diff --git a/codex-rs/codex-api/src/common.rs b/codex-rs/codex-api/src/common.rs
index bd037deb5838..e954ee7fa800 100644
--- a/codex-rs/codex-api/src/common.rs
+++ b/codex-rs/codex-api/src/common.rs
@@ -101,6 +101,7 @@ pub enum ResponseEvent {
         delta: String,
     },
     ReasoningSummaryDelta {
+        item_id: String,
         delta: String,
         summary_index: i64,
     },
@@ -109,6 +110,7 @@ pub enum ResponseEvent {
         content_index: i64,
     },
     ReasoningSummaryPartAdded {
+        item_id: String,
         summary_index: i64,
     },
     RateLimits(RateLimitSnapshot),
diff --git a/codex-rs/codex-api/src/sse/responses.rs b/codex-rs/codex-api/src/sse/responses.rs
index 71f73c0232cc..9dcc2d13654f 100644
--- a/codex-rs/codex-api/src/sse/responses.rs
+++ b/codex-rs/codex-api/src/sse/responses.rs
@@ -341,8 +341,11 @@ pub fn process_responses_event(
             }
         }
         "response.reasoning_summary_text.delta" => {
-            if let (Some(delta), Some(summary_index)) = (event.delta, event.summary_index) {
+            if let (Some(item_id), Some(delta), Some(summary_index)) =
+                (event.item_id, event.delta, event.summary_index)
+            {
                 return Ok(Some(ResponseEvent::ReasoningSummaryDelta {
+                    item_id,
                     delta,
                     summary_index,
                 }));
@@ -434,8 +437,9 @@ pub fn process_responses_event(
             }
         }
         "response.reasoning_summary_part.added" => {
-            if let Some(summary_index) = event.summary_index {
+            if let (Some(item_id), Some(summary_index)) = (event.item_id, event.summary_index) {
                 return Ok(Some(ResponseEvent::ReasoningSummaryPartAdded {
+                    item_id,
                     summary_index,
                 }));
             }
@@ -788,6 +792,44 @@ mod tests {
         }
     }
 
