I think the closest call we've had since the end of the Cold War was the Russian cruise missile that crashed in Poland near the beginning of the war in Ukraine. There was a world where that hit something more important (or at least the Russians thought it did), which would potentially lead to an Article 5 call, which if the Russians anticipated, the rational move could well be a preemptive strike. But as you said, that's miles from the "One act of open defiance by a subordinate from armaggedon" type scenarios.