Reuse parent compactions in Guardian review sessions (#37513)

## What changed

- Add the under-development `guardian_reuse_parent_compaction` feature.
- Restart Guardian review sessions after parent history rewrites and seed them with the latest encrypted compaction that has a response item ID.
- Keep the existing reviewer when a rewritten history has no reusable compaction, preserving authorization and restriction context held by that session.

## Testing

- Cover reuse-key invalidation and compaction eligibility.
- Verify review-session behavior across parent compaction and a subsequent summary-free history reset.

GitOrigin-RevId: 891805d3c3dca34ddda6e3bfc5097be4ff164267

codex-rs/core/config.schema.json

@@ -570,6 +570,9 @@
             "guardian_approval": {
               "type": "boolean"
             },
+            "guardian_reuse_parent_compaction": {
+              "type": "boolean"
+            },
             "guardianv2": {
               "type": "boolean"
             },
@@ -5235,6 +5238,9 @@
         "guardian_approval": {
           "type": "boolean"
         },
+        "guardian_reuse_parent_compaction": {
+          "type": "boolean"
+        },
         "guardianv2": {
           "type": "boolean"
         },

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

@@ -155,9 +155,9 @@ struct GuardianReviewForkSnapshot {
 
 #[derive(Debug, Clone, PartialEq)]
 struct GuardianReviewSessionReuseKey {
-    // Only include settings that affect spawned-session behavior so reuse
-    // invalidation remains explicit and does not depend on unrelated config
-    // bookkeeping.
+    // Only include settings that affect spawned-session behavior and parent
+    // history rewrites that invalidate existing reviewer context.
+    parent_history_version: u64,
     model: Option<String>,
     model_provider_id: String,
     model_provider: ModelProviderInfo,
@@ -184,8 +184,17 @@ impl GuardianReviewSessionReuseKey {
     fn from_spawn_config(
         spawn_config: &Config,
         user_instructions: Option<UserInstructions>,
+        parent_history_version: u64,
     ) -> Self {
         Self {
+            parent_history_version: if spawn_config
+                .features
+                .enabled(Feature::GuardianReuseParentCompaction)
+            {
+                parent_history_version
+            } else {
+                0
+            },
             model: spawn_config.model.clone(),
             model_provider_id: spawn_config.model_provider_id.clone(),
             model_provider: spawn_config.model_provider.clone(),
@@ -210,6 +219,29 @@ impl GuardianReviewSessionReuseKey {
     }
 }
 
