diff --git a/apps/web/src/admin/announcement/detail.vue b/apps/web/src/admin/announcement/detail.vue
index aedad34..d5ba82b 100644
--- a/apps/web/src/admin/announcement/detail.vue
+++ b/apps/web/src/admin/announcement/detail.vue
@@ -1,4 +1,5 @@
 <script lang="ts" setup>
+import { errorMessage } from "utils/api"
 import TextEditor from "shared/components/TextEditor.vue"
 import type { AnnouncementEdit } from "utils/types"
 import { createAnnouncement, editAnnouncement, getAnnouncement } from "../api"
@@ -63,8 +64,8 @@ async function submit() {
       message.success("修改已保存")
     }
     router.push({ name: "admin announcement list" })
-  } catch (err: any) {
-    message.error(err.data)
+  } catch (err) {
+    message.error(errorMessage(err))
   }
 }
 
diff --git a/apps/web/src/admin/contest/detail.vue b/apps/web/src/admin/contest/detail.vue
index ec9ac4d..99e7333 100644
--- a/apps/web/src/admin/contest/detail.vue
+++ b/apps/web/src/admin/contest/detail.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorMessage } from "utils/api"
 import { formatISO } from "date-fns"
 import TextEditor from "shared/components/TextEditor.vue"
 import { fromPickerValue, parseTime, toPickerValue } from "utils/functions"
@@ -102,8 +103,8 @@ async function submit() {
       message.success("修改已保存")
     }
     router.push({ name: "admin contest list" })
-  } catch (err: any) {
-    message.error(err.data)
+  } catch (err) {
+    message.error(errorMessage(err))
   }
 }
 
diff --git a/apps/web/src/admin/contest/helper.vue b/apps/web/src/admin/contest/helper.vue
index b6a71a8..9823fc0 100644
--- a/apps/web/src/admin/contest/helper.vue
+++ b/apps/web/src/admin/contest/helper.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorMessage } from "utils/api"
 import type { AcmHelperItem, SubmissionInfo } from "utils/types"
 import { NButton, NCheckbox, NSelect, NTag } from "naive-ui"
 import { parseTime } from "utils/functions"
@@ -70,8 +71,8 @@ async function toggleChecked(item: HelperItem) {
     submissions.value = [...submissions.value]
 
     message.success(newChecked ? "已标记为已检查" : "已取消标记")
-  } catch (err: any) {
-    message.error(err.data || "操作失败")
+  } catch (err) {
+    message.error(errorMessage(err, "操作失败"))
   }
 }
 
@@ -101,9 +102,9 @@ async function markAllAsChecked() {
 
     loadingMsg.destroy()
     message.success(`已标记 ${unchecked.length} 个提交为已检查`)
-  } catch (err: any) {
+  } catch (err) {
     loadingMsg.destroy()
-    message.error(err.data || "批量操作失败")
+    message.error(errorMessage(err, "批量操作失败"))
   }
 }
 
@@ -159,8 +160,8 @@ async function viewSubmission(item: HelperItem) {
     }
 
     toggleCodePanel(true)
-  } catch (err: any) {
-    message.error(err.data || "加载提交失败")
+  } catch (err) {
+    message.error(errorMessage(err, "加载提交失败"))
   }
 }
 
@@ -174,8 +175,8 @@ async function loadData() {
     // 再获取 AC 提交列表
     const data = await getACMHelperList(Number(props.contestID))
     submissions.value = data
-  } catch (err: any) {
-    message.error(err.data || "加载失败")
+  } catch (err) {
+    message.error(errorMessage(err, "加载失败"))
   }
 }
 
