Missing YAML frontmatter

Not sure what I might be doing wrong but I'm struggling activating skills in amp.

I copied the skill file to .agents directory and amp detects them, though it's not using them reporting "missing frontmatter":

Frontmatter is clearly there. I made sure the file is utf-8 encoded and there's no BOM character at the start, but amp is just refusing the skills. Am I doing something wrong? I'm on windows right now if that matters.