You are all way overthinking this. The Ukraines, hell even the collective west, does not have the deep strike weapons capable of penetrating the multiple levels of security that will be thrown around the event. Not without jumping in themselves and effectively doing a reverse Pearl Harbour scale attack involving almost all of their best assets in any case. And that’s WWIII if they do.
Ukrainian successful attacks deep into Russia have all involved using small, slow and cheap civilian drones to slip through lightly guarded areas; or using agents to launch small drones from closely. Neither of which has much chance punching through multiple layers of overlapping point defences on maximum alert readiness.
And given the numerous such penetrations in the past, I’m sure Chinese Presidential security will also be going above and beyond to do their own due diligence, and will put in place additional layers, systems and measures as they see fit to make sure Xi is protected to their satisfaction.
There is a vast gulf between what some idiots might want to do, and what they can do, and no amount of wishful thinking will change that.