+    #[tokio::test]
+    async fn preserves_reasoning_summary_item_ids() {
+        let events = run_sse(vec![
+            json!({
+                "type": "response.reasoning_summary_part.added",
+                "item_id": "reasoning-1",
+                "summary_index": 0
+            }),
+            json!({
+                "type": "response.reasoning_summary_text.delta",
+                "item_id": "reasoning-1",
+                "summary_index": 0,
+                "delta": "Checking"
+            }),
+            json!({
+                "type": "response.completed",
+                "response": { "id": "resp1" }
+            }),
+        ])
+        .await;
+
+        assert_matches!(
+            &events[0],
+            ResponseEvent::ReasoningSummaryPartAdded {
+                item_id,
+                summary_index: 0,
+            } if item_id == "reasoning-1"
+        );
+        assert_matches!(
+            &events[1],
+            ResponseEvent::ReasoningSummaryDelta {
+                item_id,
+                delta,
+                summary_index: 0,
+            } if item_id == "reasoning-1" && delta == "Checking"
+        );
+    }
+
     #[tokio::test]
     async fn error_when_missing_completed() {
         let item1 = json!({
diff --git a/codex-rs/core/src/session/turn.rs b/codex-rs/core/src/session/turn.rs
index f16b525002fc..1031c4291916 100644
--- a/codex-rs/core/src/session/turn.rs
+++ b/codex-rs/core/src/session/turn.rs
@@ -1928,6 +1928,7 @@ async fn try_run_sampling_request(
     let mut needs_follow_up = false;
     let mut last_agent_message: Option<String> = None;
     let mut active_item: Option<TurnItem> = None;
+    let mut streamed_items = HashMap::<String, TurnItem>::new();
     let mut active_tool_argument_diff_consumer: Option<(
         String,
         Box<dyn ToolArgumentDiffConsumer>,
@@ -1986,18 +1987,44 @@ async fn try_run_sampling_request(
         match event {
             ResponseEvent::Created => {}
             ResponseEvent::OutputItemDone(item) => {
-                if let Some((_, mut consumer)) = active_tool_argument_diff_consumer.take()
+                let completes_active_tool_call = active_tool_argument_diff_consumer
+                    .as_ref()
+                    .is_some_and(|(active_call_id, _)| {
+                        matches!(
+                            &item,
+                            ResponseItem::CustomToolCall { call_id, .. }
+                                if call_id == active_call_id
+                        )
+                    });
+                if completes_active_tool_call
+                    && let Some((_, mut consumer)) = active_tool_argument_diff_consumer.take()
                     && let Ok(Some(event)) = consumer.finish()
                 {
                     sess.send_event(&turn_context, event).await;
                 }
-                let previously_active_item = active_item.take();
-                let previously_streamed_item = if active_item_is_streaming_to_client {
-                    previously_active_item
-                } else {
-                    None
+                let completed_item_id = item.id().map(str::to_owned);
+                let is_tool_call = matches!(
+                    &item,
+                    ResponseItem::LocalShellCall { .. }
+                        | ResponseItem::FunctionCall { .. }
+                        | ResponseItem::ToolSearchCall { .. }
+                        | ResponseItem::CustomToolCall { .. }
+                );
+                if completed_item_id.is_none() && !is_tool_call {
+                    warn!("dropping non-tool output_item.done event without item ID");
+                    continue;
+                }
+                let completes_active_item = match (&completed_item_id, active_item.as_ref()) {
+                    (Some(completed_item_id), Some(active)) => completed_item_id == &active.id(),
+                    _ => false,
                 };
-                active_item_is_streaming_to_client = false;
+                let previously_streamed_item = completed_item_id
+                    .as_deref()
+                    .and_then(|item_id| streamed_items.remove(item_id));
+                if completes_active_item {
+                    active_item = None;
+                    active_item_is_streaming_to_client = false;
+                }
                 if let Some(previous) = previously_streamed_item.as_ref()
                     && matches!(previous, TurnItem::AgentMessage(_))
                 {
@@ -2152,6 +2179,7 @@ async fn try_run_sampling_request(
                             )
                             .await;
                         }
+                        streamed_items.insert(turn_item.id(), turn_item.clone());
                     }
                     active_item = Some(turn_item);
                     active_item_is_streaming_to_client = stream_item_to_client;
@@ -2288,39 +2316,47 @@ async fn try_run_sampling_request(
                 }
             }
             ResponseEvent::ReasoningSummaryDelta {
+                item_id,
                 delta,
                 summary_index,
             } => {
-                if let Some(active) = active_item.as_ref() {
-                    if !active_item_is_streaming_to_client {
-                        continue;
-                    }
+                if defer_streamed_turn_items_for_contributors {
+                    continue;
+                }
+                if streamed_items.contains_key(&item_id) {
                     let event = ReasoningContentDeltaEvent {
                         thread_id: sess.thread_id.to_string(),
                         turn_id: turn_context.sub_id.clone(),
-                        item_id: active.id(),
+                        item_id,
                         delta,
                         summary_index,
                     };
                     sess.send_event(&turn_context, EventMsg::ReasoningContentDelta(event))
                         .await;
                 } else {
-                    error_or_panic("ReasoningSummaryDelta without active item".to_string());
+                    error_or_panic(format!(
+                        "ReasoningSummaryDelta without streamed item {item_id}"
+                    ));
                 }
             }
-            ResponseEvent::ReasoningSummaryPartAdded { summary_index } => {
-                if let Some(active) = active_item.as_ref() {
-                    if !active_item_is_streaming_to_client {
-                        continue;
-                    }
+            ResponseEvent::ReasoningSummaryPartAdded {
+                item_id,
+                summary_index,
+            } => {
+                if defer_streamed_turn_items_for_contributors {
+                    continue;
+                }
+                if streamed_items.contains_key(&item_id) {
                     let event =
                         EventMsg::AgentReasoningSectionBreak(AgentReasoningSectionBreakEvent {
-                            item_id: active.id(),
+                            item_id,
                             summary_index,
                         });
                     sess.send_event(&turn_context, event).await;
                 } else {
-                    error_or_panic("ReasoningSummaryPartAdded without active item".to_string());
+                    error_or_panic(format!(
+                        "ReasoningSummaryPartAdded without streamed item {item_id}"
+                    ));
                 }
             }
             ResponseEvent::ReasoningContentDelta {
diff --git a/codex-rs/core/tests/common/responses.rs b/codex-rs/core/tests/common/responses.rs
index 9569df1c90ec..45d4cb3d99a5 100644
--- a/codex-rs/core/tests/common/responses.rs
+++ b/codex-rs/core/tests/common/responses.rs
@@ -784,11 +784,20 @@ pub fn ev_reasoning_item_added(id: &str, summary: &[&str]) -> Value {
     })
 }
 
