feat(compaction): surface checkpoint warning

code-rs/core/src/codex/compact.rs

@@ -12,6 +12,7 @@ use crate::error::Result as CodexResult;
 use crate::protocol::AgentMessageEvent;
 use crate::protocol::ErrorEvent;
 use crate::protocol::EventMsg;
+use code_protocol::protocol::CompactionCheckpointWarningEvent;
 use crate::protocol::InputItem;
 use crate::protocol::TaskCompleteEvent;
 use crate::truncate::truncate_middle;
@@ -28,6 +29,7 @@ use base64::Engine;
 use futures::prelude::*;
 
 pub const SUMMARIZATION_PROMPT: &str = include_str!("../../templates/compact/prompt.md");
+pub const COMPACTION_CHECKPOINT_MESSAGE: &str = "History checkpoint: earlier conversation compacted.";
 const COMPACT_USER_MESSAGE_MAX_TOKENS: usize = 20_000;
 const COMPACT_TEXT_CONTENT_MAX_BYTES: usize = 8 * 1024;
 const COMPACT_TOOL_ARGS_MAX_BYTES: usize = 4 * 1024;
@@ -199,6 +201,8 @@ pub(super) async fn perform_compaction(
         state.history.record_items(new_history.iter());
     }
 
+    send_compaction_checkpoint_warning(&sess, &sub_id).await;
+
     let rollout_item = RolloutItem::Compacted(CompactedItem {
         message: summary_text.clone(),
     });
@@ -305,6 +309,8 @@ async fn run_compact_task_inner_inline(
         state.history.record_items(new_history.iter());
     }
 
+    send_compaction_checkpoint_warning(&sess, &sub_id).await;
+
     let rollout_item = RolloutItem::Compacted(CompactedItem {
         message: summary_text.clone(),
     });
@@ -449,6 +455,17 @@ fn sanitize_items_for_compact(items: Vec<ResponseItem>) -> Vec<ResponseItem> {
         .collect()
 }
 
+fn compaction_checkpoint_warning_event() -> EventMsg {
+    EventMsg::CompactionCheckpointWarning(CompactionCheckpointWarningEvent {
+        message: COMPACTION_CHECKPOINT_MESSAGE.to_string(),
+    })
+}
+
+async fn send_compaction_checkpoint_warning(sess: &Arc<Session>, sub_id: &str) {
+    let event = sess.make_event(sub_id, compaction_checkpoint_warning_event());
+    sess.send_event(event).await;
+}
+
 pub(crate) fn collect_user_messages(items: &[ResponseItem]) -> Vec<String> {
     items
         .iter()
@@ -729,4 +746,14 @@ mod tests {
             "bridge should include the provided summary text"
         );
     }
+
+    #[test]
+    fn compaction_checkpoint_warning_event_has_copy() {
+        match compaction_checkpoint_warning_event() {
+            EventMsg::CompactionCheckpointWarning(payload) => {
+                assert!(payload.message.contains("checkpoint"));
+            }
+            other => panic!("unexpected variant: {other:?}"),
+        }
+    }
 }

code-rs/core/src/protocol.rs

@@ -723,6 +723,9 @@ pub enum EventMsg {
     /// Browser snapshot metadata emitted alongside environment context.
     BrowserSnapshot(BrowserSnapshotEvent),
 
+    /// Warning that the platform compacted conversation history to stay within limits.
+    CompactionCheckpointWarning(code_protocol::protocol::CompactionCheckpointWarningEvent),
+
     /// Ack the client's configure message.
     SessionConfigured(SessionConfiguredEvent),
 

code-rs/exec/src/event_processor_with_human_output.rs

@@ -618,6 +618,7 @@ impl EventProcessor for EventProcessorWithHumanOutput {
             EventMsg::UserMessage(_) => {}
             EventMsg::EnteredReviewMode(_) => {}
             EventMsg::ExitedReviewMode(_) => {}
+            EventMsg::CompactionCheckpointWarning(_) => {}
         }
         CodexStatus::Running
     }

code-rs/mcp-server/src/code_tool_runner.rs

@@ -290,6 +290,7 @@ async fn run_code_tool_session_inner(
                     | EventMsg::EnvironmentContextFull(_)
                     | EventMsg::EnvironmentContextDelta(_)
                     | EventMsg::AgentStatusUpdate(_)
+                    | EventMsg::CompactionCheckpointWarning(_)
                     | EventMsg::TurnAborted(_)
                     | EventMsg::ConversationPath(_)
                     | EventMsg::UserMessage(_)

code-rs/protocol/src/protocol.rs

@@ -538,6 +538,9 @@ pub enum EventMsg {
     /// Browser snapshot metadata emitted alongside environment context.
     BrowserSnapshot(BrowserSnapshotEvent),
 
+    /// Warning that the platform compacted conversation history to stay within limits.
+    CompactionCheckpointWarning(CompactionCheckpointWarningEvent),
+
     /// Ack the client's configure message.
     SessionConfigured(SessionConfiguredEvent),
 
@@ -626,6 +629,11 @@ pub struct TaskStartedEvent {
     pub model_context_window: Option<u64>,
 }
 
