A hash chain: tamper-evident by construction.

Each captured record stores a SHA-256 chain hash built from its commitments, selected operational metadata, and the hash of the record before it. The records link into a single chain; public anchoring is optional.

That design makes the trail tamper-evident. Changing a stored commitment or protected record field makes its recomputed hash differ; changing or deleting history also breaks the expected sequence or predecessor link. The verifier reports the affected sequence rather than silently accepting the change.

What that gives you

• Append-only in practice: the only way to keep the chain valid is to never rewrite history.
• Model provenance baked in: each hash folds in which model produced the call, so you can't quietly swap what answered.
• Independently re-computable: anyone with the chain can recompute it and confirm it's intact, no access to us needed.
• Outage-safe: the chain is append-only, so a backend outage never corrupts what's already recorded.