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/Cargo.lock

@@ -592,9 +592,9 @@ checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
 
 [[package]]
 name = "bitflags"
-version = "2.9.1"
+version = "2.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1b8e56985ec62d17e9c1001dc89c88ecd7dc08e47eba5ec7c29c7b5eeecde967"
+checksum = "812e12b5285cc515a9c72a5c1d3b6d46a19dac5acfef5265968c166106e31dd3"
 
 [[package]]
 name = "block-buffer"
@@ -1739,7 +1739,7 @@ version = "0.28.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "829d955a0bb380ef178a640b91779e3987da38c9aea133b20614cfed8cdea9c6"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "crossterm_winapi",
  "futures-core",
  "mio",
@@ -2083,7 +2083,7 @@ version = "0.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "89a09f22a6c6069a18470eb92d2298acf25463f14256d24778e1230d789a2aec"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "objc2",
 ]
 
@@ -3208,7 +3208,7 @@ version = "0.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f37dccff2791ab604f9babef0ba14fbe0be30bd368dc541e2b08d07c8aa908f3"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "inotify-sys",
  "libc",
 ]
@@ -3271,7 +3271,7 @@ version = "0.7.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d93587f37623a1a17d94ef2bc9ada592f5465fe7732084ab7beefabe5c77c0c4"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "cfg-if",
  "libc",
 ]
@@ -3517,7 +3517,7 @@ version = "0.1.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4488594b9328dee448adb906d8b126d9b7deb7cf5c22161ee591610bb1be83c0"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "libc",
 ]
 
@@ -3527,7 +3527,7 @@ version = "0.2.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "761e49ec5fd8a5a463f9b84e877c373d888935b71c6be78f3767fe2ae6bed18e"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "libc",
 ]
 
@@ -3795,7 +3795,7 @@ version = "0.28.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ab2156c4fce2f8df6c499cc1c763e4394b7482525bf2a9701c9d79d215f519e4"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "cfg-if",
  "cfg_aliases 0.1.1",
  "libc",
@@ -3807,7 +3807,7 @@ version = "0.29.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "71e2746dc3a24dd78b3cfcb7be93368c6de9963d30f43a6a73998a9cf4b17b46"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "cfg-if",
  "cfg_aliases 0.2.1",
  "libc",
@@ -3820,7 +3820,7 @@ version = "0.30.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "74523f3a35e05aba87a1d978330aef40f67b0304ac79c1c00b294c9830543db6"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "cfg-if",
  "cfg_aliases 0.2.1",
  "libc",
@@ -3848,7 +3848,7 @@ version = "8.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4d3d07927151ff8575b7087f245456e549fea62edf0ec4e565a5ee50c8402bc3"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "fsevent-sys",
  "inotify",
  "kqueue",
@@ -4018,7 +4018,7 @@ version = "0.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e6f29f568bec459b0ddff777cec4fe3fd8666d82d5a40ebd0ff7e66134f89bcc"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "objc2",
  "objc2-core-graphics",
  "objc2-foundation",
@@ -4030,7 +4030,7 @@ version = "0.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1c10c2894a6fed806ade6027bcd50662746363a9589d3ec9d9bef30a4e4bc166"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "dispatch2",
  "objc2",
 ]
@@ -4041,7 +4041,7 @@ version = "0.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "989c6c68c13021b5c2d6b71456ebb0f9dc78d752e86a98da7c716f4f9470f5a4"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "dispatch2",
  "objc2",
  "objc2-core-foundation",
@@ -4060,7 +4060,7 @@ version = "0.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "900831247d2fe1a09a683278e5384cfb8c80c79fe6b166f9d14bfdde0ea1b03c"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "objc2",
  "objc2-core-foundation",
 ]
@@ -4071,7 +4071,7 @@ version = "0.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7282e9ac92529fa3457ce90ebb15f4ecbc383e8338060960760fa2cf75420c3c"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "objc2",
  "objc2-core-foundation",
 ]
@@ -4103,7 +4103,7 @@ version = "0.10.73"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8505734d46c8ab1e19a1dce3aef597ad87dcb4c37e7188231769bd6bd51cebf8"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "cfg-if",
  "foreign-types",
  "libc",
@@ -4435,7 +4435,7 @@ version = "0.18.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "97baced388464909d42d89643fe4361939af9b7ce7a31ee32a168f832a70f2a0"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "crc32fast",
  "fdeflate",
  "flate2",
@@ -4625,7 +4625,7 @@ version = "0.10.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "76979bea66e7875e7509c4ec5300112b316af87fa7a252ca91c448b32dfe3993"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "getopts",
  "memchr",
  "pulldown-cmark-escape",
@@ -4806,7 +4806,7 @@ name = "ratatui"
 version = "0.29.0"
 source = "git+https://github.com/nornagon/ratatui?branch=nornagon-v0.29.0-patch#9b2ad1298408c45918ee9f8241a6f95498cdbed2"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "cassowary",
  "compact_str",
  "crossterm",
@@ -4836,7 +4836,7 @@ version = "0.5.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7e8af0dde094006011e6a740d4879319439489813bd0bcdc7d821beaeeff48ec"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
 ]
 
 [[package]]
@@ -5065,7 +5065,7 @@ version = "0.38.44"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fdb5bc1ae2baa591800df16c9ca78619bf65c0488b41b96ccec5d11220d8c154"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "errno",
  "libc",
  "linux-raw-sys 0.4.15",
@@ -5078,7 +5078,7 @@ version = "1.0.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "11181fbabf243db407ef8df94a6ce0b2f9a733bd8be4ad02b4eda9602296cac8"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "errno",
  "libc",
  "linux-raw-sys 0.9.4",
@@ -5144,7 +5144,7 @@ version = "14.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7803e8936da37efd9b6d4478277f4b2b9bb5cdb37a113e8d63222e58da647e63"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "cfg-if",
  "clipboard-win",
  "fd-lock",
@@ -5343,7 +5343,7 @@ version = "2.11.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "897b2245f0b511c87893af39b033e5ca9cce68824c4d7e7630b5a1d339658d02"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "core-foundation 0.9.4",
  "core-foundation-sys",
  "libc",
@@ -5356,7 +5356,7 @@ version = "3.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b3297343eaf830f66ede390ea39da1d462b6b0c1b000f420d0a83f898bbbe6ef"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "core-foundation 0.10.1",
  "core-foundation-sys",
  "libc",
@@ -6055,7 +6055,7 @@ version = "0.6.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3c879d448e9d986b661742763247d3693ed13609438cf3d006f51f5368a5ba6b"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "core-foundation 0.9.4",
  "system-configuration-sys",
 ]
@@ -6513,7 +6513,7 @@ version = "0.6.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "adc82fd73de2a9722ac5da747f12383d2bfdb93591ee6c58486e0097890f05f2"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
  "bytes",
  "futures-util",
  "http",
@@ -7588,7 +7588,7 @@ version = "0.39.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6f42320e61fe2cfd34354ecb597f86f413484a798ba44a8ca1165c58d42da6c1"
 dependencies = [
- "bitflags 2.9.1",
+ "bitflags 2.10.0",
 ]
 
