Merge pull request 'feat: support split Dashboard and API origins (ADR 0045)' (#54) from feat/split-origins into main

Reviewed-on: http://git.riverofglorymn.org/River_of_Glory_Church/Ekklesia/pulls/54 Reviewed-by: Joey <[email protected]>
2026-10-03 19:53:52 +00:00
parent cbf5962d04 f63f80f2f0
commit b2efb4b029
32 changed files with 1275 additions and 116 deletions
@@ -141,9 +141,18 @@ jobs:
  deploy-smoke:
    needs: verify
    runs-on: ubuntu-latest
-    timeout-minutes: 20
+    timeout-minutes: 30
+    # Both topologies (ADR 0045): same-origin, the default every installation gets, and split, which
+    # adds a test-only module and drives a real headless browser across the two origins.
+    strategy:
+      fail-fast: false
+      matrix:
+        topology:
+          - same-origin
+          - split
    env:
      DOCKER_BUILDKIT: "1"
+      EKKLESIA_SMOKE_TOPOLOGY: ${{ matrix.topology }}
    steps:
      - name: Check out repository
        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
@@ -158,5 +167,5 @@ jobs:
      # PostgreSQL, then the API, Dashboard, storage delivery, client-address chain, and verify-full
      # database TLS through the proxy. Every secret is generated for this run and discarded with
      # it; nothing is pushed, published, or logged in to.
-      - name: Smoke-test the reference deployment
+      - name: Smoke-test the reference deployment (${{ matrix.topology }})
        run: bash scripts/smoke-deploy.sh
@@ -200,3 +200,19 @@ export function createApiRuntimeConfig(
    storage,
  });
 }
+
+/**
+ * The exact browser origins the API trusts: CORS on `/api/auth/*` and `/api/v1/*`, and every
+ * mutation route's origin check (ADR 0045).
+ *
+ * The configured trusted origins plus the identity base URL's own origin, which is where the API
+ * lives. Better Auth already trusts its base URL implicitly; this makes the API's own checks agree,
+ * so a page the API itself serves (the display host, and the Dashboard in the same-origin topology)
+ * passes without an operator listing the API's origin. Order is preserved and duplicates removed;
+ * every entry is already a canonical origin.
+ */
+export function apiTrustedOrigins(
+  identity: Pick<IdentityConfig, "baseUrl" | "trustedOrigins">,
+): readonly string[] {
+  return Object.freeze([...new Set([...identity.trustedOrigins, identity.baseUrl])]);
+}
@@ -54,15 +54,54 @@ export function createDashboardHostAssets(html: string, script: string): Dashboa
  });
 }

-/** Loads only the two surface-declared files. A missing or unreadable build fails startup rather
- * than leaving an API whose own origin answers `/` with a 404. */
-export async function loadDashboardHostAssets(): Promise<DashboardHostAssets> {
+/**
+ * The exact element the built Dashboard page carries for its API origin (ADR 0045), empty. The shell
+ * reads the filled-in value at run time; empty means the page's own origin.
+ */
+export const DASHBOARD_API_ORIGIN_PLACEHOLDER = '<meta content="" name="ekklesia-api-origin" />';
+
+function isCanonicalHttpOrigin(value: string): boolean {
+  try {
+    const url = new URL(value);
+    return (url.protocol === "https:" || url.protocol === "http:") && url.origin === value;
+  } catch {
+    return false;
+  }
+}
+
+/**
+ * Writes the API's own origin into the Dashboard page, once, before the page's `ETag` is computed.
+ *
+ * The origin is the identity base URL's, which is where `/api` lives in either topology: the page's
+ * own origin when the Dashboard and the API share one, the API hostname when they are split. The
+ * built page must carry exactly one empty placeholder; anything else is a shell build this API does
+ * not understand, and startup fails rather than serving a page that might send credentials somewhere
+ * unintended. The value is escaped for an attribute even though a canonical origin cannot contain
+ * any character that needs it.
+ */
+export function renderDashboardPage(html: string, apiOrigin: string): string {
+  const parts = html.split(DASHBOARD_API_ORIGIN_PLACEHOLDER);
+  if (parts.length !== 2 || !isCanonicalHttpOrigin(apiOrigin)) {
+    throw new DashboardHostAssetError();
+  }
+  const escaped = apiOrigin
+    .replaceAll("&", "&amp;")
+    .replaceAll('"', "&quot;")
+    .replaceAll("<", "&lt;")
+    .replaceAll(">", "&gt;");
+  return parts.join(`<meta content="${escaped}" name="ekklesia-api-origin" />`);
+}
+
+/** Loads only the two surface-declared files, and renders the API origin into the page. A missing,
+ * unreadable, or incompatible build fails startup rather than leaving an API whose own origin answers
+ * `/` with a 404 or a page that cannot find its API. */
+export async function loadDashboardHostAssets(apiOrigin: string): Promise<DashboardHostAssets> {
  try {
    // Sequential deliberately, as for the display host: diagnostics stay deterministic and no
    // rejected sibling read is left running after this function has already failed.
    const html = await readFile(new URL(dashboardHostAssetUrls.html), "utf8");
    const script = await readFile(new URL(dashboardHostAssetUrls.script), "utf8");
-    return createDashboardHostAssets(html, script);
+    return createDashboardHostAssets(renderDashboardPage(html, apiOrigin), script);
  } catch {
    throw new DashboardHostAssetError();
  }
@@ -44,7 +44,7 @@ import {
  createClientAddressResolver,
  wrapFetchWithClientAddress,
 } from "./client-address.js";
-import { type ApiRuntimeConfig, createApiRuntimeConfig } from "./config.js";
+import { type ApiRuntimeConfig, apiTrustedOrigins, createApiRuntimeConfig } from "./config.js";
 import { loadDashboardHostAssets } from "./dashboard-host-assets.js";
 import { type ApiDatabaseHandle, createApiDatabase } from "./database.js";
 import { withDevicePrincipals } from "./device-principal.js";
@@ -550,7 +550,9 @@ export async function startApi(
      moduleUi.listDisplays().length === 0 ? undefined : await loadDisplayHostAssets();
    // Unconditional, unlike the display host: every installation serves its Dashboard (ADR 0044),
    // so a missing shell build fails here, before any module code is imported.
-    dashboardHostAssets = await loadDashboardHostAssets();
+    // The page learns its API origin from the API that serves it, so one build serves either
+    // topology (ADR 0045).
+    dashboardHostAssets = await loadDashboardHostAssets(config.identity.baseUrl);
  } catch (error) {
    await safeCloseStorage(storageProvider);
    await safeCloseMail(mailProvider);
@@ -648,7 +650,8 @@ export async function startApi(
      // Principal resolution, extended with managed devices. A human session still wins, and this
      // is the only place a device credential ever becomes a principal.
      runtime: withDevicePrincipals({ devices: deviceStore, runtime }),
-      trustedOrigins: config.identity.trustedOrigins,
+      // The configured origins plus the API's own (ADR 0045).
+      trustedOrigins: apiTrustedOrigins(config.identity),
    });
  } catch (error) {
    await safeStopModuleRuntime(moduleRuntime);
@@ -29,6 +29,7 @@ import type { ClientAddressConfigInput } from "../src/client-address.js";
 import { dashboardHostAssetUrls } from "@ekklesia/shell/dashboard-assets";
 import { createApiRuntimeConfig } from "../src/config.js";
 import { createApiDatabase } from "../src/database.js";
+import { DASHBOARD_API_ORIGIN_PLACEHOLDER } from "../src/dashboard-host-assets.js";
 import {
  DASHBOARD_HOST_PAGE_PATH,
  DASHBOARD_HOST_SCRIPT_PATH,
@@ -2989,7 +2990,7 @@ describe.sequential("live API — published module UI artifact", () => {
 });

 describe.sequential("live API — the built Dashboard on the API's own origin", () => {
-  it("serves the built shell's exact index.html at / and its exact script, and nothing beside them", async () => {
+  it("serves the built shell's index.html at /, with only its API origin written in, and its exact script, and nothing beside them", async () => {
    const database = await createDisposableDatabase("dashboard_host");
    await applyCoreMigrations(database.url);
    const running = await startMigratedApi(database.url);
@@ -3006,7 +3007,15 @@ describe.sequential("live API — the built Dashboard on the API's own origin",
      expect(page.headers.get("x-frame-options")).toBe("DENY");
      expect(page.headers.get("content-security-policy")).toBe("frame-ancestors 'none'");
      expect(page.headers.get("referrer-policy")).toBe("no-referrer");
-      expect(html).toBe(builtHtml);
+      // The built page carries one empty API-origin element; the API fills in its own origin
+      // (the identity base URL) and changes nothing else (ADR 0045).
+      expect(builtHtml.split(DASHBOARD_API_ORIGIN_PLACEHOLDER)).toHaveLength(2);
+      expect(html).toBe(
+        builtHtml.replace(
+          DASHBOARD_API_ORIGIN_PLACEHOLDER,
+          `<meta content="${identityBaseUrl}" name="ekklesia-api-origin" />`,
+        ),
+      );
      expect(html).toContain('id="ekklesia-host"');
      expect(html).toContain(`<script src="${DASHBOARD_HOST_SCRIPT_PATH}" type="module"></script>`);

@@ -3,11 +3,16 @@ import {
  createAuthenticatedPrincipal,
  type ModuleDatabase,
  type ModuleRuntimeServices,
+  moduleIdSchema,
+  parseEkklesiaUserId,
+  parsePermissionId,
 } from "@ekklesia/contracts";
 import {
  type AuthorizationEvaluator,
  type AuthorizationStore,
+  CORE_PERMISSION_DECLARATIONS,
  CORE_PERMISSION_REGISTRY,
+  createPermissionRegistry,
  type PermissionRegistry,
 } from "@ekklesia/core/authorization";
 import type { EkklesiaIdentityRuntime } from "@ekklesia/core/identity";
@@ -16,6 +21,7 @@ import {
  createModuleUiPublicationRegistry,
  EMPTY_MODULE_REALTIME_REGISTRY,
  type ModuleUiPublicationRegistry,
+  StagedModuleRealtimeRegistry,
 } from "@ekklesia/core/modules";
 import { describe, expect, it, vi } from "vitest";
 import {
@@ -910,3 +916,101 @@ describe("Ekklesia API Hono application", () => {
    });
  });
 });
+
+describe("split Dashboard and API origins (ADR 0045)", () => {
+  const moduleId = moduleIdSchema.parse("announcements");
+  const permission = parsePermissionId("announcements.slideshow.view");
+  const endpoint = "/api/v1/module-realtime/announcements/state";
+
+  /** The full application with one live channel, a signed-in caller, and an evaluator that allows
+   * it: the same composition a Dashboard on another origin reaches. */
+  function realtimeApp() {
+    const staged = new StagedModuleRealtimeRegistry();
+    const registration = staged.createRegistrationStage(moduleId, new Set([permission]));
+    registration.realtime.channel({ channel: "state", permission });
+    registration.commit();
+    staged.publisherFor(moduleId).publish("state", { mode: "on" } as never);
+    const moduleRealtime = staged.publish();
+    const app = createApiAppWithModules({
+      moduleRoutes: Object.freeze([]),
+      moduleUi: emptyModuleUiPublication(),
+      moduleLifecycle: emptyModuleLifecycle(),
+      moduleConfiguration: emptyModuleConfiguration(),
+      moduleStorage: emptyModuleStorage(),
+      moduleRealtime,
+      dashboard: createInMemoryDashboardStore(),
+      dashboardHostAssets: testDashboardHostAssets(),
+      health: readyHealth(),
+      moduleServices: fakeModuleServices(),
+      authorization: fakeAuthorization({
+        evaluator: { authorize: vi.fn().mockResolvedValue({ allowed: true }) },
+        registry: createPermissionRegistry([
+          ...CORE_PERMISSION_DECLARATIONS,
+          {
+            baseline: "restricted",
+            description: "View the announcement slideshow.",
+            id: permission,
+          },
+        ]),
+      }),
+      runtime: fakeRuntime({
+        resolvePrincipal: vi
+          .fn()
+          .mockResolvedValue(
+            createAuthenticatedPrincipal(
+              parseEkklesiaUserId("88888888-8888-4888-8888-888888888888"),
+            ),
+          ),
+      }),
+      trustedOrigins: [trustedOrigin],
+    });
+    return { app, moduleRealtime };
+  }
+
+  it("lets the Dashboard's origin open a credentialed realtime stream", async () => {
+    const { app, moduleRealtime } = realtimeApp();
+
+    const response = await app.request(endpoint, {
+      headers: { cookie: "session=1", origin: trustedOrigin },
+    });
+
+    expect(response.status).toBe(200);
+    expect(response.headers.get("content-type")).toBe("text/event-stream; charset=utf-8");
+    expect(response.headers.get("access-control-allow-origin")).toBe(trustedOrigin);
+    expect(response.headers.get("access-control-allow-credentials")).toBe("true");
+    expect(response.headers.get("vary")).toContain("Origin");
+    await response.body?.cancel();
+    moduleRealtime.closeSubscriptions();
+  });
+
+  it("gives an untrusted origin's realtime request no CORS permission to read the stream", async () => {
+    const { app, moduleRealtime } = realtimeApp();
+
+    const response = await app.request(endpoint, {
+      headers: { cookie: "session=1", origin: untrustedOrigin },
+    });
+
+    expect(response.headers.get("access-control-allow-origin")).toBeNull();
+    await response.body?.cancel();
+    moduleRealtime.closeSubscriptions();
+  });
+
+  it("allows only Content-Type beyond the CORS-safelisted request headers, and exposes none", async () => {
+    const app = createAuthWiringApp(fakeRuntime());
+
+    const response = await app.request("/api/v1/principal", {
+      headers: {
+        "access-control-request-headers": "content-type, x-module-custom",
+        "access-control-request-method": "PATCH",
+        origin: trustedOrigin,
+      },
+      method: "OPTIONS",
+    });
+
+    expect(response.headers.get("access-control-allow-origin")).toBe(trustedOrigin);
+    expect(response.headers.get("access-control-allow-headers")?.toLowerCase()).toBe(
+      "content-type",
+    );
+    expect(response.headers.get("access-control-expose-headers")).toBeNull();
+  });
+});
@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { ApiConfigError, createApiRuntimeConfig } from "../src/config.js";
+import { ApiConfigError, apiTrustedOrigins, createApiRuntimeConfig } from "../src/config.js";

 const validSecret = "correct-horse-battery-staple-0123456789";

