Consume ai-title from external sessions and add end marker (#20261)

## Summary
- Support Claude Code `ai-title` / `aiTitle` records when detecting and
importing external agent sessions.
- Preserve existing `custom-title` / `customTitle` precedence; only fall
back to `aiTitle` when no custom title is present.
- Add coverage for both detection and import title selection, including
the custom-title-over-ai-title case.

## Testing
- `cargo test -p codex-external-agent-sessions`
- `just fix -p codex-external-agent-sessions`

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

@@ -313,7 +313,17 @@ async fn external_agent_config_import_creates_session_rollouts() -> Result<()> {
     .await??;
     let response: ThreadReadResponse = to_response(response)?;
     assert_eq!(response.thread.turns.len(), 1);
-    assert_eq!(response.thread.turns[0].items.len(), 2);
+    let items = &response.thread.turns[0].items;
+    assert_eq!(items.len(), 3);
+    assert_eq!(
+        items.last(),
+        Some(&ThreadItem::AgentMessage {
+            id: "item-3".into(),
+            text: "<EXTERNAL SESSION IMPORTED>".into(),
+            phase: None,
+            memory_citation: None,
+        })
+    );
 
     let request_id = mcp
         .send_thread_resume_request(ThreadResumeParams {

codex-rs/external-agent-sessions/src/detect.rs

@@ -151,6 +151,61 @@ mod tests {
         );
     }
 
+    #[test]
+    fn detects_ai_title_over_first_user_message() {
+        let root = TempDir::new().expect("tempdir");
+        let external_agent_home = root.path().join(".external");
+        let project_root = root.path().join("repo");
+        let session_path = write_session(
+            &external_agent_home,
+            &project_root,
+            "session.jsonl",
+            &[
+                record("user", "hello there", project_root.as_path()),
+                ai_title_record("generated by source app"),
+            ],
+        );
+
+        let sessions = detect_recent_sessions(&external_agent_home, root.path()).expect("detect");
+
+        assert_eq!(
+            sessions,
+            vec![ExternalAgentSessionMigration {
+                path: session_path,
+                cwd: project_root,
+                title: Some("generated by source app".to_string()),
+            }]
+        );
+    }
+
+    #[test]
+    fn prefers_custom_title_over_later_ai_title() {
+        let root = TempDir::new().expect("tempdir");
+        let external_agent_home = root.path().join(".external");
+        let project_root = root.path().join("repo");
+        let session_path = write_session(
+            &external_agent_home,
+            &project_root,
+            "session.jsonl",
+            &[
+                record("user", "hello there", project_root.as_path()),
+                custom_title_record("custom title"),
+                ai_title_record("generated title"),
+            ],
+        );
+
+        let sessions = detect_recent_sessions(&external_agent_home, root.path()).expect("detect");
+
+        assert_eq!(
+            sessions,
+            vec![ExternalAgentSessionMigration {
+                path: session_path,
+                cwd: project_root,
+                title: Some("custom title".to_string()),
+            }]
+        );
+    }
+
     #[test]
     fn ignores_old_sessions() {
         let root = TempDir::new().expect("tempdir");
@@ -266,6 +321,13 @@ mod tests {
         })
     }
 
+    fn ai_title_record(title: &str) -> JsonValue {
+        serde_json::json!({
+            "type": "ai-title",
+            "aiTitle": title,
+        })
+    }
+
     fn jsonl(records: &[JsonValue]) -> String {
         records
             .iter()

codex-rs/external-agent-sessions/src/export.rs

@@ -2,9 +2,9 @@ use crate::ConversationMessage;
 use crate::ImportedExternalAgentSession;
 use crate::MessageRole;
 use crate::records::conversation_messages;
-use crate::records::custom_title_from_records;
 use crate::records::project_root_from_records;
 use crate::records::read_records;
+use crate::records::source_title_from_records;
 use crate::summarize_for_label;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::ResponseItem;
@@ -21,6 +21,8 @@ use codex_utils_output_truncation::approx_tokens_from_byte_count_i64;
 use std::io;
 use std::path::Path;
 