+fn encrypted_parent_compaction(items: &[ResponseItem]) -> Option<ResponseItem> {
+    let item = items.iter().rev().find(|item| {
+        matches!(
+            item,
+            ResponseItem::Compaction { .. } | ResponseItem::ContextCompaction { .. }
+        )
+    })?;
+
+    match item {
+        ResponseItem::Compaction {
+            id: Some(_),
+            encrypted_content,
+            ..
+        } if !encrypted_content.is_empty() => Some(item.clone()),
+        ResponseItem::ContextCompaction {
+            id: Some(_),
+            encrypted_content: Some(encrypted_content),
+            ..
+        } if !encrypted_content.is_empty() => Some(item.clone()),
+        _ => None,
+    }
+}
+
 pub(crate) fn prompt_cache_key_override_for_review_session(
     session_source: &SessionSource,
     parent_thread_id: Option<ThreadId>,
@@ -311,9 +343,16 @@ impl GuardianReviewSessionManager {
             let spawn_config = guardian_review_session_config(&parent_session, &parent_turn)
                 .await?
                 .spawn_config;
+            let parent_history = parent_session.clone_history().await;
+            let parent_compaction = spawn_config
+                .features
+                .enabled(Feature::GuardianReuseParentCompaction)
+                .then(|| encrypted_parent_compaction(parent_history.raw_items()))
+                .flatten();
             let reuse_key = GuardianReviewSessionReuseKey::from_spawn_config(
                 &spawn_config,
                 parent_session.user_instructions().await,
+                parent_history.history_version(),
             );
             let spawn_cancel_token = self.cancellation_token.child_token();
             let spawn_cancel_guard = spawn_cancel_token.clone().drop_guard();
@@ -323,6 +362,7 @@ impl GuardianReviewSessionManager {
                 spawn_config,
                 reuse_key,
                 spawn_cancel_token.clone(),
+                parent_compaction,
                 /*fork_snapshot*/ None,
             )
             .await?;
@@ -375,9 +415,17 @@ impl GuardianReviewSessionManager {
         params: GuardianReviewSessionParams,
     ) -> (GuardianReviewSessionOutcome, GuardianReviewAnalyticsResult) {
         let deadline = params.deadline;
-        let next_reuse_key = GuardianReviewSessionReuseKey::from_spawn_config(
+        let parent_history = params.parent_session.clone_history().await;
+        let parent_compaction = params
+            .spawn_config
+            .features
+            .enabled(Feature::GuardianReuseParentCompaction)
+            .then(|| encrypted_parent_compaction(parent_history.raw_items()))
+            .flatten();
+        let mut next_reuse_key = GuardianReviewSessionReuseKey::from_spawn_config(
             &params.spawn_config,
             params.parent_session.user_instructions().await,
+            parent_history.history_version(),
         );
         let mut stale_trunk_to_shutdown = None;
         let mut spawned_trunk = false;
@@ -389,6 +437,13 @@ impl GuardianReviewSessionManager {
         .await
         {
             Ok(mut state) => {
+                if parent_compaction.is_none()
+                    && let Some(trunk) = state.trunk.as_ref()
+                {
+                    // Without a decryptable summary, the existing reviewer may
+                    // hold the only remaining authorization or restriction.
+                    next_reuse_key.parent_history_version = trunk.reuse_key.parent_history_version;
+                }
                 if let Some(trunk) = state.trunk.as_ref()
                     && trunk.reuse_key != next_reuse_key
                     && trunk.review_lock.try_acquire().is_ok()
@@ -408,6 +463,7 @@ impl GuardianReviewSessionManager {
                             params.spawn_config.clone(),
                             next_reuse_key.clone(),
                             spawn_cancel_token.clone(),
+                            parent_compaction.clone(),
                             /*fork_snapshot*/ None,
                         )),
                     )
@@ -453,6 +509,7 @@ impl GuardianReviewSessionManager {
                 params,
                 next_reuse_key,
                 deadline,
+                parent_compaction,
                 /*fork_snapshot*/ None,
             ))
             .await;
@@ -465,6 +522,7 @@ impl GuardianReviewSessionManager {
                     params,
                     next_reuse_key,
                     deadline,
+                    parent_compaction,
                     trunk.fork_snapshot().await,
                 ))
                 .await;
@@ -503,6 +561,7 @@ impl GuardianReviewSessionManager {
         let reuse_key = GuardianReviewSessionReuseKey::from_spawn_config(
             session.get_config().await.as_ref(),
             session.user_instructions().await,
+            session.clone_history().await.history_version(),
         );
         self.state.lock().await.trunk = Some(Arc::new(GuardianReviewSession {
             reuse_key,
@@ -523,6 +582,7 @@ impl GuardianReviewSessionManager {
         let reuse_key = GuardianReviewSessionReuseKey::from_spawn_config(
             session.get_config().await.as_ref(),
             session.user_instructions().await,
+            session.clone_history().await.history_version(),
         );
         self.state
             .lock()
@@ -606,6 +666,7 @@ impl GuardianReviewSessionManager {
         params: GuardianReviewSessionParams,
         reuse_key: GuardianReviewSessionReuseKey,
         deadline: tokio::time::Instant,
+        parent_compaction: Option<ResponseItem>,
         fork_snapshot: Option<GuardianReviewForkSnapshot>,
     ) -> (GuardianReviewSessionOutcome, GuardianReviewAnalyticsResult) {
         let spawn_cancel_token = self.cancellation_token.child_token();
@@ -621,6 +682,7 @@ impl GuardianReviewSessionManager {
                 fork_config,
                 reuse_key,
                 spawn_cancel_token.clone(),
+                parent_compaction,
                 fork_snapshot,
             )),
         )
@@ -663,6 +725,7 @@ async fn spawn_guardian_review_session(
     spawn_config: Config,
     reuse_key: GuardianReviewSessionReuseKey,
     cancel_token: CancellationToken,
+    parent_compaction: Option<ResponseItem>,
     fork_snapshot: Option<GuardianReviewForkSnapshot>,
 ) -> anyhow::Result<GuardianReviewSession> {
     let (initial_history, prior_review_count, initial_transcript_cursor) = match fork_snapshot {
@@ -671,7 +734,12 @@ async fn spawn_guardian_review_session(
             fork_snapshot.prior_review_count,
             fork_snapshot.last_reviewed_transcript_cursor,
         ),
-        None => (None, 0, None),
+        None => (
+            parent_compaction
+                .map(|item| InitialHistory::Forked(vec![RolloutItem::ResponseItem(item)])),
+            0,
+            None,
+        ),
     };
     let (session, io) = Box::pin(run_codex_thread_interactive(
         spawn_config,
@@ -1163,6 +1231,7 @@ mod tests {
         let reuse_key = GuardianReviewSessionReuseKey::from_spawn_config(
             session.get_config().await.as_ref(),
             session.user_instructions().await,
+            session.clone_history().await.history_version(),
         );
 
