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/app-server/src/request_processors/command_exec_processor.rs

@@ -299,10 +299,6 @@ impl CommandExecRequestProcessor {
             network_environment_id: None,
             sandbox_permissions: SandboxPermissions::UseDefault,
             windows_sandbox_level,
-            windows_sandbox_private_desktop: self
-                .config
-                .permissions
-                .windows_sandbox_private_desktop,
             justification: None,
             arg0: None,
         };

codex-rs/app-server/src/request_processors/config_processor.rs

@@ -399,10 +399,6 @@ fn map_requirements_to_api(
         }
         None => ConfigRequirementsToml::default(),
     };
-    let windows_sandbox_private_desktop = requirements
-        .windows
-        .as_ref()
-        .and_then(|windows| windows.sandbox_private_desktop);
 
     Some(ConfigRequirements {
         model_provider: requirements.model_provider,
@@ -539,7 +535,6 @@ fn map_requirements_to_api(
         feedback: requirements.feedback.map(|feedback| FeedbackRequirements {
             enabled: feedback.enabled,
         }),
-        windows_sandbox_private_desktop,
     })
 }
 
@@ -1105,7 +1100,6 @@ mod tests {
                     codex_config::WindowsSandboxImplementationToml::Elevated,
                     codex_config::WindowsSandboxImplementationToml::Unelevated,
                 ]),
-                sandbox_private_desktop: Some(false),
             }),
             ..ConfigRequirementsToml::default()
         });
@@ -1117,7 +1111,6 @@ mod tests {
                 WindowsSandboxImplementation::Unelevated,
             ])
         );
-        assert_eq!(mapped.windows_sandbox_private_desktop, Some(false));
     }
 
     #[test]