fix(translation): preserve OpenAI Chat refusals

Signed-off-by: Atharva-Kanherkar <142440039+Atharva-Kanherkar@users.noreply.github.com>

Author: Atharva-Kanherkar

crates/switchyard-translation/src/codecs/openai_chat/buffered.rs

@@ -284,6 +284,11 @@ impl FormatCodec for OpenAiChatCodec {
                 .and_then(Value::as_object)
                 .cloned()
                 .unwrap_or_default();
+            let content_is_null = message.get("content").is_none_or(Value::is_null);
+            let refusal = message
+                .get("refusal")
+                .and_then(Value::as_str)
+                .filter(|text| !text.is_empty());
             let mut content = decode_openai_content(
                 message.get("content").unwrap_or(&Value::Null),
                 WireFormat::OpenAiChat,
@@ -292,6 +297,18 @@ impl FormatCodec for OpenAiChatCodec {
                 "$.choices[0].message.content",
             )?;
             prepend_openai_reasoning_blocks(&mut content, &message);
+            if let Some(text) = refusal {
+                // Null content normally creates an empty placeholder, but the sibling refusal
+                // field is the actual assistant content for a structured refusal.
+                if content_is_null {
+                    content.retain(
+                        |block| !matches!(block, ContentBlock::Text { text } if text.is_empty()),
+                    );
+                }
+                content.push(ContentBlock::Refusal {
+                    text: text.to_string(),
+                });
+            }
             if let Some(tool_calls) = message.get("tool_calls").and_then(Value::as_array) {
                 for (index, tool_call) in tool_calls.iter().enumerate() {
                     if let Some(call) = decode_openai_tool_call(
@@ -303,12 +320,16 @@ impl FormatCodec for OpenAiChatCodec {
                     }
                 }
             }
+            let finish_reason = choice.get("finish_reason").and_then(Value::as_str);
+            let stop_reason = if refusal.is_some() && matches!(finish_reason, Some("stop") | None) {
+                StopReason::ContentFilter
+            } else {
+                map_openai_finish_reason(finish_reason)
+            };
             response.outputs.push(ResponseOutput {
                 role: Role::Assistant,
                 content,
-                stop_reason: Some(map_openai_finish_reason(
-                    choice.get("finish_reason").and_then(Value::as_str),
-                )),
+                stop_reason: Some(stop_reason),
             });
         }
 

crates/switchyard-translation/src/codecs/openai_chat/stream.rs

@@ -134,6 +134,15 @@ fn decode_openai_chat_stream(
                     text: text.to_string(),
                 });
             }
+            if let Some(text) = delta.get("refusal").and_then(Value::as_str)
+                && !text.is_empty()
+            {
+                state.stop_reason = Some("content_filter".to_string());
+                out.push(LlmResponseChunk::TextDelta {
+                    index: 0,
+                    text: text.to_string(),
+                });
+            }
             if let Some(tool_calls) = delta.get("tool_calls").and_then(Value::as_array) {
                 for tool_call in tool_calls {
                     if let Some(tool_call) = tool_call.as_object() {
@@ -159,6 +168,12 @@ fn decode_openai_chat_stream(
             }
         }
         if let Some(reason) = choice.get("finish_reason").and_then(Value::as_str) {
+            let reason =
+                if reason == "stop" && state.stop_reason.as_deref() == Some("content_filter") {
+                    "content_filter"
+                } else {
+                    reason
+                };
             out.push(LlmResponseChunk::MessageStop {
                 reason: Some(reason.to_string()),
             });