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/exec-server/src/fs_sandbox.rs

@@ -197,8 +197,6 @@ impl FileSystemSandboxRunner {
                     use_legacy_landlock: sandbox_context.use_legacy_landlock,
                     windows_sandbox_level: windows_sandbox_level
                         .unwrap_or(WindowsSandboxLevel::Disabled),
-                    windows_sandbox_private_desktop: sandbox_context
-                        .windows_sandbox_private_desktop,
                 },
             })
             .map_err(|err| invalid_request(format!("failed to prepare fs sandbox: {err}")))
@@ -885,7 +883,7 @@ mod tests {
             ),
         ]);
         let sandbox_context = crate::FileSystemSandboxContext {
-            windows_sandbox_selection: codex_file_system::WindowsSandboxSelection::Elevated,
+            windows_sandbox_selection: codex_file_system::WindowsSandboxSelection::RestrictedToken,
             ..sandbox_context_with_cwd(&policy, cwd_uri)
         };
         selected.close().expect("remove selected directory");

codex-rs/exec-server/src/fs_sandbox_windows_tests.rs

@@ -254,7 +254,6 @@ fn powershell_command(script: &str, path: &Path) -> anyhow::Result<SandboxExecRe
         network_environment_id: None,
         sandbox: SandboxType::None,
         windows_sandbox_level: WindowsSandboxLevel::Disabled,
-        windows_sandbox_private_desktop: false,
         permission_profile: PermissionProfile::Disabled,
         arg0: None,
     })

codex-rs/exec-server/src/process_sandbox.rs

@@ -59,7 +59,6 @@ struct PreparedWindowsSandboxRequest {
     network_proxy_restricting_sid: Option<String>,
     proxy_settings_mode: WindowsSandboxProxySettingsMode,
     filesystem_overrides: Option<WindowsSandboxFilesystemOverrides>,
-    use_private_desktop: bool,
 }
 
 impl PreparedExecRequest {
@@ -74,7 +73,6 @@ impl PreparedExecRequest {
                 network_proxy_restricting_sid: request.network_proxy_restricting_sid.as_deref(),
                 proxy_settings_mode: request.proxy_settings_mode,
                 filesystem_overrides: request.filesystem_overrides.as_ref(),
-                use_private_desktop: request.use_private_desktop,
             })
     }
 }
@@ -90,9 +88,9 @@ pub(crate) async fn prepare_exec_request_with_telemetry(
     if let Some(sandbox) = params.sandbox.as_ref()
         && sandbox.windows_sandbox_selection == WindowsSandboxSelection::Mxc
     {
-        if params.arg0.is_some() || sandbox.windows_sandbox_private_desktop {
+        if params.arg0.is_some() {
             return Err(invalid_params(
-                "MXC custom argv0 and private-desktop launches are not supported".to_owned(),
+                "MXC custom argv0 is not supported".to_owned(),
             ));
         }
         if !codex_sandboxing::windows_mxc_available() {
@@ -271,7 +269,6 @@ pub(crate) async fn prepare_exec_request_with_telemetry(
             },
             use_legacy_landlock: sandbox_context.use_legacy_landlock,
             windows_sandbox_level: windows_sandbox_level.unwrap_or(WindowsSandboxLevel::Disabled),
-            windows_sandbox_private_desktop: sandbox_context.windows_sandbox_private_desktop,
         },
     };
     let mut request = if sandbox == SandboxType::WindowsRestrictedToken {
@@ -312,7 +309,6 @@ pub(crate) async fn prepare_exec_request_with_telemetry(
             network_proxy_restricting_sid,
             proxy_settings_mode: windows_sandbox_proxy_settings_mode,
             filesystem_overrides,
-            use_private_desktop: sandbox_context.windows_sandbox_private_desktop,
         })
     } else {
         None

codex-rs/exec-server/tests/file_system_windows.rs

@@ -569,8 +569,7 @@ async fn file_system_private_desktop_survives_helper_exits_and_separates_permiss
     let path = tmp.path().join("contents.txt");
     std::fs::write(&path, b"initial")?;
     let uri = PathUri::from_host_native_path(&path)?;
-    let mut sandbox = workspace_write_sandbox(tmp.path().to_path_buf());
-    sandbox.windows_sandbox_private_desktop = true;
+    let sandbox = workspace_write_sandbox(tmp.path().to_path_buf());
     let before = process_private_desktops()?;
     let write = file_system
         .write_file(
@@ -624,7 +623,6 @@ async fn file_system_private_desktop_survives_helper_exits_and_separates_permiss
 
     let mut readonly = read_only_sandbox_for_cwd(tmp.path().to_path_buf())?;
     readonly.windows_sandbox_selection = WindowsSandboxSelection::RestrictedToken;
-    readonly.windows_sandbox_private_desktop = true;
     file_system
         .write_file(
             &uri,