feat: 班级小助手 阶段1-3（monorepo + 后端 REST/Socket.IO + Web 管理端）

packages/server/src/realtime/bus.ts

@@ -0,0 +1,30 @@
+import { SOCKET_ROOMS } from '@classhelper/shared';
+
+/**
+ * 实时事件总线。
+ *
+ * 业务模块只依赖这里，不直接依赖 Socket.IO 实例，
+ * 因此「移除实时推送」只需让它注册不到 emitter，业务代码无需改动。
+ */
+export type RealtimeEmitter = (rooms: string[], event: string, payload: unknown) => void;
+
+let emitter: RealtimeEmitter | null = null;
+
+export function registerEmitter(next: RealtimeEmitter): void {
+  emitter = next;
+}
+
+export function emitToRooms(rooms: string[], event: string, payload: unknown): void {
+  if (!emitter || rooms.length === 0) return;
+  emitter(rooms, event, payload);
+}
+
+/** 按班级房间广播（class:{classId}） */
+export function emitToClass(classId: string, event: string, payload: unknown): void {
+  emitToRooms([SOCKET_ROOMS.class(classId)], event, payload);
+}
+
+/** 定向推送给单个用户 */
+export function emitToUser(userId: string, event: string, payload: unknown): void {
+  emitToRooms([SOCKET_ROOMS.user(userId)], event, payload);
+}