diff --git a/apps/web/src/oj/contest/pages/class.vue b/apps/web/src/oj/contest/pages/class.vue
index 80af22c..88a9db0 100644
--- a/apps/web/src/oj/contest/pages/class.vue
+++ b/apps/web/src/oj/contest/pages/class.vue
@@ -11,6 +11,7 @@ import { useLeaveStudents } from "shared/composables/leaveStudents"
 import { ContestStatus, LANGUAGE_FORMAT_VALUE } from "utils/constants"
 import { parseTime, secondsToDuration } from "utils/functions"
 import type { Submission } from "utils/types"
+import { useVisibleInterval } from "shared/composables/visibleInterval"
 
 /**
  * 老师的「全班情况」，考完叫「成绩」（设计稿「比赛重设计」老师两块）。学生看不到这一页。
@@ -43,7 +44,7 @@ async function load() {
 const running = computed(() => contestStore.contestStatus === ContestStatus.underway)
 const ended = computed(() => contestStore.contestStatus === ContestStatus.finished)
 
-const { pause, resume } = useIntervalFn(load, 15_000, { immediate: false })
+const { pause, resume } = useVisibleInterval(load, 15_000)
 watch(
   () => [contestStore.canEnter, running.value] as const,
   ([enter, run]) => {
diff --git a/apps/web/src/oj/contest/pages/problems.vue b/apps/web/src/oj/contest/pages/problems.vue
index 23d658e..7a27860 100644
--- a/apps/web/src/oj/contest/pages/problems.vue
+++ b/apps/web/src/oj/contest/pages/problems.vue
@@ -7,6 +7,7 @@ import { useUserStore } from "shared/store/user"
 import { ContestStatus } from "utils/constants"
 import { parseTime, secondsToDuration } from "utils/functions"
 import RankMini from "../components/RankMini.vue"
+import { useVisibleInterval } from "shared/composables/visibleInterval"
 
 /**
  * 比赛页「题目」（设计稿「比赛重设计」B，用户选的）：一页放下。
@@ -24,12 +25,9 @@ const tone = useTone()
 const running = computed(() => contestStore.contestStatus === ContestStatus.underway)
 const ended = computed(() => contestStore.contestStatus === ContestStatus.finished)
 
-const { pause, resume } = useIntervalFn(
+const { pause, resume } = useVisibleInterval(
   () => contestStore.loadScoreboard(props.contestID),
   10_000,
-  {
-    immediate: false,
-  },
 )
 watch(
   () => [contestStore.canEnter, contestStore.contestStatus] as const,
diff --git a/apps/web/src/oj/contest/pages/rank.vue b/apps/web/src/oj/contest/pages/rank.vue
index 5e37280..211dbc7 100644
--- a/apps/web/src/oj/contest/pages/rank.vue
+++ b/apps/web/src/oj/contest/pages/rank.vue
@@ -8,6 +8,7 @@ import { ContestStatus } from "utils/constants"
 import { secondsToDuration } from "utils/functions"
 import { classLabel } from "oj/submission/utils"
 import UserName from "shared/components/UserName.vue"
+import { useVisibleInterval } from "shared/composables/visibleInterval"
 
 /**
  * 比赛排名（设计稿「比赛重设计」排行榜两块）。竞争感是用户要的（「我需要竞争」）：
@@ -26,12 +27,9 @@ const running = computed(() => contestStore.contestStatus === ContestStatus.unde
 const ended = computed(() => contestStore.contestStatus === ContestStatus.finished)
 
 const autoRefresh = ref(true)
-const { pause, resume } = useIntervalFn(
+const { pause, resume } = useVisibleInterval(
   () => contestStore.loadScoreboard(props.contestID),
   10_000,
-  {
-    immediate: false,
-  },
 )
 watch(
   () => [contestStore.canEnter, running.value, autoRefresh.value] as const,
diff --git a/apps/web/src/oj/problem/composables/useSubmissionMonitor.ts b/apps/web/src/oj/problem/composables/useSubmissionMonitor.ts
index fdde300..f1f2b48 100644
--- a/apps/web/src/oj/problem/composables/useSubmissionMonitor.ts
+++ b/apps/web/src/oj/problem/composables/useSubmissionMonitor.ts
@@ -1,10 +1,10 @@
-import { ref, computed, getCurrentScope, onScopeDispose } from "vue"
-import { useIntervalFn, useTimeoutFn } from "@vueuse/core"
+import { ref, computed } from "vue"
 import { getSubmission } from "oj/api"
 import { SubmissionStatus } from "utils/constants"
 import type { PendingAchievement, Submission } from "utils/types"
 import { useAchievementStore } from "shared/store/achievement"
 import { useSubmissionWebSocket, type SubmissionUpdate } from "shared/composables/websocket"
+import { useFallbackPoll } from "shared/composables/fallbackPoll"
 
