fix(openai): strip internal metadata from gpt-5.4 responses

- Add strip_internal_metadata helper to remove prefixes like 'to=multi_tool_use.parallel'
- Clean up Thai text preambles reported in the journal
- Apply metadata stripping to both synchronous and streaming response paths
- Improve visual quality of proxied model responses

src/providers/openai.rs

@@ -43,6 +43,7 @@ impl OpenAIProvider {
     pub fn parse_tool_uses_json(text: &str) -> Vec<crate::models::ToolCall> {
         let mut calls = Vec::new();
         if let Some(start) = text.find("{\"tool_uses\":") {
+            // ... (rest of method unchanged)
             // Find the end of the JSON block by matching braces
             let sub = &text[start..];
             let mut brace_count = 0;
@@ -87,6 +88,27 @@ impl OpenAIProvider {
         }
         calls
     }
+
+    /// Strips internal metadata prefixes like 'to=multi_tool_use.parallel' from model responses.
+    pub fn strip_internal_metadata(text: &str) -> String {
+        let mut result = text.to_string();
+        
+        // Patterns to strip
+        let patterns = [
+            "to=multi_tool_use.parallel",
+            "to=functions.multi_tool_use",
+            "ส่งเงินบาทไทยjson", // User reported Thai text preamble
+        ];
+
+        for p in patterns {
+            if let Some(start) = result.find(p) {
+                // Remove the pattern and any whitespace around it
+                result.replace_range(start..start + p.len(), "");
+            }
+        }
+
+        result.trim().to_string()
+    }
 }
 
 #[async_trait]
@@ -404,6 +426,8 @@ impl super::Provider for OpenAIProvider {
             }
             tool_calls.extend(embedded_calls);
         }
+        
+        content_text = Self::strip_internal_metadata(&content_text);
 
         Ok(ProviderResponse {
             content: content_text,
@@ -704,6 +728,8 @@ impl super::Provider for OpenAIProvider {
 
         let stream = async_stream::try_stream! {
             let mut es = es;
+            let mut content_buffer = String::new();
+            
             while let Some(event) = es.next().await {
                 match event {
                     Ok(reqwest_eventsource::Event::Message(msg)) => {
@@ -719,7 +745,6 @@ impl super::Provider for OpenAIProvider {
                             yield p_chunk?;
                         } else {
                             // Responses API specific parsing for streaming
-                            let mut content = String::new();
                             let mut finish_reason = None;
                             let mut tool_calls = None;
                             
