Report completed sub-agent activity on parent turns (#40437)

## Why

A Multi-Agent V2 child can finish after the parent turn that spawned it, so its
successful completion needs to remain associated with that parent turn in
notifications and history.

## What changed

- Add `completed` to `SubAgentActivityKind` and emit the corresponding started
  and completed item events on the spawning parent turn when a child succeeds.
- Persist completed activity as a canonical turn item in both legacy and
  paginated history, and expose it through app-server history and schemas.
- Render completed activity as terminal in the TUI without counting it as a
  separate tool call or tool-runtime event.

## Testing

- Cover successful completion in legacy and paginated history, late updates to
  completed parent turns, TUI rendering, analytics, and rollout tracing.
- Verify that terminal child errors do not emit completed activity.

GitOrigin-RevId: 6c71eb8b10e7327611c6af84f70e294e27d94d02

codex-rs/analytics/src/analytics_client_tests.rs

@@ -5066,6 +5066,12 @@ async fn turn_event_counts_completed_tool_items() {
             agent_thread_id: "thread-child".to_string(),
             agent_path: "/root/child".to_string(),
         },
+        ThreadItem::SubAgentActivity {
+            id: "sub-agent-activity-completed".to_string(),
+            kind: SubAgentActivityKind::Completed,
+            agent_thread_id: "thread-child".to_string(),
+            agent_path: "/root/child".to_string(),
+        },
         ThreadItem::WebSearch(WebSearchItem {
             id: "web-1".to_string(),
             query: "codex".to_string(),

codex-rs/analytics/src/reducer.rs

@@ -143,6 +143,7 @@ use codex_app_server_protocol::RequestPermissionProfile;
 use codex_app_server_protocol::ServerNotification;
 use codex_app_server_protocol::ServerRequest;
 use codex_app_server_protocol::ServerResponse;
+use codex_app_server_protocol::SubAgentActivityKind;
 use codex_app_server_protocol::ThreadItem;
 use codex_app_server_protocol::TurnSteerResponse;
 use codex_app_server_protocol::UserInput;
@@ -476,6 +477,10 @@ impl TurnToolCounts {
             ThreadItem::FileChange { .. } => self.file_change += 1,
             ThreadItem::McpToolCall { .. } => self.mcp_tool_call += 1,
             ThreadItem::DynamicToolCall { .. } => self.dynamic_tool_call += 1,
+            ThreadItem::SubAgentActivity {
+                kind: SubAgentActivityKind::Completed,
+                ..
+            } => return,
             ThreadItem::CollabAgentToolCall { id, .. }
             | ThreadItem::SubAgentActivity { id, .. } => {
                 if !self.subagent_tool_call_ids.insert(id.clone()) {

codex-rs/app-server-protocol/schema/json/ServerNotification.json

@@ -3672,7 +3672,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json

@@ -19366,7 +19366,8 @@
         "enum": [
           "started",
           "interacted",
-          "interrupted"
+          "interrupted",
+          "completed"
         ],
         "type": "string"
       },

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json

@@ -17118,7 +17118,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/json/v2/ItemCompletedNotification.json

@@ -565,7 +565,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/json/v2/ItemStartedNotification.json

@@ -565,7 +565,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/json/v2/ReviewStartResponse.json

@@ -711,7 +711,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/json/v2/ThreadForkResponse.json

@@ -986,7 +986,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/json/v2/ThreadListResponse.json

@@ -777,7 +777,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/json/v2/ThreadMetadataUpdateResponse.json

@@ -777,7 +777,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/json/v2/ThreadReadResponse.json

@@ -777,7 +777,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/json/v2/ThreadResumeResponse.json

@@ -986,7 +986,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/json/v2/ThreadRollbackResponse.json

@@ -777,7 +777,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/json/v2/ThreadStartResponse.json

@@ -986,7 +986,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/json/v2/ThreadStartedNotification.json

@@ -777,7 +777,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/json/v2/ThreadUnarchiveResponse.json

@@ -777,7 +777,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/json/v2/TurnCompletedNotification.json

@@ -711,7 +711,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/json/v2/TurnStartResponse.json

@@ -711,7 +711,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/json/v2/TurnStartedNotification.json

@@ -711,7 +711,8 @@
       "enum": [
         "started",
         "interacted",
-        "interrupted"
+        "interrupted",
+        "completed"
       ],
       "type": "string"
     },

codex-rs/app-server-protocol/schema/typescript/v2/SubAgentActivityKind.ts

@@ -2,4 +2,4 @@
 
 // This file was generated by [ts-rs](https://github.com/Aleph-Alpha/ts-rs). Do not edit this file manually.
 