 /**
  * 判题监控 Composable
@@ -15,33 +15,6 @@ export function useSubmissionMonitor() {
   const submissionId = ref("")
   const submission = ref<Submission>()
 
-  // ==================== 轮询机制 ====================
-  const { pause: pausePolling, resume: resumePolling } = useIntervalFn(
-    async () => {
-      const id = submissionId.value
-      if (!id) return
-
-      try {
-        const res = await getSubmission(id)
-        // 请求在路上时换了题（reset）或者又交了一次：回来的是上一条，扔掉。
-        // 不扔的话上一道题判对了，会把新题标成已解决、弹点评
-        if (id !== submissionId.value) return
-        submission.value = res
-
-        const result = res.result
-        // 判题完成，停止轮询
-        if (result !== SubmissionStatus.judging && result !== SubmissionStatus.pending) {
-          pausePolling()
-        }
-      } catch (error) {
-        console.error("[SubmissionMonitor] 轮询失败:", error)
-        pausePolling()
-      }
-    },
-    2000,
-    { immediate: false },
-  )
-
   // ==================== WebSocket 处理 ====================
   const handleSubmissionUpdate = (data: SubmissionUpdate) => {
     // push_to_user 复用了 submission_update 这个 channel handler，
@@ -64,6 +37,8 @@ export function useSubmissionMonitor() {
       console.log("[SubmissionMonitor] 提交ID不匹配，忽略")
       return
     }
+    // 订阅后服务端立刻回的那一帧（还在排队也回）就算：WebSocket 是通的，轮询退到慢档
+    fallback.confirm()
 
     if (!submission.value) {
       submission.value = {} as Submission
@@ -76,7 +51,7 @@ export function useSubmissionMonitor() {
       console.log(`[SubmissionMonitor] 判题${data.status === "finished" ? "完成" : "出错"}`)
 
       // 停止轮询（WebSocket已成功）
-      pausePolling()
+      fallback.stop()
       // 结果已经到手，别让重连再去重放这条早就判完的订阅
       unsubscribe()
 
@@ -91,25 +66,23 @@ export function useSubmissionMonitor() {
   }
 
   // 初始化 WebSocket
-  const { connect, subscribe, unsubscribe, scheduleDisconnect, cancelScheduledDisconnect } =
+  const { connect, subscribe, unsubscribe, scheduleDisconnect, cancelScheduledDisconnect, status } =
     useSubmissionWebSocket(handleSubmissionUpdate)
 
-  // ==================== 轮询保底启动 ====================
-  const { start: startPollingFallback } = useTimeoutFn(
-    () => {
-      if (
-        submission.value &&
-        (submission.value.result === SubmissionStatus.judging ||
-          submission.value.result === SubmissionStatus.pending ||
-          submission.value.result === SubmissionStatus.submitting)
-      ) {
-        console.log("[SubmissionMonitor] WebSocket未及时响应，启动轮询保底")
-        resumePolling()
-      }
+  // ==================== 轮询兜底 ====================
+  const fallback = useFallbackPoll({
+    status,
+    poll: async () => {
+      const id = submissionId.value
+      if (!id) return true
+      const res = await getSubmission(id)
+      // 请求在路上时换了题（reset）或者又交了一次：回来的是上一条，扔掉。
+      // 不扔的话上一道题判对了，会把新题标成已解决、弹点评
+      if (id !== submissionId.value) return false
+      submission.value = res
+      return res.result !== SubmissionStatus.judging && res.result !== SubmissionStatus.pending
     },
-    5000,
-    { immediate: false },
-  )
+  })
 
   // ==================== 启动监控 ====================
   const startMonitoring = (id: string) => {
@@ -131,8 +104,8 @@ export function useSubmissionMonitor() {
     // 把各自那个早就判完的旧 submissionId 重新订阅一遍。
     subscribe(id)
 
