Ability Activation is a first class predictive action. Whenever a client predictively activates an ability, it explicitly asks the server and the server explicitly responds. Once an ability has been predictively activated, the client has a valid 'prediction window' where predictive side effects can happen which are not explicitly 'asked about'. (E.g., we do not explicitly ask 'Can I decrement mana, Can I put this ability on cooldown. Those actions are considered logically atomic with activating an ability).