diff --git a/Caddyfile b/Caddyfile
index 9fc5739..89e2f67 100644
--- a/Caddyfile
+++ b/Caddyfile
@@ -8,6 +8,14 @@
     }
 
     handle_path /media/* {
+        # 上传的 html/svg 直接打开时不能当成本站页面跑脚本（会读到 localStorage 里的 token）；
+        # 作为图片、样式、脚本引用时不受 sandbox 影响。预览 iframe 没有 allow-same-origin，
+        # 读字体或 fetch() 素材要跨域许可
+        header {
+            Content-Security-Policy "sandbox"
+            X-Content-Type-Options "nosniff"
+            Access-Control-Allow-Origin "*"
+        }
         root * /media
         file_server
     }
diff --git a/client/src/components/ai/PromptPanel.vue b/client/src/components/ai/PromptPanel.vue
index 237b43d..a6de48e 100644
--- a/client/src/components/ai/PromptPanel.vue
+++ b/client/src/components/ai/PromptPanel.vue
@@ -150,6 +150,10 @@ const modelOptions = [
   { label: "DeepSeek", value: "deepseek-flash" },
 ]
 const selectedModel = useStorage("prompt-model", "deepseek-flash")
+// 浏览器里可能还存着改版前的模型名
+if (!modelOptions.some((o) => o.value === selectedModel.value)) {
+  selectedModel.value = "deepseek-flash"
+}
 
 // Group messages into user+assistant pairs
 const submittingId = ref<number | null>(null)
diff --git a/client/src/components/ai/RandomRatingModal.vue b/client/src/components/ai/RandomRatingModal.vue
index f10a1be..7db8298 100644
--- a/client/src/components/ai/RandomRatingModal.vue
+++ b/client/src/components/ai/RandomRatingModal.vue
@@ -65,6 +65,8 @@ function clearReshowTimer() {
 async function fetchAndShow() {
   try {
     const item = await Submission.randomForRating(current.value?.submission_id)
+    // 请求期间 AI 已经回复完了，就不要再弹出来
+    if (!streaming.value) return
     if (item) {
       current.value = item
       previewContent.value = buildPreviewDocument({
diff --git a/client/src/components/task/TaskPanel.vue b/client/src/components/task/TaskPanel.vue
index 142b4f5..ca9adce 100644
--- a/client/src/components/task/TaskPanel.vue
+++ b/client/src/components/task/TaskPanel.vue
@@ -170,7 +170,11 @@ function syncRoute(routeName: string) {
   }
 }
 syncRoute(route.name as string)
-watch(() => route.name as string, syncRoute)
+// 只换了 display（比如浏览器后退到上一节教程）也要同步
+watch(
+  () => [route.name as string, route.params.display] as const,
+  ([name]) => syncRoute(name),
+)
 
 defineEmits(["hide"])
 
diff --git a/client/src/components/task/TutorialContent.vue b/client/src/components/task/TutorialContent.vue
index 68a45b4..d181393 100644
--- a/client/src/components/task/TutorialContent.vue
+++ b/client/src/components/task/TutorialContent.vue
@@ -3,7 +3,8 @@
 </template>
 <script lang="ts" setup>
 import { onMounted, ref, useTemplateRef, watch } from "vue"
-import { marked } from "marked"
+import { Marked } from "marked"
+import { trustedExtensions } from "../../utils/markdown"
 import copyFn from "copy-text-to-clipboard"
 import { css, html, js, tab } from "../../store/editors"
 import { Tutorial } from "../../api"
@@ -11,7 +12,8 @@ import { step, tutorialIds, loadTutorials } from "../../store/tutorial"
 import { taskId, assetBaseUrl } from "../../store/task"
 import { useRouter } from "vue-router"
 
-marked.use({
+// 独立实例：带“复制/替换”按钮的代码块只用在教程里，不能改全局的 marked
+const tutorialMarked = new Marked(...trustedExtensions, {
   renderer: {
     code({ text, lang }) {
       const language = lang?.toLowerCase() ?? "html"
@@ -36,15 +38,22 @@ const router = useRouter()
 const content = ref("")
 const $content = useTemplateRef<any>("$content")
 
+// 连点“下一节”时只用最后一次请求的结果
+let renderSeq = 0
+
 async function render() {
+  const seq = ++renderSeq
   const data = await Tutorial.get(step.value)
+  if (seq !== renderSeq) return
   taskId.value = data.task_ptr
   assetBaseUrl.value = `/media/tasks/tutorial/${step.value}/`
   html.value = data.example_html ?? ""
   css.value = data.example_css ?? ""
   js.value = data.example_js ?? ""
   const merged = `# ${data.display}. ${data.title}\n${data.content}`
-  content.value = await marked.parse(merged, { async: true })
+  const rendered = await tutorialMarked.parse(merged, { async: true })
+  if (seq !== renderSeq) return
+  content.value = rendered
 }
 
 function flash(btn: HTMLButtonElement, done: string, original: string) {
diff --git a/client/src/main.ts b/client/src/main.ts
index 181cc5c..58060b0 100644
--- a/client/src/main.ts
+++ b/client/src/main.ts
@@ -8,42 +8,12 @@ import { addAPIProvider } from "@iconify/vue"
 import "github-markdown-css/github-markdown-light.css"
 
 import { marked } from "marked"
-import alert from "marked-alert"
-import { markedHighlight } from "marked-highlight"
-import preview from "marked-code-preview"
-import { alertVariants } from "./utils/const"
-
-import hljs from "highlight.js/lib/core"
-import xml from "highlight.js/lib/languages/xml"
-import css from "highlight.js/lib/languages/css"
-import javascript from "highlight.js/lib/languages/javascript"
-import plaintext from "highlight.js/lib/languages/plaintext"
+import { trustedExtensions } from "./utils/markdown"
 //@ts-ignore
 import "highlight.js/styles/github.min.css"
 import { router } from "./router"
 
