Status: Accepted
Date: 2026-06-30

Context

The D4 (Specification Compliance) scorer checked that a skill’s claims matched its specification but had no mechanism for testing whether the specification would survive modification. A skill could be perfectly compliant in one version yet degrade to non-compliant with trivial changes. There was no “stress test” for specification robustness.

Decision

Add a “Mutation Resistance” behavioural criterion (4 pts) to D4 that tests specification robustness through hard constraints, conditional branches, and exclusion rules. The scorer checks for:

• Hard constraints that prevent invalid states
• Conditional branches that handle edge cases
• Explicit exclusions that define what is NOT covered

Specificity thresholds defined for keyword detection. Existing sub-scorers reweighted to free 4 pts.

Consequences

• D4 now measures specification robustness, not just static compliance
• Skills with defensive specification design score higher
• Threshold constants ensure consistent scoring across skills
• Reweighting preserves D4 max of 15