布置作业、提交与自动评分

- 作业：老师选实验、起点（界面已做好 / 空白工程）、截止时间、每项分值（自动评分项 + 老师评分项）；
  起点工程由设计器引擎从参考答案生成（去掉事件绑定和事件处理方法），布置时保存起点和评分规则快照
- 提交：后台排队评分（全站同时最多评 3 份、跑 6 个检查项），重启后继续评；评分中不能再交，截止后不能交
- 学生："我的作业"列表；实验页的作业模式（作业名、截止时间、提交、得分），评分结果弹出逐项显示
- 老师：班级管理页加"作业"标签页，布置、修改、删除作业，查看全班提交情况；改分值后重新算分
- 串口列表为空时提示在 Load 或 Click 事件里填充
- 测试：作业接口（可见范围、排队评分、部分得分、改分值、截止、删除）；10 个示例两种起点都能编译

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/src/grading/queue.ts

@@ -0,0 +1,70 @@
+// 评分队列：学生提交后立即返回，后台按提交顺序评分（同时最多评 MAX_ACTIVE 份），结果写回数据库。
+// 服务器重启前没评完的提交，启动时继续评。
+import type { Database } from 'bun:sqlite'
+import { mkdir, rm } from 'node:fs/promises'
+import { dirname, join } from 'node:path'
+import { assignmentChecks, pendingSubmissionIds, saveGrade, submissionForGrading } from '../assignments'
+import { config } from '../config'
+import { safeJoin } from '../run-session'
+import { grade } from './grader'
+
+const MAX_ACTIVE = 3
+
+export function createGradingQueue(db: Database) {
+  const queue: number[] = []
+  let active = 0
+  let idleWaiters: (() => void)[] = []
+
+  async function gradeOne(id: number) {
+    const submission = submissionForGrading(db, id)
+    const checks = submission && assignmentChecks(db, submission.assignmentId)
+    if (!submission || !checks) return
+    const dir = join(config.runsDir, `grade-${id}`)
+    try {
+      await rm(dir, { recursive: true, force: true })
+      for (const file of submission.files) {
+        const target = safeJoin(dir, file.path)
+        await mkdir(dirname(target), { recursive: true })
+        await Bun.write(target, file.content)
+      }
+      saveGrade(db, id, await grade(dir, checks))
+    } catch (error) {
+      console.error(`评分出错（提交 ${id}）：`, error)
+      saveGrade(db, id, null)
+    } finally {
+      await rm(dir, { recursive: true, force: true })
+    }
+  }
+
+  function pump() {
+    while (active < MAX_ACTIVE && queue.length > 0) {
+      const id = queue.shift()!
+      active++
+      void gradeOne(id).finally(() => {
+        active--
+        pump()
+      })
+    }
+    if (active === 0 && queue.length === 0) {
+      for (const resolve of idleWaiters) resolve()
+      idleWaiters = []
+    }
+  }
+
+  for (const id of pendingSubmissionIds(db)) queue.push(id)
+  pump()
+
+  return {
+    enqueue(id: number) {
+      queue.push(id)
+      pump()
+    },
+    /** 等队列全部评完（测试用） */
+    idle(): Promise<void> {
+      if (active === 0 && queue.length === 0) return Promise.resolve()
+      return new Promise((resolve) => idleWaiters.push(resolve))
+    },
+  }
+}
+
+export type GradingQueue = ReturnType<typeof createGradingQueue>