Avoid duplicate final output in GUI

src/gui/static/app.js

@@ -548,13 +548,15 @@ function renderRunResult(data) {
   }
   const tail = transcript.slice(lastUserIndex + 1);
   renderTranscriptEntries(tail);
-  // Always show the canonical final output if it isn't already present.
-  const lastMsg = els.chat.querySelector(".message.assistant:last-of-type .body");
-  if (!lastMsg || lastMsg.textContent.trim() !== (data.final_output || "").trim()) {
-    if (data.final_output && data.final_output.trim()) {
+  // transcript 通常已经包含最终 assistant 消息；只有缺失时才用 final_output 兜底。
+  const finalOutput = (data.final_output || "").trim();
+  const lastAssistant = [...tail]
+    .reverse()
+    .find((entry) => entry?.role === "assistant" && (entry.content || "").trim());
+  const lastAssistantContent = (lastAssistant?.content || "").trim();
+  if (finalOutput && finalOutput !== lastAssistantContent) {
     appendMessage({ role: "assistant", content: data.final_output });
   }
-  }
 }
 
 // ---------------------------------------------------------------------------