-hljs.registerLanguage("html", xml)
-hljs.registerLanguage("css", css)
-hljs.registerLanguage("js", javascript)
-hljs.registerLanguage("javascript", javascript)
-hljs.registerLanguage("plaintext", plaintext)
-
-marked.use({
-  gfm: true,
-})
-marked.use(
-  markedHighlight({
-    langPrefix: "hljs language-",
-    highlight(code, lang) {
-      const language = hljs.getLanguage(lang) ? lang : "plaintext"
-      return hljs.highlight(code, { language }).value
-    },
-  }),
-)
-marked.use(alert({ variants: alertVariants }))
-
-const template = `<div class="markedown-body-preview">{preview}</div>`
-marked.use(preview({ template }))
+marked.use(...trustedExtensions)
 
 const app = createApp(App)
 const naive = create()
diff --git a/client/src/pages/ChallengeDetail.vue b/client/src/pages/ChallengeDetail.vue
index edf5716..70efdcd 100644
--- a/client/src/pages/ChallengeDetail.vue
+++ b/client/src/pages/ChallengeDetail.vue
@@ -163,6 +163,7 @@ import {
   removeMessagePair,
   markMessageSubmitted,
 } from "../store/prompt"
+import { closeGuidance } from "../store/guidance"
 
 const route = useRoute()
 const router = useRouter()
@@ -221,6 +222,7 @@ async function loadChallenge() {
     Challenge.get(display),
     TaskAssets.listChallenge(display),
   ])
+  if (disposed) return
   taskId.value = data.task_ptr
   challengeAuthor.value = data.author_name ?? ""
   if (data.example_html || data.example_css || data.example_js) {
@@ -236,6 +238,7 @@ async function loadChallenge() {
     async: true,
     renderer: challengeRenderer,
   } as MarkedOptions)
+  if (disposed) return
   assets.value = fetchedAssets
   if (!authed.value) return
   connectPrompt(data.task_ptr)
@@ -291,11 +294,18 @@ function back() {
   router.push({ name: "home-challenge-list" })
 }
 
+// 加载还没完成就离开页面时，不要再建立连接
+let disposed = false
+
 onMounted(() => {
   setupCodeCopy()
   loadChallenge()
 })
-onUnmounted(disconnectPrompt)
+onUnmounted(() => {
+  disposed = true
+  disconnectPrompt()
+  closeGuidance()
+})
 </script>
 
 <style scoped>
diff --git a/client/src/pages/CreationDetail.vue b/client/src/pages/CreationDetail.vue
index 6e11c5e..576f5d8 100644
--- a/client/src/pages/CreationDetail.vue
+++ b/client/src/pages/CreationDetail.vue
@@ -125,6 +125,7 @@ import {
   setOnCodeComplete,
   streaming,
 } from "../store/prompt"
+import { closeGuidance } from "../store/guidance"
 
 const route = useRoute()
 const router = useRouter()
@@ -146,6 +147,7 @@ watch(streaming, (val) => {
 
 async function load() {
   const data = await Creation.get(display)
+  if (disposed) return
   taskId.value = data.task_id
   title.value = data.title
   content.value = data.content
@@ -212,8 +214,15 @@ function back() {
   router.push({ name: "creation-list" })
 }
 
+// 加载还没完成就离开页面时，不要再建立连接
+let disposed = false
+
 onMounted(load)
-onUnmounted(disconnectPrompt)
+onUnmounted(() => {
+  disposed = true
+  disconnectPrompt()
+  closeGuidance()
+})
 </script>
 
 <style scoped>
diff --git a/client/src/pages/Submissions.vue b/client/src/pages/Submissions.vue
index cc967de..a817881 100644
--- a/client/src/pages/Submissions.vue
+++ b/client/src/pages/Submissions.vue
@@ -341,16 +341,25 @@ function rowClassName(row: SubmissionOut) {
   return submission.value.id === row.id ? "row-active" : ""
 }
 
+// 快速翻页时只用最后一次请求的结果
+let initSeq = 0
+
 async function init() {
+  const seq = ++initSeq
   expandedKeys.value = []
   expandedData.clear()
   const res = await Submission.list(query)
+  if (seq !== initSeq) return
   data.value = res.items
   count.value = res.count
 }
 
+let detailSeq = 0
+
 async function getSubmissionByID(id: string) {
-  submission.value = await Submission.get(id)
+  const seq = ++detailSeq
+  const res = await Submission.get(id)
+  if (seq === detailSeq) submission.value = res
 }
 
 function afterScore() {
@@ -374,26 +383,34 @@ watch(
     router.push({ params: { page: v } })
   },
 )
+// 浏览器前进 / 后退时，页码跟着地址栏走
+watch(
+  () => route.params.page,
+  (v) => {
+    const page = Number(v) || 1
+    if (page !== query.page) query.page = page
+  },
+)
 watchDebounced(
   () => query.username,
   () => {
-    query.page = 1
-    init()
+    if (query.page !== 1) query.page = 1
+    else init()
   },
   { debounce: 500, maxWait: 1000 },
 )
 watch(
   () => query.flag,
   () => {
-    query.page = 1
-    init()
+    if (query.page !== 1) query.page = 1
+    else init()
   },
 )
 watch(
   () => query.zone,
   () => {
-    query.page = 1
-    init()
+    if (query.page !== 1) query.page = 1
+    else init()
   },
 )
 
diff --git a/client/src/pages/UserManage.vue b/client/src/pages/UserManage.vue
index 424ea9e..b2afc1a 100644
--- a/client/src/pages/UserManage.vue
+++ b/client/src/pages/UserManage.vue
@@ -151,8 +151,13 @@ async function batchCreateUsers() {
   }
 }
 
