fix(responses): preserve chat template arguments

lib/llm/src/http/service/openai.rs

@@ -3244,6 +3244,11 @@ async fn responses(
         return Ok(resp.into_response());
     }
 
+    if let Err(err_response) = validate_response_chat_template_args(&request) {
+        inflight_guard.mark_error(extract_error_type_from_response(&err_response));
+        return Err(err_response);
+    }
+
     // Validate sampling and output parameters
     if let Err(err_response) = validate_responses_fields(&request) {
         inflight_guard.mark_error(extract_error_type_from_response(&err_response));
@@ -3344,28 +3349,20 @@ async fn responses(
         ),
     );
 
+    let move_reasoning_to_content_when_empty =
+        crate::preprocessor::OpenAIPreprocessor::wants_reasoning_as_content_when_empty(
+            request.chat_template_args.as_ref(),
+        );
+    let parsing_options = parsing_options
+        .with_move_reasoning_to_content_when_empty(move_reasoning_to_content_when_empty);
+
     // Responses requests share the chat-completions aggregator for the unary
     // path. Thread this option through so its post-parse fallback also caps a
     // model-produced batch to the first tool call when parallel calls are
     // disabled. The streaming Responses converter enforces the same contract.
     let parsing_options =
         parsing_options.with_parallel_tool_calls(request.inner.parallel_tool_calls);
 
-    // NOTE: `move_reasoning_to_content_when_empty` is the aggregator flag and is
-    // not set here. A non-streaming Responses request DOES reach the aggregator
-    // (forcing stream=true on the converted request only drives internal
-    // streaming; the client-facing `streaming` flag still selects the aggregating
-    // branch below), so it reaches it with the flag false.
-    //
-    // That is currently unreachable rather than wrong: the Responses-to-chat
-    // conversion hard-codes `chat_template_args: None`, so
-    // `force_nonempty_content` can never be set on this path in the first place.
-    // If that conversion ever forwards chat_template_args, the streaming stage
-    // would still cover the reasoning-only case — `postprocessor_parsing_stream`
-    // gates on the request's own args via `wants_reasoning_as_content_when_empty`
-    // rather than on this flag — but the aggregator backstop should be wired here
-    // too at that point. Tracked as follow-up.
-
     let mut response_collector = state
         .metrics_clone()
         .create_response_collector(&metric_model);
@@ -3589,6 +3586,20 @@ pub fn validate_response_unsupported_fields(
     None
 }
 
+fn validate_response_chat_template_args(
+    request: &NvCreateResponse,
+) -> Result<(), ErrorResponse> {
+    crate::protocols::openai::validate::validate_chat_template_args(
+        request.chat_template_args.as_ref(),
+    )
+    .map_err(|e| {
+        ErrorMessage::from_http_error(HttpError {
+            code: 400,
+            message: VALIDATION_PREFIX.to_string() + &e.to_string(),
+        })
+    })
+}
+
 /// Validates sampling and output parameters on the Responses API request.
 pub fn validate_responses_fields(request: &NvCreateResponse) -> Result<(), ErrorResponse> {
     use crate::protocols::openai::validate;
@@ -4988,6 +4999,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         }
     }
 
@@ -5573,6 +5585,30 @@ mod tests {
         assert!(validate_response_unsupported_fields(&request).is_some());
     }
 
+    #[test]
+    fn test_validate_response_chat_template_args_rejects_nested_chat_template() {
+        let mut request = make_base_request();
+        request.chat_template_args = Some(HashMap::from([(
+            "chat_template".to_string(),
+            serde_json::json!("{{ 'pwned' }}"),
+        )]));
+
+        let (status, _) = validate_response_chat_template_args(&request).unwrap_err();
+        assert_eq!(status, StatusCode::BAD_REQUEST);
+    }
+
+    #[test]
+    fn test_validate_response_chat_template_args_accepts_ordinary_args() {
+        let mut request = make_base_request();
+        request.chat_template_args = Some(HashMap::from([(
+            "enable_thinking".to_string(),
+            serde_json::json!(true),
+        )]));
+
+        assert!(validate_response_chat_template_args(&request).is_ok());
+        assert!(validate_response_chat_template_args(&make_base_request()).is_ok());
+    }
+
     #[test]
     fn test_validate_unsupported_fields_accepts_supported_nvext_fields() {
         let mut request = make_base_request();

lib/llm/src/protocols/common/input_trigger.rs

@@ -185,6 +185,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         }
     }
 

lib/llm/src/protocols/openai/responses/mod.rs

@@ -51,6 +51,13 @@ pub struct NvCreateResponse {
     #[serde(skip_serializing_if = "Option::is_none")]
     #[schema(value_type = Object)]
     pub nvext: Option<NvExt>,
+
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        alias = "chat_template_kwargs"
+    )]
+    pub chat_template_args: Option<HashMap<String, serde_json::Value>>,
 }
 
