fix(openai): fix stream whitespace loss and finish_reason for gpt-5.4

- Remove overzealous .trim() in strip_internal_metadata which destroyed whitespace between text stream chunks, causing client hangs
- Fix finish_reason logic to only yield once at the end of the stream
- Correctly yield finish_reason: 'tool_calls' instead of 'stop' when tool calls are generated

src/providers/openai.rs

@@ -102,12 +102,12 @@ impl OpenAIProvider {
 
         for p in patterns {
             if let Some(start) = result.find(p) {
-                // Remove the pattern and any whitespace around it
+                // Remove the pattern
                 result.replace_range(start..start + p.len(), "");
             }
         }
 
-        result.trim().to_string()
+        result
     }
 }
 
@@ -730,6 +730,7 @@ impl super::Provider for OpenAIProvider {
         let stream = async_stream::try_stream! {
             let mut es = es;
             let mut content_buffer = String::new();
+            let mut has_tool_calls = false;
             
             while let Some(event) = es.next().await {
                 match event {
@@ -760,6 +761,7 @@ impl super::Provider for OpenAIProvider {
                                 "response.output_item.added" => {
                                     if let Some(item) = chunk.get("item") {
                                         if item.get("type").and_then(|v| v.as_str()) == Some("function_call") {
+                                            has_tool_calls = true;
                                             let call_id = item.get("call_id").and_then(|v| v.as_str());
                                             let name = item.get("name").and_then(|v| v.as_str());
                                             
@@ -777,6 +779,7 @@ impl super::Provider for OpenAIProvider {
                                 }
                                 "response.function_call_arguments.delta" => {
                                     if let Some(delta) = chunk.get("delta").and_then(|v| v.as_str()) {
+                                        has_tool_calls = true;
                                         tool_calls = Some(vec![crate::models::ToolCallDelta {
                                             index: chunk.get("output_index").and_then(|v| v.as_u64()).unwrap_or(0) as u32,
                                             id: None,
@@ -788,8 +791,8 @@ impl super::Provider for OpenAIProvider {
                                         }]);
                                     }
                                 }
-                                "response.output_text.done" | "response.item.done" | "response.completed" => {
+                                "response.completed" => {
-                                    finish_reason = Some("stop".to_string());
+                                    finish_reason = Some(if has_tool_calls { "tool_calls".to_string() } else { "stop".to_string() });
                                 }
                                 _ => {}
                             }
@@ -800,6 +803,7 @@ impl super::Provider for OpenAIProvider {
                                 if content_buffer.contains("{\"tool_uses\":") {
                                     let embedded_calls = Self::parse_tool_uses_json(&content_buffer);
                                     if !embedded_calls.is_empty() {
+                                        has_tool_calls = true;
                                         if let Some(start) = content_buffer.find("{\"tool_uses\":") {
                                             // Yield text before the JSON block
                                             let preamble = content_buffer[..start].to_string();