-pub fn ev_reasoning_summary_text_delta(delta: &str) -> Value {
+pub fn ev_reasoning_summary_part_added(item_id: &str, summary_index: i64) -> Value {
+    serde_json::json!({
+        "type": "response.reasoning_summary_part.added",
+        "item_id": item_id,
+        "summary_index": summary_index,
+    })
+}
+
+pub fn ev_reasoning_summary_text_delta(item_id: &str, summary_index: i64, delta: &str) -> Value {
     serde_json::json!({
         "type": "response.reasoning_summary_text.delta",
+        "item_id": item_id,
         "delta": delta,
-        "summary_index": 0,
+        "summary_index": summary_index,
     })
 }
 
diff --git a/codex-rs/core/tests/suite/apply_patch_cli.rs b/codex-rs/core/tests/suite/apply_patch_cli.rs
index d8142723b495..92f583c47072 100644
--- a/codex-rs/core/tests/suite/apply_patch_cli.rs
+++ b/codex-rs/core/tests/suite/apply_patch_cli.rs
@@ -1198,6 +1198,7 @@ async fn apply_patch_custom_tool_streaming_emits_updated_changes() -> Result<()>
                     "call_id": call_id,
                     "delta": "*** Add File: streamed.txt\n+hello",
                 }),
+                ev_assistant_message("unrelated-message", ""),
                 json!({
                     "type": "response.custom_tool_call_input.delta",
                     "call_id": call_id,
diff --git a/codex-rs/core/tests/suite/codex_delegate.rs b/codex-rs/core/tests/suite/codex_delegate.rs
index f5db9856df2f..7dab8a068841 100644
--- a/codex-rs/core/tests/suite/codex_delegate.rs
+++ b/codex-rs/core/tests/suite/codex_delegate.rs
@@ -204,7 +204,7 @@ async fn codex_delegate_ignores_legacy_deltas() {
     let sse_stream = sse(vec![
         ev_response_created("resp-1"),
         ev_reasoning_item_added("reason-1", &["initial"]),
-        ev_reasoning_summary_text_delta("think-1"),
+        ev_reasoning_summary_text_delta("reason-1", /*summary_index*/ 0, "think-1"),
         ev_completed("resp-1"),
     ]);
 
diff --git a/codex-rs/core/tests/suite/items.rs b/codex-rs/core/tests/suite/items.rs
index 515d496b8b7a..b29696fdad4d 100644
--- a/codex-rs/core/tests/suite/items.rs
+++ b/codex-rs/core/tests/suite/items.rs
@@ -20,17 +20,20 @@ use codex_utils_absolute_path::AbsolutePathBuf;
 use core_test_support::PathBufExt;
 use core_test_support::responses::ev_assistant_message;
 use core_test_support::responses::ev_completed;
+use core_test_support::responses::ev_function_call;
 use core_test_support::responses::ev_image_generation_call;
 use core_test_support::responses::ev_message_item_added;
 use core_test_support::responses::ev_output_text_delta;
 use core_test_support::responses::ev_reasoning_item;
 use core_test_support::responses::ev_reasoning_item_added;
+use core_test_support::responses::ev_reasoning_summary_part_added;
 use core_test_support::responses::ev_reasoning_summary_text_delta;
 use core_test_support::responses::ev_reasoning_text_delta;
 use core_test_support::responses::ev_response_created;
 use core_test_support::responses::ev_web_search_call_added_partial;
 use core_test_support::responses::ev_web_search_call_done;
 use core_test_support::responses::mount_sse_once;
+use core_test_support::responses::mount_sse_sequence;
 use core_test_support::responses::sse;
 use core_test_support::responses::start_mock_server;
 use core_test_support::skip_if_no_network;
@@ -1085,21 +1088,45 @@ async fn plan_mode_handles_missing_plan_close_tag() -> anyhow::Result<()> {
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn reasoning_content_delta_has_item_metadata() -> anyhow::Result<()> {
+async fn interleaved_reasoning_summary_events_keep_reasoning_item_metadata() -> anyhow::Result<()> {
     skip_if_no_network!(Ok(()));
 
     let server = start_mock_server().await;
 
     let TestCodex { codex, .. } = test_codex().build(&server).await?;
 
