I tried it with Codex as well and I got 10 GB after pulling the image like I got with Kiro. It could still increase any time youdo something in the sandbox that needs to write the filesystem. Sometimes writing different parts of the disk is better so it is evenly used during the years. I think this happens with SSDs, but when using a virtual disk without limited size, it can make your disk grow until it fills up your disk.
I shared this feedback internally with Docker, but I see you also opened a ticket (thanks for that too)