From 5ef3cb57ee66cd4acb8834cd382ccf9f1852bfbf Mon Sep 17 00:00:00 2001
From: Henry Li <henry1943@163.com>
Date: Fri, 16 Jan 2026 14:38:49 +0800
Subject: [PATCH] fix: lastStep could be empty

---
 .../components/workspace/message-list/message-group.tsx    | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/frontend/src/components/workspace/message-list/message-group.tsx b/frontend/src/components/workspace/message-list/message-group.tsx
index d9eed49..16f9d82 100644
--- a/frontend/src/components/workspace/message-list/message-group.tsx
+++ b/frontend/src/components/workspace/message-list/message-group.tsx
@@ -41,7 +41,7 @@ export function MessageGroup({
   const steps = useMemo(() => convertToSteps(messages), [messages]);
   const rehypePlugins = useRehypeSplitWordsIntoSpans(isLoading);
   const [open, setOpen] = useState(false);
-  const lastStep = steps[steps.length - 1]!;
+  const lastStep = steps[steps.length - 1];
   const { label, icon } = describeStep(lastStep);
   return (
     <ChainOfThought
@@ -289,10 +289,13 @@ function convertToSteps(messages: Message[]): CoTStep[] {
   return steps;
 }
 
-function describeStep(step: CoTStep): {
+function describeStep(step: CoTStep | undefined): {
   label: string;
   icon: React.ReactElement;
 } {
+  if (!step) {
+    return { label: "Thinking", icon: <LightbulbIcon className="size-4" /> };
+  }
   if (step.type === "reasoning") {
     return { label: "Thinking", icon: <LightbulbIcon className="size-4" /> };
   } else {