 [[package]]

codex-rs/core/src/chat_completions.rs

@@ -423,6 +423,61 @@ pub(crate) async fn stream_chat_completions(
     }
 }
 
+async fn append_assistant_text(
+    tx_event: &mpsc::Sender<Result<ResponseEvent>>,
+    assistant_item: &mut Option<ResponseItem>,
+    text: String,
+) {
+    if assistant_item.is_none() {
+        let item = ResponseItem::Message {
+            id: None,
+            role: "assistant".to_string(),
+            content: vec![],
+        };
+        *assistant_item = Some(item.clone());
+        let _ = tx_event
+            .send(Ok(ResponseEvent::OutputItemAdded(item)))
+            .await;
+    }
+
+    if let Some(ResponseItem::Message { content, .. }) = assistant_item {
+        content.push(ContentItem::OutputText { text: text.clone() });
+        let _ = tx_event
+            .send(Ok(ResponseEvent::OutputTextDelta(text.clone())))
+            .await;
+    }
+}
+
+async fn append_reasoning_text(
+    tx_event: &mpsc::Sender<Result<ResponseEvent>>,
+    reasoning_item: &mut Option<ResponseItem>,
+    text: String,
+) {
+    if reasoning_item.is_none() {
+        let item = ResponseItem::Reasoning {
+            id: String::new(),
+            summary: Vec::new(),
+            content: Some(vec![]),
+            encrypted_content: None,
+        };
+        *reasoning_item = Some(item.clone());
+        let _ = tx_event
+            .send(Ok(ResponseEvent::OutputItemAdded(item)))
+            .await;
+    }
+
+    if let Some(ResponseItem::Reasoning {
+        content: Some(content),
+        ..
+    }) = reasoning_item
+    {
+        content.push(ReasoningItemContent::ReasoningText { text: text.clone() });
+
+        let _ = tx_event
+            .send(Ok(ResponseEvent::ReasoningContentDelta(text.clone())))
+            .await;
+    }
+}
 /// Lightweight SSE processor for the Chat Completions streaming format. The
 /// output is mapped onto Codex's internal [`ResponseEvent`] so that the rest
 /// of the pipeline can stay agnostic of the underlying wire format.
@@ -450,8 +505,8 @@ async fn process_chat_sse<S>(
     }
 
     let mut fn_call_state = FunctionCallState::default();
-    let mut assistant_text = String::new();
+    let mut assistant_item: Option<ResponseItem> = None;
-    let mut reasoning_text = String::new();
+    let mut reasoning_item: Option<ResponseItem> = None;
 
     loop {
         let start = std::time::Instant::now();
@@ -492,26 +547,11 @@ async fn process_chat_sse<S>(
         if sse.data.trim() == "[DONE]" {
             // Emit any finalized items before closing so downstream consumers receive
             // terminal events for both assistant content and raw reasoning.
-            if !assistant_text.is_empty() {
+            if let Some(item) = assistant_item {
-                let item = ResponseItem::Message {
-                    role: "assistant".to_string(),
-                    content: vec![ContentItem::OutputText {
-                        text: std::mem::take(&mut assistant_text),
-                    }],
-                    id: None,
-                };
                 let _ = tx_event.send(Ok(ResponseEvent::OutputItemDone(item))).await;
             }
 
-            if !reasoning_text.is_empty() {
+            if let Some(item) = reasoning_item {
-                let item = ResponseItem::Reasoning {
-                    id: String::new(),
-                    summary: Vec::new(),
-                    content: Some(vec![ReasoningItemContent::ReasoningText {
-                        text: std::mem::take(&mut reasoning_text),
-                    }]),
-                    encrypted_content: None,
-                };
                 let _ = tx_event.send(Ok(ResponseEvent::OutputItemDone(item))).await;
             }
 
@@ -541,10 +581,7 @@ async fn process_chat_sse<S>(
                 .and_then(|c| c.as_str())
                 && !content.is_empty()
             {
-                assistant_text.push_str(content);
+                append_assistant_text(&tx_event, &mut assistant_item, content.to_string()).await;
-                let _ = tx_event
-                    .send(Ok(ResponseEvent::OutputTextDelta(content.to_string())))
-                    .await;
             }
 
             // Forward any reasoning/thinking deltas if present.
@@ -574,10 +611,7 @@ async fn process_chat_sse<S>(
 
                 if let Some(reasoning) = maybe_text {
                     // Accumulate so we can emit a terminal Reasoning item at the end.
-                    reasoning_text.push_str(&reasoning);
+                    append_reasoning_text(&tx_event, &mut reasoning_item, reasoning).await;
-                    let _ = tx_event
-                        .send(Ok(ResponseEvent::ReasoningContentDelta(reasoning)))
-                        .await;
                 }
             }
 
@@ -587,10 +621,7 @@ async fn process_chat_sse<S>(
                 // Accept either a plain string or an object with { text | content }
                 if let Some(s) = message_reasoning.as_str() {
                     if !s.is_empty() {
-                        reasoning_text.push_str(s);
+                        append_reasoning_text(&tx_event, &mut reasoning_item, s.to_string()).await;
-                        let _ = tx_event
-                            .send(Ok(ResponseEvent::ReasoningContentDelta(s.to_string())))
-                            .await;
                     }
                 } else if let Some(obj) = message_reasoning.as_object()
                     && let Some(s) = obj
@@ -599,10 +630,7 @@ async fn process_chat_sse<S>(
                         .or_else(|| obj.get("content").and_then(|v| v.as_str()))
                     && !s.is_empty()
                 {
-                    reasoning_text.push_str(s);
+                    append_reasoning_text(&tx_event, &mut reasoning_item, s.to_string()).await;
-                    let _ = tx_event
-                        .send(Ok(ResponseEvent::ReasoningContentDelta(s.to_string())))
-                        .await;
                 }
             }
 
@@ -640,15 +668,7 @@ async fn process_chat_sse<S>(
                     "tool_calls" if fn_call_state.active => {
                         // First, flush the terminal raw reasoning so UIs can finalize
                         // the reasoning stream before any exec/tool events begin.
-                        if !reasoning_text.is_empty() {
+                        if let Some(item) = reasoning_item.take() {
-                            let item = ResponseItem::Reasoning {
-                                id: String::new(),
-                                summary: Vec::new(),
-                                content: Some(vec![ReasoningItemContent::ReasoningText {
-                                    text: std::mem::take(&mut reasoning_text),
-                                }]),
-                                encrypted_content: None,
-                            };
                             let _ = tx_event.send(Ok(ResponseEvent::OutputItemDone(item))).await;
                         }
 
