@type t() :: %Riichi.Event.Discard{
  actor: Riichi.Actor.t() | nil,
  called_by: Riichi.Actor.t() | nil,
  declares_riichi: boolean(),
  tile: Riichi.Tile.t() | nil,
  tsumogiri: boolean() | nil,
  valid_actions: Riichi.Engine.ActionPredicate.all_valid_actions() | nil
}