Amp used to have an "RFC 9999" article on their website for this as well but the link now appears to be broken.
You can symlink your Cursor / Windsurf / whatever rules to AGENTS.md for backwards compatibility.
For me, that gives a 404 with no obvious way to get to https://agents.md, I think either a hyperlink or redirect would be nice to have as well.
"Guidance for Use"
Your preference for bullet lists over headers is odd. This comes down to what works best with the models - they are interpreting it. This is a moving target. If you believe that your suggestion works best you should provide some sort of evidence. The default would be to not even get into that sort of thing.
Non-Hierarchical AGENTS.md
Claude-code, Gemini, and GHCP all support hierarchical context files. Your proposal and this new one from OpenAI and friends do not, and I think that is a shame.