-    let stream = sse(vec![
-        ev_response_created("resp-1"),
-        ev_reasoning_item_added("reasoning-1", &[""]),
-        ev_reasoning_summary_text_delta("step one"),
-        ev_reasoning_item("reasoning-1", &["step one"], &[]),
-        ev_completed("resp-1"),
-    ]);
-    mount_sse_once(&server, stream).await;
+    mount_sse_sequence(
+        &server,
+        vec![
+            sse(vec![
+                ev_response_created("resp-1"),
+                ev_reasoning_item_added("reasoning-1", &[""]),
+                ev_reasoning_summary_part_added("reasoning-1", /*summary_index*/ 0),
+                ev_reasoning_summary_text_delta(
+                    "reasoning-1",
+                    /*summary_index*/ 0,
+                    "step one",
+                ),
+                ev_reasoning_item("", &["ignored"], &[]),
+                ev_function_call("call-1", "unknown_tool", "{}"),
+                ev_reasoning_summary_part_added("reasoning-1", /*summary_index*/ 1),
+                ev_reasoning_summary_text_delta(
+                    "reasoning-1",
+                    /*summary_index*/ 1,
+                    "step two",
+                ),
+                ev_reasoning_item("reasoning-1", &["step one", "step two"], &[]),
+                ev_completed("resp-1"),
+            ]),
+            sse(vec![
+                ev_message_item_added("message-1", ""),
+                ev_output_text_delta("Done"),
+                ev_assistant_message("message-1", "Done"),
+                ev_completed("resp-2"),
+            ]),
+        ],
+    )
+    .await;
 
     codex
         .submit(Op::UserInput {
@@ -1114,22 +1141,59 @@ async fn reasoning_content_delta_has_item_metadata() -> anyhow::Result<()> {
         })
         .await?;
 
-    let reasoning_item = wait_for_event_match(&codex, |ev| match ev {
-        EventMsg::ItemStarted(ItemStartedEvent {
-            item: TurnItem::Reasoning(item),
-            ..
-        }) => Some(item.clone()),
-        _ => None,
-    })
-    .await;
+    let mut reasoning_started = Vec::new();
+    let mut reasoning_completed = Vec::new();
+    let mut messages_started = Vec::new();
+    let mut messages_completed = Vec::new();
+    let mut summary_deltas = Vec::new();
+    let mut summary_sections = Vec::new();
+    loop {
+        match wait_for_event(&codex, |_| true).await {
+            EventMsg::ItemStarted(ItemStartedEvent {
+                item: TurnItem::Reasoning(item),
+                ..
+            }) => reasoning_started.push(item.id),
+            EventMsg::ItemCompleted(ItemCompletedEvent {
+                item: TurnItem::Reasoning(item),
+                ..
+            }) => reasoning_completed.push(item.id),
+            EventMsg::ItemStarted(ItemStartedEvent {
+                item: TurnItem::AgentMessage(item),
+                ..
+            }) => messages_started.push(item.id),
+            EventMsg::ItemCompleted(ItemCompletedEvent {
+                item: TurnItem::AgentMessage(item),
+                ..
+            }) => messages_completed.push(item.id),
+            EventMsg::ReasoningContentDelta(event) => {
+                summary_deltas.push((event.item_id, event.delta, event.summary_index));
+            }
+            EventMsg::AgentReasoningSectionBreak(event) => {
+                summary_sections.push((event.item_id, event.summary_index));
+            }
+            EventMsg::TurnComplete(_) => break,
+            _ => {}
+        }
+    }
 
-    let delta_event = wait_for_event_match(&codex, |ev| match ev {
-        EventMsg::ReasoningContentDelta(event) => Some(event.clone()),
-        _ => None,
-    })
-    .await;
-    assert_eq!(delta_event.item_id, reasoning_item.id);
-    assert_eq!(delta_event.delta, "step one");
+    assert_eq!(reasoning_started, vec!["reasoning-1"]);
+    assert_eq!(reasoning_completed, vec!["reasoning-1"]);
+    assert_eq!(messages_started, vec!["message-1"]);
+    assert_eq!(messages_completed, vec!["message-1"]);
+    assert_eq!(
+        summary_deltas,
+        vec![
+            ("reasoning-1".to_string(), "step one".to_string(), 0),
+            ("reasoning-1".to_string(), "step two".to_string(), 1),
+        ]
+    );
+    assert_eq!(
+        summary_sections,
+        vec![
+            ("reasoning-1".to_string(), 0),
+            ("reasoning-1".to_string(), 1)
+        ]
+    );
 
