[drk-ram]

What

Enforce delegation credential validity windows (iat, nbf, exp) and non-decreasing hop timestamps (iat) against parent hops inside cross_check_trace_dag (ca2a verify-lineage).

Why

cross_check_trace_dag checked hop signatures, subject/issuer continuity, and scope attenuation, but never compared a hop record's iat against the matched delegation credential's [nbf, exp] validity window or the parent hop's iat. As a result, hop records signed after credential expiry, before nbf/iat, or backdated before their parent hop were reported as authenticated_lineage.

Closes #306

Security impact

Prevents expired, premature, or backdated hop records from passing cross_check_trace_dag and ca2a verify-lineage as authenticated_lineage.

Test plan

• pytest passes (pytest tests/unit/test_trace_binding.py tests/unit/test_lineage_cli.py — 71 passed)
• ruff check passes (ruff check src tests — passed)
• mypy passes (mypy src — passed)
• Manual test performed (describe steps below if applicable)

DCO sign-off

• My commits include Signed-off-by: (git commit -s)

[github-actions]

🔴 Contributor Check: HIGH

Check	Result
Profile	HIGH
Credential	LOW
Overall	HIGH

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[carloshvp]

Reviewed commit 622bc061b564419c451e397097992dd2ef0a7e1e.

The new checks bind each signed hop's iat to its credential's inclusive validity window and reject a hop that precedes its parent. Equal timestamps and inclusive endpoints remain accepted. The documentation correctly separates signer-asserted time from independent evidence of creation time and from verify_chain(at_time=...).

In a credential-free, network-disabled Python 3.12 environment installed from this head's hash lock, all 47 tests in test_trace_binding.py and test_lineage_cli.py pass. Full-source Ruff, mypy (47 files), and configured Bandit pass. Restoring only the base dag.py while retaining the new tests produces four failures, including the CLI falsely returning success; the reviewed source was then restored. DCO sign-off is present.

Security impact: the offline verifier now refuses the out-of-window and backward-ordered signed histories described in #306, while preserving signature and credential checks. This is one of the two maintainer approvals required for src/ca2a_verify/. Hosted CI remains action_required and has not supplied runtime-test evidence on this head; the full hosted matrix and remaining approval are still required before merge.

[dinakarjs]

Reviewed 622bc06. The change checks each hop against its matched credential's inclusive not_before/not_after bounds and rejects decreasing hop times, preserving equal timestamps and optional bounds. I found no blocking defect in this bounded change. Signed iat remains a signer assertion, not independent evidence of creation time; verify_chain and verify_trace_dag remain prerequisites.

Independent local validation on Linux/Python 3.12.14, installed editable after the unchanged hash-required dev lock: 47 focused trace-binding/lineage CLI tests pass; full-source Ruff, mypy (47 files), Bandit and pip dependency installation complete. Ten additional signed-record boundary controls passed, covering absent/one-sided bounds and out-of-window records at each of three positions. Replacing only dag.py with its parent version produces four behavioral failures (including CLI false success), with 43 controls still passing; source restored exactly. Initial exploratory timestamps below the TRACE schema minimum were corrected before these boundary results.

Security impact: refuses signed out-of-window and backward-ordered histories at the credential/record reconciliation boundary. Current hosted CI/CodeQL remain action_required; this is a bounded code approval, not hosted-matrix completion, merge authorization, or a claim to satisfy the required two-maintainer gate. PR description says 71 focused tests; this exact head collects 47, so please align that count. Prepared with OpenAI Codex.