[signet] Spec breaking-change detector

## Observed symptom Spec breaking-change detector **Depends on:** #545, #547, #529, #441 Replays only exercise calls someone made. The spec shows the whole interface. Comparing the deployed and new spec catches changes that break every existing client (generated TS bindings, wallets, the Signet docs page) before any transaction does. ## Environment GitHub blockchain-maxis/signet #570 ## Trigger / context Public GitHub report in blockchain-maxis/signet (FRESH_7D). ## Source evidence - https://github.com/blockchain-maxis/signet/issues/570 (2026-09-27T07:22:45Z) — evidence_class: PRIMARY_ISSUE_REPORT — #570 ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T10:42:44.319212Z - scout_id: C0d176cb67a ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome. Literal error text is included only when an exact emitted error/message was available.