-export type SubAgentActivityKind = "started" | "interacted" | "interrupted";
+export type SubAgentActivityKind = "started" | "interacted" | "interrupted" | "completed";

codex-rs/app-server-protocol/src/protocol/thread_history.rs

@@ -1631,6 +1631,7 @@ mod tests {
     use codex_protocol::items::EnteredReviewModeItem as CoreEnteredReviewModeItem;
     use codex_protocol::items::ExitedReviewModeItem as CoreExitedReviewModeItem;
     use codex_protocol::items::HookPromptFragment as CoreHookPromptFragment;
+    use codex_protocol::items::SubAgentActivityItem as CoreSubAgentActivityItem;
     use codex_protocol::items::TurnItem as CoreTurnItem;
     use codex_protocol::items::UserMessageItem as CoreUserMessageItem;
     use codex_protocol::items::build_hook_prompt_message;
@@ -1654,6 +1655,7 @@ mod tests {
     use codex_protocol::protocol::McpToolCallEndEvent;
     use codex_protocol::protocol::PatchApplyBeginEvent;
     use codex_protocol::protocol::ReviewTarget;
+    use codex_protocol::protocol::SubAgentActivityKind as CoreSubAgentActivityKind;
     use codex_protocol::protocol::ThreadRolledBackEvent;
     use codex_protocol::protocol::TurnAbortReason;
     use codex_protocol::protocol::TurnAbortedEvent;
@@ -4480,6 +4482,57 @@ mod tests {
         );
     }
 
+    #[test]
+    fn completed_sub_agent_activity_updates_completed_parent_turn() {
+        let child_thread_id = ThreadId::new();
+        let child_path = codex_protocol::AgentPath::root()
+            .join("worker")
+            .expect("worker path");
+        let items = vec![
+            RolloutItem::EventMsg(EventMsg::TurnStarted(TurnStartedEvent {
+                turn_id: "turn-a".into(),
+                trace_id: None,
+                started_at: None,
+                model_context_window: None,
+                collaboration_mode_kind: Default::default(),
+            })),
+            RolloutItem::EventMsg(EventMsg::TurnComplete(TurnCompleteEvent {
+                turn_id: "turn-a".into(),
+                started_at: None,
+                last_agent_message: None,
+                error: None,
+                completed_at: None,
+                duration_ms: None,
+                time_to_first_token_ms: None,
+            })),
+            RolloutItem::EventMsg(EventMsg::ItemCompleted(ItemCompletedEvent {
+                thread_id: ThreadId::new(),
+                turn_id: "turn-a".into(),
+                item: CoreTurnItem::SubAgentActivity(CoreSubAgentActivityItem {
+                    id: "child-turn-completed".into(),
+                    kind: CoreSubAgentActivityKind::Completed,
+                    agent_thread_id: child_thread_id,
+                    agent_path: child_path,
+                }),
+                started_at_ms: None,
+                completed_at_ms: 0,
+            })),
+        ];
+
+        let turns = build_turns_from_rollout_items(&items);
+
+        assert_eq!(turns.len(), 1);
+        assert_eq!(
+            turns[0].items,
+            vec![ThreadItem::SubAgentActivity {
+                id: "child-turn-completed".into(),
+                kind: crate::protocol::v2::SubAgentActivityKind::Completed,
+                agent_thread_id: child_thread_id.to_string(),
+                agent_path: "/root/worker".into(),
+            }]
+        );
+    }
+
     #[test]
     fn ignores_plain_user_response_items_in_rollout_replay() {
         let items = vec![

codex-rs/app-server-protocol/src/protocol/v2/item.rs

@@ -1180,6 +1180,7 @@ pub enum SubAgentActivityKind {
     Started,
     Interacted,
     Interrupted,
+    Completed,
 }
 
 impl From<CoreSubAgentActivityKind> for SubAgentActivityKind {
@@ -1188,6 +1189,7 @@ impl From<CoreSubAgentActivityKind> for SubAgentActivityKind {
             CoreSubAgentActivityKind::Started => SubAgentActivityKind::Started,
             CoreSubAgentActivityKind::Interacted => SubAgentActivityKind::Interacted,
             CoreSubAgentActivityKind::Interrupted => SubAgentActivityKind::Interrupted,
+            CoreSubAgentActivityKind::Completed => SubAgentActivityKind::Completed,
         }
     }
 }

codex-rs/app-server-protocol/src/protocol/v2/tests.rs

@@ -3187,7 +3187,7 @@ fn core_turn_item_into_thread_item_converts_supported_variants() {
 
     let sub_agent_activity_item = TurnItem::SubAgentActivity(SubAgentActivityItem {
         id: "activity-1".to_string(),
-        kind: CoreSubAgentActivityKind::Interrupted,
+        kind: CoreSubAgentActivityKind::Completed,
         agent_thread_id: receiver_thread_id,
         agent_path: codex_protocol::AgentPath::root()
             .join("worker")
@@ -3198,7 +3198,7 @@ fn core_turn_item_into_thread_item_converts_supported_variants() {
         ThreadItem::from(sub_agent_activity_item),
         ThreadItem::SubAgentActivity {
             id: "activity-1".to_string(),
-            kind: SubAgentActivityKind::Interrupted,
+            kind: SubAgentActivityKind::Completed,
             agent_thread_id: receiver_thread_id.to_string(),
             agent_path: "/root/worker".to_string(),
         }

