feat(dashboard,diagnostic,elective): add widgets, layout, parent dashboard, role-config, services, elective components

dashboard: - Add comparison-badge, dashboard-notification-widget, dashboard-responsive-layout, dashboard-time-range-filter - Add parent-dashboard components directory - Add config, hooks, and services directories diagnostic: - Add role-config and services directory elective: - Add elective-course-detail, elective-stats-cards, parent-selection-view components - Add data-access-settings and data-access-stats
2026-07-03 10:25:46 +08:00
parent dfffb61e94
commit 138b6f1b00
58 changed files with 3313 additions and 695 deletions
--- a/src/modules/elective/actions.ts
+++ b/src/modules/elective/actions.ts
@@ -23,15 +23,25 @@ import {
  openSelection,
  closeSelection,
 } from "./data-access"
-import { runLottery, selectCourse, dropCourse } from "./data-access-operations"
+import {
+  runLottery,
+  selectCourse,
+  dropCourse,
+  ElectiveBusinessError,
+  type ElectiveErrorCode,
+} from "./data-access-operations"
+import { COURSE_SELECTION_STATUS_LABEL_KEYS } from "./constants"

 const revalidateElectivePaths = (id?: string) => {
  revalidatePath("/admin/elective")
  revalidatePath("/teacher/elective")
  revalidatePath("/student/elective")
+  revalidatePath("/parent/elective")
  if (id) {
    revalidatePath(`/admin/elective/${id}`)
    revalidatePath(`/admin/elective/${id}/edit`)
+    revalidatePath(`/teacher/elective/${id}`)
+    revalidatePath(`/teacher/elective/${id}/edit`)
  }
 }

@@ -41,6 +51,24 @@ const requireCourseId = (formData: FormData): string => {
  return id
 }