         (
@@ -1303,6 +1372,7 @@ mod tests {
         let cached_reuse_key = GuardianReviewSessionReuseKey::from_spawn_config(
             &cached_spawn_config,
             /*user_instructions*/ None,
+            /*parent_history_version*/ 0,
         );
 
         let mut changed_parent_config = parent_config;
@@ -1319,6 +1389,7 @@ mod tests {
         let next_reuse_key = GuardianReviewSessionReuseKey::from_spawn_config(
             &next_spawn_config,
             /*user_instructions*/ None,
+            /*parent_history_version*/ 0,
         );
 
         assert_eq!(
@@ -1331,8 +1402,60 @@ mod tests {
             GuardianReviewSessionReuseKey::from_spawn_config(
                 &cached_spawn_config,
                 /*user_instructions*/ None,
+                /*parent_history_version*/ 0,
             )
         );
+
+        assert_eq!(
+            cached_reuse_key,
+            GuardianReviewSessionReuseKey::from_spawn_config(
+                &cached_spawn_config,
+                /*user_instructions*/ None,
+                /*parent_history_version*/ 1,
+            )
+        );
+
+        let mut compaction_enabled_config = cached_spawn_config;
+        compaction_enabled_config
+            .features
+            .enable(Feature::GuardianReuseParentCompaction)
+            .expect("Guardian parent-compaction reuse should be configurable");
+        assert_ne!(
+            GuardianReviewSessionReuseKey::from_spawn_config(
+                &compaction_enabled_config,
+                /*user_instructions*/ None,
+                /*parent_history_version*/ 0,
+            ),
+            GuardianReviewSessionReuseKey::from_spawn_config(
+                &compaction_enabled_config,
+                /*user_instructions*/ None,
+                /*parent_history_version*/ 1,
+            )
+        );
+    }
+
+    #[test]
+    fn encrypted_parent_compaction_requires_original_item_id() {
+        let item = ResponseItem::Compaction {
+            id: Some(codex_protocol::ResponseItemId::from_server(
+                "cmp_guardian_parent_summary".to_string(),
+            )),
+            encrypted_content: "encrypted guardian parent summary".to_string(),
+            internal_chat_message_metadata_passthrough: None,
+        };
+
+        assert_eq!(
+            encrypted_parent_compaction(std::slice::from_ref(&item)),
+            Some(item)
+        );
+        assert_eq!(
+            encrypted_parent_compaction(&[ResponseItem::Compaction {
+                id: None,
+                encrypted_content: "encrypted guardian parent summary".to_string(),
+                internal_chat_message_metadata_passthrough: None,
+            }]),
+            None
+        );
     }
 
     #[tokio::test]
@@ -1389,6 +1512,7 @@ mod tests {
         let cached_reuse_key = GuardianReviewSessionReuseKey::from_spawn_config(
             &cached_spawn_config,
             /*user_instructions*/ None,
+            /*parent_history_version*/ 0,
         );
 
         let mut changed_parent_config = parent_config;
@@ -1405,6 +1529,7 @@ mod tests {
         let next_reuse_key = GuardianReviewSessionReuseKey::from_spawn_config(
             &next_spawn_config,
             /*user_instructions*/ None,
+            /*parent_history_version*/ 0,
         );
 
         assert_ne!(cached_reuse_key, next_reuse_key);
@@ -1767,6 +1892,11 @@ mod tests {
         review_session.reuse_key = GuardianReviewSessionReuseKey::from_spawn_config(
             &params.spawn_config,
             params.parent_session.user_instructions().await,
+            params
+                .parent_session
+                .clone_history()
+                .await
+                .history_version(),
         );
         let manager = GuardianReviewSessionManager {
             state: Arc::new(Mutex::new(GuardianReviewSessionState {

