Kinda ironic this description is so verbose.

> Use when user says "caveman mode", "talk like caveman", "use caveman", "less tokens", "be brief", or invokes /caveman

For the first part of this: couldn’t this just be a UserSubmitPrompt hook with regex against these?

See additionalContext in the json output of a script: https://code.claude.com/docs/en/hooks#structured-json-output

For the second, /caveman will always invoke the skill /caveman: https://code.claude.com/docs/en/skills