diff --git a/apps/web/src/admin/problem/components/Actions.vue b/apps/web/src/admin/problem/components/Actions.vue
index 9068cc4..070fbed 100644
--- a/apps/web/src/admin/problem/components/Actions.vue
+++ b/apps/web/src/admin/problem/components/Actions.vue
@@ -1,4 +1,5 @@
 <script lang="ts" setup>
+import { errorCode, errorMessage } from "utils/api"
 import {
   deleteContestProblem,
   deleteProblem,
@@ -33,8 +34,8 @@ async function handleDeleteProblem() {
     }
     message.success("删除成功")
     emit("updated")
-  } catch (err: any) {
-    if (err.error === "problem-has-submissions") {
+  } catch (err) {
+    if (errorCode(err) === "problem-has-submissions") {
       message.error("这道题有提交之后，就不能被删除")
     } else {
       message.error("删除失败")
@@ -81,13 +82,13 @@ async function handleMakePublic() {
     message.success("已成功转为公开题目（需要手动设置可见）")
     showMakePublicModal.value = false
     emit("updated") // 刷新列表
-  } catch (err: any) {
-    if (err.error === "display-id-exists") {
+  } catch (err) {
+    if (errorCode(err) === "display-id-exists") {
       message.error("该题目编号已存在，请使用其他编号")
-    } else if (err.error === "already-public") {
+    } else if (errorCode(err) === "already-public") {
       message.error("该题目已经是公开题目")
     } else {
-      message.error("转换失败：" + (err.data || "未知错误"))
+      message.error("转换失败：" + errorMessage(err, "未知错误"))
     }
   }
 }
diff --git a/apps/web/src/admin/problem/components/AddButton.vue b/apps/web/src/admin/problem/components/AddButton.vue
index bda9d67..e9be76c 100644
--- a/apps/web/src/admin/problem/components/AddButton.vue
+++ b/apps/web/src/admin/problem/components/AddButton.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorCode, errorMessage } from "utils/api"
 import { addProblemForContest } from "admin/api"
 
 interface Props {
@@ -22,13 +23,13 @@ async function addProblem() {
       displayID.value,
     )
     emit("added")
-  } catch (err: any) {
-    if (err.error === "display-id-exists") {
+  } catch (err) {
+    if (errorCode(err) === "display-id-exists") {
       message.error("显示编号重复了，请重新写一个")
-    } else if (err.error === "contest-ended") {
+    } else if (errorCode(err) === "contest-ended") {
       message.error("这场比赛已经结束了，不能添加题目")
     } else {
-      message.error(err.data)
+      message.error(errorMessage(err))
     }
   }
 }
diff --git a/apps/web/src/admin/problem/components/SQLTestcaseEditor.vue b/apps/web/src/admin/problem/components/SQLTestcaseEditor.vue
index 5d9cd78..cc74cea 100644
--- a/apps/web/src/admin/problem/components/SQLTestcaseEditor.vue
+++ b/apps/web/src/admin/problem/components/SQLTestcaseEditor.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorCode, isApiError } from "utils/api"