codex-rs/app-server/README.md

@@ -1640,6 +1640,7 @@ The app-server streams JSON-RPC notifications while a turn is running. Each turn
 - `fileChange` — `{id, changes, status}` describing proposed edits; `changes` list `{path, kind, diff}` and `status` is `inProgress`, `completed`, `failed`, or `declined`.
 - `mcpToolCall` — `{id, server, tool, status, arguments, appContext, mcpAppResourceUri?, pluginId, readOnlyHint, result?, error?}` describing MCP calls; `appContext` is `{connectorId, linkId, resourceUri, appName, actionName}` for calls through a trusted MCP app, where `connectorId` identifies the connector that owns the tool, `linkId` identifies the app link, `resourceUri` points to the widget template, `appName` is the connector's display name, and `actionName` is the stable connector `Action.name`. `readOnlyHint` is `true` for read-only tools, `false` for write-capable tools, and `null` when the annotation is unavailable, including older rollout entries. The hint describes tool capability, not whether an invocation succeeded or performed a write; use `status`, `result`, and `error` to determine the execution outcome. `appName` and `actionName` may be null for older rollout entries. The top-level `mcpAppResourceUri` is deprecated and temporarily duplicated for client migration. `tool` identifies the raw MCP tool. `status` is `inProgress`, `completed`, or `failed`.
 - `collabToolCall` — `{id, tool, status, senderThreadId, receiverThreadId?, newThreadId?, prompt?, agentStatus?}` describing collab tool calls (`spawn_agent`, `send_input`, `resume_agent`, `wait`, `close_agent`); `status` is `inProgress`, `completed`, or `failed`.
+- `subAgentActivity` — `{id, kind, agentThreadId, agentPath}` describing Multi-Agent V2 lifecycle activity; `kind` is `started`, `interacted`, `interrupted`, or `completed`. A successful child completion is attributed to the parent turn that spawned it, so its `item/completed` notification may arrive after that turn's `turn/completed` notification and is included with that turn when history is read.
 - `webSearch` — `{id, query, action?, results?}` for a web search request issued by the agent; `action` mirrors the Responses API web_search action payload (`search`, `open_page`, `find_in_page`) and may be omitted until completion. For standalone web search, `results` contains the out-of-band structured result DTOs returned by `/v1/alpha/search`; clients should ignore result types and fields they do not understand.
 - `imageGeneration` — `{id, status, revisedPrompt, result, transparentBackground, savedPath?}` for a generated image. `transparentBackground` is `true` when the Images API reports a transparent background, `false` when it reports an opaque background, and `null` when the background is automatic, unavailable, or the item has not completed. The field is always present on v2 item payloads, including persisted and resumed items.
 - `imageView` — `{id, path}` emitted when the agent invokes the image viewer tool.

codex-rs/core/src/agent/control.rs

@@ -24,6 +24,7 @@ use crate::thread_manager::ThreadIdGenerator;
 use crate::thread_manager::ThreadManagerState;
 use crate::thread_manager::default_thread_id_generator;
 use crate::thread_rollout_truncation::truncate_rollout_to_last_n_fork_turns;
+use crate::turn_timing::now_unix_timestamp_ms;
 use codex_history::InitialHistory;
 use codex_history::ResumedHistory;
 use codex_history::RolloutItem;
@@ -33,11 +34,17 @@ use codex_protocol::ThreadId;
 use codex_protocol::error::CodexErr;
 use codex_protocol::error::CodexErrorDetails;
 use codex_protocol::error::Result as CodexResult;
+use codex_protocol::items::SubAgentActivityItem;
+use codex_protocol::items::TurnItem;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::MessagePhase;
 use codex_protocol::models::ResponseItem;
+use codex_protocol::protocol::Event;
 use codex_protocol::protocol::EventMsg;
+use codex_protocol::protocol::HasLegacyEvent;
 use codex_protocol::protocol::InterAgentCommunication;
+use codex_protocol::protocol::ItemCompletedEvent;
+use codex_protocol::protocol::ItemStartedEvent;
 use codex_protocol::protocol::MultiAgentVersion;
 use codex_protocol::protocol::Op;
 use codex_protocol::protocol::SessionSource;
@@ -233,6 +240,55 @@ impl AgentControl {
         .await
     }
 
