Use Guardian model limits for review sessions (#34847)

## Why

Parent context-window and auto-compaction overrides may describe a different
model than the one selected for Guardian review.

## What changed

- Clear `model_context_window` and `model_auto_compact_token_limit` when the
  effective Guardian model differs from the parent model, allowing the review
  model's own limits to apply.
- Preserve those overrides when Guardian uses the same effective model.

## Testing

Add unit coverage for both model-selection paths and verify that a Guardian
rollout records the selected review model's context window.

GitOrigin-RevId: ebc399f4eba37c7f279fd0d258154c00d45e2d00

codex-rs/core/src/guardian/review.rs

@@ -730,13 +730,17 @@ pub(super) async fn guardian_review_session_config(
             &turn.config.to_models_manager_config(),
         )
         .await;
-    let spawn_config = build_guardian_review_session_config(
+    let mut spawn_config = build_guardian_review_session_config(
         turn.config.as_ref(),
         live_network_config,
         guardian_model.as_str(),
         guardian_reasoning_effort.clone(),
         guardian_model_info.model_messages.as_ref(),
     )?;
+    if guardian_model != turn.model_info.slug {
+        spawn_config.model_context_window = None;
+        spawn_config.model_auto_compact_token_limit = None;
+    }
     Ok(GuardianReviewSessionConfig {
         spawn_config,
         model: guardian_model,

codex-rs/core/src/guardian/tests.rs

@@ -9,6 +9,7 @@ use crate::guardian::approval_request::guardian_request_target_item_id;
 use crate::guardian::prompt::BUNDLED_GUARDIAN_POLICY;
 use crate::guardian::prompt::BUNDLED_GUARDIAN_POLICY_TEMPLATE;
 use crate::guardian::prompt::guardian_policy_prompt_with_config_and_template;
+use crate::guardian::review::guardian_review_session_config;
 use crate::session::session::Session;
 use crate::session::turn_context::TurnContext;
 use crate::test_support;
@@ -2932,6 +2933,69 @@ async fn guardian_review_session_config_preserves_parent_network_proxy() {
     );
 }
 
+#[tokio::test]
+async fn guardian_review_session_config_clears_context_overrides_for_distinct_effective_model() {
+    let server = start_mock_server().await;
+    let (session, mut turn) = guardian_test_session_and_turn(&server).await;
+    let mut config = (*turn.config).clone();
+    config.model = Some("codex-auto-review".to_string());
+    config.model_context_window = Some(900_000);
+    config.model_auto_compact_token_limit = Some(600_000);
+    Arc::get_mut(&mut turn)
+        .expect("turn should be unique")
+        .config = Arc::new(config);
+
+    let guardian_config = guardian_review_session_config(session.as_ref(), turn.as_ref())
+        .await
+        .expect("guardian config")
+        .spawn_config;
+
+    assert_eq!(
+        (
+            guardian_config.model_context_window,
+            guardian_config.model_auto_compact_token_limit,
+        ),
+        (None, None)
+    );
+}
+
+#[tokio::test]
+async fn guardian_review_session_config_preserves_context_overrides_for_same_effective_model() {
+    let server = start_mock_server().await;
+    let (mut session, mut turn) = guardian_test_session_and_turn(&server).await;
+    let parent_model = turn.model_info.clone();
+    let auth_manager = Arc::clone(&session.services.auth_manager);
+    Arc::get_mut(&mut session)
+        .expect("session should be unique")
+        .services
+        .models_manager = Arc::new(StaticModelsManager::new(
+        Some(auth_manager),
+        ModelsResponse {
+            models: vec![parent_model],
+        },
+    ));
+    let mut config = (*turn.config).clone();
+    config.model = Some("stale-parent-model".to_string());
+    config.model_context_window = Some(128_000);
+    config.model_auto_compact_token_limit = Some(100_000);
+    Arc::get_mut(&mut turn)
+        .expect("turn should be unique")
+        .config = Arc::new(config);
+
+    let guardian_config = guardian_review_session_config(session.as_ref(), turn.as_ref())
+        .await
+        .expect("guardian config")
+        .spawn_config;
+
+    assert_eq!(
+        (
+            guardian_config.model_context_window,
+            guardian_config.model_auto_compact_token_limit,
+        ),
+        (Some(128_000), Some(100_000))
+    );
+}
+
 #[tokio::test]
 async fn guardian_review_session_config_clears_parent_developer_instructions() {
     let mut parent_config = test_config().await;

codex-rs/core/tests/suite/guardian_review.rs

@@ -9,6 +9,8 @@ use codex_protocol::openai_models::ModelsResponse;
 use codex_protocol::protocol::AskForApproval;
 use codex_protocol::protocol::EventMsg;
 use codex_protocol::protocol::Op;
+use codex_protocol::protocol::RolloutItem;
+use codex_protocol::protocol::RolloutLine;
 use codex_protocol::protocol::SandboxPolicy;
 use codex_protocol::user_input::UserInput;
 use core_test_support::fs_wait;
@@ -69,6 +71,16 @@ async fn guardian_session_prewarms_and_is_reused_for_first_review() -> Result<()
         ]],
         vec![vec![
             ev_response_created("guardian-review"),
+            ev_assistant_message(
+                "guardian-assessment",
+                &json!({
+                    "risk_level": "low",
+                    "user_authorization": "high",
+                    "outcome": "allow",
+                    "rationale": "The command is safe to execute.",
+                })
+                .to_string(),
+            ),
             ev_completed("guardian-review"),
         ]],
     ])
@@ -77,6 +89,8 @@ async fn guardian_session_prewarms_and_is_reused_for_first_review() -> Result<()
         config.model_catalog = Some(ModelsResponse {
             models: vec![review_model],
         });
+        config.model_context_window = Some(900_000);
+        config.model_auto_compact_token_limit = Some(600_000);
         config.permissions.approval_policy = Constrained::allow_any(AskForApproval::OnRequest);
         config.approvals_reviewer = ApprovalsReviewer::AutoReview;
     });
@@ -133,7 +147,23 @@ async fn guardian_session_prewarms_and_is_reused_for_first_review() -> Result<()
     );
     assert_eq!(guardian_review.get("generate"), None);
 
+    let guardian_rollout_path = test
+        .codex
+        .guardian_trunk_rollout_path()
+        .await
+        .expect("guardian trunk rollout path");
     test.codex.shutdown_and_wait().await?;
+    let guardian_context_windows = fs::read_to_string(guardian_rollout_path)?
+        .lines()
+        .map(serde_json::from_str::<RolloutLine>)
+        .collect::<serde_json::Result<Vec<_>>>()?
+        .into_iter()
+        .filter_map(|line| match line.item {
+            RolloutItem::EventMsg(EventMsg::TurnStarted(event)) => Some(event.model_context_window),
+            _ => None,
+        })
+        .collect::<Vec<_>>();
+    assert_eq!(guardian_context_windows, vec![Some(258_400)]);
     server.shutdown().await;
     Ok(())
 }