AML verifier contract evolution

Old evidence keeps its historical meaning when AML evolves.

Current lineage

Current snapshot: aml-verifier-contract-2026-09-09-01

Migration edges: 1

Snapshot 2 is the first real verifier-contract evolution. It adds exact challenge and witness-vector SHA-256 bindings to archived conformance evidence. Snapshot 1 remains an immutable historical target.

Snapshot 1 → Snapshot 2

Classification: breaking at the conformance-result artifact layer.

The four black-box verifier cases are unchanged. The result artifact is stricter: Snapshot 2 requires the exact challenge bytes and golden witness-vector bytes to be identified by SHA-256.

Old Snapshot 1 result artifacts remain Snapshot 1 evidence. They are not silently reinterpreted as Snapshot 2 artifacts.

The invariant

Snapshot N is immutable.
Snapshot N+1 must declare what changed.
Old artifacts keep Snapshot N meaning.

Migration classes

backward-compatible — old behavior remains accepted without additional conditions.
conditionally-compatible — an explicit adapter, condition, or migration step is required.
breaking — behavior intentionally changes; historical verification remains anchored to the old snapshot.

Inspect the machine contracts

Compatibility metadata describes project-defined verifier behavior. It is not certification, standards-body approval, or proof that declared interface meaning is objectively true.