1. 教室容量按 1/2 计算

- ExamArrangementService.cs: SelectRooms() 使用 Capacity / 2 选择房间、计算剩余座位和总容量
  - MakeupExamArrangementService.cs: 数据库查询用 x.Capacity >= enrolledCount * 2（等价于 Capacity/2 >=
  enrolledCount），消息显示有效座位数

  2. 教学楼限制多选

  - Domain: ExamSession 和 MakeupExamSession 新增 RequiredBuildingIds (JSON string)，保留旧 RequiredBuildingId 向后兼容
  - Service: RoomGroupKey 改为字符串键确保值相等；GroupKey() 合并新旧字段
  - Controller: 请求 DTO 增加 RequiredBuildingIds (Guid 数组)，响应包含该字段
  - DB: MySQL 迁移 + SQLite migrator 添加新列
  - Frontend: <el-select> 改为 multiple，新增 parseBuildingIds() 解析服务器返回的 JSON

  3. 导出签名单后台任务

  - 新增: ExamSignInExportJob 实体、ExamSignInExportJobProcessor、ExamSignInExportJobStatus 枚举
  - BackgroundJobKind: 新增 ExamSignInExport = 5
  - RabbitMQ: routing key exam.sign-in-export，队列 jiaowu.background-jobs.exam.sign-in-export
  - API: POST /sign-in-export 创建任务返回 202；GET /sign-in-exports/{jobId} 查询状态；GET
  /sign-in-exports/{jobId}/download 下载文件
  - Frontend: 导出改为异步任务 + 轮询 + 自动下载，显示进度条
  - 恢复: OutboxPublisher 启动时恢复未完成的任务，重试超限自动标记失败

web/src/views/MakeupExamsView.vue

@@ -171,6 +171,7 @@ function openSession(existing?: any) {
     startPeriod: existing?.startPeriod ?? (firstSlot?.periodNumber ?? 1),
     periodCount: existing?.periodCount ?? 2,
     requiredBuildingId: existing?.requiredBuildingId ?? undefined,
+    requiredBuildingIds: parseBuildingIds(existing?.requiredBuildingIds),
     requiredInvigilatorCount: existing?.requiredInvigilatorCount ?? 2,
     invigilatorIds: existing?.invigilatorIds ?? [],
     notes: existing?.notes ?? '',
@@ -193,6 +194,7 @@ async function saveSession() {
         startPeriod: payload.startPeriod,
         periodCount: payload.periodCount,
         requiredBuildingId: payload.requiredBuildingId,
+        requiredBuildingIds: payload.requiredBuildingIds,
         requiredInvigilatorCount: payload.requiredInvigilatorCount,
         notes: payload.notes,
       })
@@ -357,8 +359,12 @@ function classroomLabel(room: any) {
   return `${room.name} · ${room.capacity}座 · ${room.buildingName}`
 }
 function filteredRooms() {
-  if (!sessionForm.requiredBuildingId) return rooms.value
-  return rooms.value.filter((r: any) => r.buildingId === sessionForm.requiredBuildingId)
+  if (!sessionForm.requiredBuildingIds || sessionForm.requiredBuildingIds.length === 0) return rooms.value
+  return rooms.value.filter((r: any) => sessionForm.requiredBuildingIds.includes(r.buildingId))
+}
+function parseBuildingIds(raw: string | undefined | null): string[] {
+  if (!raw) return []
+  try { return JSON.parse(raw) } catch { return [] }
 }
 
 function openEnrollment(session: any) {
@@ -782,7 +788,7 @@ onBeforeUnmount(() => {
         </div>
         <div class="form-grid">
           <el-form-item label="教学楼限制">
-            <el-select v-model="sessionForm.requiredBuildingId" clearable placeholder="不限教学楼">
+            <el-select v-model="sessionForm.requiredBuildingIds" multiple clearable placeholder="不限教学楼">
               <el-option v-for="x in buildings" :key="x.id" :label="x.name" :value="x.id" />
             </el-select>
           </el-form-item>