Yeah, good luck with that. It will never happen. The world won't respond with military even if Russia drops a nuke on Kyiv.
There would be hell, Putin would lose all his allies, the world would protest and everyone would cut ties with Russia, but there would be no "invasion on Russia". No military act.
They have nukes in other countries, ships, submarines, not just inside Russia. No other country would risk eating a nuke in a major city. Putin is untouchable by the west and he knows it.