Ah, but you're missing perhaps the most probable scenario from the Russia side. Their primary goal for Ukraine was not particularly extreme - they wanted Ukraine to agree to remain a neutral country outside of NATO. That's asking basically nothing relative to the cost of a real war, and so I do think they expected those negotiations to succeed, because it's like being given the choice of setting your [uninsured] house on fire or agreeing to never buy fire insurance. Yeah both suck, but one is clearly much worse.

And this is even more likely given that negotiations for the end of the war started on February 28th, 4 days after the war began! Furthermore, the large convoy was completely inappropriate for actual military purposes and Russia didn't even have the logistics in place to keep it running. It makes no sense from a military perspective, but is 100% logical from an intimidation one.

I do think the airborne troops were a genuine decapitation strike attempt, as is tried in most of every war. It rarely works, but there was a chance it would (and in such a scenario you'd want a draft of the 'victory speech' written, much as we wrote a public obituary for the Apollo astronauts before they embarked for the Moon). But even if it failed, it also plays into the intimidation.

And those negotiations would have indeed almost certainly succeeded if the West didn't jump in and encourage Ukraine to "just fight". And I think the West did this expecting to rapidly inflict a 'strategic defeat' on Russia. Nobody got their quick victory, and instead we ended up with a real war that I don't think anybody thought would happen.