优化历史会话排序逻辑，按首条消息时间排序

src/components/chat/AgentHistoryPanel.tsx

@@ -73,7 +73,6 @@ const getSessionGroupLabel = (timestamp: number) => {
 };
 
 export const AgentHistoryPanel = ({
-
   sessions,
   activeSessionId,
   isHydrating = false,
@@ -95,11 +94,25 @@ export const AgentHistoryPanel = ({
     return sessions.filter((session) => session.title.toLowerCase().includes(normalizedKeyword));
   }, [keyword, sessions]);
 
+  const sortedFilteredSessions = React.useMemo(
+    () =>
+      [...filteredSessions].sort((left, right) => {
+        const createdAtDiff = right.createdAt - left.createdAt;
+        if (createdAtDiff !== 0) return createdAtDiff;
+
+        const updatedAtDiff = right.updatedAt - left.updatedAt;
+        if (updatedAtDiff !== 0) return updatedAtDiff;
+
+        return right.id.localeCompare(left.id);
+      }),
+    [filteredSessions],
+  );
+
   const groupedSessions = React.useMemo(() => {
     const groups = new Map<string, ChatSessionSummary[]>();
 
-    filteredSessions.forEach((session) => {
-      const label = getSessionGroupLabel(session.updatedAt);
+    sortedFilteredSessions.forEach((session) => {
+      const label = getSessionGroupLabel(session.createdAt);
       const existing = groups.get(label);
       if (existing) {
         existing.push(session);
@@ -109,7 +122,7 @@ export const AgentHistoryPanel = ({
     });
 
     return Array.from(groups.entries());
-  }, [filteredSessions]);
+  }, [sortedFilteredSessions]);
 
   const pendingDeleteSession = filteredSessions.find(
     (session) => session.id === pendingDeleteSessionId,
@@ -390,7 +403,7 @@ export const AgentHistoryPanel = ({
                                     {session.title}
                                   </Typography>
                                   <Typography variant="caption" color="text.secondary" sx={{ mt: 0.5, display: "block" }}>
-                                    {formatRelativeDate(session.updatedAt)}
+                                    {formatRelativeDate(session.createdAt)}
                                   </Typography>
                                 </Box>
                               )}