Enable Guardian parent-compaction reuse by default (#46522)

## What changed

Promote `guardian_reuse_parent_compaction` to stable and enable it by default, allowing Guardian to reuse encrypted parent compaction when restarting review sessions.

## Testing

Update Guardian tests to rely on the default setting, including evidence retention after compaction and resume. Adjust cache-key assertions to verify that parent-history changes invalidate cached review sessions by default, while explicitly disabling reuse preserves the previous behavior.

GitOrigin-RevId: 196aff1e91d022490b3782f6c7b5f168907efab9

codex-rs/app-server/tests/suite/v2/guardian_v2_history_tests.rs

@@ -280,7 +280,6 @@ async fn guardians_retain_evidence_after_compaction_and_resume(
         .with_root_config("approvals_reviewer = \"auto_review\"\nmodel_auto_compact_token_limit = 1000000")
         .enable_feature(Feature::DefaultModeRequestUserInput)
         .enable_feature(Feature::GuardianApproval)
-        .enable_feature(Feature::GuardianReuseParentCompaction)
         .disable_feature(Feature::EnableRequestCompression)
         .disable_feature(Feature::TokenBudget)
         .with_extra_config(&format!(

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

@@ -366,7 +366,7 @@ async fn guardian_review_session_config_change_invalidates_cached_session() {
         )
     );
 
-    assert_eq!(
+    assert_ne!(
         cached_reuse_key,
         GuardianReviewSessionReuseKey::from_spawn_config(
             &cached_spawn_config,
@@ -414,20 +414,20 @@ async fn guardian_review_session_config_change_invalidates_cached_session() {
         "changing the effective Node REPL policy must invalidate reviewer history"
     );
 
-    let mut compaction_enabled_config = cached_spawn_config;
-    compaction_enabled_config
+    let mut compaction_disabled_config = cached_spawn_config;
+    compaction_disabled_config
         .features
-        .enable(Feature::GuardianReuseParentCompaction)
+        .disable(Feature::GuardianReuseParentCompaction)
         .expect("Guardian parent-compaction reuse should be configurable");
-    assert_ne!(
+    assert_eq!(
         GuardianReviewSessionReuseKey::from_spawn_config(
-            &compaction_enabled_config,
+            &compaction_disabled_config,
             SessionInstructions::default(),
             /*parent_history_version*/ 0,
             GuardianContextMode::Legacy,
         ),
         GuardianReviewSessionReuseKey::from_spawn_config(
-            &compaction_enabled_config,
+            &compaction_disabled_config,
             SessionInstructions::default(),
             /*parent_history_version*/ 1,
             GuardianContextMode::Legacy,
@@ -441,9 +441,6 @@ async fn guardian_review_session_config_change_invalidates_cached_session() {
 async fn encrypted_parent_compaction_requires_original_item_id(thread_context_enabled: bool) {
     let (session, _) = crate::session::tests::make_session_and_context().await;
     let mut features = session.get_config().await.features.clone();
-    features
-        .enable(Feature::GuardianReuseParentCompaction)
-        .expect("legacy reuse");
     features
         .set_enabled(Feature::GuardianThreadContext, thread_context_enabled)
         .expect("context mode");

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

@@ -2225,17 +2225,11 @@ async fn guardian_reuses_prompt_cache_key_and_appends_prior_reviews() -> anyhow:
     .await;
 
     let (session, mut turn) = guardian_test_session_and_turn(&server).await;
-    let mut config = (*turn.config).clone();
-    config
-        .features
-        .enable(Feature::GuardianReuseParentCompaction)
-        .expect("Guardian parent-compaction reuse should be configurable");
     let turn_mut = Arc::get_mut(&mut turn).expect("turn should be unique");
     update_turn_settings_for_test(turn_mut, |settings| {
         Arc::make_mut(&mut settings.model_info).auto_review_model_override =
             Some("codex-auto-review".to_string());
     });
-    turn_mut.config = Arc::new(config);
     seed_guardian_parent_history(&session, &turn).await;
 
     let first_request = GuardianApprovalRequest::ExecCommand {

codex-rs/features/src/lib.rs

@@ -1612,8 +1612,8 @@ pub const FEATURES: &[FeatureSpec] = &[
     FeatureSpec {
         id: Feature::GuardianReuseParentCompaction,
         key: "guardian_reuse_parent_compaction",
-        stage: Stage::UnderDevelopment,
-        default_enabled: false,
+        stage: Stage::Stable,
+        default_enabled: true,
     },
     FeatureSpec {
         id: Feature::GuardianEnhancedNodeReplTranscripts,