visionOS: add “run in background” setting and respect it

Mini vMac/AppDelegate.m

@@ -334,16 +334,20 @@ NSString *DocumentsChangedNotification = @"documentsChanged";
         }
     }
     if ([self sceneWithName:@"Default"] == nil) {
+        [[AppDelegate sharedEmulator] setRunning:YES];
         return [UISceneConfiguration configurationWithName:@"Default" sessionRole:UIWindowSceneSessionRoleApplication];
     }
     return nil;
 }
 
 - (void)application:(UIApplication *)application didDiscardSceneSessions:(NSSet<UISceneSession *> *)sceneSessions {
-    // if only keyboard is left, close it too
     if ([self sceneWithName:@"Default"] == nil) {
+        if ([[NSUserDefaults standardUserDefaults] boolForKey:@"runInBackground"] == NO) {
+            [[AppDelegate sharedEmulator] setRunning:NO];
+        }
         UIScene *keyboardScene = [self sceneWithName:@"Keyboard"];
         if (keyboardScene != nil) {
+            // if only keyboard is left, close it too
             [application requestSceneSessionDestruction:keyboardScene.session options:nil errorHandler:nil];
         }
     }

Mini vMac/DefaultSceneDelegate.swift

@@ -32,4 +32,14 @@ class DefaultSceneDelegate: UIResponder, UIWindowSceneDelegate {
             window.makeKeyAndVisible()
         }
     }
+
+    func sceneDidEnterBackground(_ scene: UIScene) {
+        if UserDefaults.standard.bool(forKey: "runInBackground") == false {
+            AppDelegate.emulator.isRunning = false
+        }
+    }
+
+    func sceneDidBecomeActive(_ scene: UIScene) {
+        AppDelegate.emulator.isRunning = true
+    }
 }

Mini vMac/SettingsMenu.swift

@@ -25,6 +25,7 @@ struct SettingsMenu: View {
 
 struct SpeedMenu: View {
     @AppStorage("speedValue") var currentSpeed: EmulatorSpeed = .speed1x
+    @AppStorage("runInBackground") var runInBackground: Bool = false
     private var currentSpeedImage: String {
         switch currentSpeed {
         case .speed1x:
@@ -54,6 +55,8 @@ struct SpeedMenu: View {
             SpeedButton(label: "16x", speed: .speed16x)
             SpeedButton(label: "32x", speed: .speed32x)
             SpeedButton(label: "Unlimited", speed: .speedAllOut)
+            Divider()
+            Toggle("Run in Background", isOn: $runInBackground)
         }.menuOrder(.fixed)
     }
 }