// RegisterEventDefinition registers an [EventDefinition] for the given event type.
// Returns an [ErrDuplicateRegistration] if a definition for the type has already been registered.
t := def.Type()
prev, ok := r.events[t]
if ok {
return fmt.Errorf("%w: event definition for event type %v: %v", ErrDuplicateRegistration, t, prev)
}
return nil
}