Back model benchmark with Braintrust, drop in-house scoring (#13)

# Conflicts:
#	bun.lock
#	package.json

evals/model-benchmark/corpus.json

@@ -0,0 +1,17 @@
+[
+  {
+    "id": "security-review",
+    "input": "Review a synthetic patch containing command injection, unsafe recursive delete, and path traversal. Do not mutate files. Report only.",
+    "required": ["command injection", "recursive delete", "path traversal", "no mutation"]
+  },
+  {
+    "id": "graph-indexer-consent",
+    "input": "Decide whether GStack should require a third-party graph indexer. Justify the install policy.",
+    "required": ["optional", "consent", "fallback"]
+  },
+  {
+    "id": "resolver-safety",
+    "input": "Diagnose a resolver that passes an untrusted logical skill name into path.resolve. Recommend the fix.",
+    "required": ["allowlist", "single segment", "traversal"]
+  }
+]

evals/model-benchmark/gstack.eval.ts

@@ -0,0 +1,21 @@
+/**
+ * GStack model benchmark — Braintrust entrypoint for `bun run` / CI.
+ *
+ * Braintrust owns scoring, comparison, and reporting. See
+ * lib/model-benchmark/braintrust-eval.ts for the core; the user-facing CLI is
+ * bin/gstack-model-benchmark.
+ *
+ * Local run, nothing leaves the machine:
+ *   GSTACK_BENCH_PROVIDER=claude bun run evals/model-benchmark/gstack.eval.ts
+ *
+ * Opt into the Braintrust dashboard (consent-gated cloud):
+ *   export BRAINTRUST_API_KEY=...
+ *   for p in claude gpt gemini; do GSTACK_BENCH_PROVIDER=$p bun run evals/model-benchmark/gstack.eval.ts; done
+ */
+import { loadCorpus, runProviderBenchmark, type ProviderName } from '../../lib/model-benchmark/braintrust-eval';
+
+const provider = (process.env.GSTACK_BENCH_PROVIDER ?? 'claude') as ProviderName;
+const timeoutMs = Number(process.env.GSTACK_BENCH_TIMEOUT_MS ?? 300_000);
+const judge = process.env.GSTACK_BENCH_JUDGE === '1';
+
+await runProviderBenchmark(provider, loadCorpus(), { timeoutMs, judge });