Add item streaming events (#5546)

Adds AgentMessageContentDelta, ReasoningContentDelta,
ReasoningRawContentDelta item streaming events while maintaining
compatibility for old events.

---------

Co-authored-by: Owen Lin <owen@openai.com>

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

@@ -9,7 +9,12 @@ use codex_protocol::items::TurnItem;
 use codex_protocol::user_input::UserInput;
 use core_test_support::responses::ev_assistant_message;
 use core_test_support::responses::ev_completed;
+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_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;
 use core_test_support::responses::ev_web_search_call_done;
@@ -234,3 +239,181 @@ async fn web_search_item_is_emitted() -> anyhow::Result<()> {
 
     Ok(())
 }
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn agent_message_content_delta_has_item_metadata() -> anyhow::Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = start_mock_server().await;
+
+    let TestCodex {
+        codex,
+        session_configured,
+        ..
+    } = test_codex().build(&server).await?;
+
+    let stream = sse(vec![
+        ev_response_created("resp-1"),
+        ev_message_item_added("msg-1", ""),
+        ev_output_text_delta("streamed response"),
+        ev_assistant_message("msg-1", "streamed response"),
+        ev_completed("resp-1"),
+    ]);
+    mount_sse_once_match(&server, any(), stream).await;
+
+    codex
+        .submit(Op::UserInput {
+            items: vec![UserInput::Text {
+                text: "please stream text".into(),
+            }],
+        })
+        .await?;
+
+    let (started_turn_id, started_item) = wait_for_event_match(&codex, |ev| match ev {
+        EventMsg::ItemStarted(ItemStartedEvent {
+            turn_id,
+            item: TurnItem::AgentMessage(item),
+            ..
+        }) => Some((turn_id.clone(), item.clone())),
+        _ => None,
+    })
+    .await;
+
+    let delta_event = wait_for_event_match(&codex, |ev| match ev {
+        EventMsg::AgentMessageContentDelta(event) => Some(event.clone()),
+        _ => None,
+    })
+    .await;
+    let legacy_delta = wait_for_event_match(&codex, |ev| match ev {
+        EventMsg::AgentMessageDelta(event) => Some(event.clone()),
+        _ => None,
+    })
+    .await;
+    let completed_item = wait_for_event_match(&codex, |ev| match ev {
+        EventMsg::ItemCompleted(ItemCompletedEvent {
+            item: TurnItem::AgentMessage(item),
+            ..
+        }) => Some(item.clone()),
+        _ => None,
+    })
+    .await;
+
+    let session_id = session_configured.session_id.to_string();
+    assert_eq!(delta_event.thread_id, session_id);
+    assert_eq!(delta_event.turn_id, started_turn_id);
+    assert_eq!(delta_event.item_id, started_item.id);
+    assert_eq!(delta_event.delta, "streamed response");
+    assert_eq!(legacy_delta.delta, "streamed response");
+    assert_eq!(completed_item.id, started_item.id);
+
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn reasoning_content_delta_has_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_match(&server, any(), stream).await;
+
+    codex
+        .submit(Op::UserInput {
+            items: vec![UserInput::Text {
+                text: "reason through it".into(),
+            }],
+        })
+        .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 delta_event = wait_for_event_match(&codex, |ev| match ev {
+        EventMsg::ReasoningContentDelta(event) => Some(event.clone()),
+        _ => None,
+    })
+    .await;
+    let legacy_delta = wait_for_event_match(&codex, |ev| match ev {
+        EventMsg::AgentReasoningDelta(event) => Some(event.clone()),
+        _ => None,
+    })
+    .await;
+
+    assert_eq!(delta_event.item_id, reasoning_item.id);
+    assert_eq!(delta_event.delta, "step one");
+    assert_eq!(legacy_delta.delta, "step one");
+
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn reasoning_raw_content_delta_respects_flag() -> anyhow::Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = start_mock_server().await;
+
+    let TestCodex { codex, .. } = test_codex()
+        .with_config(|config| {
+            config.show_raw_agent_reasoning = true;
+        })
+        .build(&server)
+        .await?;
+
+    let stream = sse(vec![
+        ev_response_created("resp-1"),
+        ev_reasoning_item_added("reasoning-raw", &[""]),
+        ev_reasoning_text_delta("raw detail"),
+        ev_reasoning_item("reasoning-raw", &["complete"], &["raw detail"]),
+        ev_completed("resp-1"),
+    ]);
+    mount_sse_once_match(&server, any(), stream).await;
+
+    codex
+        .submit(Op::UserInput {
+            items: vec![UserInput::Text {
+                text: "show raw reasoning".into(),
+            }],
+        })
+        .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 delta_event = wait_for_event_match(&codex, |ev| match ev {
+        EventMsg::ReasoningRawContentDelta(event) => Some(event.clone()),
+        _ => None,
+    })
+    .await;
+    let legacy_delta = wait_for_event_match(&codex, |ev| match ev {
+        EventMsg::AgentReasoningRawContentDelta(event) => Some(event.clone()),
+        _ => None,
+    })
+    .await;
+
+    assert_eq!(delta_event.item_id, reasoning_item.id);
+    assert_eq!(delta_event.delta, "raw detail");
+    assert_eq!(legacy_delta.delta, "raw detail");
+
+    Ok(())
+}