+/**
+ * 将 ElectiveBusinessError 翻译为用户可见的 i18n 文案。
+ * 在 catch 中调用，返回 null 表示非业务错误（交给 handleActionError）。
+ */
+async function translateBusinessError(
+  e: unknown,
+  t: Awaited<ReturnType<typeof getTranslations>>
+): Promise<string | null> {
+  if (e instanceof ElectiveBusinessError) {
+    const code = e.code satisfies ElectiveErrorCode
+    if (e.params) {
+      return t(`errors.${code}`, e.params)
+    }
+    return t(`errors.${code}`)
+  }
+  return null
+}
+
 /**
 * 校验当前用户对课程的管理权限（资源归属校验）。
 * - admin（scope=all）：直接放行
@@ -101,6 +129,9 @@ export async function createElectiveCourseAction(
    })
    return { success: true, message: t("messages.created"), data: id }
  } catch (e) {
+    const t = await getTranslations("elective")
+    const translated = await translateBusinessError(e, t)
+    if (translated) return { success: false, message: translated }
    return handleActionError(e)
  }
 }
@@ -153,6 +184,9 @@ export async function updateElectiveCourseAction(
    })
    return { success: true, message: t("messages.updated"), data: id }
  } catch (e) {
+    const t = await getTranslations("elective")
+    const translated = await translateBusinessError(e, t)
+    if (translated) return { success: false, message: translated }
    return handleActionError(e)
  }
 }
@@ -181,6 +215,9 @@ export async function deleteElectiveCourseAction(
    })
    return { success: true, message: t("messages.deleted") }
  } catch (e) {
+    const t = await getTranslations("elective")
+    const translated = await translateBusinessError(e, t)
+    if (translated) return { success: false, message: translated }
    return handleActionError(e)
  }
 }
@@ -209,6 +246,9 @@ export async function openSelectionAction(
    })
    return { success: true, message: t("messages.selectionOpened") }
  } catch (e) {
+    const t = await getTranslations("elective")
+    const translated = await translateBusinessError(e, t)
+    if (translated) return { success: false, message: translated }
    return handleActionError(e)
  }
 }
@@ -237,6 +277,9 @@ export async function closeSelectionAction(
    })
    return { success: true, message: t("messages.selectionClosed") }
  } catch (e) {
+    const t = await getTranslations("elective")
+    const translated = await translateBusinessError(e, t)
+    if (translated) return { success: false, message: translated }
    return handleActionError(e)
  }
 }
@@ -279,6 +322,9 @@ export async function runLotteryAction(
      data: result,
    }
  } catch (e) {
+    const t = await getTranslations("elective")
+    const translated = await translateBusinessError(e, t)
+    if (translated) return { success: false, message: translated }
    return handleActionError(e)
  }
 }
@@ -310,8 +356,13 @@ export async function selectCourseAction(
      targetType: "course_selection",
      properties: { status: result.status, priority: parsed.data.priority },
    })
-    return { success: true, message: result.message, data: result.status }
+    // 通过 i18n 翻译选课结果状态（result.status 已是 CourseSelectionStatus 类型）
+    const statusKey = COURSE_SELECTION_STATUS_LABEL_KEYS[result.status]
+    return { success: true, message: t(statusKey), data: result.status }
  } catch (e) {
+    const t = await getTranslations("elective")
+    const translated = await translateBusinessError(e, t)
+    if (translated) return { success: false, message: translated }
    return handleActionError(e)
  }
 }
@@ -333,7 +384,7 @@ export async function dropCourseAction(
        errors: parsed.error.flatten().fieldErrors,
      }
    }
-    await dropCourse(parsed.data.courseId, ctx.userId)
+    await dropCourse(parsed.data.courseId, ctx.userId, parsed.data.dropReason)
    revalidateElectivePaths(parsed.data.courseId)
    await trackEvent({
      event: "elective.course_dropped",
@@ -343,6 +394,9 @@ export async function dropCourseAction(
    })
    return { success: true, message: t("messages.courseDropped") }
  } catch (e) {
+    const t = await getTranslations("elective")
+    const translated = await translateBusinessError(e, t)
+    if (translated) return { success: false, message: translated }
    return handleActionError(e)
  }
 }
--- a/src/modules/elective/components/elective-course-detail.tsx
+++ b/src/modules/elective/components/elective-course-detail.tsx
@@ -0,0 +1,198 @@
+import Link from "next/link"
+import { useTranslations } from "next-intl"
+import { ArrowLeft, Pencil, Users } from "lucide-react"
+
+import { Badge } from "@/shared/components/ui/badge"
+import { Button } from "@/shared/components/ui/button"
+import { Card, CardContent, CardHeader, CardTitle } from "@/shared/components/ui/card"
+import { EmptyState } from "@/shared/components/ui/empty-state"
+
+import {
+  COURSE_SELECTION_STATUS_BADGE_VARIANTS,
+  COURSE_SELECTION_STATUS_LABEL_KEYS,
+  ELECTIVE_STATUS_BADGE_VARIANTS,
+  ELECTIVE_STATUS_LABEL_KEYS,
+  SELECTION_MODE_LABEL_KEYS,
+} from "../constants"
+import type {
+  CourseSelectionWithDetails,
+  ElectiveCourseWithDetails,
+} from "../types"
+
+/**
+ * 选修课程详情视图（admin/teacher 共用）。
+ *
+ * 设计原则：
+ * - 通过 props 注入数据，不直接调用 data-access（便于测试与复用）
+ * - 组合优先：分成课程信息卡片 + 选课名单表格两个独立区块
+ * - 编辑按钮通过 editHref 参数化，admin/teacher 路由各自传入
+ */
+export function ElectiveCourseDetail({
+  course,
+  selections,
+  editHref,
+  backHref,
+  showEditButton = true,
+}: {
+  course: ElectiveCourseWithDetails
+  selections: CourseSelectionWithDetails[]
+  editHref?: string
+  backHref: string
+  showEditButton?: boolean
+}) {
+  const t = useTranslations("elective")
+
+  const activeSelections = selections.filter((s) =>
+    ["selected", "enrolled", "waitlist"].includes(s.status)
+  )
+
+  return (
+    <div className="space-y-6">
+      <div className="flex flex-wrap items-center justify-between gap-3">
+        <Button asChild variant="ghost" size="sm">
+          <Link href={backHref}>
+            <ArrowLeft className="mr-1 h-4 w-4" />
+            {t("detail.back")}
+          </Link>
+        </Button>
+        {showEditButton && editHref ? (
+          <Button asChild size="sm">
+            <Link href={editHref}>
+              <Pencil className="mr-1 h-4 w-4" />
+              {t("detail.editCourse")}
+            </Link>
+          </Button>
+        ) : null}
+      </div>
+
+      <Card>
+        <CardHeader className="flex flex-row items-start justify-between gap-2 space-y-0">
+          <div className="space-y-1">
+            <CardTitle className="text-2xl">{course.name}</CardTitle>
+            <p className="text-sm text-muted-foreground">
+              {t("description.detail")}
+            </p>
+          </div>
+          <Badge variant={ELECTIVE_STATUS_BADGE_VARIANTS[course.status]} className="shrink-0">
+            {t(ELECTIVE_STATUS_LABEL_KEYS[course.status])}
+          </Badge>
+        </CardHeader>
+        <CardContent>
+          <div className="grid grid-cols-1 gap-4 md:grid-cols-2 lg:grid-cols-3">
+            <DetailField label={t("fields.subject")} value={course.subjectName} />
+            <DetailField label={t("fields.grade")} value={course.gradeName} />
+            <DetailField label={t("fields.teacher")} value={course.teacherName} />
+            <DetailField
+              label={t("fields.capacity")}
+              value={`${course.enrolledCount} / ${course.capacity}`}
+            />
+            <DetailField label={t("fields.classroom")} value={course.classroom} />
+            <DetailField
+              label={t("fields.selectionMode")}
+              value={t(SELECTION_MODE_LABEL_KEYS[course.selectionMode])}
+            />
+            <DetailField label={t("fields.credit")} value={course.credit} />
+            <DetailField label={t("fields.startDate")} value={course.startDate} />
+            <DetailField label={t("fields.endDate")} value={course.endDate} />
+            <DetailField label={t("fields.selectionStart")} value={course.selectionStartAt} />
+            <DetailField label={t("fields.selectionEnd")} value={course.selectionEndAt} />
+          </div>
+          {course.schedule ? (
+            <div className="mt-4">
+              <p className="text-sm font-medium text-muted-foreground">{t("fields.schedule")}</p>
+              <p className="mt-1 text-sm">{course.schedule}</p>
+            </div>
+          ) : null}
+          {course.description ? (
+            <div className="mt-4">
+              <p className="text-sm font-medium text-muted-foreground">{t("fields.description")}</p>
+              <p className="mt-1 text-sm">{course.description}</p>
+            </div>
+          ) : null}
+        </CardContent>
+      </Card>
+
+      <Card>
+        <CardHeader>
+          <div className="flex items-center justify-between">
+            <CardTitle className="flex items-center gap-2 text-lg">
+              <Users className="h-5 w-5" />
+              {t("detail.studentsTitle")}
+            </CardTitle>
+            <span className="text-sm text-muted-foreground">
+              {activeSelections.length}
+            </span>
+          </div>
+        </CardHeader>
+        <CardContent>
+          {activeSelections.length === 0 ? (
+            <EmptyState
+              title={t("detail.noStudents")}
+              description={t("detail.noStudentsDescription")}
+              icon={Users}
+              className="h-auto border-none shadow-none"
+            />
+          ) : (
+            <div className="overflow-x-auto">
+              <table className="w-full text-sm">
+                <thead>
+                  <tr className="border-b text-left text-muted-foreground">
+                    <th className="pb-2 pr-4 font-medium">#</th>
+                    <th className="pb-2 pr-4 font-medium">{t("detail.studentName")}</th>
+                    <th className="pb-2 pr-4 font-medium">{t("export.statusHeader")}</th>
+                    <th className="pb-2 pr-4 font-medium">{t("detail.priority")}</th>
+                    <th className="pb-2 pr-4 font-medium">{t("detail.selectedAt")}</th>
+                    <th className="pb-2 pr-4 font-medium">{t("detail.enrolledAt")}</th>
+                  </tr>
+                </thead>
+                <tbody>
+                  {activeSelections.map((sel, idx) => (
+                    <tr key={sel.id} className="border-b last:border-0">
+                      <td className="py-2 pr-4 text-muted-foreground">{idx + 1}</td>
+                      <td className="py-2 pr-4 font-medium">
+                        {sel.studentName ?? "—"}
+                      </td>
+                      <td className="py-2 pr-4">
+                        <Badge variant={COURSE_SELECTION_STATUS_BADGE_VARIANTS[sel.status]}>
+                          {t(COURSE_SELECTION_STATUS_LABEL_KEYS[sel.status])}
+                        </Badge>
+                      </td>
+                      <td className="py-2 pr-4 tabular-nums">
+                        {sel.priority ?? "—"}
+                      </td>
+                      <td className="py-2 pr-4 text-muted-foreground">
+                        {sel.selectedAt
+                          ? new Date(sel.selectedAt).toLocaleDateString()
+                          : "—"}
+                      </td>
+                      <td className="py-2 pr-4 text-muted-foreground">
+                        {sel.enrolledAt
+                          ? new Date(sel.enrolledAt).toLocaleDateString()
+                          : "—"}
+                      </td>
+                    </tr>
+                  ))}
+                </tbody>
+              </table>
+            </div>
+          )}
+        </CardContent>
+      </Card>
+    </div>
+  )
+}
+
+function DetailField({
+  label,
+  value,
+}: {
+  label: string
+  value: string | null | undefined
+}) {
+  return (
+    <div>
+      <p className="text-xs font-medium text-muted-foreground">{label}</p>
+      <p className="mt-1 text-sm font-medium">{value ?? "—"}</p>
+    </div>
+  )
+}
--- a/src/modules/elective/components/elective-course-form.tsx
+++ b/src/modules/elective/components/elective-course-form.tsx
@@ -2,6 +2,7 @@

 import { useState } from "react"
 import { useRouter } from "next/navigation"
+import Link from "next/link"
 import { useTranslations } from "next-intl"
 import { toast } from "sonner"

