fix: preserve auto review across config and delegation (#26230)

## Why

Auto Review should remain the effective approval reviewer when settings
cross runtime boundaries. A config or app-server round trip must not
change the reviewer identity, and delegated work must not silently fall
back to user review.

This requires both a stable canonical serialized value and propagation
of the effective setting. `auto_review` is the canonical value across
protocol and app-server output, while `guardian_subagent` remains
accepted as backward-compatible input.

## What changed

- serialize `ApprovalsReviewer::AutoReview` consistently as
`auto_review` across core protocol and app-server v2
- continue accepting `guardian_subagent` when reading existing config or
client requests
- carry the active turn's approval reviewer into spawned agents
- update config/debug expectations and add delegated-task regression
coverage

## Scope

This does not change Guardian policy or remove compatibility with
existing `guardian_subagent` inputs. It preserves the selected reviewer
across serialization, config reloads, app-server settings, and delegated
task setup.

Related Guardian changes are split independently:

- #26231 adds denials and soft denials
- #26334 retries transient reviewer failures
- #26333 reuses narrowly scoped low-risk approvals
- #26232 adds TUI denial recovery

## Validation

- `just test -p codex-app-server-protocol` (224 passed)
- regression coverage for delegated task reviewer propagation
- serialization coverage for canonical `auto_review` output and legacy
`guardian_subagent` input

---------

Co-authored-by: saud-oai <saud@openai.com>

codex-rs/app-server-protocol/src/protocol/v2/shared.rs

@@ -233,7 +233,7 @@ impl From<CoreAskForApproval> for AskForApproval {
 pub enum ApprovalsReviewer {
     #[serde(rename = "user")]
     User,
-    #[serde(rename = "guardian_subagent", alias = "auto_review")]
+    #[serde(rename = "auto_review", alias = "guardian_subagent")]
     AutoReview,
 }
 

codex-rs/app-server-protocol/src/protocol/v2/tests.rs

@@ -65,7 +65,7 @@ fn approvals_reviewer_serializes_auto_review_and_accepts_legacy_guardian_subagen
     );
     assert_eq!(
         serde_json::to_string(&ApprovalsReviewer::AutoReview).expect("serialize reviewer"),
-        "\"guardian_subagent\""
+        "\"auto_review\""
     );
 
     for value in ["user", "auto_review", "guardian_subagent"] {

codex-rs/config/src/loader/mod.rs

@@ -1467,7 +1467,7 @@ foo = "xyzzy"
             TomlValue::Table(toml::map::Map::from_iter([(
                 "allowed_approvals_reviewers".to_string(),
                 TomlValue::Array(vec![
-                    TomlValue::String("guardian_subagent".to_string()),
+                    TomlValue::String("auto_review".to_string()),
                     TomlValue::String("user".to_string()),
                 ]),
             )]))

codex-rs/core/src/tools/handlers/multi_agents_common.rs

@@ -262,6 +262,7 @@ pub(crate) fn apply_spawn_agent_runtime_overrides(
         .map_err(|err| {
             FunctionCallError::RespondToModel(format!("approval_policy is invalid: {err}"))
         })?;
+    config.approvals_reviewer = turn.config.approvals_reviewer;
     config.permissions.shell_environment_policy = turn.shell_environment_policy.clone();
     config.codex_linux_sandbox_exe = turn.codex_linux_sandbox_exe.clone();
     #[allow(deprecated)]

