Always use private desktops for legacy Windows sandboxes (#46554)

## What changed

- Remove the private-desktop opt-out from elevated and unelevated Windows sandbox launches.
- Remove `windows.sandbox_private_desktop` and its managed requirement and API fields. Warn users to remove the obsolete setting.
- Require a private desktop name when launching through the Windows sandbox wrapper and command runner.

## Testing

Add coverage for the obsolete-setting migration warning and update wrapper tests to verify a live private desktop is passed and a missing desktop name is rejected.

GitOrigin-RevId: c7135f8d211aac8d812180691c2c1e433d77cde4

codex-rs/file-system/src/lib.rs

@@ -362,8 +362,6 @@ pub struct FileSystemSandboxContext {
     pub temporary_directories: Option<Vec<PathUri>>,
     #[serde(rename = "windowsSandboxLevel")]
     pub windows_sandbox_selection: WindowsSandboxSelection,
-    #[serde(default)]
-    pub windows_sandbox_private_desktop: bool,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub windows_sandbox_proxy_settings_mode: Option<WindowsSandboxProxySettingsMode>,
     #[serde(default)]
@@ -399,7 +397,6 @@ impl FileSystemSandboxContext {
             user_home_dir: None,
             temporary_directories: None,
             windows_sandbox_selection: WindowsSandboxSelection::Disabled,
-            windows_sandbox_private_desktop: false,
             windows_sandbox_proxy_settings_mode: None,
             use_legacy_landlock: false,
         }
@@ -476,8 +473,6 @@ pub struct WireFileSystemSandboxContext {
     temporary_directories: Option<Vec<PathUri>>,
     #[serde(rename = "windowsSandboxLevel")]
     windows_sandbox_selection: WindowsSandboxSelection,
-    #[serde(default)]
-    windows_sandbox_private_desktop: bool,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     windows_sandbox_proxy_settings_mode: Option<WindowsSandboxProxySettingsMode>,
     #[serde(default)]
@@ -503,7 +498,6 @@ impl From<FileSystemSandboxContext> for WireFileSystemSandboxContext {
             user_home_dir,
             temporary_directories,
             windows_sandbox_selection,
-            windows_sandbox_private_desktop,
             windows_sandbox_proxy_settings_mode,
             use_legacy_landlock,
         } = sandbox;
@@ -548,7 +542,6 @@ impl From<FileSystemSandboxContext> for WireFileSystemSandboxContext {
             user_home_dir,
             temporary_directories,
             windows_sandbox_selection,
-            windows_sandbox_private_desktop,
             windows_sandbox_proxy_settings_mode,
             use_legacy_landlock,
         }
@@ -595,7 +588,6 @@ impl WireFileSystemSandboxContext {
             user_home_dir: self.user_home_dir,
             temporary_directories: self.temporary_directories,
             windows_sandbox_selection: self.windows_sandbox_selection,
-            windows_sandbox_private_desktop: self.windows_sandbox_private_desktop,
             windows_sandbox_proxy_settings_mode: self.windows_sandbox_proxy_settings_mode,
             use_legacy_landlock: self.use_legacy_landlock,
         }