These files also generally work in a nested fashion, like .gitignore and the like. So you want something that can be injected into the namespace of any directory in your project with relatively low likelihood of conflicts.

Not exactly (or unclear), .gitignore files combine, much like copilot files with glob or other matching. All the instructions are put into the context

> Agents automatically read the nearest file in the directory tree, so the closest one takes precedence

How about an underscore instead?

Fair. I didn't think about that.