+// 快速翻页时只用最后一次请求的结果
+let initSeq = 0
+
 async function init() {
+  const seq = ++initSeq
   const data = await Account.list(query)
+  if (seq !== initSeq) return
   users.value = data.items
   count.value = data.count
 }
@@ -160,15 +165,15 @@ async function init() {
 watch(
   () => query.role,
   () => {
-    query.page = 1
-    init()
+    if (query.page !== 1) query.page = 1
+    else init()
   },
 )
 watchDebounced(
   () => query.username,
   () => {
-    query.page = 1
-    init()
+    if (query.page !== 1) query.page = 1
+    else init()
   },
   { debounce: 500, maxWait: 1000 },
 )
@@ -179,6 +184,14 @@ watch(
     router.push({ params: { page: v } })
   },
 )
+// 浏览器前进 / 后退时，页码跟着地址栏走
+watch(
+  () => route.params.page,
+  (v) => {
+    const page = Number(v) || 1
+    if (page !== query.page) query.page = page
+  },
+)
 
 onMounted(init)
 </script>
diff --git a/client/src/store/guidance.ts b/client/src/store/guidance.ts
index 6c30468..3d55e7d 100644
--- a/client/src/store/guidance.ts
+++ b/client/src/store/guidance.ts
@@ -1,5 +1,5 @@
 import { ref } from "vue"
-import { wsUrl } from "../token"
+import { ReconnectingSocket } from "../utils/socket"
 
 export interface GuidanceMessage {
   role: "user" | "assistant"
@@ -15,31 +15,19 @@ export const isReady = ref(false)
 export const isOpen = ref(false)
 export const initialPrompt = ref("")
 
-let ws: WebSocket | null = null
 let _taskId = 0
-// 取 token 要等一下，期间又重连或关闭时作废这次连接
-let connectSeq = 0
+// 打开弹窗时带过来的提示词，连上后发一次；重连时不再重发
+let unsentPrompt = ""
 
-async function connect(taskId: number) {
-  if (ws) ws.close()
-  ws = null
-  const seq = ++connectSeq
-  const url = await wsUrl(`/ws/guidance/${taskId}/`)
-  if (seq !== connectSeq) return
-  ws = new WebSocket(url)
-  setupHandlers(ws)
-}
-
-function setupHandlers(socket: WebSocket) {
-  socket.onopen = () => {
+const socket = new ReconnectingSocket({
+  onOpen() {
     connected.value = true
-    if (initialPrompt.value) {
-      sendToSocket(initialPrompt.value)
+    if (unsentPrompt) {
+      sendToSocket(unsentPrompt)
+      unsentPrompt = ""
     }
-  }
-
-  socket.onmessage = (event) => {
-    const data = JSON.parse(event.data)
+  },
+  onMessage(data) {
     if (data.type === "init") {
       streaming.value = false
       streamingContent.value = ""
@@ -57,18 +45,38 @@ function setupHandlers(socket: WebSocket) {
       streamingContent.value = ""
       messages.value.push({ role: "assistant", content: data.content })
     }
-  }
-
-  socket.onclose = () => {
+  },
+  onDrop() {
     connected.value = false
-  }
+    if (streaming.value) dropPendingMessage()
+  },
+  onGiveUp() {
+    messages.value.push({
+      role: "assistant",
+      content: "与服务器的连接已断开，请刷新页面重试",
+    })
+  },
+})
+
+function connect(taskId: number) {
+  socket.connect(`/ws/guidance/${taskId}/`)
 }
 
 function sendToSocket(content: string) {
-  if (!ws || ws.readyState !== WebSocket.OPEN) return
+  if (!socket.send({ type: "message", content })) return
   streaming.value = true
   messages.value.push({ role: "user", content })
-  ws.send(JSON.stringify({ type: "message", content }))
+}
+
+function dropPendingMessage() {
+  if (
+    messages.value.length > 0 &&
+    messages.value[messages.value.length - 1].role === "user"
+  ) {
+    messages.value.pop()
+  }
+  streaming.value = false
+  streamingContent.value = ""
 }
 
 export function openGuidance(taskId: number, prompt: string) {
@@ -76,6 +84,7 @@ export function openGuidance(taskId: number, prompt: string) {
 
   _taskId = taskId
   initialPrompt.value = prompt
+  unsentPrompt = prompt
   messages.value = []
   isReady.value = false
   streamingContent.value = ""
@@ -89,26 +98,17 @@ export function sendGuidance(content: string) {
 }
 
 export function stopGuidance() {
-  if (
-    messages.value.length > 0 &&
-    messages.value[messages.value.length - 1].role === "user"
-  ) {
-    messages.value.pop()
-  }
-  streaming.value = false
-  streamingContent.value = ""
+  dropPendingMessage()
   if (_taskId) {
     initialPrompt.value = ""
+    unsentPrompt = ""
     connect(_taskId)
   }
 }
 
 export function closeGuidance() {
-  connectSeq++
-  if (ws) {
-    ws.close()
-    ws = null
-  }
+  socket.close()
+  unsentPrompt = ""
   isOpen.value = false
   messages.value = []
   isReady.value = false
diff --git a/client/src/store/prompt.ts b/client/src/store/prompt.ts
index a95af8a..bad3574 100644
--- a/client/src/store/prompt.ts
+++ b/client/src/store/prompt.ts
@@ -1,5 +1,5 @@
 import { ref } from "vue"
-import { wsUrl } from "../token"
+import { ReconnectingSocket } from "../utils/socket"
 import { html, css, js } from "./editors"
 
 export interface PromptMessage {
@@ -28,81 +28,75 @@ export function setOnCodeComplete(fn: typeof _onCodeComplete) {
   _onCodeComplete = fn
 }
 
