Request for persistent BuildKit cache across builds for custom Dockerfiles

I hope Zeabur's shared CI can persist Docker / BuildKit cache across deployments when building custom Dockerfiles.

The Build Spec states that build machines are ephemeral and released immediately after the image is pushed. This matches my observations: in two consecutive deployments where only a small amount of source code was changed and the lockfile and most layers remained the same, the wall-clock time was still a ~5-minute cold build, and there were no CACHED logs. The RUN --mount=type=cache in the Dockerfile did not persist across builds either.

The Node documentation's cache_dependencies only applies to installation steps generated by zbpack and does not affect custom Dockerfiles. The Dockerfile documentation also does not specify whether layer caching is persisted across builds.

Suggestions in order of priority:

1. Implement registry-based layer caching for custom Dockerfiles (--cache-from / --cache-to type=registry) so it can be reused even if the build machine changes.
2. Or, pin the BuildKit worker per project / service.
3. Before this is implemented, please clarify in the documentation that: custom Dockerfiles do not guarantee cross-build cache reuse; cache_dependencies only applies to zbpack.

I am not asking to host the cache on a Dedicated Server / VPS. The build is already on shared CI, and the VPS only pulls the image.