 import type { LANGUAGE, SqlDisplay, Testcase } from "utils/types"
 import { createZipBlob } from "utils/functions"
 import SQLDataTable from "oj/problem/components/SQLDataTable.vue"
@@ -81,15 +82,15 @@ onMounted(async () => {
     if (res.length) {
       scripts.value = res.map((f) => ({ ...blankEntry(), sql: f.content }))
     }
-  } catch (err: any) {
+  } catch (err) {
     // 新题、以及旧格式（非 SQL）测试点，后端回 404/409，保持空白就是对的，不该报错。
     // 但**其它**失败必须说出来：读不出来时编辑器长得和「这题本来就没测试点」一模一样，
     // 教师看不出区别，会以为要自己重新填。保存本身是安全的（后端读不到测试点信息会拒绝
     // 整个保存），所以这里只提示、不阻塞。
-    const code = err?.error
+    const code = errorCode(err)
     if (code && code !== "problem-not-found" && code !== "not-sql-test-case") {
       // 后端那句话（如"测试点信息读取失败"）只说了现象，教师需要的是「下面是空的、别存」
-      const detail = err?.data ? `（${err.data}）` : ""
+      const detail = isApiError(err) && err.data ? `（${err.data}）` : ""
       loadError.value =
         `已有测试点脚本没能读出来${detail}。下方是空白模板，不是本题真实的测试点 —— ` +
         `直接保存不会丢数据（后端会拒绝），但也不会生效。请先排查测试点文件，或重新上传。`
diff --git a/apps/web/src/admin/problem/detail.vue b/apps/web/src/admin/problem/detail.vue
index 7bb40c9..db0a443 100644
--- a/apps/web/src/admin/problem/detail.vue
+++ b/apps/web/src/admin/problem/detail.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorCode, errorMessage } from "utils/api"
 import { PROBLEM_TAG_MAX_LENGTH } from "@oj2/contract"
 import { getProblemTagList } from "shared/api"
 import TextEditor from "shared/components/TextEditor.vue"
@@ -484,11 +485,11 @@ async function submit() {
         params: { contestID: props.contestID },
       })
     }
-  } catch (err: any) {
-    if (err.error === "display-id-exists") {
+  } catch (err) {
+    if (errorCode(err) === "display-id-exists") {
       message.error("显示编号重复了，请换一个显示编号")
     } else {
-      message.error(err.data)
+      message.error(errorMessage(err))
     }
   }
 }
@@ -515,9 +516,9 @@ async function generateMermaid() {
     )
     problem.value.mermaidCode = res.flowchart
     message.warning("如果渲染不成功，请复制到外部 AI 网站检查语法")
-  } catch (err: any) {
+  } catch (err) {
     // 没有 finally 的话，AI 接口回 502 时按钮永远卡在 loading，只能刷页面
-    message.error(err.data || "生成失败，请稍后再试")
+    message.error(errorMessage(err, "生成失败，请稍后再试"))
   } finally {
     isAIGenerating.value = false
   }
diff --git a/apps/web/src/admin/problemset/components/Actions.vue b/apps/web/src/admin/problemset/components/Actions.vue
index 97d1b7b..e8b3980 100644
--- a/apps/web/src/admin/problemset/components/Actions.vue
+++ b/apps/web/src/admin/problemset/components/Actions.vue
@@ -1,4 +1,5 @@
 <script lang="ts" setup>
+import { errorMessage } from "utils/api"
 import { deleteProblemSet, updateProblemSetStatus } from "admin/api"
 
