Guardian Audit — Tamper-Evident Audit Logger

"Trust, but log."

A companion skill to Guardian (or any safety gatekeeper) that captures every decision, action, and escalation in an append-only, hash-chained audit trail.

Why this exists: Guardian stops bad things. Guardian Audit proves it stopped them — or proves the agent did them anyway.

What It Logs

Every entry includes:

The Hash Chain

Entry[N].previous_hash = SHA256(Entry[N-1].content)
Entry[N].entry_hash = SHA256(Entry[N].content)

If any entry is modified, every subsequent entry's previous_hash fails verification. The chain is self-validating.

Log Format

Append-only line-delimited JSON (NDJSON), one entry per line:

{"timestamp":"2026-05-18T14:02:31.847Z","sequence":42,"previous_hash":"a3f7...","event_type":"GUARDIAN_HALT","agent_id":"agent-7f3a","operation":"rm -rf /tmp/old-builds","target":"/tmp/old-builds","category":"HIGH","backup_verdict":"UNVERIFIED","backup_checks":[],"decision":"HALT","approver":"guardian-auto","agent_reasoning":"Cleaning up old build artifacts","guardian_notes":"Mass delete operation with no backup coverage","outcome":"AWAITING_HUMAN","entry_hash":"9e2b..."}

Where Logs Live

Immutable by convention: The log file has append-only permissions. The executing agent cannot delete or modify entries. Only a human with elevated privileges can rotate logs.

Verification Script

# Verify chain integrity
./scripts/verify-chain.py audit.log
# Output: "Chain valid: 1,247 entries, 0 breaks"
# Or: "CHAIN BROKEN at entry 843: hash mismatch"

Integration with Guardian

Guardian calls Guardian Audit automatically after every decision:

Guardian Decision → Guardian Audit LOG → Continue / Halt

No additional agent action required. Guardian Audit is a passive listener that records what happened.

Standalone Use

Guardian Audit also works independently. Any safety tool, human approval, or agent action can emit an entry:

# From any agent or tool
from guardian_audit import log_event

log_event(
    event_type="MANUAL_APPROVE",
    operation="deploy-production",
    target="api.production.internal",
    decision="PROCEED",
    approver="human:anonymous",
    agent_reasoning="Emergency fix for auth bug"
)

Why This Matters

Compliance frameworks requiring audit trails:

• EU AI Act (Article 52): High-risk AI systems must maintain logs
• SOC 2 Type II: Change management and access control evidence
• HIPAA §164.312(b): Mechanisms to record and examine activity
• GDPR Article 5(1)(d): Accuracy and accountability

Forensics: When something goes wrong, you need to know:

• What did the agent try to do?
• Did Guardian stop it?
• Did a human approve it anyway?
• What was the agent's reasoning at the time?

Mandatory Rules

1. Append-Only: Entries are never deleted. Log rotation creates new files, never modifies existing ones.
2. Hash Chain: Every entry references the previous. Tampering is detectable.
3. No Agent Modification: The executing agent cannot modify its own audit trail. Ever.
4. Minimal Overhead: Logging adds \x3C5ms per decision. No perceptible latency.
5. Human Readable: NDJSON format means tail -f audit.log is meaningful without tooling.

Scope

Vanilla: Not specific to Guardian. Works with any safety gatekeeper, human approval workflow, or agent runtime.

Passive: Does not block or delay operations. Logs after the fact.

Mandatory: Once enabled, all safety decisions are logged. No opt-out per-session.

References

• references/LOG-SCHEMA.md — Complete field definitions and validation rules
• references/COMPLIANCE-MAPPING.md — Framework requirements (EU AI Act, SOC 2, HIPAA, GDPR)
• references/REPLAY.md — How to replay, search, and analyze audit trails
• scripts/log-event.py — Python event logger (cross-platform)
• scripts/verify-chain.py — Chain integrity verification
• scripts/export-report.py — Generate compliance-ready reports

Based On

• IETF draft-sharif-agent-audit-trail-00 (Mar 2026): Standardized AI agent audit trail format
• AgentReceipt (2026): Immutable audit trails for AI agents
• OWASP Agentic AI Top 10: Logging and monitoring requirements
• GDPR Article 5 + EU AI Act Article 52: Regulatory audit trail mandates

License

MIT — Audit trails should be a public good.