I mean no disrespect, but this simply doesn't reflect reality.

You begin by casually assuming penetration of Russian communications is so absolute we'd know of a launch order, based on our abilities to monitor battlefield communications and track the mass mobilization of the hundreds of thousands of troops?

Then you seem to misunderstand that "30 minutes" is the time until the missile hits Washington DC, not the time until the launch, and frankly it wouldn't make much difference even if that were the case.

Also, we somehow have the ability to hit all their launch sites before they even fire?

Also, we're tracking all Russian subs 24/7?

Then you compare all of this to cyber-sabotage of Iranian centrifuges. Which isn't at all related and also hasn't stopped Iran's nuclear program.

The US has amazing capabilities, but it's not magic. There is zero chance we would be able to prevent or even significantly mitigate a nuclear attack were it to occur.

If North Korea happens to launch a single missile our way, we might be able to stop it, but I wouldn't count on it. A country like Russia launching an attack would be the end of the world for everyone.