@@ -69,20 +70,21 @@ export function ElectiveCourseForm({
            : null

      if (!res) {
-        toast.error("Invalid form state")
+        toast.error(t("form.invalidFormState"))
        return
      }

      if (res.success) {
        toast.success(res.message)
+        // 根据 backHref 推断返回列表页路径
        const redirectBase = backHref?.includes("/teacher/") ? "/teacher/elective" : "/admin/elective"
        router.push(redirectBase)
        router.refresh()
      } else {
-        toast.error(res.message || "Failed to save course")
+        toast.error(res.message || t("form.saveFailed"))
      }
    } catch {
-      toast.error("Failed to save course")
+      toast.error(t("form.saveFailed"))
    } finally {
      setIsWorking(false)
    }
@@ -92,14 +94,14 @@ export function ElectiveCourseForm({
    <Card>
      <CardHeader>
        <CardTitle>
-          {mode === "create" ? "New Elective Course" : "Edit Elective Course"}
+          {mode === "create" ? t("form.createTitle") : t("form.editTitle")}
        </CardTitle>
      </CardHeader>
      <CardContent>
        <form action={handleSubmit} className="space-y-6">
          <div className="grid grid-cols-1 gap-4 md:grid-cols-2">
            <div className="grid gap-2">
-              <Label htmlFor="name">Course Name *</Label>
+              <Label htmlFor="name">{t("form.nameLabel")}</Label>
              <Input
                id="name"
                name="name"
@@ -109,10 +111,10 @@ export function ElectiveCourseForm({
            </div>

            <div className="grid gap-2">
-              <Label>Subject</Label>
+              <Label>{t("form.subjectLabel")}</Label>
              <Select value={subjectId} onValueChange={setSubjectId}>
                <SelectTrigger>
-                  <SelectValue placeholder="Select a subject" />
+                  <SelectValue placeholder={t("form.selectSubjectPlaceholder")} />
                </SelectTrigger>
                <SelectContent>
                  {subjects.map((s) => (
@@ -126,10 +128,10 @@ export function ElectiveCourseForm({
            </div>

            <div className="grid gap-2">
-              <Label>Grade</Label>
+              <Label>{t("form.gradeLabel")}</Label>
              <Select value={gradeId} onValueChange={setGradeId}>
                <SelectTrigger>
-                  <SelectValue placeholder="Select a grade" />
+                  <SelectValue placeholder={t("form.selectGradePlaceholder")} />
                </SelectTrigger>
                <SelectContent>
                  {grades.map((g) => (
@@ -143,15 +145,15 @@ export function ElectiveCourseForm({
            </div>

            <div className="grid gap-2">
-              <Label>Teacher</Label>
+              <Label>{t("form.teacherLabel")}</Label>
              <Select value={teacherId} onValueChange={setTeacherId}>
                <SelectTrigger>
-                  <SelectValue placeholder="Select a teacher" />
+                  <SelectValue placeholder={t("form.selectTeacherPlaceholder")} />
                </SelectTrigger>
                <SelectContent>
-                  {teachers.map((t) => (
-                    <SelectItem key={t.id} value={t.id}>
-                      {t.name}
+                  {teachers.map((teacher) => (
+                    <SelectItem key={teacher.id} value={teacher.id}>
+                      {teacher.name}
                    </SelectItem>
                  ))}
                </SelectContent>
@@ -160,7 +162,7 @@ export function ElectiveCourseForm({
            </div>

            <div className="grid gap-2">
-              <Label htmlFor="capacity">Capacity</Label>
+              <Label htmlFor="capacity">{t("form.capacityLabel")}</Label>
              <Input
                id="capacity"
                name="capacity"
@@ -172,7 +174,7 @@ export function ElectiveCourseForm({
            </div>

            <div className="grid gap-2">
-              <Label htmlFor="classroom">Classroom</Label>
+              <Label htmlFor="classroom">{t("form.classroomLabel")}</Label>
              <Input
                id="classroom"
                name="classroom"
@@ -181,17 +183,17 @@ export function ElectiveCourseForm({
            </div>

            <div className="grid gap-2">
-              <Label htmlFor="schedule">Schedule</Label>
+              <Label htmlFor="schedule">{t("form.scheduleLabel")}</Label>
              <Input
                id="schedule"
                name="schedule"
-                placeholder="e.g. Mon 14:00-15:30"
+                placeholder={t("form.schedulePlaceholder")}
                defaultValue={course?.schedule ?? ""}
              />
            </div>

            <div className="grid gap-2">
-              <Label htmlFor="credit">Credit</Label>
+              <Label htmlFor="credit">{t("form.creditLabel")}</Label>
              <Input
                id="credit"
                name="credit"
@@ -222,7 +224,7 @@ export function ElectiveCourseForm({
            </div>

            <div className="grid gap-2">
-              <Label htmlFor="startDate">Start Date</Label>
+              <Label htmlFor="startDate">{t("form.startDateLabel")}</Label>
              <Input
                id="startDate"
                name="startDate"
@@ -232,7 +234,7 @@ export function ElectiveCourseForm({
            </div>

            <div className="grid gap-2">
-              <Label htmlFor="endDate">End Date</Label>
+              <Label htmlFor="endDate">{t("form.endDateLabel")}</Label>
              <Input
                id="endDate"
                name="endDate"
@@ -242,7 +244,7 @@ export function ElectiveCourseForm({
            </div>

            <div className="grid gap-2">
-              <Label htmlFor="selectionStartAt">Selection Start</Label>
+              <Label htmlFor="selectionStartAt">{t("form.selectionStartLabel")}</Label>
              <Input
                id="selectionStartAt"
                name="selectionStartAt"
@@ -256,7 +258,7 @@ export function ElectiveCourseForm({
            </div>

            <div className="grid gap-2">
-              <Label htmlFor="selectionEndAt">Selection End</Label>
+              <Label htmlFor="selectionEndAt">{t("form.selectionEndLabel")}</Label>
              <Input
                id="selectionEndAt"
                name="selectionEndAt"
@@ -268,14 +270,32 @@ export function ElectiveCourseForm({
                }
              />
            </div>
+
+            {/* P2-4：退课截止时间 */}
+            <div className="grid gap-2">
+              <Label htmlFor="dropDeadline">{t("form.dropDeadlineLabel")}</Label>
+              <Input
+                id="dropDeadline"
+                name="dropDeadline"
+                type="datetime-local"
+                defaultValue={
+                  course?.dropDeadline
+                    ? new Date(course.dropDeadline).toISOString().slice(0, 16)
+                    : ""
+                }
+              />
+              <p className="text-xs text-muted-foreground">
+                {t("form.dropDeadlineHint")}
+              </p>
+            </div>
          </div>

