Launch managed network proxies on remote executors (#33906)

## Why

Remote executions need managed-network proxy listeners in the executor so their
loopback proxy addresses are reachable by the launched process.

## What changed

- Add a capability-gated exec-server protocol field for executor-local proxy
  launch configuration, including network policy, audit metadata, and execution
  attribution.
- Start the proxy while preparing a remote process, replace inherited proxy
  environment variables with its local addresses, and derive the sandbox
  context from its listeners.
- Keep the proxy alive until inherited output streams close, then shut it down.
- Reject unsupported remote settings such as MITM and credential injection.

## Testing

- Cover configuration round trips and rejection of unsupported settings.
- Verify executor-local startup, blocked-domain enforcement, protocol
  compatibility, and proxy lifetime through process closure.

GitOrigin-RevId: c984f54e3e600aa9ebcbf8cf4574046e2c199d11

codex-rs/core/src/unified_exec/process_manager.rs

@@ -193,6 +193,7 @@ fn exec_server_params_for_request(
         sandbox: request.exec_server_sandbox.clone(),
         enforce_managed_network: request.exec_server_enforce_managed_network,
         managed_network: request.exec_server_managed_network.clone(),
+        network_proxy: request.exec_server_network_proxy.clone(),
     }
 }
 
@@ -959,6 +960,7 @@ impl UnifiedExecProcessManager {
         options: ExecOptions,
         attempt: &SandboxAttempt<'_>,
         network: Option<&NetworkProxy>,
+        network_proxy_launch: Option<codex_network_proxy::RemoteNetworkProxyLaunchConfig>,
         environment_id: Option<&str>,
         exec_server_env_config: Option<ExecServerEnvConfig>,
         tty: bool,
@@ -966,11 +968,12 @@ impl UnifiedExecProcessManager {
         environment: &codex_exec_server::Environment,
     ) -> Result<UnifiedExecProcess, ToolError> {
         let mut request = if environment.is_remote() {
-            attempt.env_for_exec_server(command, options, network, environment_id)
+            attempt.env_for_exec_server(command, options)
         } else {
             attempt.env_for(command, options, network, environment_id)
         }
         .map_err(ToolError::Codex)?;
+        request.exec_server_network_proxy = network_proxy_launch;
         request.exec_server_env_config = exec_server_env_config;
         self.open_session_with_prepared_exec_env(
             process_id,

codex-rs/core/src/unified_exec/process_manager_tests.rs

@@ -174,6 +174,7 @@ fn exec_server_params_use_path_uri_and_env_policy_overlay_contract() {
         exec_server_sandbox: None,
         exec_server_enforce_managed_network: true,
         exec_server_managed_network: Some(managed_network.clone()),
+        exec_server_network_proxy: None,
     };
 
     let params =