Codex FIX7 Final Hardcode / PG-Native-Driven Design Review

Final verdict: PG_NATIVE_DRIVEN_READY_FOR_T1_IMPLEMENTATION. Original FIX7 was not sufficient before this review; ten disguised-hardcode/authority ambiguities plus writer/activation TOCTOU were corrected in the original package. No production mutation occurred. T1 may author/test FIX7a; any live deployment remains operator-gated and Stage 2.6B remains blocked.