A prompt library is usually a blob you paste into a system prompt. It has no folder contract and no guarantee the client will load it on a matching task.
A skill is a folder plus SKILL.md: trigger, steps, bans. Cursor or Codex invoke it by name and you can reuse it across repos.
Do not keep a long workflow only in a pinned chat. Stable constraints go in Rules or AGENTS.md. Reusable steps go in a skill.
Pick one development skill with install notes from this directory and read how to write a SKILL.md. Prompts are drafts; skills are the unit you can ship.