For the benefit of the ignorant barbarian, how does reaction work right now?
Well, the short version would be "they don't".
But putting more effort into it...
So far we have just some of the most basic types of reactions (attack of opportunity if someone moves in your area of control, Riposte (if have the skill) when someone attacks you and misses, etc) and the way they work is that they are toggles that you can activate to take that type of reaction automatically when the chance comes.
If the toggle is disabled, on the other hand, you just pass on the reaction without any request of confirmation.
Now, this is fairly lame but mostly functional when it comes to basic reactions that don't consume resources. The problem will come as stuff like Shield (the spell), counter-spell, etc will enter the arena (OR NOT, if Larian decides to skip on them), since these are reactions that consume limited resources AND what's at stake is a bit more than "taking your chance to give a bonus swing). For instance an automated Counter-spell would have high chances to get wasted on a cantrip or stopping some stupid buff, when you ideally want to save it to intercept the enemy caster throwing a fireball at your party.
Admittedly I can understand a dev wanting to find some alternate solution for something like Cutting Words, something that can be called at will (like an instant/interrupt in Magic) to debuff basically ANY ongoing enemy action... But I don't think fringe cases like this should dictate the entirety of how the reaction system works.
It's also somewhat amusing that Larian is rubbing salt on the wound, making the final boss of their EA (a massive iron golem) an encounter that is built around the idea of kiting the fucker around since he keeps chasing the "last hitter"... And a misplaced AoO there can turn into a serious middle finger to your entire game plan.
