',
+];
+
+describe('Setup object designer — a locked item gets a read-only canvas (objectstack#26888)', () => {
+  it('control: a writable object offers the canvas add / move / remove controls', async () => {
+    await openObject(true);
+    for (const name of CANVAS_WRITES) {
+      expect(screen.queryAllByRole('button', { name }).length).toBeGreaterThan(0);
+    }
+    expect(screen.getByRole('button', { name: 'Add field' })).toBeInTheDocument();
+  });
+
+  it('a locked object offers none of them, and nothing reads "Unsaved"', async () => {
+    await openObject(false);
+    expect(await screen.findByTestId('lock-banner-title')).toBeInTheDocument();
+    for (const name of CANVAS_WRITES) {
+      expect(screen.queryAllByRole('button', { name })).toEqual([]);
+    }
+    expect(screen.queryByRole('button', { name: 'Add field' })).toBeNull();
+    expect(screen.queryByText('Unsaved')).toBeNull();
+  });
+});
@@ -3081,8 +3081,17 @@ function MetadataResourceEditPageImpl({
                           onSelectionChange={setSelection}
                           locale={locale}
                           diagnostics={previewDiagnostics}
-                          onPatch={(patch) =>
-                            handleDraftChange((d) => ({ ...(d as Record<string, unknown>), ...patch }))
+                          // objectstack#26888 — an item this page cannot write (a
+                          // locked package item, a caller without the capability)
+                          // gets no `onPatch`: per the preview contract the canvas
+                          // is then read-only, as Studio does for a read-only
+                          // package (objectui#11136). A live canvas here took
+                          // edits the page offers no Save for, and dropped them.
+                          onPatch={
+                            readOnly
+                              ? undefined
+                              : (patch) =>
+                                  handleDraftChange((d) => ({ ...(d as Record<string, unknown>), ...patch }))
                           }
                         />
                       </div>