diff --git a/apps/api/src/routes/flowchart.ts b/apps/api/src/routes/flowchart.ts
index b8ae5b5..790be9e 100644
--- a/apps/api/src/routes/flowchart.ts
+++ b/apps/api/src/routes/flowchart.ts
@@ -25,6 +25,7 @@ import { problemSetJoinTimes } from "../services/problemset"
 import { consumeToken } from "../services/throttling"
 import { buildWordFrequencies } from "../services/word-frequency"
 import { dayStart } from "../time"
+import { unknownDisplayIds } from "./submission-statistics"
 import {
   isAdminRole,
   matchedUsers,
@@ -278,7 +279,7 @@ flowchartRoutes.get("/flowcharts", requireAuth, async (c) => {
   // submission_list_show_all 时非管理员看不到列表。流程图这边一直漏了这道门，
   // 学生把语言切成「流程图」、用户名随便填一个字就能翻出全班的 AI 评分。
   if (!(await getBooleanOption("submission_list_show_all", true)) && !isAdminRole(user)) {
-    return success(c, { results: [], total: 0 } satisfies FlowchartList)
+    return success(c, { results: [], total: 0, unknownProblems: [] } satisfies FlowchartList)
   }
   // 「只看自己」盖过用户名；普通学生不填用户名时也只看自己
   const className = c.req.query("className")?.trim()
@@ -300,7 +301,7 @@ flowchartRoutes.get("/flowcharts", requireAuth, async (c) => {
   if (["S", "A", "B", "C"].includes(grade ?? ""))
     filters.push(eq(schema.flowchartSubmission.aiGrade, grade!))
   const where = and(...filters)
-  const [totalRows, rows] = await Promise.all([
+  const [totalRows, rows, unknownProblems] = await Promise.all([
     // 筛条件已经全落在 flowchart_submission 自己的列上，count 不挂任何 join
     db.select({ value: count() }).from(schema.flowchartSubmission).where(where),
     db
@@ -312,6 +313,7 @@ flowchartRoutes.get("/flowcharts", requireAuth, async (c) => {
       .orderBy(desc(schema.flowchartSubmission.createTime))
       .limit(limit)
       .offset(offset),
+    displayId ? unknownDisplayIds(displayId, null) : [],
   ])
   const joinTimes = await joinTimesFor(
     user,
@@ -337,6 +339,7 @@ flowchartRoutes.get("/flowcharts", requireAuth, async (c) => {
         }) satisfies FlowchartListItem,
     ),
     total: totalRows[0]?.value ?? 0,
+    unknownProblems,
   } satisfies FlowchartList)
 })
 
diff --git a/apps/api/src/routes/submission-statistics.ts b/apps/api/src/routes/submission-statistics.ts
index f878db1..c575f7c 100644
--- a/apps/api/src/routes/submission-statistics.ts
+++ b/apps/api/src/routes/submission-statistics.ts
@@ -236,6 +236,31 @@ export async function classNameFilter(className: string) {
  * 和公开题撞号是常态），而公开提交从不指向比赛题（快照核过，0 条）。
  * 查无此题时留恒假条件，少推一个 filter 就成了「不筛」。
  */
+/**
+ * 题号框里查不到的那几个（范围同 problemFilter：公开列表只认公开题，比赛列表只认本场的题）。
+ * 列表把它们回给前端，打错一个字的时候老师能看到提示
+ */
+export async function unknownDisplayIds(displayId: string, contestId: number | null) {
+  const ids = parseDisplayIds(displayId)
+  if (!ids.length) return []
+  const rows = await db
+    .select({ displayId: schema.problem.displayId })
+    .from(schema.problem)
+    .where(
+      and(
+        inArray(
+          sql`lower(${schema.problem.displayId})`,
+          ids.map((id) => id.toLowerCase()),
+        ),
+        contestId === null
+          ? isNull(schema.problem.contestId)
+          : eq(schema.problem.contestId, contestId),
+      ),
+    )
+  const found = new Set(rows.map((row) => row.displayId.toLowerCase()))
+  return ids.filter((id) => !found.has(id.toLowerCase()))
+}
+
 export async function problemFilter(displayId: string, contestId: number | null) {
   // 一次可以筛几道（「这节课」那颗按钮一带就是五道），分隔符和统计面板同一套
   const lowered = parseDisplayIds(displayId).map((id) => id.toLowerCase())
diff --git a/apps/api/src/routes/submission.ts b/apps/api/src/routes/submission.ts
index 20879cc..c03fe6c 100644
--- a/apps/api/src/routes/submission.ts
+++ b/apps/api/src/routes/submission.ts
@@ -37,6 +37,7 @@ import {
   exactUsernameFilter,
   problemFilter,
   submissionStatisticsRoutes,
+  unknownDisplayIds,
   usernameFilter,
 } from "./submission-statistics"
 