-let ws: WebSocket | null = null
-// 取 token 要等一下，期间又连了别的题或断开时作废这次连接
-let connectSeq = 0
-
-export async function connectPrompt(taskId: number) {
-  currentTaskId.value = taskId
-  if (ws) ws.close()
-  ws = null
-
-  const seq = ++connectSeq
-  const url = await wsUrl(`/ws/prompt/${taskId}/`)
-  if (seq !== connectSeq) return
-  ws = new WebSocket(url)
-
-  ws.onopen = () => {
-    connected.value = true
-  }
-
-  ws.onmessage = (event) => {
-    const data = JSON.parse(event.data)
-
-    if (data.type === "init") {
-      streaming.value = false
-      streamingContent.value = ""
-      const alreadyLoaded = conversationId.value === data.conversation_id
-      conversationId.value = data.conversation_id
-      if (!alreadyLoaded) {
-        messages.value = data.messages || []
-        const lastAssistant = [...messages.value]
-          .reverse()
-          .find((m) => m.role === "assistant" && m.code)
-        if (lastAssistant?.code) {
-          applyCode(lastAssistant.code)
-        }
+function onMessage(data: any) {
+  if (data.type === "init") {
+    streaming.value = false
+    streamingContent.value = ""
+    const alreadyLoaded = conversationId.value === data.conversation_id
+    conversationId.value = data.conversation_id
+    if (!alreadyLoaded) {
+      messages.value = data.messages || []
+      const lastAssistant = [...messages.value]
+        .reverse()
+        .find((m) => m.role === "assistant" && m.code)
+      if (lastAssistant?.code) {
+        applyCode(lastAssistant.code)
       }
-    } else if (data.type === "stream") {
-      streaming.value = true
-      streamingContent.value += data.content
-    } else if (data.type === "complete") {
-      streaming.value = false
-      messages.value.push({
-        role: "assistant",
-        content: streamingContent.value,
-        id: data.message_id,
-        code: data.code,
-        submitted: false,
-      })
-      streamingContent.value = ""
-      if (data.code) {
-        applyCode(data.code)
-        if (_onCodeComplete) {
-          _onCodeComplete(data.code, data.message_id)
-        }
-      }
-    } else if (data.type === "error") {
-      streaming.value = false
-      streamingContent.value = ""
-      messages.value.push({
-        role: "assistant",
-        content: data.content,
-      })
     }
-  }
-
-  ws.onclose = () => {
-    connected.value = false
+  } else if (data.type === "stream") {
+    streaming.value = true
+    streamingContent.value += data.content
+  } else if (data.type === "complete") {
+    streaming.value = false
+    messages.value.push({
+      role: "assistant",
+      content: streamingContent.value,
+      id: data.message_id,
+      code: data.code,
+      submitted: false,
+    })
+    streamingContent.value = ""
+    if (data.code) {
+      applyCode(data.code)
+      if (_onCodeComplete) {
+        _onCodeComplete(data.code, data.message_id)
+      }
+    }
+  } else if (data.type === "error") {
+    streaming.value = false
+    streamingContent.value = ""
+    messages.value.push({
+      role: "assistant",
+      content: data.content,
+    })
   }
 }
 
+const socket = new ReconnectingSocket({
+  onOpen() {
+    connected.value = true
+  },
+  onMessage,
+  onDrop() {
+    connected.value = false
+    // 断开时服务端会删掉还没有回复的提问，这边也去掉
+    if (streaming.value) dropPendingPrompt()
+  },
+  onGiveUp() {
+    messages.value.push({
+      role: "assistant",
+      content: "与服务器的连接已断开，请刷新页面重试",
+    })
+  },
+})
+
+export function connectPrompt(taskId: number) {
+  currentTaskId.value = taskId
+  socket.connect(`/ws/prompt/${taskId}/`)
+}
+
 export function disconnectPrompt() {
-  connectSeq++
-  if (ws) {
-    ws.close()
-    ws = null
-  }
+  socket.close()
   messages.value = []
   conversationId.value = ""
   connected.value = false
@@ -113,13 +107,12 @@ export function disconnectPrompt() {
 }
 
 export function sendPrompt(content: string, model: string = "") {
-  if (!ws || ws.readyState !== WebSocket.OPEN) return
+  if (!socket.send({ type: "message", content, model })) return
   streaming.value = true
   messages.value.push({ role: "user", content })
-  ws.send(JSON.stringify({ type: "message", content, model }))
 }
 
