diff --git a/apps/api/src/routes/submission.ts b/apps/api/src/routes/submission.ts
index 0aad5fc..9f2a294 100644
--- a/apps/api/src/routes/submission.ts
+++ b/apps/api/src/routes/submission.ts
@@ -413,6 +413,8 @@ async function submissionDetail(id: string, user: AuthUser) {
     // 首轮修复只处理了 info 与 ip，这里补齐。
     contestId: full ? row.submission.contestId : null,
     problemId: row.submission.problemId,
+    // problem 表本来就 join 了，不额外查库
+    problemDisplayId: row.problem.displayId,
     showLink: true,
     canUnshare: canViewSubmission(user, row.submission, row.problem, row.contest, false),
   })
diff --git a/apps/web/src/oj/submission/detail.vue b/apps/web/src/oj/submission/detail.vue
index 6d32baa..14677e0 100644
--- a/apps/web/src/oj/submission/detail.vue
+++ b/apps/web/src/oj/submission/detail.vue
@@ -78,10 +78,13 @@ function copyToCat() {
 
 function copyToProblem() {
   const { code, language, contestId } = submission.value!
-  // 编辑器的 storageKey 用 display id（problem._id），等于 props.problemID，
-  // 而非 submission.problem（内部数字 id）
+  // 编辑器的 storageKey 用 display id（problem._id），不是 submission.problemId
+  // （内部数字 id）。**不能只靠 props.problemID** —— 独立的 /submission/:id 路由
+  // 只喂 submissionID，那个 prop 是 undefined，原来会一路带进 router.push 抛
+  // `Missing required param "problemID"`。响应里的 problemDisplayId 就是干这个的。
+  const problemID = props.problemID ?? submission.value!.problemDisplayId
   const contestIDForKey = contestId || null
-  const storageKey = `problem_${props.problemID}_contest_${contestIDForKey}_lang_${language}`
+  const storageKey = `problem_${problemID}_contest_${contestIDForKey}_lang_${language}`
   storage.set(storageKey, code)
   // 设置语言 + 代码：localStorage 覆盖全新挂载的编辑器，
   // setCode 覆盖已挂载（同页 modal）的编辑器
@@ -92,17 +95,17 @@ function copyToProblem() {
   if (contestId) {
     router.push({
       name: "contest problem",
-      params: { contestID: String(contestId), problemID: props.problemID },
+      params: { contestID: String(contestId), problemID },
     })
   } else if (problemSetId) {
     router.push({
       name: "problemset problem",
-      params: { problemSetId, problemID: props.problemID },
+      params: { problemSetId, problemID },
     })
   } else {
     router.push({
       name: "problem",
-      params: { problemID: props.problemID },
+      params: { problemID },
     })
   }
 
diff --git a/packages/contract/src/submission.ts b/packages/contract/src/submission.ts
index bc257a5..8d06ab6 100644
--- a/packages/contract/src/submission.ts
+++ b/packages/contract/src/submission.ts
@@ -42,6 +42,13 @@ export const submissionDetailSchema = z.object({
   ip: z.string().nullable(),
   contestId: z.number().int().nullable(),
   problemId: z.number().int(),
+  /**
+   * 题目的展示编号（problem._id）。**独立的 /submission/:id 页面要靠它** ——
+   * 那条路由只喂 submissionID，组件拿不到 display id，而「复制回到题目」要用它
+   * 拼路由。原来只给内部数字 id，于是那个按钮在这条路由上一点就抛
+   * `Missing required param "problemID"`。
+   */
+  problemDisplayId: z.string(),
   showLink: z.boolean(),
   canUnshare: z.boolean(),
 })