> This would be much more interesting if it detailed how the prompt/skills were reverse-engineered

That would enable Anthropic to block the technique.

They have never attempted to hide their system prompts in fact they explicitly publish them for Claude (https://platform.claude.com/docs/en/release-notes/system-pro...) and Claude Code they provide a proxy option which then makes it trivial to see the full requests and responses including the prompts and tool usage...