@@ -337,3 +337,24 @@ describe("API runtime configuration", () => {
    expect(publicText).not.toContain("db.internal.example");
  });
 });
+
+describe("the API's trusted browser origins (ADR 0045)", () => {
+  it("adds the API's own origin to the configured ones, as Better Auth does", () => {
+    const origins = apiTrustedOrigins({
+      baseUrl: "https://api.example.test",
+      trustedOrigins: ["https://dash.example.test"],
+    });
+
+    expect(origins).toEqual(["https://dash.example.test", "https://api.example.test"]);
+    expect(Object.isFrozen(origins)).toBe(true);
+  });
+
+  it("does not duplicate an API origin already listed (the same-origin topology)", () => {
+    expect(
+      apiTrustedOrigins({
+        baseUrl: "https://ekklesia.example.test",
+        trustedOrigins: ["https://ekklesia.example.test"],
+      }),
+    ).toEqual(["https://ekklesia.example.test"]);
+  });
+});
@@ -13,10 +13,14 @@ vi.mock("@ekklesia/shell/dashboard-assets", () => ({

 import {
  createDashboardHostAssets,
+  DASHBOARD_API_ORIGIN_PLACEHOLDER,
  DashboardHostAssetError,
  loadDashboardHostAssets,
+  renderDashboardPage,
 } from "../src/dashboard-host-assets.js";

+const API_ORIGIN = "https://api.example.test";
+
 function sha256Etag(text: string): string {
  return `"${createHash("sha256").update(text).digest("base64url")}"`;
 }
@@ -25,19 +29,20 @@ describe("Dashboard host asset loading", () => {
  beforeEach(() => readFileMock.mockReset());

  it("reads only the two declared file URLs in order and freezes one consistent snapshot", async () => {
-    const html = '<!doctype html><div id="ekklesia-host"></div>';
+    const html = `<!doctype html>${DASHBOARD_API_ORIGIN_PLACEHOLDER}<div id="ekklesia-host"></div>`;
    const script = "export const dashboardHost = true;\n";
    readFileMock.mockResolvedValueOnce(html).mockResolvedValueOnce(script);

-    const assets = await loadDashboardHostAssets();
+    const assets = await loadDashboardHostAssets(API_ORIGIN);

    expect(readFileMock.mock.calls).toEqual([
      [new URL("file:///surface/browser/index.html"), "utf8"],
      [new URL("file:///surface/browser/assets/ekklesia-dashboard/app.js"), "utf8"],
    ]);
+    const rendered = `<!doctype html><meta content="${API_ORIGIN}" name="ekklesia-api-origin" /><div id="ekklesia-host"></div>`;
    expect(assets).toEqual({
-      html,
-      htmlEtag: sha256Etag(html),
+      html: rendered,
+      htmlEtag: sha256Etag(rendered),
      script,
      scriptEtag: sha256Etag(script),
    });
@@ -49,7 +54,7 @@ describe("Dashboard host asset loading", () => {
      new Error("ENOENT /home/operator/private/surface-build secret-token"),
    );

-    const failure = await loadDashboardHostAssets().catch((error: unknown) => error);
+    const failure = await loadDashboardHostAssets(API_ORIGIN).catch((error: unknown) => error);

    expect(readFileMock).toHaveBeenCalledTimes(1);
    expect(failure).toBeInstanceOf(DashboardHostAssetError);
@@ -69,10 +74,12 @@ describe("Dashboard host asset loading", () => {

  it("fails when the script is missing even though the page was read", async () => {
    readFileMock
-      .mockResolvedValueOnce("<!doctype html>")
+      .mockResolvedValueOnce(`<!doctype html>${DASHBOARD_API_ORIGIN_PLACEHOLDER}`)
      .mockRejectedValueOnce(new Error("ENOENT app.js"));

-    await expect(loadDashboardHostAssets()).rejects.toBeInstanceOf(DashboardHostAssetError);
+    await expect(loadDashboardHostAssets(API_ORIGIN)).rejects.toBeInstanceOf(
+      DashboardHostAssetError,
+    );
    expect(readFileMock).toHaveBeenCalledTimes(2);
  });

@@ -84,4 +91,41 @@ describe("Dashboard host asset loading", () => {
      expect(() => createDashboardHostAssets(html, script)).toThrow(DashboardHostAssetError);
    }
  });
+
+  it("fails startup on a page without exactly one empty API-origin element (ADR 0045)", async () => {
+    for (const html of [
+      "<!doctype html>",
+      `<!doctype html>${DASHBOARD_API_ORIGIN_PLACEHOLDER}${DASHBOARD_API_ORIGIN_PLACEHOLDER}`,
+      '<!doctype html><meta content="https://elsewhere.test" name="ekklesia-api-origin" />',
+    ]) {
+      readFileMock.mockReset();
+      readFileMock.mockResolvedValueOnce(html).mockResolvedValueOnce("export {};\n");
+      await expect(loadDashboardHostAssets(API_ORIGIN)).rejects.toBeInstanceOf(
+        DashboardHostAssetError,
+      );
+    }
+  });
+});
+
+describe("Dashboard page API origin (ADR 0045)", () => {
+  const page = `<head>${DASHBOARD_API_ORIGIN_PLACEHOLDER}</head>`;
+
+  it("writes the API's origin into the one placeholder, in either topology", () => {
+    expect(renderDashboardPage(page, "https://api.example.test")).toBe(
+      '<head><meta content="https://api.example.test" name="ekklesia-api-origin" /></head>',
+    );
+    expect(renderDashboardPage(page, "http://127.0.0.1:3000")).toBe(
+      '<head><meta content="http://127.0.0.1:3000" name="ekklesia-api-origin" /></head>',
+    );
+  });
+
+  it.each([
+    "https://api.example.test/",
+    "https://api.example.test/api",
+    'https://api.example.test"><script>',
+    "javascript:alert(1)",
+    "",
+  ])("refuses a value that is not a canonical http(s) origin: %s", (origin) => {
+    expect(() => renderDashboardPage(page, origin)).toThrow(DashboardHostAssetError);
+  });
 });
@@ -757,6 +757,35 @@ function identitySchemaSummary(): string {
  return `Core identity schema defines ${tableNames.length} ${plural(tableNames.length, "table")} (${tableNames.join(", ")}).`;
 }

+/**
+ * A heuristic for "same site" between two canonical origins, for a warning only (ADR 0045).
+ *
+ * The same hostname on another port is the same site. Otherwise the two hostnames must be siblings:
+ * identical after their first label, with that parent itself holding at least one dot
+ * (`dash.example.org` and `api.example.org`). Without the Public Suffix List this can be wrong in
+ * both directions for unusual names, which is why its result is a warning and never a failure.
+ */
+function plausiblySameSite(dashboardOrigin: string, apiOrigin: string): boolean {
+  const dashboard = new URL(dashboardOrigin).hostname;
+  const api = new URL(apiOrigin).hostname;
+  if (dashboard === api) {
+    return true;
+  }
+  // An IP address is a site of its own; two different ones never share one.
+  const isIpAddress = (hostname: string): boolean =>
+    hostname.startsWith("[") || /^[0-9]+(\.[0-9]+){3}$/u.test(hostname);
+  if (isIpAddress(dashboard) || isIpAddress(api)) {
+    return false;
+  }
+  const parent = (hostname: string): string => hostname.slice(hostname.indexOf(".") + 1);
+  return (
+    dashboard.includes(".") &&
+    api.includes(".") &&
+    parent(dashboard) === parent(api) &&
+    parent(dashboard).includes(".")
+  );
+}
+
 /**
 * Pure configuration validation only: never constructs Better Auth, never opens a database
 * connection, and never prints the configured secret, base URL, or trusted origins. Missing
@@ -769,6 +798,7 @@ function identityConfigurationCheck(
  const hasAnyValue =
    input?.secret !== undefined ||
    input?.baseUrl !== undefined ||
+    (input?.dashboardOrigin ?? "") !== "" ||
    input?.publicSignupEnabled !== undefined ||
    (input?.trustedOrigins?.length ?? 0) > 0;

@@ -783,17 +813,43 @@ function identityConfigurationCheck(
    const config = createIdentityConfig(
      {
        baseUrl: input?.baseUrl,
+        // Validated exactly as the API validates it at startup, so a Dashboard origin the API would
+        // refuse (untrusted, insecure, malformed) fails here first.
+        dashboardOrigin: input?.dashboardOrigin,
        publicSignupEnabled: input?.publicSignupEnabled,
        secret: input?.secret,
        trustedOrigins: input?.trustedOrigins,
      },
      { environment: input?.environment ?? "production" },
    );
+    const signupDetail = config.publicSignupEnabled
+      ? "Public signup is explicitly ENABLED."
+      : "Public signup is disabled (safe default).";
+    if (config.dashboardOrigin === config.baseUrl) {
+      return freezeCheck("identity.configuration", "pass", "Identity configuration valid", [
+        schemaDetail,
+        signupDetail,
+        "Topology: same-origin (the Dashboard is served from the API's origin).",
+      ]);
+    }
+    const topologyDetail = "Topology: split (the Dashboard and the API are on separate origins).";
+    if (!plausiblySameSite(config.dashboardOrigin, config.baseUrl)) {
+      return freezeCheck(
+        "identity.configuration",
+        "warning",
+        "Identity configuration valid; split origins may not share a site",
+        [
+          schemaDetail,
+          signupDetail,
+          topologyDetail,
+          "The Dashboard and API hostnames are not siblings under one parent domain. Browsers send the session cookie across split origins only within one registrable domain (ADR 0045); Doctor cannot check the Public Suffix List, so confirm it.",
+        ],
+      );
+    }
    return freezeCheck("identity.configuration", "pass", "Identity configuration valid", [
      schemaDetail,
-      config.publicSignupEnabled
-        ? "Public signup is explicitly ENABLED."
-        : "Public signup is disabled (safe default).",
+      signupDetail,
+      topologyDetail,
    ]);
  } catch (error) {
    const code =
@@ -705,6 +705,88 @@ describe("Ekklesia Doctor diagnostics", () => {
    expect(report.result).toBe("ready-with-warnings"); // PostgreSQL is still skipped in this fixture
  });