@@ -511,7 +512,7 @@ submissionRoutes.get("/submissions", optionalAuth, async (c) => {
   // 「非管理员即受限」，不能写成「是普通用户才受限」——
   // 后者对匿名用户（user 为 null）会短路，匿名反而能看到全部提交，权限大于登录学生。
   if (!(await getBooleanOption("submission_list_show_all", true)) && !isAdminRole(user)) {
-    return success(c, { results: [], total: 0 } satisfies SubmissionList)
+    return success(c, { results: [], total: 0, unknownProblems: [] } satisfies SubmissionList)
   }
   const displayId = c.req.query("problemDisplayId")?.trim()
   const myself = c.req.query("myself") === "1" ? user : null
@@ -542,10 +543,11 @@ submissionRoutes.get("/submissions", optionalAuth, async (c) => {
   const where = and(...filters)
   // count 不 join problem：无条件 join 会让计划器把 count 退化成 seq scan
   // （生产快照实测 7.5ms → 78ms）。题号已经解析成 problem_id，也用不着 join。
-  const [totalRows, rows] = await Promise.all([
+  const [totalRows, rows, unknownProblems] = await Promise.all([
     db.select({ value: count() }).from(schema.submission).where(where),
     // 班级和用户名一样是「圈一小撮人」，走同一条圈选路（见 paginateSubmissionRows）
     paginateSubmissionRows(where, limit, offset, Boolean(username || className)),
+    displayId ? unknownDisplayIds(displayId, null) : [],
   ])
   // 闸门只对学生自己的提交生效，所以只拿这一页里属于他自己的题目去查，一页一次查询
   const [joinTimes, problemsetTitles] = await Promise.all([
@@ -587,6 +589,7 @@ submissionRoutes.get("/submissions", optionalAuth, async (c) => {
         }) satisfies SubmissionListItem,
     ),
     total: totalRows[0]?.value ?? 0,
+    unknownProblems,
   } satisfies SubmissionList)
 })
 
@@ -618,7 +621,7 @@ submissionRoutes.get(
     const where = and(...filters)
     // 一场比赛最多一两千条提交，按 contest_create_time_idx 定位之后怎么滤都不贵，
     // 所以不像公开列表那样分游标 / 圈选两条路
-    const [totalRows, rows] = await Promise.all([
+    const [totalRows, rows, unknownProblems] = await Promise.all([
       db.select({ value: count() }).from(schema.submission).where(where),
       db
         .select(submissionListColumns)
@@ -629,6 +632,7 @@ submissionRoutes.get(
         .orderBy(desc(schema.submission.createTime))
         .limit(limit)
         .offset(offset),
+      displayId ? unknownDisplayIds(displayId, contest.id) : [],
     ])
     // 这里不挂题单防作弊闸门（对比公开列表）：题单里的题必定是非比赛题——加题时卡了
     // `isNull(problem.contestId)`（admin/problemset.ts:232）——而这条列表只出比赛提交，
@@ -656,6 +660,7 @@ submissionRoutes.get(
           }) satisfies SubmissionListItem,
       ),
       total: totalRows[0]?.value ?? 0,
+      unknownProblems,
     } satisfies SubmissionList)
   },
 )
diff --git a/apps/web/src/oj/api.ts b/apps/web/src/oj/api.ts
index 9ee7c1b..1e4b806 100644
--- a/apps/web/src/oj/api.ts
+++ b/apps/web/src/oj/api.ts
@@ -150,10 +150,13 @@ export function getSubmissions(params: Partial<SubmissionListPayload>) {
     : "submissions"
   // 契约里 language 是 z.string()（语言是配置项，随时可能加，收紧成枚举会让
   // 新加的语言在后端 parse 时直接抛），前端在这一处收窄成 LANGUAGE
-  return api.get<{ results: SubmissionListItem[]; total: number }>(endpoint, {
-    // contestId 走的是路径，page 只有前端分页器用
-    params: { ...params, contestId: undefined, page: undefined },
-  })
+  return api.get<{ results: SubmissionListItem[]; total: number; unknownProblems: string[] }>(
+    endpoint,
+    {
+      // contestId 走的是路径，page 只有前端分页器用
+      params: { ...params, contestId: undefined, page: undefined },
+    },
+  )
 }
 
