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+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * ADR-0146 D3 — each read-only base's Studio landing card says what this
+ * deployment changed on it, "n customized, m switched off", from the server's
+ * per-package customization read (`GET /api/v1/packages/:id/customizations`).
+ *
+ * The real `BuilderLanding` and the real reader (`packageCustomizations-io`)
+ * run under a real router; only the package list and the wire are stubbed.
+ * The stubbed answers are shaped by the route's declaration,
+ * `GetPackageCustomizationsResponseSchema`, inside the dispatcher envelope.
+ */
+
+import '@testing-library/jest-dom/vitest';
+import * as React from 'react';
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { cleanup, fireEvent, render, screen, waitFor, within } from '@testing-library/react';
+import { MemoryRouter, Route, Routes, useLocation } from 'react-router-dom';
+import { t, tFormat } from '../metadata-admin/i18n';
+import { resetRuntimeConfigForTesting } from '../../runtime-config';
+
+const packages = vi.hoisted(() => ({ list: [] as Array<Record<string, unknown>> }));
+
+vi.mock('./packages-io', async (importOriginal) => {
+  const mod = await importOriginal<typeof import('./packages-io')>();
+  return { ...mod, fetchPackages: vi.fn(async () => packages.list) };
+});
+
+// The create dialog is closed throughout; its form stack is not under test.
+vi.mock('../metadata-admin/PackageFormDialog', () => ({ PackageFormDialog: () => null }));
+
+import { BuilderLanding } from './BuilderLanding';
+
+const HOTCRM = { id: 'hotcrm', name: 'HotCRM', writable: false, namespace: 'hotcrm' };
+const HOTCRM_PAIR = { id: 'hotcrm.custom', name: 'HotCRM customizations', writable: true, namespace: 'hotcrm_custom' };
+const SHOWCASE = { id: 'com.example.showcase', name: 'Showcase', writable: false, namespace: 'showcase' };
+const WRITABLE = { id: 'com.acme.app', name: 'Acme', writable: true, namespace: 'acme' };
+/** A pair served read-only (code-shipped): still a pair, so still no line. */
+const READONLY_PAIR = { id: 'com.example.showcase.custom', name: 'Showcase pair', writable: false, namespace: 'showcase_custom' };
+
+const CUSTOMIZATIONS_RE = /^\/api\/v1\/packages\/([^/]+)\/customizations$/;
+
+/** A served answer for `id`: `overrides` overrides, `extensions` field members, `switchedOff` flows. */
+function served(id: string, overrides: number, extensions: number, switchedOff: number) {
+  const data = {
+    packageId: id,
+    overrides: Array.from({ length: overrides }, (_, i) => ({ type: 'view', name: `view_${i}` })),
+    extensions: Array.from({ length: extensions }, (_, i) => ({ object: 'account', kind: 'field' as const, name: `field_${i}` })),
+    switchedOff: Array.from({ length: switchedOff }, (_, i) => ({ type: 'flow', name: `flow_${i}` })),
+    counts: { overrides, extensions, switchedOff },
+  };
+  return { status: 200, body: { success: true, data } };
+}
+
+type Answer = { status: number; body: unknown } | 'never';
+
+/**
+ * Stub the wire: each customization request is answered from `answers` by
+ * base id; every request URL is recorded.
+ */
+function stubWire(answers: Record<string, Answer>) {
+  const requested: string[] = [];
+  const fetchMock = vi.fn(async (input: RequestInfo | URL) => {
+    const url = String(input);
+    requested.push(url);
+    const m = CUSTOMIZATIONS_RE.exec(url);
+    const answer = m ? answers[decodeURIComponent(m[1])] : undefined;
+    if (answer === 'never') return new Promise<Response>(() => {});
+    if (!answer) throw new Error(`unexpected request ${url}`);
+    return {
+      ok: answer.status >= 200 && answer.status < 300,
+      status: answer.status,
+      json: async () => answer.body,
+      text: async () => JSON.stringify(answer.body),
+    } as Response;
+  });
+  vi.stubGlobal('fetch', fetchMock);
+  return { requested };
+}
+
+const customizationRequests = (requested: string[]) => requested.filter((u) => CUSTOMIZATIONS_RE.test(u));
+
+function LocationProbe() {
+  const { pathname } = useLocation();
+  return <div data-testid="location">{pathname}</div>;
+}
+
+function renderLanding() {
+  return render(
+    <MemoryRouter initialEntries={['/studio']}>
+      <LocationProbe />
+      <Routes>
+        <Route path="/studio" element={<BuilderLanding />} />
+        <Route path="/studio/:packageId/:tab" element={<div data-testid="pillar-builder" />} />
+      </Routes>
+    </MemoryRouter>,
+  );
+}
+
+/** The card a package renders in: the element holding both its name and its links. */
+function cardOf(name: string): HTMLElement {
+  const card = screen.getByText(name).closest('.rounded-lg.border');
+  if (!(card instanceof HTMLElement)) throw new Error(`no card found for ${name}`);
+  return card;
+}
+
+const customizedText = (n: number) => tFormat('engine.studio.landing.customizations.customized', 'en-US', { customized: n });
+const switchedOffText = (n: number) => tFormat('engine.studio.landing.customizations.switchedOff', 'en-US', { switchedOff: n });
+
+afterEach(() => {
+  cleanup();
+  packages.list = [];
+  vi.unstubAllGlobals();
+  resetRuntimeConfigForTesting();
+});
+
+describe('Studio landing: a read-only base says "n customized, m switched off" (ADR-0146 D3)', () => {
+  it('reads 3 overrides + 1 extension and 2 switched off as "4 customized, 2 switched off", linking the pair and the Automations pillar', async () => {
+    packages.list = [HOTCRM_PAIR, HOTCRM];
+    const { requested } = stubWire({ hotcrm: served('hotcrm', 3, 1, 2) });
+    renderLanding();
+
+    const line = await within(await waitFor(() => cardOf('HotCRM'))).findByTestId('studio-landing-customizations');
+    await waitFor(() => expect(line).toHaveAttribute('data-state', 'read'));
+    expect(line).toHaveTextContent('4 customized, 2 switched off');
+
+    const pairLink = within(line).getByTestId('studio-landing-customizations-pair');
+    expect(pairLink).toHaveTextContent(customizedText(4));
+    expect(pairLink).toHaveAttribute('href', '/studio/hotcrm.custom/data');
+    const offLink = within(line).getByTestId('studio-landing-customizations-switched-off');
+    expect(offLink).toHaveTextContent(switchedOffText(2));
+    expect(offLink).toHaveAttribute('href', '/studio/hotcrm/automations');
+
+    fireEvent.click(pairLink);
+    await waitFor(() => expect(screen.getByTestId('location')).toHaveTextContent('/studio/hotcrm.custom/data'));
+    // One read, for the base; never for its pair.
