Fix ExistingDartDevelopmentServiceException

✅ Solution

This error usually means another instance of the Dart Development Service (DDS) is already running, preventing the Flutter tool from launching a new one. To fix it, try closing all running Flutter apps/emulators/browsers and ensure no stray `dart` processes are lingering in your system's task manager/activity monitor. Running `flutter clean` can also resolve package conflicts that trigger DDS issues.