+const EXTERNAL_SESSION_IMPORTED_MARKER: &str = "<EXTERNAL SESSION IMPORTED>";
+
 pub fn load_session_for_import(path: &Path) -> io::Result<Option<ImportedExternalAgentSession>> {
     let records = read_records(path)?;
     let Some(cwd) = project_root_from_records(&records) else {
@@ -31,7 +33,7 @@ pub fn load_session_for_import(path: &Path) -> io::Result<Option<ImportedExterna
     if rollout_items.is_empty() {
         return Ok(None);
     }
-    let title = custom_title_from_records(&records).or_else(|| {
+    let title = source_title_from_records(&records).or_else(|| {
         messages
             .iter()
             .find(|message| message.role == MessageRole::User)
@@ -103,6 +105,7 @@ fn rollout_items_from_messages(messages: &[ConversationMessage]) -> Vec<RolloutI
     }
 
     if let Some((turn_id, last_agent_message)) = current_turn {
+        items.push(external_session_imported_marker_item());
         items.push(token_count_item(&response_items));
         let completed_at = messages.last().and_then(|message| message.timestamp);
         items.push(turn_complete_item(
@@ -115,6 +118,14 @@ fn rollout_items_from_messages(messages: &[ConversationMessage]) -> Vec<RolloutI
     items
 }
 
+fn external_session_imported_marker_item() -> RolloutItem {
+    RolloutItem::EventMsg(EventMsg::AgentMessage(AgentMessageEvent {
+        message: EXTERNAL_SESSION_IMPORTED_MARKER.to_string(),
+        phase: None,
+        memory_citation: None,
+    }))
+}
+
 fn response_item(message: &ConversationMessage) -> ResponseItem {
     let content = match message.role {
         MessageRole::Assistant => ContentItem::OutputText {
@@ -185,6 +196,7 @@ fn turn_complete_item(
 #[cfg(test)]
 mod tests {
     use super::*;
+    use codex_app_server_protocol::ThreadItem;
     use codex_app_server_protocol::build_turns_from_rollout_items;
     use serde_json::Value as JsonValue;
     use std::path::Path;
@@ -213,7 +225,60 @@ mod tests {
 
         assert_eq!(turns.len(), 2);
         assert_eq!(turns[0].items.len(), 2);
-        assert_eq!(turns[1].items.len(), 1);
+        assert_eq!(turns[1].items.len(), 2);
+        assert_eq!(
+            turns[1].items[1],
+            ThreadItem::AgentMessage {
+                id: "item-4".into(),
+                text: EXTERNAL_SESSION_IMPORTED_MARKER.into(),
+                phase: None,
+                memory_citation: None,
+            }
+        );
+    }
+
+    #[test]
+    fn adds_import_marker_without_replacing_last_agent_message() {
+        let root = TempDir::new().expect("tempdir");
+        let project_root = root.path().join("repo");
+        std::fs::create_dir_all(&project_root).expect("project root");
+        let path = root.path().join("session.jsonl");
+        std::fs::write(
+            &path,
+            jsonl(&[
+                record("user", "first request", &project_root),
+                record("assistant", "first answer", &project_root),
+            ]),
+        )
+        .expect("session");
+
+        let imported = load_session_for_import(&path)
+            .expect("load")
+            .expect("session");
+        let turns = build_turns_from_rollout_items(&imported.rollout_items);
+
+        assert_eq!(turns.len(), 1);
+        assert_eq!(
+            turns[0].items.last(),
+            Some(&ThreadItem::AgentMessage {
+                id: "item-3".into(),
+                text: EXTERNAL_SESSION_IMPORTED_MARKER.into(),
+                phase: None,
+                memory_citation: None,
+            })
+        );
+        let last_turn_complete = imported
+            .rollout_items
+            .iter()
+            .rev()
+            .find_map(|item| match item {
+                RolloutItem::EventMsg(EventMsg::TurnComplete(event)) => Some(event),
+                _ => None,
+            });
+        assert_eq!(
+            last_turn_complete.and_then(|event| event.last_agent_message.as_deref()),
+            Some("first answer")
+        );
     }
 
     #[test]
@@ -238,6 +303,51 @@ mod tests {
         assert_eq!(imported.title.as_deref(), Some("named by source app"));
     }
 
