context: Update Codex mutation-scope integration plan

Record the accepted boundary-aware unconfirmed-Codex attribution semantics from the fifth PR #268 follow-up, correcting the prior no-protocol-change narrative and updating AC22, T06, and T07 constraints. Preserve MCP/unknown untracked behavior while documenting the SQL/schema exclusions and frozen production baseline.

Plan: codex-mutation-scope-integration (T06, T07)

Co-authored-by: SCE <sce@crocoder.dev>

Author: davidabram