## What changed
- Add `codex-mxc-sandbox` with native MXC availability detection and a launcher that inherits standard I/O and waits for the sandboxed process.
- Reject unsupported learning-mode and fallback policies, and verify deny-path support before launch.
- Route the existing Windows MXC availability metric through the new crate and move its Windows linking dependencies alongside the adapter.
GitOrigin-RevId: e2a220b85718e00b0e710c30bbe66b6c56958176