+  describe("Dashboard and API topology (ADR 0045)", () => {
+    const secret = "correct-horse-battery-staple-0123456789";
+    async function identityCheck(identity: {
+      readonly baseUrl: string;
+      readonly dashboardOrigin?: string;
+      readonly environment?: "development" | "production";
+      readonly trustedOrigins: readonly string[];
+    }) {
+      const report = await diagnoseEkklesia(
+        {
+          ...options(),
+          identityConfiguration: { environment: "production", secret, ...identity },
+        },
+        dependencies(),
+      );
+      return { check: check(report, "identity.configuration"), report };
+    }
+
+    it("reports the same-origin topology when no Dashboard origin is set", async () => {
+      const { check: identity } = await identityCheck({
+        baseUrl: "https://ekklesia.example.test",
+        trustedOrigins: ["https://ekklesia.example.test"],
+      });
+      expect(identity.status).toBe("pass");
+      expect(identity.details).toContain(
+        "Topology: same-origin (the Dashboard is served from the API's origin).",
+      );
+    });
+
+    it("reports the split topology for sibling hostnames without printing either", async () => {
+      const { check: identity, report } = await identityCheck({
+        baseUrl: "https://api.example.test",
+        dashboardOrigin: "https://dash.example.test",
+        trustedOrigins: ["https://dash.example.test"],
+      });
+      expect(identity.status).toBe("pass");
+      expect(identity.details).toContain(
+        "Topology: split (the Dashboard and the API are on separate origins).",
+      );
+      expect(JSON.stringify(report)).not.toContain("dash.example.test");
+      expect(JSON.stringify(report)).not.toContain("api.example.test");
+    });
+
+    it.each([
+      ["different registrable domains", "https://dash.example.test", "https://api.example.org"],
+      ["two IP addresses", "https://10.0.0.2", "https://10.0.0.1"],
+      ["a parent that is only a top-level domain", "https://dash.test", "https://api.test"],
+    ])("warns, without failing, when split hostnames may not share a site: %s", async (_case, dashboardOrigin, baseUrl) => {
+      const { check: identity, report } = await identityCheck({
+        baseUrl,
+        dashboardOrigin,
+        trustedOrigins: [dashboardOrigin],
+      });
+      expect(identity.status).toBe("warning");
+      expect(identity.details.join("\n")).toContain("not siblings under one parent domain");
+      expect(doctorExitCode(report)).toBe(0);
+    });
+
+    it("treats another port on the same host as the same site (split development)", async () => {
+      const { check: identity } = await identityCheck({
+        baseUrl: "http://localhost:3000",
+        dashboardOrigin: "http://localhost:5173",
+        environment: "development",
+        trustedOrigins: ["http://localhost:5173"],
+      });
+      expect(identity.status).toBe("pass");
+    });
+
+    it("fails, as the API's startup would, for a Dashboard origin the API does not trust", async () => {
+      const { check: identity, report } = await identityCheck({
+        baseUrl: "https://api.example.test",
+        dashboardOrigin: "https://dash.example.test",
+        trustedOrigins: ["https://other.example.test"],
+      });
+      expect(identity.status).toBe("failure");
+      expect(identity.details.some((detail) => detail.includes("DASHBOARD_ORIGIN_UNTRUSTED"))).toBe(
+        true,
+      );
+      expect(doctorExitCode(report)).toBe(1);
+    });
+  });
+
  it("fails identity configuration for an invalid secret without leaking it", async () => {
    const hostileSecret = "s3cr3t-do-not-log";
    const report = await diagnoseEkklesia(
@@ -0,0 +1,109 @@
+# Ekklesia reference proxy configuration for the split topology (ADR 0045): the Dashboard and the API
+# on separate hostnames of one site, for example dash.example.org and api.example.org. For the
+# default same-origin topology use Caddyfile.example instead. Copy this file to deploy/Caddyfile.
+#
+# Hostnames, the ACME contact, and the tunnel connector's address come from the proxy service's
+# environment (deploy/.env): EKKLESIA_DASHBOARD_HOSTNAME is the Dashboard's, EKKLESIA_HOSTNAME the
+# API's (which also serves the display host), EKKLESIA_STORAGE_HOSTNAME the storage origin's. Only
+# the two site blocks below differ from Caddyfile.example.
+{
+	# ACME account contact. Certificates use the HTTP-01 challenge on port 80 by default, which needs
+	# all three hostnames to resolve publicly to this host with 80 and 443 reachable.
+	email {$EKKLESIA_ACME_EMAIL}
+
+	# DNS-01, for an installation that keeps Ekklesia off the public Internet, serves only a LAN
+	# (split-horizon DNS), or is reachable only through Cloudflare Tunnel. Cloudflare terminates TLS at
+	# its edge, so HTTP-01 cannot reach this proxy through a tunnel.
+	#
+	# DNS-01 needs a DNS provider module that the stock Caddy image does not contain. Build an image
+	# with it (for example `xcaddy build --with github.com/caddy-dns/cloudflare`), pin that image by
+	# digest in your own overlay, give it CLOUDFLARE_API_TOKEN through a root-owned env file, then
+	# enable:
+	#
+	# acme_dns cloudflare {env.CLOUDFLARE_API_TOKEN}
+
+	servers {
+		# A client-address header is honored only from the tunnel connector's fixed address
+		# (compose.tunnel.yaml). From every other peer, the client address is the TCP peer itself and
+		# any such header is ignored. Without a tunnel, nothing has this address.
+		trusted_proxies static {$EKKLESIA_TUNNEL_ADDRESS}/32
+		client_ip_headers CF-Connecting-IP
+		trusted_proxies_strict
+	}
+
+	# Access logs are off unless enabled. If you enable them, keep request headers out: they carry
+	# cookies and forwarding chains (docs/development/security.md, launch checklist item 7).
+}
+
+# What every request to the API carries upstream: exactly one forwarding header, overwritten with
+# the client address Caddy resolved, and none of the headers a caller could use to choose its own.
+(ekklesia_forwarding) {
+	header_up X-Forwarded-For {client_ip}
+	header_up -CF-Connecting-IP
+	header_up -X-Real-IP
+	header_up -Forwarded
+	header_up -True-Client-IP
+}
+
+# The Dashboard: its page and its one script, nothing else. Emailed verification and reset links land
+# on `/` with a query. `/api/*` is refused here on purpose, so the session cookie has exactly one
+# home, the API hostname, and the Dashboard can never fall back to a same-origin API.
+{$EKKLESIA_DASHBOARD_HOSTNAME} {
+	@dashboard path / /assets/ekklesia-dashboard/*
+
+	handle @dashboard {
+		reverse_proxy api:3000 {
+			import ekklesia_forwarding
+		}
+	}
+
+	handle {
+		respond 404
+	}
+}
+
+# The API, and the display host on the API's own origin: a screen's pages, service worker, device
+# cookies, and requests are all same-origin (ADR 0045). Nothing is served at `/`.
+{$EKKLESIA_HOSTNAME} {
+	@api path /api/* /display/* /assets/ekklesia-display/*
+
+	# Module realtime is Server-Sent Events: flush every event immediately.
+	@realtime path /api/v1/module-realtime/*
+
+	handle @realtime {
+		reverse_proxy api:3000 {
+			import ekklesia_forwarding
+			flush_interval -1
+		}
+	}
+
+	handle @api {
+		# Request bodies stream through unbuffered and unlimited here; the API enforces the platform's
+		# ceilings itself (8 KiB for authentication, up to 32 MiB for a streamed module route).
+		reverse_proxy api:3000 {
+			import ekklesia_forwarding
+		}
+	}
+
+	handle {
+		respond 404
+	}
+}
+
+# Browsers fetch signed object URLs here (S3_DELIVERY_ENDPOINT, ADR 0031).
+{$EKKLESIA_STORAGE_HOSTNAME} {
+	reverse_proxy https://object-storage:8443 {
+		# An S3 signature covers the Host header: pass the original through unchanged, or every signed
+		# URL fails verification.
+		header_up Host {host}
+		header_up -CF-Connecting-IP
+		header_up -X-Real-IP
+		header_up -Forwarded
+		header_up -True-Client-IP
+		transport http {
+			# object-storage presents a certificate from the installation-private CA.
+			tls_trust_pool file /etc/caddy/ekklesia-ca.crt
+			tls_server_name object-storage
+		}
+	}
+}
@@ -10,7 +10,8 @@ specific to one organization.
 | [`compose.yaml`](compose.yaml) | The base: `api`, `postgres`, `object-storage`, and the operator-only `migrate`. Publishes no port. |
 | [`compose.proxy.yaml`](compose.proxy.yaml) | Overlay: Caddy as the TLS proxy, the only service with published ports. |
 | [`compose.tunnel.yaml`](compose.tunnel.yaml) | Overlay on top of the proxy: a Cloudflare Tunnel connector. |
-| [`Caddyfile.example`](Caddyfile.example) | The proxy's configuration; copy to `Caddyfile`. |
+| [`Caddyfile.example`](Caddyfile.example) | The proxy's configuration for the default same-origin topology; copy to `Caddyfile`. |
+| [`Caddyfile.split.example`](Caddyfile.split.example) | The proxy's configuration when the Dashboard and the API have separate hostnames ([Split Dashboard and API origins](#split-dashboard-and-api-origins)); copy to `Caddyfile` instead. |
 | [`postgres/pg_hba.conf`](postgres/pg_hba.conf) | PostgreSQL client authentication: TLS only, SCRAM passwords. |
 | [`env/`](env/) | Commented examples of every env file. No values. |
 | [`scripts/init-tls.sh`](scripts/init-tls.sh) | Creates the installation-private CA and the `postgres` and `object-storage` server certificates. |
@@ -142,6 +143,41 @@ image, because it was not built for the newer schema.
 Slice 6 adds the scheduled backup job and the restore procedure (ADR 0044, Backups). Until then,
 take a `pg_dump` and a copy of every bucket before each upgrade by hand.

+### Split Dashboard and API origins
+
+By default one hostname serves the Dashboard (`/`), the API (`/api/*`), and displays (`/display/*`).
+An installation may instead give the Dashboard its own hostname, for example `dash.example.org`
+beside `api.example.org` ([ADR 0045](../docs/architecture/decisions/0045-split-dashboard-and-api-origins.md)).
+The same image serves both; only configuration differs.
+
+| Hostname | Serves | Refuses (`404`) |
+| --- | --- | --- |
+| Dashboard (`EKKLESIA_DASHBOARD_HOSTNAME`) | `/` and `/assets/ekklesia-dashboard/*` | everything else, including `/api/*` |
+| API (`EKKLESIA_HOSTNAME`) | `/api/*`, `/display/*`, `/assets/ekklesia-display/*` | everything else, including `/` |
+| Storage (`EKKLESIA_STORAGE_HOSTNAME`) | signed object URLs, unchanged | |
+
+Displays live on the API's hostname (`https://api.example.org/display/<module>`), because their
+device cookies are bound to it and their offline cache keeps only same-origin responses. That
+hostname is what every screen and paired device depends on: choose it once.
+
+To run split:
+
+1. Copy `Caddyfile.split.example` to `Caddyfile` instead of `Caddyfile.example`.
+2. In `deploy/.env`, set `EKKLESIA_HOSTNAME` to the API's hostname and `EKKLESIA_DASHBOARD_HOSTNAME`
+   to the Dashboard's.
+3. In `ekklesia.env`, set `EKKLESIA_IDENTITY_BASE_URL` to `https://` and the API's hostname,
+   `EKKLESIA_DASHBOARD_ORIGIN` to `https://` and the Dashboard's, and
+   `EKKLESIA_IDENTITY_TRUSTED_ORIGINS` to the Dashboard's origin. The API always trusts its own
+   origin, so it need not be listed.
+
+**Both hostnames must belong to one registrable domain** (`dash.example.org` and `api.example.org`,
+not `dash.example.org` and `api.example.net`). The session cookie stays host-only on the API's
+hostname; browsers send it from the Dashboard only between origins of the same site. Doctor reports
+the topology and warns when the two hostnames are not siblings.
+
+The Dashboard learns the API's origin at run time: the API writes its identity base URL into the page
+it serves (`<meta name="ekklesia-api-origin">`). Nothing about the topology is built into the image.
+
 ### Behind an existing reverse proxy

 Run the base alone and attach `api` and `object-storage` to your proxy's network with an overlay of
@@ -203,8 +239,9 @@ dashboard. No Cloudflare API is called from here.
   the Ekklesia hostname. Service type **HTTPS**, URL `proxy:443`.
 3. Under that hostname's **TLS** settings, set **Origin Server Name** to the same Ekklesia hostname,
   and leave **No TLS Verify** off. The connector then verifies the proxy's certificate for that name.
-4. Add a second public hostname for the storage hostname, the same way, with its own origin server
-   name.
+4. Add a public hostname for the storage hostname, the same way, with its own origin server name.
+   In the [split topology](#split-dashboard-and-api-origins), add one for the Dashboard's hostname
+   too: three in all, each with its own origin server name.
 5. Start with all three files. The proxy honors `CF-Connecting-IP` only from the connector's fixed
   address. From any other peer it is stripped.

@@ -232,7 +269,7 @@ deployment:

 | # | Item | Where it is met |
 | --- | --- | --- |
-| 1 | The proxy forwards the Dashboard and `/api` on the intended origin | `Caddyfile.example` routes `/`, `/api/*`, `/display/*`, `/assets/*` on one hostname to `api`; the API serves the Dashboard itself. |
+| 1 | The proxy forwards the Dashboard and `/api` on the intended origin | `Caddyfile.example` routes `/`, `/api/*`, `/display/*`, `/assets/*` on one hostname to `api`; the API serves the Dashboard itself. In the split topology, `Caddyfile.split.example` gives each hostname exactly its own paths and the exact trusted-origin CORS of ADR 0045 covers the rest. |
 | 2 | The origin port is unreachable from the Internet | The base publishes no port; only `proxy` publishes 80 and 443. |
 | 3 | The origin port is unreachable from untrusted networks | `api` is reachable only on Docker networks; `EKKLESIA_PUBLISH_ADDRESS` limits the proxy to one interface. Firewall the host itself. |
 | 4 | The proxy overwrites the trusted client-IP header | `header_up X-Forwarded-For {client_ip}` in `Caddyfile.example`. |
@@ -258,7 +295,15 @@ deployment:
    wrong host name;
  - Doctor.

-  CI runs it on every change.
+  `EKKLESIA_SMOKE_TOPOLOGY=split` runs the [split topology](#split-dashboard-and-api-origins)
+  instead: an image with the repository's module template installed as a test-only module, every
+  hostname's served and refused paths, exact CORS for the Dashboard's origin and none for others,
+  and then a real headless Chromium (pinned by digest, driven over the DevTools protocol) that signs
+  in on the Dashboard's hostname, checks the session cookie lives only on the API's, mounts the
+  module's UI from the API's origin and sees its own credentialed requests succeed, mounts its display
+  on the API's hostname with its service worker, and signs out.
+
+  CI runs both topologies on every change.
 - **Test-only:** the smoke test runs Caddy with its internal CA (`local_certs`), because a test run
  has no public hostname. Never use it in an installation; `Caddyfile.example` does not contain it.

