diff --git a/package.json b/package.json
index d7ae086b..2127aa24 100644
--- a/package.json
+++ b/package.json
@@ -8,6 +8,7 @@
     "dev": "vite",
     "build": "tsc && vite build",
     "test:desktop-reopen": "node --experimental-strip-types --test tests/desktopReopen.test.ts",
+    "test:browser-runtime": "node --experimental-strip-types --test tests/browserRuntime.test.ts",
     "test:close-preference": "node --experimental-strip-types --test tests/codexClosePreference.test.ts",
     "test:reset-credits": "node --experimental-strip-types --test tests/resetCredits.test.ts",
     "test:updater": "node --experimental-strip-types --test tests/updateInstallation.test.ts tests/updaterToolchain.test.ts",
diff --git a/src/App.tsx b/src/App.tsx
index 6b11a1e2..9e836c6c 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -1,5 +1,4 @@
 import { useState, useEffect, useCallback, useMemo, useRef } from "react";
-import { getCurrentWindow } from "@tauri-apps/api/window";
 import { useAccounts } from "./hooks/useAccounts";
 import { useDesktopReopen } from "./hooks/useDesktopReopen";
 import { useCodexClosePreference } from "./hooks/useCodexClosePreference";
@@ -42,6 +41,7 @@ import {
   type AutoWarmupWindow,
   type AutoWarmupWindowKind,
 } from "./lib/autoWarmupPolicy";
+import { getTauriWindow } from "./lib/tauriWindow";
 import "./App.css";
 
 const AUTO_WARMUP_CHECK_INTERVAL_MS = 30 * 1000;
@@ -65,7 +65,6 @@ type AutoWarmupLedger = Record<
     lastAutoWindowKind?: AutoWarmupWindowKind;
   }
 >;
-const appWindow = getCurrentWindow();
 const isMacOs =
   typeof navigator !== "undefined" &&
   /(Mac|iPhone|iPod|iPad)/i.test(navigator.userAgent);
@@ -388,14 +387,14 @@ function App() {
   const handleTitlebarDrag = useCallback(
     (event: React.MouseEvent<HTMLDivElement>) => {
       if (!isTauriRuntime() || event.button !== 0) return;
-      void appWindow.startDragging();
+      void getTauriWindow()?.startDragging();
     },
     []
   );
 
   const handleTitlebarDoubleClick = useCallback(() => {
     if (!isTauriRuntime()) return;
-    void appWindow.toggleMaximize();
+    void getTauriWindow()?.toggleMaximize();
   }, []);
 
   const toggleMask = (accountId: string) => {
@@ -522,6 +521,9 @@ function App() {
   useEffect(() => {
     if (!isTauriRuntime() || isMacOs) return;
 
+    const appWindow = getTauriWindow();
+    if (!appWindow) return;
+
     let unlisten: (() => void) | undefined;
 
     const syncMaximizedState = async () => {
@@ -1354,11 +1356,11 @@ function App() {
             onDoubleClick={handleTitlebarDoubleClick}
             className={`h-full flex-1 select-none cursor-default ${isMacOs ? "ml-18 mr-2" : "mr-3"}`}
           />
-          {!isMacOs && (
+          {isTauriRuntime() && !isMacOs && (
             <div className="flex items-center gap-1">
               <button
                 onClick={() => {
-                  void appWindow.minimize();
+                  void getTauriWindow()?.minimize();
                 }}
                 className="flex h-8 w-8 items-center justify-center rounded-md text-gray-500 transition-colors hover:bg-gray-100 hover:text-gray-900 dark:text-gray-400 dark:hover:bg-gray-800 dark:hover:text-gray-100"
                 title="Minimize"
@@ -1369,7 +1371,7 @@ function App() {
               </button>
               <button
                 onClick={() => {
-                  void appWindow.toggleMaximize();
+                  void getTauriWindow()?.toggleMaximize();
                 }}
                 className="flex h-8 w-8 items-center justify-center rounded-md text-gray-500 transition-colors hover:bg-gray-100 hover:text-gray-900 dark:text-gray-400 dark:hover:bg-gray-800 dark:hover:text-gray-100"
                 title={isWindowMaximized ? "Restore" : "Maximize"}
@@ -1387,7 +1389,7 @@ function App() {
               </button>
               <button
                 onClick={() => {
-                  void appWindow.close();
+                  void getTauriWindow()?.close();
                 }}
                 className="flex h-8 w-8 items-center justify-center rounded-md text-gray-500 transition-colors hover:bg-red-500 hover:text-white dark:text-gray-400 dark:hover:bg-red-500 dark:hover:text-white"
                 title="Close"
diff --git a/src/lib/tauriWindow.ts b/src/lib/tauriWindow.ts
new file mode 100644
index 00000000..1ab14b2c
--- /dev/null
+++ b/src/lib/tauriWindow.ts
@@ -0,0 +1,14 @@
+import { getCurrentWindow, type Window as TauriWindow } from "@tauri-apps/api/window";
+
+let cachedWindow: TauriWindow | null = null;
+
+/**
+ * Resolve the Tauri window only inside the Tauri runtime. Browser/LAN mode
+ * must be able to evaluate the React bundle without touching Tauri internals.
+ */
+export function getTauriWindow(): TauriWindow | null {
+  if (typeof window === "undefined" || !("__TAURI_INTERNALS__" in window)) {
+    return null;
+  }
+  return (cachedWindow ??= getCurrentWindow());
+}
diff --git a/tests/browserRuntime.test.ts b/tests/browserRuntime.test.ts
new file mode 100644
index 00000000..7f3d13e6
--- /dev/null
+++ b/tests/browserRuntime.test.ts
@@ -0,0 +1,21 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { getTauriWindow } from "../src/lib/tauriWindow.ts";
+
+test("browser runtime does not resolve a Tauri window", () => {
+  assert.equal(getTauriWindow(), null);
+});
+
+test("a plain browser-like window without Tauri internals remains safe", () => {
+  const previous = Object.getOwnPropertyDescriptor(globalThis, "window");
+  Object.defineProperty(globalThis, "window", {
+    configurable: true,
+    value: {},
+  });
+  try {
+    assert.equal(getTauriWindow(), null);
+  } finally {
+    if (previous) Object.defineProperty(globalThis, "window", previous);
+    else delete (globalThis as { window?: unknown }).window;
+  }
+});