Verbose Agent Logs Are Not Audit Trails Without Evidence Contracts and Tests

AI agent runtimes can generate thousands of log lines yet still fail to answer what actions were actually taken after a failure, making true audit trails distinct from verbose logging. A reliable audit trail requires append-only events with stable run IDs, monotonically increasing sequence numbers, and a hash chain that makes tampering or omission detectable. Sensitive data such as tokens, credentials, and raw prompts must be redacted at write time rather than filtered later in a dashboard query. Each externally visible tool call should progress through defined states — from intent recorded through dispatch to confirmed or unknown outcome — with stable request keys to prevent duplicate effects during retries. The test suite must actively mutate the ledger and confirm the verifier rejects deleted, reordered, or forged records, ensuring the system fails closed rather than silently accepting corrupted evidence.