fix(出题页): 改了挑战点保存，提示「保存好了」其实一条都没存上

出题页发请求时漏了 challenges 这个字段，后端又把「不带」当成「不动原来的」，
所以改动被静默丢掉。现在出题页带上它，接口也改成必须带（null 是清空），
以后再漏传会直接报错，不会再悄悄丢。

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

apps/api/src/routes/admin/problem.ts

@@ -260,9 +260,7 @@ type ProblemInput = ReturnType<typeof createProblemRequestSchema.parse>
 async function validateProblem(data: ProblemInput, previousChallenges: ProblemChallenges | null = null): Promise<{ error: string } | Validated> {
   const checked = commonChecks(data)
   if ('error' in checked) return checked
-  // 不带挑战（旧版出题页）就原样留着，见契约 createProblemRequestSchema.challenges
-  const normalized =
-    data.challenges === undefined ? { challenges: previousChallenges } : normalizeChallenges(data.challenges, previousChallenges, data.languages)
+  const normalized = normalizeChallenges(data.challenges, previousChallenges, data.languages)
   if ('error' in normalized) return normalized
   const { challenges } = normalized
   if (!checked.sql) return { sql: false, sqlDisplay: null, challenges }

apps/web/src/admin/api.ts

@@ -1,6 +1,7 @@
 import { toAdminType, toProblemPermission } from '@oj2/contract'
 import type {
   AddContestProblemRequest,
+  ChallengeInput,
   ChallengeSuggestionsResponse,
   AddProblemsToSetRequest,
   BatchProblemTagRequest,
@@ -358,8 +359,9 @@ export function generateTestInputs(data: GenerateTestInputsRequest) {
 
 /** 出站补默认值。字段名两边已经一致，不再做键名转换 */
 function toProblemBody(problem: AdminProblem | BlankProblem) {
-  const p = problem as Partial<Omit<AdminProblem, 'flowchartData'>> & {
+  const p = problem as Partial<Omit<AdminProblem, 'flowchartData' | 'challenges'>> & {
     flowchartData?: Record<string, unknown> | null
+    challenges?: Record<string, ChallengeInput[]> | null
   }
   return {
     _id: p._id,
@@ -387,6 +389,7 @@ function toProblemBody(problem: AdminProblem | BlankProblem) {
     flowchartData: p.flowchartData ?? null,
     flowchartHint: p.flowchartHint ?? null,
     astRules: p.astRules ?? null,
+    challenges: p.challenges ?? null,
     sqlConfig: p.sqlConfig ?? null,
   }
 }

packages/contract/src/admin.ts

@@ -1004,10 +1004,10 @@ export const createProblemRequestSchema = z.object({
   flowchartHint: z.string().nullable().default(null),
   astRules: astRulesSchema.nullable().default(null),
   /**
-   * 不带这个键 = 不动原来的挑战。上线那一刻浏览器里还开着旧版出题页，它保存时不带挑战，
-   * 给个默认 null 的话一保存就把挑战清了；null 才是「清空」
+   * 必须带：null 是「清空」。不给默认值是故意的 —— 前端漏传这个键的话，给默认 null
+   * 会一保存就把挑战清了，而「不带 = 不动」又会让出题页改的挑战静默存不上
    */
-  challenges: challengeInputsSchema.nullable().optional(),
+  challenges: challengeInputsSchema.nullable(),
   // order_sensitive 缺省补 false —— 与旧后端 SQLConfigSerializer 的
   // `BooleanField(default=False)` 一致
   sqlConfig: sqlConfigSchema