Add docs/claims_ledger.md (every public claim -> in-repo evidence, with the
four GSM8K numbers separated and labeled) and ADR-0200 recording the
mathematics_logic expert fail-closed revert as designed behavior (proven
single-source evidence-drift; determinism intact).
Additive only: no existing claim, eval gate, or test is touched. The
review-gated reconciliation diffs (reviewers.yaml quarantine note, ADR-0120
header note, signed-JSON regen, README narrative, 3 test reconciliations) are
listed in ADR-0200 section 4 and await operator ratification.
