diff --git a/packages/ui/src/lib/runtime-url.test.ts b/packages/ui/src/lib/runtime-url.test.ts
index ba38e790..631076cf 100644
--- a/packages/ui/src/lib/runtime-url.test.ts
+++ b/packages/ui/src/lib/runtime-url.test.ts
@@ -8,6 +8,19 @@ import {
 import { setRuntimeBearerToken, setRuntimeUrlAuthToken } from './runtime-auth';
 
 describe('createRuntimeUrlResolver', () => {
+  const withWindow = <T>(value: unknown, callback: () => T): T => {
+    const originalWindow = globalThis.window;
+    try {
+      Object.defineProperty(globalThis, 'window', {
+        configurable: true,
+        value,
+      });
+      return callback();
+    } finally {
+      Object.defineProperty(globalThis, 'window', { configurable: true, value: originalWindow });
+    }
+  };
+
   test('preserves relative same-origin URLs by default', () => {
     const urls = createRuntimeUrlResolver({ currentHref: () => 'http://127.0.0.1:3000/app' });
 
@@ -52,6 +65,29 @@ describe('createRuntimeUrlResolver', () => {
     expect(urls.websocket('/api/terminal/ws')).toBe('ws://localhost:5173/api/terminal/ws');
   });
 
+  test('uses injected desktop API base URL for packaged WebSocket URLs', () => {
+    withWindow({
+      location: { origin: 'openchamber-ui://app', href: 'openchamber-ui://app/index.html' },
+      __OPENCHAMBER_API_BASE_URL__: 'http://127.0.0.1:57123',
+    }, () => {
+      const urls = createRuntimeUrlResolver({});
+
+      expect(urls.websocket('/api/global/event/ws')).toBe('ws://127.0.0.1:57123/api/global/event/ws');
+    });
+  });
+
+  test('reads injected desktop API base URL at call time', () => {
+    withWindow({
+      location: { origin: 'openchamber-ui://app', href: 'openchamber-ui://app/index.html' },
+    }, () => {
+      const urls = createRuntimeUrlResolver({});
+      (window as typeof window & { __OPENCHAMBER_API_BASE_URL__?: string }).__OPENCHAMBER_API_BASE_URL__ = 'http://127.0.0.1:57123';
+
+      expect(urls.api('/api/config/settings')).toBe('http://127.0.0.1:57123/api/config/settings');
+      expect(urls.websocket('/api/global/event/ws')).toBe('ws://127.0.0.1:57123/api/global/event/ws');
+    });
+  });
+
   test('allows runtime-wide resolver configuration', () => {
     const previous = getRuntimeUrlResolver();
     try {
diff --git a/packages/ui/src/lib/runtime-url.ts b/packages/ui/src/lib/runtime-url.ts
index 6eafc9c9..d3449113 100644
--- a/packages/ui/src/lib/runtime-url.ts
+++ b/packages/ui/src/lib/runtime-url.ts
@@ -33,6 +33,12 @@ const normalizeBaseUrl = (value: string | null | undefined): string => {
   return value.trim().replace(/\/+$/, '');
 };
 
+const readInjectedApiBaseUrl = (): string => {
+  if (typeof window === 'undefined') return '';
+  const injected = (window as typeof window & { __OPENCHAMBER_API_BASE_URL__?: string }).__OPENCHAMBER_API_BASE_URL__;
+  return normalizeBaseUrl(injected);
+};
+
 const currentHref = (config: RuntimeUrlConfig): string => {
   const configured = config.currentHref?.();
   if (configured) return configured;
@@ -107,11 +113,14 @@ const toWebSocketUrl = (candidate: string, config: RuntimeUrlConfig): string =>
 };
 
 export const createRuntimeUrlResolver = (config: RuntimeUrlConfig = {}): RuntimeUrlResolver => {
-  const apiBaseUrl = normalizeBaseUrl(config.apiBaseUrl);
-  const realtimeBaseUrl = normalizeBaseUrl(config.realtimeBaseUrl) || apiBaseUrl;
+  const configuredApiBaseUrl = normalizeBaseUrl(config.apiBaseUrl);
+  const configuredRealtimeBaseUrl = normalizeBaseUrl(config.realtimeBaseUrl);
 
-  const http = (path: string, query?: RuntimeUrlQuery): string => buildHttpUrl(apiBaseUrl, path, query);
-  const realtime = (path: string, query?: RuntimeUrlQuery): string => buildHttpUrl(realtimeBaseUrl, path, query);
+  const apiBaseUrl = (): string => configuredApiBaseUrl || readInjectedApiBaseUrl();
+  const realtimeBaseUrl = (): string => configuredRealtimeBaseUrl || apiBaseUrl();
+
+  const http = (path: string, query?: RuntimeUrlQuery): string => buildHttpUrl(apiBaseUrl(), path, query);
+  const realtime = (path: string, query?: RuntimeUrlQuery): string => buildHttpUrl(realtimeBaseUrl(), path, query);
 
   return {
     api: http,