@@ -35,6 +35,10 @@ services:
    environment:
      EKKLESIA_HOSTNAME: ${EKKLESIA_HOSTNAME:?EKKLESIA_HOSTNAME is required, for example ekklesia.example.org}
      EKKLESIA_STORAGE_HOSTNAME: ${EKKLESIA_STORAGE_HOSTNAME:?EKKLESIA_STORAGE_HOSTNAME is required, for example storage.ekklesia.example.org}
+      # The split topology only (ADR 0045, Caddyfile.split.example), where EKKLESIA_HOSTNAME is the
+      # API's hostname and this is the Dashboard's. Caddyfile.example ignores it; the split
+      # configuration refuses to start without it.
+      EKKLESIA_DASHBOARD_HOSTNAME: ${EKKLESIA_DASHBOARD_HOSTNAME:-}
      EKKLESIA_ACME_EMAIL: ${EKKLESIA_ACME_EMAIL:?EKKLESIA_ACME_EMAIL is required for ACME account notices}
      EKKLESIA_TUNNEL_ADDRESS: ${EKKLESIA_TUNNEL_ADDRESS:-10.249.250.253}
    volumes:
@@ -10,9 +10,14 @@ EKKLESIA_ENV_DIR=/etc/ekklesia
 EKKLESIA_TLS_DIR=/etc/ekklesia/tls

 # --- compose.proxy.yaml ---------------------------------------------------------------------------
-# The Ekklesia hostname (Dashboard, API, displays) and the storage hostname (signed object URLs).
+# The Ekklesia hostname and the storage hostname (signed object URLs). In the default same-origin
+# topology (Caddyfile.example) EKKLESIA_HOSTNAME serves the Dashboard, the API, and displays.
 EKKLESIA_HOSTNAME=
 EKKLESIA_STORAGE_HOSTNAME=
+# The split topology only (ADR 0045, Caddyfile.split.example): the Dashboard's own hostname, while
+# EKKLESIA_HOSTNAME is the API's and the displays'. Both must share one registrable domain, for
+# example dash.example.org and api.example.org. Leave empty for the same-origin topology.
+EKKLESIA_DASHBOARD_HOSTNAME=
 # Contact address for the ACME account (certificate expiry notices).
 EKKLESIA_ACME_EMAIL=
 # EKKLESIA_CADDYFILE=./Caddyfile
@@ -23,15 +23,19 @@ EKKLESIA_DATABASE_TLS_MODE=verify-full
 # scripts/init-tls.sh prints this exact line. It is the only CA the database connection trusts.
 EKKLESIA_DATABASE_CA=

-# --- Identity (ADR 0011, ADR 0018, ADR 0034) ----------------------------------------------------
-# The public https origin of the Ekklesia hostname, with no path. Production rejects http and
-# loopback origins.
+# --- Identity (ADR 0011, ADR 0018, ADR 0034, ADR 0045) -----------------------------------------
+# The public https origin of the API, with no path: the Ekklesia hostname in the same-origin
+# topology, the API's hostname in the split one. Production rejects http and loopback origins.
 EKKLESIA_IDENTITY_BASE_URL=
-# Comma-separated exact origins allowed to make credentialed requests. Normally just the base URL.
+# Comma-separated exact origins allowed to make credentialed requests. The API's own origin is
+# always trusted and need not be listed. Same-origin topology: the base URL. Split topology: the
+# Dashboard's origin.
 EKKLESIA_IDENTITY_TRUSTED_ORIGINS=
 # At least 32 random characters. Rotating it signs every user out.
 EKKLESIA_IDENTITY_SECRET=
-# Leave unset: the Dashboard is served from the base URL (ADR 0044).
+# Same-origin topology: leave unset; the Dashboard is served from the base URL (ADR 0044).
+# Split topology: the Dashboard's https origin, which must also be in the trusted origins. Emailed
+# verification and reset links land here (ADR 0045).
 # EKKLESIA_DASHBOARD_ORIGIN=
 # Production refuses public sign-up. Leave unset.
 # EKKLESIA_PUBLIC_SIGNUP_ENABLED=
@@ -1,6 +1,6 @@
 # 0045: The Dashboard and the API may live on separate origins

- Status: Proposed
+- Status: Accepted
 - Date: 2026-10-03
 - Amends: [0034](0034-host-owned-browser-authentication.md)
 - Extends: [0044](0044-self-hosted-reference-deployment.md)
@@ -53,5 +53,5 @@ ADRs capture durable choices that affect more than one package or phase.
 - [0042: Explicit, bounded streaming request bodies](0042-bounded-streaming-request-bodies.md) — Accepted
 - [0043: The display caches its shell and declared code, and nothing else](0043-display-offline-code-fallback.md) — Accepted
 - [0044: Ekklesia ships one self-hosted reference deployment, composed from pinned sources](0044-self-hosted-reference-deployment.md) — Accepted
- [0045: The Dashboard and the API may live on separate origins](0045-split-dashboard-and-api-origins.md) — Proposed
+- [0045: The Dashboard and the API may live on separate origins](0045-split-dashboard-and-api-origins.md) — Accepted
 - [0046: Ekklesia's branding is never forced on an installation](0046-installation-owned-branding.md) — Proposed
@@ -62,7 +62,7 @@ No real values are shown here — configure per environment and never commit the
 | `EKKLESIA_API_PORT` | Optional. Listen port, `0`–`65535` (`0` requests an OS-assigned port). Defaults to `3000`. |
 | `EKKLESIA_IDENTITY_SECRET` | At least 32 characters, high entropy (for example `openssl rand -base64 32`). Same requirement as Phase 4A. |
 | `EKKLESIA_IDENTITY_BASE_URL` | Exactly one canonical `http`/`https` origin — scheme, host, and non-default port only, with no path, trailing slash, query, fragment, credentials, or explicit default port. `https` is required in production; loopback and unspecified hosts are rejected in production. |
-| `EKKLESIA_IDENTITY_TRUSTED_ORIGINS` | Comma-separated list of canonical origins, validated identically to the base URL (no wildcards). Used for both Better Auth's own CSRF/origin checks and the API's CORS policy — there is only one trusted-origin list. |
+| `EKKLESIA_IDENTITY_TRUSTED_ORIGINS` | Comma-separated list of canonical origins, validated identically to the base URL (no wildcards). Used for both Better Auth's own CSRF/origin checks and the API's CORS policy — there is only one trusted-origin list. The base URL's own origin is always trusted as well and need not be listed ([ADR 0045](../architecture/decisions/0045-split-dashboard-and-api-origins.md)). |
 | `EKKLESIA_PUBLIC_SIGNUP_ENABLED` | Optional, **development/test only**. Exactly `"true"` enables public sign-up when `NODE_ENV=development`; defaults to disabled, and a production configuration rejects `"true"` outright. Omitted, misspelled, or any other value never enables it. See [Public registration policy](#public-registration-policy). |
 | `EKKLESIA_CLIENT_ADDRESS_MODE` | Optional. `"direct"` (default when unset) or `"trusted-proxy"`. See [Client-address resolution](#client-address-resolution). |
 | `EKKLESIA_CLIENT_ADDRESS_HEADER` | Required only when `EKKLESIA_CLIENT_ADDRESS_MODE=trusted-proxy`. The one forwarded-header name the reverse proxy is trusted to set (for example `x-forwarded-for`). |
@@ -77,7 +77,7 @@ No real values are shown here — configure per environment and never commit the
 | `/api/auth/{get-session,list-sessions,update-session,change-password}` | Deliberately unavailable | Token-bearing native session inspection/mutation endpoints are denied at the Ekklesia HTTP boundary with sanitized `404 {"code":"NOT_FOUND"}`. Use `/api/v1/principal`; no browser session-list/update or password-management contract exists. |
 | `POST\|GET /api/auth/*` | Better Auth (mounted directly) | Supported Better Auth routes retain their native shapes except for the successful email sign-in normalization above. The four denied paths above never reach Better Auth. See [Better Auth's email/password docs](https://www.better-auth.com/docs/authentication/email-password) for supported endpoints such as `/sign-up/email` and `/sign-out`. |
 | `GET /api/v1/principal` | Ekklesia | Returns the minimal `EkklesiaPrincipal` contract as JSON. `Cache-Control: no-store`. |
-| `GET /` | Ekklesia | The built Dashboard page (`surfaces/shell`'s `index.html`), served from the same origin as `/api`. `no-cache` with a strong `ETag`; framing refused. See [Dashboard host](#dashboard-host). |
+| `GET /` | Ekklesia | The built Dashboard page (`surfaces/shell`'s `index.html`), with the API's origin written into it. Served from the API's origin, or from the Dashboard's own hostname through the proxy in the split topology. `no-cache` with a strong `ETag`; framing refused. See [Dashboard host](#dashboard-host). |
 | `GET /assets/ekklesia-dashboard/app.js` | Ekklesia | The Dashboard's one script. `no-cache` with a strong `ETag`; its source map is never served. See [Dashboard host](#dashboard-host). |
 | `GET /api/v1/health/live` | Ekklesia | Unauthenticated liveness: fixed `200 {"status":"live"}` whenever the process is serving HTTP. `Cache-Control: no-store`; GET only. See [Health](#health). |
 | `GET /api/v1/health/ready` | Ekklesia | Unauthenticated readiness: fixed `200 {"status":"ready"}` only when a bounded database ping succeeds and module startup completed, otherwise `503 {"code":"NOT_READY"}`. `Cache-Control: no-store`; GET only. See [Health](#health). |
@@ -140,19 +140,29 @@ role, permission, membership, or volunteer data.

 ## Dashboard host

-`apps/api` serves the built Dashboard itself, from the same origin as `/api`
-([ADR 0044](../architecture/decisions/0044-self-hosted-reference-deployment.md)). That keeps the
-identity system's default same-origin shape: `EKKLESIA_DASHBOARD_ORIGIN` stays unset, the session
-cookie stays host-only, and no second static server or proxy file root is needed. It works exactly
-like the display host:
+`apps/api` serves the built Dashboard itself
+([ADR 0044](../architecture/decisions/0044-self-hosted-reference-deployment.md)). In the default
+same-origin topology it does so from the same origin as `/api`: `EKKLESIA_DASHBOARD_ORIGIN` stays
+unset, the session cookie stays host-only, and no second static server or proxy file root is
+needed. In the split topology
+([ADR 0045](../architecture/decisions/0045-split-dashboard-and-api-origins.md)) the proxy forwards
+the Dashboard's own hostname to the same two routes; the API does not inspect `Host`. It works
+exactly like the display host:

 - **A closed set of files, read once at startup.** `@ekklesia/shell/dashboard-assets` exports the
  exact URLs of two built files, `dist/browser/index.html` and
  `dist/browser/assets/ekklesia-dashboard/app.js`. `startApi()` reads both before importing any
  module code or binding the listener, and keeps one frozen snapshot of their text with a SHA-256
  strong `ETag` for each.
- **A missing build fails startup.** An absent, unreadable, or empty file stops `startApi()` with a
-  fixed `DashboardHostAssetError` (`DASHBOARD_HOST_ASSET_UNAVAILABLE`), after closing the resources
+- **The API's origin is written in at startup.** The built page carries one empty
+  `<meta content="" name="ekklesia-api-origin" />`. Before computing the page's `ETag`, `startApi()`
+  fills it with the identity base URL's origin, which is where `/api` lives in either topology. The
+  shell reads it before rendering, uses the page's own origin when it is empty, and fails closed,
+  making no request, when it is anything but a canonical `http(s)` origin. Nothing about the topology
+  is built into the bundle.
+- **A missing or incompatible build fails startup.** An absent, unreadable, or empty file, or a page
+  without exactly one empty API-origin element, stops `startApi()` with a fixed
+  `DashboardHostAssetError` (`DASHBOARD_HOST_ASSET_UNAVAILABLE`), after closing the resources
  already opened. It never carries a path or the filesystem error. Build the shell first;
  `pnpm api:start` already runs the full build.
 - **Two exact routes, never a directory.** `GET /` answers the page and
@@ -195,7 +205,9 @@ strips that token from the address bar before it renders anything.

 **Development.** `pnpm --filter @ekklesia/shell dev` serves `dist/browser` at the same absolute
 paths, because the build emits the script at `assets/ekklesia-dashboard/app.js`. `index.html` names
-that path absolutely, so the page never depends on the URL that served it.
+that path absolutely, so the page never depends on the URL that served it. For a split-origin
+development API, set `EKKLESIA_API_BASE_URL` for the development server: it writes that origin into
+its copy of the page exactly as the API does in production. A production build ignores it.