 export function getRankOfProblem(problemId: string) {
diff --git a/apps/web/src/oj/submission/components/FlowchartPane.vue b/apps/web/src/oj/submission/components/FlowchartPane.vue
index a5e106a..298f951 100644
--- a/apps/web/src/oj/submission/components/FlowchartPane.vue
+++ b/apps/web/src/oj/submission/components/FlowchartPane.vue
@@ -243,7 +243,7 @@ const canRetry = computed(
     </div>
 
     <div v-if="!narrow" class="foot">
-      <span class="keys"><kbd>↑</kbd><kbd>↓</kbd></span>
+      <span class="keys"><kbd>↑</kbd><kbd>↓</kbd><kbd>←</kbd><kbd>→</kbd></span>
       <span>换上一张 / 下一张</span>
       <div class="spacer"></div>
       <span v-if="position">本页第 {{ position.index }} / {{ position.count }} 条</span>
diff --git a/apps/web/src/oj/submission/components/SubmissionPane.vue b/apps/web/src/oj/submission/components/SubmissionPane.vue
index 9b9f5af..6e529e3 100644
--- a/apps/web/src/oj/submission/components/SubmissionPane.vue
+++ b/apps/web/src/oj/submission/components/SubmissionPane.vue
@@ -391,7 +391,7 @@ function openStandalone() {
     </template>
 
     <div v-if="!narrow" class="foot">
-      <span class="keys"><kbd>↑</kbd><kbd>↓</kbd></span>
+      <span class="keys"><kbd>↑</kbd><kbd>↓</kbd><kbd>←</kbd><kbd>→</kbd></span>
       <span>
         {{
           teacher
diff --git a/apps/web/src/oj/submission/list.vue b/apps/web/src/oj/submission/list.vue
index 4698421..6781ce5 100644
--- a/apps/web/src/oj/submission/list.vue
+++ b/apps/web/src/oj/submission/list.vue
@@ -96,6 +96,8 @@ const submissions = ref<SubmissionListItem[]>([])
 const flowcharts = ref<FlowchartSubmissionListItem[]>([])
 const total = ref(0)
 const todayCount = ref(0)
+/** 题号框里查不到的题号（打错了）。一次填好几道时打错的那道会被忽略，得告诉老师 */
+const unknownProblems = ref<string[]>([])
 const loading = ref(false)
 const loaded = ref(false)
 
@@ -162,6 +164,7 @@ async function listSubmissions() {
     if (mode) flowcharts.value = res.results as FlowchartSubmissionListItem[]
     else submissions.value = res.results as SubmissionListItem[]
     total.value = res.total
+    unknownProblems.value = res.unknownProblems
     newCount.value = 0
     loaded.value = true
     // 翻了页、换了条件就回到列表顶上（往回翻到上一页末尾的，settleSelection 会滚到那一条）
@@ -311,7 +314,8 @@ function move(step: 1 | -1) {
 
 const [todayPanel, toggleTodayPanel] = useToggle(false)
 
