https://api.flutter.dev/flutter/dart-ui/AppLifecycleState-class.html

Currently, the majority of desktop embedding that go through embedder.h does not send AppLifeCycleState message to framework. That means the state is always null. This was ok because framework always enables the frame scheduling if it receives unknown state.

However, with the introducing of detached state, the engine will default to detached state and framework will disable the frame until engine become active. This become a problem because the desktop embedding does not send AppLifeCycleState.resumed message to framework, which causes the framework think engine is never going to be active.