How to keep the queue consumer flow open?

That's a number of questions, but I can provide some tips on the first one.

So the tutorial samples are based on the source code found in GitHub here. Note that any .NET application will terminate as soon as it has no foreground threads active. So in order to keep the process running requires us to suspend the main thread (or some other foreground thread) with a WaitHandle.WaitOne() (or similar thread-blocking operation).

That being said, there are two simple ways to keep an application like this open - depending on when you want the application to actually close down.

Option 1: replace the statement WaitEventWaitHandle.WaitOne() with Thread.Sleep(Timeout.Infinite) and remove all other references to WaitEventWaitHandle field. This application will run until it receives a sig-term signal or is force killed.

Option 2: move WaitEventWaitHandle.Set() to the HandleFlowEvent callback, and invoke it when args.Event == FlowEvent.FlowInactive. This application will terminate whenever the application disconnects from the broker (either due to network issues or the broker force disconnects the client).

Yes, so the exact nature of "how to keep the process alive" is very flexible - blocking the caller thread is one primitive example if you are writing a console style application. Other .NET Application types, such as ASP.NET Core / MVC apps will likely have other processes and tasks keeping the process alive (though typically at the end of initialization there is some kind of implicit main thread blocking that occurs).

However, if you wanted a less heavy handed and slightly more modern approach you could swap out the WaitEventWaitHandle field with a TaskCompletionSource:

class QueueConsumer : IDisposeable
{
  // all the other properties and fields…
  private TaskCompletionSource<object> runCompletion = new TaskCompletionSource<object>();
     
  Task Run(IContext context, string host)
  {
    // all the existing implementation…
    return runCompletion.Task;  
  }
     
  public void HandleFlowEvent(object sender, FlowEventArgs args)
  {
     if(args.Event == FlowEvent.FlowInactive)
     {
       runCompletion.SetResult(null);
    }
  }

}

So elsewhere in code you would now have the ability to:

await queueConsumer.Run(context, host);