Reinject context for summary-only mid-turn compaction

codex-rs/core/src/compact.rs

@@ -300,7 +300,7 @@ async fn run_compact_task_inner(
             // These callsites do not get a later post-compaction canonical-context write in
             // `run_turn`, so replacement history must carry canonical context directly.
             let initial_context = sess.build_initial_context(turn_context.as_ref()).await;
-            insert_initial_context_before_last_real_user(&mut new_history, initial_context);
+            insert_initial_context_before_last_user_anchor(&mut new_history, initial_context);
         }
         CompactCallsite::ManualCompact => {
             // Manual `/compact` intentionally rewrites transcript history without reseeding turn
@@ -389,15 +389,27 @@ pub(crate) fn process_compacted_history(
     compacted_history
 }
 
-pub(crate) fn insert_initial_context_before_last_real_user(
+pub(crate) fn insert_initial_context_before_last_user_anchor(
     compacted_history: &mut Vec<ResponseItem>,
     initial_context: Vec<ResponseItem>,
 ) {
     if initial_context.is_empty() {
         return;
     }
-    if let Some(last_real_user_index) = compacted_history.iter().rposition(is_real_user_message) {
-        compacted_history.splice(last_real_user_index..last_real_user_index, initial_context);
+    let insertion_index = compacted_history
+        .iter()
+        .rposition(is_real_user_message)
+        .or_else(|| {
+            compacted_history.iter().rposition(|item| {
+                matches!(
+                    crate::event_mapping::parse_turn_item(item),
+                    Some(TurnItem::UserMessage(user_message))
+                        if is_summary_message(&user_message.message())
+                )
+            })
+        });
+    if let Some(index) = insertion_index {
+        compacted_history.splice(index..index, initial_context);
     }
 }
 
@@ -1268,4 +1280,70 @@ keep me updated
         }];
         assert_eq!(refreshed, expected);
     }
+
+    #[test]
+    fn insert_initial_context_before_last_user_anchor_falls_back_to_last_summary() {
+        let mut compacted_history = vec![
+            ResponseItem::Message {
+                id: None,
+                role: "user".to_string(),
+                content: vec![ContentItem::InputText {
+                    text: format!("{SUMMARY_PREFIX}\nolder summary"),
+                }],
+                end_turn: None,
+                phase: None,
+            },
+            ResponseItem::Message {
+                id: None,
+                role: "user".to_string(),
+                content: vec![ContentItem::InputText {
+                    text: format!("{SUMMARY_PREFIX}\nlatest summary"),
+                }],
+                end_turn: None,
+                phase: None,
+            },
+        ];
+        let initial_context = vec![ResponseItem::Message {
+            id: None,
+            role: "developer".to_string(),
+            content: vec![ContentItem::InputText {
+                text: "fresh permissions".to_string(),
+            }],
+            end_turn: None,
+            phase: None,
+        }];
+
+        insert_initial_context_before_last_user_anchor(&mut compacted_history, initial_context);
+
+        let expected = vec![
+            ResponseItem::Message {
+                id: None,
+                role: "user".to_string(),
+                content: vec![ContentItem::InputText {
+                    text: format!("{SUMMARY_PREFIX}\nolder summary"),
+                }],
+                end_turn: None,
+                phase: None,
+            },
+            ResponseItem::Message {
+                id: None,
+                role: "developer".to_string(),
+                content: vec![ContentItem::InputText {
+                    text: "fresh permissions".to_string(),
+                }],
+                end_turn: None,
+                phase: None,
+            },
+            ResponseItem::Message {
+                id: None,
+                role: "user".to_string(),
+                content: vec![ContentItem::InputText {
+                    text: format!("{SUMMARY_PREFIX}\nlatest summary"),
+                }],
+                end_turn: None,
+                phase: None,
+            },
+        ];
+        assert_eq!(compacted_history, expected);
+    }
 }

codex-rs/core/src/compact_remote.rs

@@ -6,7 +6,7 @@ use crate::codex::TurnContext;
 use crate::compact::CompactCallsite;
 use crate::compact::extract_latest_model_switch_update_from_items;
 use crate::compact::extract_trailing_model_switch_update_for_compaction_request;
-use crate::compact::insert_initial_context_before_last_real_user;
+use crate::compact::insert_initial_context_before_last_user_anchor;
 use crate::compact::process_compacted_history;
 use crate::compact::should_keep_compacted_history_item;
 use crate::context_manager::ContextManager;
@@ -162,7 +162,7 @@ async fn run_remote_compact_task_inner_impl(
             // These callsites do not get a later post-compaction canonical-context write in
             // `run_turn`, so replacement history must carry canonical context directly.
             let initial_context = sess.build_initial_context(turn_context.as_ref()).await;
-            insert_initial_context_before_last_real_user(&mut new_history, initial_context);
+            insert_initial_context_before_last_user_anchor(&mut new_history, initial_context);
         }
         CompactCallsite::ManualCompact => {
             // Manual `/compact` intentionally rewrites transcript history without reseeding turn

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

@@ -1790,7 +1790,7 @@ async fn snapshot_request_shape_remote_mid_turn_compaction_summary_only_layout()
     insta::assert_snapshot!(
         "remote_mid_turn_compaction_summary_only_shapes",
         format_labeled_requests_snapshot(
-            "Remote mid-turn compaction where compact output has only summary user content: continuation layout keeps the summary-only compact output without inserting extra context items.",
+            "Remote mid-turn compaction where compact output has only summary user content: continuation layout reinjects canonical context before the latest summary.",
             &[
                 ("Remote Compaction Request", &compact_request),
                 (

codex-rs/core/tests/suite/snapshots/all__suite__compact_remote__remote_mid_turn_compaction_summary_only_shapes.snap

@@ -1,9 +1,8 @@
 ---
 source: core/tests/suite/compact_remote.rs
-assertion_line: 1790
-expression: "format_labeled_requests_snapshot(\"Remote mid-turn compaction where compact output has only summary user content: continuation layout keeps the summary-only compact output without inserting extra context items.\",\n&[(\"Remote Compaction Request\", &compact_request),\n(\"Remote Post-Compaction History Layout\", &post_compact_turn_request),])"
+expression: "format_labeled_requests_snapshot(\"Remote mid-turn compaction where compact output has only summary user content: continuation layout reinjects canonical context before the latest summary.\",\n&[(\"Remote Compaction Request\", &compact_request),\n(\"Remote Post-Compaction History Layout\", &post_compact_turn_request),])"
 ---
-Scenario: Remote mid-turn compaction where compact output has only summary user content: continuation layout keeps the summary-only compact output without inserting extra context items.
+Scenario: Remote mid-turn compaction where compact output has only summary user content: continuation layout reinjects canonical context before the latest summary.
 
 ## Remote Compaction Request
 00:message/developer:<PERMISSIONS_INSTRUCTIONS>
@@ -14,4 +13,7 @@ Scenario: Remote mid-turn compaction where compact output has only summary user
 05:function_call_output:unsupported call: test_tool
 
 ## Remote Post-Compaction History Layout
-00:message/user:<COMPACTION_SUMMARY>\nREMOTE_SUMMARY_ONLY
+00:message/developer:<PERMISSIONS_INSTRUCTIONS>
+01:message/user:<AGENTS_MD>
+02:message/user:<ENVIRONMENT_CONTEXT:cwd=<CWD>>
+03:message/user:<COMPACTION_SUMMARY>\nREMOTE_SUMMARY_ONLY