修复Dashboard数据加载问题：添加错误日志、修复strict mode重复渲染导致的selectedId闭包问题

web/src/pages/agent/Dashboard.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect } from 'react'
+import { useState, useEffect, useRef } from 'react'
 import { Input, Spin, message } from 'antd'
 import { SearchOutlined, UserOutlined, StarFilled } from '@ant-design/icons'
 import { useAuth } from '@/stores/auth'
@@ -29,21 +29,25 @@ const Dashboard = () => {
   const [detail, setDetail] = useState<SessionDetail | null>(null)
   const [detailLoading, setDetailLoading] = useState(false)
   const [messageInput, setMessageInput] = useState('')
+  const initialLoad = useRef(true)
 
   useEffect(() => {
     loadSessions()
   }, [])
 
   const loadSessions = async () => {
+    setLoading(true)
     try {
-      setLoading(true)
       const res = await getSessions()
+      console.log('Sessions loaded:', res)
       setSessions(res.list)
-      if (res.list.length > 0 && !selectedId) {
+      if (res.list.length > 0 && initialLoad.current) {
         setSelectedId(res.list[0].id)
+        initialLoad.current = false
       }
-    } catch {
+    } catch (err) {
-      // fallback to empty
+      console.error('Failed to load sessions:', err)
+      message.error('加载会话失败，请重新登录')
     } finally {
       setLoading(false)
     }