The shortest path to something like that (assuming it's a good idea) would probably not be writing an in-memory incremental compile state server, but storing in

The shortest path to something like that (assuming it's a good idea) would probably not be writing an in-memory incremental compile state server, but storing intermediate artifacts as very cheap-to-serialize files (flatpak or just mmap and a cast), and then storing the files on /dev/shm or some other memory filesystem. That would give you most of the benefits you discussed (unless you clear out the cache/restart the machine) without requiring a huge rewrite of how state is stored. Most of the assumptions I'm making here are unverified, though, so take it with a large grain of salt.