Disclosure: I work in marketing at BOMTOBE, maker of orke, a workspace for Claude Code and Codex. A small model-upgrade regression set could preserve the reason for each rule: one task that once failed without it, the expected result, and any safety invariant. Rerun those same tasks against the old and new model; remove a line only after the replacement still passes. That makes the skill diff an auditable hypothesis rather than a cleanup based on one fresh demo.