Codex Security: now in research preview

Same-day competitive counter to Anthropic with stronger receipts: 15 named CVEs in the appendix (GnuTLS heap overflows, GnuPG stack buffer overflow, GOGS 2FA bypass), published improvement curves (84% noise reduction, 90%+ severity over-reporting reduction, 50%+ false positive reduction). The threat model architecture -- building an editable intermediate artifact before scanning -- is the most interesting pattern: it generalizes as "make the agent's understanding inspectable before execution." Broader tier access (Pro through Edu) weakens the dual-use containment narrative but maximizes adoption velocity.