From cce6f6dd6045cd7d2d1664b7ab7fc01e9df7a076 Mon Sep 17 00:00:00 2001
From: "richard-for-bugen[bot]"
 <342439978+richard-for-bugen[bot]@users.noreply.github.com>
Date: Tue, 3 Nov 2026 19:26:35 +0000
Subject: [PATCH] [Rust Frontend] Accept refusal content parts in assistant
 messages

OpenAI's chat API allows `refusal` parts in assistant message content
(`ChatCompletionContentPartRefusalParam`), and the Python frontend
replays them as text. The Rust frontend rejected them with a
deserialization error. Lower them onto assistant text blocks, include
them in the `echo` text like Python, and reject them in other roles
with OpenAI's message.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: richard-for-bugen[bot] <342439978+richard-for-bugen[bot]@users.noreply.github.com>
---
 .../routes/openai/chat_completions/convert.rs | 65 ++++++++++++++++++-
 .../server/src/routes/openai/utils/types.rs   |  4 ++
 2 files changed, 67 insertions(+), 2 deletions(-)

diff --git a/rust/src/server/src/routes/openai/chat_completions/convert.rs b/rust/src/server/src/routes/openai/chat_completions/convert.rs
index 251cbcd59dc0..c1b63ea42d83 100644
--- a/rust/src/server/src/routes/openai/chat_completions/convert.rs
+++ b/rust/src/server/src/routes/openai/chat_completions/convert.rs
@@ -271,7 +271,9 @@ fn extract_last_assistant_content(messages: &[ChatMessage]) -> Option<String> {
         MessageContent::Parts(parts) => parts
             .iter()
             .filter_map(|p| match p {
-                ContentPart::Text { text } => Some(text.as_str()),
+                ContentPart::Text { text } | ContentPart::Refusal { refusal: text } => {
+                    Some(text.as_str())
+                }
                 _ => None,
             })
             .collect::<Vec<_>>()
@@ -346,6 +348,9 @@ fn convert_content(content: MessageContent) -> Result<ChatContent, ApiError> {
             .into_iter()
             .map(|part| match part {
                 ContentPart::Text { text } => Ok(ChatContentPart::text(text)),
+                ContentPart::Refusal { .. } => bail_invalid_request!(
+                    "Only assistant messages can have a 'refusal' content type."
+                ),
                 ContentPart::ImageUrl { image_url, uuid } => Ok(ChatContentPart::ImageUrl {
                     image_url: image_url.url,
                     detail: image_url.detail,
@@ -380,7 +385,9 @@ fn convert_assistant_text_blocks(
         MessageContent::Parts(parts) => parts
             .into_iter()
             .map(|part| match part {
-                ContentPart::Text { text } => Ok(AssistantContentBlock::Text { text }),
+                ContentPart::Text { text } | ContentPart::Refusal { refusal: text } => {
+                    Ok(AssistantContentBlock::Text { text })
+                }
                 _ => bail_invalid_request!(
                     "Only text content parts are supported for assistant messages."
                 ),
@@ -1380,6 +1387,60 @@ mod tests {
             .assert_eq(&error.to_error_response().error.message);
     }
 
+    #[test]
+    fn prepare_chat_request_replays_assistant_refusal_parts_as_text() {
+        let request: ChatCompletionRequest = serde_json::from_value(json!({
+            "model": "Qwen/Qwen1.5-0.5B-Chat",
+            "messages": [
+                {"role": "user", "content": "hello"},
+                {"role": "assistant", "content": [
+                    {"type": "refusal", "refusal": "I can't help with that."},
+                ]},
+            ],
+            "echo": true,
+        }))
+        .expect("refusal parts parse in assistant messages");
+
+        let prepared = prepare_chat_request(
+            request,
+            &served(&["Qwen/Qwen1.5-0.5B-Chat"]),
+            ResolvedRequestContext::default(),
+        )
+        .expect("request is valid");
+
+        assert_eq!(
+            prepared.chat_request.messages[1],
+            VllmChatMessage::assistant_blocks(vec![AssistantContentBlock::Text {
+                text: "I can't help with that.".to_string(),
+            }])
+        );
+        assert_eq!(
+            prepared.options.echo.as_deref(),
+            Some("I can't help with that.")
+        );
+    }
+
+    #[test]
+    fn prepare_chat_request_rejects_refusal_parts_outside_assistant_messages() {
+        let request: ChatCompletionRequest = serde_json::from_value(json!({
+            "model": "Qwen/Qwen1.5-0.5B-Chat",
+            "messages": [{"role": "user", "content": [
+                {"type": "refusal", "refusal": "no"},
+            ]}],
+        }))
+        .expect("refusal parts parse in any message");
+
+        let error = prepare_chat_request(
+            request,
+            &served(&["Qwen/Qwen1.5-0.5B-Chat"]),
+            ResolvedRequestContext::default(),
+        )
+        .unwrap_err();
+
+        expect!["Only assistant messages can have a 'refusal' content type."]
+            .assert_eq(&error.to_error_response().error.message);
+    }
+
     #[test]
     fn prepare_chat_request_accepts_assistant_reasoning_history() {
         let message = ChatCompletionMessage {
diff --git a/rust/src/server/src/routes/openai/utils/types.rs b/rust/src/server/src/routes/openai/utils/types.rs
index 5d868f045dd2..6997d37fda2e 100644
--- a/rust/src/server/src/routes/openai/utils/types.rs
+++ b/rust/src/server/src/routes/openai/utils/types.rs
@@ -218,6 +218,10 @@ pub fn validate_top_p_value(top_p: f32) -> Result<(), validator::ValidationError
 pub enum ContentPart {
     #[serde(rename = "text")]
     Text { text: String },
+    /// A refusal the model gave earlier. Valid only in assistant messages,
+    /// where it is replayed as text.
+    #[serde(rename = "refusal")]
+    Refusal { refusal: String },
     #[serde(rename = "image_url")]
     ImageUrl {
         image_url: ImageUrl,