Use step environments for Guardian approval reviews (#37618)

## Why

Deferred environments can become ready after a turn starts. Guardian approval
reviews must use the environment selected for the current step so their working
directory and permission context are not taken from the stale turn snapshot.

## What changed

- Carry `StepContext` through tool execution and approval handling.
- Add a Guardian review context that pairs the parent turn with the current
  step's environment snapshot.
- Use that snapshot for Guardian prompts, reviewer sessions, and delegated
  reviewer threads while retaining turn-level fallbacks for callers without a
  step context.

## Testing

Added an integration test that makes a deferred remote environment ready before
an escalated command and verifies Guardian receives that environment's working
directory and denied-read policy instead of the initial local environment's.

GitOrigin-RevId: 779096bc7d0e0c7453a009c02141029714b9b407

codex-rs/core/src/codex_delegate_tests.rs

@@ -201,6 +201,7 @@ async fn run_codex_thread_interactive_respects_pre_cancelled_spawn() {
         crate::session::tests::make_session_and_context_with_rx().await;
     let cancel_token = CancellationToken::new();
     cancel_token.cancel();
+    let parent_environments = parent_ctx.environments.clone();
 
     let result = timeout(
         Duration::from_secs(/*secs*/ 1),
@@ -210,6 +211,7 @@ async fn run_codex_thread_interactive_respects_pre_cancelled_spawn() {
             Arc::clone(&parent_session.services.models_manager),
             parent_session,
             parent_ctx,
+            parent_environments,
             cancel_token,
             SubAgentSource::Review,
             /*initial_history*/ None,