Pair displays at the platform's own /display/setup, with or without modules

Displays are platform-owned, but a screen could only start pairing on a
module's display page: every pairing request named a module, so an
installation with no module that uses displays could not set one up.

- /display/setup is the platform's own display page, served whenever
  the deployment has device support, whatever is installed. It pairs a
  platform display with no module. Once paired, it opens the module it
  is set to show; with none set, it shows its name and waits, rechecking
  so it stays alive and notices revocation. "setup" is now a reserved
  module id.
- Migration core:0009_platform_display_pairing lets a pairing request
  name no module. It relaxes module_id and permission_id and adds a
  both-or-neither check. It is additive and destroys nothing.
- POST /api/v1/device-pairing/requests accepts {} for a platform
  display. Approval accepts an optional moduleId, so the administrator
  can choose an installed display module and the device gets that
  module's declared permission. A module display's own request can't be
  redirected.
- GET /api/v1/device-pairing/self lets a paired device describe itself:
  its name and the module displays it may show. It renews the device's
  cookie.
- GET /api/v1/devices/setup is replaced by
  GET /api/v1/devices/display-modules: the modules a display can be set
  to show.
- Settings -> Displays always offers the /display/setup address, Copy
  setup link and Add display. Add display has an optional "Show on this
  screen" choice, and each paired display says what it shows.
- /display/<module-id> is unchanged, so released Signage 0.1.5 works as
  before.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/api/tests/module-display-routes.test.ts

@@ -22,14 +22,16 @@ import {
   type LegacyModuleRuntimeServices,
   type ModuleDatabase,
 } from "@ekklesia/core/modules";
-import type { Hono } from "hono";
+import { Hono } from "hono";
 import { afterEach, describe, expect, it, vi } from "vitest";
 import { createApiApp } from "../src/app.js";
 import { createDisplayHostAssets, type DisplayHostAssets } from "../src/display-host-assets.js";
 import {
   DISPLAY_HOST_SCRIPT_PATH,
   DISPLAY_SERVICE_WORKER_PATH,
+  DISPLAY_SETUP_PAGE_URL,
   ModuleDisplayConfigurationError,
+  mountModuleDisplayRoutes,
   moduleDisplayDescriptorUrl,
   moduleDisplayPageUrl,
 } from "../src/module-display-routes.js";
@@ -568,3 +570,47 @@ describe("module display host asset publication", () => {
     }
   });
 });
+
+describe("the platform display setup page (ADR 0065)", () => {
+  function bare(options: { readonly platformSetup?: boolean; readonly assets?: boolean }) {
+    const app = new Hono();
+    mountModuleDisplayRoutes(app, {
+      evaluator: createAuthorizationEvaluator({
+        grants: { hasActiveGrant: async () => false },
+        platformOwners: { isPlatformOwner: async () => false },
+      }),
+      // No installed module has a display at all.
+      moduleUi: createModuleUiPublicationRegistry([]),
+      registry: composePlatformPermissionRegistry([]),
+      runtime: {
+        handleAuthRequest: vi.fn(),
+        resolvePrincipal: vi.fn().mockResolvedValue(ANONYMOUS_PRINCIPAL),
+      },
+      ...(options.assets === false ? {} : { assets: displayHostAssets }),
+      ...(options.platformSetup === undefined ? {} : { platformSetup: options.platformSetup }),
+    });
+    return app;
+  }
+
+  it("serves /display/setup and the display host with zero display modules installed", async () => {
+    const app = bare({ platformSetup: true });
+
+    expect(DISPLAY_SETUP_PAGE_URL).toBe("/display/setup");
+    const page = await app.request(DISPLAY_SETUP_PAGE_URL);
+    expect(page.status).toBe(200);
+    expect(page.headers.get("cache-control")).toBe("no-store");
+    // The same inert, module-agnostic page every display is served.
+    expect(await page.text()).toBe(displayHostAssets.html);
+    expect((await app.request(DISPLAY_HOST_SCRIPT_PATH)).status).toBe(200);
+    expect((await app.request(DISPLAY_SERVICE_WORKER_PATH)).status).toBe(200);
+    // Nothing else beneath /display/ exists.
+    expect((await app.request("/display/signage")).status).toBe(404);
+  });
+
+  it("is not served without device support, and device support needs the display host", async () => {
+    expect((await bare({}).request(DISPLAY_SETUP_PAGE_URL)).status).toBe(404);
+    expect(() => bare({ assets: false, platformSetup: true })).toThrow(
+      ModuleDisplayConfigurationError,
+    );
+  });
+});