-    // 5秒后启动轮询保底（防止WebSocket失败）
-    startPollingFallback()
+    // 轮询兜底：WebSocket 通的话 20 秒才问一次，不通才快拉（见 fallbackPoll.ts）
+    fallback.start()
   }
 
   /**
@@ -141,7 +114,7 @@ export function useSubmissionMonitor() {
    * 判完触发的「通过」处理会把**新题**标成已解决。提交本身照常判完落库，只是这边不再跟。
    */
   const reset = () => {
-    pausePolling()
+    fallback.stop()
     unsubscribe()
     // 连接由 store 持有，离开题目页组件卸了它也还在。和判完之后一样，空闲 15 分钟断开；
     // 不在这里立刻断，是因为刚交的那条判完之后还可能推成就过来
@@ -161,11 +134,6 @@ export function useSubmissionMonitor() {
     return judging.value || pending.value || submitting.value
   })
 
-  // ==================== 清理 ====================
-  // 现在由 submission store 持有（见 oj/store/submission.ts），store 不销毁就一直在；
-  // 用 onScopeDispose 是为了在组件里调用时照样能收尾
-  if (getCurrentScope()) onScopeDispose(pausePolling)
-
   return {
     // 状态
     submissionId,
@@ -179,7 +147,6 @@ export function useSubmissionMonitor() {
 
     // 方法
     startMonitoring,
-    pausePolling,
     reset,
   }
 }
diff --git a/apps/web/src/oj/store/flowchart.ts b/apps/web/src/oj/store/flowchart.ts
index a373d78..7522745 100644
--- a/apps/web/src/oj/store/flowchart.ts
+++ b/apps/web/src/oj/store/flowchart.ts
@@ -14,6 +14,7 @@ import { getFlowchartScores, getFlowchartSubmission, submitFlowchart } from "oj/
 import { useProblemStore } from "oj/store/problem"
 import { useSubmissionStore } from "oj/store/submission"
 import { useFlowchartWebSocket, type FlowchartEvaluationUpdate } from "shared/composables/websocket"
+import { useFallbackPoll } from "shared/composables/fallbackPoll"
 import { useMyFlowchartStore } from "shared/store/myFlowchart"
 import { useUserStore } from "shared/store/user"
 import { useAchievementStore } from "shared/store/achievement"
@@ -50,8 +51,6 @@ export { isFlowchartPass }
  */
 export type FlowchartPhase = "idle" | "evaluating" | "done" | "failed"
 
-/** AI 评分比判题慢得多，轮询放缓一点 */
-const POLL_INTERVAL = 3000
 /** 到点还没结果就收手，别无限轮询下去 */
 const POLL_TIMEOUT = 3 * 60 * 1000
 
@@ -141,41 +140,6 @@ export const useFlowchartStore = defineStore("flowchart", () => {
   /** 正在跟的那一次是哪道题的，结算时再对一遍 */
   let monitoringProblemId: number | null = null
 
-  const { pause: pausePolling, resume: resumePolling } = useIntervalFn(
-    async () => {
-      if (!monitoringId) {
-        pausePolling()
-        return
-      }
-      try {
-        const data = await getFlowchartSubmission(monitoringId)
-        if (data.status === 2) {
-          settle(data.id, {
-            ok: true,
-            score: data.aiScore ?? 0,
-            grade: data.aiGrade ?? "",
-          })
-        } else if (data.status === 3) {
-          settle(data.id, { ok: false })
-        }
-      } catch (error) {
-        console.error("[Flowchart] 轮询失败:", error)
-        pausePolling()
-      }
-    },
-    POLL_INTERVAL,
-    { immediate: false },
-  )
-
-  // WebSocket 正常时压根用不上轮询，先给它 5 秒，到点还没结果才开始拉
-  const { start: startPollingFallback, stop: stopPollingFallback } = useTimeoutFn(
-    () => {
-      if (monitoringId) resumePolling()
-    },
-    5000,
-    { immediate: false },
-  )
-
   const { start: startPollingDeadline, stop: stopPollingDeadline } = useTimeoutFn(
     () => {
       if (!monitoringId) return
@@ -191,8 +155,7 @@ export const useFlowchartStore = defineStore("flowchart", () => {
     monitoringId = ""
     monitoringProblemId = null
     unsubscribe()
-    pausePolling()
-    stopPollingFallback()
+    fallback.stop()
     stopPollingDeadline()
     loading.value = false
     // 连接挂在 store 上，离开题目页也不会跟着组件断。不立刻断：接着还可能再交一次，
@@ -252,6 +215,8 @@ export const useFlowchartStore = defineStore("flowchart", () => {
       useAchievementStore().enqueue(frame.achievements ?? [])
       return
     }
+    // 订阅后服务端立刻回一帧当前状态（还在评也回 evaluation_update）：WebSocket 是通的
+    if (monitoringId && data.submissionId === monitoringId) fallback.confirm()
     if (data.type === "flowchart_evaluation_completed") {
       settle(data.submissionId, {
         ok: true,
@@ -263,9 +228,27 @@ export const useFlowchartStore = defineStore("flowchart", () => {
     }
   }
 
