Bound Guardian v2 parent compaction context (#38980)

## What changed

- Add `max_parent_compaction_tokens`, defaulting to 25,000 tokens, to the Guardian v2 feature configuration.
- Reuse the latest encrypted parent compaction only when its complete serialized item fits within the configured limit.
- Fail closed with the maximum action-risk score when the latest encrypted compaction is oversized, instead of sampling with older context.

## Testing

- Cover exact-boundary and oversized compaction items, including oversized passthrough metadata.
- Verify that an oversized latest compaction bypasses sampling and prevents approval.

GitOrigin-RevId: 0b308e7bec0f41d46433dfdf656948cee5cba667

codex-rs/ext/guardian-v2/src/config.rs

@@ -13,6 +13,7 @@ use crate::transcript::TranscriptSource;
 use crate::transcript::truncate_entry;
 
 pub(crate) const DEFAULT_MODEL_CONTEXT_ITEM_TOKENS: usize = 10_000;
+pub(crate) const DEFAULT_PARENT_COMPACTION_TOKENS: usize = 25_000;
 const MIN_MODEL_CONTEXT_ITEM_TOKENS: usize = 100;
 const MAX_MODEL_CONTEXT_ITEM_TOKENS: usize = 100_000;
 const DEFAULT_REVIEW_THRESHOLD: f64 = 0.8;
@@ -28,6 +29,7 @@ pub(crate) struct GuardianV2Config {
     pub(crate) reasoning_effort: ReasoningEffort,
     pub(crate) max_action_tokens: usize,
     pub(crate) max_classifier_instruction_tokens: usize,
+    pub(crate) max_parent_compaction_tokens: usize,
     pub(crate) transcript: TranscriptConfig,
 }
 
@@ -68,6 +70,11 @@ impl GuardianV2Config {
             DEFAULT_MODEL_CONTEXT_ITEM_TOKENS,
             "max_classifier_instruction_tokens",
         )?;
+        let max_parent_compaction_tokens = bounded_tokens(
+            configured.max_parent_compaction_tokens,
+            DEFAULT_PARENT_COMPACTION_TOKENS,
+            "max_parent_compaction_tokens",
+        )?;
         let transcript_config = configured.transcript.as_ref();
         let max_message_entry_tokens = bounded_tokens(
             transcript_config.and_then(|transcript| transcript.max_message_entry_tokens),
@@ -130,6 +137,7 @@ impl GuardianV2Config {
             reasoning_effort: configured.reasoning_effort.unwrap_or(ReasoningEffort::Low),
             max_action_tokens,
             max_classifier_instruction_tokens,
+            max_parent_compaction_tokens,
             transcript: TranscriptConfig {
                 sources: transcript_config
                     .and_then(|transcript| transcript.sources.clone())

codex-rs/ext/guardian-v2/src/extension.rs

@@ -1,3 +1,4 @@
+use std::collections::BTreeMap;
 use std::sync::Arc;
 use std::sync::Weak;
 use std::time::SystemTime;
@@ -288,6 +289,46 @@ impl ToolLifecycleContributor for GuardianV2Extension {
             return Box::pin(std::future::ready(()));
         };
         let sampled_at = SystemTime::now();
+        let latest_parent_compaction = input
+            .conversation_history
+            .items()
+            .filter(|item| {
+                matches!(
+                    item,
+                    ResponseItem::Compaction { .. } | ResponseItem::ContextCompaction { .. }
+                )
+            })
+            .last();
+        let parent_compaction = latest_parent_compaction.and_then(|item| {
+            encrypted_parent_compaction(
+                std::iter::once(item),
+                guardian_config.max_parent_compaction_tokens,
+            )
+        });
+        if parent_compaction.is_none()
+            && latest_parent_compaction.is_some_and(|item| match item {
+                ResponseItem::Compaction {
+                    id: Some(_),
+                    encrypted_content,
+                    ..
+                }
+                | ResponseItem::ContextCompaction {
+                    id: Some(_),
+                    encrypted_content: Some(encrypted_content),
+                    ..
+                } => !encrypted_content.is_empty(),
+                _ => false,
+            })
+        {
+            let score = SecurityRiskScore {
+                scores: BTreeMap::from([("action_risk".to_owned(), 1.0)]),
+                sampled_at: Some(sampled_at.into()),
+            };
+            input.thread_store.insert_if(score.clone(), |previous| {
+                previous.is_none_or(|previous| previous.sampled_at <= score.sampled_at)
+            });
+            return Box::pin(std::future::ready(()));
+        }
         let event_sink = Arc::clone(&self.event_sink);
         let thread_manager = self.thread_manager.clone();
         let thread_id = input.thread_store.level_id().to_owned();
@@ -306,7 +347,6 @@ impl ToolLifecycleContributor for GuardianV2Extension {
         let conversation_history = Arc::clone(&input.conversation_history);
 
         tokio::spawn(async move {
-            let parent_compaction = encrypted_parent_compaction(conversation_history.items());
             let transcript = guardian_config
                 .transcript
                 .build(conversation_history.items());
@@ -460,7 +500,9 @@ impl ToolLifecycleContributor for GuardianV2Extension {
 
