The AuditLog class implements an append-only, hash-chained log that links each entry to its predecessor via SHA-256. It is self-contained (no internal imports beyond standard library), parameterized by file path, and can be extracted into any project requiring tamper-evident logging. The class handles sequence numbering, hash computation, and JSONL output. This is a clean, reusable pattern for audit trails in regulated systems.

The overall engine architecture (classify -> assure -> decide -> override -> break -> credential -> log) is a well-structured pipeline pattern for governance middleware. The Session class encapsulates state (session_id, auth count) and provides a single handle() method. The separation of concerns into pure functions (classify_utterance, apply_assurance, core_decision, apply_action_override, maybe_break) makes the logic testable and modifiable. While the specific classification is deterministic and fintech-specific, the pipeline pattern is reusable for any domain requiring multi-stage authorization decisions.

The test suite demonstrates a robust pattern for testing a governance framework: it loads gold-standard JSONL fixtures, tests mapping divergence (same utterance different decisions under different mappings), verifies no secrets in model context, checks vulnerability breaker activation, and ensures visible authority state completeness. The test_gold_actions_not_weaker_than_label function specifically validates that the classifier never produces a weaker action than the gold label for high-cost false negatives. This testing pattern is reusable for any classification-based governance system.