That sounds nice and I have the same pain, but not sure AGENT.md is the right abstraction either. After all, these models are indeed different and will respond

That sounds nice and I have the same pain, but not sure AGENT.md is the right abstraction either. After all, these models are indeed different and will respond differently even given the same prompting. Not to mention that different wrappers around those models have different capabilities. e.g. maybe for CURSOR.md you just want to provide context and best practices without any tool-calling context (because you've found it doesn't do a great job of tool-calling), while for CLAUDE.md (for use with Claude Code) you might want to specify tools that are available to it (because it does a great job with tool calling). Probably best if you have an AGENT.md that applies to all, and then the tools can also ingest their particular flavor in addition, which (if anything is in conflict) would trump the baseline AGENT file.