I'm not sure if this differs greatly from skills. Maybe my wording makes these "skills" less likely to be read at the correct times, but I haven't seen an issue.
Skills are more for things you do often. I run mutation tests, type check,linting,etc. I _could_ just prompt and copy/paste the same prompt each time I need to, or I can just run /tests.
I also have skills for specialized tasks I need every once in a while, like a ux skill, a text skill optimized for xyz, etc.
This documentation is its own git repo, and the agents.md file has an explicit instruction to update the docs when it has learned something general that can be useful in future sessions. I then occasionally review and prune those docs.
The description in the front-matter (at the top of the skill markdown file) is the only thing in the context and used by the agent to determine when to read in the rest of the skill file.
skills are just an agents.md broken up into chunks so you can manage and share them separately. unfortunately there's no real good workflow for managing or sharing them separately, so most people end up treating them exactly the same way they do agents.md.
Skills itself may be lengthy so...