Plan Mode in Codex. Similar to Claude code

Please add a user-facing “Plan Mode” toggle similar to Claude’s. In Plan Mode, Codex should inspect the repo, ask clarifying questions if needed, and produce a proposed implementation/validation plan without editing files, running destructive actions, committing, or pushing. The user should then be able to approve the plan, request changes, or switch back to normal execution mode. This would be especially useful for coordinating multi-agent work, reviewing risky migrations, and separating design discussion from implementation.