Yes exactly. Skills are just sub agents.md files + an index. The index tells the agent about the content of the .md files and when to use them. Just a short paragraph per file, so it's token efficient and doesn't take much of your context.

Poor man's "skills" is just manually managing and adding different .md files to the context.

Importantly every time you instruct the agent to do something correctly that it did incorrectly before, you ask it to revise a relevant .md file/"skill", so it has that correction from now on. This is how you slowly build up relevant skills. Things start out as sections in your agents.md file, and then graduate to a separate file when they get large enough.

Yes but also because skills are a semi special construct, agents are both better at leveraging them when needed and you can easily tap into them explicitly (eg “use the PR skill to open a PR”)