## What changed
- Dispatch `--__codex-windows-mxc` before normal CLI parsing, launch the decoded request, and propagate the child exit code.
- Build the native request from the helper's environment and working directory, discovered Windows platform directories, and volume roots, including UNC working-directory roots. Reject non-Unicode environment values and empty child environments.
- Allow Win32k calls and desktop handles needed for PowerShell startup while retaining clipboard, input-injection, and desktop/system-control restrictions.
- Keep policy, transport, and native launch internals private, and report an explicit error when the helper is invoked outside Windows.
## Testing
Add a wrapper regression test covering exact argument preservation, Windows quoting, separate policy and command working directories, and explicit environment forwarding.
GitOrigin-RevId: 674d0d61a3265bd517b77da9f9de2cd9fad62917
42cd1ec497