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Cato Gap Fixes — Kraken Closure Verdict

Auditor: Kraken (Project Reality Manager) Audit Date: 2026-03-06 Scope: Two gap fixes raised in prior Kraken audits (2A Issue 1, 2B Issue 1) Branch: build/2c-epistemic-layer (commits 47fc064 + 32a5694)

Executive Summary

Both gap fixes are CONFIRMED CLOSED. The implementations are correct, minimal, and covered by dedicated tests. No regressions introduced.

Overall confidence: 98%

The 2% gap: floating-point str() representation of confidence_score and reversibility in the re-hash formula is platform-dependent in theory (different Python builds could format 0.5 differently). In practice on CPython 3.11+ this is deterministic. Documented, not blocking.

Fix 1 — verify_chain() Field Re-Hash (Gap 2A Issue 1)

File: cato/audit/ledger.py — verify_chain() function Commit: 47fc064 Status: CLOSED

What was missing

Prior implementation only verified prev_hash linkage. An attacker could mutate any field (confidence_score, tool_name, reasoning_excerpt, etc.) without breaking the chain — the tamper would go undetected.

What was added

After the prev_hash check, verify_chain() now re-computes:

expected_hash = _sha256("|".join([
    row["record_id"], row["prev_hash"], row["timestamp"],
    row["agent_session_id"], row["tool_name"],
    row["tool_input_hash"], row["tool_output_hash"],
    row["reasoning_excerpt"], str(row["confidence_score"]),
    row["model_source"], str(row["reversibility"]),
    row["delegation_token_id"] or "",
]))
if expected_hash != row["record_hash"]:
    return False, (
        f"TAMPERED at record {row['record_id']} (index {i}) — "
        f"field hash mismatch: stored {row['record_hash'][:16]}…, "
        f"recomputed {expected_hash[:16]}…"
    )

This exactly mirrors the record_data string built in append() — same fields, same order, same "|" delimiter. The fix is both correct and complete.

Test evidence

tests/test_ledger.py::TestVerifyChain::test_field_mutation_detected_by_rehash

  • Creates 1 record
  • Mutates confidence_score via raw SQLite (bypassing middleware)
  • Asserts verify_chain() returns (False, "...field hash mismatch...")
  • PASSES ✓

tests/test_e2e_full_pipeline.py::TestLedgerMiddleware::test_field_tamper_detected

  • Same scenario via E2E path
  • PASSES ✓

Total ledger tests: 28 passed (was 27 before fix — 1 new test added).

Edge cases verified

  • Empty chain → still returns (True, "VALID (0 records...)") ✓
  • Single record field tamper → caught ✓
  • Chain of 5, tamper in middle → caught at tampered row ✓
  • delegation_token_id = NULL → mapped to "" correctly ✓
  • Concurrent appends → chain still valid ✓

Fix 2 — OutcomeObserver Configurable Windows (Gap 2B Issue 1)

File: cato/memory/outcome_observer.py — OutcomeObserver.__init__() Commit: 32a5694 Status: CLOSED

What was missing

OutcomeObserver used the module-level _OBSERVATION_WINDOWS constant directly, hardcoded into _check_open_records(). The window values could not be overridden without monkey-patching, making unit testing of window logic impossible and production customisation impractical.

What was added

def __init__(
    self,
    decision_memory: DecisionMemory,
    poll_interval_sec: float = 300.0,
    observation_windows: Optional[dict[str, float]] = None,
) -> None:
    self._memory = decision_memory
    self._poll_interval = poll_interval_sec
    self._observation_windows = observation_windows or _OBSERVATION_WINDOWS
    ...

_check_open_records() uses self._observation_windows instead of the module constant. Backward compatibility is preserved: callers that pass no observation_windows get the unchanged defaults via or _OBSERVATION_WINDOWS.

The identity check obs._observation_windows is _OBSERVATION_WINDOWS passes when None is passed — the exact same object is used (no copy), confirming the or short-circuit semantics.

Test evidence

tests/test_decision_memory.py::test_observation_window_email — PASSES ✓ tests/test_decision_memory.py::test_observation_window_commit — PASSES ✓ tests/test_decision_memory.py::test_observation_window_default — PASSES ✓ tests/test_e2e_full_pipeline.py::TestOutcomeObserver::test_instantiates_with_custom_windows — PASSES ✓ tests/test_e2e_full_pipeline.py::TestOutcomeObserver::test_default_windows_used_when_none — PASSES ✓

Total outcome observer tests: 5 targeted + 2 decision memory integration = 7 all passing.

Behavioral correctness

  • Custom windows {"email": 10.0} stored in self._observation_windows ✓
  • Default _OBSERVATION_WINDOWS used without copy when None passed ✓
  • _check_open_records() loop references self._observation_windows ✓
  • Module-level _get_observation_window() helper is now unused by the class (left in place for external callers — no regression)

Regression Check

Full test suite run post-fixes:

1271 passed, 1 skipped, 32 warnings in 103.02s

Zero regressions across all 1271 tests. The 1 skipped test is the existing test_e2e_latency_target skip (dev environment, not a failure).

Final Scores

Fix Category Result
verify_chain() field re-hash Implementation correctness CONFIRMED
verify_chain() field re-hash Test coverage CONFIRMED (1 dedicated + 1 E2E)
verify_chain() field re-hash Backward compatibility CONFIRMED
OutcomeObserver configurable windows Implementation correctness CONFIRMED
OutcomeObserver configurable windows Test coverage CONFIRMED (5 tests)
OutcomeObserver configurable windows Backward compatibility CONFIRMED
Full suite regression 1271 tests 0 failures

Production Readiness Verdict

BOTH GAPS CLOSED — APPROVED FOR MERGE TO MAIN

The two fixes are minimal, correct, and fully tested. No new dependencies introduced. No public API changes (only additions). Safe to merge.

Signed: Kraken — 2026-03-06
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