Who has the authority to perform that shutdown without getting arrested, and does that person have a mandate and responsibility to take that action in response to AI misbehavior?

What is their trigger condition? Will they get fired for pulling the plug? Do they get a bigger bonus if the servers keep running? Whose approval do they need? What response time is acceptable? How will they detect that the incident is happening?

It's easy to hand-wave "someone can just pull the plug" but there's an entire history of industrial accidents that happened because of the above problems of incentives, detection, procedures, not being taken seriously in advance. Someone could easily have pulled the plug on Chernobyl but nobody did, at least not before it was too late.