Evals: the two implement-spec cases carry identical copies of the calc-subtract spec #35

Before you file

• I searched the existing issues.
• I read evals/README.md.

Component

implement-spec (skill)

Behaviour

evals/skills/implement-spec/works-one-wave/files/.claude/specs/calc-subtract/ and evals/skills/implement-spec/works-all-waves/files/.claude/specs/calc-subtract/ are byte-identical copies of the same three spec files (diff -r on 2026-10-16 reports no difference). A change to the calc-subtract spec has to be made in both or the two cases drift apart. Noted as a known gap in the description of PR #25.

Proposed: keep one copy, under evals/fixtures/ beside the calc tree, and have both cases' scaffold.sh copy it in, the way they already call evals/fixtures/setup.sh. Each case's files/ then holds only what is specific to that case, or goes away.

Grading

No grader changes. Both cases keep passing: make eval-skill-implement-spec EVAL_ARGS="--runs 1", with the cost ceiling raised as evals/README.md says. make validate still passes.

Prompt

Unchanged.