Yup, this is basically what I was thinking - the daemon would run as a system user (e.g. root or something that could access user files) would "commit" the chan

Yup, this is basically what I was thinking - the daemon would run as a system user (e.g. root or something that could access user files) would "commit" the changes on write, pulling from the user's files, creating a read-only copy. Obviously there are of course issues running stuff like this as root - if the daemon was compromised in any way it's game over.