v2.0.3 — ABA-anchored benchmark task-hygiene lint

Patch release. Adds an ABA-anchored task-hygiene lint to the
benchmark pack so a suspect regression-gate corpus can be caught
before its scores are consumed by CI.

Added

• scripts/bench_lint.py — offline, stdlib-only hygiene lint for
  the regression-gate manifest. Implements four rules adapted from
  the Auto Benchmark Audit framework (Wang et al. 2026,
  arXiv:2605.26079, "Automated Benchmark Auditing for AI Agents
  and Large Language Models", v1 2026-05-25):

  • VBL001 SpecificationGap — missing name/skill, or no
    expected_* bound declared (case asserts nothing).
  • VBL002 EnvironmentCoupling — absolute transcript path,
    path escapes the manifest dir via .., transcript file
    missing on disk, or declared adapter doesn't match the
    file suffix.
  • VBL003 BrittleGrading — single-point composite/grade/dim
    bounds (min == max), or composite range narrower than 0.5.
  • VBL004 MissingGroundTruth — transcript is 0-bytes or
    contains zero non-blank lines.

  Aggregate bench_hygiene_score = 1 - flagged_cases / total_cases.
  Emits text (default), JSON (--json), or SARIF v2.1.0
  (--sarif PATH). Exits 0 above threshold (default 0.85), 1 below,
  2 on IO/arg failure. No LLM call — the offline heuristic is the
  moat.

• Ship-gate wire-up in scripts/benchmark_pack.py: new --lint
  flag runs the hygiene pass before the regression suite and
  aborts non-zero if bench_hygiene_score is below
  --hygiene-threshold (default 0.85). --sarif PATH implies
  --lint and writes the SARIF document. CI now surfaces "this
  benchmark may not be trustworthy" instead of greenwashing a
  suspect corpus. Legacy positional manifest argument preserved.

Tests

• tests/test_bench_lint.py (21 tests): the shipped
  benchmarks/manifest.json scores 1.0 and exits 0; each of the
  four rule classes fires on an injected bad case; SARIF v2.1.0
  envelope and rule inventory pinned; exit-code matrix verified
  (0 above / 1 below / 2 IO-or-arg); benchmark_pack --lint
  aborts before the regression suite when the corpus is dirty
  and surfaces the VBL ruleId in stderr.

Notes

• Verdict's benchmark pack scores transcripts against expected
  score bounds, not tasks against ground-truth outputs. The four
  ABA classes therefore apply by analogy, not literally; the lint
  output and README both state this adaptation explicitly so
  nobody reads it as a 1:1 ABA implementation. The 25.7%-of-tasks
  flaw rate ABA reports across 168 benchmarks is the motivation
  for catching the same shape of issue before scores ship.

• O17 — bench_lint.py adapts ABA to a transcript-regression
  manifest. If Verdict ever grows a true task benchmark (prompt +
  expected output + grader), the four rules will need a literal
  pass: spec gaps against the prompt text, env coupling against
  the grader's external calls, brittle grading against
  exact-match-only graders, missing ground truth against empty
  expected outputs.