Add curated quality-baseline corpus + auto-diff (#252 Phase 1) (#397)

Phase 1 (offline): the wrapper, the corpus home, and the test gate. Phase 2
(GPU) curates the actual baselines against the live RECOMMENDED_DEFAULT_MODELS
configs.

- scripts/quality-baseline.sh: thin wrapper over quality-test.sh --full that
  captures (--capture -> --save-json) or diffs (default -> --previous-result)
  an n>=3 aggregate per (registry-slug, thinking-mode). no-thinking is
  canonical (temp-0); enable-thinking is the reasoning-on companion. --dry-run
  prints the resolved command; extra args pass through to benchlocal-cli.
- scripts/quality-test.sh: forward --repeat / --previous-result and honor a
  --save-json path override, so the wrapper's blessed layout works.
- results/baselines/: committed corpus home (whitelisted in .gitignore) + a
  README documenting the convention, usage, and an empty index table.
- scripts/tests/test-quality-baseline.sh: offline gate (--dry-run) — asserts
  command/path resolution per mode + the required-slug / valid-mode /
  positive-repeat / missing-baseline guards.
- docs/QUALITY_TEST.md: regression-baseline subsection pointing at the corpus.

Co-authored-by: noonghunna <10742901+noonghunna@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

results/baselines/README.md

@@ -0,0 +1,56 @@
+# Quality baseline corpus (#252)
+
+Curated, **committed** quality 8-pack baselines — the trusted `n≥3` aggregates that
+[`scripts/quality-baseline.sh`](../../scripts/quality-baseline.sh) diffs a fresh run
+against to catch quality regressions on a config change (quant swap, pin bump, Genesis
+env-flip, KV change).
+
+This is distinct from the runtime **measurement-record** TPS corpus
+(`scripts/lib/profiles/measurement_record.py`) — that tracks throughput; this tracks
+*behavioral quality* (ToolCall / InstructFollow / StructOutput / DataExtract / …).
+
+## What lives here
+
+One JSON per `(registry-slug, thinking-mode)`, named:
+
+```
+<slug-with-slashes-as-dashes>__<mode>.json
+```
+
+- `<mode>` ∈ `no-thinking` | `enable-thinking`.
+- `no-thinking` is **canonical** — temp-0, reproducible, the one a CI-style regression
+  gate should diff against. `enable-thinking` is the non-canonical companion for
+  reasoning-on configs.
+- e.g. `vllm-qwen-35b-a3b-dual__no-thinking.json` ← slug `vllm/qwen-35b-a3b-dual`.
+
+Each file is a benchlocal-cli `RunResult` JSON written with `--repeat N` (N≥3), so a
+baseline is an **aggregate**, not a single run — run-to-run noise (~±5–7 / 150 on the
+8-pack) doesn't read as a regression.
+
+## How to use
+
+```bash
+# capture / refresh a baseline (needs a live endpoint for the slug)
+bash scripts/quality-baseline.sh --slug vllm/qwen-35b-a3b-dual --capture
+
+# diff a fresh run vs the committed baseline (the regression check)
+bash scripts/quality-baseline.sh --slug vllm/qwen-35b-a3b-dual
+
+# thinking-on variant
+bash scripts/quality-baseline.sh --slug vllm/qwen-35b-a3b-dual --mode enable-thinking --capture
+```
+
+Endpoint/model are inherited by `quality-test.sh` (auto-detect, or `MODEL=`/`URL=`).
+Extra args pass through to `quality-test.sh` → benchlocal-cli (e.g.
+`--exit-on-regression` for a CI gate, `--sampling-from-server`). `--dry-run` prints the
+resolved command without running.
+
+**Refresh a baseline only deliberately** — a baseline that drifts upward silently to
+track a regression defeats the purpose. Re-capture when the config legitimately changes
+(new quant, intentional sampling change) and note why in the commit.
+
+## Index
+
+| Baseline file | Slug | Mode | Score (/150) | Captured | Notes |
+|---|---|---|---|---|---|
+| _(none yet — Phase 2 curates these against the live `RECOMMENDED_DEFAULT_MODELS` configs)_ | | | | | |