@@ -665,26 +685,11 @@ async fn process_chat_sse<S>(
                     "stop" => {
                         // Regular turn without tool-call. Emit the final assistant message
                         // as a single OutputItemDone so non-delta consumers see the result.
-                        if !assistant_text.is_empty() {
+                        if let Some(item) = assistant_item.take() {
-                            let item = ResponseItem::Message {
-                                role: "assistant".to_string(),
-                                content: vec![ContentItem::OutputText {
-                                    text: std::mem::take(&mut assistant_text),
-                                }],
-                                id: None,
-                            };
                             let _ = tx_event.send(Ok(ResponseEvent::OutputItemDone(item))).await;
                         }
                         // Also emit a terminal Reasoning item so UIs can finalize raw reasoning.
-                        if !reasoning_text.is_empty() {
+                        if let Some(item) = reasoning_item.take() {
-                            let item = ResponseItem::Reasoning {
-                                id: String::new(),
-                                summary: Vec::new(),
-                                content: Some(vec![ReasoningItemContent::ReasoningText {
-                                    text: std::mem::take(&mut reasoning_text),
-                                }]),
-                                encrypted_content: None,
-                            };
                             let _ = tx_event.send(Ok(ResponseEvent::OutputItemDone(item))).await;
                         }
                     }
@@ -903,8 +908,8 @@ where
                 Poll::Ready(Some(Ok(ResponseEvent::ReasoningSummaryPartAdded))) => {
                     continue;
                 }
-                Poll::Ready(Some(Ok(ResponseEvent::WebSearchCallBegin { call_id }))) => {
+                Poll::Ready(Some(Ok(ResponseEvent::OutputItemAdded(item)))) => {
-                    return Poll::Ready(Some(Ok(ResponseEvent::WebSearchCallBegin { call_id })));
+                    return Poll::Ready(Some(Ok(ResponseEvent::OutputItemAdded(item))));
                 }
             }
         }

codex-rs/core/src/client.rs

@@ -869,21 +869,15 @@ async fn process_sse<S>(
             | "response.in_progress"
             | "response.output_text.done" => {}
             "response.output_item.added" => {
-                if let Some(item) = event.item.as_ref() {
+                let Some(item_val) = event.item else { continue };
-                    // Detect web_search_call begin and forward a synthetic event upstream.
+                let Ok(item) = serde_json::from_value::<ResponseItem>(item_val) else {
-                    if let Some(ty) = item.get("type").and_then(|v| v.as_str())
+                    debug!("failed to parse ResponseItem from output_item.done");
-                        && ty == "web_search_call"
+                    continue;
-                    {
+                };
-                        let call_id = item
+
-                            .get("id")
+                let event = ResponseEvent::OutputItemAdded(item);
-                            .and_then(|v| v.as_str())
+                if tx_event.send(Ok(event)).await.is_err() {
-                            .unwrap_or("")
+                    return;
-                            .to_string();
-                        let ev = ResponseEvent::WebSearchCallBegin { call_id };
-                        if tx_event.send(Ok(ev)).await.is_err() {
-                            return;
-                        }
-                    }
                 }
             }
             "response.reasoning_summary_part.added" => {

codex-rs/core/src/client_common.rs

@@ -197,6 +197,7 @@ fn strip_total_output_header(output: &str) -> Option<&str> {
 pub enum ResponseEvent {
     Created,
     OutputItemDone(ResponseItem),
+    OutputItemAdded(ResponseItem),
     Completed {
         response_id: String,
         token_usage: Option<TokenUsage>,
@@ -205,9 +206,6 @@ pub enum ResponseEvent {
     ReasoningSummaryDelta(String),
     ReasoningContentDelta(String),
     ReasoningSummaryPartAdded,
-    WebSearchCallBegin {
-        call_id: String,
-    },
     RateLimits(RateLimitSnapshot),
 }
 

codex-rs/core/src/codex.rs

@@ -15,11 +15,13 @@ use crate::parse_turn_item;
 use crate::response_processing::process_items;
 use crate::terminal;
 use crate::user_notification::UserNotifier;
+use crate::util::error_or_panic;
 use async_channel::Receiver;
 use async_channel::Sender;
 use codex_protocol::ConversationId;
 use codex_protocol::items::TurnItem;
 use codex_protocol::protocol::FileChange;
+use codex_protocol::protocol::HasLegacyEvent;
 use codex_protocol::protocol::ItemCompletedEvent;
 use codex_protocol::protocol::ItemStartedEvent;
 use codex_protocol::protocol::RawResponseItemEvent;
@@ -69,9 +71,7 @@ use crate::mcp_connection_manager::McpConnectionManager;
 use crate::model_family::find_family_for_model;
 use crate::openai_model_info::get_model_info;
 use crate::project_doc::get_user_instructions;
-use crate::protocol::AgentMessageDeltaEvent;
+use crate::protocol::AgentMessageContentDeltaEvent;
-use crate::protocol::AgentReasoningDeltaEvent;
-use crate::protocol::AgentReasoningRawContentDeltaEvent;
 use crate::protocol::AgentReasoningSectionBreakEvent;
 use crate::protocol::ApplyPatchApprovalRequestEvent;
 use crate::protocol::AskForApproval;
@@ -83,6 +83,8 @@ use crate::protocol::EventMsg;
 use crate::protocol::ExecApprovalRequestEvent;
 use crate::protocol::Op;
 use crate::protocol::RateLimitSnapshot;
+use crate::protocol::ReasoningContentDeltaEvent;
+use crate::protocol::ReasoningRawContentDeltaEvent;
 use crate::protocol::ReviewDecision;
 use crate::protocol::SandboxCommandAssessment;
 use crate::protocol::SandboxPolicy;
@@ -92,7 +94,6 @@ use crate::protocol::Submission;
 use crate::protocol::TokenCountEvent;
 use crate::protocol::TokenUsage;
 use crate::protocol::TurnDiffEvent;
-use crate::protocol::WebSearchBeginEvent;
 use crate::rollout::RolloutRecorder;
 use crate::rollout::RolloutRecorderParams;
 use crate::shell;
@@ -729,11 +730,21 @@ impl Session {
 
     /// Persist the event to rollout and send it to clients.
     pub(crate) async fn send_event(&self, turn_context: &TurnContext, msg: EventMsg) {
+        let legacy_source = msg.clone();
         let event = Event {
             id: turn_context.sub_id.clone(),
             msg,
         };
         self.send_event_raw(event).await;
+
+        let show_raw_agent_reasoning = self.show_raw_agent_reasoning();
+        for legacy in legacy_source.as_legacy_events(show_raw_agent_reasoning) {
+            let legacy_event = Event {
+                id: turn_context.sub_id.clone(),
+                msg: legacy,
+            };
+            self.send_event_raw(legacy_event).await;
+        }
     }
 
     pub(crate) async fn send_event_raw(&self, event: Event) {
@@ -757,45 +768,16 @@ impl Session {
         .await;
     }
 
