This "undo record" sounds like (essentially) the same thing as storing the (compressed) diff from the current state to the prior state which you were arguing ag

This "undo record" sounds like (essentially) the same thing as storing the (compressed) diff from the current state to the prior state which you were arguing against. If you have an operation that is changing a lot and isn't reversible, either you are reexecuting from the beginning of time (which particularly for image editing would be ridiculous: even a single operation on the image is often annoyingly slow, much less suddenly doing tons as you rapidly make changes and then undo back through them) or you are storing checkpoints at some frequency in the form of diffs on the full serialized state (which seems to be what you are returning to re-suggest anyway).