+    pub(crate) async fn emit_sub_agent_activity(
+        &self,
+        thread_id: ThreadId,
+        turn_id: String,
+        item: SubAgentActivityItem,
+    ) -> CodexResult<()> {
+        let state = self.upgrade()?;
+        let thread = state.get_thread(thread_id).await?;
+        let started_at_ms = now_unix_timestamp_ms();
+        let item = TurnItem::SubAgentActivity(item);
+        thread
+            .session
+            .send_event_raw(Event {
+                id: turn_id.clone(),
+                msg: EventMsg::ItemStarted(ItemStartedEvent {
+                    thread_id,
+                    turn_id: turn_id.clone(),
+                    item: item.clone(),
+                    started_at_ms,
+                }),
+            })
+            .await;
+        let completed_at_ms = now_unix_timestamp_ms();
+        let completed = ItemCompletedEvent {
+            thread_id,
+            turn_id: turn_id.clone(),
+            item,
+            started_at_ms: Some(started_at_ms),
+            completed_at_ms,
+        };
+        thread
+            .session
+            .send_event_raw(Event {
+                id: turn_id.clone(),
+                msg: EventMsg::ItemCompleted(completed.clone()),
+            })
+            .await;
+        for legacy in completed.as_legacy_events(/*show_raw_agent_reasoning*/ false) {
+            thread
+                .session
+                .send_event_raw(Event {
+                    id: turn_id.clone(),
+                    msg: legacy,
+                })
+                .await;
+        }
+        Ok(())
+    }
+
     async fn send_inter_agent_communication_after_capacity_check(
         &self,
         agent_id: ThreadId,

codex-rs/core/src/session/mod.rs

@@ -101,6 +101,7 @@ use codex_protocol::config_types::WebSearchMode;
 use codex_protocol::dynamic_tools::DynamicToolResponse;
 use codex_protocol::dynamic_tools::DynamicToolSpec;
 use codex_protocol::items::EnteredReviewModeItem;
+use codex_protocol::items::SubAgentActivityItem;
 use codex_protocol::items::TurnItem;
 use codex_protocol::items::UserMessageItem;
 use codex_protocol::models::ActivePermissionProfile;
@@ -126,6 +127,7 @@ use codex_protocol::protocol::MULTI_AGENT_MODE_OPEN_TAG;
 use codex_protocol::protocol::MultiAgentVersion;
 use codex_protocol::protocol::RawResponseItemEvent;
 use codex_protocol::protocol::SessionSource;
+use codex_protocol::protocol::SubAgentActivityKind;
 use codex_protocol::protocol::SubAgentSource;
 use codex_protocol::protocol::ThreadHistoryMode;
 use codex_protocol::protocol::ThreadSettingsOverrides;
@@ -2016,6 +2018,26 @@ impl Session {
         child_agent_path: &codex_protocol::AgentPath,
         status: AgentStatus,
     ) {
+        if matches!(status, AgentStatus::Completed(_))
+            && let Some(parent_turn_id) = turn_context.turn_metadata_state.parent_turn_id()
+            && let Err(err) = self
+                .services
+                .agent_control
+                .emit_sub_agent_activity(
+                    parent_thread_id,
+                    parent_turn_id,
+                    SubAgentActivityItem {
+                        id: format!("subagent-completed-{}", turn_context.sub_id),
+                        kind: SubAgentActivityKind::Completed,
+                        agent_thread_id: self.thread_id,
+                        agent_path: child_agent_path.clone(),
+                    },
+                )
+                .await
+        {
+            debug!("failed to emit completed activity to parent thread {parent_thread_id}: {err}");
+        }
+
         let Some(parent_agent_path) = child_agent_path
             .as_str()
             .rsplit_once('/')

codex-rs/core/src/turn_metadata.rs

@@ -268,6 +268,10 @@ impl TurnMetadataState {
         let _ = self.parent_turn_id.set(parent_turn_id);
     }
 
+    pub(crate) fn parent_turn_id(&self) -> Option<String> {
+        self.parent_turn_id.get().cloned()
+    }
+
     pub(crate) fn set_root_turn_id(&self, root_turn_id: String) {
         if root_turn_id.trim().is_empty() {
             return;

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

@@ -9,6 +9,8 @@ use codex_history::RolloutItem;
 use codex_models_manager::bundled_models_response;
 use codex_protocol::ThreadId;
 use codex_protocol::config_types::ReasoningSummary;
+use codex_protocol::items::SubAgentActivityItem;
+use codex_protocol::items::TurnItem;
 use codex_protocol::models::PermissionProfile;
 use codex_protocol::openai_models::MultiAgentMessages;
 use codex_protocol::openai_models::MultiAgentRoleMessages;
@@ -20,6 +22,7 @@ use codex_protocol::protocol::EventMsg;
 use codex_protocol::protocol::MULTI_AGENT_MODE_OPEN_TAG;
 use codex_protocol::protocol::Op;
 use codex_protocol::protocol::SessionSource;
+use codex_protocol::protocol::SubAgentActivityKind;
 use codex_protocol::protocol::SubAgentSource;
 use codex_protocol::protocol::ThreadHistoryMode;
 use codex_protocol::protocol::ThreadSettingsOverrides;
@@ -59,6 +62,7 @@ use std::time::Duration;
 use test_case::test_case;
 use tokio::time::Instant;
 use tokio::time::sleep;
+use tokio::time::timeout;
 use tracing::Level;
 use tracing_test::internal::MockWriter;
 use wiremock::MockServer;
@@ -1982,11 +1986,25 @@ enum CompletionScenario {
     TerminalError,
 }
 