          <div className="grid gap-2">
-            <Label htmlFor="description">Description</Label>
+            <Label htmlFor="description">{t("form.descriptionLabel")}</Label>
            <Textarea
              id="description"
              name="description"
-              placeholder="Course description..."
+              placeholder={t("form.descriptionPlaceholder")}
              className="min-h-[80px]"
              defaultValue={course?.description ?? ""}
            />
@@ -285,13 +305,12 @@ export function ElectiveCourseForm({
            <Button
              type="button"
              variant="outline"
-              onClick={() => router.push(backHref ?? "/admin/elective")}
-              disabled={isWorking}
+              asChild
            >
-              Cancel
+              <Link href={backHref ?? "/admin/elective"}>{t("form.cancelButton")}</Link>
            </Button>
            <Button type="submit" disabled={isWorking}>
-              {isWorking ? "Saving..." : mode === "create" ? "Create" : "Save"}
+              {isWorking ? t("form.savingButton") : mode === "create" ? t("form.createButton") : t("form.saveButton")}
            </Button>
          </CardFooter>
        </form>
--- a/src/modules/elective/components/elective-course-list.tsx
+++ b/src/modules/elective/components/elective-course-list.tsx
@@ -2,6 +2,7 @@

 import { useState, useTransition } from "react"
 import { useRouter } from "next/navigation"
+import Link from "next/link"
 import { useTranslations } from "next-intl"
 import { toast } from "sonner"
 import { Plus, Pencil, Lock, Unlock, Shuffle, Trash2 } from "lucide-react"
@@ -89,10 +90,10 @@ export function ElectiveCourseList({
        </p>
        {manageResolved && createHref ? (
          <Button asChild>
-            <a href={createHref}>
+            <Link href={createHref}>
              <Plus className="mr-2 h-4 w-4" />
              {t("actions.create")}
-            </a>
+            </Link>
          </Button>
        ) : null}
      </div>
@@ -174,10 +175,10 @@ export function ElectiveCourseList({
                          variant="outline"
                          size="sm"
                        >
-                          <a href={`${editBaseHref}/${course.id}/edit`}>
+                          <Link href={`${editBaseHref}/${course.id}/edit`}>
                            <Pencil className="mr-1 h-3 w-3" />
                            {t("actions.edit")}
-                          </a>
+                          </Link>
                        </Button>
                      ) : null}
                      {course.status === "draft" || course.status === "closed" ? (
--- a/src/modules/elective/components/elective-stats-cards.tsx
+++ b/src/modules/elective/components/elective-stats-cards.tsx
@@ -0,0 +1,71 @@
+import { BookOpen, Users, Gauge, Shuffle } from "lucide-react"
+import { useTranslations } from "next-intl"
+
+import { Card, CardContent, CardHeader, CardTitle } from "@/shared/components/ui/card"
+import { cn } from "@/shared/lib/utils"
+import type { ElectiveOverviewStats } from "../data-access-stats"
+
+/**
+ * 选课模块管理员概览统计卡片网格。
+ *
+ * 复用模式：与 attendance-stats-cards 一致的 4 卡片网格。
+ * 设计原则：
+ * - 通过 props 注入数据，不直接调用 data-access（便于测试与复用）
+ * - 使用 i18n key 解析标题，value 由父组件传入已格式化的数据
+ */
+export function ElectiveStatsCards({ stats }: { stats: ElectiveOverviewStats }) {
+  const t = useTranslations("elective")
+
+  const cards = [
+    {
+      title: t("stats.totalCourses"),
+      value: stats.totalCourses,
+      icon: BookOpen,
+      color: "text-blue-500",
+      bgColor: "bg-blue-500/10",
+    },
+    {
+      title: t("stats.totalEnrolled"),
+      value: stats.totalEnrolled,
+      icon: Users,
+      color: "text-green-500",
+      bgColor: "bg-green-500/10",
+    },
+    {
+      title: t("stats.avgUtilization"),
+      value: t("stats.utilizationRate", { rate: stats.avgUtilization }),
+      icon: Gauge,
+      color: "text-purple-500",
+      bgColor: "bg-purple-500/10",
+    },
+    {
+      title: t("stats.pendingLottery"),
+      value: stats.pendingLottery,
+      icon: Shuffle,
+      color: "text-orange-500",
+      bgColor: "bg-orange-500/10",
+    },
+  ]
+
+  return (
+    <div
+      className="grid gap-4 md:grid-cols-2 lg:grid-cols-4"
+      role="region"
+      aria-label={t("stats.totalCourses")}
+    >
+      {cards.map((card) => (
+        <Card key={card.title} className="shadow-none">
+          <CardHeader className="flex flex-row items-center justify-between space-y-0 pb-2">
+            <CardTitle className="text-sm font-medium">{card.title}</CardTitle>
+            <div className={cn("flex h-8 w-8 items-center justify-center rounded-md", card.bgColor)}>
+              <card.icon className={cn("h-4 w-4", card.color)} />
+            </div>
+          </CardHeader>
+          <CardContent>
+            <div className="text-2xl font-bold tabular-nums">{card.value}</div>
+          </CardContent>
+        </Card>
+      ))}
+    </div>
+  )
+}
--- a/src/modules/elective/components/parent-selection-view.tsx
+++ b/src/modules/elective/components/parent-selection-view.tsx
@@ -0,0 +1,85 @@
+import { useTranslations } from "next-intl"
+import { BookOpen } from "lucide-react"
+
+import { Badge } from "@/shared/components/ui/badge"
+import { Card, CardContent, CardHeader, CardTitle } from "@/shared/components/ui/card"
+import { EmptyState } from "@/shared/components/ui/empty-state"
+
+import {
+  COURSE_SELECTION_STATUS_BADGE_VARIANTS,
+  COURSE_SELECTION_STATUS_LABEL_KEYS,
+} from "../constants"
+import type { CourseSelectionWithDetails } from "../types"
+
+/**
+ * 家长视角下查看子女选课的只读视图。
+ *
+ * 设计原则：
+ * - 只读：家长不能替子女选/退课，仅展示已选记录
+ * - 复用：复用 Badge variant 映射 + i18n key，与 StudentSelectionView 一致
+ * - 安全：组件本身不依赖 studentId，由父页面注入已过滤的数据
+ */
+export function ParentSelectionView({
+  selections,
+  studentName,
+}: {
+  selections: CourseSelectionWithDetails[]
+  studentName: string
+}) {
+  const t = useTranslations("elective")
+
+  const activeSelections = selections.filter((s) =>
+    ["selected", "enrolled", "waitlist"].includes(s.status)
+  )
+
+  return (
+    <div className="space-y-4">
+      <div className="flex items-center justify-between">
+        <h3 className="text-lg font-semibold border-b pb-2">{studentName}</h3>
+        <span className="text-sm text-muted-foreground">
+          {activeSelections.length}
+        </span>
+      </div>
+      {activeSelections.length === 0 ? (
+        <EmptyState
+          title={t("parent.noRecordsTitle")}
+          description={t("parent.noRecordsDescription")}
+          icon={BookOpen}
+          className="h-auto border-none shadow-none"
+        />
+      ) : (
+        <div className="grid grid-cols-1 gap-4 md:grid-cols-2 lg:grid-cols-3">
+          {activeSelections.map((sel) => (
+            <Card key={sel.id}>
+              <CardHeader className="flex flex-row items-start justify-between gap-2 space-y-0">
+                <CardTitle className="text-base">
+                  {sel.courseName ?? t("errors.notFound")}
+                </CardTitle>
+                <Badge variant={COURSE_SELECTION_STATUS_BADGE_VARIANTS[sel.status]}>
+                  {t(COURSE_SELECTION_STATUS_LABEL_KEYS[sel.status])}
+                </Badge>
+              </CardHeader>
+              <CardContent className="space-y-2">
+                {sel.courseCapacity !== null && sel.courseEnrolledCount !== null ? (
+                  <p className="text-xs text-muted-foreground">
+                    {t("fields.enrolled")}: {sel.courseEnrolledCount}/{sel.courseCapacity}
+                  </p>
+                ) : null}
+                {sel.lotteryRank ? (
+                  <p className="text-xs text-muted-foreground">
+                    #{sel.lotteryRank}
+                  </p>
+                ) : null}
+                {sel.selectedAt ? (
+                  <p className="text-xs text-muted-foreground">
+                    {t("export.selectedAtHeader")}: {new Date(sel.selectedAt).toLocaleDateString()}
+                  </p>
+                ) : null}
+              </CardContent>
+            </Card>
+          ))}
+        </div>
+      )}
+    </div>
+  )
+}
--- a/src/modules/elective/components/student-selection-view.tsx
+++ b/src/modules/elective/components/student-selection-view.tsx
@@ -21,6 +21,8 @@ import { Badge } from "@/shared/components/ui/badge"
 import { Button } from "@/shared/components/ui/button"
 import { Card, CardContent, CardHeader, CardTitle } from "@/shared/components/ui/card"
 import { EmptyState } from "@/shared/components/ui/empty-state"
+import { Label } from "@/shared/components/ui/label"
+import { Textarea } from "@/shared/components/ui/textarea"