-export function stopPrompt() {
+function dropPendingPrompt() {
   if (
     messages.value.length > 0 &&
     messages.value[messages.value.length - 1].role === "user"
@@ -128,6 +121,10 @@ export function stopPrompt() {
   }
   streaming.value = false
   streamingContent.value = ""
+}
+
+export function stopPrompt() {
+  dropPendingPrompt()
   if (currentTaskId.value) {
     connectPrompt(currentTaskId.value)
   }
diff --git a/client/src/utils/markdown.ts b/client/src/utils/markdown.ts
index d153075..a1b8af2 100644
--- a/client/src/utils/markdown.ts
+++ b/client/src/utils/markdown.ts
@@ -1,4 +1,36 @@
-import { Marked } from "marked"
+import { Marked, type MarkedExtension } from "marked"
+import alert from "marked-alert"
+import { markedHighlight } from "marked-highlight"
+import preview from "marked-code-preview"
+import hljs from "highlight.js/lib/core"
+import xml from "highlight.js/lib/languages/xml"
+import css from "highlight.js/lib/languages/css"
+import javascript from "highlight.js/lib/languages/javascript"
+import plaintext from "highlight.js/lib/languages/plaintext"
+import { alertVariants } from "./const"
+
+hljs.registerLanguage("html", xml)
+hljs.registerLanguage("css", css)
+hljs.registerLanguage("js", javascript)
+hljs.registerLanguage("javascript", javascript)
+hljs.registerLanguage("plaintext", plaintext)
+
+const highlight = markedHighlight({
+  langPrefix: "hljs language-",
+  highlight(code, lang) {
+    const language = hljs.getLanguage(lang) ? lang : "plaintext"
+    return hljs.highlight(code, { language }).value
+  },
+})
+const alerts = alert({ variants: alertVariants })
+
+// 老师写的教程、挑战描述用：带 preview 的代码块会渲染成真实的 HTML
+export const trustedExtensions: MarkedExtension[] = [
+  { gfm: true },
+  highlight,
+  alerts,
+  preview({ template: `<div class="markedown-body-preview">{preview}</div>` }),
+]
 
 // 提示词和 AI 回复是用户可控的内容，渲染进 v-html 前必须去掉可执行的部分：
 // 原始 HTML 一律转义成文本，链接和图片只放行 http(s)/mailto 和相对地址
@@ -12,7 +44,8 @@ const escapeHtml = (s: string) =>
 const isSafeUrl = (href: string) =>
   !/^\s*[a-z][a-z0-9+.-]*:/i.test(href) || /^\s*(https?|mailto):/i.test(href)
 
-const safeMarked = new Marked({
+// 独立实例，不带 preview 扩展（它会把代码块原样当 HTML 渲染）
+const safeMarked = new Marked({ gfm: true }, highlight, alerts, {
   renderer: {
     html({ text }) {
       return escapeHtml(text)
diff --git a/client/src/utils/socket.ts b/client/src/utils/socket.ts
new file mode 100644
index 0000000..4ca2303
--- /dev/null
+++ b/client/src/utils/socket.ts
@@ -0,0 +1,80 @@
+import { getRefreshToken, refreshAccessToken, wsUrl } from "../token"
+
+const MAX_DELAY_MS = 30_000
+// 连续这么多次没连上就放弃，让用户刷新页面
+const MAX_FAILURES = 6
+
+interface Handlers {
+  onOpen?: () => void
+  onMessage: (data: any) => void
+  // 非主动断开（服务器重启、网络断了），之后会自动重连
+  onDrop?: () => void
+  onGiveUp?: () => void
+}
+
+// 带断线重连的 WebSocket：非主动关闭时按 1s、2s、4s… 退避重连。
+// 握手就失败多半是 access token 失效（比如服务端重启换了密钥），重连前先强制刷新
+export class ReconnectingSocket {
+  private ws: WebSocket | null = null
+  private path = ""
+  // 取 token、等重连期间又调用了 connect/close 时，作废旧的那次
+  private seq = 0
+  private timer: ReturnType<typeof setTimeout> | undefined
+  private failures = 0
+
+  constructor(private handlers: Handlers) {}
+
+  connect(path: string) {
+    this.close()
+    this.path = path
+    this.failures = 0
+    this.open(this.seq)
+  }
+
+  close() {
+    this.seq++
+    clearTimeout(this.timer)
+    const ws = this.ws
+    this.ws = null
+    ws?.close()
+  }
+
+  send(data: unknown) {
+    if (this.ws?.readyState !== WebSocket.OPEN) return false
+    this.ws.send(JSON.stringify(data))
+    return true
+  }
+
+  private async open(seq: number) {
+    const url = await wsUrl(this.path)
+    if (seq !== this.seq) return
+    const socket = new WebSocket(url)
+    this.ws = socket
+    let opened = false
+
+    socket.onopen = () => {
+      if (socket !== this.ws) return
+      opened = true
+      this.failures = 0
+      this.handlers.onOpen?.()
+    }
+    socket.onmessage = (event) => {
+      if (socket === this.ws) this.handlers.onMessage(JSON.parse(event.data))
+    }
+    socket.onclose = async () => {
+      if (socket !== this.ws) return
+      this.ws = null
+      this.handlers.onDrop?.()
+      if (++this.failures > MAX_FAILURES || !getRefreshToken()) {
+        this.handlers.onGiveUp?.()
+        return
+      }
+      if (!opened) await refreshAccessToken()
+      if (seq !== this.seq) return
+      const delay = Math.min(1000 * 2 ** (this.failures - 1), MAX_DELAY_MS)
+      this.timer = setTimeout(() => {
+        if (seq === this.seq) this.open(seq)
+      }, delay)
+    }
+  }
+}
diff --git a/server/src/auth.ts b/server/src/auth.ts
index 4419468..fdf3db9 100644
--- a/server/src/auth.ts
+++ b/server/src/auth.ts
@@ -161,3 +161,7 @@ export const requireSuper = (c: Ctx) => requireRoles(c, [Role.SUPER])
 
 export const isStaff = (user: User) =>
   user.role === Role.ADMIN || user.role === Role.SUPER
+
+// 未公开的教程只有超管能看，未公开的挑战管理员也能看（和能编辑它们的人一致）
+export const canSeeUnpublished = (user: User | null | undefined, kind: "tutorial" | "challenge") =>
+  !!user && (kind === "tutorial" ? user.role === Role.SUPER : isStaff(user))
diff --git a/server/src/routes/account.ts b/server/src/routes/account.ts
index ba02bd8..8485ee7 100644
--- a/server/src/routes/account.ts
+++ b/server/src/routes/account.ts
@@ -54,19 +54,6 @@ async function insertUser(u: {
 const userExists = (username: string) =>
   !!get(`SELECT 1 FROM account_user WHERE username = $username`, { username })
 
