Ranked recommendation: fix the docker system prune -af --volumes step
first (it deletes BuildKit's build cache before every build, so no
Dockerfile change can help until that stops), then split the
apt-get install layer from the Godot/Blender download layer so the
~470s apt layer becomes cache-eligible across nightly runs. Registry
cache and Gitea Actions' actions/cache don't fit this repo's single
persistent runner / multi-GB nightly-changing layers.
Research only, no code changes.
haylan