 interface Props {
@@ -24,8 +25,8 @@ async function handleDeleteProblemSet() {
     await deleteProblemSet(props.problemSetId)
     message.success("删除成功")
     emit("updated")
-  } catch (err: any) {
-    message.error("删除失败：" + (err.data || "未知错误"))
+  } catch (err) {
+    message.error("删除失败：" + errorMessage(err, "未知错误"))
   }
 }
 
@@ -53,8 +54,8 @@ async function handleUpdateStatus() {
     message.success("状态更新成功")
     showStatusModal.value = false
     emit("updated")
-  } catch (err: any) {
-    message.error("状态更新失败：" + (err.data || "未知错误"))
+  } catch (err) {
+    message.error("状态更新失败：" + errorMessage(err, "未知错误"))
   }
 }
 </script>
diff --git a/apps/web/src/admin/problemset/detail.vue b/apps/web/src/admin/problemset/detail.vue
index 789acc3..340c391 100644
--- a/apps/web/src/admin/problemset/detail.vue
+++ b/apps/web/src/admin/problemset/detail.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorMessage } from "utils/api"
 import { NTabPane, NTabs, NButton, NFlex } from "naive-ui"
 import type {
   AdminProblemSet,
@@ -61,8 +62,8 @@ async function loadProblemSetDetail() {
   try {
     const res = await getProblemSetDetail(problemSetId.value)
     problemSet.value = res
-  } catch (err: any) {
-    message.error("加载题单详情失败：" + (err.data || "未知错误"))
+  } catch (err) {
+    message.error("加载题单详情失败：" + errorMessage(err, "未知错误"))
   }
 }
 
@@ -70,8 +71,8 @@ async function loadProblems() {
   try {
     const res = await getProblemSetProblems(problemSetId.value)
     problems.value = res
-  } catch (err: any) {
-    message.error("加载题目列表失败：" + (err.data || "未知错误"))
+  } catch (err) {
+    message.error("加载题目列表失败：" + errorMessage(err, "未知错误"))
   }
 }
 
@@ -79,8 +80,8 @@ async function loadBadges() {
   try {
     const res = await getProblemSetBadges(problemSetId.value)
     badges.value = res
-  } catch (err: any) {
-    message.error("加载奖章列表失败：" + (err.data || "未知错误"))
+  } catch (err) {
+    message.error("加载奖章列表失败：" + errorMessage(err, "未知错误"))
   }
 }
 
@@ -88,8 +89,8 @@ async function loadProgress() {
   try {
     const res = await getProblemSetProgress(problemSetId.value)
     progress.value = res
-  } catch (err: any) {
-    message.error("加载进度列表失败：" + (err.data || "未知错误"))
+  } catch (err) {
+    message.error("加载进度列表失败：" + errorMessage(err, "未知错误"))
   }
 }
 
@@ -100,8 +101,8 @@ async function handleAddProblem(data: AddProblemToSetRequest) {
     showAddProblemModal.value = false
     loadProblems()
     loadProblemSetDetail() // 刷新题目数量
-  } catch (err: any) {
-    message.error("添加题目失败：" + (err.data || "未知错误"))
+  } catch (err) {
+    message.error("添加题目失败：" + errorMessage(err, "未知错误"))
   }
 }
 
@@ -111,8 +112,8 @@ async function handleRemoveProblem(problemSetProblemId: number) {
     message.success("题目移除成功")
     loadProblems()
     loadProblemSetDetail() // 刷新题目数量
-  } catch (err: any) {
-    message.error("移除题目失败：" + (err.data || "未知错误"))
+  } catch (err) {
+    message.error("移除题目失败：" + errorMessage(err, "未知错误"))
   }
 }
 