-router.post("/register", async (c) => {
-  const payload = await body(
-    c,
-    z.object({
-      username: z.string(),
-      email: z.email(),
-      password: z.string().min(6).max(20),
-    }),
-  )
-  await insertUser(payload)
-  return c.json({ message: "创建成功" })
-})
-
 router.post("/login", async (c) => {
   const payload = await body(c, z.object({ username: z.string(), password: z.string() }))
   const user = await authenticate(payload.username, payload.password)
diff --git a/server/src/routes/files.ts b/server/src/routes/files.ts
index 4a1a08e..cba4591 100644
--- a/server/src/routes/files.ts
+++ b/server/src/routes/files.ts
@@ -4,8 +4,8 @@ import { existsSync } from "node:fs"
 import { dirname, extname, join, resolve, sep } from "node:path"
 import { config } from "../config"
 import { all, get, run } from "../db"
-import { requireAdmin, requireSuper, type User } from "../auth"
-import { HttpError, ValidationError, intParam, orNotFound, type Ctx, type Env } from "../http"
+import { canSeeUnpublished, requireAdmin, requireSuper, type User } from "../auth"
+import { HttpError, ValidationError, intParam, notFound, orNotFound, type Ctx, type Env } from "../http"
 
 // 与 Django 的 get_valid_filename 一致：空格换成下划线，去掉除字母数字、-、_、. 以外的字符
 export function validFilename(name: string) {
@@ -53,8 +53,8 @@ type Kind = "challenge" | "tutorial"
 
 function findTask(kind: Kind, display: number) {
   return orNotFound(
-    get<{ id: number; task_type: string; display: number }>(
-      `SELECT t.id, t.task_type, t.display FROM task_task t
+    get<{ id: number; task_type: string; display: number; is_public: number }>(
+      `SELECT t.id, t.task_type, t.display, t.is_public FROM task_task t
        JOIN task_${kind} x ON x.task_ptr_id = t.id WHERE t.display = $display`,
       { display },
     ),
@@ -72,6 +72,7 @@ for (const kind of ["challenge", "tutorial"] as const) {
 
   assets.get(`/${kind}/:display`, (c) => {
     const task = findTask(kind, intParam(c, "display"))
+    if (!task.is_public && !canSeeUnpublished(c.get("user"), kind)) notFound()
     const rows = all<{ name: string; file: string }>(
       `SELECT name, file FROM task_taskasset WHERE task_id = $id ORDER BY id`,
       { id: task.id },
diff --git a/server/src/routes/tasks.ts b/server/src/routes/tasks.ts
index 77a3250..997b72a 100644
--- a/server/src/routes/tasks.ts
+++ b/server/src/routes/tasks.ts
@@ -1,8 +1,8 @@
 import { Hono } from "hono"
 import { z } from "zod"
 import { all, get, run, tx, now, iso } from "../db"
-import { Role, requireAdmin, requireSuper, requireUser, type User } from "../auth"
-import { HttpError, body, bool, intParam, orNotFound, type Env } from "../http"
+import { Role, canSeeUnpublished, requireAdmin, requireSuper, requireUser, type User } from "../auth"
+import { HttpError, body, bool, intParam, notFound, orNotFound, type Env } from "../http"
 import { deleteTask } from "../services/cascade"
 
 const TASK_COLUMNS = `t.id, t.created, t.modified, t.display, t.title, t.content, t.task_type,
@@ -134,6 +134,7 @@ tutorial.get("/:display", (c) => {
       { display: intParam(c, "display") },
     ),
   )
+  if (!row.is_public && !canSeeUnpublished(c.get("user"), "tutorial")) notFound()
   return c.json(taskOut(row))
 })
 
@@ -227,6 +228,7 @@ challenge.get("/:display", (c) => {
       display: intParam(c, "display"),
     }),
   )
+  if (!r.is_public && !canSeeUnpublished(c.get("user"), "challenge")) notFound()
   return c.json({
     ...taskOut(r),
     score: r.score,
diff --git a/server/src/services/llm.ts b/server/src/services/llm.ts
index 77b5080..cc137f1 100644
--- a/server/src/services/llm.ts
+++ b/server/src/services/llm.ts
@@ -46,10 +46,14 @@ export const GUIDANCE_SYSTEM_PROMPT = `你是一个提示词写作教练，帮
 5. 如果回复以 [READY] 开头，[READY] 不要加粗，必须保持原始文本
 6. 不要生成任何代码`
 
-const DEFAULT_MODEL = "deepseek-flash"
 // 走火山方舟（ARK）接口的模型
 const ARK_MODELS = new Set(["doubao-seed-2-1-lite-260915"])
 
+// 客户端可选的模型；不认识的（比如浏览器里存着改版前的模型名）一律换成默认模型
+export function chatModel(model?: string) {
+  return model && (model === config.llmModel || ARK_MODELS.has(model)) ? model : config.llmModel
+}
+
 export interface ChatMessage {
   role: "system" | "user" | "assistant"
   content: string
@@ -63,10 +67,14 @@ interface CompletionOptions {
   timeoutMs?: number
 }
 
