AIIR verification and policy gates could report success without enforcing the control (fail-open)

Summary

### Summary Several of AIIR's verification and policy paths could return a success/"verified" result without actually enforcing the control they represent — they could **fail open** rather than fail closed. For a tool whose purpose is trustworthy verification, a consumer relying on these gates may have treated unverified or non-conforming input as verified.

Found during an internal adversarial hardening review of AIIR (not a third-party audit). All paths are fixed in **1.7.0**.

### Affected paths - A `require_signing` policy gate could be satisfied by a forgeable/empty field, so an unsigned or forged-bundle receipt could pass a "signing required" check without a valid signature. - A CI verification path could report `success` regardless of the underlying verification result. - A release-verification gate could advertise policy limits it did not actually enforce. - A signature-verification path could be silently skipped for certain input categories, exiting success without verifying.

### Impact A consumer relying on these gates (e.g. `require_signing`, release/policy verification, or the CI check) to block unsigned, forged, or non-conforming receipts could have received a false "verified"/"pass". Exploitation requires reliance on the affected gate; it does not forge valid signatures, nor does it compromise content-addressing or correctly-signed receipts.

### Patches Fixed in **1.7.0**. Every affected path now fails closed, each with a regression test. Upgrade to `aiir >= 1.7.0`.

### Workarounds None for earlier versions other than upgrading. Full cryptographic Sigstore verification (`pip install aiir[sign]`, `--verify-signature` with `--signer-identity`/`--signer-issuer`) provides defense in depth.

### Scope note This advisory covers code present in released versions (`< 1.7.0`). Separately, an unreleased agent-receipt feature had pre-release forgery findings fixed before it shipped — those were never in a released version and are out of scope.