-#[test_case(CompletionScenario::Completed ; "completed")]
-#[test_case(CompletionScenario::TerminalError ; "terminal_error")]
+#[test_case(
+    CompletionScenario::Completed,
+    ThreadHistoryMode::Paginated;
+    "completed_paginated"
+)]
+#[test_case(
+    CompletionScenario::Completed,
+    ThreadHistoryMode::Legacy;
+    "completed_legacy"
+)]
+#[test_case(
+    CompletionScenario::TerminalError,
+    ThreadHistoryMode::Paginated;
+    "terminal_error"
+)]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn plaintext_multi_agent_v2_completion_sends_agent_message(
     scenario: CompletionScenario,
+    history_mode: ThreadHistoryMode,
 ) -> Result<()> {
     let server = start_mock_server().await;
     let spawn_args = serde_json::to_string(&json!({
@@ -2018,14 +2036,28 @@ async fn plaintext_multi_agent_v2_completion_sends_agent_message(
     };
     let child_request = mount_response_once_match(
         &server,
-        |req: &wiremock::Request| request_has_input_type(req, "agent_message"),
+        |req: &wiremock::Request| {
+            request_has_input_type(req, "agent_message")
+                && decoded_body(req)
+                    .and_then(|body| serde_json::from_slice::<Value>(&body).ok())
+                    .and_then(|body| {
+                        body["client_metadata"]["x-codex-turn-metadata"]
+                            .as_str()
+                            .and_then(|metadata| serde_json::from_str::<Value>(metadata).ok())
+                    })
+                    .is_some_and(|metadata| {
+                        metadata.get("parent_turn_id").is_some_and(Value::is_string)
+                    })
+        },
         sse_response(sse(child_events)).set_delay(Duration::from_secs(1)),
     )
     .await;
     mount_sse_once_match(
         &server,
         |req: &wiremock::Request| {
-            body_contains(req, SPAWN_CALL_ID) && !body_contains(req, "Message Type: FINAL_ANSWER")
+            body_contains(req, SPAWN_CALL_ID)
+                && !request_has_input_type(req, "agent_message")
+                && !body_contains(req, "Message Type: FINAL_ANSWER")
         },
         sse(vec![
             ev_response_created("resp-parent-2"),
@@ -2096,12 +2128,106 @@ async fn plaintext_multi_agent_v2_completion_sends_agent_message(
             config.model_provider.stream_max_retries = Some(0);
             config.model_provider.supports_websockets = false;
         })
+        .with_history_mode(history_mode)
         .build(&server)
         .await?;
 
