> Yeah, it's not like a line in the sand, admitted as such by both sides, was broken, one with explicit promises that it wouldn't be.
Ah, your oddly-vague wording must of course be referring to how Russia explicitly promised to respect Ukraine's borders [0], a line they are violently crossing as we speak. First with an undeclared guerrilla-war and annexation, and more-recently with a massive "surprise" invasion--after spending several weeks of lying about their buildup and pretending that other countries were just trying to make them look bad.
If you are sarcastically suggesting something else... Well, go ahead, share the evidence for whatever-it-is, the kind of documentary evidence which countries ensure is always abundant for any remotely important international promise. (That is in contrast to self-serving lies from the Kremlin, which rely heavily on refusing to explain.)
[0] https://en.m.wikipedia.org/wiki/Budapest_Memorandum