-    async fn emit_turn_item_completed(
+    async fn emit_turn_item_completed(&self, turn_context: &TurnContext, item: TurnItem) {
-        &self,
-        turn_context: &TurnContext,
-        item: TurnItem,
-        emit_raw_agent_reasoning: bool,
-    ) {
         self.send_event(
             turn_context,
             EventMsg::ItemCompleted(ItemCompletedEvent {
                 thread_id: self.conversation_id,
                 turn_id: turn_context.sub_id.clone(),
-                item: item.clone(),
+                item,
             }),
         )
         .await;
-        self.emit_turn_item_legacy_events(turn_context, &item, emit_raw_agent_reasoning)
-            .await;
-    }
-
-    async fn emit_turn_item_started_completed(
-        &self,
-        turn_context: &TurnContext,
-        item: TurnItem,
-        emit_raw_agent_reasoning: bool,
-    ) {
-        self.emit_turn_item_started(turn_context, &item).await;
-        self.emit_turn_item_completed(turn_context, item, emit_raw_agent_reasoning)
-            .await;
-    }
-
-    async fn emit_turn_item_legacy_events(
-        &self,
-        turn_context: &TurnContext,
-        item: &TurnItem,
-        emit_raw_agent_reasoning: bool,
-    ) {
-        for event in item.as_legacy_events(emit_raw_agent_reasoning) {
-            self.send_event(turn_context, event).await;
-        }
     }
 
     pub(crate) async fn assess_sandbox_command(
@@ -1092,8 +1074,8 @@ impl Session {
         let turn_item = parse_turn_item(&response_item);
 
         if let Some(item @ TurnItem::UserMessage(_)) = turn_item {
-            self.emit_turn_item_started_completed(turn_context, item, false)
+            self.emit_turn_item_started(turn_context, &item).await;
-                .await;
+            self.emit_turn_item_completed(turn_context, item).await;
         }
     }
 
@@ -1910,14 +1892,13 @@ async fn run_turn(
             Err(CodexErr::EnvVar(var)) => return Err(CodexErr::EnvVar(var)),
             Err(e @ CodexErr::Fatal(_)) => return Err(e),
             Err(e @ CodexErr::ContextWindowExceeded) => {
-                sess.set_total_tokens_full(turn_context.as_ref()).await;
+                sess.set_total_tokens_full(&turn_context).await;
                 return Err(e);
             }
             Err(CodexErr::UsageLimitReached(e)) => {
                 let rate_limits = e.rate_limits.clone();
                 if let Some(rate_limits) = rate_limits {
-                    sess.update_rate_limits(turn_context.as_ref(), rate_limits)
+                    sess.update_rate_limits(&turn_context, rate_limits).await;
-                        .await;
                 }
                 return Err(CodexErr::UsageLimitReached(e));
             }
@@ -1939,8 +1920,8 @@ async fn run_turn(
                     // user understands what is happening instead of staring
                     // at a seemingly frozen screen.
                     sess.notify_stream_error(
-                        turn_context.as_ref(),
+                        &turn_context,
-                        format!("Reconnecting... {retries}/{max_retries}"),
+                        format!("Re-connecting... {retries}/{max_retries}"),
                     )
                     .await;
 
@@ -2004,6 +1985,8 @@ async fn try_run_turn(
     let mut output: FuturesOrdered<BoxFuture<CodexResult<ProcessedResponseItem>>> =
         FuturesOrdered::new();
 
+    let mut active_item: Option<TurnItem> = None;
+
     loop {
         // Poll the next item from the model stream. We must inspect *both* Ok and Err
         // cases so that transient stream failures (e.g., dropped SSE connection before
@@ -2035,6 +2018,7 @@ async fn try_run_turn(
         match event {
             ResponseEvent::Created => {}
             ResponseEvent::OutputItemDone(item) => {
+                let previously_active_item = active_item.take();
                 match ToolRouter::build_tool_call(sess.as_ref(), item.clone()) {
                     Ok(Some(call)) => {
                         let payload_preview = call.payload.log_payload().into_owned();
@@ -2054,14 +2038,19 @@ async fn try_run_turn(
                         );
                     }
                     Ok(None) => {
-                        let response = handle_non_tool_response_item(
+                        if let Some(turn_item) = handle_non_tool_response_item(&item).await {
-                            sess.as_ref(),
+                            if previously_active_item.is_none() {
-                            Arc::clone(&turn_context),
+                                sess.emit_turn_item_started(&turn_context, &turn_item).await;
-                            item.clone(),
+                            }
-                            sess.show_raw_agent_reasoning(),
+
-                        )
+                            sess.emit_turn_item_completed(&turn_context, turn_item)
-                        .await?;
+                                .await;
-                        add_completed(ProcessedResponseItem { item, response });
+                        }
+
+                        add_completed(ProcessedResponseItem {
+                            item,
+                            response: None,
+                        });
                     }
                     Err(FunctionCallError::MissingLocalShellCallId) => {
                         let msg = "LocalShellCall without call_id or id";
@@ -2102,26 +2091,24 @@ async fn try_run_turn(
                     }
                 }
             }
-            ResponseEvent::WebSearchCallBegin { call_id } => {
+            ResponseEvent::OutputItemAdded(item) => {
-                let _ = sess
+                if let Some(turn_item) = handle_non_tool_response_item(&item).await {
-                    .tx_event
+                    let tracked_item = turn_item.clone();
-                    .send(Event {
+                    sess.emit_turn_item_started(&turn_context, &turn_item).await;
-                        id: turn_context.sub_id.clone(),
+
-                        msg: EventMsg::WebSearchBegin(WebSearchBeginEvent { call_id }),
+                    active_item = Some(tracked_item);
-                    })
+                }
-                    .await;
             }
             ResponseEvent::RateLimits(snapshot) => {
                 // Update internal state with latest rate limits, but defer sending until
                 // token usage is available to avoid duplicate TokenCount events.
-                sess.update_rate_limits(turn_context.as_ref(), snapshot)
+                sess.update_rate_limits(&turn_context, snapshot).await;
-                    .await;
             }
             ResponseEvent::Completed {
                 response_id: _,
                 token_usage,
             } => {
-                sess.update_token_usage_info(turn_context.as_ref(), token_usage.as_ref())
+                sess.update_token_usage_info(&turn_context, token_usage.as_ref())
                     .await;
                 let processed_items = output.try_collect().await?;
                 let unified_diff = {
@@ -2141,12 +2128,34 @@ async fn try_run_turn(
                 return Ok(result);
             }
             ResponseEvent::OutputTextDelta(delta) => {
-                let event = EventMsg::AgentMessageDelta(AgentMessageDeltaEvent { delta });
+                // In review child threads, suppress assistant text deltas; the
-                sess.send_event(&turn_context, event).await;
+                // UI will show a selection popup from the final ReviewOutput.
+                if let Some(active) = active_item.as_ref() {
+                    let event = AgentMessageContentDeltaEvent {
+                        thread_id: sess.conversation_id.to_string(),
+                        turn_id: turn_context.sub_id.clone(),
+                        item_id: active.id(),
+                        delta: delta.clone(),
+                    };
+                    sess.send_event(&turn_context, EventMsg::AgentMessageContentDelta(event))
+                        .await;
+                } else {
+                    error_or_panic("ReasoningSummaryDelta without active item".to_string());
+                }
             }
             ResponseEvent::ReasoningSummaryDelta(delta) => {
-                let event = EventMsg::AgentReasoningDelta(AgentReasoningDeltaEvent { delta });
+                if let Some(active) = active_item.as_ref() {
-                sess.send_event(&turn_context, event).await;
+                    let event = ReasoningContentDeltaEvent {
+                        thread_id: sess.conversation_id.to_string(),
+                        turn_id: turn_context.sub_id.clone(),
+                        item_id: active.id(),
+                        delta: delta.clone(),
+                    };
+                    sess.send_event(&turn_context, EventMsg::ReasoningContentDelta(event))
+                        .await;
+                } else {
+                    error_or_panic("ReasoningSummaryDelta without active item".to_string());
+                }
             }
             ResponseEvent::ReasoningSummaryPartAdded => {
                 let event =
@@ -2154,46 +2163,36 @@ async fn try_run_turn(
                 sess.send_event(&turn_context, event).await;
             }
             ResponseEvent::ReasoningContentDelta(delta) => {
-                if sess.show_raw_agent_reasoning() {
+                if let Some(active) = active_item.as_ref() {
-                    let event = EventMsg::AgentReasoningRawContentDelta(
+                    let event = ReasoningRawContentDeltaEvent {
-                        AgentReasoningRawContentDeltaEvent { delta },
+                        thread_id: sess.conversation_id.to_string(),
-                    );
+                        turn_id: turn_context.sub_id.clone(),
-                    sess.send_event(&turn_context, event).await;
+                        item_id: active.id(),
+                        delta: delta.clone(),
+                    };
+                    sess.send_event(&turn_context, EventMsg::ReasoningRawContentDelta(event))
+                        .await;
+                } else {
+                    error_or_panic("ReasoningRawContentDelta without active item".to_string());
                 }
             }
         }
     }
 }
 
