What it does. Codex metadata for the skill: display name “Codebase Design” and short description “Vocabulary for deep-module design”. It has no policy block, so Codex may start the skill on its own.
Why it’s here. Codex reads it for its skill picker. The repo’s .agents/invocation.md says every skill carries one and that “It holds Codex UI metadata”. Leaving out the policy block keeps the skill model-invoked, matching its SKILL.md. SKILL.md itself does not refer to this file.