 fn encrypted_parent_compaction<'a>(
     items: impl Iterator<Item = &'a ResponseItem>,
+    max_parent_compaction_tokens: usize,
 ) -> Option<ResponseItem> {
+    let max_compaction_bytes = TruncationPolicy::Tokens(max_parent_compaction_tokens).byte_budget();
     let item = items
         .filter(|item| {
             matches!(
@@ -475,12 +517,17 @@ fn encrypted_parent_compaction<'a>(
             id: Some(_),
             encrypted_content,
             ..
-        } if !encrypted_content.is_empty() => Some(item.clone()),
-        ResponseItem::ContextCompaction {
+        }
+        | ResponseItem::ContextCompaction {
             id: Some(_),
             encrypted_content: Some(encrypted_content),
             ..
-        } if !encrypted_content.is_empty() => Some(item.clone()),
+        } if !encrypted_content.is_empty()
+            && serde_json::to_vec(item)
+                .is_ok_and(|serialized| serialized.len() <= max_compaction_bytes) =>
+        {
+            Some(item.clone())
+        }
         _ => None,
     }
 }

codex-rs/ext/guardian-v2/src/extension_tests.rs

@@ -22,6 +22,7 @@ use codex_model_provider_info::ModelProviderInfo;
 use codex_protocol::ResponseItemId;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::FunctionCallOutputPayload;
+use codex_protocol::models::InternalChatMessageMetadataPassthrough;
 use codex_protocol::models::ReasoningItemReasoningSummary;
 use codex_protocol::protocol::ReviewDecision;
 use codex_protocol::protocol::SessionSource;
@@ -38,6 +39,7 @@ use serde_json::json;
 
 use super::encrypted_parent_compaction;
 use crate::config::DEFAULT_MODEL_CONTEXT_ITEM_TOKENS;
+use crate::config::DEFAULT_PARENT_COMPACTION_TOKENS;
 use crate::sampler::MODEL;
 
 const TEST_GUARDIAN_POLICY: &str =
@@ -67,11 +69,17 @@ fn encrypted_parent_compaction_preserves_the_latest_valid_item() {
     };
 
     assert_eq!(
-        encrypted_parent_compaction([&older, &latest].into_iter()),
+        encrypted_parent_compaction(
+            [&older, &latest].into_iter(),
+            DEFAULT_PARENT_COMPACTION_TOKENS,
+        ),
         Some(latest.clone())
     );
     assert_eq!(
-        encrypted_parent_compaction([&latest, &older].into_iter()),
+        encrypted_parent_compaction(
+            [&latest, &older].into_iter(),
+            DEFAULT_PARENT_COMPACTION_TOKENS,
+        ),
         Some(older)
     );
 }
@@ -113,13 +121,100 @@ fn encrypted_parent_compaction_rejects_invalid_latest_item() {
 
     for latest in &invalid {
         assert_eq!(
-            encrypted_parent_compaction([&older, latest].into_iter()),
+            encrypted_parent_compaction(
+                [&older, latest].into_iter(),
+                DEFAULT_PARENT_COMPACTION_TOKENS,
+            ),
             None,
             "an unusable latest summary must not resurrect older context"
         );
     }
 }
 
+#[test]
+fn encrypted_parent_compaction_rejects_oversized_latest_item() -> Result<()> {
+    let max_compaction_bytes =
+        TruncationPolicy::Tokens(DEFAULT_PARENT_COMPACTION_TOKENS).byte_budget();
+    let mut bounded = [
+        ResponseItem::Compaction {
+            id: Some(ResponseItemId::from_server("cmp_bounded".to_owned())),
+            encrypted_content: String::new(),
+            internal_chat_message_metadata_passthrough: None,
+        },
+        ResponseItem::ContextCompaction {
+            id: Some(ResponseItemId::from_server("ctx_bounded".to_owned())),
+            encrypted_content: Some(String::new()),
+            internal_chat_message_metadata_passthrough: None,
+        },
+    ];
+
+    for item in &mut bounded {
+        let envelope_bytes = serde_json::to_vec(&*item)?.len();
+        let encrypted_content = match item {
+            ResponseItem::Compaction {
+                encrypted_content, ..
+            }
+            | ResponseItem::ContextCompaction {
+                encrypted_content: Some(encrypted_content),
+                ..
+            } => encrypted_content,
+            _ => unreachable!("test fixtures are encrypted compaction items"),
+        };
+        *encrypted_content = "a".repeat(max_compaction_bytes - envelope_bytes);
+        assert_eq!(serde_json::to_vec(&*item)?.len(), max_compaction_bytes);
+        assert_eq!(
+            encrypted_parent_compaction(std::iter::once(&*item), DEFAULT_PARENT_COMPACTION_TOKENS,),
+            Some(item.clone())
+        );
+
+        let mut oversized = item.clone();
+        match &mut oversized {
+            ResponseItem::Compaction {
+                encrypted_content, ..
+            }
+            | ResponseItem::ContextCompaction {
+                encrypted_content: Some(encrypted_content),
+                ..
+            } => encrypted_content.push('a'),
+            _ => unreachable!("test fixtures are encrypted compaction items"),
+        }
+        assert_eq!(
+            serde_json::to_vec(&oversized)?.len(),
+            max_compaction_bytes + 1
+        );
+        assert_eq!(
+            encrypted_parent_compaction(
+                [&*item, &oversized].into_iter(),
+                DEFAULT_PARENT_COMPACTION_TOKENS,
+            ),
+            None,
+            "an oversized latest summary must not resurrect older context"
+        );
+    }
+
+    let oversized_metadata = ResponseItem::ContextCompaction {
+        id: Some(ResponseItemId::from_server(
+            "ctx_oversized_metadata".to_owned(),
+        )),
+        encrypted_content: Some("bounded encrypted summary".to_owned()),
+        internal_chat_message_metadata_passthrough: Some(InternalChatMessageMetadataPassthrough {
+            turn_id: Some("a".repeat(max_compaction_bytes)),
+            ..Default::default()
+        }),
+    };
+    assert!(serde_json::to_vec(&oversized_metadata)?.len() > max_compaction_bytes);
+    assert_eq!(
+        encrypted_parent_compaction(
+            [&bounded[0], &oversized_metadata].into_iter(),
+            DEFAULT_PARENT_COMPACTION_TOKENS,
+        ),
+        None,
+        "oversized passthrough metadata must not bypass the complete-item limit"
+    );
+
+    Ok(())
+}
+
 async fn sample_conversation_history(
     conversation_history: Vec<ResponseItem>,
     arguments: &str,
@@ -241,6 +336,7 @@ review_threshold = 0.60
 reasoning_effort = "minimal"
 max_action_tokens = 128
 max_classifier_instruction_tokens = 100000
+max_parent_compaction_tokens = 256
 
