A deep dive into Debian 13 /tmp: What's new, and what to do if you don't like it

Why is there no write through unionfs in Linux? Feels like a very useful tool to have. Does no one else need this? Have half a mind to write one with an NFS interface.

EDIT: Thank you, jaunty. But all of these are device level. Even bcachefs was block device level. It doesn't allow union over a FUSE FS etc. It seems strange to not have it at the filesystem level.