public void Unsubscribe(string id)
 => coordinatorAgent.Post(CoordinatorMessage.NewUnsubscribe(id));
 public void PublishCommand(CoordinatorMessage command)
 => coordinatorAgent.Post(command);
 public void Subscribe(string id, float initialAmount, IHubCallerConnectionContext <IStockTickerHubClient> caller)
 => coordinatorAgent.Post(CoordinatorMessage.NewSubscribe(id, initialAmount, caller));