+    expect(customizationRequests(requested)).toEqual(['/api/v1/packages/hotcrm/customizations']);
+  });
+
+  it('reads a base with no pair as "0 customized, 0 switched off", with no pair link', async () => {
+    packages.list = [SHOWCASE];
+    stubWire({ 'com.example.showcase': served('com.example.showcase', 0, 0, 0) });
+    renderLanding();
+
+    const line = await within(await waitFor(() => cardOf('Showcase'))).findByTestId('studio-landing-customizations');
+    await waitFor(() => expect(line).toHaveAttribute('data-state', 'read'));
+    expect(line).toHaveTextContent('0 customized, 0 switched off');
+    expect(within(line).queryByTestId('studio-landing-customizations-pair')).not.toBeInTheDocument();
+    expect(within(line).getByText(customizedText(0))).not.toHaveAttribute('href');
+    expect(within(line).getByTestId('studio-landing-customizations-switched-off')).toHaveAttribute(
+      'href',
+      '/studio/com.example.showcase/automations',
+    );
+  });
+
+  it('shows no number on a failed read: a muted "couldn’t read" with the server’s sentence as its title', async () => {
+    packages.list = [SHOWCASE];
+    const sentence = 'Metadata service not available';
+    stubWire({ 'com.example.showcase': { status: 503, body: { success: false, error: { message: sentence } } } });
+    renderLanding();
+
+    const line = await within(await waitFor(() => cardOf('Showcase'))).findByTestId('studio-landing-customizations');
+    await waitFor(() => expect(line).toHaveAttribute('data-state', 'failed'));
+    expect(line).toHaveTextContent(t('engine.studio.landing.customizations.failed', 'en-US'));
+    expect(line).toHaveAttribute('title', expect.stringContaining(sentence));
+    expect(line.textContent).not.toMatch(/\d/);
+  });
+
+  it('shows no number when the answer is one the route’s declaration refuses', async () => {
+    packages.list = [SHOWCASE];
+    // `counts` missing: off-contract, so no count is read out of it.
+    stubWire({
+      'com.example.showcase': { status: 200, body: { success: true, data: { packageId: 'com.example.showcase', overrides: [] } } },
+    });
+    renderLanding();
+
+    const line = await within(await waitFor(() => cardOf('Showcase'))).findByTestId('studio-landing-customizations');
+    await waitFor(() => expect(line).toHaveAttribute('data-state', 'failed'));
+    expect(line.textContent).not.toMatch(/\d/);
+  });
+
+  it('draws no line and sends no request for a writable package or a pair', async () => {
+    packages.list = [WRITABLE, HOTCRM_PAIR, READONLY_PAIR, SHOWCASE];
+    const { requested } = stubWire({ 'com.example.showcase': served('com.example.showcase', 1, 0, 0) });
+    renderLanding();
+
+    await screen.findByText('Showcase pair');
+    await waitFor(() =>
+      expect(within(cardOf('Showcase')).getByTestId('studio-landing-customizations')).toHaveAttribute('data-state', 'read'),
+    );
+    expect(within(cardOf('Acme')).queryByTestId('studio-landing-customizations')).not.toBeInTheDocument();
+    expect(within(cardOf('HotCRM customizations')).queryByTestId('studio-landing-customizations')).not.toBeInTheDocument();
+    expect(within(cardOf('Showcase pair')).queryByTestId('studio-landing-customizations')).not.toBeInTheDocument();
+    expect(customizationRequests(requested)).toEqual(['/api/v1/packages/com.example.showcase/customizations']);
+  });
+
+  it('paints the landing before the counts arrive, with no number on the line', async () => {
+    packages.list = [HOTCRM, SHOWCASE];
+    const { requested } = stubWire({ hotcrm: 'never', 'com.example.showcase': 'never' });
+    renderLanding();
+
+    await screen.findByText('HotCRM');
+    expect(screen.getByText('Showcase')).toBeInTheDocument();
+    await waitFor(() => expect(customizationRequests(requested)).toHaveLength(2));
+    for (const name of ['HotCRM', 'Showcase']) {
+      const line = within(cardOf(name)).getByTestId('studio-landing-customizations');
+      expect(line).toHaveAttribute('data-state', 'loading');
+      expect(line.textContent).not.toMatch(/\d/);
+    }
+  });
+});