AI Compliance - EU AI Act Article 12 (tamper-evident inference receipts)

PSIS / AtoM-AHG ships ahgAiCompliancePlugin to satisfy EU AI Act Article 12's "automatic event logs across the lifecycle ... in a form that ensures traceability and cannot be silently modified" obligation for AI inference calls.

Same byte format as the Heratio sibling, so receipts from either stack can be cross-verified by any consumer of the standalone ahg/inference-receipts Composer library.

Why

Plain database rows do not meet the Article 12 bar. The plugin layers three primitives on top of an append-only table:

SHA-256 hash chain - each receipt embeds the hash of its predecessor, so modifying or deleting an entry breaks the chain at a detectable point.
RFC 8785 JCS (JSON Canonicalization Scheme) - deterministic byte serialization, so any verifier agrees on what was hashed and signed.
Ed25519 detached signatures - each entry is signed under a per-server key. Auditors verify off-host using the public key served at /.well-known/ai-inference-pubkey.

EU AI Act enforcement: 2 August 2026.

Architecture

+--------------------+         +-------------------------+
|  AI service call   |  --->   |  InferenceLogger::log() |
|  (NER / HTR / LLM) |         +-----------+-------------+
+--------------------+                     |
                                           v
                              +-----------------------------+
                              |  ReceiptChain::append()     |
                              |  (ahg/inference-receipts)   |
                              +-----------+-----------------+
                                          |
                                          v
                              +-----------------------------+
                              |  PropelChainStore           |
                              |    -> ai_inference_log row  |
                              +-----------+-----------------+
                                          |
                                          v
                              +-----------------------------+
                              |  ai_inference_log (chain)   |
                              |  ai_inference_key (kids)    |
                              +-----------------------------+

External auditor:  curl /.well-known/ai-inference-pubkey
                   -> verifies offline against any exported receipt

Tables

ai_inference_log - one row per inference. Columns: seq (monotonic, UNIQUE), ts (millisecond precision), prev_hash, entry_hash, signature, kid, service, model_id, model_version, input_fingerprint (SHA-256 of input body), output_fingerprint, request_id, user_id, tenant_id, latency_ms, tokens_in/out, payload_json (canonical JSON used for hashing), payload_pruned_at.
ai_inference_key - per-kid public key registry. Rotation appends a new row and demotes the old to active=0 with rotated_at stamped, so old receipts remain verifiable against their original key.

Both tables live alongside the existing ahg_* sidecar tables; no AtoM/Qubit base tables are altered.

Operator workflow

# 1. Back up the database before schema changes
mysqldump archive > /var/backups/archive-before-ai-compliance.sql

# 2. Apply the schema
mysql archive < /usr/share/nginx/archive/atom-ahg-plugins/ahgAiCompliancePlugin/database/install.sql

# 3. Add the composer dep and install
( cd /usr/share/nginx/archive && composer require ahg/inference-receipts:^0.1 --no-scripts )

# 4. Generate the signing key
sudo -u www-data php symfony ai-compliance:install-key

# 5. Clear cache so the new module + route load
php symfony cc

# 6. Verify the public-key endpoint
curl -s https://psis.theahg.co.za/.well-known/ai-inference-pubkey | jq .

# 7. Schedule weekly verification (cron / systemd timer)
#    php symfony ai-compliance:verify-inference-log --quiet-pass

# 8. Schedule the retention sweep (daily / weekly)
#    php symfony ai-compliance:prune

Verifying a receipt off-host

Any external party can verify a receipt by:

Pulling /.well-known/ai-inference-pubkey to obtain the public key matching the receipt's kid.
JCS-encoding the receipt's signing view (everything except entry_hash and signature).
SHA-256 over the JCS bytes - must equal the stored entry_hash.
Ed25519 verify the signature against the entry_hash bytes under the public key from step 1.

Test vectors that pass against PSIS receipts must also pass against Heratio receipts and against the nobulex reference - this is the cross-verification contract.

Retention

Default 7 years (configurable via the AtoM setting ai_compliance_retention_years or --years=N on ai-compliance:prune). Prune nulls payload_json past the retention window while preserving seq / prev_hash / entry_hash / signature, so the chain stays structurally verifiable indefinitely even when the PII-bearing payload has been wiped.

Phase-2 follow-up

Wiring the actual AtoM AI service classes (ahgAIPlugin/lib/Services/*) to call InferenceLogger::log() after each inference is a separate phase. This phase ships:

the plugin scaffold + tables
the ai-compliance:install-key, verify-inference-log, prune tasks
the /.well-known/ai-inference-pubkey endpoint
the reference / help docs

Once Phase 2 lands, the existing observability instrumentation in ahgProvenancePlugin and ahgAIPlugin will route through the same chain.

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