 ## Dashboard browser authentication

@@ -340,7 +352,10 @@ real server: 7 characters rejected, 8 accepted, 128 accepted, 129 rejected.
 ## Origin, CORS, and cookies

 The API reuses the same `EKKLESIA_IDENTITY_TRUSTED_ORIGINS` list for both CORS and Better Auth's
-own origin/CSRF checks — there is no second, competing configuration. CORS reflects a request's
+own origin/CSRF checks — there is no second, competing configuration. Like Better Auth, the API also
+trusts the identity base URL's own origin without it being listed, so a page the API itself serves
+(the display host, or the Dashboard in the same-origin topology) passes the API's origin checks
+([ADR 0045](../architecture/decisions/0045-split-dashboard-and-api-origins.md)). CORS reflects a request's
 `Origin` header back only when it exactly matches a configured trusted origin (never a wildcard,
 since `Access-Control-Allow-Origin: *` cannot be combined with `Access-Control-Allow-Credentials:
 true`); a disallowed origin never receives the header at all, though the request itself may still
@@ -374,10 +389,18 @@ Cookies keep Better Auth's defaults: `HttpOnly` always, `SameSite=Lax` always, `
 configured base URL is `https://`. Cross-subdomain cookies are not enabled and no cookie `Domain`
 attribute is set, so every cookie is host-only. See [Client-address resolution](#client-address-resolution)
 for how (and whether) a reverse proxy's forwarded headers are trusted — a separate concern from
-CORS/CSRF above. The Dashboard does not broaden this policy: same-origin `/api` proxying is the
-simplest production topology, while a deliberately split browser/API origin must use the exact
-trusted-origin allowlist and credentialed CORS. Sibling subdomains do not implicitly share the
-cookie. No production Dashboard hostname or proxy deployment exists in this repository.
+CORS/CSRF above. The Dashboard does not broaden this policy. In the split topology
+([ADR 0045](../architecture/decisions/0045-split-dashboard-and-api-origins.md)) the cookie stays
+host-only on the API's hostname, and the Dashboard on a sibling hostname reaches the API with
+credentialed CORS; browsers send the cookie because the two hostnames are origins of one site, which
+is therefore a requirement of that topology. The reference deployment provides both topologies
+([`deploy/README.md`](../../deploy/README.md#split-dashboard-and-api-origins)).
+
+**CORS request and response headers are deliberately narrow, and part of the module UI contract.**
+Beyond the CORS-safelisted request headers, only `Content-Type` is allowed, and no response header is
+exposed beyond the safelisted ones. A module UI's `api.request` inherits this policy, so portable
+module UI code sends only safelisted headers plus `Content-Type` and reads only safelisted response
+headers. That keeps one module artifact working in either topology.

 ## Logging

@@ -1613,7 +1636,7 @@ Cookie: better-auth.session_token=<redacted, now revoked>
 See the repository root [README](../../README.md#current-status) and
 [platform architecture](../architecture/platform-architecture.md#current-implementation-status)
 for what has landed across every phase and what remains. Surface work is underway; the API now
-serves the built Dashboard ([Dashboard host](#dashboard-host)), while its production proxy, TLS,
-full Content-Security-Policy, enrollment/recovery, display device identity, and public Website
+serves the built Dashboard ([Dashboard host](#dashboard-host)) in either topology, while the full
+Content-Security-Policy, enrollment/recovery, display device identity, and public Website
 routing remain separate work. This document tracks `apps/api`'s own HTTP, module-runtime, and
 database-composition contracts as they evolve.
@@ -153,7 +153,8 @@ enforced by `requirePermission` regardless; the test suite proves it by having a
 "denied" call its API anyway and still receive `403`.

 **The host executes trusted module code in its own page and does not pretend otherwise.** The loader
-performs a same-origin dynamic `import()` — no `eval`, no `new Function`, no `blob:` URL — and the
+performs a dynamic `import()` from the API's origin (the page's own in the same-origin topology, the
+API hostname in the split one, ADR 0045) — no `eval`, no `new Function`, no `blob:` URL — and the
 shell owns the container, the loading state, and every error, so a failing module costs its own panel
 rather than the shell. None of that is containment: once imported, a module UI is ordinary same-realm
 JavaScript, exactly as described above.
@@ -493,7 +494,9 @@ outstanding.
   split origin is covered by the exact trusted-origin/CORS configuration. `apps/api` serves the
   built Dashboard itself at `/` ([API § Dashboard host](api.md#dashboard-host)), and the
   reference deployment's proxy routes it ([deploy/README.md](../../deploy/README.md#launch-checklist)
-   maps every item here to its configuration).
+   maps every item here to its configuration). A split installation (ADR 0045) puts its Dashboard
+   and API hostnames on one registrable domain and uses `Caddyfile.split.example`, which refuses
+   `/api/*` on the Dashboard's hostname so the session cookie has exactly one home.
 2. The origin port is unreachable from the public Internet.
 3. The origin port is also unreachable from any untrusted network/VLAN — only the intended private
   proxy path connects. Security must not depend on an unpublished DNS name or origin IP.
@@ -125,6 +125,11 @@ export interface ModuleUiDisplayLocation {
 *
 * A host is responsible for credentials, base URL, and any platform headers. A module UI neither
 * supplies nor sees a session token.
+ *
+ * The module's API may be on another origin than the page (Ekklesia's split topology, ADR 0045), so
+ * a portable module UI keeps to what cross-origin requests always allow: CORS-safelisted request
+ * headers plus `Content-Type`, and only CORS-safelisted response headers read back. Anything more
+ * works under one host topology and fails under another.
 */
 export interface ModuleUiApiClient {
  /**
@@ -0,0 +1,287 @@
+// Real-browser assertions for scripts/smoke-deploy.sh in the split topology (ADR 0045). Runs inside a
+// disposable container on the deployment's `edge` network and drives a headless Chromium, itself a
+// disposable container on the same network, over the Chrome DevTools Protocol, with Node.js's own
+// fetch and WebSocket and no other dependency.
+//
+//   node deploy-smoke-browser.mjs
+//
+// What only a browser can prove: that a person signing in on the Dashboard's hostname gets a session
+// cookie on the API's hostname alone, that the Dashboard then imports a module's UI from the API's
+// origin and the module's credentialed requests succeed under CORS, that the module's display page
+// mounts on the API's origin with that same session, and that sign-out ends it. Output is one line
+// per check; nothing printed carries a credential, cookie value, or response body.
+
+function required(name) {
+  const value = process.env[name];
+  if (!value) {
+    throw new Error(`${name} is required.`);
+  }
+  return value;
+}
+
+const apiOrigin = `https://${required("SMOKE_HOSTNAME")}`;
+const dashboardOrigin = `https://${required("SMOKE_DASHBOARD_HOSTNAME")}`;
+const apiHostname = new URL(apiOrigin).hostname;
+const devtools = required("SMOKE_CDP_ADDRESS");
+const timeoutMs = 30_000;
+
+let failures = 0;
+function check(condition, description) {
+  console.log(`${condition ? "ok  " : "FAIL"} ${description}`);
+  if (!condition) {
+    failures += 1;
+  }
+}
+
+/** The smallest Chrome DevTools Protocol client: numbered commands, flat sessions, and events. */
+async function connect() {
+  // The browser container was started moments ago; give it time to listen.
+  // One overall deadline, with every attempt bounded, so a browser that never comes up fails the
+  // run in seconds rather than waiting out TCP timeouts.
+  const deadline = Date.now() + 30_000;
+  let version;
+  while (version === undefined) {
+    try {
+      const response = await fetch(`http://${devtools}/json/version`, {
+        signal: AbortSignal.timeout(2_000),
+      });
+      version = await response.json();
+    } catch {
+      if (Date.now() > deadline) {
+        throw new Error("The headless browser never answered.");
+      }
+      await new Promise((resolve) => setTimeout(resolve, 500));
+    }
+  }
+  // Chromium names its WebSocket after the Host it was asked on; ask on the same address.
+  const socketUrl = version.webSocketDebuggerUrl.replace(/^ws:\/\/[^/]+/u, `ws://${devtools}`);
+  const socket = new WebSocket(socketUrl);
+  await new Promise((resolve, reject) => {
+    socket.addEventListener("open", resolve, { once: true });
+    socket.addEventListener("error", () => reject(new Error("DevTools connection failed.")), {
+      once: true,
+    });
+  });
+  let nextId = 1;
+  const pending = new Map();
+  const listeners = [];
+  socket.addEventListener("message", (event) => {
+    const message = JSON.parse(String(event.data));
+    if (message.id !== undefined) {
+      const waiter = pending.get(message.id);
+      pending.delete(message.id);
+      if (message.error) {
+        waiter?.reject(new Error(`DevTools ${waiter.method} failed.`));
+      } else {
+        waiter?.resolve(message.result);
+      }
+      return;
+    }
+    for (const listener of listeners) {
+      listener(message);
+    }
+  });
+  return {
+    close: () => socket.close(),
+    on: (listener) => listeners.push(listener),
+    send(method, params = {}, sessionId = undefined) {
+      const id = nextId;
+      nextId += 1;
+      socket.send(JSON.stringify({ id, method, params, ...(sessionId ? { sessionId } : {}) }));
+      return new Promise((resolve, reject) => pending.set(id, { method, reject, resolve }));
+    },
+  };
+}
+
+const cdp = await connect();
+const { targetId } = await cdp.send("Target.createTarget", { url: "about:blank" });
+const { sessionId } = await cdp.send("Target.attachToTarget", { flatten: true, targetId });
+const send = (method, params) => cdp.send(method, params, sessionId);
+
+/** Every response and failure the page sees, for the API's origin. A CORS refusal is a
+ * `loadingFailed` here, never a response. */
+const responses = [];
+const failed = [];
+cdp.on((message) => {
+  if (message.sessionId !== sessionId) {
+    return;
+  }
+  if (message.method === "Network.responseReceived") {
+    const { response, type } = message.params;
+    responses.push({ status: response.status, type, url: response.url });
+  } else if (message.method === "Network.loadingFailed") {
+    failed.push(message.params);
+  }
+});
+await send("Network.enable");
+await send("Page.enable");
+await send("Runtime.enable");
+// A desktop-sized window: a module may reasonably decline to render its management UI on a small one.
+await send("Emulation.setDeviceMetricsOverride", {
+  deviceScaleFactor: 1,
+  height: 1080,
+  mobile: false,
+  width: 1920,
+});
+
+async function evaluate(expression) {
+  const result = await send("Runtime.evaluate", {
+    awaitPromise: true,
+    expression,
+    returnByValue: true,
+  });
+  if (result.exceptionDetails) {
+    throw new Error("A page expression threw.");
+  }
+  return result.result.value;
+}
+
+async function waitFor(expression, description) {
+  const deadline = Date.now() + timeoutMs;
+  while (Date.now() < deadline) {
+    if (await evaluate(`Boolean(${expression})`).catch(() => false)) {
+      return true;
+    }
+    await new Promise((resolve) => setTimeout(resolve, 250));
+  }
+  console.log(`FAIL timed out waiting for ${description}`);
+  failures += 1;
+  return false;
+}
+
+async function navigate(url) {
+  await send("Page.navigate", { url });
+}
+
+const selector = (testId) => `document.querySelector('[data-testid="${testId}"]')`;
+
+async function cookiesFor(origin) {
+  const { cookies } = await send("Network.getCookies", { urls: [`${origin}/`] });
+  return cookies;
+}
+
+// --- Sign in on the Dashboard's hostname -------------------------------------------------------
+await navigate(`${dashboardOrigin}/`);
+await waitFor(selector("login-email"), "the sign-in form on the Dashboard hostname");
+await evaluate(`(() => {
+  // React tracks input values through the native setter; assigning .value alone is invisible to it.
+  const setValue = (element, value) => {
+    Object.getOwnPropertyDescriptor(HTMLInputElement.prototype, "value").set.call(element, value);
+    element.dispatchEvent(new Event("input", { bubbles: true }));
+  };
+  setValue(${selector("login-email")}, ${JSON.stringify(required("SMOKE_OWNER_EMAIL"))});
+  setValue(${selector("login-password")}, ${JSON.stringify(required("SMOKE_OWNER_PASSWORD"))});
+  ${selector("login-email")}.form.requestSubmit();
+})()`);
+check(
+  await waitFor(selector("host-shell"), "the signed-in Dashboard"),
+  "a person signs in through the real form on the Dashboard hostname",
+);
+
+const apiCookies = await cookiesFor(apiOrigin);
+const dashboardCookies = await cookiesFor(dashboardOrigin);
+check(
+  apiCookies.some((cookie) => cookie.httpOnly && cookie.secure && cookie.domain === apiHostname) &&
+    dashboardCookies.length === 0,
+  "the session cookie is host-only on the API hostname, and the Dashboard hostname holds none",
+);
+
+// --- A module UI, imported from the API's origin -------------------------------------------------
+const moduleButton = "document.querySelector('[data-testid^=\"select-\"]')";
+const hasModule = await waitFor(moduleButton, "a module in the Dashboard navigation");
+if (hasModule) {
+  const moduleId = await evaluate(`${moduleButton}.dataset.testid.slice("select-".length)`);
+  await evaluate(`${moduleButton}.click()`);
+  const mounted = await waitFor(
+    `${selector("module-container")}?.childElementCount > 0 && !${selector("module-loading")} && !${selector("module-error")}`,
+    "the module UI to mount",
+  );
+  check(
+    mounted && !(await evaluate(`Boolean(${selector("module-error")})`)),
+    `the ${moduleId} module UI mounts`,
+  );
+  // Give the module's first requests a moment to settle before judging them.
+  await new Promise((resolve) => setTimeout(resolve, 1_000));
+  check(
+    responses.some(
+      (response) =>
+        response.url.startsWith(`${apiOrigin}/api/v1/module-ui/${moduleId}/`) &&
+        response.status === 200,
+    ),
+    "its UI artifact was imported from the API's origin",
+  );
+  check(
+    responses.some(
+      (response) =>
+        response.url.startsWith(`${apiOrigin}/api/v1/modules/${moduleId}`) &&
+        response.status >= 200 &&
+        response.status < 300,
+    ),
+    "its own credentialed API request to the API's origin succeeded under CORS",
+  );
+  const streams = responses.filter((response) => response.type === "EventSource");
+  check(
+    streams.every((response) => response.status === 200),
+    `every realtime stream it opened was accepted (${streams.length} opened)`,
+  );
+}
+// A CORS refusal or a blocked request is always a failure. A request the page itself cancelled (a
+// module unmounting, a navigation) is not.
+const refused = failed.filter(
+  (failure) =>
+    failure.corsErrorStatus !== undefined ||
+    failure.blockedReason !== undefined ||
+    !(failure.canceled || failure.errorText === "net::ERR_ABORTED"),
+);
+check(
+  refused.length === 0,
+  `no request from the Dashboard failed or was refused by CORS (${refused.length} refused)`,
+);
+
+// --- The display host, on the API's origin, with the same session --------------------------------
+const displayPath =
+  await evaluate(`fetch(${JSON.stringify(`${apiOrigin}/api/v1/dashboard/navigation`)}, {
+  credentials: "include",
+}).then((response) => response.json()).then((navigation) => {
+  const entries = [...navigation.ungrouped, ...navigation.groups.flatMap((group) => group.modules)];
+  return entries.find((entry) => entry.module.display !== null)?.module.display.url ?? null;
+})`);
+if (displayPath === null) {
+  console.log("skip no installed module publishes a display");
+} else {
+  await navigate(`${apiOrigin}${displayPath}`);
+  check(
+    await waitFor(
+      `${selector("display-module-container")}?.childElementCount > 0 && !${selector("display-error")}`,
+      "the display to mount",
+    ),
+    "the module's display page mounts on the API hostname with the same session",
+  );
+  check(
+    await waitFor(
+      "navigator.serviceWorker.getRegistrations().then((registrations) => registrations.length > 0)",
+      "the display's service worker",
+    ),
+    "the display's offline service worker registers on the API's origin",
+  );
+}
+
+// --- Sign out on the Dashboard -------------------------------------------------------------------
+await navigate(`${dashboardOrigin}/`);
+await waitFor(selector("host-logout"), "the sign-out control");
+await evaluate(`${selector("host-logout")}.click()`);
+check(
+  await waitFor(selector("login-email"), "the sign-in form after sign-out"),
+  "sign-out returns the Dashboard to the sign-in form",
+);
+const principal = await evaluate(`fetch(${JSON.stringify(`${apiOrigin}/api/v1/principal`)}, {
+  credentials: "include",
+}).then((response) => response.json()).then((body) => body.kind)`);
+check(principal === "anonymous", "after sign-out, the API answers anonymous to the same browser");
+
+await cdp.send("Target.closeTarget", { targetId });
+cdp.close();
+if (failures > 0) {
+  console.error(`${failures} check(s) failed`);
+  process.exit(1);
+}
@@ -7,12 +7,20 @@
 //   node deploy-smoke-client.mjs tunnel   the Cloudflare Tunnel connector's fixed address
 //   node deploy-smoke-client.mjs session  the initial owner signing in and out through the proxy
 //
+// Either topology (ADR 0045): SMOKE_HOSTNAME is the API's hostname, and SMOKE_DASHBOARD_HOSTNAME,
+// when set, the Dashboard's. Unset means the same-origin topology, where both are one hostname. Every
+// request goes to the API's origin and carries the Dashboard's origin as `Origin`, as a browser would.
+//
 // Output is one line per check; any failed check exits non-zero. Nothing printed carries a
 // credential, cookie, signed URL, or response body beyond the fixed shapes asserted here.