 #[derive(ToSchema, Deserialize, Validate, Debug, Clone)]
@@ -891,7 +898,7 @@ impl TryFrom<NvCreateResponse> for NvCreateChatCompletionRequest {
             },
             common: Default::default(),
             nvext: resp.nvext,
-            chat_template_args: None,
+            chat_template_args: resp.chat_template_args,
             thinking: None,
             media_io_kwargs: None,
             return_tokens_as_token_ids: None,
@@ -1348,6 +1355,7 @@ mod tests {
                 annotations: Some(vec!["debug".into(), "trace".into()]),
                 ..Default::default()
             }),
+            chat_template_args: None,
         }
     }
 
@@ -1424,6 +1432,64 @@ mod tests {
         assert_eq!(nv_req.inner.store, Some(true));
     }
 
+    #[test]
+    fn test_responses_chat_template_args_forwarded_to_chat_completion() {
+        let req: NvCreateResponse = serde_json::from_value(serde_json::json!({
+            "model": "dummy-model",
+            "input": "hello",
+            "chat_template_args": { "enable_thinking": true }
+        }))
+        .unwrap();
+
+        let chat_req = NvCreateChatCompletionRequest::try_from(req).unwrap();
+
+        let args = chat_req
+            .chat_template_args
+            .expect("chat_template_args must survive the Responses to Chat conversion");
+        assert_eq!(args.get("enable_thinking"), Some(&serde_json::json!(true)));
+    }
+
+    #[test]
+    fn test_responses_chat_template_kwargs_alias_forwarded_to_chat_completion() {
+        let req: NvCreateResponse = serde_json::from_value(serde_json::json!({
+            "model": "dummy-model",
+            "input": "hello",
+            "chat_template_kwargs": { "enable_thinking": true }
+        }))
+        .unwrap();
+
+        let chat_req = NvCreateChatCompletionRequest::try_from(req).unwrap();
+
+        let args = chat_req
+            .chat_template_args
+            .expect("chat_template_kwargs alias must bind chat_template_args");
+        assert_eq!(args.get("enable_thinking"), Some(&serde_json::json!(true)));
+    }
+
+    #[test]
+    fn test_responses_without_chat_template_args_converts_to_none() {
+        let req: NvCreateResponse = serde_json::from_value(serde_json::json!({
+            "model": "dummy-model",
+            "input": "hello"
+        }))
+        .unwrap();
+
+        let chat_req = NvCreateChatCompletionRequest::try_from(req).unwrap();
+
+        assert!(chat_req.chat_template_args.is_none());
+    }
+
+    #[test]
+    fn test_responses_chat_template_args_rejects_non_object() {
+        let err = serde_json::from_value::<NvCreateResponse>(serde_json::json!({
+            "model": "dummy-model",
+            "input": "hello",
+            "chat_template_args": "enable_thinking"
+        }));
+
+        assert!(err.is_err());
+    }
+
     #[test]
     fn test_instructions_prepended_as_system_message() {
         let req = NvCreateResponse {
@@ -1434,6 +1500,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
 
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
@@ -1478,6 +1545,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
 
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
@@ -1557,6 +1625,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
 
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
@@ -1598,6 +1667,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
 
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
@@ -1641,6 +1711,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
 
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
@@ -1689,6 +1760,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
 
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
@@ -1728,6 +1800,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
 
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
@@ -1762,6 +1835,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
 
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
@@ -1804,6 +1878,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
 
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
@@ -1865,6 +1940,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
 
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
@@ -1937,6 +2013,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
 
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
@@ -1994,6 +2071,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
 
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
@@ -2049,6 +2127,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
 
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
@@ -2096,6 +2175,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
 
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
@@ -2161,6 +2241,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
 
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
@@ -2240,6 +2321,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
 
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
@@ -2313,6 +2395,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
         let messages = &chat_req.inner.messages;
@@ -2382,6 +2465,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
         let messages = &chat_req.inner.messages;
@@ -2448,6 +2532,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
         let messages = &chat_req.inner.messages;
@@ -2505,6 +2590,7 @@ mod tests {
                 ..Default::default()
             },
             nvext: None,
+            chat_template_args: None,
         };
         let chat_req: NvCreateChatCompletionRequest = req.try_into().unwrap();
         let messages = &chat_req.inner.messages;