     test.submit_turn(TURN_1_PROMPT).await?;
-    let _ = wait_for_requests(&child_request).await?;
-    test.submit_turn(TURN_2_NO_WAIT_PROMPT).await?;
+    let deadline = Instant::now() + Duration::from_secs(2);
+    let (child_request, child_turn_metadata) = loop {
+        let child_request = child_request.requests().into_iter().find_map(|request| {
+            let body = request.body_json();
+            let turn_metadata: Value =
+                serde_json::from_str(body["client_metadata"]["x-codex-turn-metadata"].as_str()?)
+                    .ok()?;
+            turn_metadata
+                .get("parent_turn_id")
+                .and_then(Value::as_str)?;
+            Some((request, turn_metadata))
+        });
+        if let Some(child_request) = child_request {
+            break child_request;
+        }
+        assert!(
+            Instant::now() < deadline,
+            "timed out waiting for child request"
+        );
+        sleep(Duration::from_millis(10)).await;
+    };
+    let expected_completed_activity = if matches!(scenario, CompletionScenario::Completed) {
+        let child_body = child_request.body_json();
+        let parent_turn_id = child_turn_metadata["parent_turn_id"]
+            .as_str()
+            .expect("child parent turn ID")
+            .to_string();
+        let child_turn_id = child_body["client_metadata"]["turn_id"]
+            .as_str()
+            .expect("child turn ID")
+            .to_string();
+        let child_thread_id = ThreadId::from_string(
+            child_body["client_metadata"]["thread_id"]
+                .as_str()
+                .expect("child thread ID"),
+        )?;
+        Some((parent_turn_id, child_turn_id, child_thread_id))
+    } else {
+        None
+    };
+    test.codex
+        .start_or_steer_turn(TurnInputRequest::user_input(vec![UserInput::Text {
+            text: TURN_2_NO_WAIT_PROMPT.to_string(),
+            text_elements: Vec::new(),
+        }]))
+        .await?;
+    let (completed_activity_started, completed_activity_completed) =
+        timeout(Duration::from_secs(5), async {
+            let mut active_turn_id = None;
+            let mut completed_activity_started = None;
+            let mut completed_activity_completed = None;
+            loop {
+                let event = test
+                    .codex
+                    .next_event()
+                    .await
+                    .expect("event stream should remain open");
+                match event.msg {
+                    EventMsg::TurnStarted(event) => {
+                        active_turn_id = Some(event.turn_id);
+                    }
+                    EventMsg::ItemStarted(event)
+                        if matches!(
+                            &event.item,
+                            TurnItem::SubAgentActivity(SubAgentActivityItem {
+                                kind: SubAgentActivityKind::Completed,
+                                ..
+                            })
+                        ) =>
+                    {
+                        completed_activity_started = Some(event);
+                    }
+                    EventMsg::ItemCompleted(event)
+                        if matches!(
+                            &event.item,
+                            TurnItem::SubAgentActivity(SubAgentActivityItem {
+                                kind: SubAgentActivityKind::Completed,
+                                ..
+                            })
+                        ) =>
+                    {
+                        completed_activity_completed = Some(event);
+                    }
+                    EventMsg::TurnComplete(event)
+                        if active_turn_id.as_deref() == Some(event.turn_id.as_str()) =>
+                    {
+                        break;
+                    }
+                    _ => {}
+                }
+            }
+            (completed_activity_started, completed_activity_completed)
+        })
+        .await
+        .expect("timed out waiting for parent turn completion");
 
     let request = wait_for_requests(&agent_request)
         .await?
@@ -2122,6 +2248,85 @@ async fn plaintext_multi_agent_v2_completion_sends_agent_message(
         })])
     );
 
+    if let Some((parent_turn_id, child_turn_id, child_thread_id)) = expected_completed_activity {
+        let started = completed_activity_started.expect("completed activity start event");
+        let completed_event =
+            completed_activity_completed.expect("completed activity completion event");
+        let TurnItem::SubAgentActivity(started_item) = &started.item else {
+            panic!("expected started sub-agent activity");
+        };
+        let TurnItem::SubAgentActivity(completed_event_item) = &completed_event.item else {
+            panic!("expected completed sub-agent activity");
+        };
+        assert_eq!(
+            (
+                started.thread_id,
+                &started.turn_id,
+                started_item,
+                Some(started.started_at_ms),
+            ),
+            (
+                completed_event.thread_id,
+                &completed_event.turn_id,
+                completed_event_item,
+                completed_event.started_at_ms,
+            )
+        );
+        assert_eq!(started.turn_id, parent_turn_id);
+
+        test.codex.ensure_rollout_materialized().await;
+        test.codex.flush_rollout().await?;
+        let rollout = codex_rollout::RolloutRecorder::get_rollout_history(
+            &test.codex.rollout_path().expect("parent rollout path"),
+        )
+        .await?;
+        assert!(
+            !rollout.get_rollout_items().iter().any(|item| matches!(
+                item,
+                RolloutItem::EventMsg(EventMsg::SubAgentActivity(activity))
+                    if activity.kind == SubAgentActivityKind::Completed
+            )),
+            "legacy completed activity should not be persisted without its parent turn ID"
+        );
+        let completed = rollout
+            .get_rollout_items()
+            .iter()
+            .find_map(|item| match item {
+                RolloutItem::EventMsg(EventMsg::ItemCompleted(completed))
+                    if matches!(
+                        &completed.item,
+                        TurnItem::SubAgentActivity(SubAgentActivityItem {
+                            kind: SubAgentActivityKind::Completed,
+                            ..
+                        })
+                    ) =>
+                {
+                    Some(completed)
+                }
+                _ => None,
+            })
+            .expect("persisted completed sub-agent activity");
+
+        assert_eq!(completed.turn_id, parent_turn_id);
+        let TurnItem::SubAgentActivity(completed_item) = &completed.item else {
+            panic!("expected completed sub-agent activity");
+        };
+        assert_eq!(
+            completed_item,
+            &SubAgentActivityItem {
+                id: format!("subagent-completed-{child_turn_id}"),
+                kind: SubAgentActivityKind::Completed,
+                agent_thread_id: child_thread_id,
+                agent_path: codex_protocol::AgentPath::root()
+                    .join("worker")
+                    .expect("worker path"),
+            }
+        );
+    } else {
+        assert!(completed_activity_started.is_none());
+        assert!(completed_activity_completed.is_none());
+    }
+
     Ok(())
 }
 

codex-rs/protocol/src/protocol.rs

@@ -4117,6 +4117,7 @@ pub enum SubAgentActivityKind {
     Started,
     Interacted,
     Interrupted,
+    Completed,
 }
 