 const mode = process.argv[2];
-const hostname = required("SMOKE_HOSTNAME");
-const origin = `https://${hostname}`;
+const apiOrigin = `https://${required("SMOKE_HOSTNAME")}`;
+const dashboardOrigin = process.env.SMOKE_DASHBOARD_HOSTNAME
+  ? `https://${process.env.SMOKE_DASHBOARD_HOSTNAME}`
+  : apiOrigin;
+const split = dashboardOrigin !== apiOrigin;
+const untrustedOrigin = "https://untrusted.smoke.test";

 function required(name) {
  const value = process.env[name];
@@ -34,9 +42,9 @@ function check(condition, description) {
 /** A sign-in attempt that can only fail authentication; what matters is whether the API's
 * per-client limiter (3 attempts per 10 seconds) counts it against the expected client. */
 async function signInAttempt(headers = {}) {
-  const response = await fetch(`${origin}/api/auth/sign-in/email`, {
+  const response = await fetch(`${apiOrigin}/api/auth/sign-in/email`, {
    body: JSON.stringify({ email: "[email protected]", password: "definitely-not-the-password" }),
-    headers: { "content-type": "application/json", origin, ...headers },
+    headers: { "content-type": "application/json", origin: dashboardOrigin, ...headers },
    method: "POST",
  });
  await response.arrayBuffer();
@@ -44,13 +52,13 @@ async function signInAttempt(headers = {}) {
 }

 async function edgeChecks() {
-  const ready = await fetch(`${origin}/api/v1/health/ready`);
+  const ready = await fetch(`${apiOrigin}/api/v1/health/ready`);
  check(
    ready.status === 200 && (await ready.text()) === '{"status":"ready"}',
    "GET /api/v1/health/ready through the proxy is 200 ready",
  );

-  const page = await fetch(`${origin}/`);
+  const page = await fetch(`${dashboardOrigin}/`);
  const html = await page.text();
  check(page.status === 200, "GET / through the proxy is 200");
  check(
@@ -66,22 +74,32 @@ async function edgeChecks() {
    "the Dashboard page keeps its security headers through the proxy",
  );

-  const script = await fetch(`${origin}/assets/ekklesia-dashboard/app.js`);
+  check(
+    html.includes(`<meta content="${apiOrigin}" name="ekklesia-api-origin" />`),
+    "the Dashboard page names the API's origin, rendered at run time (ADR 0045)",
+  );
+
+  const script = await fetch(`${dashboardOrigin}/assets/ekklesia-dashboard/app.js`);
  await script.arrayBuffer();
  check(script.status === 200, "GET /assets/ekklesia-dashboard/app.js is 200");

-  const outside = await fetch(`${origin}/favicon.ico`);
+  const outside = await fetch(`${dashboardOrigin}/favicon.ico`);
  check(
    outside.status === 404 && !(outside.headers.get("content-type") ?? "").includes("json"),
    "a path the API does not serve is refused by the proxy, never forwarded",
  );

-  const unknownApi = await fetch(`${origin}/api/v1/does-not-exist`);
+  const unknownApi = await fetch(`${apiOrigin}/api/v1/does-not-exist`);
  check(
    unknownApi.status === 404 && (await unknownApi.text()) === '{"code":"NOT_FOUND"}',
    "an unknown /api/* path reaches the API and gets its sanitized 404",
  );

+  if (split) {
+    await splitRoutingChecks();
+    await splitCorsChecks();
+  }
+
  await storageDeliveryCheck();

  // Every caller-supplied forwarding header rotates on every attempt. If any of them reached the
@@ -106,6 +124,74 @@ async function edgeChecks() {
  );
 }

+/** A proxy refusal: Caddy's own empty `404`, never the API's JSON one, so the request was not
+ * forwarded at all. */
+async function refusedByProxy(url) {
+  const response = await fetch(url);
+  const body = await response.text();
+  return response.status === 404 && body === "";
+}
+
+/** Each hostname serves exactly its own paths (ADR 0045, "Routing per hostname"). */
+async function splitRoutingChecks() {
+  check(
+    await refusedByProxy(`${dashboardOrigin}/api/v1/health/ready`),
+    "the Dashboard hostname refuses /api/*, so the session cookie has one home",
+  );
+  check(
+    await refusedByProxy(`${dashboardOrigin}/display/example`),
+    "the Dashboard hostname refuses /display/*",
+  );
+  check(await refusedByProxy(`${apiOrigin}/`), "the API hostname serves nothing at /");
+  check(
+    await refusedByProxy(`${apiOrigin}/assets/ekklesia-dashboard/app.js`),
+    "the API hostname refuses the Dashboard's script",
+  );
+  const display = await fetch(`${apiOrigin}/display/does-not-exist`);
+  check(
+    display.status === 404 && (await display.text()) === '{"code":"NOT_FOUND"}',
+    "the API hostname forwards /display/* to the API (the display host's origin)",
+  );
+}
+
+/** Credentialed CORS for exactly the Dashboard's origin, and for nothing else. */
+async function splitCorsChecks() {
+  const preflight = await fetch(`${apiOrigin}/api/auth/sign-in/email`, {
+    headers: {
+      "access-control-request-headers": "content-type",
+      "access-control-request-method": "POST",
+      origin: dashboardOrigin,
+    },
+    method: "OPTIONS",
+  });
+  await preflight.arrayBuffer();
+  check(
+    preflight.status === 204 &&
+      preflight.headers.get("access-control-allow-origin") === dashboardOrigin &&
+      preflight.headers.get("access-control-allow-credentials") === "true",
+    "a preflight from the Dashboard's origin is allowed, with credentials",
+  );
+  const foreignPreflight = await fetch(`${apiOrigin}/api/auth/sign-in/email`, {
+    headers: { "access-control-request-method": "POST", origin: untrustedOrigin },
+    method: "OPTIONS",
+  });
+  await foreignPreflight.arrayBuffer();
+  check(
+    foreignPreflight.headers.get("access-control-allow-origin") === null,
+    "a preflight from any other origin gets no CORS permission",
+  );
+  const principal = await fetch(`${apiOrigin}/api/v1/principal`, {
+    headers: { origin: dashboardOrigin },
+  });
+  await principal.arrayBuffer();
+  check(
+    principal.headers.get("access-control-allow-origin") === dashboardOrigin &&
+      principal.headers.get("access-control-allow-credentials") === "true" &&
+      (principal.headers.get("vary") ?? "").includes("Origin"),
+    "an API response to the Dashboard's origin reflects exactly that origin, with credentials",
+  );
+}
+
 async function storageDeliveryCheck() {
  // Core's own provider, from the image, exactly as the API composes it: it reaches object-storage
  // over HTTPS on the private network and signs read URLs for the storage hostname.
@@ -184,9 +270,9 @@ async function sessionChecks() {
    "/api/auth/update-session",
    "/api/auth/change-password",
  ]) {
-    const response = await fetch(`${origin}${path}`, {
+    const response = await fetch(`${apiOrigin}${path}`, {
      method: path.endsWith("get-session") || path.endsWith("list-sessions") ? "GET" : "POST",
-      headers: { origin },
+      headers: { origin: dashboardOrigin },
    });
    check(
      response.status === 404 && (await response.text()) === '{"code":"NOT_FOUND"}',
@@ -194,12 +280,12 @@ async function sessionChecks() {
    );
  }

-  const signIn = await fetch(`${origin}/api/auth/sign-in/email`, {
+  const signIn = await fetch(`${apiOrigin}/api/auth/sign-in/email`, {
    body: JSON.stringify({
      email: required("SMOKE_OWNER_EMAIL"),
      password: required("SMOKE_OWNER_PASSWORD"),
    }),
-    headers: { "content-type": "application/json", origin },
+    headers: { "content-type": "application/json", origin: dashboardOrigin },
    method: "POST",
  });
  const signInBody = await signIn.text();
@@ -218,20 +304,24 @@ async function sessionChecks() {
  );
  const cookie = setCookie.split(";")[0] ?? "";

-  const principal = await fetch(`${origin}/api/v1/principal`, { headers: { cookie, origin } });
+  const principal = await fetch(`${apiOrigin}/api/v1/principal`, {
+    headers: { cookie, origin: dashboardOrigin },
+  });
  const principalBody = await principal.json();
  check(
    principal.status === 200 && principalBody.kind === "authenticated",
    "the session resolves an authenticated principal through the proxy",
  );

