audit_chain 1.5.1

Audit Chain 1.5.1 is a backward-compatible bug-fix release.

Fixed

- Cross-environment prefix seals no longer create false tampering alarms (https://www.drupal.org/project/audit_chain/issues/3616792). Verification now distinguishes a changed sealed-prefix digest (seal_broken) from an intact digest whose MAC cannot be authenticated with the target environment's current or retired keys (seal_foreign).
- Foreign seals remain fail-closed: verification exits non-zero, scheduled health records failure, and evidence export remains blocked. They surface as an operational warning without dispatching the integrity-failure event; actual prefix changes remain errors and events.
- Seal verification no longer accepts an unkeyed MAC.

Drupal 12 compatibility remains preparatory-only and is intentionally not declared until the dependency chain supports it.

No schema changes and no update hooks.