When you want to manually manage a reaction's lifecycle in MobX, you would typically use the ________ utility.

When you want to manually manage a reaction's lifecycle in MobX, you would typically use the reaction utility. The reaction function allows you to explicitly define when and how a reaction should run, giving you fine-grained control over reactivity. The other options (@transaction, @observable, @computed) are decorators or annotations in MobX and are not used for managing reaction lifecycles explicitly.