Commands

• ModelCommand / ModelCommand<T> — sync; weak CanExecuteChanged.
• AsyncModelCommand / AsyncModelCommand<T> — async, IsRunning, Cancel, ExecuteAsync; weak CanExecuteChanged.
• ICommand.Execute never throws. Failures go to IErrorSink / IDialogs. ExecuteAsync still rethrows.
• AsyncCommandOptions: timeout, retry, Debounce, Throttle, ConcurrencyMode (Prevent, CancelPrevious, Queue, Allow, Replace).

SaveCommand = new AsyncModelCommand(
    SaveAsync,
    () => CanSave,
    new AsyncCommandOptions
    {
        Concurrency = ConcurrencyMode.Prevent,
        Timeout = TimeSpan.FromSeconds(15),
        RetryCount = 2,
        RetryDelay = TimeSpan.FromSeconds(1),
    });