Topic is the base interface used to define synchronous Message Broker topics. It is used by the IMessageBroker to constrain a broadcast to the synchronous messaging flow and to bind the Topic to the type of BaseMessage it carries.

Topics implement Topic<T>, where T specifies the message payload accepted by that Topic and must derive from BaseMessage. This association ensures that subscriptions and broadcasts for a Topic use the corresponding message type.

A Topic is intended to represent a specific event or notification within the application. Subscribers register an EventCallback for a Topic and a specific broadcaster, and the IMessageBroker invokes those callbacks when that broadcaster synchronously broadcasts the Topic.