-async fn handle_non_tool_response_item(
+async fn handle_non_tool_response_item(item: &ResponseItem) -> Option<TurnItem> {
-    sess: &Session,
-    turn_context: Arc<TurnContext>,
-    item: ResponseItem,
-    show_raw_agent_reasoning: bool,
-) -> CodexResult<Option<ResponseInputItem>> {
     debug!(?item, "Output item");
 
-    match &item {
+    match item {
         ResponseItem::Message { .. }
         | ResponseItem::Reasoning { .. }
-        | ResponseItem::WebSearchCall { .. } => {
+        | ResponseItem::WebSearchCall { .. } => parse_turn_item(item),
-            let turn_item = parse_turn_item(&item);
-            if let Some(turn_item) = turn_item {
-                sess.emit_turn_item_started_completed(
-                    turn_context.as_ref(),
-                    turn_item,
-                    show_raw_agent_reasoning,
-                )
-                .await;
-            }
-        }
         ResponseItem::FunctionCallOutput { .. } | ResponseItem::CustomToolCallOutput { .. } => {
             debug!("unexpected tool output from stream");
+            None
         }
-        _ => {}
+        _ => None,
     }
-
-    Ok(None)
 }
 
 pub(super) fn get_last_assistant_message_from_turn(responses: &[ResponseItem]) -> Option<String> {

codex-rs/core/src/conversation_history.rs

@@ -1,12 +1,13 @@
 use codex_protocol::models::FunctionCallOutputContentItem;
 use codex_protocol::models::FunctionCallOutputPayload;
 use codex_protocol::models::ResponseItem;
+
+use crate::util::error_or_panic;
 use codex_protocol::protocol::TokenUsage;
 use codex_protocol::protocol::TokenUsageInfo;
 use codex_utils_string::take_bytes_at_char_boundary;
 use codex_utils_string::take_last_bytes_at_char_boundary;
 use std::ops::Deref;
-use tracing::error;
 
 // Model-formatting limits: clients get full streams; only content sent to the model is truncated.
 pub(crate) const MODEL_FORMAT_MAX_BYTES: usize = 10 * 1024; // 10 KiB
@@ -501,15 +502,6 @@ fn truncate_formatted_exec_output(content: &str, total_lines: usize) -> String {
     result
 }
 
-#[inline]
-fn error_or_panic(message: String) {
-    if cfg!(debug_assertions) || env!("CARGO_PKG_VERSION").contains("alpha") {
-        panic!("{message}");
-    } else {
-        error!("{message}");
-    }
-}
-
 /// Anything that is not a system message or "reasoning" message is considered
 /// an API message.
 fn is_api_message(message: &ResponseItem) -> bool {

codex-rs/core/src/event_mapping.rs

@@ -11,6 +11,7 @@ use codex_protocol::models::ResponseItem;
 use codex_protocol::models::WebSearchAction;
 use codex_protocol::user_input::UserInput;
 use tracing::warn;
+use uuid::Uuid;
 
 fn is_session_prefix(text: &str) -> bool {
     let trimmed = text.trim_start();
@@ -46,7 +47,7 @@ fn parse_user_message(message: &[ContentItem]) -> Option<UserMessageItem> {
     Some(UserMessageItem::new(&content))
 }
 
-fn parse_agent_message(message: &[ContentItem]) -> AgentMessageItem {
+fn parse_agent_message(id: Option<&String>, message: &[ContentItem]) -> AgentMessageItem {
     let mut content: Vec<AgentMessageContent> = Vec::new();
     for content_item in message.iter() {
         match content_item {
@@ -61,14 +62,18 @@ fn parse_agent_message(message: &[ContentItem]) -> AgentMessageItem {
             }
         }
     }
-    AgentMessageItem::new(&content)
+    let id = id.cloned().unwrap_or_else(|| Uuid::new_v4().to_string());
+    AgentMessageItem { id, content }
 }
 
 pub fn parse_turn_item(item: &ResponseItem) -> Option<TurnItem> {
     match item {
-        ResponseItem::Message { role, content, .. } => match role.as_str() {
+        ResponseItem::Message { role, content, id } => match role.as_str() {
             "user" => parse_user_message(content).map(TurnItem::UserMessage),
-            "assistant" => Some(TurnItem::AgentMessage(parse_agent_message(content))),
+            "assistant" => Some(TurnItem::AgentMessage(parse_agent_message(
+                id.as_ref(),
+                content,
+            ))),
             "system" => None,
             _ => None,
         },

