feat(product-benchmark): add product bundle contract

[drewstone]

Summary

• add @tangle-network/agent-eval/product-benchmark for product-owned benchmark manifests, records, runtime receipts, artifact lookup, and run validation
• export the subpath from package.json, tsup, root index, and package export verification
• cover fake real-backend rows, integrity failures, missing artifacts, disk bundle reads, and successful run summaries

Verification

• pnpm exec vitest run src/product-benchmark/index.test.ts: 1 file, 4 tests passed
• pnpm typecheck: passed
• NODE_OPTIONS=--max-old-space-size=8192 pnpm build: passed; emitted dist/product-benchmark/index.js and index.d.ts
• pnpm verify:package: passed; throwaway app imported @tangle-network/agent-eval/product-benchmark
• pnpm lint: passed with existing warnings only
• dist validator on /tmp/creative-product-smoke-r176-kimi: records=1, passed=1, failed=0, inputTokens=26469, outputTokens=4184, costUsd=0.0263414, integrityFailures=0, missingArtifacts=0

Notes

• This intentionally lifts the shared product benchmark contract now. Agent-lab should switch from its local copy after this subpath is released or locally linked in a controlled follow-up.

[tangletools]

✅ Auto-approved drewstone PR — 80bd2de0

This PR was opened by the trusted drewstone account.
The full PR reviewer audit still runs separately and will publish findings if it detects issues.

_{tangletools · auto-approval · reason: drewstone_author · 2026-07-01T02:02:39Z}