registerActionHandler
public abstract void registerActionHandler(Plugin owner, NamespacedKey powerKey, NamespacedKey actionKey, ElitePowerActionHandler handler)
Adds an optional Java integration handler for one attached power and semantic action. Multiple attached powers may register the same action key; handlers run in exact power attachment order after Lua hooks have had the first opportunity to accept it. The handler runs synchronously on the server thread and must perform or durably enqueue any work before returning ACCEPTED.