[codex] add prod-like accuracy benchmark roadmap

[InfoSecHack]

Summary

• Add a finite roadmap/spec for a prod-like AWS sandbox accuracy benchmark.
• Define phases 0-6 with gates, stop conditions, target shape, oracle categories, report shape, claim ladder, and risk controls.
• Keep the next slice local/design-only: implement local prod-like oracle fixture design.

Boundaries

• Docs/spec only.
• No code, tests, Terraform, live AWS, AWS CLI, STS/Lambda/API calls, iam:PassRole calls, reasoner changes, benchmark semantic changes, release/version change, or new evidence claims.
• No composite benchmark score or pass/fail benchmark label.

Validation

• roadmap grep for baseline, phases, gates, max v1 scope, non-claims, and next slice
• account/ARN hygiene scans
• generated live/Terraform artifact scan
• ./scripts/check.sh
• ./scripts/test_fast.sh
• git diff --check