 #[derive(Debug, Clone, Deserialize, Serialize, PartialEq, Eq, JsonSchema, TS)]

codex-rs/rollout-trace/src/protocol_event.rs

@@ -22,6 +22,7 @@ use codex_protocol::protocol::PatchApplyBeginEvent;
 use codex_protocol::protocol::PatchApplyEndEvent;
 use codex_protocol::protocol::PatchApplyStatus;
 use codex_protocol::protocol::SubAgentActivityEvent;
+use codex_protocol::protocol::SubAgentActivityKind;
 use codex_protocol::protocol::TurnAbortReason;
 use serde::Serialize;
 use std::time::Duration;
@@ -352,11 +353,14 @@ pub(crate) fn tool_runtime_trace_event(event: &EventMsg) -> Option<ToolRuntimeTr
             status: ExecutionStatus::Completed,
             payload: ToolRuntimePayload::CollabCloseEnd(event),
         }),
-        EventMsg::SubAgentActivity(event) => Some(ToolRuntimeTraceEvent::Ended {
-            tool_call_id: &event.event_id,
-            status: ExecutionStatus::Completed,
-            payload: ToolRuntimePayload::SubAgentActivity(event),
-        }),
+        EventMsg::SubAgentActivity(event) if event.kind != SubAgentActivityKind::Completed => {
+            Some(ToolRuntimeTraceEvent::Ended {
+                tool_call_id: &event.event_id,
+                status: ExecutionStatus::Completed,
+                payload: ToolRuntimePayload::SubAgentActivity(event),
+            })
+        }
+        EventMsg::SubAgentActivity(_) => None,
         EventMsg::Error(_)
         | EventMsg::Warning(_)
         | EventMsg::GuardianWarning(_)

codex-rs/rollout-trace/src/protocol_event_tests.rs

@@ -50,6 +50,20 @@ fn sub_agent_activity_is_a_terminal_tool_runtime_event() -> anyhow::Result<()> {
     Ok(())
 }
 
+#[test]
+fn completed_sub_agent_activity_is_not_a_tool_runtime_event() -> anyhow::Result<()> {
+    let event = EventMsg::SubAgentActivity(SubAgentActivityEvent {
+        event_id: "child-turn-completed".to_string(),
+        occurred_at_ms: 1234,
+        agent_thread_id: ThreadId::new(),
+        agent_path: AgentPath::try_from("/root/reviewer").map_err(anyhow::Error::msg)?,
+        kind: SubAgentActivityKind::Completed,
+    });
+
+    assert!(tool_runtime_trace_event(&event).is_none());
+    Ok(())
+}
+
 #[test]
 fn exec_command_trace_payloads_use_inferred_native_cwd() -> anyhow::Result<()> {
     // Convention inference depends on the URI spelling, not the test host, so exercise both

codex-rs/rollout-trace/src/reducer/tool/agents.rs

@@ -235,6 +235,7 @@ impl TraceReducer {
                     target_thread_id,
                     Some(wall_time_unix_ms),
                 ),
+            (_, SubAgentActivityKind::Completed) => Ok(()),
             _ => bail!(
                 "sub-agent activity {:?} does not match tool call kind {tool_kind:?}",
                 payload.kind

codex-rs/rollout/src/policy.rs

@@ -3,6 +3,7 @@ use crate::protocol::EventMsg;
 use codex_extension_items::ExtensionItem;
 use codex_protocol::items::TurnItem;
 use codex_protocol::models::ResponseItem;
+use codex_protocol::protocol::SubAgentActivityKind;
 use codex_protocol::protocol::ThreadHistoryMode;
 
 /// Whether a rollout `item` should be persisted in rollout files.
@@ -89,12 +90,18 @@ pub fn should_persist_event_msg(ev: &EventMsg, history_mode: ThreadHistoryMode)
     match ev {
         EventMsg::ItemCompleted(event) => {
             // Paginated rollouts store TurnItems.
-            // Legacy rollouts keep only items with no raw ResponseItem or legacy equivalent.
+            // Legacy rollouts keep only items with no lossless raw ResponseItem or legacy
+            // equivalent.
             matches!(history_mode, ThreadHistoryMode::Paginated)
                 || matches!(
                     event.item,
                     TurnItem::Plan(_) | TurnItem::Extension(ExtensionItem::Sleep(_))
                 )
+                || matches!(
+                    &event.item,
+                    TurnItem::SubAgentActivity(item)
+                        if item.kind == SubAgentActivityKind::Completed
+                )
         }
         EventMsg::TokenCount(_)
         | EventMsg::ThreadGoalUpdated(_)
@@ -116,8 +123,13 @@ pub fn should_persist_event_msg(ev: &EventMsg, history_mode: ThreadHistoryMode)
         | EventMsg::ContextCompacted(_)
         | EventMsg::McpToolCallEnd(_)
         | EventMsg::WebSearchEnd(_)
-        | EventMsg::ImageGenerationEnd(_)
-        | EventMsg::SubAgentActivity(_) => matches!(history_mode, ThreadHistoryMode::Legacy),
+        | EventMsg::ImageGenerationEnd(_) => {
+            matches!(history_mode, ThreadHistoryMode::Legacy)
+        }
+        EventMsg::SubAgentActivity(event) => {
+            matches!(history_mode, ThreadHistoryMode::Legacy)
+                && event.kind != SubAgentActivityKind::Completed
+        }
 
