Do not attempt to append after response.completed

codex-rs/codex-api/src/common.rs

@@ -63,6 +63,8 @@ pub enum ResponseEvent {
     Completed {
         response_id: String,
         token_usage: Option<TokenUsage>,
+        /// Whether the client can append more items to a long-running websocket response.
+        can_append: bool,
     },
     OutputTextDelta(String),
     ReasoningSummaryDelta {

codex-rs/codex-api/src/endpoint/aggregate.rs

@@ -66,6 +66,7 @@ impl Stream for AggregatedStream {
                 Poll::Ready(Some(Ok(ResponseEvent::Completed {
                     response_id,
                     token_usage,
+                    can_append: _can_append,
                 }))) => {
                     let mut emitted_any = false;
 
@@ -102,6 +103,7 @@ impl Stream for AggregatedStream {
                         this.pending.push_back(ResponseEvent::Completed {
                             response_id: response_id.clone(),
                             token_usage: token_usage.clone(),
+                            can_append: false,
                         });
                         if let Some(ev) = this.pending.pop_front() {
                             return Poll::Ready(Some(Ok(ev)));
@@ -111,6 +113,7 @@ impl Stream for AggregatedStream {
                     return Poll::Ready(Some(Ok(ResponseEvent::Completed {
                         response_id,
                         token_usage,
+                        can_append: false,
                     })));
                 }
                 Poll::Ready(Some(Ok(ResponseEvent::Created))) => continue,

codex-rs/codex-api/src/endpoint/responses_websocket.rs

@@ -343,6 +343,7 @@ async fn run_websocket_response_stream(
             )));
         }
     };
+    trace!("websocket request: {request_text}");
 
     let request_start = Instant::now();
     let result = ws_stream

codex-rs/codex-api/src/sse/responses.rs

@@ -259,6 +259,7 @@ pub fn process_responses_event(
                         return Ok(Some(ResponseEvent::Completed {
                             response_id: resp.id,
                             token_usage: resp.usage.map(Into::into),
+                            can_append: false,
                         }));
                     }
                     Err(err) => {
@@ -276,6 +277,7 @@ pub fn process_responses_event(
                         return Ok(Some(ResponseEvent::Completed {
                             response_id: resp.id.unwrap_or_default(),
                             token_usage: resp.usage.map(Into::into),
+                            can_append: true,
                         }));
                     }
                     Err(err) => {
@@ -290,6 +292,7 @@ pub fn process_responses_event(
             return Ok(Some(ResponseEvent::Completed {
                 response_id: String::new(),
                 token_usage: None,
+                can_append: true,
             }));
         }
         "response.output_item.added" => {
@@ -548,9 +551,11 @@ mod tests {
             Ok(ResponseEvent::Completed {
                 response_id,
                 token_usage,
+                can_append,
             }) => {
                 assert_eq!(response_id, "resp1");
                 assert!(token_usage.is_none());
+                assert!(!can_append);
             }
             other => panic!("unexpected third event: {other:?}"),
         }
@@ -585,7 +590,7 @@ mod tests {
     }
 
     #[tokio::test]
-    async fn response_done_emits_completed() {
+    async fn response_done_emits_incremental_completed() {
         let done = json!({
             "type": "response.done",
             "response": {
@@ -610,9 +615,11 @@ mod tests {
             Ok(ResponseEvent::Completed {
                 response_id,
                 token_usage,
+                can_append,
             }) => {
                 assert_eq!(response_id, "");
                 assert!(token_usage.is_some());
+                assert!(*can_append);
             }
             other => panic!("unexpected event: {other:?}"),
         }
@@ -635,9 +642,11 @@ mod tests {
             Ok(ResponseEvent::Completed {
                 response_id,
                 token_usage,
+                can_append,
             }) => {
                 assert_eq!(response_id, "");
                 assert!(token_usage.is_none());
+                assert!(*can_append);
             }
             other => panic!("unexpected event: {other:?}"),
         }
@@ -673,9 +682,11 @@ mod tests {
             Ok(ResponseEvent::Completed {
                 response_id,
                 token_usage,
+                can_append,
             }) => {
                 assert_eq!(response_id, "resp1");
                 assert!(token_usage.is_none());
+                assert!(!can_append);
             }
             other => panic!("unexpected event: {other:?}"),
         }

