I am curious, how do you handle latency issues for on demand access? I saw you use FUSE (and FSKit), and from my experience it is pain to make filesystems in userspace work on-demand over WAN because a) latency, and variable RTT; and b) you can't saturate the wire and aggressively read ahead things, otherwise native apps will freeze, lag, or just make the UX unpleasant, especially if there are too many placeholder files, or large files with random jumps in them.
I think what makes FUSE/FSKit great here is that agents usually only need to see the file metadata + read a handful of actual files, rather than some applications needing read many things. If you're doing huge rewrites, this is a problem, but most tasks are usually somewhat small. Definitely is a problem that I've ran into though, we do cache aggressively to try to solve some of this, but it'll never be as fast as reading/writing directly to disk. We have benchmarks [1] if you want to take a look at how we're testing some of the performance there.
[1] https://oak.space/oak/benchmarks