-onKeyStroke(["ArrowUp", "ArrowDown"], (e: KeyboardEvent) => {
+// ← → 和 ↑ ↓ 一样（9 月加方向键时就是四个键都能翻，老师已经用惯了）
+onKeyStroke(["ArrowUp", "ArrowDown", "ArrowLeft", "ArrowRight"], (e: KeyboardEvent) => {
   if (!isDesktop.value || todayPanel.value) return
   // 别的控件已经处理了这次按键（下拉框自己会开菜单、换选项）
   if (e.defaultPrevented) return
@@ -331,7 +335,7 @@ onKeyStroke(["ArrowUp", "ArrowDown"], (e: KeyboardEvent) => {
   }
   if (!rows.value.length) return
   e.preventDefault()
-  move(e.key === "ArrowUp" ? -1 : 1)
+  move(e.key === "ArrowUp" || e.key === "ArrowLeft" ? -1 : 1)
 })
 
 // 手机上没有右栏：点一行从右边滑出整屏的详情
@@ -723,6 +727,7 @@ function dayBreak(index: number) {
         size="small"
         clearable
         placeholder="题号"
+        :status="unknownProblems.length ? 'warning' : undefined"
       >
         <template #prefix><Icon icon="ph:hash" /></template>
       </n-input>
@@ -814,6 +819,10 @@ function dayBreak(index: number) {
     <div class="split">
       <!-- 左栏：列表 -->
       <section class="list">
+        <div v-if="unknownProblems.length" class="unknown-bar">
+          <Icon icon="ph:warning" :width="13" />
+          题号 {{ unknownProblems.join("、") }} 没有这道题，下面只有其余题号的提交
+        </div>
         <button v-if="newCount" class="new-bar" @click="showNew">
           <Icon icon="ph:arrow-up-bold" :width="13" />
           有 {{ newCount }}{{ newCountCapped ? "+" : "" }} 条新提交，点这里显示
@@ -1224,6 +1233,20 @@ function dayBreak(index: number) {
   cursor: pointer;
 }
 
+.unknown-bar {
+  height: 32px;
+  flex: none;
+  box-sizing: border-box;
+  padding: 0 20px;
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  font-size: 13px;
+  color: v-bind("tone('warning').color");
+  background: v-bind("tone('warning').background");
+  border-bottom: 1px solid v-bind("theme.dividerColor");
+}
+
 .rows {
   flex: 1 1 0;
   min-height: 0;
diff --git a/packages/contract/src/flowchart.ts b/packages/contract/src/flowchart.ts
index c2f768b..f50fcf5 100644
--- a/packages/contract/src/flowchart.ts
+++ b/packages/contract/src/flowchart.ts
@@ -58,7 +58,10 @@ export const flowchartListItemSchema = z.object({
   showLink: z.boolean(),
 })
 
-export const flowchartListSchema = paginatedSchema(flowchartListItemSchema)
+export const flowchartListSchema = paginatedSchema(flowchartListItemSchema).extend({
+  /** 题号框里查不到的题号，口径同 submissionListSchema.unknownProblems */
+  unknownProblems: z.array(z.string()),
+})
 export const createFlowchartResponseSchema = z.object({
   submissionId: z.string(),
   status: z.literal("pending"),
diff --git a/packages/contract/src/submission.ts b/packages/contract/src/submission.ts
index 30dcbfe..ae5f04c 100644
--- a/packages/contract/src/submission.ts
+++ b/packages/contract/src/submission.ts
@@ -287,7 +287,13 @@ export const submissionListItemSchema = z.object({
   caseSummary: caseSummarySchema,
 })
 
-export const submissionListSchema = paginatedSchema(submissionListItemSchema)
+export const submissionListSchema = paginatedSchema(submissionListItemSchema).extend({
+  /**
+   * 题号框里填了、但查不到的题号（打错了，或不在这个范围里 —— 比赛列表只认本场的题）。
+   * 一次填好几道时，打错的那道原来被悄悄忽略，老师看到的列表少一道自己却不知道
+   */
+  unknownProblems: z.array(z.string()),
+})
 
 /**
  * **一条都没交**的学生。`realName` 是从用户名里剥掉 `ks<班级号>` 前缀后剩下的那一段，