+    #[test]
+    fn loads_ai_title_for_imported_session() {
+        let root = TempDir::new().expect("tempdir");
+        let project_root = root.path().join("repo");
+        std::fs::create_dir_all(&project_root).expect("project root");
+        let path = root.path().join("session.jsonl");
+        std::fs::write(
+            &path,
+            jsonl(&[
+                record("user", "first request", &project_root),
+                ai_title_record("generated by source app"),
+            ]),
+        )
+        .expect("session");
+
+        let imported = load_session_for_import(&path)
+            .expect("load")
+            .expect("session");
+
+        assert_eq!(imported.title.as_deref(), Some("generated by source app"));
+    }
+
+    #[test]
+    fn loads_custom_title_over_later_ai_title_for_imported_session() {
+        let root = TempDir::new().expect("tempdir");
+        let project_root = root.path().join("repo");
+        std::fs::create_dir_all(&project_root).expect("project root");
+        let path = root.path().join("session.jsonl");
+        std::fs::write(
+            &path,
+            jsonl(&[
+                record("user", "first request", &project_root),
+                custom_title_record("named by source app"),
+                ai_title_record("generated by source app"),
+            ]),
+        )
+        .expect("session");
+
+        let imported = load_session_for_import(&path)
+            .expect("load")
+            .expect("session");
+
+        assert_eq!(imported.title.as_deref(), Some("named by source app"));
+    }
+
     #[test]
     fn emits_token_usage_for_imported_history() {
         let root = TempDir::new().expect("tempdir");
@@ -287,6 +397,13 @@ mod tests {
         })
     }
 
+    fn ai_title_record(title: &str) -> JsonValue {
+        serde_json::json!({
+            "type": "ai-title",
+            "aiTitle": title,
+        })
+    }
+
     fn jsonl(records: &[JsonValue]) -> String {
         records
             .iter()

codex-rs/external-agent-sessions/src/records.rs

@@ -24,6 +24,7 @@ pub fn summarize_session(path: &Path) -> io::Result<Option<SessionSummary>> {
     let reader = BufReader::new(file);
     let mut cwd = None;
     let mut custom_title = None;
+    let mut ai_title = None;
     let mut title = None;
     let mut latest_timestamp = None;
     let mut saw_message = false;
@@ -46,6 +47,9 @@ pub fn summarize_session(path: &Path) -> io::Result<Option<SessionSummary>> {
         if let Some(title) = custom_title_from_record(&record) {
             custom_title = Some(title.to_string());
         }
+        if let Some(title) = ai_title_from_record(&record) {
+            ai_title = Some(title.to_string());
+        }
         let Some(message) = conversation_message_from_record(&record) else {
             continue;
         };
@@ -73,17 +77,14 @@ pub fn summarize_session(path: &Path) -> io::Result<Option<SessionSummary>> {
         migration: ExternalAgentSessionMigration {
             path: path.to_path_buf(),
             cwd,
-            title: custom_title.or(title),
+            title: custom_title.or(ai_title).or(title),
         },
     }))
 }
 
-pub(super) fn custom_title_from_records(records: &[JsonValue]) -> Option<String> {
-    records
-        .iter()
-        .filter_map(custom_title_from_record)
-        .next_back()
-        .map(ToOwned::to_owned)
+pub(super) fn source_title_from_records(records: &[JsonValue]) -> Option<String> {
+    latest_title_from_records(records, custom_title_from_record)
+        .or_else(|| latest_title_from_records(records, ai_title_from_record))
 }
 
 pub(super) fn read_records(path: &Path) -> io::Result<Vec<JsonValue>> {
@@ -120,9 +121,28 @@ pub(super) fn conversation_messages(records: &[JsonValue]) -> Vec<ConversationMe
         .collect()
 }
 
+fn latest_title_from_records<'a>(
+    records: &'a [JsonValue],
+    title_from_record: impl Fn(&'a JsonValue) -> Option<&'a str>,
+) -> Option<String> {
+    records
+        .iter()
+        .filter_map(title_from_record)
+        .next_back()
+        .map(ToOwned::to_owned)
+}
+
 fn custom_title_from_record(record: &JsonValue) -> Option<&str> {
-    (record.get("type").and_then(JsonValue::as_str) == Some("custom-title"))
-        .then(|| record.get("customTitle").and_then(JsonValue::as_str))
+    title_from_record(record, "custom-title", "customTitle")
+}
+
+fn ai_title_from_record(record: &JsonValue) -> Option<&str> {
+    title_from_record(record, "ai-title", "aiTitle")
+}
+
+fn title_from_record<'a>(record: &'a JsonValue, record_type: &str, field: &str) -> Option<&'a str> {
+    (record.get("type").and_then(JsonValue::as_str) == Some(record_type))
+        .then(|| record.get(field).and_then(JsonValue::as_str))
         .flatten()
         .map(str::trim)
         .filter(|title| !title.is_empty())