I always heard hexagonal architecture has to be agnostic of any framework and use interfaces (SPI) to delegate each part of code which does not belong to the business layer.
But how to create a reactive business layer thanks to hexagonal architecture without using additional framework? Most of the time SPI's implementations will be reactive (API's implementations/adaptations also) and the core of the business layer should also be reactive.
Is there any JSR (implemented by each reactive framework) to use? Or should I define my own and perform adaptations with the final framework I will use in infra part?