fix(提交): C 代码编译不过时，提交前的自动格式化把出错的几行并成一行，学生认不出自己的代码

clang-format 不认中文分号、缺了分号的语句，会把它和下一行并起来（int n； 和 scanf 成了
一行），报错的行号也对不上学生记得的位置。现在 C / C++ 格式化之前先套上题目模板、在
判题机上编一次，编不过就原样返回、不格式化，代码照常提交、照常判成编译错误。

api 容器里没有 gcc，判题机的编译器和参数本来就是判的标准，所以借它编。这一下不进判题
队列、不建提交记录；判题机连不上时照旧格式化。代价是每次交 C 多一次编译，零点几秒。

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

apps/api/src/routes/submission.ts

@@ -17,7 +17,9 @@ import { optionalAuth, requireAuth, requireTeacher } from "../auth/middleware"
 import type { AuthUser } from "../auth/session"
 import { db, schema } from "../db"
 import { failure, parseBody, success } from "../http"
+import { compileFails, templateForLanguage } from "../judge/run"
 import { JudgeStatus } from "../judge/status"
+import { parseProblemTemplate } from "../judge/template"
 import { judgeQueue } from "../queue"
 import {
   canAccessContest,
@@ -244,8 +246,28 @@ submissionRoutes.post("/submissions/:id/rejudge", requireTeacher, async (c) => {
 submissionRoutes.post("/code/format", requireAuth, async (c) => {
   const parsed = await parseBody(c, formatCodeRequestSchema, "Invalid format payload")
   if (!parsed.success) return parsed.response
+  // C / C++ 编不过就原样返回，不格式化（理由见 judge/run.ts 的 compileFails）。
+  // 代码照常提交、照常判成编译错误，只是不改动学生的代码
+  const { code: source, language, problemId } = parsed.data
+  if (language === "c" || language === "cpp") {
+    const judgeLanguage = language === "c" ? "C" : "C++"
+    const [problem] =
+      problemId === undefined
+        ? []
+        : await db
+            .select({ template: schema.problem.template })
+            .from(schema.problem)
+            .where(eq(schema.problem.id, problemId))
+            .limit(1)
+    const rawTemplate = problem ? templateForLanguage(problem.template, judgeLanguage) : null
+    const template = rawTemplate ? parseProblemTemplate(rawTemplate) : null
+    const full = template ? `${template.prepend}\n${source}\n${template.append}` : source
+    if (await compileFails(judgeLanguage, full)) {
+      return success(c, { code: source } satisfies FormatCodeResponse)
+    }
+  }
   try {
-    const code = await formatCode(parsed.data.code, parsed.data.language)
+    const code = await formatCode(source, language)
     return success(c, { code } satisfies FormatCodeResponse)
   } catch (error) {
     if (error instanceof CodeFormatError) {