Where an agent's events go: a log, a broadcast, anything a client reads from.

defmodule MyApp.Events do
  @behaviour WardrikCore.Events

  @impl true
  def handle_event(%WardrikCore.Event{} = event, _opts) do
    Phoenix.PubSub.broadcast(MyApp.PubSub, "agent:#{event.metadata.agent_id}", event)
  end
end

Give it to an agent as events: {MyApp.Events, opts}. Core calls it with every WardrikCore.Event, in the process the event happens in. Keep it quick: store or send the event, and return.