codex-rs/core/src/rollout/policy.rs

@@ -77,6 +77,9 @@ pub(crate) fn should_persist_event_msg(ev: &EventMsg) -> bool {
         | EventMsg::ViewImageToolCall(_)
         | EventMsg::DeprecationNotice(_)
         | EventMsg::ItemStarted(_)
-        | EventMsg::ItemCompleted(_) => false,
+        | EventMsg::ItemCompleted(_)
+        | EventMsg::AgentMessageContentDelta(_)
+        | EventMsg::ReasoningContentDelta(_)
+        | EventMsg::ReasoningRawContentDelta(_) => false,
     }
 }

codex-rs/core/src/tasks/review.rs

@@ -1,11 +1,13 @@
 use std::sync::Arc;
 
 use async_trait::async_trait;
+use codex_protocol::items::TurnItem;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::ResponseItem;
 use codex_protocol::protocol::Event;
 use codex_protocol::protocol::EventMsg;
 use codex_protocol::protocol::ExitedReviewModeEvent;
+use codex_protocol::protocol::ItemCompletedEvent;
 use codex_protocol::protocol::ReviewOutputEvent;
 use tokio_util::sync::CancellationToken;
 
@@ -109,6 +111,13 @@ async fn process_review_events(
                 }
                 prev_agent_message = Some(event);
             }
+            // Suppress ItemCompleted for assistant messages: forwarding it would
+            // trigger legacy AgentMessage via as_legacy_events(), which this
+            // review flow intentionally hides in favor of structured output.
+            EventMsg::ItemCompleted(ItemCompletedEvent {
+                item: TurnItem::AgentMessage(_),
+                ..
+            }) => {}
             EventMsg::TaskComplete(task_complete) => {
                 // Parse review output from the last agent message (if present).
                 let out = task_complete

codex-rs/core/src/util.rs

@@ -2,6 +2,7 @@ use std::time::Duration;
 
 use rand::Rng;
 use tracing::debug;
+use tracing::error;
 
 const INITIAL_DELAY_MS: u64 = 200;
 const BACKOFF_FACTOR: f64 = 2.0;
@@ -13,6 +14,14 @@ pub(crate) fn backoff(attempt: u64) -> Duration {
     Duration::from_millis((base as f64 * jitter) as u64)
 }
 
+pub(crate) fn error_or_panic(message: String) {
+    if cfg!(debug_assertions) || env!("CARGO_PKG_VERSION").contains("alpha") {
+        panic!("{message}");
+    } else {
+        error!("{message}");
+    }
+}
+
 pub(crate) fn try_parse_error_message(text: &str) -> String {
     debug!("Parsing server error response: {}", text);
     let json = serde_json::from_str::<serde_json::Value>(text).unwrap_or_default();

codex-rs/core/tests/chat_completions_sse.rs

@@ -171,19 +171,24 @@ async fn streams_text_without_reasoning() {
     );
 
     let events = run_stream(sse).await;
-    assert_eq!(events.len(), 3, "unexpected events: {events:?}");
+    assert_eq!(events.len(), 4, "unexpected events: {events:?}");
 
     match &events[0] {
+        ResponseEvent::OutputItemAdded(ResponseItem::Message { .. }) => {}
+        other => panic!("expected initial assistant item, got {other:?}"),
+    }
+
+    match &events[1] {
         ResponseEvent::OutputTextDelta(text) => assert_eq!(text, "hi"),
         other => panic!("expected text delta, got {other:?}"),
     }
 
-    match &events[1] {
+    match &events[2] {
         ResponseEvent::OutputItemDone(item) => assert_message(item, "hi"),
         other => panic!("expected terminal message, got {other:?}"),
     }
 
-    assert_matches!(events[2], ResponseEvent::Completed { .. });
+    assert_matches!(events[3], ResponseEvent::Completed { .. });
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
@@ -202,29 +207,39 @@ async fn streams_reasoning_from_string_delta() {
     );
 
     let events = run_stream(sse).await;
-    assert_eq!(events.len(), 5, "unexpected events: {events:?}");
+    assert_eq!(events.len(), 7, "unexpected events: {events:?}");
 
     match &events[0] {
+        ResponseEvent::OutputItemAdded(ResponseItem::Reasoning { .. }) => {}
+        other => panic!("expected initial reasoning item, got {other:?}"),
+    }
+
+    match &events[1] {
         ResponseEvent::ReasoningContentDelta(text) => assert_eq!(text, "think1"),
         other => panic!("expected reasoning delta, got {other:?}"),
     }
 
-    match &events[1] {
+    match &events[2] {
+        ResponseEvent::OutputItemAdded(ResponseItem::Message { .. }) => {}
+        other => panic!("expected initial message item, got {other:?}"),
+    }
+
+    match &events[3] {
         ResponseEvent::OutputTextDelta(text) => assert_eq!(text, "ok"),
         other => panic!("expected text delta, got {other:?}"),
     }
 
-    match &events[2] {
+    match &events[4] {
         ResponseEvent::OutputItemDone(item) => assert_reasoning(item, "think1"),
-        other => panic!("expected reasoning item, got {other:?}"),
+        other => panic!("expected terminal reasoning, got {other:?}"),
     }
 
-    match &events[3] {
+    match &events[5] {
         ResponseEvent::OutputItemDone(item) => assert_message(item, "ok"),
-        other => panic!("expected message item, got {other:?}"),
+        other => panic!("expected terminal message, got {other:?}"),
     }
 
-    assert_matches!(events[4], ResponseEvent::Completed { .. });
+    assert_matches!(events[6], ResponseEvent::Completed { .. });
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
@@ -244,34 +259,44 @@ async fn streams_reasoning_from_object_delta() {
     );
 
     let events = run_stream(sse).await;
-    assert_eq!(events.len(), 6, "unexpected events: {events:?}");
+    assert_eq!(events.len(), 8, "unexpected events: {events:?}");
 
     match &events[0] {
+        ResponseEvent::OutputItemAdded(ResponseItem::Reasoning { .. }) => {}
+        other => panic!("expected initial reasoning item, got {other:?}"),
+    }
+
+    match &events[1] {
         ResponseEvent::ReasoningContentDelta(text) => assert_eq!(text, "partA"),
         other => panic!("expected reasoning delta, got {other:?}"),
     }
 
-    match &events[1] {
+    match &events[2] {
         ResponseEvent::ReasoningContentDelta(text) => assert_eq!(text, "partB"),
         other => panic!("expected reasoning delta, got {other:?}"),
     }
 
-    match &events[2] {
+    match &events[3] {
+        ResponseEvent::OutputItemAdded(ResponseItem::Message { .. }) => {}
+        other => panic!("expected initial message item, got {other:?}"),
+    }
+
+    match &events[4] {
         ResponseEvent::OutputTextDelta(text) => assert_eq!(text, "answer"),
         other => panic!("expected text delta, got {other:?}"),
     }
 
