I think the actual algo weighting stuff about what action follows a nuclear detonation is more heavy on the actual loses the nuclear incident caused. Then a political approach has to be triggered, someone would call Putin or whoever is at the phone in Russia, "look guys, we saw your flare from here, nothing remarkable happened BUT just don't push it anymore".
If Putin decides to go wild nuking one more thing, again, you should look at what the heck was actually blowed up, and then look what's next on your side.
At some point, even if Putin detonates 3 nuclear devices on his own land, some serious sh*t will unfold, most probably from inside Russia's top leadership, which exists and probably is constantly looking for practical crazyness in his new czar.
Spoiler Alert: czars are not meant to last forever.
If you remember, something like this already happened when North Korea started its underground testing. Nobody was saying it aloud, but most certainly lots of military resources were at least half awake, ready to go into WWIII at moments notice. But nothing happened.