+#[derive(Debug, Clone, Deserialize, Serialize, TS)]
+pub struct CompactionCheckpointWarningEvent {
+    pub message: String,
+}
+
 #[derive(Debug, Clone, Default, PartialEq, Eq, Deserialize, Serialize, TS)]
 pub struct TokenUsage {
     pub input_tokens: u64,
@@ -1507,4 +1515,23 @@ mod tests {
         assert_eq!(deserialized, event);
         Ok(())
     }
+
+    #[test]
+    fn compaction_checkpoint_warning_round_trips() -> Result<()> {
+        let event = EventMsg::CompactionCheckpointWarning(CompactionCheckpointWarningEvent {
+            message: "History checkpoint: earlier conversation compacted.".to_string(),
+        });
+
+        let serialized = serde_json::to_string(&event)?;
+        let restored: EventMsg = serde_json::from_str(&serialized)?;
+
+        match restored {
+            EventMsg::CompactionCheckpointWarning(payload) => {
+                assert!(payload.message.contains("checkpoint"));
+            }
+            other => panic!("unexpected variant: {other:?}"),
+        }
+
+        Ok(())
+    }
 }

code-rs/tui/src/chatwidget.rs

@@ -161,6 +161,7 @@ use code_core::protocol::PatchApplyEndEvent;
 use code_core::protocol::TaskCompleteEvent;
 use code_core::protocol::TokenUsage;
 use code_core::protocol::TurnDiffEvent;
+use code_core::codex::compact::COMPACTION_CHECKPOINT_MESSAGE;
 use crate::bottom_pane::{
     AutoActiveViewModel,
     AutoCoordinatorButton,
@@ -10385,6 +10386,9 @@ impl ChatWidget<'_> {
             EventMsg::BrowserSnapshot(ev) => {
                 self.handle_browser_snapshot_event(&ev);
             }
+            EventMsg::CompactionCheckpointWarning(event) => {
+                self.history_push_plain_paragraphs(PlainMessageKind::Notice, [event.message]);
+            }
             EventMsg::SessionConfigured(event) => {
                 // Remove stale "Connecting MCP servers…" status from the startup notice
                 // now that MCP initialization has completed in core.
@@ -14995,6 +14999,10 @@ Have we met every part of this goal and is there no further work to do?"#
         self.auto_history.replace_all(conversation.clone());
         self.auto_compaction_overlay =
             self.derive_compaction_overlay(&previous_items, &previous_indices, &conversation);
+        self.history_push_plain_paragraphs(
+            PlainMessageKind::Notice,
+            [COMPACTION_CHECKPOINT_MESSAGE],
+        );
         self.auto_rebuild_live_ring();
         self.request_redraw();
     }

code-rs/tui/tests/snapshots/vt100_chatwidget_snapshot__compaction_checkpoint_warning_notice.snap

@@ -0,0 +1,24 @@
+---
+source: tui/tests/vt100_chatwidget_snapshot.rs
+assertion_line: 2006
+expression: frame
+---
+ +----------------------------------------------------------------------------+
+ |                                    Code                                    |
+ +----------------------------------------------------------------------------+
+
+
+
+ • I can help with various tasks including:
+
+   - Writing code
+   - Reading files
+   - Running commands
+
+
+ ★ History checkpoint: earlier conversation compacted.
+
+ +----------------------------------------------------------------------------+
+ | What can I code for you today?                                             |
+ +----------------------------------------------------------------------------+
+   Read Only  (Shift+Tab change)                       Ctrl+H help  •  API key

code-rs/tui/tests/vt100_chatwidget_snapshot.rs

@@ -32,6 +32,8 @@ use code_tui::test_helpers::{
     AutoContinueModeFixture,
     ChatWidgetHarness,
 };
+use code_core::codex::compact::COMPACTION_CHECKPOINT_MESSAGE;
+use code_protocol::protocol::CompactionCheckpointWarningEvent;
 use crossterm::event::{KeyCode, KeyEvent, KeyEventKind, KeyEventState, KeyModifiers};
 use regex_lite::{Captures, Regex};
 use serde_json::json;
@@ -1986,6 +1988,24 @@ fn settings_help_overlay_from_section() {
     insta::assert_snapshot!("settings_help_overlay_section_closed", section_closed);
 }
 
+#[test]
+fn compaction_checkpoint_warning_notice() {
+    let _guard = ENV_LOCK.lock().unwrap();
+    let mut harness = ChatWidgetHarness::new();
+
+    harness.handle_event(Event {
+        id: "compaction-warning".into(),
+        event_seq: 0,
+        msg: EventMsg::CompactionCheckpointWarning(CompactionCheckpointWarningEvent {
+            message: COMPACTION_CHECKPOINT_MESSAGE.to_string(),
+        }),
+        order: None,
+    });
+
+    let frame = normalize_output(render_chat_widget_to_vt100(&mut harness, 80, 20));
+    insta::assert_snapshot!("compaction_checkpoint_warning_notice", frame);
+}
+
 #[test]
 fn agent_status_missing_batch_displays_error() {
     let mut harness = ChatWidgetHarness::new();