     Ok(())
 }
diff --git a/codex-rs/core/tests/suite/otel.rs b/codex-rs/core/tests/suite/otel.rs
index 4a2b2993ad7e..060a9079a906 100644
--- a/codex-rs/core/tests/suite/otel.rs
+++ b/codex-rs/core/tests/suite/otel.rs
@@ -821,7 +821,7 @@ async fn record_responses_sets_span_fields_for_response_events() {
         ev_message_item_added("msg-added", "hi there"),
         ev_reasoning_item_added("reasoning-1", &["summary"]),
         ev_output_text_delta("delta"),
-        ev_reasoning_summary_text_delta("summary-delta"),
+        ev_reasoning_summary_text_delta("reasoning-1", /*summary_index*/ 0, "summary-delta"),
         ev_reasoning_text_delta("raw-delta"),
         ev_function_call("call-1", "fn", "{\"key\":\"value\"}"),
         ev_assistant_message("msg-1", "agent"),
diff --git a/codex-rs/tui/src/chatwidget/tests/history_replay.rs b/codex-rs/tui/src/chatwidget/tests/history_replay.rs
index f8626dfcc0ba..300978cf4d55 100644
--- a/codex-rs/tui/src/chatwidget/tests/history_replay.rs
+++ b/codex-rs/tui/src/chatwidget/tests/history_replay.rs
@@ -995,34 +995,30 @@ async fn live_reasoning_summary_is_not_rendered_twice_when_item_completes() {
     let (mut chat, mut rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;
     chat.show_welcome_banner = false;
 
-    chat.handle_server_notification(
-        ServerNotification::TurnStarted(TurnStartedNotification {
-            thread_id: "thread-1".to_string(),
-            turn: AppServerTurn {
-                id: "turn-1".to_string(),
-                items_view: codex_app_server_protocol::TurnItemsView::Full,
-                items: Vec::new(),
-                status: AppServerTurnStatus::InProgress,
-                error: None,
-                started_at: Some(0),
-                completed_at: None,
-                duration_ms: None,
-            },
-        }),
-        /*replay_kind*/ None,
-    );
-    let _ = drain_insert_history(&mut rx);
+    handle_turn_started(&mut chat, "turn-1");
+    while rx.try_recv().is_ok() {}
 
+    handle_agent_reasoning_delta(&mut chat, "**Step one**\nFirst summary");
+    handle_agent_message_delta(&mut chat, "Final answer");
+    complete_assistant_message(
+        &mut chat,
+        "msg-1",
+        "Final answer",
+        Some(MessagePhase::FinalAnswer),
+    );
     chat.handle_server_notification(
-        ServerNotification::ReasoningSummaryTextDelta(ReasoningSummaryTextDeltaNotification {
-            thread_id: "thread-1".to_string(),
-            turn_id: "turn-1".to_string(),
-            item_id: "reasoning-1".to_string(),
-            delta: "Summary only".to_string(),
-            summary_index: 0,
-        }),
+        ServerNotification::ReasoningSummaryPartAdded(
+            codex_app_server_protocol::ReasoningSummaryPartAddedNotification {
+                thread_id: chat.thread_id.map(|id| id.to_string()).unwrap_or_default(),
+                turn_id: "turn-1".to_string(),
+                item_id: "reasoning-1".to_string(),
+                summary_index: 1,
+            },
+        ),
         /*replay_kind*/ None,
     );
+    handle_agent_reasoning_delta(&mut chat, "**Step two**\nSecond summary");
+    handle_agent_reasoning_final(&mut chat);
 
     chat.handle_server_notification(
         ServerNotification::ItemCompleted(ItemCompletedNotification {
@@ -1031,20 +1027,35 @@ async fn live_reasoning_summary_is_not_rendered_twice_when_item_completes() {
             completed_at_ms: 0,
             item: AppServerThreadItem::Reasoning {
                 id: "reasoning-1".to_string(),
-                summary: vec!["Summary only".to_string()],
+                summary: vec![
+                    "**Step one**\nFirst summary".to_string(),
+                    "**Step two**\nSecond summary".to_string(),
+                ],
                 content: Vec::new(),
             },
         }),
         /*replay_kind*/ None,
     );
 
-    let rendered = match rx.try_recv() {
-        Ok(AppEvent::InsertHistoryCell(cell)) => {
-            lines_to_single_string(&cell.transcript_lines(/*width*/ 80))
+    let mut consolidated_answer = None;
+    let mut inserted_history = String::new();
+    while let Ok(event) = rx.try_recv() {
+        match event {
+            AppEvent::ConsolidateAgentMessage { source, .. } => {
+                consolidated_answer = Some(source);
+            }
+            AppEvent::InsertHistoryCell(cell) => {
+                inserted_history.push_str(&lines_to_single_string(
+                    &cell.transcript_lines(/*width*/ 80),
+                ));
+            }
+            _ => {}
         }
-        other => panic!("expected InsertHistoryCell, got {other:?}"),
-    };
-    assert_eq!(rendered.matches("Summary only").count(), 1);
+    }
+
+    assert_eq!(consolidated_answer.as_deref(), Some("Final answer"));
+    assert_eq!(inserted_history.matches("First summary").count(), 1);
+    assert_eq!(inserted_history.matches("Second summary").count(), 1);
 }
 
 #[tokio::test]