feat: Stage 2 Phase 3 — labelled corpus seed + executable cull (offline prove)

[aisona-lab]

Summary

Stage 2 (corpus / precision) offline half — not more harness packaging.

• Labelled corpus/seed.jsonl: 22 clean / 15 defective from merged OSS PRs (requests, httpx, click, urllib3) — meets the pre-registered shape floor (≥20 / ≥15).
• Executable cull: decide_cull + fail_on_gate encode the 2026-08-26 thresholds from docs/hardening-plan.md.
• python scripts/corpus_cli.py prove corpus/seed.jsonl → exit 0, artifact docs/eval-runs/corpus-prove.txt.
• Live corpus_cli.py run is BLOCKED without ANTHROPIC_API_KEY (exit 2). No invented precision numbers.
• Action fail-on stays never — metrics do not justify flipping it.

Proof

uv run python scripts/corpus_cli.py prove corpus/seed.jsonl
# EXIT 0 — OFFLINE_PROVE: PASS  LIVE_SCORING: BLOCKED  FAIL_ON: never

Test plan

• pytest -q green locally (114 passed)
• ruff / black / mypy clean
• prove command exit 0 + artifact
• CI test workflow green

[github-actions]

lazycoder review — 💥 ERROR

Downloading pydantic-core (2.0MiB)
Downloading anthropic (1.3MiB)
 Downloaded pydantic-core
 Downloaded anthropic
Installed 16 packages in 32ms
error: Error code: 400 - {'type': 'error', 'error': {'type': 'invalid_request_error', 'message': 'Your credit balance is too low to access the Anthropic API. Please go to Plans & Billing to upgrade or purchase credits.'}, 'request_id': 'req_011CfXjB5fhFH42Qj9kMXqZX'}

_{0 finding(s), 0 abstention(s), 0 rule error(s) — R1..R17 rubric via lazycoder}