 import {
  COURSE_SELECTION_STATUS_BADGE_VARIANTS,
@@ -35,24 +37,171 @@ import type {
 } from "../types"
 import { selectCourseAction, dropCourseAction } from "../actions"

-export function StudentSelectionView({
-  availableCourses,
+/**
+ * 已选课程区块（我的选课）
+ * - 独立 Suspense 边界内的客户端组件
+ * - 仅负责"退课"操作与展示
+ */
+export function StudentMySelectionsSection({
  mySelections,
 }: {
-  availableCourses: ElectiveCourseWithDetails[]
  mySelections: CourseSelectionWithDetails[]
 }) {
  const router = useRouter()
  const t = useTranslations("elective")
  const [pendingId, setPendingId] = useState<string | null>(null)
  const [isPending, startTransition] = useTransition()
+  // P2-4：退课理由输入（按课程 ID 隔离，便于多卡片独立填写）
+  const [dropReasonMap, setDropReasonMap] = useState<Record<string, string>>({})

  const activeSelections = mySelections.filter((s) =>
    ["selected", "enrolled", "waitlist"].includes(s.status)
  )
-  const selectedCourseIds = new Set(
-    activeSelections.map((s) => s.courseId)
+
+  const handleDrop = (courseId: string) => {
+    setPendingId(courseId)
+    startTransition(async () => {
+      const formData = new FormData()
+      formData.set("courseId", courseId)
+      // P2-4：透传退课理由
+      const reason = dropReasonMap[courseId]
+      if (reason && reason.trim().length > 0) {
+        formData.set("dropReason", reason.trim())
+      }
+      const res = await dropCourseAction(null, formData)
+      if (res.success) {
+        toast.success(res.message || t("student.dropSuccess"))
+        router.refresh()
+        // 清空该课程的退课理由
+        setDropReasonMap((prev) => {
+          const next = { ...prev }
+          delete next[courseId]
+          return next
+        })
+      } else {
+        toast.error(res.message ?? t("errors.unexpected"))
+      }
+      setPendingId(null)
+    })
+  }
+
+  return (
+    <section className="space-y-4" aria-labelledby="student-my-selections-heading">
+      <div className="flex items-center justify-between">
+        <h3
+          id="student-my-selections-heading"
+          className="text-lg font-semibold"
+        >
+          {t("student.mySelections")}
+        </h3>
+        <span className="text-sm text-muted-foreground" aria-live="polite">
+          {activeSelections.length}
+        </span>
+      </div>
+      {activeSelections.length === 0 ? (
+        <EmptyState
+          title={t("list.empty")}
+          description={t("description.student")}
+          icon={BookOpen}
+          className="h-auto border-none shadow-none"
+        />
+      ) : (
+        <div className="grid grid-cols-1 gap-4 md:grid-cols-2 lg:grid-cols-3">
+          {activeSelections.map((sel) => (
+            <Card key={sel.id}>
+              <CardHeader className="flex flex-row items-start justify-between gap-2 space-y-0">
+                <CardTitle className="text-base">
+                  {sel.courseName ?? t("errors.notFound")}
+                </CardTitle>
+                <Badge variant={COURSE_SELECTION_STATUS_BADGE_VARIANTS[sel.status]}>
+                  {t(COURSE_SELECTION_STATUS_LABEL_KEYS[sel.status])}
+                </Badge>
+              </CardHeader>
+              <CardContent className="space-y-3">
+                {sel.courseCapacity !== null && sel.courseEnrolledCount !== null ? (
+                  <p className="text-xs text-muted-foreground">
+                    {t("fields.enrolled")}: {sel.courseEnrolledCount}/{sel.courseCapacity}
+                  </p>
+                ) : null}
+                {sel.lotteryRank ? (
+                  <p className="text-xs text-muted-foreground">
+                    #{sel.lotteryRank}
+                  </p>
+                ) : null}
+                <AlertDialog>
+                  <AlertDialogTrigger asChild>
+                    <Button
+                      variant="outline"
+                      size="sm"
+                      className="text-destructive hover:text-destructive"
+                      disabled={isPending && pendingId === sel.courseId}
+                    >
+                      <XCircle className="mr-1 h-3 w-3" />
+                      {t("actions.drop")}
+                    </Button>
+                  </AlertDialogTrigger>
+                  <AlertDialogContent>
+                    <AlertDialogHeader>
+                      <AlertDialogTitle>{t("student.confirmDrop")}</AlertDialogTitle>
+                      <AlertDialogDescription>
+                        {t("student.confirmDrop")}
+                      </AlertDialogDescription>
+                    </AlertDialogHeader>
+                    {/* P2-4：可选退课理由输入 */}
+                    <div className="grid gap-2 py-2">
+                      <Label htmlFor={`dropReason-${sel.courseId}`}>
+                        {t("fields.dropReason")}
+                      </Label>
+                      <Textarea
+                        id={`dropReason-${sel.courseId}`}
+                        value={dropReasonMap[sel.courseId] ?? ""}
+                        onChange={(e) =>
+                          setDropReasonMap((prev) => ({
+                            ...prev,
+                            [sel.courseId]: e.target.value,
+                          }))
+                        }
+                        placeholder={t("student.dropReasonPlaceholder")}
+                        className="min-h-[60px]"
+                        maxLength={255}
+                      />
+                    </div>
+                    <AlertDialogFooter>
+                      <AlertDialogCancel>{t("actions.cancel")}</AlertDialogCancel>
+                      <AlertDialogAction
+                        onClick={() => handleDrop(sel.courseId)}
+                      >
+                        {t("actions.drop")}
+                      </AlertDialogAction>
+                    </AlertDialogFooter>
+                  </AlertDialogContent>
+                </AlertDialog>
+              </CardContent>
+            </Card>
+          ))}
+        </div>
+      )}
+    </section>
  )
+}
+
+/**
+ * 可选课程区块
+ * - 独立 Suspense 边界内的客户端组件
+ * - 仅负责"选课"操作与展示
+ * - 通过 selectedCourseIds prop 接收已选课程 ID 集合，避免与已选区块直接耦合
+ */
+export function StudentAvailableCoursesSection({
+  availableCourses,
+  selectedCourseIds,
+}: {
+  availableCourses: ElectiveCourseWithDetails[]
+  selectedCourseIds: Set<string>
+}) {
+  const router = useRouter()
+  const t = useTranslations("elective")
+  const [pendingId, setPendingId] = useState<string | null>(null)
+  const [isPending, startTransition] = useTransition()

  const handleSelect = (courseId: string) => {
    setPendingId(courseId)
@@ -70,179 +219,93 @@ export function StudentSelectionView({
    })
  }

