Add network policy metadata to environment configuration (#39055)

## What changed

- Add `EnvironmentNetworkPolicy` as a serializable view of portable domain,
  Unix-socket, upstream-proxy, and local-binding restrictions without exposing
  controller-owned proxy runtime settings.
- Add an optional `network_policy` field to `EnvironmentConfig` and re-export
  the policy and related permission types through the core APIs.
- Reject owner-provided network policies during environment preview and
  readiness until runtime enforcement is implemented, while preserving the
  existing controller policy when the field is absent.

## Testing

- Cover rejection through both environment preview and readiness, including
  preservation of the existing environment selection.

GitOrigin-RevId: 80ad4cf4d4a45632daa7a823e6cf568eb0e8bb80

codex-rs/protocol/src/environment.rs

@@ -2,6 +2,7 @@ use crate::capabilities::SelectedCapabilityRoot;
 use crate::config_types::ShellEnvironmentPolicy;
 use crate::models::PermissionProfileSnapshot;
 use codex_execpolicy::RequirementsExecPolicy;
+use codex_network_proxy::EnvironmentNetworkPolicy;
 
 /// Configuration supplied for a thread's selected environment.
 #[allow(clippy::large_enum_variant)]
@@ -28,6 +29,9 @@ pub struct EnvironmentConfig {
     pub shell_environment_policy: ShellEnvironmentPolicy,
     /// Additional managed command restrictions for this environment attachment.
     pub exec_policy: Option<RequirementsExecPolicy>,
+    /// Owner-provided traffic restrictions. `None` keeps the existing controller policy.
+    /// Core rejects `Some` until attachment-owned network enforcement is implemented.
+    pub network_policy: Option<EnvironmentNetworkPolicy>,
     /// Capability roots selected for this thread's environment attachment.
     pub selected_capability_roots: Vec<SelectedCapabilityRoot>,
 }
@@ -40,6 +44,7 @@ impl std::fmt::Debug for EnvironmentConfig {
             .field("permission_profile", &self.permission_profile)
             .field("shell_environment_policy", &"<redacted>")
             .field("exec_policy", &self.exec_policy)
+            .field("network_policy", &self.network_policy)
             .field("selected_capability_roots", &self.selected_capability_roots)
             .finish()
     }