-    match &events[3] {
+    match &events[5] {
         ResponseEvent::OutputItemDone(item) => assert_reasoning(item, "partApartB"),
-        other => panic!("expected reasoning item, got {other:?}"),
+        other => panic!("expected terminal reasoning, got {other:?}"),
     }
 
-    match &events[4] {
+    match &events[6] {
         ResponseEvent::OutputItemDone(item) => assert_message(item, "answer"),
-        other => panic!("expected message item, got {other:?}"),
+        other => panic!("expected terminal message, got {other:?}"),
     }
 
-    assert_matches!(events[5], ResponseEvent::Completed { .. });
+    assert_matches!(events[7], ResponseEvent::Completed { .. });
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
@@ -286,19 +311,24 @@ async fn streams_reasoning_from_final_message() {
     let sse = "data: {\"choices\":[{\"message\":{\"reasoning\":\"final-cot\"},\"finish_reason\":\"stop\"}]}\n\n";
 
     let events = run_stream(sse).await;
-    assert_eq!(events.len(), 3, "unexpected events: {events:?}");
+    assert_eq!(events.len(), 4, "unexpected events: {events:?}");
 
     match &events[0] {
+        ResponseEvent::OutputItemAdded(ResponseItem::Reasoning { .. }) => {}
+        other => panic!("expected initial reasoning item, got {other:?}"),
+    }
+
+    match &events[1] {
         ResponseEvent::ReasoningContentDelta(text) => assert_eq!(text, "final-cot"),
         other => panic!("expected reasoning delta, got {other:?}"),
     }
 
-    match &events[1] {
+    match &events[2] {
         ResponseEvent::OutputItemDone(item) => assert_reasoning(item, "final-cot"),
         other => panic!("expected reasoning item, got {other:?}"),
     }
 
-    assert_matches!(events[2], ResponseEvent::Completed { .. });
+    assert_matches!(events[3], ResponseEvent::Completed { .. });
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
@@ -316,19 +346,24 @@ async fn streams_reasoning_before_tool_call() {
     );
 
     let events = run_stream(sse).await;
-    assert_eq!(events.len(), 4, "unexpected events: {events:?}");
+    assert_eq!(events.len(), 5, "unexpected events: {events:?}");
 
     match &events[0] {
+        ResponseEvent::OutputItemAdded(ResponseItem::Reasoning { .. }) => {}
+        other => panic!("expected initial reasoning item, got {other:?}"),
+    }
+
+    match &events[1] {
         ResponseEvent::ReasoningContentDelta(text) => assert_eq!(text, "pre-tool"),
         other => panic!("expected reasoning delta, got {other:?}"),
     }
 
-    match &events[1] {
+    match &events[2] {
         ResponseEvent::OutputItemDone(item) => assert_reasoning(item, "pre-tool"),
         other => panic!("expected reasoning item, got {other:?}"),
     }
 
-    match &events[2] {
+    match &events[3] {
         ResponseEvent::OutputItemDone(ResponseItem::FunctionCall {
             name,
             arguments,
@@ -342,7 +377,7 @@ async fn streams_reasoning_before_tool_call() {
         other => panic!("expected function call, got {other:?}"),
     }
 
-    assert_matches!(events[3], ResponseEvent::Completed { .. });
+    assert_matches!(events[4], ResponseEvent::Completed { .. });
 }
 
 #[tokio::test]

codex-rs/core/tests/common/responses.rs

@@ -217,6 +217,25 @@ pub fn ev_assistant_message(id: &str, text: &str) -> Value {
     })
 }
 
+pub fn ev_message_item_added(id: &str, text: &str) -> Value {
+    serde_json::json!({
+        "type": "response.output_item.added",
+        "item": {
+            "type": "message",
+            "role": "assistant",
+            "id": id,
+            "content": [{"type": "output_text", "text": text}]
+        }
+    })
+}
+
+pub fn ev_output_text_delta(delta: &str) -> Value {
+    serde_json::json!({
+        "type": "response.output_text.delta",
+        "delta": delta,
+    })
+}
+
 pub fn ev_reasoning_item(id: &str, summary: &[&str], raw_content: &[&str]) -> Value {
     let summary_entries: Vec<Value> = summary
         .iter()
@@ -243,6 +262,36 @@ pub fn ev_reasoning_item(id: &str, summary: &[&str], raw_content: &[&str]) -> Va
     event
 }
 
+pub fn ev_reasoning_item_added(id: &str, summary: &[&str]) -> Value {
+    let summary_entries: Vec<Value> = summary
+        .iter()
+        .map(|text| serde_json::json!({"type": "summary_text", "text": text}))
+        .collect();
+
+    serde_json::json!({
+        "type": "response.output_item.added",
+        "item": {
+            "type": "reasoning",
+            "id": id,
+            "summary": summary_entries,
+        }
+    })
+}
+
+pub fn ev_reasoning_summary_text_delta(delta: &str) -> Value {
+    serde_json::json!({
+        "type": "response.reasoning_summary_text.delta",
+        "delta": delta,
+    })
+}
+
+pub fn ev_reasoning_text_delta(delta: &str) -> Value {
+    serde_json::json!({
+        "type": "response.reasoning_text.delta",
+        "delta": delta,
+    })
+}
+
 pub fn ev_web_search_call_added(id: &str, status: &str, query: &str) -> Value {
     serde_json::json!({
         "type": "response.output_item.added",

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

@@ -1262,6 +1262,10 @@ async fn history_dedupes_streamed_and_final_messages_across_turns() {
     // Build a small SSE stream with deltas and a final assistant message.
     // We emit the same body for all 3 turns; ids vary but are unused by assertions.
     let sse_raw = r##"[
+        {"type":"response.output_item.added", "item":{
+            "type":"message", "role":"assistant",
+            "content":[{"type":"output_text","text":""}]
+        }},
         {"type":"response.output_text.delta", "delta":"Hey "},
         {"type":"response.output_text.delta", "delta":"there"},
         {"type":"response.output_text.delta", "delta":"!\n"},

