ab-equivalence

# A/B equivalence - a transform-agnostic behavioural-equivalence capability A thin capability that compares two versions of an LLM-directed document - an `original` (the teacher) and a `candidate` (the student) - across a transfer set, and returns a per-case verdict on whether the candidate still induces the behaviour the original induced. It is **transform-agnostic**: it judges *behavioural equivalence between two versions* and neither knows nor cares which transform produced the candidate. It therefore serves every optimizer transform that claims to preserve behaviour - compression today, directive-clarity next - not just compression. It is a **library capability** other skills compose: `semantic-compress` invokes it to gate a distillation, and `skill-forge` exposes it alongside its own quality gate. It does **not** judge *absolute quality* ("is this skill good?") - that is a different question answered by different judges. A/B equivalence judges *sameness between two versions* ("does the candidate still do what the original did?"). This skill **owns the runner** (`references/runner-prompt.md`, the pure-wrapper template, paths relative to this skill directory). The runner is the shared execution primitive: it applies one version of a document to one case input and returns a transcript and self-report. Skills that need behavioural comparison compose this capability rather than re-implementing the runner. The runner ships in **two variants**, both pure wrappers returning ...