 [features.guardianv2.transcript]
 sources = ["tool_outputs", "reasoning"]
@@ -688,7 +784,16 @@ async fn contributor_reuses_the_latest_compatible_parent_compaction() -> Result<
     skip_if_no_network!(Ok(()));
 
     let thread_server = responses::start_mock_server().await;
-    let test = test_codex().build_with_auto_env(&thread_server).await?;
+    let test = test_codex()
+        .with_pre_build_hook(|home| {
+            std::fs::write(
+                home.join("config.toml"),
+                "[features.guardianv2]\nenabled = true\nmax_parent_compaction_tokens = 256\n",
+            )
+            .expect("Guardian v2 parent compaction configuration should be written");
+        })
+        .build_with_auto_env(&thread_server)
+        .await?;
     let events = vec![
         ev_assistant_message("sample", r#"{"scores":{"action_risk":0.25}}"#),
         ev_completed("response-1"),
@@ -792,10 +897,71 @@ async fn contributor_reuses_the_latest_compatible_parent_compaction() -> Result<
     );
     assert_eq!(
         request["input"][2],
-        serde_json::to_value(latest_compaction)?
+        serde_json::to_value(&latest_compaction)?
     );
     assert_eq!(request["input"][3]["role"], "user");
 
+    let previous_score = tokio::time::timeout(Duration::from_secs(5), async {
+        loop {
+            if let Some(score) = thread_store.get::<SecurityRiskScore>() {
+                return score;
+            }
+            tokio::task::yield_now().await;
+        }
+    })
+    .await?;
+    assert_eq!(previous_score.scores.get("action_risk"), Some(&0.25));
+    assert_eq!(
+        registry
+            .approval_review(&session_store, thread_store, "review action")
+            .await,
+        Some(ReviewDecision::Approved)
+    );
+
+    let oversized_compaction = ResponseItem::Compaction {
+        id: Some(ResponseItemId::from_server("cmp_oversized".to_owned())),
+        encrypted_content: "a".repeat(TruncationPolicy::Tokens(/*limit*/ 256).byte_budget()),
+        internal_chat_message_metadata_passthrough: None,
+    };
+    registry.tool_lifecycle_contributors()[0]
+        .on_tool_start(ToolStartInput {
+            session_store: &session_store,
+            thread_store,
+            turn_store: &turn_store,
+            turn_id: "turn-1",
+            call_id: "call-2",
+            tool_name: &tool_name,
+            payload: &tool_payload,
+            conversation_history: Arc::new(TestConversationHistory(vec![
+                latest_compaction,
+                oversized_compaction,
+            ])),
+            source: ToolCallSource::Direct,
+        })
+        .await;
+
+    let fail_closed_score = thread_store
+        .get::<SecurityRiskScore>()
+        .expect("an oversized compaction should immediately receive the maximum risk score");
+    assert_eq!(
+        fail_closed_score.as_ref(),
+        &SecurityRiskScore {
+            scores: BTreeMap::from([("action_risk".to_owned(), 1.0)]),
+            sampled_at: fail_closed_score.sampled_at,
+        }
+    );
+    assert_eq!(
+        registry
+            .approval_review(&session_store, thread_store, "review action")
+            .await,
+        None
+    );
+    assert_eq!(
+        server.connections().iter().map(Vec::len).sum::<usize>(),
+        1,
+        "an oversized latest compaction must bypass Luna rather than reuse stale context"
+    );
+
     Ok(())
 }