Help me integrate WorldEdit into my Spigot-based plug-in for undo support

This is just a bug fix request. Should be quick for someone with experience using the WorldEdit API. I'm trying to integrate WorldEdit (7.2.13) into my Spigot-based Java Minecraft (1.19.3) plug-in. I want to change some blocks in a WorldEdit editing session that can be later undone using the "//undo" command. My code is supposed to be creating a floating island. It works fine without the WorldEdit integration (but no undo ability, of course). With WorldEdit, it acts like there is something that can be undone, but it never actually changes the blocks. I don't see any runtime exceptions. It just doesn't change the blocks. I've attached the relevant code. If you know what I'm missing, then I'd love to hire you!