feat(collab): 教师端弹框补上代码提示，语言跟着学生走

教师端的协作编辑器只有高亮和括号匹配，没装 autocompletion —— 老师替学生
写代码时没有下拉补全，只能盲敲。而且语言写死 cpp()，学生写 Python 时老师
看到的是 C 的高亮。

- 求助协议带上语言：help_request 记到 HelpRequest，accept 时写进 Room，
  room_open 发给两端；认不出的语言一律当 C（老客户端不带这个字段，而它
  以前就是写死 C 的）
- 新增 help_language / room_language：学生在排队或协作期间切语言，只更新
  语言，不动队列位置和房间；已开房就把新语言推给老师，弹框的高亮和补全
  实时跟着换
- CollabModal 装上 autocompletion，和学生端用同一套 enhanceCompletion +
  completeAnyWord；语言→高亮扩展的映射抽到 shared/extensions/language.ts
  两端共用，免得再分叉
- 学生端求助按钮合并状态提示：原来按钮旁边还挂一个 n-tag，一行工具栏在
  1280 的机房屏上放不下，改成状态全进 label（已求助 · 待接入 / 已求助 ·
  前面 N 人 / xxx 老师帮你中）

扩展数组变了 vue-codemirror 会整体 reconfigure，但 CM6 对已存在的
compartment 取 `compartments.get() || ext.inner`，collabDoc 那个装 yCollab
的 compartment 内容会被沿用，切语言、切主题都不会把协作弄断 —— 实跑验证过
双向同步、补全下拉、协作中切语言三条路径。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015APGLsyaCUa7XFMYAaCho4

apps/api/src/collab/handler.ts

@@ -11,6 +11,7 @@ import {
   getRoom,
   hasTeacherOnline,
   listRequests,
+  normalizeLanguage,
   openRoom,
   queueAheadOf,
   removeRequest,
@@ -179,7 +180,12 @@ export function handleCollabClose(ws: CollabSocket) {
 }
 
 export async function handleCollabMessage(ws: CollabSocket, raw: string) {
-  let message: { type?: unknown; problemId?: unknown; studentId?: unknown }
+  let message: {
+    type?: unknown
+    problemId?: unknown
+    studentId?: unknown
+    language?: unknown
+  }
   try {
     message = JSON.parse(raw) as typeof message
   } catch {
@@ -201,7 +207,10 @@ export async function handleCollabMessage(ws: CollabSocket, raw: string) {
 
   switch (message.type) {
     case "help_request":
-      await handleHelpRequest(ws, message.problemId)
+      await handleHelpRequest(ws, message.problemId, message.language)
+      return
+    case "help_language":
+      handleHelpLanguage(ws, message.language)
       return
     case "help_cancel":
       handleHelpCancel(ws)
@@ -220,7 +229,11 @@ export async function handleCollabMessage(ws: CollabSocket, raw: string) {
   }
 }
 
-async function handleHelpRequest(ws: CollabSocket, problemId: unknown) {
+async function handleHelpRequest(
+  ws: CollabSocket,
+  problemId: unknown,
+  language: unknown,
+) {
   if (typeof problemId !== "string" || !problemId) {
     ws.send(JSON.stringify({ type: "error", message: "Invalid problemId" }))
     return
@@ -266,6 +279,7 @@ async function handleHelpRequest(ws: CollabSocket, problemId: unknown) {
     className: student?.className ?? null,
     problemId,
     problemTitle: problem.title,
+    language: normalizeLanguage(language),
     createdAt: Date.now(),
     status: "pending",
     socket: ws,
@@ -274,6 +288,29 @@ async function handleHelpRequest(ws: CollabSocket, problemId: unknown) {
   broadcastRequests()
 }
 
+/**
+ * 学生在求助期间换了语言。
+ *
+ * 只更新语言，不动队列位置、不动房间 —— 换语言不该让他重新排队。已经在协作中的
+ * 话再推一条 room_language，老师端的高亮和补全立刻跟着换；不推的话老师会拿着
+ * 建房那一刻的语言，对着一套错的补全替学生写代码。
+ */
+function handleHelpLanguage(ws: CollabSocket, language: unknown) {
+  const request = getRequest(ws.data.userId)
+  // 比对 socket 归属：同账号的另一个标签页停在别的题上切语言，不该改这条求助
+  if (!request || request.socket !== ws) return
+  const next = normalizeLanguage(language)
+  if (request.language === next) return
+  request.language = next
+
+  const room = getRoom(ws.data.userId)
+  if (!room) return
+  room.language = next
+  room.teacherSocket.send(
+    JSON.stringify({ type: "room_language", language: next }),
+  )
+}
+
 function handleHelpCancel(ws: CollabSocket) {
   const request = getRequest(ws.data.userId)
   // 不比对 socket 归属：取消的是这个学生自己的求助，不管从他哪个标签页发起都
@@ -341,6 +378,7 @@ async function handleAccept(ws: CollabSocket, studentId: unknown) {
     studentSocket: request.socket,
     teacherSocket: ws,
     problemId: request.problemId,
+    language: request.language,
   })
 
   const openFrame = (peerName: string, peerRole: "student" | "teacher") =>
@@ -348,6 +386,7 @@ async function handleAccept(ws: CollabSocket, studentId: unknown) {
       type: "room_open",
       peer: { name: peerName, role: peerRole },
       problemId: request.problemId,
+      language: request.language,
     })
   request.socket.send(openFrame(request.teacherName, "teacher"))
   ws.send(openFrame(request.studentName, "student"))

apps/api/src/collab/state.ts

@@ -8,6 +8,30 @@
 
 export type CollabSocket = Bun.ServerWebSocket<import("../websocket").SubmissionSocketData>
 
+/**
+ * 协作支持的语言。和前端 utils/types.ts 里的 LANGUAGE 对齐，去掉 Flowchart ——
+ * 流程图题没有代码编辑器，求助入口本身就是隐藏的。
+ */
+export const COLLAB_LANGUAGES = [
+  "C",
+  "C++",
+  "Python2",
+  "Python3",
+  "Java",
+  "JavaScript",
+  "Golang",
+  "SQL",
+] as const
+
+export type CollabLanguage = (typeof COLLAB_LANGUAGES)[number]
+
+/** 认不出来的一律当 C：老客户端不带这个字段，而它以前就是写死 C 的 */
+export function normalizeLanguage(value: unknown): CollabLanguage {
+  return (COLLAB_LANGUAGES as readonly string[]).includes(value as string)
+    ? (value as CollabLanguage)
+    : "C"
+}
+
 export interface HelpRequest {
   studentId: number
   studentName: string
@@ -15,6 +39,11 @@ export interface HelpRequest {
   /** 题目的展示号（problem._id 列，前端一路用的都是它），不是自增主键 */
   problemId: string
   problemTitle: string
+  /**
+   * 学生编辑器当前的语言。决定教师端弹框用哪套高亮和补全 —— 求助时带上，
+   * 协作期间学生切语言会用 help_language 更新这里
+   */
+  language: CollabLanguage
   createdAt: number
   status: "pending" | "active"
   teacherId?: number
@@ -83,6 +112,8 @@ export interface Room {
   studentSocket: CollabSocket
   teacherSocket: CollabSocket
   problemId: string
+  /** 建房那一刻学生的语言，之后跟着 help_language 走 */
+  language: CollabLanguage
 }
 
 const rooms = new Map<number, Room>()