Keep desktop smoke on the configured backend

Browser-mode startup now respects an explicit Vite desktop server URL before falling back to same-origin H5 serving. This keeps local desktop smoke tests pointed at the real API server while preserving same-origin behavior for packaged H5 access.

Constraint: Vite dev smoke serves the web app and API on different loopback ports
Rejected: Treat same-origin as always preferred | Vite would answer /api requests with HTML and the chat surface never becomes ready
Confidence: high
Scope-risk: narrow
Tested: cd desktop && bun run test -- src/lib/desktopRuntime.test.ts src/api/client.test.ts --run
Tested: bun run check:desktop
Tested: bun run quality:gate --mode baseline --allow-live --only 'provider-smoke:*' --only 'desktop-smoke:*' --provider-model codingplan:main:codingplan-main
Not-tested: Full bun run quality:pr after this commit; it will run again during push

desktop/src/api/client.ts

@@ -44,6 +44,10 @@ export function getDefaultBaseUrl() {
   return DEFAULT_BASE_URL
 }
 
+export function hasExplicitDefaultBaseUrl() {
+  return Boolean(ENV_BASE_URL)
+}
+
 export class ApiError extends Error {
   constructor(
     public status: number,

desktop/src/lib/desktopRuntime.test.ts

@@ -2,6 +2,7 @@ import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 
 const clientMocks = vi.hoisted(() => ({
   defaultBaseUrl: 'http://127.0.0.1:3456',
+  explicitDefaultBaseUrl: false,
   setBaseUrl: vi.fn(),
   setAuthToken: vi.fn(),
   postVerify: vi.fn(),
@@ -12,6 +13,7 @@ vi.mock('../api/client', () => ({
     post: clientMocks.postVerify,
   },
   getDefaultBaseUrl: () => clientMocks.defaultBaseUrl,
+  hasExplicitDefaultBaseUrl: () => clientMocks.explicitDefaultBaseUrl,
   setAuthToken: clientMocks.setAuthToken,
   setBaseUrl: clientMocks.setBaseUrl,
 }))
@@ -31,6 +33,8 @@ describe('desktopRuntime browser H5 bootstrap', () => {
 
   beforeEach(() => {
     vi.clearAllMocks()
+    clientMocks.defaultBaseUrl = 'http://127.0.0.1:3456'
+    clientMocks.explicitDefaultBaseUrl = false
     vi.useRealTimers()
     window.localStorage.clear()
     window.history.pushState({}, '', '/')
@@ -111,6 +115,26 @@ describe('desktopRuntime browser H5 bootstrap', () => {
     })
   })
 
+  it('prefers an explicit Vite desktop server URL over the dev server origin', async () => {
+    clientMocks.defaultBaseUrl = 'http://127.0.0.1:55189'
+    clientMocks.explicitDefaultBaseUrl = true
+    window.history.pushState({}, '', '/')
+    globalThis.fetch = vi.fn().mockResolvedValue(
+      new Response(null, { status: 200 }),
+    ) as typeof fetch
+
+    await expect(initializeDesktopServerUrl()).resolves.toBe('http://127.0.0.1:55189')
+
+    expect(clientMocks.setBaseUrl).toHaveBeenLastCalledWith('http://127.0.0.1:55189')
+    expect(clientMocks.setAuthToken).toHaveBeenLastCalledWith(null)
+    expect(globalThis.fetch).toHaveBeenCalledWith('http://127.0.0.1:55189/health', {
+      cache: 'no-store',
+    })
+    expect(globalThis.fetch).toHaveBeenCalledWith('http://127.0.0.1:55189/api/status', {
+      cache: 'no-store',
+    })
+  })
+
   it('normalizes unreachable remote browser startup into a recoverable H5 error', async () => {
     vi.useFakeTimers()
     globalThis.fetch = vi.fn().mockRejectedValue(new TypeError('Failed to fetch')) as typeof fetch

desktop/src/lib/desktopRuntime.ts

@@ -1,4 +1,10 @@
-import { api, getDefaultBaseUrl, setAuthToken, setBaseUrl } from '../api/client'
+import {
+  api,
+  getDefaultBaseUrl,
+  hasExplicitDefaultBaseUrl,
+  setAuthToken,
+  setBaseUrl,
+} from '../api/client'
 
 export const H5_SERVER_URL_STORAGE_KEY = 'cc-haha-h5-server-url'
 export const H5_TOKEN_STORAGE_KEY = 'cc-haha-h5-token'
@@ -133,7 +139,7 @@ async function initializeBrowserServerUrl(fallbackUrl: string) {
   const requestedUrl =
     normalizeServerUrl(queryUrl) ??
     stored.serverUrl ??
-    getSameOriginServerUrl() ??
+    getConfiguredBrowserServerUrl(fallbackUrl) ??
     fallbackUrl
   const token = stored.token
   const browserH5Runtime = requiresH5AuthForServerUrl(requestedUrl)
@@ -249,6 +255,14 @@ function getSameOriginServerUrl() {
   return normalizeServerUrl(window.location.origin)
 }
 
+function getConfiguredBrowserServerUrl(fallbackUrl: string) {
+  if (hasExplicitDefaultBaseUrl()) {
+    return normalizeServerUrl(fallbackUrl)
+  }
+
+  return getSameOriginServerUrl()
+}
+
 export function isLoopbackHostname(hostname: string) {
   const normalized = hostname.trim().replace(/^\[/, '').replace(/\]$/, '').toLowerCase()
   return normalized === '127.0.0.1' || normalized === 'localhost' || normalized === '::1'