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(())
+}

codex-rs/exec/src/event_processor_with_human_output.rs

@@ -519,6 +519,9 @@ impl EventProcessor for EventProcessorWithHumanOutput {
             | EventMsg::AgentReasoningRawContentDelta(_)
             | EventMsg::ItemStarted(_)
             | EventMsg::ItemCompleted(_)
+            | EventMsg::AgentMessageContentDelta(_)
+            | EventMsg::ReasoningContentDelta(_)
+            | EventMsg::ReasoningRawContentDelta(_)
             | EventMsg::UndoCompleted(_)
             | EventMsg::UndoStarted(_) => {}
         }

codex-rs/mcp-server/src/codex_tool_runner.rs

@@ -288,6 +288,9 @@ async fn run_codex_tool_session_inner(
                     | EventMsg::EnteredReviewMode(_)
                     | EventMsg::ItemStarted(_)
                     | EventMsg::ItemCompleted(_)
+                    | EventMsg::AgentMessageContentDelta(_)
+                    | EventMsg::ReasoningContentDelta(_)
+                    | EventMsg::ReasoningRawContentDelta(_)
                     | EventMsg::UndoStarted(_)
                     | EventMsg::UndoCompleted(_)
                     | EventMsg::ExitedReviewMode(_)

codex-rs/protocol/src/protocol.rs

@@ -546,6 +546,10 @@ pub enum EventMsg {
 
     ItemStarted(ItemStartedEvent),
     ItemCompleted(ItemCompletedEvent),
+
+    AgentMessageContentDelta(AgentMessageContentDeltaEvent),
+    ReasoningContentDelta(ReasoningContentDeltaEvent),
+    ReasoningRawContentDelta(ReasoningRawContentDeltaEvent),
 }
 
 #[derive(Debug, Clone, Deserialize, Serialize, TS, JsonSchema)]
@@ -560,6 +564,17 @@ pub struct ItemStartedEvent {
     pub item: TurnItem,
 }
 
+impl HasLegacyEvent for ItemStartedEvent {
+    fn as_legacy_events(&self, _: bool) -> Vec<EventMsg> {
+        match &self.item {
+            TurnItem::WebSearch(item) => vec![EventMsg::WebSearchBegin(WebSearchBeginEvent {
+                call_id: item.id.clone(),
+            })],
+            _ => Vec::new(),
+        }
+    }
+}
+
 #[derive(Debug, Clone, Deserialize, Serialize, TS, JsonSchema)]
 pub struct ItemCompletedEvent {
     pub thread_id: ConversationId,
@@ -567,6 +582,84 @@ pub struct ItemCompletedEvent {
     pub item: TurnItem,
 }
 
+pub trait HasLegacyEvent {
+    fn as_legacy_events(&self, show_raw_agent_reasoning: bool) -> Vec<EventMsg>;
+}
+
+impl HasLegacyEvent for ItemCompletedEvent {
+    fn as_legacy_events(&self, show_raw_agent_reasoning: bool) -> Vec<EventMsg> {
+        self.item.as_legacy_events(show_raw_agent_reasoning)
+    }
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize, TS, JsonSchema)]
+pub struct AgentMessageContentDeltaEvent {
+    pub thread_id: String,
+    pub turn_id: String,
+    pub item_id: String,
+    pub delta: String,
+}
+
+impl HasLegacyEvent for AgentMessageContentDeltaEvent {
+    fn as_legacy_events(&self, _: bool) -> Vec<EventMsg> {
+        vec![EventMsg::AgentMessageDelta(AgentMessageDeltaEvent {
+            delta: self.delta.clone(),
+        })]
+    }
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize, TS, JsonSchema)]
+pub struct ReasoningContentDeltaEvent {
+    pub thread_id: String,
+    pub turn_id: String,
+    pub item_id: String,
+    pub delta: String,
+}
+
+impl HasLegacyEvent for ReasoningContentDeltaEvent {
+    fn as_legacy_events(&self, _: bool) -> Vec<EventMsg> {
+        vec![EventMsg::AgentReasoningDelta(AgentReasoningDeltaEvent {
+            delta: self.delta.clone(),
+        })]
+    }
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize, TS, JsonSchema)]
+pub struct ReasoningRawContentDeltaEvent {
+    pub thread_id: String,
+    pub turn_id: String,
+    pub item_id: String,
+    pub delta: String,
+}
+
+impl HasLegacyEvent for ReasoningRawContentDeltaEvent {
+    fn as_legacy_events(&self, _: bool) -> Vec<EventMsg> {
+        vec![EventMsg::AgentReasoningRawContentDelta(
+            AgentReasoningRawContentDeltaEvent {
+                delta: self.delta.clone(),
+            },
+        )]
+    }
+}
+
+impl HasLegacyEvent for EventMsg {
+    fn as_legacy_events(&self, show_raw_agent_reasoning: bool) -> Vec<EventMsg> {
+        match self {
+            EventMsg::ItemCompleted(event) => event.as_legacy_events(show_raw_agent_reasoning),
+            EventMsg::AgentMessageContentDelta(event) => {
+                event.as_legacy_events(show_raw_agent_reasoning)
+            }
+            EventMsg::ReasoningContentDelta(event) => {
+                event.as_legacy_events(show_raw_agent_reasoning)
+            }
+            EventMsg::ReasoningRawContentDelta(event) => {
+                event.as_legacy_events(show_raw_agent_reasoning)
+            }
+            _ => Vec::new(),
+        }
+    }
+}
+
 #[derive(Debug, Clone, Deserialize, Serialize, JsonSchema, TS)]
 #[ts(optional_fields = nullable)]
 pub struct ExitedReviewModeEvent {
@@ -1392,10 +1485,42 @@ pub enum TurnAbortReason {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::items::UserMessageItem;
+    use crate::items::WebSearchItem;
     use anyhow::Result;
     use serde_json::json;
     use tempfile::NamedTempFile;
 
+    #[test]
+    fn item_started_event_from_web_search_emits_begin_event() {
+        let event = ItemStartedEvent {
+            thread_id: ConversationId::new(),
+            turn_id: "turn-1".into(),
+            item: TurnItem::WebSearch(WebSearchItem {
+                id: "search-1".into(),
+                query: "find docs".into(),
+            }),
+        };
+
+        let legacy_events = event.as_legacy_events(false);
+        assert_eq!(legacy_events.len(), 1);
+        match &legacy_events[0] {
+            EventMsg::WebSearchBegin(event) => assert_eq!(event.call_id, "search-1"),
+            _ => panic!("expected WebSearchBegin event"),
+        }
+    }
+
+    #[test]
+    fn item_started_event_from_non_web_search_emits_no_legacy_events() {
+        let event = ItemStartedEvent {
+            thread_id: ConversationId::new(),
+            turn_id: "turn-1".into(),
+            item: TurnItem::UserMessage(UserMessageItem::new(&[])),
+        };
+
+        assert!(event.as_legacy_events(false).is_empty());
+    }
+
     /// Serialize Event to verify that its JSON representation has the expected
     /// amount of nesting.
     #[test]

codex-rs/tui/src/chatwidget.rs

@@ -1521,7 +1521,10 @@ impl ChatWidget {
             EventMsg::ExitedReviewMode(review) => self.on_exited_review_mode(review),
             EventMsg::RawResponseItem(_)
             | EventMsg::ItemStarted(_)
-            | EventMsg::ItemCompleted(_) => {}
+            | EventMsg::ItemCompleted(_)
+            | EventMsg::AgentMessageContentDelta(_)
+            | EventMsg::ReasoningContentDelta(_)
+            | EventMsg::ReasoningRawContentDelta(_) => {}
         }
     }