@@ -124,8 +125,8 @@ async function handleEditProblem(data: UpdateProblemInSetRequest) {
     message.success("题目编辑成功")
     showEditProblemModal.value = false
     loadProblems()
-  } catch (err: any) {
-    message.error("编辑题目失败：" + (err.data || "未知错误"))
+  } catch (err) {
+    message.error("编辑题目失败：" + errorMessage(err, "未知错误"))
   }
 }
 
@@ -135,8 +136,8 @@ async function handleAddBadge(data: BadgeFormData) {
     message.success("奖章创建成功")
     showAddBadgeModal.value = false
     loadBadges()
-  } catch (err: any) {
-    message.error("创建奖章失败：" + (err.data || "未知错误"))
+  } catch (err) {
+    message.error("创建奖章失败：" + errorMessage(err, "未知错误"))
   }
 }
 
@@ -145,8 +146,8 @@ async function handleDeleteBadge(badgeId: number) {
     await deleteProblemSetBadge(problemSetId.value, badgeId)
     message.success("奖章删除成功")
     loadBadges()
-  } catch (err: any) {
-    message.error("删除奖章失败：" + (err.data || "未知错误"))
+  } catch (err) {
+    message.error("删除奖章失败：" + errorMessage(err, "未知错误"))
   }
 }
 
@@ -158,8 +159,8 @@ async function handleEditBadge(data: BadgeFormData) {
     message.success("奖章编辑成功")
     showEditBadgeModal.value = false
     loadBadges()
-  } catch (err: any) {
-    message.error("编辑奖章失败：" + (err.data || "未知错误"))
+  } catch (err) {
+    message.error("编辑奖章失败：" + errorMessage(err, "未知错误"))
   }
 }
 
@@ -168,8 +169,8 @@ async function handleRemoveUser(userId: number) {
     await removeUserFromProblemSet(problemSetId.value, userId)
     message.success("用户移除成功")
     loadProgress()
-  } catch (err: any) {
-    message.error("移除用户失败：" + (err.data || "未知错误"))
+  } catch (err) {
+    message.error("移除用户失败：" + errorMessage(err, "未知错误"))
   }
 }
 
diff --git a/apps/web/src/admin/problemset/edit.vue b/apps/web/src/admin/problemset/edit.vue
index bb25e84..b32cd2d 100644
--- a/apps/web/src/admin/problemset/edit.vue
+++ b/apps/web/src/admin/problemset/edit.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorMessage } from "utils/api"
 import type { CreateProblemSetData, EditProblemSetData } from "utils/types"
 import { fromPickerValue, toPickerValue } from "utils/functions"
 import { getProblemSetDetail, createProblemSet, editProblemSet } from "../api"
@@ -60,8 +61,8 @@ async function loadProblemSetDetail() {
       visible: data.visible,
       endTime: data.endTime ? new Date(data.endTime) : null,
     }
-  } catch (err: any) {
-    message.error("加载题单详情失败：" + (err.data || "未知错误"))
+  } catch (err) {
+    message.error("加载题单详情失败：" + errorMessage(err, "未知错误"))
   }
 }
 
@@ -87,11 +88,11 @@ async function handleSubmit() {
       message.success("题单创建成功")
     }
     router.push({ name: "admin problemset list" })
-  } catch (err: any) {
+  } catch (err) {
     message.error(
       (isEdit.value ? "更新" : "创建") +
         "题单失败：" +
-        (err.data || "未知错误"),
+        errorMessage(err, "未知错误"),
     )
   } finally {
     loading.value = false
diff --git a/apps/web/src/admin/setting/config.vue b/apps/web/src/admin/setting/config.vue
index b9f905c..f9b75dc 100644
--- a/apps/web/src/admin/setting/config.vue
+++ b/apps/web/src/admin/setting/config.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorMessage } from "utils/api"
 import { NButton, NTag } from "naive-ui"
 import {
   CLASS_NAME_MAX_DIGITS,
@@ -210,8 +211,8 @@ async function saveWebsiteConfig() {
   }
   try {
     await editWebsite(websiteConfig)
-  } catch (err: any) {
-    message.error("保存失败：" + err.data)
+  } catch (err) {
+    message.error("保存失败：" + errorMessage(err))
     return
   }
   message.success("网站配置保存成功")
diff --git a/apps/web/src/admin/tutorial/components/Actions.vue b/apps/web/src/admin/tutorial/components/Actions.vue
index e2e535b..3744705 100644
--- a/apps/web/src/admin/tutorial/components/Actions.vue
+++ b/apps/web/src/admin/tutorial/components/Actions.vue
@@ -1,4 +1,5 @@
 <script lang="ts" setup>
+import { errorMessage } from "utils/api"
 import { deleteTutorial } from "admin/api"
 