-  const { connect, subscribe, unsubscribe, scheduleDisconnect, cancelScheduledDisconnect } =
+  const { connect, subscribe, unsubscribe, scheduleDisconnect, cancelScheduledDisconnect, status } =
     useFlowchartWebSocket(handleWebSocketMessage)
 
+  // WebSocket 通的话 20 秒才问一次，不通才快拉（见 fallbackPoll.ts）
+  const fallback = useFallbackPoll({
+    status,
+    poll: async () => {
+      if (!monitoringId) return true
+      const data = await getFlowchartSubmission(monitoringId)
+      if (data.status === 2) {
+        settle(data.id, { ok: true, score: data.aiScore ?? 0, grade: data.aiGrade ?? "" })
+        return true
+      }
+      if (data.status === 3) {
+        settle(data.id, { ok: false })
+        return true
+      }
+      return false
+    },
+  })
+
   // ==================== 提交 ====================
   /** 交一张图：Mermaid 给 AI 看、给缩略图画，结构树压缩后存着（载回画布、亮路径用） */
   async function submit(doc: FlowDoc) {
@@ -309,7 +292,7 @@ export const useFlowchartStore = defineStore("flowchart", () => {
         monitoringId = response.submissionId
         monitoringProblemId = problem.id
         subscribe(response.submissionId)
-        startPollingFallback()
+        fallback.start()
         startPollingDeadline()
       }
     } catch (error) {
diff --git a/apps/web/src/shared/composables/fallbackPoll.ts b/apps/web/src/shared/composables/fallbackPoll.ts
new file mode 100644
index 0000000..2485dfd
--- /dev/null
+++ b/apps/web/src/shared/composables/fallbackPoll.ts
@@ -0,0 +1,123 @@
+import { getCurrentScope, onScopeDispose, watch, type Ref } from "vue"
+import { useDocumentVisibility } from "@vueuse/core"
+import type { ConnectionStatus } from "shared/composables/websocket"
+
+/** 交上去之后先等 WebSocket 这么久，再开始兜底 */
+const GRACE = 5000
+/** WebSocket 不通时从这个间隔起拉，每次乘 1.5，最慢到 MAX_FAST */
+const MIN_FAST = 2000
+const MAX_FAST = 10_000
+/** WebSocket 好好的：结果会推过来，轮询只是防 pub/sub 丢那一条，隔这么久问一次 */
+const SLOW = 20_000
+/** 连着失败这么多次就不拉了 */
+const MAX_ERRORS = 5
+
+/**
+ * 判题、流程图评分的结果「WebSocket 推、轮询兜底」里的兜底那一半。
+ *
+ * 原来是交上去 5 秒还没结果就每 2 秒（流程图 3 秒）拉一次，分不清「WebSocket 断了」和
+ * 「队列排得长」。服务器只有两核，一个班 50 人一起交时判题队列要排一分钟，几乎每个人都
+ * 进了轮询，每秒二十几个请求全在和判题抢 CPU。
+ *
+ * 能分清的依据：服务端收到 subscribe 会立刻回一帧当前状态（pending / judging 也回），
+ * 断线重连后 websocket.ts 会自动重新订阅、再回一帧。所以调用方收到**这一条**的任何帧就
+ * `confirm()`，此后只要连接没断，就知道结果会推过来，轮询退到 20 秒一次；连接一断立刻
+ * 回到快档。页面藏在后台时不拉：切回来时 WebSocket 会自己重连、重放当前状态。
+ *
+ * `poll` 返回 true 表示有结果了、不用再拉。抛错按快档退避接着拉（掉线那几秒拉失败是
+ * 常事，原来一次失败就永久停掉，之后要是又丢了推送就一直转圈），连着失败
+ * MAX_ERRORS 次才放弃，别对着一个坏掉的接口一直刷。
+ */
+export function useFallbackPoll(options: {
+  status: Ref<ConnectionStatus>
+  poll: () => Promise<boolean>
+}) {
+  const visibility = useDocumentVisibility()
+  let timer: ReturnType<typeof setTimeout> | undefined
+  let active = false
+  let confirmed = false
+  let fastDelay = MIN_FAST
+  let lastPolledAt = 0
+  let errors = 0
+
