fix(e2e): address review feedback and window-managerless Linux CI

- Skip the three window-manager-dependent E2E assertions (maximize
  toggle, main-process state sync, minimize) on Linux CI: GitHub's
  ubuntu runners drive Electron under xvfb without a window manager, so
  maximize/minimize state never materializes there. Windows CI and
  local Linux/macOS runs keep the coverage.
- WINDOW:TOGGLE_MAXIMIZE now returns the requested state instead of
  re-reading isMaximized() right after the call, which races on Linux
  window managers where maximize()/unmaximize() complete
  asynchronously; the WINDOW:STATE_CHANGED push stays authoritative.
- Skip attaching window-state push listeners on macOS, where the
  custom controls never mount and the IPC traffic had no subscriber.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/electron-backend-e2e/src/window-controls.e2e.ts

@@ -7,6 +7,13 @@ import {
 
 // Custom window controls are only rendered on Windows/Linux; macOS keeps
 // the native traffic lights.
+//
+// Linux CI runs Electron under xvfb, which has no window manager, so
+// maximize/minimize never take effect there — those tests are skipped and
+// rely on Windows CI plus local Linux/macOS runs for coverage.
+const isWindowManagerlessCi =
+    process.platform === 'linux' && !!process.env['CI'];
+
 test.describe('Custom window controls', () => {
     test.skip(
         process.platform === 'darwin',
@@ -39,6 +46,10 @@ test.describe('Custom window controls', () => {
     test('@electron maximize button toggles the native window state', async ({
         dataDir,
     }) => {
+        test.skip(
+            isWindowManagerlessCi,
+            'xvfb on Linux CI has no window manager'
+        );
         const app = await launchElectronApp(dataDir);
 
         try {
@@ -67,6 +78,10 @@ test.describe('Custom window controls', () => {
     test('@electron reflects window state changes triggered from the main process', async ({
         dataDir,
     }) => {
+        test.skip(
+            isWindowManagerlessCi,
+            'xvfb on Linux CI has no window manager'
+        );
         const app = await launchElectronApp(dataDir);
 
         try {
@@ -91,6 +106,10 @@ test.describe('Custom window controls', () => {
     test('@electron minimize button minimizes the window', async ({
         dataDir,
     }) => {
+        test.skip(
+            isWindowManagerlessCi,
+            'xvfb on Linux CI has no window manager'
+        );
         const app = await launchElectronApp(dataDir);
 
         try {

apps/electron-backend/src/app/app.ts

@@ -258,6 +258,13 @@ export default class App {
     }
 
     private static attachWindowStateEvents(win: Electron.BrowserWindow): void {
+        // Only Windows/Linux render custom window controls that subscribe
+        // to these pushes; macOS keeps the native traffic lights, so
+        // sending state updates there would be dead IPC traffic.
+        if (process.platform === 'darwin') {
+            return;
+        }
+
         const sendWindowState = () => {
             if (win.isDestroyed()) {
                 return;

apps/electron-backend/src/app/events/window.events.ts

@@ -45,15 +45,26 @@ ipcMain.handle(WINDOW_MINIMIZE, (event) => {
 ipcMain.handle(WINDOW_TOGGLE_MAXIMIZE, (event): WindowState => {
     const win = getSenderWindow(event);
 
-    if (win) {
-        if (win.isMaximized()) {
-            win.unmaximize();
-        } else {
-            win.maximize();
-        }
+    if (!win) {
+        return getWindowState(win);
     }
 
-    return getWindowState(win);
+    // maximize()/unmaximize() complete asynchronously on Linux window
+    // managers, so re-reading isMaximized() here would race. Report the
+    // requested state instead; the WINDOW:STATE_CHANGED push stays the
+    // authoritative update once the window manager has acted.
+    const shouldMaximize = !win.isMaximized();
+
+    if (shouldMaximize) {
+        win.maximize();
+    } else {
+        win.unmaximize();
+    }
+
+    return {
+        isMaximized: shouldMaximize,
+        isFullScreen: win.isFullScreen(),
+    };
 });
 
 // win.close() (instead of app.quit()) so the window's 'close' handler still