 interface Props {
@@ -22,8 +23,8 @@ async function handleDelete() {
     await deleteTutorial(props.tutorialID)
     message.success("删除成功")
     emit("deleted")
-  } catch (err: any) {
-    message.error(err.data)
+  } catch (err) {
+    message.error(errorMessage(err))
   }
 }
 </script>
diff --git a/apps/web/src/admin/tutorial/components/ExerciseManager.vue b/apps/web/src/admin/tutorial/components/ExerciseManager.vue
index 5ff3a95..e5f7ef6 100644
--- a/apps/web/src/admin/tutorial/components/ExerciseManager.vue
+++ b/apps/web/src/admin/tutorial/components/ExerciseManager.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorMessage } from "utils/api"
 import type {
   Exercise,
   ExerciseType,
@@ -317,8 +318,8 @@ async function save() {
     }
     showForm.value = false
     await load()
-  } catch (e: any) {
-    message.error(e.data ?? "保存失败")
+  } catch (e) {
+    message.error(errorMessage(e, "保存失败"))
   }
 }
 
diff --git a/apps/web/src/admin/tutorial/detail.vue b/apps/web/src/admin/tutorial/detail.vue
index e0c6ad3..378e259 100644
--- a/apps/web/src/admin/tutorial/detail.vue
+++ b/apps/web/src/admin/tutorial/detail.vue
@@ -1,4 +1,5 @@
 <script lang="ts" setup>
+import { errorMessage } from "utils/api"
 import CodeEditor from "shared/components/CodeEditor.vue"
 import MarkdownEditor from "shared/components/MarkdownEditor.vue"
 import type { TutorialEdit } from "utils/types"
@@ -63,8 +64,8 @@ async function submit() {
       await updateTutorial(tutorial)
       message.success("修改已保存")
     }
-  } catch (err: any) {
-    message.error(err.data)
+  } catch (err) {
+    message.error(errorMessage(err))
   }
 }
 
diff --git a/apps/web/src/admin/tutorial/list.vue b/apps/web/src/admin/tutorial/list.vue
index 21ed067..908d687 100644
--- a/apps/web/src/admin/tutorial/list.vue
+++ b/apps/web/src/admin/tutorial/list.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorMessage } from "utils/api"
 import { NSwitch } from "naive-ui"
 import { parseTime } from "utils/functions"
 import type { TutorialListItem } from "utils/types"
@@ -63,8 +64,8 @@ async function toggleVisible(tutorial: TutorialListItem) {
   try {
     await setTutorialVisibility(tutorial.id, tutorial.isPublic)
     message.success("更新成功")
-  } catch (err: any) {
-    message.error(err.data)
+  } catch (err) {
+    message.error(errorMessage(err))
     tutorial.isPublic = !tutorial.isPublic
   }
 }
diff --git a/apps/web/src/admin/user/generate.vue b/apps/web/src/admin/user/generate.vue
index f5006e3..0316b75 100644
--- a/apps/web/src/admin/user/generate.vue
+++ b/apps/web/src/admin/user/generate.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorMessage } from "utils/api"
 import {
   CLASS_NAME_MAX_DIGITS,
   CLASS_NAME_MAX_VALUE,
@@ -66,8 +67,8 @@ async function uploadUsers() {
     hiddenElement.download = prefix.value + ".csv"
     hiddenElement.click()
     hiddenElement.remove()
-  } catch (err: any) {
-    message.error("上传失败：" + err.data)
+  } catch (err) {
+    message.error("上传失败：" + errorMessage(err))
   } finally {
     toggleLoading(false)
   }
diff --git a/apps/web/src/admin/user/list.vue b/apps/web/src/admin/user/list.vue
index 58a541d..09b9160 100644
--- a/apps/web/src/admin/user/list.vue
+++ b/apps/web/src/admin/user/list.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorMessage } from "utils/api"
 import { DataTableRowKey, NFlex, NTag, SelectOption } from "naive-ui"
 import Pagination from "shared/components/Pagination.vue"
 import { usePagination } from "shared/composables/pagination"
@@ -250,8 +251,8 @@ async function handleEditUser() {
       })
       await editUser(user)
     }
-  } catch (err: any) {
-    message.error("保存失败：" + err.data)
+  } catch (err) {
+    message.error("保存失败：" + errorMessage(err))
     return
   }
   userEditing.value = null
diff --git a/apps/web/src/oj/problem/components/SubmitCode.vue b/apps/web/src/oj/problem/components/SubmitCode.vue
index 4850096..03611f0 100644
--- a/apps/web/src/oj/problem/components/SubmitCode.vue
+++ b/apps/web/src/oj/problem/components/SubmitCode.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorCode, errorMessage } from "utils/api"
 import { Icon } from "@iconify/vue"
 import { storeToRefs } from "pinia"
 import { formatCode, getReaction, submitCode } from "oj/api"
@@ -133,10 +134,10 @@ async function submit() {
         language: formatLang,
       })
       codeStore.setCode(res.code)
-    } catch (e: any) {
-      if (e?.error === "format-error") {
+    } catch (e) {
+      if (errorCode(e) === "format-error") {
         // 仅 Python 会出现：代码本身存在语法错误
-        message.warning(`代码格式化失败：${e.data}，请检查代码后重试`)
+        message.warning(`代码格式化失败：${errorMessage(e)}，请检查代码后重试`)
         return
       }
       // server-error / 网络异常：格式化工具问题，静默降级，提交原代码
diff --git a/apps/web/src/oj/problem/components/SubmitFlowchart.vue b/apps/web/src/oj/problem/components/SubmitFlowchart.vue
index ae761a9..928b84e 100644
--- a/apps/web/src/oj/problem/components/SubmitFlowchart.vue
+++ b/apps/web/src/oj/problem/components/SubmitFlowchart.vue
@@ -1,4 +1,5 @@
 <script lang="ts" setup>
+import { errorCode } from "utils/api"
 import { toRefs } from "vue"
 
