Select the elevated Windows sandbox for network proxies (#33445)

## Why

Windows firewall enforcement is tied to the logon-user sandbox identities. Proxy-enforced commands therefore need the elevated backend even when the configured sandbox mode is the default restricted-token mode.

## What changed

- Select the elevated Windows sandbox backend whenever a command uses the managed network proxy.
- Remove configuration and startup checks that required users or managed requirements to select the elevated sandbox explicitly.
- Start and expose managed network proxy state consistently on Windows.

## Testing

- Verify that proxy enforcement selects the elevated backend for the restricted-token sandbox mode.

GitOrigin-RevId: e01ac052587721c468a8fbcf4e2c7c5a185a3e05

codex-rs/core/src/context/environment_context.rs

@@ -215,26 +215,22 @@ pub(crate) fn push_xml_escaped_text(rendered: &mut String, value: &str) {
 
 #[derive(Debug, Clone, PartialEq, Eq, Default)]
 pub(crate) struct NetworkContext {
-    enabled: bool,
     allowed_domains: Vec<String>,
     denied_domains: Vec<String>,
 }
 
 impl NetworkContext {
-    pub(crate) fn new(enabled: bool, allowed: Vec<String>, denied: Vec<String>) -> Self {
+    pub(crate) fn new(allowed_domains: Vec<String>, denied_domains: Vec<String>) -> Self {
         Self {
-            enabled,
-            allowed_domains: allowed,
-            denied_domains: denied,
+            allowed_domains,
+            denied_domains,
         }
     }
 
     pub(super) fn render(&self) -> String {
-        let mut rendered = format!("<network enabled=\"{}\">", self.enabled);
-        if self.enabled {
-            Self::push_rendered_domain_element(&mut rendered, "allowed", &self.allowed_domains);
-            Self::push_rendered_domain_element(&mut rendered, "denied", &self.denied_domains);
-        }
+        let mut rendered = "<network enabled=\"true\">".to_string();
+        Self::push_rendered_domain_element(&mut rendered, "allowed", &self.allowed_domains);
+        Self::push_rendered_domain_element(&mut rendered, "denied", &self.denied_domains);
         rendered.push_str("</network>");
         rendered
     }

codex-rs/core/src/context/world_state/environment.rs

@@ -374,7 +374,6 @@ fn network_from_turn_context(turn_context: &TurnContext) -> Option<NetworkContex
         .as_ref()?;
 
     Some(NetworkContext::new(
-        turn_context.network.is_some(),
         network
             .domains
             .as_ref()

codex-rs/core/src/context/world_state/environment_render_tests.rs

@@ -115,7 +115,6 @@ fn serialize_environment_context_with_foreign_windows_cwd() {
 #[test]
 fn serialize_environment_context_with_network() {
     let network = NetworkContext::new(
-        /*enabled*/ true,
         vec!["api.example.com".to_string(), "*.openai.com".to_string()],
         vec!["blocked.example.com".to_string()],
     );

codex-rs/core/src/context/world_state/environment_tests.rs

@@ -60,7 +60,6 @@ fn snapshots() -> Result<()> {
         current_date: Some("2026-06-19".to_string()),
         timezone: Some("UTC".to_string()),
         network: Some(NetworkContext::new(
-            /*enabled*/ true,
             vec!["old.example.com".to_string()],
             vec![],
         )),
@@ -74,7 +73,6 @@ fn snapshots() -> Result<()> {
         current_date: Some("2026-06-20".to_string()),
         timezone: Some("America/Los_Angeles".to_string()),
         network: Some(NetworkContext::new(
-            /*enabled*/ true,
             vec!["new.example.com".to_string()],
             vec!["blocked.example.com".to_string()],
         )),