One of the reasons we created Depot is that cache mounts aren't supported in GitHub Actions, since each CI run is entirely ephemeral, so the files saved in a cache mount aren't saved across runs. BuildKit doesn't export those cache types via cache-to. There are some manual workarounds creating tarballs of the BuildKit context directory, but we wanted something that just works without needing to save/load tarballs, which can be quite slow.
How do you invalidate the cache / do a clean build? I've previously seen errors sneak in to docker builds due to cache - where perhaps an upstream docker image was gone, or other dependencies had changed (most likely to happen if a license is changed, or something is yanked due to a security issue).
One of the reasons we created Depot is that cache mounts aren't supported in GitHub Actions, since each CI run is entirely ephemeral, so the files saved in a cache mount aren't saved across runs. BuildKit doesn't export those cache types via cache-to. There are some manual workarounds creating tarballs of the BuildKit context directory, but we wanted something that just works without needing to save/load tarballs, which can be quite slow.