 // 工具函数
@@ -256,13 +257,13 @@ async function submitFlowchartData() {
     }
 
     message.success("流程图已提交，请耐心等待评分")
-  } catch (error: any) {
+  } catch (error) {
     loading.value = false
     // 按错误码分支（见 utils/api.ts 的约定）。限流是最容易撞上的一种：
     // 只说「提交失败」的话，学生会以为是自己的图有问题，然后反复点，越点越久
-    if (error?.error === "too-many-submissions") {
+    if (errorCode(error) === "too-many-submissions") {
       message.warning("提交太频繁了，缓一会儿再交")
-    } else if (error?.error === "flowchart-not-allowed") {
+    } else if (errorCode(error) === "flowchart-not-allowed") {
       message.error("这道题不接受流程图提交")
     } else {
       message.error("流程图提交失败")
diff --git a/apps/web/src/oj/problem/detail.vue b/apps/web/src/oj/problem/detail.vue
index 26a6370..74acca9 100644
--- a/apps/web/src/oj/problem/detail.vue
+++ b/apps/web/src/oj/problem/detail.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorCode } from "utils/api"
 import { getProblem } from "oj/api"
 import { useBreakpoints } from "shared/composables/breakpoints"
 import { storeToRefs } from "pinia"
@@ -120,9 +121,9 @@ async function init() {
   try {
     const res = await getProblem(problemID, contestID)
     problem.value = res
-  } catch (err: any) {
+  } catch (err) {
     problem.value = null
-    if (err.error === "contest-not-started") {
+    if (errorCode(err) === "contest-not-started") {
       errMsg.value = "比赛还没有开始"
     }
   }
diff --git a/apps/web/src/oj/problem/utils/pythonSyntaxCheck.ts b/apps/web/src/oj/problem/utils/pythonSyntaxCheck.ts
index d7071ac..a101136 100644
--- a/apps/web/src/oj/problem/utils/pythonSyntaxCheck.ts
+++ b/apps/web/src/oj/problem/utils/pythonSyntaxCheck.ts
@@ -46,8 +46,10 @@ export async function checkPythonSyntax(
   try {
     Sk.compile(code, "prog.py", "exec")
     return null
-  } catch (e: any) {
-    const line: number = e?.traceback?.[0]?.lineno ?? 1
+  } catch (e) {
+    // Skulpt 的语法错误对象，不是 Error 的子类
+    const traceback = (e as { traceback?: { lineno?: number }[] }).traceback
+    const line = traceback?.[0]?.lineno ?? 1
     return { line }
   }
 }
diff --git a/apps/web/src/oj/problemset/components/UserProgressView.vue b/apps/web/src/oj/problemset/components/UserProgressView.vue
index 67e118f..520e0be 100644
--- a/apps/web/src/oj/problemset/components/UserProgressView.vue
+++ b/apps/web/src/oj/problemset/components/UserProgressView.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorMessage } from "utils/api"
 import { h, computed, ref, onMounted, watch } from "vue"
 import { watchDebounced } from "@vueuse/core"
 import { parseTime } from "utils/functions"
@@ -68,10 +69,10 @@ async function loadUserProgress() {
     if (res.problems) {
       allProblems.value = res.problems
     }
-  } catch (err: any) {
+  } catch (err) {
     // finally 里收掉 loading：以前 loading.value = false 写在 await 之后，
     // 请求一失败（403、断网）转圈就永远停不下来
-    message.error("加载用户进度失败：" + (err.data || "未知错误"))
+    message.error("加载用户进度失败：" + errorMessage(err, "未知错误"))
   } finally {
     loading.value = false
   }
diff --git a/apps/web/src/oj/problemset/detail.vue b/apps/web/src/oj/problemset/detail.vue
index 58e0557..0c2810f 100644
--- a/apps/web/src/oj/problemset/detail.vue
+++ b/apps/web/src/oj/problemset/detail.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorMessage } from "utils/api"
 import {
   getProblemSetDetail,
   getProblemSetProblems,
@@ -90,8 +91,8 @@ async function handleJoinProblemSet() {
     message.success("成功加入题单！")
     // 加入题单后加载用户徽章
     await loadUserBadges()
-  } catch (err: any) {
-    message.error("加入题单失败：" + (err.data || "未知错误"))
+  } catch (err) {
+    message.error("加入题单失败：" + errorMessage(err, "未知错误"))
   } finally {
     isJoining.value = false
   }
diff --git a/apps/web/src/oj/rank/list.vue b/apps/web/src/oj/rank/list.vue
index 0d9ebfa..60ac15b 100644
--- a/apps/web/src/oj/rank/list.vue
+++ b/apps/web/src/oj/rank/list.vue
@@ -505,7 +505,7 @@ async function listMyClassRank() {
     if (myClassScope.value === "window") {
       myClassQuery.page = 1
     }
-  } catch (err: any) {
+  } catch (err) {
     console.error(err)
   }
 }
@@ -517,7 +517,7 @@ async function listWeeklyRank() {
     weeklyMe.value = res.me
     weeklyTotal.value = res.total
     weeklyStart.value = res.start
-  } catch (err: any) {
+  } catch (err) {
     console.error(err)
   }
 }
diff --git a/apps/web/src/oj/store/contest.ts b/apps/web/src/oj/store/contest.ts
index e01fa29..d23c791 100644
--- a/apps/web/src/oj/store/contest.ts
+++ b/apps/web/src/oj/store/contest.ts
@@ -1,3 +1,4 @@
+import { errorCode } from "utils/api"
 import { formatISO, getTime, parseISO } from "date-fns"
 import { useUserStore } from "shared/store/user"
 import { ContestStatus, ContestType } from "utils/constants"
@@ -96,9 +97,9 @@ export const useContestStore = defineStore("contest", () => {
         _getProblems(contestID)
       }
       return null
-    } catch (err: any) {
+    } catch (err) {
       toggleAccess(false)
-      return (err?.error as string | undefined) ?? "unknown"
+      return errorCode(err) ?? "unknown"
     }
   }
 