-  const signOut = await fetch(`${origin}/api/auth/sign-out`, {
+  const signOut = await fetch(`${apiOrigin}/api/auth/sign-out`, {
    body: "{}",
-    headers: { "content-type": "application/json", cookie, origin },
+    headers: { "content-type": "application/json", cookie, origin: dashboardOrigin },
    method: "POST",
  });
  await signOut.arrayBuffer();
-  const after = await fetch(`${origin}/api/v1/principal`, { headers: { cookie, origin } });
+  const after = await fetch(`${apiOrigin}/api/v1/principal`, {
+    headers: { cookie, origin: dashboardOrigin },
+  });
  check(
    signOut.status === 200 && (await after.json()).kind === "anonymous",
    "sign-out ends the session",
@@ -5,6 +5,15 @@
 #
 #   bash scripts/smoke-deploy.sh                 builds the image first
 #   EKKLESIA_SMOKE_IMAGE=<image> bash scripts/smoke-deploy.sh
+#   EKKLESIA_SMOKE_TOPOLOGY=split bash scripts/smoke-deploy.sh
+#
+# Either topology (ADR 0045). `same-origin` (the default) serves the Dashboard, the API, and displays
+# from one hostname with Caddyfile.example and a platform-only image. `split` serves the Dashboard on
+# its own hostname with Caddyfile.split.example, builds an image with the repository's module
+# template installed as a test-only module (so a module UI, its API routes, and a display exist), and
+# then drives a real headless Chromium through the Dashboard, the module, the display, and sign-out.
+# With EKKLESIA_SMOKE_IMAGE, the given image is used as is in either topology; a split run then
+# exercises whichever of its modules publishes UI and a display.
 #
 # TEST-ONLY: the proxy runs with Caddy's internal CA (`local_certs`) instead of ACME, because a test
 # run has no public hostname. Never use that option in an installation.
@@ -39,14 +48,36 @@ docker compose version >/dev/null 2>&1 || {
 # The pinned PostgreSQL image doubles as a root shell for file ownership, so the run needs neither
 # root nor sudo on the host.
 postgres_image="postgres:18.4-alpine3.24@sha256:9a8afca54e7861fd90fab5fdf4c42477a6b1cb7d293595148e674e0a3181de15"
+# The split topology's real browser: headless Chromium, pinned by its multi-architecture index digest.
+browser_image="chromedp/headless-shell:151.0.7922.109@sha256:2d349b544a1ea6b5b5fd7c0fe99215ff662339c57407ee2e8c0a11af93516b04"
+
+topology="${EKKLESIA_SMOKE_TOPOLOGY:-same-origin}"
+case "$topology" in
+same-origin | split) ;;
+*)
+  echo "smoke-deploy: EKKLESIA_SMOKE_TOPOLOGY must be same-origin or split." >&2
+  exit 1
+  ;;
+esac

 run_id="$(openssl rand -hex 4)"
 project="ekklesia-deploy-smoke-${run_id}"
 work="$(mktemp -d)"
 image="${EKKLESIA_SMOKE_IMAGE:-}"
 built_image=""
-hostname="ekklesia.smoke.test"
+# `hostname` is always the API's (and the display host's); the Dashboard has its own only when split.
+if [[ "$topology" == split ]]; then
+  hostname="api.smoke.test"
+  dashboard_hostname="dash.smoke.test"
+  caddyfile_example="deploy/Caddyfile.split.example"
+else
+  hostname="ekklesia.smoke.test"
+  dashboard_hostname=""
+  caddyfile_example="deploy/Caddyfile.example"
+fi
+dashboard_origin="https://${dashboard_hostname:-$hostname}"
 storage_hostname="storage.smoke.test"
+browser_container=""

 # choose_edge_network: a per-run edge subnet that no network on this Docker daemon already uses, so
 # concurrent runs sharing a runner's daemon do not collide. Two runs can still pick the same free
@@ -69,6 +100,8 @@ choose_edge_network() {
      tunnel_address="10.249.${octet}.253"
      # A test-only client address, also outside the dynamic range, so its limiter bucket is its own.
      session_client_address="10.249.${octet}.252"
+      # The headless browser's fixed address, likewise (split topology only).
+      browser_address="10.249.${octet}.251"
      return 0
    fi
  done
@@ -105,6 +138,9 @@ compose=(
 cleanup() {
  local status=$?
  trap - EXIT INT TERM
+  if [[ -n "$browser_container" ]]; then
+    docker rm --force "$browser_container" >/dev/null 2>&1 || true
+  fi
  if [[ -f "$work/compose.env" ]]; then
    "${compose[@]}" --profile ops down --volumes --remove-orphans --timeout 10 >/dev/null 2>&1 || status=1
  fi
@@ -135,11 +171,32 @@ fail() {
  exit 1
 }

-if [[ -z "$image" ]]; then
+if [[ -z "$image" && "$topology" == same-origin ]]; then
  step "Building the platform-only image"
  built_image="ekklesia-deploy-smoke:${run_id}"
  DOCKER_BUILDKIT=1 docker build --quiet --file deploy/Dockerfile --tag "$built_image" . >/dev/null
  image="$built_image"
+elif [[ -z "$image" ]]; then
+  # TEST-ONLY: the repository's module template, installed as the module `example`, in a copy of the
+  # working tree. Its lockfile importer moves with it; the depth is the same, so every relative link
+  # in that importer stays correct and the install stays frozen.
+  step "Building an image with the module template installed as a test-only module"
+  command -v git >/dev/null || fail "git is required to build the split topology's test image."
+  context="$work/build-context"
+  mkdir -p "$context"
+  git ls-files -z --cached --others --exclude-standard |
+    tar --null --files-from=- --create --file=- |
+    tar -C "$context" -xf -
+  mkdir -p "$context/modules"
+  mv "$context/templates/module" "$context/modules/example"
+  [[ "$(grep -c '^  templates/module:$' "$context/pnpm-lock.yaml")" == 1 ]] ||
+    fail "the lockfile has no single templates/module importer to move."
+  sed -i 's|^  templates/module:$|  modules/example:|' "$context/pnpm-lock.yaml"
+  built_image="ekklesia-deploy-smoke:${run_id}"
+  DOCKER_BUILDKIT=1 docker build --quiet --file "$context/deploy/Dockerfile" --tag "$built_image" \
+    "$context" >/dev/null || fail "the test-module image did not build."
+  rm -rf "$context"
+  image="$built_image"
 fi

 # The compose project directory: its relative bind mount (postgres/pg_hba.conf) resolves here.
@@ -197,7 +254,10 @@ ekklesia_env="$work/env/ekklesia.env"
 set_env "$ekklesia_env" DATABASE_URL "postgresql://ekklesia:${postgres_password}@postgres:5432/ekklesia"
 set_env "$ekklesia_env" EKKLESIA_DATABASE_CA "${database_ca_line#EKKLESIA_DATABASE_CA=}"
 set_env "$ekklesia_env" EKKLESIA_IDENTITY_BASE_URL "https://${hostname}"
-set_env "$ekklesia_env" EKKLESIA_IDENTITY_TRUSTED_ORIGINS "https://${hostname}"
+set_env "$ekklesia_env" EKKLESIA_IDENTITY_TRUSTED_ORIGINS "$dashboard_origin"
+if [[ "$topology" == split ]]; then
+  set_env "$ekklesia_env" EKKLESIA_DASHBOARD_ORIGIN "$dashboard_origin"
+fi
 set_env "$ekklesia_env" EKKLESIA_IDENTITY_SECRET "$identity_secret"
 set_env "$ekklesia_env" S3_DELIVERY_ENDPOINT "https://${storage_hostname}"
 set_env "$ekklesia_env" S3_ACCESS_KEY "$s3_access_key"
@@ -209,7 +269,7 @@ chmod 600 "$work"/env/*.env

 # TEST-ONLY: Caddy's internal CA instead of ACME. Inserted as the first global option.
 awk '!done && $0 == "{" { print; print "\tlocal_certs"; done = 1; next } { print }' \
-  deploy/Caddyfile.example >"$work/Caddyfile"
+  "$caddyfile_example" >"$work/Caddyfile"
 grep -q $'^\tlocal_certs$' "$work/Caddyfile" || fail "could not enable local_certs for the test proxy."
 stage Caddyfile

@@ -218,6 +278,7 @@ EKKLESIA_IMAGE=${image}
 EKKLESIA_ENV_DIR=${work}/env
 EKKLESIA_TLS_DIR=${daemon_work}/tls
 EKKLESIA_HOSTNAME=${hostname}
+EKKLESIA_DASHBOARD_HOSTNAME=${dashboard_hostname}
 EKKLESIA_STORAGE_HOSTNAME=${storage_hostname}
 EKKLESIA_ACME_EMAIL=[email protected]
 EKKLESIA_CADDYFILE=${daemon_work}/Caddyfile
@@ -281,13 +342,17 @@ stage client-ca.pem
 stage client.mjs

 edge_network="${project}_edge"
+host_mappings=(--add-host "${hostname}:${proxy_address}" --add-host "${storage_hostname}:${proxy_address}")
+if [[ -n "$dashboard_hostname" ]]; then
+  host_mappings+=(--add-host "${dashboard_hostname}:${proxy_address}")
+fi
 client() {
  local mode="$1"
  shift
  docker run --rm --read-only --cap-drop ALL --security-opt no-new-privileges \
-    --network "$edge_network" "$@" \
-    --add-host "${hostname}:${proxy_address}" --add-host "${storage_hostname}:${proxy_address}" \
+    --network "$edge_network" "$@" "${host_mappings[@]}" \
    -e NODE_EXTRA_CA_CERTS=/smoke/client-ca.pem -e SMOKE_HOSTNAME="$hostname" \
+    -e SMOKE_DASHBOARD_HOSTNAME="$dashboard_hostname" \
    -e SMOKE_STORAGE_HOSTNAME="$storage_hostname" \
    -e S3_ACCESS_KEY="$s3_access_key" -e S3_SECRET_KEY="$s3_secret_key" \
    -v "$daemon_work/client.mjs:/smoke/client.mjs:ro" \
@@ -312,6 +377,35 @@ client session --ip "$session_client_address" \
  -e SMOKE_OWNER_EMAIL="$owner_email" -e SMOKE_OWNER_PASSWORD="$owner_password" ||
  fail "session checks failed."

+if [[ "$topology" == split ]]; then
+  step "Driving a real browser through the split Dashboard, a module, its display, and sign-out"
+  # Chromium trusts this run's proxy through the public-key hash of Caddy's internal intermediate CA,
+  # which signs every certificate the test proxy serves: no CA is installed anywhere, and nothing but
+  # this run's certificates is accepted.
+  "${compose[@]}" exec -T proxy cat /data/caddy/pki/authorities/local/intermediate.crt \
+    >"$work/caddy-intermediate.crt" || fail "the test proxy's intermediate CA is unavailable."
+  spki="$(openssl x509 -in "$work/caddy-intermediate.crt" -pubkey -noout |
+    openssl pkey -pubin -outform der | openssl dgst -sha256 -binary | openssl base64 -A)"
+  browser_container="${project}-browser"
+  # The image's entry script passes its arguments on unquoted, so none may contain a space: the
+  # hostnames reach Chromium through /etc/hosts, which it reads, rather than a resolver rule.
+  docker run --detach --rm --name "$browser_container" \
+    --cap-drop ALL --security-opt no-new-privileges --tmpfs /tmp \
+    --network "$edge_network" --ip "$browser_address" "${host_mappings[@]}" \
+    "$browser_image" \
+    "--ignore-certificate-errors-spki-list=${spki}" \
+    --user-data-dir=/tmp/profile >/dev/null || fail "the headless browser did not start."
+  cp scripts/lib/deploy-smoke-browser.mjs "$work/browser.mjs"
+  stage browser.mjs
+  docker run --rm --read-only --cap-drop ALL --security-opt no-new-privileges \
+    --network "$edge_network" \
+    -e SMOKE_CDP_ADDRESS="${browser_address}:9222" \
+    -e SMOKE_HOSTNAME="$hostname" -e SMOKE_DASHBOARD_HOSTNAME="$dashboard_hostname" \
+    -e SMOKE_OWNER_EMAIL="$owner_email" -e SMOKE_OWNER_PASSWORD="$owner_password" \
+    -v "$daemon_work/browser.mjs:/smoke/browser.mjs:ro" \
+    --entrypoint node "$image" /smoke/browser.mjs || fail "browser checks failed."
+fi
+
 step "Proving the API's database connection is certificate-verified TLS"
 api_container="$("${compose[@]}" ps -q api)"
 api_data_address="$(
@@ -3,6 +3,10 @@
  <head>
    <meta charset="utf-8" />
    <meta content="width=device-width, initial-scale=1" name="viewport" />
+    <!-- The API's origin (ADR 0045). The API serving this page fills it in at startup; empty means
+         this page's own origin, the same-origin topology. Never an inline script, so a strict
+         script-src needs no exception for it. -->
+    <meta content="" name="ekklesia-api-origin" />
    <title>Ekklesia</title>
  </head>
  <body style="margin: 0; min-width: 0">
@@ -1,4 +1,4 @@
-import { copyFile, mkdir, rm } from "node:fs/promises";
+import { copyFile, mkdir, readFile, rm, writeFile } from "node:fs/promises";
 import path from "node:path";
 import { fileURLToPath } from "node:url";
 import esbuild from "esbuild";
@@ -23,12 +23,16 @@ const outputDirectory = path.join(packageDirectory, "dist", "browser");
 const serve = process.argv.includes("--serve");