-  const handleDrop = (courseId: string) => {
-    setPendingId(courseId)
-    startTransition(async () => {
-      const formData = new FormData()
-      formData.set("courseId", courseId)
-      const res = await dropCourseAction(null, formData)
-      if (res.success) {
-        toast.success(res.message || t("student.dropSuccess"))
-        router.refresh()
-      } else {
-        toast.error(res.message ?? t("errors.unexpected"))
-      }
-      setPendingId(null)
-    })
-  }
-
  return (
-    <div className="space-y-8">
-      <section className="space-y-4">
-        <div className="flex items-center justify-between">
-          <h3 className="text-lg font-semibold">{t("student.mySelections")}</h3>
-          <span className="text-sm text-muted-foreground">
-            {activeSelections.length}
-          </span>
-        </div>
-        {activeSelections.length === 0 ? (
-          <EmptyState
-            title={t("list.empty")}
-            description={t("description.student")}
-            icon={BookOpen}
-            className="h-auto border-none shadow-none"
-          />
-        ) : (
-          <div className="grid grid-cols-1 gap-4 md:grid-cols-2 lg:grid-cols-3">
-            {activeSelections.map((sel) => (
-              <Card key={sel.id}>
+    <section className="space-y-4" aria-labelledby="student-available-courses-heading">
+      <div className="flex items-center justify-between">
+        <h3
+          id="student-available-courses-heading"
+          className="text-lg font-semibold"
+        >
+          {t("student.availableCourses")}
+        </h3>
+        <span className="text-sm text-muted-foreground" aria-live="polite">
+          {availableCourses.length}
+        </span>
+      </div>
+      {availableCourses.length === 0 ? (
+        <EmptyState
+          title={t("list.emptyStudent")}
+          description={t("description.student")}
+          icon={BookOpen}
+          className="h-auto border-none shadow-none"
+        />
+      ) : (
+        <div className="grid grid-cols-1 gap-4 md:grid-cols-2 lg:grid-cols-3">
+          {availableCourses.map((course) => {
+            const isFull = course.enrolledCount >= course.capacity
+            const alreadySelected = selectedCourseIds.has(course.id)
+            const isPendingThis = isPending && pendingId === course.id
+            return (
+              <Card key={course.id} className="flex h-full flex-col" role="article" aria-label={course.name}>
                <CardHeader className="flex flex-row items-start justify-between gap-2 space-y-0">
-                  <CardTitle className="text-base">
-                    {sel.courseName ?? t("errors.notFound")}
-                  </CardTitle>
-                  <Badge variant={COURSE_SELECTION_STATUS_BADGE_VARIANTS[sel.status]}>
-                    {t(COURSE_SELECTION_STATUS_LABEL_KEYS[sel.status])}
+                  <CardTitle className="line-clamp-2 text-base">{course.name}</CardTitle>
+                  <Badge variant={ELECTIVE_STATUS_BADGE_VARIANTS[course.status]}>
+                    {t(ELECTIVE_STATUS_LABEL_KEYS[course.status])}
                  </Badge>
                </CardHeader>
-                <CardContent className="space-y-3">
-                  {sel.courseCapacity !== null && sel.courseEnrolledCount !== null ? (
-                    <p className="text-xs text-muted-foreground">
-                      {t("fields.enrolled")}: {sel.courseEnrolledCount}/{sel.courseCapacity}
+                <CardContent className="flex flex-1 flex-col gap-3">
+                  <div className="flex flex-wrap items-center gap-2 text-xs text-muted-foreground">
+                    {course.subjectName ? (
+                      <Badge variant="outline">{course.subjectName}</Badge>
+                    ) : null}
+                    <span>{t("fields.credit")}: {course.credit}</span>
+                    <span>· {t(SELECTION_MODE_LABEL_KEYS[course.selectionMode])}</span>
+                  </div>
+                  {course.description ? (
+                    <p className="line-clamp-2 text-sm text-muted-foreground">
+                      {course.description}
                    </p>
                  ) : null}
-                  {sel.lotteryRank ? (
+                  <div className="grid grid-cols-2 gap-2 text-xs">
+                    <div>
+                      <span className="text-muted-foreground">{t("fields.teacher")}:</span>{" "}
+                      <span className="font-medium">{course.teacherName ?? "—"}</span>
+                    </div>
+                    <div>
+                      <span className="text-muted-foreground">{t("fields.capacity")}:</span>{" "}
+                      <span className="font-medium">
+                        {course.enrolledCount}/{course.capacity}
+                        {isFull ? ` (${t("student.capacityFull")})` : ""}
+                      </span>
+                    </div>
+                  </div>
+                  {course.schedule ? (
                    <p className="text-xs text-muted-foreground">
-                      #{sel.lotteryRank}
+                      <span className="font-medium">{t("fields.schedule")}:</span> {course.schedule}
                    </p>
                  ) : null}
-                  <AlertDialog>
-                    <AlertDialogTrigger asChild>
-                      <Button
-                        variant="outline"
-                        size="sm"
-                        className="text-destructive hover:text-destructive"
-                        disabled={isPending && pendingId === sel.courseId}
-                      >
-                        <XCircle className="mr-1 h-3 w-3" />
-                        {t("actions.drop")}
+                  <div className="mt-auto pt-2">
+                    {alreadySelected ? (
+                      <Button variant="secondary" size="sm" disabled>
+                        <CheckCircle2 className="mr-1 h-3 w-3" />
+                        {t("student.selected")}
                      </Button>
-                    </AlertDialogTrigger>
-                    <AlertDialogContent>
-                      <AlertDialogHeader>
-                        <AlertDialogTitle>{t("student.confirmDrop")}</AlertDialogTitle>
-                        <AlertDialogDescription>
-                          {t("student.confirmDrop")}
-                        </AlertDialogDescription>
-                      </AlertDialogHeader>
-                      <AlertDialogFooter>
-                        <AlertDialogCancel>{t("actions.cancel")}</AlertDialogCancel>
-                        <AlertDialogAction
-                          onClick={() => handleDrop(sel.courseId)}
-                        >
-                          {t("actions.drop")}
-                        </AlertDialogAction>
-                      </AlertDialogFooter>
-                    </AlertDialogContent>
-                  </AlertDialog>
+                    ) : (
+                      <Button
+                        size="sm"
+                        disabled={isPendingThis}
+                        onClick={() => handleSelect(course.id)}
+                      >
+                        {isPendingThis ? t("actions.select") + "..." : t("actions.select")}
+                      </Button>
+                    )}
+                  </div>
                </CardContent>
              </Card>
-            ))}
-          </div>
-        )}
-      </section>
-
-      <section className="space-y-4">
-        <div className="flex items-center justify-between">
-          <h3 className="text-lg font-semibold">{t("student.availableCourses")}</h3>
-          <span className="text-sm text-muted-foreground">
-            {availableCourses.length}
-          </span>
+            )
+          })}
        </div>
-        {availableCourses.length === 0 ? (
-          <EmptyState
-            title={t("list.emptyStudent")}
-            description={t("description.student")}
-            icon={BookOpen}
-            className="h-auto border-none shadow-none"
-          />
-        ) : (
-          <div className="grid grid-cols-1 gap-4 md:grid-cols-2 lg:grid-cols-3">
-            {availableCourses.map((course) => {
-              const isFull = course.enrolledCount >= course.capacity
-              const alreadySelected = selectedCourseIds.has(course.id)
-              const isPendingThis = isPending && pendingId === course.id
-              return (
-                <Card key={course.id} className="flex h-full flex-col" role="article" aria-label={course.name}>
-                  <CardHeader className="flex flex-row items-start justify-between gap-2 space-y-0">
-                    <CardTitle className="line-clamp-2 text-base">{course.name}</CardTitle>
-                    <Badge variant={ELECTIVE_STATUS_BADGE_VARIANTS[course.status]}>
-                      {t(ELECTIVE_STATUS_LABEL_KEYS[course.status])}
-                    </Badge>
-                  </CardHeader>
-                  <CardContent className="flex flex-1 flex-col gap-3">
-                    <div className="flex flex-wrap items-center gap-2 text-xs text-muted-foreground">
-                      {course.subjectName ? (
-                        <Badge variant="outline">{course.subjectName}</Badge>
-                      ) : null}
-                      <span>{t("fields.credit")}: {course.credit}</span>
-                      <span>· {t(SELECTION_MODE_LABEL_KEYS[course.selectionMode])}</span>
-                    </div>
-                    {course.description ? (
-                      <p className="line-clamp-2 text-sm text-muted-foreground">
-                        {course.description}
-                      </p>
-                    ) : null}
-                    <div className="grid grid-cols-2 gap-2 text-xs">
-                      <div>
-                        <span className="text-muted-foreground">{t("fields.teacher")}:</span>{" "}
-                        <span className="font-medium">{course.teacherName ?? "—"}</span>
-                      </div>
-                      <div>
-                        <span className="text-muted-foreground">{t("fields.capacity")}:</span>{" "}
-                        <span className="font-medium">
-                          {course.enrolledCount}/{course.capacity}
-                          {isFull ? ` (${t("student.capacityFull")})` : ""}
-                        </span>
-                      </div>
-                    </div>
-                    {course.schedule ? (
-                      <p className="text-xs text-muted-foreground">
-                        <span className="font-medium">{t("fields.schedule")}:</span> {course.schedule}
-                      </p>
-                    ) : null}
-                    <div className="mt-auto pt-2">
-                      {alreadySelected ? (
-                        <Button variant="secondary" size="sm" disabled>
-                          <CheckCircle2 className="mr-1 h-3 w-3" />
-                          {t("student.selected")}
-                        </Button>
-                      ) : (
-                        <Button
-                          size="sm"
-                          disabled={isPendingThis}
-                          onClick={() => handleSelect(course.id)}
-                        >
-                          {isPendingThis ? t("actions.select") + "..." : t("actions.select")}
-                        </Button>
-                      )}
-                    </div>
-                  </CardContent>
-                </Card>
-              )
-            })}
-          </div>
-        )}
-      </section>
-    </div>
+      )}
+    </section>
  )
 }
--- a/src/modules/elective/data-access-operations.ts
+++ b/src/modules/elective/data-access-operations.ts
@@ -2,17 +2,48 @@ import "server-only"

