## Why
Guardian review commands can run without the proxy-port environment used to
configure the parent session. Reconciling persistent Windows sandbox settings
for those commands can discard the parent's proxy configuration.
## What changed
- Add a session-level Windows sandbox proxy-settings mode and use `Preserve`
for guardian review sessions while keeping `Reconcile` as the default.
- Carry the mode through unified exec and the exec-server sandbox context to
Windows process launches.
- In preserve mode, reuse the proxy settings recorded by the existing sandbox
setup marker.
## Testing
Added coverage for guardian session configuration, exec-server transport, and
preserving an existing setup marker when proxy-port environment variables are
absent.
GitOrigin-RevId: 214655c6e6d97360906431773dc0de0fdda2db6e
b115de97d7