+// 流式生成：超过这么久没收到新数据才算超时，另有一个总时长上限
+const STREAM_IDLE_MS = 120_000
+const STREAM_MAX_MS = 15 * 60_000
+
 export const llmConfigured = () => !!config.llmApiKey
 
 function buildRequest(messages: ChatMessage[], opts: CompletionOptions) {
-  const model = opts.model || DEFAULT_MODEL
+  const model = opts.model || config.llmModel
   const ark = ARK_MODELS.has(model)
   const body: Record<string, unknown> = {
     model,
@@ -102,30 +110,60 @@ async function* streamCompletion(
   model?: string,
   signal?: AbortSignal,
 ): AsyncGenerator<string> {
-  const res = await buildRequest(messages, { model, stream: true, signal })
-  await ensureOk(res)
-  if (!res.body) return
-  const decoder = new TextDecoder()
-  let buffer = ""
-  for await (const chunk of res.body) {
-    buffer += decoder.decode(chunk, { stream: true })
-    let idx: number
-    while ((idx = buffer.indexOf("\n")) >= 0) {
-      const line = buffer.slice(0, idx).trim()
-      buffer = buffer.slice(idx + 1)
-      if (!line.startsWith("data:")) continue
-      const data = line.slice(5).trim()
-      if (data === "[DONE]") return
-      const json = JSON.parse(data)
-      if (json.error) throw new Error(json.error.message ?? JSON.stringify(json.error))
-      const content = json.choices?.[0]?.delta?.content
-      if (content) yield content
+  // 带思考的模型生成整页代码可能超过两分钟，只要一直有数据就不该中断
+  const idle = new AbortController()
+  let timer = setTimeout(() => idle.abort(new Error("模型响应超时")), STREAM_IDLE_MS)
+  const resetIdle = () => {
+    clearTimeout(timer)
+    timer = setTimeout(() => idle.abort(new Error("模型响应超时")), STREAM_IDLE_MS)
+  }
+  const signals = [idle.signal]
+  if (signal) signals.push(signal)
+  try {
+    const res = await buildRequest(messages, {
+      model,
+      stream: true,
+      signal: AbortSignal.any(signals),
+      timeoutMs: STREAM_MAX_MS,
+    })
+    await ensureOk(res)
+    if (!res.body) return
+    const decoder = new TextDecoder()
+    let buffer = ""
+    // 返回 true 表示收到了 [DONE]
+    function* parse(lines: string[]): Generator<string, boolean> {
+      for (const raw of lines) {
+        const line = raw.trim()
+        if (!line.startsWith("data:")) continue
+        const data = line.slice(5).trim()
+        if (data === "[DONE]") return true
+        const json = JSON.parse(data)
+        if (json.error) throw new Error(json.error.message ?? JSON.stringify(json.error))
+        const content = json.choices?.[0]?.delta?.content
+        if (content) yield content
+      }
+      return false
     }
+    for await (const chunk of res.body) {
+      resetIdle()
+      buffer += decoder.decode(chunk, { stream: true })
+      const lines = buffer.split("\n")
+      buffer = lines.pop()!
+      if (yield* parse(lines)) return
+    }
+    // 最后一行可能没有换行
+    yield* parse([buffer + decoder.decode()])
+  } finally {
+    clearTimeout(timer)
   }
 }
 
 export function streamChat(history: ChatMessage[], model?: string, signal?: AbortSignal) {
-  return streamCompletion([{ role: "system", content: SYSTEM_PROMPT }, ...history], model, signal)
+  return streamCompletion(
+    [{ role: "system", content: SYSTEM_PROMPT }, ...history],
+    chatModel(model),
+    signal,
+  )
 }
 
 export function streamGuidance(history: ChatMessage[], signal?: AbortSignal) {
diff --git a/server/src/ws.ts b/server/src/ws.ts
index 49f2718..4b92330 100644
--- a/server/src/ws.ts
+++ b/server/src/ws.ts
@@ -1,5 +1,5 @@
 import type { Server, ServerWebSocket, WebSocketHandler } from "bun"
-import { all, run, iso, uuidOut } from "./db"
+import { all, get, run, iso, uuidOut } from "./db"
 import { userFromAccessToken, type User } from "./auth"
 import { canAccessTask, getOrCreateActiveConversation, insertMessage } from "./services/prompt"
 import {
@@ -41,8 +41,12 @@ export async function upgrade(
   const match = PATH_RE.exec(url.pathname)
   if (!match) return null
   const user = await userFromAccessToken(url.searchParams.get("token"))
+  if (!user) return new Response("Unauthorized", { status: 401 })
   const taskId = Number(match[2])
-  if (!user || !canAccessTask(user, taskId)) return new Response("Forbidden", { status: 403 })
+  if (!get(`SELECT 1 FROM task_task WHERE id = $id`, { id: taskId })) {
+    return new Response("Not Found", { status: 404 })
+  }
+  if (!canAccessTask(user, taskId)) return new Response("Forbidden", { status: 403 })
 
   const ok = server.upgrade(req, {
     data: {
@@ -155,6 +159,8 @@ async function handleGuidance(ws: WS, data: any) {
     try {
       full = await streamToClient(ws, streamGuidance(ws.data.guidanceHistory, ws.data.abort.signal))
     } catch (e) {
+      // 这条提问没有回复，留在上下文里会出现连续两条用户消息
+      ws.data.guidanceHistory.pop()
       send(ws, { type: "error", content: `AI 服务出错：${e instanceof Error ? e.message : e}` })
       return
     }
@@ -182,7 +188,14 @@ export const websocket: WebSocketHandler<WsData> = {
 