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

@@ -2053,15 +2053,27 @@ async fn guardian_reuses_prompt_cache_key_and_appends_prior_reviews() -> anyhow:
                 ),
                 ev_completed("resp-guardian-3"),
             ]),
+            sse(vec![
+                ev_response_created("resp-guardian-4"),
+                ev_assistant_message(
+                    "msg-guardian-4",
+                    "{\"risk_level\":\"low\",\"user_authorization\":\"high\",\"outcome\":\"allow\",\"rationale\":\"fourth guardian rationale\"}",
+                ),
+                ev_completed("resp-guardian-4"),
+            ]),
         ],
     )
     .await;
 
     let (session, mut turn) = guardian_test_session_and_turn(&server).await;
-    Arc::get_mut(&mut turn)
-        .expect("turn should be unique")
-        .model_info
-        .auto_review_model_override = Some("codex-auto-review".to_string());
+    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");
+    turn_mut.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::Shell {
@@ -2135,10 +2147,32 @@ async fn guardian_reuses_prompt_cache_key_and_appends_prior_reviews() -> anyhow:
         /*max_attempts*/ 1,
     )
     .await;
+    let committed_rollout_items = session
+        .guardian_review_session
+        .committed_fork_rollout_items_for_test()
+        .await
+        .expect("committed guardian fork snapshot");
+    assert_eq!(
+        committed_rollout_items
+            .iter()
+            .filter(|item| rollout_item_contains_message_text(
+                item,
+                "Use prior reviews as context, not binding precedent."
+            ))
+            .count(),
+        1,
+        "follow-up reminder should be persisted for guardian forks"
+    );
     session
-        .record_conversation_items(
-            turn.as_ref(),
-            &[
+        .replace_history(
+            vec![
+                ResponseItem::Compaction {
+                    id: Some(codex_protocol::ResponseItemId::from_server(
+                        "cmp_guardian_parent_summary".to_string(),
+                    )),
+                    encrypted_content: "encrypted guardian parent summary".to_string(),
+                    internal_chat_message_metadata_passthrough: None,
+                },
                 ResponseItem::Message {
                     id: None,
                     role: "user".to_string(),
@@ -2158,6 +2192,7 @@ async fn guardian_reuses_prompt_cache_key_and_appends_prior_reviews() -> anyhow:
                     internal_chat_message_metadata_passthrough: None,
                 },
             ],
+            /*reference_context_item*/ None,
         )
         .await;
     let third_request = GuardianApprovalRequest::Shell {
@@ -2181,6 +2216,30 @@ async fn guardian_reuses_prompt_cache_key_and_appends_prior_reviews() -> anyhow:
         /*max_attempts*/ 1,
     )
     .await;
+    session
+        .replace_history(
+            vec![ResponseItem::Message {
+                id: None,
+                role: "user".to_string(),
+                content: vec![ContentItem::InputText {
+                    text: "Please review after a summary-free context reset.".to_string(),
+                }],
+                phase: None,
+                internal_chat_message_metadata_passthrough: None,
+            }],
+            /*reference_context_item*/ None,
+        )
+        .await;
+    let fourth_outcome = run_guardian_review_session_for_test(
+        Arc::clone(&session),
+        Arc::clone(&turn),
+        guardian_shell_request("shell-4"),
+        ApprovalRequestReasons::default(),
+        guardian_output_schema(),
+        /*external_cancel*/ None,
+        /*max_attempts*/ 1,
+    )
+    .await;
 
     let (GuardianReviewOutcome::Completed(first_assessment), first_metadata) = first_outcome else {
         panic!("expected first guardian assessment");
@@ -2192,9 +2251,14 @@ async fn guardian_reuses_prompt_cache_key_and_appends_prior_reviews() -> anyhow:
     let (GuardianReviewOutcome::Completed(third_assessment), third_metadata) = third_outcome else {
         panic!("expected third guardian assessment");
     };
+    let (GuardianReviewOutcome::Completed(fourth_assessment), fourth_metadata) = fourth_outcome
+    else {
+        panic!("expected fourth guardian assessment");
+    };
     assert_eq!(first_assessment.outcome, GuardianAssessmentOutcome::Allow);
     assert_eq!(second_assessment.outcome, GuardianAssessmentOutcome::Allow);
     assert_eq!(third_assessment.outcome, GuardianAssessmentOutcome::Allow);
+    assert_eq!(fourth_assessment.outcome, GuardianAssessmentOutcome::Allow);
     assert!(matches!(
         first_metadata.guardian_session_kind,
         Some(codex_analytics::GuardianReviewSessionKind::TrunkNew)
@@ -2205,6 +2269,10 @@ async fn guardian_reuses_prompt_cache_key_and_appends_prior_reviews() -> anyhow:
     ));
     assert!(matches!(
         third_metadata.guardian_session_kind,
+        Some(codex_analytics::GuardianReviewSessionKind::TrunkNew)
+    ));
+    assert!(matches!(
+        fourth_metadata.guardian_session_kind,
         Some(codex_analytics::GuardianReviewSessionKind::TrunkReused)
     ));
     ThreadId::from_string(
@@ -2230,26 +2298,49 @@ async fn guardian_reuses_prompt_cache_key_and_appends_prior_reviews() -> anyhow:
     .expect("third guardian thread id should be a valid UUID");
     assert_eq!(first_metadata.had_prior_review_context, Some(false));
     assert_eq!(second_metadata.had_prior_review_context, Some(true));
-    assert_eq!(third_metadata.had_prior_review_context, Some(true));
+    assert_eq!(third_metadata.had_prior_review_context, Some(false));
+    assert_eq!(fourth_metadata.had_prior_review_context, Some(true));
     assert_eq!(
         first_metadata.guardian_thread_id,
         second_metadata.guardian_thread_id
     );
-    assert_eq!(
+    assert_ne!(
         second_metadata.guardian_thread_id,
         third_metadata.guardian_thread_id
     );
+    assert_eq!(
+        third_metadata.guardian_thread_id,
+        fourth_metadata.guardian_thread_id
+    );
 