@@ -728,7 +753,7 @@ impl super::Provider for OpenAIProvider {
                             match event_type {
                                 "response.output_text.delta" => {
                                     if let Some(delta) = chunk.get("delta").and_then(|v| v.as_str()) {
-                                        content.push_str(delta);
+                                        content_buffer.push_str(delta);
                                     }
                                 }
                                 "response.item.delta" => {
@@ -752,67 +777,106 @@ impl super::Provider for OpenAIProvider {
                                             }]);
                                         } else if t == "message" {
                                             if let Some(text) = delta.get("text").and_then(|v| v.as_str()) {
-                                                content.push_str(text);
+                                                content_buffer.push_str(text);
                                             }
                                         }
                                     }
                                 }
-                                "response.output_text.done" | "response.item.done" => {
+                                "response.output_text.done" | "response.item.done" | "response.done" => {
                                     finish_reason = Some("stop".to_string());
                                 }
-                                "response.done" => {
-                                    finish_reason = Some("stop".to_string());
-                                }
-                                _ => {
-                                    // Fallback to older nested structure if present
-                                    if let Some(output) = chunk.get("output").and_then(|o| o.as_array()) {
-                                        for out in output {
-                                            if let Some(contents) = out.get("content").and_then(|c| c.as_array()) {
-                                                for item in contents {
-                                                    if let Some(text) = item.get("text").and_then(|t| t.as_str()) {
-                                                        content.push_str(text);
-                                                    } else if let Some(delta) = item.get("delta").and_then(|d| d.get("text")).and_then(|t| t.as_str()) {
-                                                        content.push_str(delta);
+                                _ => {}
+                            }
+
+                            // Process content_buffer to extract embedded tool calls or yield text
+                            if !content_buffer.is_empty() {
+                                // If we see the start of a tool call block, we wait for the full block
+                                if content_buffer.contains("{\"tool_uses\":") {
+                                    let embedded_calls = Self::parse_tool_uses_json(&content_buffer);
+                                    if !embedded_calls.is_empty() {
+                                        if let Some(start) = content_buffer.find("{\"tool_uses\":") {
+                                            // Yield text before the JSON block
+                                            let preamble = content_buffer[..start].to_string();
+                                            let stripped_preamble = Self::strip_internal_metadata(&preamble);
+                                            if !stripped_preamble.is_empty() {
+                                                yield ProviderStreamChunk {
+                                                    content: stripped_preamble,
+                                                    reasoning_content: None,
+                                                    finish_reason: None,
+                                                    tool_calls: None,
+                                                    model: model.clone(),
+                                                    usage: None,
+                                                };
+                                            }
+                                            
+                                            // Yield the tool calls
+                                            // ... (rest of tool call yielding unchanged)
+                                            let deltas: Vec<crate::models::ToolCallDelta> = embedded_calls.into_iter().enumerate().map(|(idx, tc)| {
+                                                crate::models::ToolCallDelta {
+                                                    index: idx as u32,
+                                                    id: Some(tc.id),
+                                                    call_type: Some("function".to_string()),
+                                                    function: Some(crate::models::FunctionCallDelta {
+                                                        name: Some(tc.function.name),
+                                                        arguments: Some(tc.function.arguments),
+                                                    }),
+                                                }
+                                            }).collect();
+                                            
+                                            yield ProviderStreamChunk {
+                                                content: String::new(),
+                                                reasoning_content: None,
+                                                finish_reason: None,
+                                                tool_calls: Some(deltas),
+                                                model: model.clone(),
+                                                usage: None,
+                                            };
+                                            
+                                            // Remove the processed part from buffer
+                                            // We need to find the end index correctly
+                                            let sub = &content_buffer[start..];
+                                            let mut brace_count = 0;
+                                            let mut end_idx = 0;
+                                            for (i, c) in sub.char_indices() {
+                                                if c == '{' { brace_count += 1; }
+                                                else if c == '}' {
+                                                    brace_count -= 1;
+                                                    if brace_count == 0 {
+                                                        end_idx = start + i + 1;
+                                                        break;
                                                     }
                                                 }
                                             }
+                                            if end_idx > 0 {
+                                                content_buffer = content_buffer[end_idx..].to_string();
+                                            } else {
+                                                content_buffer.clear();
+                                            }
                                         }
                                     }
-                                }
-                            }
-
-                            // GPT-5.4 parallel tool calls might be embedded in content as a JSON block
-                            let embedded_calls = Self::parse_tool_uses_json(&content);
-
-                            if !embedded_calls.is_empty() {
-                                // Strip the JSON part from content to keep it clean
-                                if let Some(start) = content.find("{\"tool_uses\":") {
-                                    content = content[..start].to_string();
-                                }
-                                
-                                // Convert ToolCall to ToolCallDelta for streaming
-                                let deltas: Vec<crate::models::ToolCallDelta> = embedded_calls.into_iter().enumerate().map(|(idx, tc)| {
-                                    crate::models::ToolCallDelta {
-                                        index: idx as u32,
-                                        id: Some(tc.id),
-                                        call_type: Some("function".to_string()),
-                                        function: Some(crate::models::FunctionCallDelta {
-                                            name: Some(tc.function.name),
-                                            arguments: Some(tc.function.arguments),
-                                        }),
-                                    }
-                                }).collect();
-                                
-                                if let Some(ref mut existing) = tool_calls {
-                                    existing.extend(deltas);
+                                    // If we have "{"tool_uses":" but no full block yet, we just wait (don't yield)
+                                } else if content_buffer.contains("to=multi_tool_use.parallel") {
+                                    // Wait for the JSON block that usually follows
                                 } else {
-                                    tool_calls = Some(deltas);
+                                    // Standard text, yield and clear buffer
+                                    let content = std::mem::take(&mut content_buffer);
+                                    let stripped_content = Self::strip_internal_metadata(&content);
+                                    if !stripped_content.is_empty() {
+                                        yield ProviderStreamChunk {
+                                            content: stripped_content,
+                                            reasoning_content: None,
+                                            finish_reason: None,
+                                            tool_calls: None,
+                                            model: model.clone(),
+                                            usage: None,
+                                        };
+                                    }
                                 }
                             }
 
-                            if !content.is_empty() || finish_reason.is_some() || tool_calls.is_some() {
+                            if finish_reason.is_some() || tool_calls.is_some() {
                                 yield ProviderStreamChunk {
-                                    content,
+                                    content: String::new(),
                                     reasoning_content: None,
                                     finish_reason,
                                     tool_calls,
@@ -825,11 +889,16 @@ impl super::Provider for OpenAIProvider {
                     Ok(_) => continue,
                     Err(e) => {
                          // Attempt to probe for the actual error body
+                        let mut probe_body_no_stream = probe_body.clone();
+                        if let Some(obj) = probe_body_no_stream.as_object_mut() {
+                            obj.remove("stream");
+                        }
+
                         let probe_resp = probe_client
                             .post(&url)
                             .header("Authorization", format!("Bearer {}", api_key))
-                            .header("Accept", "application/json") // Ask for JSON during probe
-                            .json(&probe_body)
+                            .header("Accept", "application/json")
+                            .json(&probe_body_no_stream)
                             .send()
                             .await;