SKILL.md, in the Agent Skills format.
Install from the CLI
The skills ship inside thesimforge binary, so they always match its commands:
skills install records what it wrote. Installing again updates those files; a file you changed by hand is refused (exit 2, skills_modified) unless you pass --force.
Download the pack
simforge-skills.zip holds the same skills, anAGENTS.md index and a README: