fix(translator): stop emitting empty <think> markers into OpenAI content

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

@@ -129,12 +129,16 @@ export function openaiToOpenAIResponsesResponse(chunk, state) {
     }
 
     if (content) {
+      // The answer starts, so thinking is over. Upstreams that send reasoning via
+      // reasoning_content never emit "</think>", so close it here rather than at finish.
+      closeReasoning(state, emit);
       emitTextContent(state, emit, idx, content);
     }
   }
 
   // Handle tool_calls (empty array is truthy; require a real call)
   if (delta.tool_calls && delta.tool_calls.length) {
+    closeReasoning(state, emit);
     closeMessage(state, emit, idx);
     for (const tc of delta.tool_calls) {
       emitToolCall(state, emit, tc);