Why would any state be concerned about casus beli (FYI you keep misspelling it) when the big dog in the room doesn’t give a shit?

Because international politics is still politics. Your argument doesn't make sense in the same way that "Iran's only goal ever is to wipe Israel off the map and if we don't do something right now they'll do it tomorrow" doesn't make sense. It's because every country weighs the risks and consequences of an action. These things matter in as much as the reaction to them by other states. That's literally the lynch pin of international law. There is no big mommy, the only potential mommy is a complex calculus of geopolitics.

You’re arguing international law like we’re in some kind of 4X.

If you don't understand that's what Russia (and Kuchinich) is also doing and from a point of realpolitik rather than international law then this conversation is pointless. I did not drag us to this crossroads. I merely saw some people yelling and decided to join in the fun.

If the problem Russia has is that it feels NATO is attacking it, then in reality Russia has no real leg to stand on, because it's complaints are "this is a shadow war", and a rectification of that is to just make it into a real war. They're pushing an issue they would heavily stand to lose in if they actually believed it was a real issue.

To rephrase Russia is only making the case that NATO is being unfair by playing in the shadows because it has extreme certainty that NATO is not going to enter the war over Ukraine, and it also knows that the Russian escalation that they are threatening would change that calculus for all NATO countries overnight. Also the situation that they themselves would use that escalation in, isn't happening and is not going to happen unless NATO heavily joins the war and digs into Russian territory. So it's not going to actually make good on its threats.

While I agree that NATO should not provoke Russia, understanding the motives behind these political plays and consequences of what could happen in response shows that Russia itself doesn't believe this is a provocation. What's happening right now is there's 3 kids in a back seat one is 5, one is 12, and one is 16. The 12 year old is beating the shit out of the 5 year old for agreeing with the 16 year old who goaded the 5 year old to do so. The 16 year old is doing the "I'm not touching you" to the 12 year old and the 12 year old while still beating the shit out of the 5 year old is saying "MOM HE'S TOUCHING ME".