I really like the idea of standardizing on AGENT.md, although it's too bad it doesn't really work with the .cursor/rules/ approach of having several rules files that get included based on matching the descriptions or file globs in frontmatter. Then again, I'm not sure if any other agents support an approach like that, and in my experience Cursor isn't entirely predictable about which rules files it ends up including in the context.

I guess having links to supplementary rules files is an option, but I'm not sure which agents (if any) would work well with that.