I dont understand how the state is await for by its systems - documentation can be improved

[ethereumdegen]

HI, i do not fully understand this example

 App::new()
        // Init bevy
        .add_plugins(DefaultPlugins)
        // Add our state type
        .add_state::<AppState>()
        // Add plugin for the splash screen
        .add_plugins(
            ProgressPlugin::new(AppState::Splash)
                .continue_to(AppState::MainMenu)
                .track_assets(),
        )
        // Add plugin for our game loading screen
        .add_plugins(ProgressPlugin::new(AppState::GameLoading).continue_to(AppState::InGame))
        // Load our UI assets during our splash screen
        .add_systems(OnEnter(AppState::Splash), load_ui_assets)
        // Our game loading screen
        // systems that implement tasks to be tracked for completion:
        .add_systems(
            Update,
            (
                net_init_session.track_progress(),
                world_generation.track_progress(),
                internal_thing.track_progress(),
                // we can also add regular untracked systems to our loading screen,
                // like to draw our progress bar:
                ui_progress_bar.after(TrackedProgressSet),
            )
                .run_if(in_state(AppState::GameLoading)),
        )
        .run();

So i am confused because it seems like in this example, if load_ui_assets takes a LONG time, the state would transition to AppState::MainMenu before that task is complete. If so, that is not helpful because main_main may require the ui assets. If not, how the heck is that being constrained? what part of load_ui_assets is indicating and telling the state manager to wait or go to the next state ?

[ethereumdegen]

OH i think i see, is it the assetHandles being added to AssetsLoading?

Well what if that system doesnt get a chance to do a cycle before the progress plugin tries to go to the next state? wouldnt it just go right to the next state like a race condition?

furthermore, how could a system like that be defined such that it returns Progress instead like in an instance where i am loading something or doing some work that doesnt involve Asset Handles ?