 import { createId } from "@paralleldrive/cuid2"
 import { and, asc, eq, inArray, sql, type SQL } from "drizzle-orm"
+import { getTranslations } from "next-intl/server"

 import { db } from "@/shared/db"
 import {
  courseSelections,
  electiveCourses,
 } from "@/shared/db/schema"
+import { BusinessError } from "@/shared/lib/action-utils"
+import { sendNotification } from "@/modules/notifications"

+import { getElectiveCreditLimit, getCapacityNotifyThreshold } from "./data-access-settings"
+import { getStudentGradeId } from "./data-access-selections"
 import type { CourseSelectionStatus } from "./types"

-/** 学分上限（K12 选修课学期学分上限，可按需调整） */
-const MAX_CREDIT_PER_TERM = 10
+/**
+ * 选课模块业务错误码（与 i18n key `errors.*` 对应）。
+ * 由 actions 层根据 code 通过 getTranslations 翻译为用户可见文案。
+ */
+export type ElectiveErrorCode =
+  | "courseNotFound"
+  | "selectionNotOpen"
+  | "selectionNotStarted"
+  | "selectionEnded"
+  | "alreadySelected"
+  | "scheduleConflict"
+  | "creditExceeded"
+  | "noActiveSelection"
+  | "dropDeadlinePassed"
+
+/**
+ * 选课模块业务错误（带 i18n code 与参数）。
+ * actions 层捕获后用 getTranslations(`elective.errors.${code}`) 翻译。
+ */
+export class ElectiveBusinessError extends BusinessError {
+  constructor(
+    public readonly code: ElectiveErrorCode,
+    public readonly params?: Record<string, string | number>
+  ) {
+    super(`elective.errors.${code}`, code)
+    this.name = "ElectiveBusinessError"
+  }
+}

 /**
 * 构建 lotteryRank 的 CASE SQL 表达式（纯函数，便于测试 SQL 片段结构）。
@@ -25,35 +56,76 @@ export function buildLotteryRankCase(ids: string[], startRank: number): SQL {
 }

 /**
- * 解析课程 schedule 字段为可比较的时间段（纯函数，便于测试）。
- * schedule 格式约定："周一 14:00-15:30" 或 "Mon 14:00-15:30"。
- * 返回 null 表示无法解析（不参与冲突检测）。
+ * 星期字符串归一化映射（纯函数，便于测试）。
+ * 支持中英文全称与缩写，统一映射为 1-7 数字字符串。
 */
-export function parseSchedule(schedule: string | null): { day: string; start: string; end: string } | null {
-  if (!schedule || schedule.length === 0) return null
-  // 匹配 "周X HH:MM-HH:MM" 或 "Day HH:MM-HH:MM"
-  const match = schedule.match(/^(周[一二三四五六日天]|[MonTueWedThuFriSatSun]+)\s+(\d{1,2}:\d{2})\s*[-~]\s*(\d{1,2}:\d{2})/i)
-  if (!match) return null
-  const [, day, start, end] = match
-  return { day: day ?? "", start: start ?? "", end: end ?? "" }
+const DAY_NORMALIZE_MAP: Readonly<Record<string, string>> = Object.freeze({
+  // 中文
+  "周一": "1", "周二": "2", "周三": "3", "周四": "4",
+  "周五": "5", "周六": "6", "周日": "7", "周天": "7",
+  "星期一": "1", "星期二": "2", "星期三": "3", "星期四": "4",
+  "星期五": "5", "星期六": "6", "星期日": "7", "星期天": "7",
+  // 英文全称
+  monday: "1", tuesday: "2", wednesday: "3", thursday: "4",
+  friday: "5", saturday: "6", sunday: "7",
+  // 英文缩写
+  mon: "1", tue: "2", wed: "3", thu: "4",
+  fri: "5", sat: "6", sun: "7",
+})
+
+export function normalizeDay(day: string): string {
+  return DAY_NORMALIZE_MAP[day.toLowerCase()] ?? day
 }

