EU AI Act — audit log export

The EU AI Act (enforceable from 2 August 2026 for GPAI providers) requires retention of event logs with integrity controls and a path to export records for AI Office document requests. Mnemo’s mnemo-compliance crate ships a matching surface.

export_audit_log

#![allow(unused)]
fn main() {
use mnemo_compliance::{
    AuditFormat, AuditSigner, export_audit_log, verify_ndjson_signed,
};

let events = engine.storage.list_events("agent-id", 10_000, 0).await?;
let signer = AuditSigner::from_secret_bytes(&ed25519_secret);

// NDJSON with detached Ed25519 signature chain
let bundle = export_audit_log(
    &events,
    AuditFormat::NdjsonSigned,
    Some(&signer),
)?;
std::fs::write("audit.ndjson", bundle.bytes)?;

// Reverse: verify
let verified = verify_ndjson_signed(
    &std::fs::read("audit.ndjson")?,
    bundle.verifying_key_hex.as_ref().unwrap(),
)?;
}

Supported formats

• AuditFormat::NdjsonSigned — one JSON line per event plus a detached Ed25519 signature that covers SHA256(index ∥ prev_hash ∥ event_json). Canonicalises through serde_json::Value so the signer and verifier agree on bytes regardless of struct field ordering. Tampering breaks the chain at the first mutated byte and verify_ndjson_signed returns ComplianceError::ChainBroken { index, reason }.
• AuditFormat::EuAiOfficeCsv — the columnar template the AI Office consumes for GPAI document requests. RFC4180-escaped; header row first. Columns: event_id, timestamp, agent_id, event_type, model, thread_id, tokens_input, tokens_output, content_hash.

Key management

AuditSigner never generates or stores keys on its own. Operators are expected to keep the 32-byte Ed25519 secret behind an HSM or KMS and pass it through AuditSigner::from_secret_bytes. generate_ephemeral exists purely for tests.

Integration with forget_subject

When a DPDPA consent withdrawal triggers forget_subject, the emitted MemoryRedact events land in the audit trail with a proper prev_hash link. A later export_audit_log call signs the chain end-to-end, giving regulators a single artefact that covers both the original write and its regulated erasure.

What’s NOT in v0.3.1

• No encryption-key rotation story (deferred to v0.4.0).
• No streaming export from the REST / gRPC surfaces — today the export function is synchronous against an in-memory event list. For very long audit windows, callers should batch via storage.list_events(agent_id, limit, offset) and feed slices into export_audit_log.
• No retention-policy enforcement. The trail retains whatever the storage backend retains.