feat: implement issue #1097 — [Phase 1] Held-out eval regression gate: Sonnet 5 >= Sonnet 4.6 on triage + deep-review

[don-petry]

Closes #1097

Implemented by dev-lead agent. Please review.

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 558824c2-cc9d-4d1b-84ac-4ee3fa981155

📥 Commits

Reviewing files that changed from the base of the PR and between 71ab5d4 and 4844834.

📒 Files selected for processing (4)

• .github/workflows/lint.yml
• docs/evals/model-ab-regression.md
• scripts/evals/model-ab.sh
• tests/test_model_ab.bats

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch dev-lead/issue-1097-20260704-1944

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[gemini-code-assist]

Code Review

This pull request introduces a model non-regression A/B testing framework, including documentation, a comparison script (scripts/evals/model-ab.sh), and offline BATS tests (tests/test_model_ab.bats). The feedback suggests improving the BATS tests by creating temporary directories inside $BATS_TEST_TMPDIR for automatic cleanup, and safely referencing positional parameters with ${1:-} in the test stubs to prevent unbound variable crashes under set -u.

[github-actions]

CI Failure: SonarCloud Code Analysis

Step: Quality Gate (SonarCloud)
Root cause: Lint/style

The Quality Gate failed because the Security Rating on New Code is D, below the required A. SonarCloud flagged three uses of md5sum in scripts/evals/model-ab.sh (lines 100-103) as a weak hash algorithm used in a security-sensitive context. MD5 is used there to fingerprint eval fixture files (holdout cases, scorer config, judge prompt) to detect changes — not for any cryptographic/security purpose, but Sonar's rule still flags any MD5/SHA-1 usage regardless of intent.

Suggested fix: Replace md5sum with sha256sum in scripts/evals/model-ab.sh (lines 100-103, and the corresponding check at line 547/555), or add an inline // NOSONAR / issue-suppression comment if MD5 is intentionally kept for non-cryptographic fingerprinting.

View analysis details

[Copilot]

Pull request overview

Adds a Phase-1 “model A/B non-regression” gate to compare a candidate Claude model (e.g., Sonnet 5) against the incumbent (Sonnet 4.6) on the held-out triage and deep-review eval sets, producing a single JSON evidence artifact and enforcing a per-set >= bar while distinguishing infra failures from quality regressions.

Changes:

• Introduces scripts/evals/model-ab.sh to run the two-model × two-set matrix, hold the deep-review judge model fixed, and enforce held-out artifact immutability checks.
• Adds fully-offline Bats coverage for accept/regress/tie/infra outcomes, judge confound control, and immutability detection.
• Documents the repeatable procedure and how to interpret the verdict/evidence JSON.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
tests/test_model_ab.bats	Offline Bats tests covering A/B comparator verdict logic, infra semantics, judge fixed-model control, and immutability guard.
scripts/evals/model-ab.sh	New model A/B comparator script that drives run-eval.sh, pins generator per arm, pins judge model via a shim, and emits evidence JSON + exit status.
docs/evals/model-ab-regression.md	Runbook describing how to execute the model A/B procedure and read the outputs.
.github/workflows/lint.yml	Includes the new Bats test in the Lint workflow’s test list.

[don-petry]

Dev-Lead — review-changes (applied)

Changes committed and pushed.

[don-petry]

Dev-Lead — review-changes (applied)

Changes committed and pushed.

[don-petry]

Dev-Lead — fix-bot-comment (no-changes)

Agent reasoning

Issues addressed: 0
Files changed: None
Skipped (informational): 0
```
The SonarCloud quality gate passed with zero new issues. The PR is not blocked by any CI checks or blocking reviews. No fixes are required from the automated code analysis bot.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[don-petry]

Dev-Lead — review-changes (no-changes)

No changes were needed for this PR.

[donpetry-bot]

Automated review — APPROVED ✓

Risk: MEDIUM
Reviewed commit: 48448343488ad6d16dbc3b7057359ab44d9b398b
Review mode: triage-approved (single reviewer)

Summary

Adds a self-contained model A/B non-regression comparator (scripts/evals/model-ab.sh), fully-offline bats coverage, a runbook doc, and a one-line lint-matrix addition. Confirms the triage tier's low-risk assessment: no auth/secrets/migration surface, all CI green, all review threads resolved, and issue #1097's five acceptance criteria are substantively implemented.

Linked issue analysis

Closes #1097 ([Phase 1] Held-out eval regression gate: Sonnet 5 >= Sonnet 4.6). All ACs addressed: (1) documented repeatable procedure driving run-eval.sh per (model, set) arm with the generator pinned via CLAUDE_TRIAGE_MODEL_CHAIN; (2) holdout-only reads with a before/after sha256 immutability guard over cases.jsonl, scorer.json, and judge.md (hard exit 2 on mutation), plus the outer git-status check in the runbook; (3) per-set '>=' non-regression bar with a regression verdict that is blocking (exit 1), deliberately not gate.sh's strict '>'; (4) infra-vs-quality per run-eval.sh #920 semantics — an un-scored arm (rc 2) marks the set infra/re-run, never a candidate regression, with regression outranking infra in verdict precedence; (5) a single JSON evidence object carrying both models' per-set scores, rc/scored flags, and the verdict for the Phase-3 go/no-go. The judge model is held fixed across arms via a shim (confound control), verified by a dedicated test.

Findings

No blocking findings. Review threads from gemini-code-assist (BATS_TEST_TMPDIR, ${1:-} under set -u) and Copilot (md5sum availability) are all resolved — later commits use $BATS_TEST_TMPDIR, ${1:-} in stubs, and sha256sum with a command -v guard. Prior SonarCloud weak-hash flag (md5sum) was fixed by switching to sha256sum; quality gate now passes with 0 new issues. CodeRabbit approved at head. Secret scan: run_secret_scanning MCP tool unavailable in this run; gitleaks CI check passed. Minor, non-blocking: die() and the infra verdict both exit 2, but only the infra path emits the JSON evidence object on stdout — consumers should not unconditionally parse stdout on exit 2. The judge-shim heredoc interpolates AB_JUDGE_MODEL/EVAL_JUDGE_CMD into a generated script; these are operator-supplied env for a locally-invoked tool, not untrusted input, so acceptable.

CI status

All checks green at 4844834: Lint, ShellCheck (x2), bats, CodeQL (actions/python), gitleaks secret scan, SonarCloud Code Analysis + quality gate, holdout-guard, test-deletion guard, unit-tests, AgentShield, Agent Security Scan, template-drift, validate-agent-profiles, gh-aw-compile. Dependency-audit jobs skipped (no matching ecosystems). mergeable=MERGEABLE; mergeStateStatus=BLOCKED only pending required review.

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