+  const healthy = () => confirmed && options.status.value === "connected"
+
+  function schedule(delay: number) {
+    clearTimeout(timer)
+    timer = setTimeout(tick, delay)
+  }
+
+  async function tick() {
+    if (!active) return
+    if (visibility.value === "hidden") {
+      schedule(SLOW)
+      return
+    }
+    // 刚失败过的不算健康：WebSocket 看着连着，拉却失败了，多半是网刚断、它还没察觉
+    if (healthy() && errors === 0 && Date.now() - lastPolledAt < SLOW) {
+      schedule(SLOW - (Date.now() - lastPolledAt))
+      return
+    }
+    lastPolledAt = Date.now()
+    try {
+      if (await options.poll()) {
+        stop()
+        return
+      }
+      errors = 0
+    } catch (error) {
+      console.error("[FallbackPoll] 轮询失败:", error)
+      if (++errors >= MAX_ERRORS) {
+        stop()
+        return
+      }
+    }
+    if (!active) return
+    if (healthy() && errors === 0) {
+      schedule(SLOW)
+    } else {
+      schedule(fastDelay)
+      fastDelay = Math.min(MAX_FAST, fastDelay * 1.5)
+    }
+  }
+
+  /** 开始跟一条新的。lastPolledAt 记成现在：WebSocket 一直好的话，第一次拉在 20 秒后 */
+  function start() {
+    active = true
+    confirmed = false
+    fastDelay = MIN_FAST
+    errors = 0
+    lastPolledAt = Date.now()
+    schedule(GRACE)
+  }
+
+  function stop() {
+    active = false
+    clearTimeout(timer)
+    timer = undefined
+  }
+
+  /** 收到了这一条的推送：WebSocket 是通的 */
+  function confirm() {
+    confirmed = true
+  }
+
+  // 连接一断，之前的确认就不算数了，回到快档；重连上之后的重放帧会再确认一次。
+  // 本来就没确认的不管：连不上时每次重连都要走一遍 connecting → error → disconnected，
+  // 在这里重置的话退避永远退不上去
+  watch(options.status, (status) => {
+    if (!active || !confirmed || status === "connected") return
+    confirmed = false
+    fastDelay = MIN_FAST
+    schedule(MIN_FAST)
+  })
+
+  // 切回前台：WebSocket 还没确认的话别等满 20 秒
+  watch(visibility, (value) => {
+    if (active && value === "visible" && !healthy()) schedule(MIN_FAST)
+  })
+
+  if (getCurrentScope()) onScopeDispose(stop)
+
+  return { start, stop, confirm }
+}
diff --git a/apps/web/src/shared/composables/visibleInterval.ts b/apps/web/src/shared/composables/visibleInterval.ts
new file mode 100644
index 0000000..d975105
--- /dev/null
+++ b/apps/web/src/shared/composables/visibleInterval.ts
@@ -0,0 +1,24 @@
+import { watch } from "vue"
+import { useDocumentVisibility, useIntervalFn } from "@vueuse/core"
+
+/**
+ * 定时刷新，但页面藏在后台时不拉，切回来立刻补一次。
+ *
+ * 比赛榜单 10 秒一次、比赛班级页 15 秒一次，原来在后台标签页里照样拉：考试时一个班
+ * 几十个人开着题目页又开着榜单，后台那几十个请求是白付的，服务器只有两核。
+ * 用法和 useIntervalFn 一样，默认不立即开始，由调用方 resume()。
+ */
+export function useVisibleInterval(fn: () => unknown, interval: number) {
+  const visibility = useDocumentVisibility()
+  const { pause, resume, isActive } = useIntervalFn(
+    () => {
+      if (visibility.value === "visible") fn()
+    },
+    interval,
+    { immediate: false },
+  )
+  watch(visibility, (value) => {
+    if (value === "visible" && isActive.value) fn()
+  })
+  return { pause, resume }
+}