fix(responses): don't close message on empty tool_calls array

Some providers (e.g. codebuddy/cbcn) attach an empty tool_calls array to every streaming chunk. An empty array is truthy in JS, so the guard 'if (delta.tool_calls)' closed the message on the first content token and emitted response.output_text.done early, dropping the remaining deltas. Guard on a non-empty array; finish_reason still closes the message and real tool calls still close it before emitting function_call items.

fixes #3234

open-sse/translator/response/openai-responses.js

@@ -99,8 +99,8 @@ export function openaiToOpenAIResponsesResponse(chunk, state) {
     }
   }
 
-  // Handle tool_calls
-  if (delta.tool_calls) {
+  // Handle tool_calls (empty array is truthy; require a real call)
+  if (delta.tool_calls && delta.tool_calls.length) {
     closeMessage(state, emit, idx);
     for (const tc of delta.tool_calls) {
       emitToolCall(state, emit, tc);