feat(express): derive api.<bare-domain> for OpenAPI servers.url

When config.domain is a bare host (e.g. trawl.me), the OpenAPI
servers.url previously pointed at the frontend host verbatim.

Extracts computeOpenApiServerUrl() — a pure named export that prepends
https://api. when the domain has no scheme, and returns the value
verbatim when it already starts with http(s)://. Backward-compatible
for all existing downstreams that set a full URL domain.

Promote-up from trawl_node (production-validated). Every devkit
downstream with a split frontend/backend topology (bare domain →
api.<bare>) now gets the correct OpenAPI host for free.

Tests: 5 unit cases covering bare host, https URL, http URL,
custom-subdomain URL, and falsy fallback.

Author: PierreBrisorgueil

lib/services/express.js

@@ -26,6 +26,18 @@ import errorTracker from './errorTracker.js';
 import AnalyticsService from './analytics.js';
 import analyticsMiddleware from '../middlewares/analytics.js';
 
+/**
+ * Compute the OpenAPI `servers.url` from `config.domain`.
+ * - If `domain` already has http(s):// → return verbatim (backward-compatible).
+ * - Otherwise prepend `https://api.` (api subdomain convention for split frontend/backend topologies).
+ * @param {string} domain - config.domain value
+ * @returns {string} OpenAPI servers.url
+ */
+export const computeOpenApiServerUrl = (domain) => {
+  const d = domain || 'http://localhost:3000';
+  return /^https?:\/\//.test(d) ? d : `https://api.${d}`;
+};
+
 /**
  * Default Redoc theme — Inter + JetBrains Mono, tighter sidebar, refined right panel.
  * No hardcoded brand color. Downstream projects override via config.docs.redocTheme
@@ -116,7 +128,7 @@ const initSwagger = (app) => {
       description: config.app.description,
       ...(xLogo ? { 'x-logo': xLogo } : {}),
     };
-    spec.servers = [{ url: config.domain || 'http://localhost:3000' }];
+    spec.servers = [{ url: computeOpenApiServerUrl(config.domain) }];
 
     // Merge per-module markdown guides into info.description so Redoc
     // renders them in its sidebar alongside the OpenAPI reference.

lib/services/tests/express.openapi-servers.unit.tests.js

@@ -0,0 +1,85 @@
+import { jest, describe, test, expect, beforeEach } from '@jest/globals';
+
+/**
+ * Unit tests for computeOpenApiServerUrl — pure function, no Express/config side-effects.
+ * express.js has transitive deps (logger, config) so we mock all module-level deps
+ * before importing to isolate the pure computation.
+ */
+describe('lib/services/express — OpenAPI servers.url derivation:', () => {
+  beforeEach(() => jest.resetModules());
+
+  const getComputeOpenApiServerUrl = async () => {
+    jest.unstable_mockModule('../../../config/index.js', () => ({
+      default: {
+        domain: 'http://localhost:3000',
+        swagger: { enable: false },
+        app: { title: 'test', description: 'd' },
+        files: { swagger: [], guides: [], routes: [], configs: [], policies: [], preRoutes: [] },
+        bodyParser: {},
+        cors: { origin: [], credentials: false },
+        csrf: {},
+        posthog: {},
+        analytics: {},
+        trust: {},
+        log: { fileLogger: { directoryPath: '/tmp', fileName: 'test.log' } },
+      },
+    }));
+    jest.unstable_mockModule('../../../lib/services/logger.js', () => ({
+      default: {
+        warn: jest.fn(),
+        error: jest.fn(),
+        info: jest.fn(),
+        debug: jest.fn(),
+        getLogFormat: jest.fn().mockReturnValue('dev'),
+        getMorganOptions: jest.fn().mockReturnValue({}),
+      },
+    }));
+    jest.unstable_mockModule('../../../lib/services/errorTracker.js', () => ({
+      default: { setupExpressErrorHandler: jest.fn(), init: jest.fn() },
+    }));
+    jest.unstable_mockModule('../../../lib/services/analytics.js', () => ({
+      default: { init: jest.fn().mockResolvedValue(undefined), isConfigured: jest.fn().mockReturnValue(false) },
+    }));
+    jest.unstable_mockModule('../../../lib/helpers/guides.js', () => ({
+      default: { loadGuides: jest.fn().mockReturnValue([]), mergeGuidesIntoSpec: jest.fn() },
+    }));
+    jest.unstable_mockModule('../../../lib/middlewares/requestId.js', () => ({ default: jest.fn() }));
+    jest.unstable_mockModule('../../../lib/middlewares/analytics.js', () => ({ default: jest.fn() }));
+    jest.unstable_mockModule('../../../lib/middlewares/policy.js', () => ({
+      default: { discoverPolicies: jest.fn().mockResolvedValue(undefined) },
+    }));
+    jest.unstable_mockModule('../../../lib/middlewares/posthog-context.middleware.js', () => ({
+      posthogContextMiddleware: jest.fn(),
+    }));
+
+    const mod = await import('../../../lib/services/express.js');
+    return mod.computeOpenApiServerUrl;
+  };
+
+  test('keeps full URL when domain already has http:// scheme', async () => {
+    const fn = await getComputeOpenApiServerUrl();
+    expect(fn('http://localhost:3000')).toBe('http://localhost:3000');
+  });
+
+  test('keeps full URL when domain already has https:// scheme with custom subdomain', async () => {
+    const fn = await getComputeOpenApiServerUrl();
+    expect(fn('https://app.example.com')).toBe('https://app.example.com');
+  });
+
+  test('prepends https://api. when domain is a bare host (no scheme)', async () => {
+    const fn = await getComputeOpenApiServerUrl();
+    expect(fn('trawl.me')).toBe('https://api.trawl.me');
+  });
+
+  test('prepends https://api. for any bare host', async () => {
+    const fn = await getComputeOpenApiServerUrl();
+    expect(fn('example.com')).toBe('https://api.example.com');
+  });
+
+  test('falls back to http://localhost:3000 when domain is falsy', async () => {
+    const fn = await getComputeOpenApiServerUrl();
+    expect(fn('')).toBe('http://localhost:3000');
+    expect(fn(null)).toBe('http://localhost:3000');
+    expect(fn(undefined)).toBe('http://localhost:3000');
+  });
+});