[DFL-AUDIT-121] Coverage/mutation metrics

[Anionix]

Finding

Original score: 4/10
Owner: Agent
Priority: P2
Workstream: typing

Evidence

No coverage threshold or mutation-testing evidence.

Acceptance

Resolve the finding with reproducible evidence, or record an explicit accepted-risk decision.

Dependencies: none.

[Anionix]

Post-merge artifact verification found that run https://github.com/Anionix/data-format-lab/actions/runs/30079480822 passed 598 tests but published a 0% empty coverage report. Tracked as bug #508. #303 remains open until the fix is merged and a nonzero main-SHA artifact is verified.

[Anionix]

Acceptance is satisfied with reproducible evidence plus an explicit time-bounded accepted-risk decision.

• Descriptive generated artifact-mutation metrics merged in Report coverage and artifact-mutation evidence #507 (5e5305e3dd297c05efb489c8285480ba1f0256bc), with named boundary cases excluded by persisted recipe identity.
• The legacy-summary review defect was fixed before merge, replied to, and its thread resolved.
• The post-merge 0% artifact bug was tracked as [Bug] Manual coverage workflow publishes a 0% empty report #508 and fixed by Reject empty coverage evidence #509 (315cc61487c29d0e51a4189d6a4f743d71c86c43).
• Verified main run: https://github.com/Anionix/data-format-lab/actions/runs/30080954866 — 599 passed, 3 skipped, 6m29s, total coverage 83%.
• Verified artifact: branch-coverage-315cc61487c29d0e51a4189d6a4f743d71c86c43 (ID 8591918992, non-expired, exact main SHA).
• Remaining threshold/source-mutation risk is owned by [DFL-AUDIT-121 follow-up] Set coverage gate and source-mutation baseline #506, expires after three distinct-main reports or 2026-08-07, and now contains baseline 1/3.

No benchmark ranking or lifecycle eligibility is changed by these code-quality metrics.