Complete durable workload result export

[chubes4]

Summary

• export recipe-collected workload results as materialized typed artifacts
• preserve allowlisted semantic identity through runtime and fuzz references
• collect bounded large JSON artifacts directly from the runtime filesystem
• keep large payloads out of declared-result and typed-index references

Follow-up to #2469, which merged while this end-to-end work was still in progress.

Verification

• npm run build
• npx tsx tests/artifact-redaction-integrity.test.ts
• npx tsx tests/public-fuzz-workload-cli.test.ts
• npx tsx tests/fuzz-suite-runner.test.ts
• npx tsx tests/runtime-episode-contracts.test.ts
• npx tsx tests/playground-fuzz-suite-public.test.ts
• full downstream MDI campaign: 249 cases, 247 passed, 2 reasoned skips, 0 failures, 7 proven operations

AI assistance disclosure

GPT-5.6 Sol via OpenCode traced the nested artifact lifecycle, implemented the runtime and materialization changes, added behavioral coverage, reviewed the patch, and ran end-to-end verification. I directed the implementation and reviewed the resulting changes.