codex-rs/codex-api/tests/sse_end_to_end.rs

@@ -161,9 +161,11 @@ async fn responses_stream_parses_items_and_completed_end_to_end() -> Result<()>
         ResponseEvent::Completed {
             response_id,
             token_usage,
+            can_append,
         } => {
             assert_eq!(response_id, "resp1");
             assert!(token_usage.is_none());
+            assert!(!can_append);
         }
         other => panic!("unexpected third event: {other:?}"),
     }

codex-rs/core/src/client.rs

@@ -81,6 +81,7 @@ use tokio::sync::oneshot;
 use tokio::sync::oneshot::error::TryRecvError;
 use tokio_tungstenite::tungstenite::Error;
 use tokio_tungstenite::tungstenite::Message;
+use tracing::trace;
 use tracing::warn;
 
 use crate::AuthManager;
@@ -185,6 +186,7 @@ pub struct ModelClientSession {
 struct LastResponse {
     response_id: String,
     items_added: Vec<ResponseItem>,
+    can_append: bool,
 }
 
 enum WebsocketStreamOutcome {
@@ -550,6 +552,9 @@ impl ModelClientSession {
         let mut request_without_input = request.clone();
         request_without_input.input.clear();
         if previous_without_input != request_without_input {
+            trace!(
+                "incremental request failed, properties didn't match {previous_without_input:?} != {request_without_input:?}"
+            );
             return None;
         }
 
@@ -565,6 +570,7 @@ impl ModelClientSession {
         {
             Some(request.input[baseline_len..].to_vec())
         } else {
+            trace!("incremental request failed, items didn't match");
             None
         }
     }
@@ -583,18 +589,19 @@ impl ModelClientSession {
         payload: ResponseCreateWsRequest,
         request: &ResponsesApiRequest,
     ) -> ResponsesWsRequest {
-        let last_response = self.get_last_response();
+        let Some(last_response) = self.get_last_response() else {
+            return ResponsesWsRequest::ResponseCreate(payload);
+        };
         let responses_websockets_v2_enabled = self.client.responses_websockets_v2_enabled();
-        let incremental_items = self.get_incremental_items(request, last_response.as_ref());
+        if !responses_websockets_v2_enabled && !last_response.can_append {
+            trace!("incremental request failed, can't append");
+            return ResponsesWsRequest::ResponseCreate(payload);
+        }
+        let incremental_items = self.get_incremental_items(request, Some(&last_response));
         if let Some(append_items) = incremental_items {
-            if responses_websockets_v2_enabled
-                && let Some(previous_response_id) = last_response
-                    .as_ref()
-                    .map(|last_response| last_response.response_id.clone())
-                    .filter(|id| !id.is_empty())
-            {
+            if responses_websockets_v2_enabled && !last_response.response_id.is_empty() {
                 let payload = ResponseCreateWsRequest {
-                    previous_response_id: Some(previous_response_id),
+                    previous_response_id: Some(last_response.response_id),
                     input: append_items,
                     ..payload
                 };
@@ -1014,6 +1021,7 @@ where
                 Ok(ResponseEvent::Completed {
                     response_id,
                     token_usage,
+                    can_append,
                 }) => {
                     if let Some(usage) = &token_usage {
                         otel_manager.sse_event_completed(
@@ -1028,12 +1036,14 @@ where
                         let _ = sender.send(LastResponse {
                             response_id: response_id.clone(),
                             items_added: std::mem::take(&mut items_added),
+                            can_append,
                         });
                     }
                     if tx_event
                         .send(Ok(ResponseEvent::Completed {
                             response_id,
                             token_usage,
+                            can_append,
                         }))
                         .await
                         .is_err()

codex-rs/core/src/codex.rs

@@ -4990,6 +4990,7 @@ async fn try_run_sampling_request(
             ResponseEvent::Completed {
                 response_id: _,
                 token_usage,
+                can_append: _,
             } => {
                 if let Some(state) = plan_mode_state.as_mut() {
                     flush_proposed_plan_segments_all(&sess, &turn_context, state).await;

