diff --git a/apps/web/package.json b/apps/web/package.json
index 52e5714..e596a16 100644
--- a/apps/web/package.json
+++ b/apps/web/package.json
@@ -40,6 +40,7 @@
     "date-fns": "^4.4.0",
     "fflate": "^0.8.3",
     "highlight.js": "^11.12.0",
+    "lib0": "0.2.117",
     "md-editor-v3": "^6.5.6",
     "mermaid": "^11.17.2",
     "mermaid-legacy": "npm:mermaid@^9.4.3",
diff --git a/apps/web/src/shared/components/Header.vue b/apps/web/src/shared/components/Header.vue
index 4924de5..6a4dea5 100644
--- a/apps/web/src/shared/components/Header.vue
+++ b/apps/web/src/shared/components/Header.vue
@@ -4,6 +4,7 @@ import { RouterLink } from "vue-router"
 import { useBreakpoints } from "shared/composables/breakpoints"
 import { useLearnProgress } from "shared/composables/learnProgress"
 import { useAuthModalStore } from "shared/store/authModal"
+import { useCollabStore } from "shared/store/collab"
 import { useScreenModeStore } from "shared/store/screenMode"
 import { logout } from "../api"
 import CollabModal from "./CollabModal.vue"
@@ -14,6 +15,23 @@ import { trickOrTreat } from "utils/functions"
 
 const userStore = useUserStore()
 const configStore = useConfigStore()
+const collabStore = useCollabStore()
+const message = useMessage()
+
+/**
+ * 课堂求助的一次性提示，统一在这里弹。
+ *
+ * 原来挂在题目页的 Form.vue 上：学生排着队切去看提交记录，老师这时候取消了
+ * 他的求助，那条「老师已取消你的求助」就永远没人消费。顶栏是全局的，放这儿
+ * 才收得全 —— 教师端的 error 提示（比如「请先退出当前协作」）同理。
+ */
+watch(
+  () => collabStore.noticeSeq,
+  () => {
+    const text = collabStore.consumeNotice()
+    if (text) message.info(text)
+  },
+)
 const authStore = useAuthModalStore()
 const screenModeStore = useScreenModeStore()
 const route = useRoute()
diff --git a/apps/web/src/shared/store/collab.ts b/apps/web/src/shared/store/collab.ts
index c1d8b7b..06a34f6 100644
--- a/apps/web/src/shared/store/collab.ts
+++ b/apps/web/src/shared/store/collab.ts
@@ -32,8 +32,21 @@ export const useCollabStore = defineStore("collab", () => {
   const teacherName = ref("")
   /** 双方：当前房间。null 表示不在协作中 */
   const room = ref<RoomInfo | null>(null)
-  /** 一次性提示，由组件消费后清空 */
+  /** 一次性提示，由 Header 统一消费后清空 */
   const notice = ref("")
+  /**
+   * 提示序号，每次设置都自增。
+   *
+   * 消费方 watch 的是这个，不是 notice 本身：连着两次同样的文案（老师取消了
+   * 求助、学生又求助、又被取消）在 Vue 眼里 `===` 相等，watch(notice) 不会
+   * 第二次触发，第二条提示就这么没了。
+   */
+  const noticeSeq = ref(0)
+
+  function setNotice(text: string) {
+    notice.value = text
+    noticeSeq.value += 1
+  }
 
   const pendingCount = computed(
     () => requests.value.filter((it) => it.status === "pending").length,
@@ -74,10 +87,10 @@ export const useCollabStore = defineStore("collab", () => {
           teacherName.value = String(data.teacherName ?? "")
         } else if (data.status === "cancelled") {
           helpStatus.value = "idle"
-          notice.value = "老师已取消你的求助"
+          setNotice("老师已取消你的求助")
         } else if (data.status === "no_teacher") {
           helpStatus.value = "idle"
-          notice.value = "当前没有老师在线"
+          setNotice("当前没有老师在线")
         }
         return
       case "room_open":
@@ -97,11 +110,12 @@ export const useCollabStore = defineStore("collab", () => {
         // 这里先归零，那条 pending 补发会立刻把它纠正回来，不会被这次重置盖掉
         room.value = null
         helpStatus.value = "idle"
-        notice.value =
-          data.reason === "peer_offline" ? "对方已断开连接" : "协作已结束"
+        setNotice(
+          data.reason === "peer_offline" ? "对方已断开连接" : "协作已结束",
+        )
         return
       case "error":
-        notice.value = String(data.message ?? "")
+        setNotice(String(data.message ?? ""))
         return
     }
   }
@@ -179,6 +193,7 @@ export const useCollabStore = defineStore("collab", () => {
     teacherName,
     room,
     notice,
+    noticeSeq,
     isTeacher: computed(() => userStore.isTeacherOrAbove),
     connect,
     disconnect,
diff --git a/bun.lock b/bun.lock
index d28cd3d..5a6a447 100644
--- a/bun.lock
+++ b/bun.lock
@@ -67,6 +67,7 @@
         "date-fns": "^4.4.0",
         "fflate": "^0.8.3",
         "highlight.js": "^11.12.0",
+        "lib0": "0.2.117",
         "md-editor-v3": "^6.5.6",
         "mermaid": "^11.17.2",
         "mermaid-legacy": "npm:mermaid@^9.4.3",