feat(web): 课堂求助 store 与全局 collab 连接

连接全局常驻，不跟题目页起落 —— 老师在任何页面都要能收到求助。
列表按题目聚合，同题多人时能一眼看出该全班讲。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K1d8B3f4SXJwDvUY625eQd

apps/web/src/shared/store/collab.ts

@@ -0,0 +1,172 @@
+import {
+  CollabWebSocket,
+  type CollabMessage,
+  type CollabRequestItem,
+} from "shared/composables/websocket"
+import { useUserStore } from "shared/store/user"
+
+export type HelpStatus = "idle" | "pending" | "active"
+
+export interface RoomInfo {
+  peerName: string
+  peerRole: "student" | "teacher"
+  problemId: string
+}
+
+/**
+ * 课堂求助的全局状态。
+ *
+ * 连接是**全局常驻**的，不跟着题目页起落 —— 老师可能正在后台改题时收到求助，
+ * 学生也需要在等待期间一直挂着。所以这里不用 onUnmounted，由 App.vue 按登录态开关。
+ */
+export const useCollabStore = defineStore("collab", () => {
+  const userStore = useUserStore()
+
+  const ws = new CollabWebSocket()
+
+  /** 老师端：待处理列表 */
+  const requests = ref<CollabRequestItem[]>([])
+  /** 学生端：自己的求助状态 */
+  const helpStatus = ref<HelpStatus>("idle")
+  const queueAhead = ref(0)
+  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 */
+  const notice = ref("")
+
+  const pendingCount = computed(
+    () => requests.value.filter((it) => it.status === "pending").length,
+  )
+
+  /** 按题目聚合，同题多人时老师能一眼看出该停下来全班讲 */
+  const groupedRequests = computed(() => {
+    const groups = new Map<string, { problemId: string; problemTitle: string; items: CollabRequestItem[] }>()
+    for (const item of requests.value) {
+      const group = groups.get(item.problemId)
+      if (group) group.items.push(item)
+      else
+        groups.set(item.problemId, {
+          problemId: item.problemId,
+          problemTitle: item.problemTitle,
+          items: [item],
+        })
+    }
+    // 人多的题排前面；人数相同按最久等待排
+    return Array.from(groups.values()).sort(
+      (a, b) =>
+        b.items.length - a.items.length ||
+        a.items[0].createdAt - b.items[0].createdAt,
+    )
+  })
+
+  const handleMessage = (data: CollabMessage) => {
+    switch (data.type) {
+      case "requests":
+        requests.value = (data.list ?? []) as CollabRequestItem[]
+        return
+      case "help_status":
+        if (data.status === "pending") {
+          helpStatus.value = "pending"
+          queueAhead.value = Number(data.queueAhead ?? 0)
+        } else if (data.status === "active") {
+          helpStatus.value = "active"
+          teacherName.value = String(data.teacherName ?? "")
+        } else if (data.status === "cancelled") {
+          helpStatus.value = "idle"
+          notice.value = "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"
+        }
+        return
+      case "room_open":
+        room.value = {
+          peerName: String(data.peer?.name ?? ""),
+          peerRole: data.peer?.role === "teacher" ? "teacher" : "student",
+          problemId: String(data.problemId ?? ""),
+        }
+        return
+      case "room_closed":
+        room.value = null
+        // 老师掉线时服务端会另发一条 help_status:pending，这里不抢着改学生状态
+        if (data.reason === "done") helpStatus.value = "idle"
+        notice.value =
+          data.reason === "peer_offline" ? "对方已断开连接" : "协作已结束"
+        return
+      case "error":
+        notice.value = String(data.message ?? "")
+        return
+    }
+  }
+
+  ws.addHandler(handleMessage)
+
+  function connect() {
+    ws.connect()
+  }
+
+  function disconnect() {
+    ws.disconnect()
+    requests.value = []
+    helpStatus.value = "idle"
+    room.value = null
+  }
+
+  function requestHelp(problemId: string) {
+    ws.send({ type: "help_request", problemId })
+  }
+
+  function cancelHelp() {
+    ws.send({ type: "help_cancel" })
+    helpStatus.value = "idle"
+  }
+
+  function accept(studentId: number) {
+    ws.send({ type: "accept", studentId })
+  }
+
+  function reject(studentId: number) {
+    ws.send({ type: "reject", studentId })
+  }
+
+  function leave() {
+    ws.send({ type: "leave" })
+  }
+
+  function sendBinary(data: Uint8Array) {
+    ws.sendRaw(data)
+  }
+
+  function setBinaryHandler(handler: ((data: ArrayBuffer) => void) | null) {
+    ws.setBinaryHandler(handler)
+  }
+
+  function consumeNotice() {
+    const value = notice.value
+    notice.value = ""
+    return value
+  }
+
+  return {
+    requests,
+    pendingCount,
+    groupedRequests,
+    helpStatus,
+    queueAhead,
+    teacherName,
+    room,
+    notice,
+    isTeacher: computed(() => userStore.isTeacherOrAbove),
+    connect,
+    disconnect,
+    requestHelp,
+    cancelHelp,
+    accept,
+    reject,
+    leave,
+    sendBinary,
+    setBinaryHandler,
+    consumeNotice,
+  }
+})