diff --git a/apps/web/src/oj/submission/list.vue b/apps/web/src/oj/submission/list.vue
index 623ff1b..37c0b3d 100644
--- a/apps/web/src/oj/submission/list.vue
+++ b/apps/web/src/oj/submission/list.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorCode } from "utils/api"
 import { NButton, NFlex, NTag, NText } from "naive-ui"
 import { useRouteQuery } from "@vueuse/router"
 import {
@@ -225,8 +226,8 @@ async function retryFlowchart(submissionId: string) {
   }
   try {
     await retryFlowchartSubmission(submissionId)
-  } catch (err: any) {
-    message.error(retryTips[err?.error] ?? "重新评分失败")
+  } catch (err) {
+    message.error(retryTips[errorCode(err) ?? ""] ?? "重新评分失败")
     return
   }
   message.success("重新评分已提交")
diff --git a/apps/web/src/shared/components/Login.vue b/apps/web/src/shared/components/Login.vue
index 6d5223c..a75841a 100644
--- a/apps/web/src/shared/components/Login.vue
+++ b/apps/web/src/shared/components/Login.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorCode } from "utils/api"
 import { STORAGE_KEY } from "utils/constants"
 import storage from "utils/storage"
 import { getClassUsernames, login } from "../api"
@@ -124,13 +125,13 @@ function submit() {
         merged.username = form.value.class + merged.username
       }
       await login(merged)
-    } catch (err: any) {
+    } catch (err) {
       // 判错误码而不是错误文案：文案在后端，改一个字这里就静默掉进「无法登录」
-      if (err.error === "account-disabled") {
+      if (errorCode(err) === "account-disabled") {
         authStore.setLoginError("此账号已被封禁")
-      } else if (err.error === "invalid-credentials") {
+      } else if (errorCode(err) === "invalid-credentials") {
         authStore.setLoginError("用户名或密码不正确")
-      } else if (err.error === "too-many-login-attempts") {
+      } else if (errorCode(err) === "too-many-login-attempts") {
         authStore.setLoginError("密码错误次数太多，请 15 分钟后再试")
       } else {
         authStore.setLoginError("无法登录")
diff --git a/apps/web/src/shared/components/Signup.vue b/apps/web/src/shared/components/Signup.vue
index 4ef25b0..4626415 100644
--- a/apps/web/src/shared/components/Signup.vue
+++ b/apps/web/src/shared/components/Signup.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { errorCode } from "utils/api"
 import { signup } from "../api"
 import { storeToRefs } from "pinia"
 import { useAuthModalStore } from "../store/authModal"
@@ -47,12 +48,12 @@ function submit() {
           email: form.value.email,
           password: form.value.password,
         })
-      } catch (err: any) {
-        if (err.error === "username-exists") {
+      } catch (err) {
+        if (errorCode(err) === "username-exists") {
           authStore.setSignupError("用户名已存在")
-        } else if (err.error === "email-exists") {
+        } else if (errorCode(err) === "email-exists") {
           authStore.setSignupError("邮箱已存在")
-        } else if (err.error === "too-many-registrations") {
+        } else if (errorCode(err) === "too-many-registrations") {
           authStore.setSignupError("注册太频繁，请稍后再试")
         } else {
           authStore.setSignupError("无法注册")
diff --git a/apps/web/src/utils/api.ts b/apps/web/src/utils/api.ts
index 0ec9f5e..790e632 100644
--- a/apps/web/src/utils/api.ts
+++ b/apps/web/src/utils/api.ts
@@ -6,13 +6,45 @@ import storage from "./storage"
 
 const { message: toast } = createDiscreteApi(["message"])
 
-interface ApiError {
+/** 后端失败响应体的形状，见 apps/api/src/http.ts 的 failure */
+interface ErrorPayload {
   error?: {
     code?: string
     message?: string
   }
 }
 
+/**
+ * 拦截器 reject 出来的就是它：`error` 是错误码，`data` 是后端文案。
+ *
+ * 字段名沿用原来那个裸对象 `{ error, data }`，存量调用点读 `err.error` / `err.data`
+ * 的语义不变；做成 Error 的子类是为了在 catch 里能和代码 bug（TypeError 之类）分开，
+ * 也顺带有了堆栈。catch 块里别写 `err: any`，用下面的 errorCode / errorMessage。
+ */
+export class ApiError extends Error {
+  constructor(
+    readonly error: string,
+    readonly data: string,
+  ) {
+    super(data)
+    this.name = "ApiError"
+  }
+}
+
+export function isApiError(err: unknown): err is ApiError {
+  return err instanceof ApiError
+}
+
+/** 接口错误的错误码；不是接口错误（代码 bug、被中止……）就是 undefined */
+export function errorCode(err: unknown) {
+  return isApiError(err) ? err.error : undefined
+}
+
+/** 给用户看的文案：接口错误用后端文案，其它一律 fallback —— 别把 TypeError 的英文甩给学生 */
+export function errorMessage(err: unknown, fallback = "未知错误") {
+  return isApiError(err) && err.data ? err.data : fallback
+}
+
 /**
  * 成功时直接拿到业务数据本身。后端成功响应是 `{ data }`（见 apps/api/src/http.ts
  * 的 success），拦截器把 axios 外层和这层信封一起剥掉。
@@ -74,12 +106,13 @@ instance.interceptors.response.use(
     response: AxiosResponse,
   ) => AxiosResponse,
   (error) => {
-    const payload = error.response?.data as ApiError | undefined
+    const payload = error.response?.data as ErrorPayload | undefined
     const code = payload?.error?.code ?? "network-error"
-    const message = payload?.error?.message ?? "Request failed"
+    // 没有响应体 = 请求根本没到后端（断网、反代挂了、超时），学生看到的就是这一句
+    const message = payload?.error?.message ?? "网络异常，请检查网络后重试"
 
     handleGlobalApiError(code, message)
-    return Promise.reject({ error: code, data: message })
+    return Promise.reject(new ApiError(code, message))
   },
 )