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

@@ -431,6 +431,16 @@ pub fn ev_done() -> Value {
     })
 }
 
+pub fn ev_done_with_id(id: &str) -> Value {
+    serde_json::json!({
+        "type": "response.done",
+        "response": {
+            "id": id,
+            "usage": {"input_tokens":0,"input_tokens_details":null,"output_tokens":0,"output_tokens_details":null,"total_tokens":0}
+        }
+    })
+}
+
 /// Convenience: SSE event for a created response with a specific id.
 pub fn ev_response_created(id: &str) -> Value {
     serde_json::json!({

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

@@ -31,6 +31,8 @@ use core_test_support::responses::WebSocketConnectionConfig;
 use core_test_support::responses::WebSocketTestServer;
 use core_test_support::responses::ev_assistant_message;
 use core_test_support::responses::ev_completed;
+use core_test_support::responses::ev_done;
+use core_test_support::responses::ev_done_with_id;
 use core_test_support::responses::ev_response_created;
 use core_test_support::responses::start_websocket_server;
 use core_test_support::responses::start_websocket_server_with_headers;
@@ -574,7 +576,7 @@ async fn responses_websocket_appends_on_prefix() {
         vec![
             ev_response_created("resp-1"),
             ev_assistant_message("msg-1", "assistant output"),
-            ev_completed("resp-1"),
+            ev_done(),
         ],
         vec![ev_response_created("resp-2"), ev_completed("resp-2")],
     ]])
@@ -610,6 +612,45 @@ async fn responses_websocket_appends_on_prefix() {
     server.shutdown().await;
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn responses_websocket_creates_on_prefix_when_previous_completion_cannot_append() {
+    skip_if_no_network!();
+
+    let server = start_websocket_server(vec![vec![
+        vec![
+            ev_response_created("resp-1"),
+            ev_assistant_message("msg-1", "assistant output"),
+            ev_completed("resp-1"),
+        ],
+        vec![ev_response_created("resp-2"), ev_completed("resp-2")],
+    ]])
+    .await;
+
+    let harness = websocket_harness(&server).await;
+    let mut client_session = harness.client.new_session();
+    let prompt_one = prompt_with_input(vec![message_item("hello")]);
+    let prompt_two = prompt_with_input(vec![
+        message_item("hello"),
+        assistant_message_item("msg-1", "assistant output"),
+        message_item("second"),
+    ]);
+
+    stream_until_complete(&mut client_session, &harness, &prompt_one).await;
+    stream_until_complete(&mut client_session, &harness, &prompt_two).await;
+
+    let connection = server.single_connection();
+    assert_eq!(connection.len(), 2);
+    let second = connection.get(1).expect("missing request").body_json();
+
+    assert_eq!(second["type"].as_str(), Some("response.create"));
+    assert_eq!(
+        second["input"],
+        serde_json::to_value(&prompt_two.input).expect("serialize full input")
+    );
+
+    server.shutdown().await;
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn responses_websocket_creates_on_non_prefix() {
     skip_if_no_network!();
@@ -687,7 +728,7 @@ async fn responses_websocket_v2_creates_with_previous_response_id_on_prefix() {
         vec![
             ev_response_created("resp-1"),
             ev_assistant_message("msg-1", "assistant output"),
-            ev_completed("resp-1"),
+            ev_done_with_id("resp-1"),
         ],
         vec![ev_response_created("resp-2"), ev_completed("resp-2")],
     ]])