If one were planning to recreate the whole Deus incident in controlled circumstances, how would you go about it? Assuming megacorp level assets, and a desire to keep things from going out of control (again).

use an oil platform with no connetion to the matrix.

I would recommend doing it under the oil rig in a submerged dome.

First sign of AI trouble they blow the dome and soak all the electronics.

Main question is: How can you monitor what the AI is doing? I'm assuming a controlled experiment such as the dome idea. If you're on site, you wouldn't want to blow the dome (or trigger whatever device to terminate the experiment) with you in it. If you're offsite, well the AI isn't truly contained if an electronic signal/cable can get to you. Also, the site must have no drones in the vicinity, no signal device of any kind (or even the material to create one?), no rogue agent, etc. So many things can go wrong, including some that are hard to plan for. An experiment like this is just begging to blow up in your face imo.

And this doesn't usually stop megacorps from still trying dumb things

I'm currently going with a facility underneath an awakened island in the middle of the pacific. There are three networks: the hard-wired network with no external feeds for the AI, the local network, and one heavily guarded terminal that connects to the outside world. The signal tower at the airport doubles as a smart jammer so that only authorized signals are going anywhere, and in any case most of the facility is underground and can't access the main matrix.

Now the AI is contained with no chance of escape, but it's still better all around if they use living security to prevent industrial spying/sabotage.

The island has an airport and a dock, both of which take constant effort to keep clear as the jungle is constantly trying to reclaim them and awakened critters stalk the night.

Red Queen!
Red Queen!

Maybe I should add neurotoxin dispensers to the facility's defenses...

Contaminated neurotoxin where a few ghouls fell into the batch that was being made so it infects the place when it goes off.

So we have this shiny new AI, what should we do with it?

As experience shows, even airgapped networks won't stop a superAI like Deus. Your safest bet, if you've come into possession of one, it doing the responsible thing and destroying it.