@Larvitz Thanks for writing this up! Glad you found them useful!
For most builds, we anticipate users using a multi-stage build using a builder image, followed by a non-builder. Since the builder images contain a shell, you shouldn't need to use the `RUN ["echo", "hello"]` syntax - the regular `RUN echo hello` would work in the build stage.
We're working on minimising the images further too, including removing a bunch of tools used for managing certificates (which rely on Bash and are since broken) on the non-builders.