 /**
- * Empty means "the API is on this page's own origin" — the expected production shape. Set it to an
- * absolute origin for split-origin development (`EKKLESIA_API_BASE_URL=http://127.0.0.1:3000`), and
- * add this page's own origin to `EKKLESIA_IDENTITY_TRUSTED_ORIGINS` so the API reflects it for CORS
- * and the session cookie travels.
+ * Development only: the API origin the development server writes into its copy of the Dashboard page,
+ * exactly as `apps/api` does at startup in production (ADR 0045). Empty means "the API is on this
+ * page's own origin". Set it to an absolute origin for split-origin development
+ * (`EKKLESIA_API_BASE_URL=http://127.0.0.1:3000`), and add this page's own origin to
+ * `EKKLESIA_IDENTITY_TRUSTED_ORIGINS` so the API reflects it for CORS and the session cookie travels.
+ * A production build never reads it: the built page always carries an empty value, and the bundle
+ * carries no origin at all.
 */
-const apiBaseUrl = process.env.EKKLESIA_API_BASE_URL ?? "";
+const apiBaseUrl = serve ? (process.env.EKKLESIA_API_BASE_URL ?? "") : "";
+const API_ORIGIN_PLACEHOLDER = '<meta content="" name="ekklesia-api-origin" />';

 /** @type {import("esbuild").BuildOptions} */
 const buildOptions = {
@@ -37,7 +41,6 @@ const buildOptions = {
  // artifacts it is told about, which are real URLs rather than bare specifiers.
  bundle: true,
  define: {
-    __EKKLESIA_API_BASE_URL__: JSON.stringify(apiBaseUrl),
    // React reads this at module scope and a browser has no `process`.
    "process.env.NODE_ENV": JSON.stringify(serve ? "development" : "production"),
  },
@@ -67,7 +70,17 @@ const buildOptions = {
 await rm(outputDirectory, { force: true, recursive: true });
 await mkdir(outputDirectory, { recursive: true });
 await mkdir(path.join(outputDirectory, "display"), { recursive: true });
-await copyFile(path.join(packageDirectory, "index.html"), path.join(outputDirectory, "index.html"));
+const dashboardPage = await readFile(path.join(packageDirectory, "index.html"), "utf8");
+if (dashboardPage.split(API_ORIGIN_PLACEHOLDER).length !== 2) {
+  throw new Error("index.html must contain exactly one empty ekklesia-api-origin meta element.");
+}
+await writeFile(
+  path.join(outputDirectory, "index.html"),
+  dashboardPage.replace(
+    API_ORIGIN_PLACEHOLDER,
+    `<meta content="${apiBaseUrl.replaceAll("&", "&amp;").replaceAll('"', "&quot;")}" name="ekklesia-api-origin" />`,
+  ),
+);
 await copyFile(
  path.join(packageDirectory, "display.html"),
  path.join(outputDirectory, "display", "index.html"),
@@ -2,29 +2,22 @@ import { installEkklesiaDesignTokens } from "@ekklesia/design-tokens";
 import { EkklesiaUiStyles } from "@ekklesia/ui";
 import { createRoot } from "react-dom/client";
 import { consumeAuthLanding } from "../auth-protocol.js";
-import type { EkklesiaHostConfig } from "../host-protocol.js";
+import { type EkklesiaHostConfig, resolveApiOrigin } from "../host-protocol.js";
 import { HostApp } from "./HostApp.js";

-/**
- * Replaced at build time by `scripts/build-browser.mjs` with a JSON string literal: the API origin
- * when `EKKLESIA_API_BASE_URL` was set for the build, and `""` otherwise. Declared rather than read
- * from `process.env`, because a browser has no `process` and the substitution must be visible here
- * instead of hidden in bundler configuration.
- */
-declare const __EKKLESIA_API_BASE_URL__: string;
-
 /**
 * The one place the shell touches a browser global.
 *
- * An empty build-time value means the API is served from the same origin as this page, which is the
- * expected production shape; a non-empty one is the split-origin development shape the platform's
- * trusted-origin configuration already supports (`EKKLESIA_IDENTITY_TRUSTED_ORIGINS` must list this
- * page's origin for the session cookie to travel). Everything downstream receives the resolved
- * origin as a plain argument, so no other file in this package reads `window`.
+ * The API that served this page wrote its own origin into `<meta name="ekklesia-api-origin">`
+ * (ADR 0045): empty in the same-origin topology, the API's hostname when the Dashboard and the API
+ * live on separate origins. Read at run time, so one built shell serves either topology. Everything
+ * downstream receives the resolved origin as a plain argument, so no other file in this package
+ * reads `window`.
 */
-const config: EkklesiaHostConfig = {
-  apiBaseUrl: __EKKLESIA_API_BASE_URL__ || window.location.origin,
-};
+const apiBaseUrl = resolveApiOrigin(
+  document.querySelector<HTMLMetaElement>('meta[name="ekklesia-api-origin"]')?.content,
+  window.location.origin,
+);

 /** Read once, before anything renders, and stripped from the address bar in the same step. See
 * `consumeAuthLanding` for why the token must not stay in the URL. */
@@ -46,13 +39,29 @@ if (!container) {
 */
 installEkklesiaDesignTokens(document);

+/**
+ * A page whose API origin is not a canonical origin fails closed: it makes no request at all, because
+ * every request it would make carries credentials to an address it cannot vouch for. The message is
+ * fixed and names no address.
+ */
+function renderHost(config: EkklesiaHostConfig | undefined) {
+  if (!config) {
+    return (
+      <main data-testid="host-configuration-invalid" role="alert">
+        This page cannot start: the server address it was given is not valid.
+      </main>
+    );
+  }
+  return authLanding ? (
+    <HostApp authLanding={authLanding} config={config} />
+  ) : (
+    <HostApp config={config} />
+  );
+}
+
 createRoot(container).render(
  <>
    <EkklesiaUiStyles />
-    {authLanding ? (
-      <HostApp authLanding={authLanding} config={config} />
-    ) : (
-      <HostApp config={config} />
-    )}
+    {renderHost(apiBaseUrl === undefined ? undefined : { apiBaseUrl })}
  </>,
 );
@@ -6,10 +6,13 @@ import { parseDisplayRoute } from "../host-protocol.js";
 import { DisplayApp } from "./DisplayApp.js";
 import { type DisplayConnectivitySource, registerDisplayServiceWorker } from "./offline-status.js";

-declare const __EKKLESIA_API_BASE_URL__: string;
-
+/**
+ * The display host is always served from the API's own origin, in either topology (ADR 0045): its
+ * device cookies, pairing, descriptors, module requests, and realtime are all same-origin, and its
+ * offline cache stores only same-origin responses (ADR 0043).
+ */
 const config: EkklesiaHostConfig = {
-  apiBaseUrl: __EKKLESIA_API_BASE_URL__ || window.location.origin,
+  apiBaseUrl: window.location.origin,
 };

 const container = document.getElementById("ekklesia-display");
@@ -4,10 +4,11 @@ import type { ModuleUiPrincipal } from "@ekklesia/module-ui-sdk";
 * How this shell reaches the Ekklesia API.
 *
 * `apiBaseUrl` is an absolute **origin** (`https://ekklesia.example.test`, `http://127.0.0.1:3000`)
- * rather than something read from a global. The browser entry point supplies it — from a build-time
- * value when the shell and the API are served from different origins in development, and from
- * `window.location.origin` otherwise — so every function below is a pure function of its arguments
- * and can be exercised without a DOM, a `window`, or a page. Nothing here reads a global.
+ * rather than something read from a global. The browser entry point supplies it — from the API
+ * origin the serving API wrote into the Dashboard page (ADR 0045, {@link resolveApiOrigin}), and from
+ * `window.location.origin` for the display host, which is always served from the API's own origin —
+ * so every function below is a pure function of its arguments and can be exercised without a DOM, a
+ * `window`, or a page. Nothing here reads a global.
 */
 export interface EkklesiaHostConfig {
  readonly apiBaseUrl: string;
@@ -702,6 +703,34 @@ export function parseHostPrincipal(payload: unknown): ModuleUiPrincipal {
  throw new HostProtocolError("HOST_RESPONSE_INVALID");
 }

+/**
+ * The API origin a Dashboard page was served with (ADR 0045).
+ *
+ * `declared` is the `content` of the page's `<meta name="ekklesia-api-origin">`, which the serving API
+ * fills in at startup. Absent or empty means the API shares this page's origin, the same-origin
+ * topology. Anything else must be exactly a canonical `http(s)` origin — no path, no trailing slash,
+ * no credentials, no query — or the result is `undefined` and the page must fail closed rather than
+ * send credentialed requests to an address it cannot vouch for.
+ */
+export function resolveApiOrigin(
+  declared: string | null | undefined,
+  pageOrigin: string,
+): string | undefined {
+  if (declared === null || declared === undefined || declared === "") {
+    return pageOrigin;
+  }
+  let url: URL;
+  try {
+    url = new URL(declared);
+  } catch {
+    return undefined;
+  }
+  if ((url.protocol !== "https:" && url.protocol !== "http:") || url.origin !== declared) {
+    return undefined;
+  }
+  return url.origin;
+}
+
 /** Resolves a root-relative platform path against the configured API origin. The one place the
 * shell turns a server-produced path into an absolute URL. */
 export function resolveApiUrl(config: EkklesiaHostConfig, rootRelativePath: string): string {
@@ -32,6 +32,7 @@ export {
  parseDisplayRoute,
  parseHostModuleDisplay,
  parseHostPrincipal,
+  resolveApiOrigin,
  resolveApiUrl,
 } from "./host-protocol.js";
 export {
@@ -44,6 +44,22 @@ describe("Dashboard host asset locator", () => {
    );
  });

+  it("carries exactly one empty API-origin meta element for the serving API to fill (ADR 0045)", async () => {
+    const html = await readFile(path.join(packageDirectory, "index.html"), "utf8");
+
+    expect(html.match(/name="ekklesia-api-origin"/gu)).toHaveLength(1);
+    expect(html).toContain('<meta content="" name="ekklesia-api-origin" />');
+  });
+
+  it("bakes no API origin into the bundle: the build defines nothing but NODE_ENV", async () => {
+    const buildScript = await readFile(
+      path.join(packageDirectory, "scripts/build-browser.mjs"),
+      "utf8",
+    );
+
+    expect(buildScript).not.toContain("__EKKLESIA_API_BASE_URL__");
+  });
+
  it("builds the Dashboard entry at the exact path the locator names", async () => {
    const buildScript = await readFile(
      path.join(packageDirectory, "scripts/build-browser.mjs"),
@@ -6,6 +6,7 @@ import {
  loadHostPrincipal,
  parseDashboardNavigation,
  parseHostPrincipal,
+  resolveApiOrigin,
 } from "../src/host-protocol.js";
 import { createModuleUiContext, moduleUiSourceUrl } from "../src/module-context.js";

@@ -101,6 +102,39 @@ function navigationWithModule(module: unknown): unknown {
  return { groups: [], ungrouped: [{ module, name: "Example Module" }] };
 }

+describe("host protocol — API origin (ADR 0045)", () => {
+  const pageOrigin = "https://dash.example.test";
+
+  it("uses the page's own origin when the page declares none (same-origin topology)", () => {
+    expect(resolveApiOrigin(undefined, pageOrigin)).toBe(pageOrigin);
+    expect(resolveApiOrigin(null, pageOrigin)).toBe(pageOrigin);
+    expect(resolveApiOrigin("", pageOrigin)).toBe(pageOrigin);
+  });
+
+  it("uses a declared canonical origin (split topology)", () => {
+    expect(resolveApiOrigin("https://api.example.test", pageOrigin)).toBe(
+      "https://api.example.test",
+    );
+    expect(resolveApiOrigin("http://127.0.0.1:3000", pageOrigin)).toBe("http://127.0.0.1:3000");
+  });
+
+  it.each([
+    ["a trailing slash", "https://api.example.test/"],
+    ["a path", "https://api.example.test/api"],
+    ["a query", "https://api.example.test?x=1"],
+    ["credentials", "https://user:[email protected]"],
+    ["a non-canonical spelling", "HTTPS://API.example.test"],
+    ["a default port spelled out", "https://api.example.test:443"],
+    ["another scheme", "javascript:alert(1)"],
+    ["a protocol-relative value", "//api.example.test"],
+    ["a relative value", "/api"],
+    ["surrounding whitespace", " https://api.example.test"],
+    ["something that is not a URL", "api.example.test"],
+  ])("refuses %s, so the page fails closed", (_case, declared) => {
+    expect(resolveApiOrigin(declared, pageOrigin)).toBeUndefined();
+  });
+});
+
 describe("host protocol — descriptor validation", () => {
  it("parses a well-formed descriptor out of the navigation view", () => {
    const navigation = parseDashboardNavigation(navigationWithModule(inventoryPayload.modules[0]));
@@ -120,7 +120,6 @@ describe("the shell builds no module knowledge into its bundle", () => {
      absWorkingDir: packageDirectory,
      bundle: true,
      define: {
-        __EKKLESIA_API_BASE_URL__: '""',
        "process.env.NODE_ENV": '"production"',
      },
      entryPoints: [path.join(sourceDirectory, "browser", "main.tsx")],
@@ -200,7 +199,6 @@ describe("the display host is a separate generic browser bundle", () => {
      absWorkingDir: packageDirectory,
      bundle: true,
      define: {
-        __EKKLESIA_API_BASE_URL__: '""',
        "process.env.NODE_ENV": '"production"',
      },
      entryPoints: [path.join(sourceDirectory, "display", "main.tsx")],