Nice work! Regarding your question on how to handle undoing a command on a shape that doesn't exist anymore, is there a way we could automatically recreate the shape?
Let's imagine that we work together on a design file that contains hundreds of icons. I'm responsible for adjusting the color palette while you're removing the old icons that are not used anymore. If I undo my last color update on all icons, I probably don't want to recreate the icon inadvertently and override the triage you're doing! So IMO, it's more of UX question than a technical question. Is there a better default solution that we can find to improve these edge cases? My initial thought is to have a small "toast" letting the user know that the undo operation couldn't be applied because X does not exist anymore, with a link to the version history panel to allow him to reinsert X if it wants to.