ARK-455 — ProofRecord Verification After Tampering (v1.1, FAIL + erratum)

ARK-455: ProofRecord Verification After Tampering Verdict: FAIL (stands as recorded) — with v1.1 root-cause erratum. ARK-455 tested whether dual independent verifiers (V1 JavaScript, V2 Python), built from the same prose specification with no shared source, can detect tampering in a signed ProofRecord. All 8 preregistered arms (800 records) executed after a passing kill-gate. v1.1 ERRATUM (2026-07-17) — root cause reclassified. A post-publication source audit established that the Arm-3 (timestamp) 0% detection was caused by a test-harness no-op: the tamper (microsecond + 1000000) % 1000000 equals the original microsecond for every value and never touches the seconds field, so the "tampered" records were byte-identical to the controls. Both verifiers therefore correctly accepted unaltered inputs. The timestamp is in the RFC 8785 (JCS) signed payload and both verifiers do check it. The failure was not a verifier defect and not a specification gap — it was a generator defect. The FAIL verdict is not rescinded; only its root cause is corrected. See ark-455/CORRECTION.md (also included as ARK-455-CORRECTION-v1.1.pdf). Follow-up: ARK-455b re-runs the study with a corrected timestamp tamper, a new pre-signing expired-timestamp arm (validity-window semantics), and a mutation-effectiveness gate. ARK-455b verdict: PASS (corrected Arm-3 detected 100%; expired-record arm rejected 100%; V1–V2 concordance 100% over 900 records), empirically confirming this erratum. Substrate: classical software (no QPU). License: CC-BY-4.0.