Will Ukraine Rain (Missiles) on Putin’s Parade?

Russia's President Putin is gearing up for the annual grand military parade in Moscow. This year is a big one because it's the 80th anniversary of the end of World War 2, and bigger names from the subset of the geopolitical world prepared to be seen in Russia are going to be attending. But Ukraine has rejected Putin's offer of a 3-day ceasefire during the period of the parade, and has said that it cannot guarantee the safety of dignitaries who attend the Moscow event. Are they planning an attack? Is it a big bluff? And just how much has it rattled Putin as he contemplates being humiliated by Ukraine in front of Xi Jinping?