Human-in-the-Loop Override

The override must be recorded as an immutable state transition within the decision log. The system captures the exact pre-override machine inference, the post-override human decision, and the delta between them. This creates a cryptographically verifiable chain of custody that proves the human intervention definitively altered the outcome, preventing disputes over whether the override was merely advisory or authoritative.

To ensure the override is reproducible for auditors, the entire decision context must undergo deterministic serialization before the human intervenes. This involves converting the model's input snapshot, active feature attributions (e.g., SHAP values), and system state into a canonical byte stream (like Canonical JSON). This guarantees that the exact information the human saw is preserved without ambiguity, enabling a perfect deterministic replay of the override event.

A valid override requires cryptographic non-repudiation to bind the human operator's identity to the action. This is achieved through digital signatures using hardware-backed keys (e.g., FIDO2 or secure enclave signing). The system logs:

• The operator's unique signature over the override payload.
• A secure timestamp from a Trusted Timestamp Authority (RFC 3161). This provides undeniable proof of who acted and when, preventing the operator from later denying the intervention.

The override action must be gated by a policy-as-code enforcement layer. Before the human decision is accepted, a rules engine validates the operator's role-based access against the specific risk classification of the automated decision. For example, a high-risk financial transaction override might require multi-party authorization. This prevents unauthorized overrides and ensures every intervention is compliant with internal governance before it is committed to the immutable audit trail.

The override event must be linked back to the original machine prediction to maintain a complete decision provenance graph. The system records a model inference fingerprint—a composite hash of the model version, input data hash, and configuration parameters—and connects it to the human override record. This bidirectional linkage allows auditors to trace any human-amended outcome back to the specific model and data that triggered the initial automated action.

The final, authoritative record of the override must reside on WORM (Write-Once-Read-Many) storage. Once the human decision is serialized, signed, and committed, the storage medium physically or logically prevents any modification or deletion. This satisfies the strictest regulatory retention requirements by ensuring that the override record cannot be tampered with post hoc, even by system administrators, preserving the integrity of the chain of custody for the entire lifecycle of the audit log.