CircleCI has a couple of steps that run before user-defined steps within jobs (i.e "Spin Up Environment", "Preparing Environment Variables"). We'd like to be able to similarly define our own steps which can run on our host before the job steps are executed (but after the environment variables and job information are prepared/known). The rationale is to run custom logic to validate environment variables or contents of steps or gate the run based on the committer, etc.