     let requests = request_log.requests();
-    assert_eq!(requests.len(), 3);
+    assert_eq!(requests.len(), 4);
 
     let first_body = requests[0].body_json();
     let second_body = requests[1].body_json();
     let third_body = requests[2].body_json();
+    let fourth_body = requests[3].body_json();
+    let third_input = third_body["input"]
+        .as_array()
+        .expect("guardian review should include input items");
+    assert!(third_input.iter().any(|item| {
+        item["type"] == "compaction"
+            && item["id"] == "cmp_guardian_parent_summary"
+            && item["encrypted_content"] == "encrypted guardian parent summary"
+    }));
     assert_eq!(
         first_body["prompt_cache_key"],
         second_body["prompt_cache_key"]
     );
+    assert_eq!(
+        second_body["prompt_cache_key"],
+        third_body["prompt_cache_key"]
+    );
+    assert_eq!(
+        third_body["prompt_cache_key"],
+        fourth_body["prompt_cache_key"]
+    );
+    assert!(fourth_body.to_string().contains("third guardian rationale"));
     assert!(
         second_body.to_string().contains(concat!(
             "Use prior reviews as context, not binding precedent. ",
@@ -2269,25 +2360,17 @@ async fn guardian_reuses_prompt_cache_key_and_appends_prior_reviews() -> anyhow:
             .to_string()
             .matches("Use prior reviews as context, not binding precedent.")
             .count(),
-        1,
-        "later follow-up guardian requests should not append the reminder again"
-    );
-    let committed_rollout_items = session
-        .guardian_review_session
-        .committed_fork_rollout_items_for_test()
-        .await
-        .expect("committed guardian fork snapshot");
-    assert_eq!(
-        committed_rollout_items
-            .iter()
-            .filter(|item| rollout_item_contains_message_text(
-                item,
-                "Use prior reviews as context, not binding precedent."
-            ))
-            .count(),
-        1,
-        "follow-up reminder should be persisted for guardian forks"
+        0,
+        "a fresh guardian session should not inherit the follow-up reminder"
     );
+    let third_user_message = requests[2]
+        .message_input_text_groups("user")
+        .last()
+        .expect("fresh guardian user message")
+        .join("");
+    assert!(third_user_message.contains(">>> TRANSCRIPT START\n"));
+    assert!(third_user_message.contains("Please push the third docs fix too."));
+    assert!(!third_body.to_string().contains(first_rationale));
     let second_user_message = requests[1]
         .message_input_text_groups("user")
         .last()

codex-rs/features/src/lib.rs

@@ -247,6 +247,8 @@ pub enum Feature {
     DefaultModeRequestUserInput,
     /// Enable automatic review for approval prompts.
     GuardianApproval,
+    /// Reuse encrypted parent compaction when restarting Guardian review sessions.
+    GuardianReuseParentCompaction,
     /// Enable Guardian V2 automatic approval reviews.
     GuardianV2,
     /// Enable persisted thread goals and automatic goal continuation.
@@ -1365,6 +1367,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::Stable,
         default_enabled: true,
     },
+    FeatureSpec {
+        id: Feature::GuardianReuseParentCompaction,
+        key: "guardian_reuse_parent_compaction",
+        stage: Stage::UnderDevelopment,
+        default_enabled: false,
+    },
     FeatureSpec {
         id: Feature::GuardianV2,
         key: "guardianv2",