codex-rs/core/src/tools/handlers/multi_agents_tests.rs

@@ -24,6 +24,7 @@ use codex_model_provider::create_model_provider;
 use codex_model_provider_info::built_in_model_providers;
 use codex_protocol::AgentPath;
 use codex_protocol::ThreadId;
+use codex_protocol::config_types::ApprovalsReviewer;
 use codex_protocol::config_types::ServiceTier;
 use codex_protocol::config_types::ShellEnvironmentPolicy;
 use codex_protocol::models::BaseInstructions;
@@ -2331,6 +2332,9 @@ async fn spawn_agent_reapplies_runtime_sandbox_after_role_config() {
     turn.approval_policy
         .set(AskForApproval::OnRequest)
         .expect("approval policy should be set");
+    let mut config = (*turn.config).clone();
+    config.approvals_reviewer = ApprovalsReviewer::AutoReview;
+    set_turn_config(&mut turn, config);
     turn.permission_profile = expected_permission_profile.clone();
     assert_ne!(
         expected_permission_profile,
@@ -2370,6 +2374,7 @@ async fn spawn_agent_reapplies_runtime_sandbox_after_role_config() {
         .await;
     assert_eq!(snapshot.sandbox_policy(), expected_sandbox);
     assert_eq!(snapshot.approval_policy, AskForApproval::OnRequest);
+    assert_eq!(snapshot.approvals_reviewer, ApprovalsReviewer::AutoReview);
     assert_eq!(snapshot.permission_profile, expected_permission_profile);
     let child_thread = manager
         .get_thread(agent_id)

codex-rs/protocol/src/config_types.rs

@@ -166,8 +166,8 @@ pub enum ApprovalsReviewer {
     #[default]
     #[serde(rename = "user")]
     User,
-    #[serde(rename = "guardian_subagent", alias = "auto_review")]
-    #[strum(serialize = "guardian_subagent")]
+    #[serde(rename = "auto_review", alias = "guardian_subagent")]
+    #[strum(serialize = "auto_review")]
     AutoReview,
 }
 
@@ -760,7 +760,7 @@ mod tests {
         );
         assert_eq!(
             serde_json::to_string(&ApprovalsReviewer::AutoReview).expect("serialize reviewer"),
-            "\"guardian_subagent\""
+            "\"auto_review\""
         );
 
         for value in ["user", "auto_review", "guardian_subagent"] {

codex-rs/tui/src/app/tests.rs

@@ -1824,7 +1824,7 @@ async fn update_feature_flags_enabling_guardian_selects_auto_review() -> Result<
 
     let config = std::fs::read_to_string(codex_home.path().join("config.toml"))?;
     assert!(config.contains("guardian_approval = true"));
-    assert!(config.contains("approvals_reviewer = \"guardian_subagent\""));
+    assert!(config.contains("approvals_reviewer = \"auto_review\""));
     assert!(config.contains("approval_policy = \"on-request\""));
     assert!(config.contains("sandbox_mode = \"workspace-write\""));
     app_server.shutdown().await?;
@@ -1988,7 +1988,7 @@ async fn update_feature_flags_enabling_guardian_overrides_explicit_manual_review
     );
 
     let config = std::fs::read_to_string(codex_home.path().join("config.toml"))?;
-    assert!(config.contains("approvals_reviewer = \"guardian_subagent\""));
+    assert!(config.contains("approvals_reviewer = \"auto_review\""));
     assert!(config.contains("guardian_approval = true"));
     assert!(config.contains("approval_policy = \"on-request\""));
     assert!(config.contains("sandbox_mode = \"workspace-write\""));

codex-rs/tui/src/debug_config.rs

@@ -755,7 +755,7 @@ mod tests {
             "allowed_approval_policies: on-request (source: {requirements_source})"
         )));
         assert!(rendered.contains(
-            "allowed_approvals_reviewers: guardian_subagent (source: MDM managed_config.toml (legacy))"
+            "allowed_approvals_reviewers: auto_review (source: MDM managed_config.toml (legacy))"
         ));
         assert!(
             rendered.contains(
@@ -818,7 +818,7 @@ mod tests {
 
         let rendered = render_to_text(&render_debug_config_lines(&stack));
         assert!(rendered.contains(
-            "allowed_approvals_reviewers: guardian_subagent (source: MDM managed_config.toml (legacy))"
+            "allowed_approvals_reviewers: auto_review (source: MDM managed_config.toml (legacy))"
         ));
         assert!(!rendered.contains("Requirements:\n  <none>"));
     }