   open(ws) {
     const d = ws.data
-    d.conversationId = getOrCreateActiveConversation(d.user.id, d.taskId)
+    try {
+      d.conversationId = getOrCreateActiveConversation(d.user.id, d.taskId)
+    } catch (e) {
+      // 比如任务刚被删掉；不关掉的话客户端会一直等 init
+      console.error("websocket open failed:", e)
+      ws.close(1011, "conversation unavailable")
+      return
+    }
     if (d.kind === "guidance") {
       send(ws, { type: "init", messages: [] })
       return
@@ -212,7 +225,10 @@ export const websocket: WebSocketHandler<WsData> = {
     const handler = ws.data.kind === "prompt" ? handlePrompt : handleGuidance
     ws.data.queue = ws.data.queue
       .then(() => (ws.data.closed ? undefined : handler(ws, data)))
-      .catch((e) => console.error("websocket handler failed:", e))
+      .catch((e) => {
+        console.error("websocket handler failed:", e)
+        send(ws, { type: "error", content: "服务器出错，请刷新页面重试" })
+      })
   },
 
   close(ws) {
diff --git a/server/tests/api.test.ts b/server/tests/api.test.ts
index 3e2ad5a..18886cf 100644
--- a/server/tests/api.test.ts
+++ b/server/tests/api.test.ts
@@ -17,6 +17,34 @@ describe("权限", () => {
     expect((await adm("GET", "/api/submission/gradebook/?classname=a")).status).toBe(403)
   })
 
+  test("未公开的教程只有超管能看，未公开的挑战管理员也能看", async () => {
+    makeUser("stu")
+    makeUser("adm", "admin")
+    makeUser("boss", "super")
+    makeTask("草稿教程", "tutorial", 1, false)
+    makeTask("草稿挑战", "challenge", 2, false)
+    makeTask("公开挑战", "challenge", 3, true)
+    const [anon, stu, adm, boss] = await Promise.all([client(), client("stu"), client("adm"), client("boss")])
+    for (const path of ["/api/tutorial/1", "/api/challenge/2", "/api/assets/challenge/2"]) {
+      expect((await anon("GET", path)).status).toBe(404)
+      expect((await stu("GET", path)).status).toBe(404)
+    }
+    expect((await stu("GET", "/api/challenge/3")).status).toBe(200)
+    expect((await adm("GET", "/api/tutorial/1")).status).toBe(404)
+    expect((await adm("GET", "/api/challenge/2")).status).toBe(200)
+    expect((await adm("GET", "/api/assets/challenge/2")).status).toBe(200)
+    expect((await boss("GET", "/api/tutorial/1")).status).toBe(200)
+  })
+
+  test("没有公开注册接口", async () => {
+    const res = await (await client())("POST", "/api/account/register", {
+      username: "x",
+      email: "x@x.com",
+      password: "123456",
+    })
+    expect(res.status).toBe(404)
+  })
+
   test("封号后 access token 和 refresh token 都失效", async () => {
     const id = makeUser("stu")
     makeUser("boss", "super")
diff --git a/server/tests/unit.test.ts b/server/tests/unit.test.ts
index a7fdda0..3311c39 100644
--- a/server/tests/unit.test.ts
+++ b/server/tests/unit.test.ts
@@ -1,6 +1,7 @@
 import { describe, expect, test } from "bun:test"
 import { pyRound, pySum } from "../src/services/pyround"
-import { extractCode, parseGuidanceResponse } from "../src/services/llm"
+import { chatModel, extractCode, parseGuidanceResponse, streamChat } from "../src/services/llm"
+import { config } from "../src/config"
 import { checkPassword, makePassword } from "../src/auth"
 import { formatMicros, iso, uuidHex, uuidOut } from "../src/db"
 import { toCsv } from "../src/services/gradebook"
@@ -67,3 +68,49 @@ test("时间与 UUID 格式", () => {
 test("CSV 转义", () => {
   expect(toCsv([["a", 'b"c', "d,e"], [1, 2.5, ""]])).toBe('a,"b""c","d,e"\r\n1,2.5,\r\n')
 })
+
+describe("streamChat", () => {
+  test("不认识的模型换成默认模型，最后一行没有换行也能读到", async () => {
+    let model = ""
+    const server = Bun.serve({
+      port: 0,
+      async fetch(req) {
+        model = ((await req.json()) as any).model
+        const line = (s: string) => `data: ${JSON.stringify({ choices: [{ delta: { content: s } }] })}`
+        // 一行拆在两个分块之间，最后一行不带换行
+        const body = `${line("你好")}\n\n${line("世")}\n${line("界")}`
+        const enc = new TextEncoder()
+        const cut = body.indexOf("世") + 2
+        return new Response(
+          new ReadableStream({
+            async start(ctrl) {
+              ctrl.enqueue(enc.encode(body.slice(0, cut)))
+              await Bun.sleep(5)
+              ctrl.enqueue(enc.encode(body.slice(cut)))
+              ctrl.close()
+            },
+          }),
+          { headers: { "content-type": "text/event-stream" } },
+        )
+      },
+    })
+    const saved = { ...config }
+    Object.assign(config, { llmApiKey: "k", llmBaseUrl: `http://localhost:${server.port}` })
+    try {
+      let out = ""
+      for await (const s of streamChat([{ role: "user", content: "hi" }], "deepseek-v4-flash-thinking")) out += s
+      expect(out).toBe("你好世界")
+      expect(model).toBe(config.llmModel)
+    } finally {
+      Object.assign(config, saved)
+      server.stop(true)
+    }
+  })
+
+  test("chatModel 只放行配置里的模型", () => {
+    expect(chatModel("doubao-seed-2-1-lite-260915")).toBe("doubao-seed-2-1-lite-260915")
+    expect(chatModel(config.llmModel)).toBe(config.llmModel)
+    expect(chatModel("gpt-5")).toBe(config.llmModel)
+    expect(chatModel("")).toBe(config.llmModel)
+  })
+})