         // Transient, non-durable events.
         EventMsg::Error(_)

codex-rs/tui/src/app/agent_status_feed.rs

@@ -173,6 +173,7 @@ fn activity_summary(item: &ThreadItem) -> Option<String> {
                 SubAgentActivityKind::Started => "Started",
                 SubAgentActivityKind::Interacted => "Contacted",
                 SubAgentActivityKind::Interrupted => "Interrupted",
+                SubAgentActivityKind::Completed => "Completed",
             };
             return bounded_summary(&format!("{action} {agent_path}"));
         }

codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__app_server_sub_agent_activity_renders_once.snap

@@ -1,5 +1,5 @@
 ---
-source: tui/src/chatwidget/tests.rs
+source: tui/src/chatwidget/tests/app_server.rs
 expression: rendered
 ---
-• Interacted with `/root/researcher`
+• Completed `/root/researcher`

codex-rs/tui/src/chatwidget/tests/app_server.rs

@@ -963,7 +963,7 @@ async fn live_app_server_sub_agent_activity_renders_once() {
     let (mut chat, mut rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;
     let activity = AppServerThreadItem::SubAgentActivity {
         id: "activity-1".to_string(),
-        kind: codex_app_server_protocol::SubAgentActivityKind::Interacted,
+        kind: codex_app_server_protocol::SubAgentActivityKind::Completed,
         agent_thread_id: ThreadId::new().to_string(),
         agent_path: "/root/researcher".to_string(),
     };

codex-rs/tui/src/multi_agents.rs

@@ -291,7 +291,7 @@ pub(crate) fn sub_agent_activity_display(item: &ThreadItem) -> Option<SubAgentAc
     let is_running_hint = match kind {
         SubAgentActivityKind::Started => true,
         SubAgentActivityKind::Interacted => return None,
-        SubAgentActivityKind::Interrupted => false,
+        SubAgentActivityKind::Interrupted | SubAgentActivityKind::Completed => false,
     };
     Some(SubAgentActivityDisplay {
         thread_id: parse_thread_id(agent_thread_id)?,
@@ -318,6 +318,7 @@ pub(crate) fn sub_agent_activity_summary(kind: SubAgentActivityKind, agent_path:
         SubAgentActivityKind::Started => format!("Started `{agent_path}`"),
         SubAgentActivityKind::Interacted => format!("Interacted with `{agent_path}`"),
         SubAgentActivityKind::Interrupted => format!("Interrupted `{agent_path}`"),
+        SubAgentActivityKind::Completed => format!("Completed `{agent_path}`"),
     }
 }
 
@@ -326,6 +327,7 @@ fn sub_agent_activity_title(kind: SubAgentActivityKind, agent_path: &str) -> Lin
         SubAgentActivityKind::Started => ("Started ", agent_path),
         SubAgentActivityKind::Interacted => ("Interacted with ", agent_path),
         SubAgentActivityKind::Interrupted => ("Interrupted ", agent_path),
+        SubAgentActivityKind::Completed => ("Completed ", agent_path),
     };
     title_spans_line(vec![
         Span::from(prefix).bold(),
@@ -691,6 +693,26 @@ mod tests {
         assert_eq!(sub_agent_activity_display(&item), None);
     }
 
+    #[test]
+    fn completed_sub_agent_activity_stops_running_liveness() {
+        let thread_id = ThreadId::new();
+        let item = ThreadItem::SubAgentActivity {
+            id: "activity-1".to_string(),
+            kind: SubAgentActivityKind::Completed,
+            agent_thread_id: thread_id.to_string(),
+            agent_path: "/root/child".to_string(),
+        };
+
+        assert_eq!(
+            sub_agent_activity_display(&item),
+            Some(SubAgentActivityDisplay {
+                thread_id,
+                agent_path: "/root/child".to_string(),
+                is_running_hint: false,
+            })
+        );
+    }
+
     #[test]
     fn collab_events_snapshot() {
         let sender_thread_id = ThreadId::from_string("00000000-0000-0000-0000-000000000001")