Show HN: An incremental build cache for Rust on GHA

Hi HN,

I'm Kyle, the creator of Clipper, a container registry with 7x faster builds via lazy pulls and cache mount exports. In the process of implementing cache mount exports I ended up with a FUSE mounted filesystem backed by a remote content defined store. I went looking for fun things to do with it and found that there's not really a good way to keep Rust incremental build state around on ephemeral runners, so here we are.

Rust generally uses https://github.com/mozilla/sccache for caching, but sccache disables itself when incremental compilation is enabled (https://github.com/mozilla/sccache/issues/236) and it isn't on Mozilla's roadmap to fix.

It unfortunately doesn't really work on stable Rust (which uses mtime to decide when files have changed, rather than file contents), but maybe once https://github.com/rust-lang/cargo/issues/14136 is stable it will be useful to someone.