 /**
- * 检测两个时间段是否冲突（纯函数，便于测试）。
- * 仅当 day 相同且时间区间重叠时判定为冲突。
+ * 解析课程 schedule 字段为可比较的时间段数组（纯函数，便于测试）。
+ *
+ * 支持多时段（以逗号或分号分隔），例如：
+ * - "周一 14:00-15:30"
+ * - "Mon 14:00-15:30, Wed 16:00-17:30"
+ * - "周一 14:00-15:30；周三 16:00-17:30"
+ *
+ * 返回空数组表示无法解析（不参与冲突检测）。
+ */
+export function parseSchedule(
+  schedule: string | null
+): Array<{ day: string; start: string; end: string }> {
+  if (!schedule || schedule.length === 0) return []
+
+  // 按逗号、分号、中文分号拆分多个时段
+  const segments = schedule.split(/[,，;；]/).map((s) => s.trim()).filter(Boolean)
+  const result: Array<{ day: string; start: string; end: string }> = []
+
+  // 支持中英文星期与英文全称/缩写
+  const dayPattern = "周[一二三四五六日天]|星期[一二三四五六日天]|[Mm]on(?:day)?|[Tt]ue(?:sday)?|[Ww]ed(?:nesday)?|[Tt]hu(?:rsday)?|[Ff]ri(?:day)?|[Ss]at(?:urday)?|[Ss]un(?:day)?"
+  const timePattern = "(\\d{1,2}):(\\d{2})"
+  const re = new RegExp(
+    `^(${dayPattern})\\s+${timePattern}\\s*[-~～至到]\\s*${timePattern}$`,
+    "i"
+  )
+
+  for (const seg of segments) {
+    const match = seg.match(re)
+    if (!match) continue
+    const [, day, startH, startM, endH, endM] = match
+    if (!day || !startH || !startM || !endH || !endM) continue
+    result.push({
+      day,
+      start: `${startH.padStart(2, "0")}:${startM}`,
+      end: `${endH.padStart(2, "0")}:${endM}`,
+    })
+  }
+  return result
+}
+
+/**
+ * 检测两组时间段是否存在冲突（纯函数，便于测试）。
+ * 仅当 day 相同（归一化后）且时间区间重叠时判定为冲突。
 */
 export function isScheduleConflict(
  a: { day: string; start: string; end: string },
  b: { day: string; start: string; end: string }
 ): boolean {
-  // 归一化星期表示（周一/Mon → 1，周二/Tue → 2 ...）
-  const normalizeDay = (d: string): string => {
-    const dayMap: Record<string, string> = {
-      "周一": "1", "周二": "2", "周三": "3", "周四": "4", "周五": "5", "周六": "6", "周日": "7", "周天": "7",
-      "mon": "1", "tue": "2", "wed": "3", "thu": "4", "fri": "5", "sat": "6", "sun": "7",
-    }
-    return dayMap[d.toLowerCase()] ?? d
-  }
  if (normalizeDay(a.day) !== normalizeDay(b.day)) return false
  return a.start < b.end && b.start < a.end
 }
@@ -72,8 +144,8 @@ async function checkScheduleConflict(
    .from(electiveCourses)
    .where(eq(electiveCourses.id, newCourseId))
    .limit(1)
-  const newSchedule = parseSchedule(newCourse?.schedule ?? null)
-  if (!newSchedule) return false
+  const newSlots = parseSchedule(newCourse?.schedule ?? null)
+  if (newSlots.length === 0) return false

  const existingCourses = await tx
    .select({
@@ -89,22 +161,32 @@ async function checkScheduleConflict(
    )

  for (const row of existingCourses) {
-    const existing = parseSchedule(row.schedule)
-    if (existing && isScheduleConflict(newSchedule, existing)) {
-      return true
+    const existingSlots = parseSchedule(row.schedule)
+    for (const newSlot of newSlots) {
+      for (const existingSlot of existingSlots) {
+        if (isScheduleConflict(newSlot, existingSlot)) {
+          return true
+        }
+      }
    }
  }
  return false
 }

 /**
- * 检测学生学分是否超限（P2 建议：学分上限校验）。
+ * 检测学生学分是否超限（P2-4 重构：使用 system_settings 配置化上限）。
 * 查询学生已选课程的学分总和，加上新课程学分后是否超过上限。
+ *
+ * 上限来源（按优先级）：
+ * 1. `creditLimit:grade:<studentGradeId>`（按年级配置）
+ * 2. `creditLimit:default`（全局配置）
+ * 3. 默认值 10
 */
 async function checkCreditLimit(
  tx: Parameters<Parameters<typeof db.transaction>[0]>[0],
  studentId: string,
-  newCourseId: string
+  newCourseId: string,
+  studentGradeId: string | null
 ): Promise<{ exceeded: boolean; current: number; max: number }> {
  const [newCourse] = await tx
    .select({ credit: electiveCourses.credit })
@@ -128,10 +210,12 @@ async function checkCreditLimit(

  const currentCredit = existing.reduce((sum, row) => sum + Number(row.credit ?? 0), 0)
  const total = currentCredit + newCredit
+  // 配置化上限：按年级或全局，默认 10
+  const max = await getElectiveCreditLimit(studentGradeId)
  return {
-    exceeded: total > MAX_CREDIT_PER_TERM,
+    exceeded: total > max,
    current: total,
-    max: MAX_CREDIT_PER_TERM,
+    max,
  }
 }

@@ -157,7 +241,7 @@ export async function runLottery(courseId: string): Promise<{
      .orderBy(asc(courseSelections.priority), asc(courseSelections.selectedAt)),
  ])
  const course = courseRows[0]
-  if (!course) throw new Error("Course not found")
+  if (!course) throw new ElectiveBusinessError("courseNotFound")

  if (selections.length === 0) {
    return { enrolled: 0, waitlist: 0 }
@@ -185,6 +269,8 @@ export async function runLottery(courseId: string): Promise<{
  const enrolledCount = enrolledIds.length
  const waitlistCount = waitlistIds.length

+  // P1-12 改进：抽签后不强制 close 课程，保留 status="open" 以便管理员重抽。
+  // 管理员可手动通过 closeSelection 关闭选课。
  await db.transaction(async (tx) => {
    if (enrolledIds.length > 0) {
      await tx
@@ -207,9 +293,10 @@ export async function runLottery(courseId: string): Promise<{
        })
        .where(inArray(courseSelections.id, waitlistIds))
    }
+    // 仅更新 enrolledCount，不自动关闭课程
    await tx
      .update(electiveCourses)
-      .set({ enrolledCount, status: "closed", updatedAt: now })
+      .set({ enrolledCount, updatedAt: now })
      .where(eq(electiveCourses.id, courseId))
  })

@@ -220,7 +307,10 @@ export async function selectCourse(
  courseId: string,
  studentId: string,
  priority?: number
-): Promise<{ status: CourseSelectionStatus; message: string }> {
+): Promise<{ status: CourseSelectionStatus }> {
+  // P2-4：先查询学生年级 ID（用于按年级配置的学分上限）
+  const studentGradeId = await getStudentGradeId(studentId)
+
  return db.transaction(async (tx) => {
    // 锁定课程行，防止 FCFS 模式下并发超卖
    const [course] = await tx
@@ -229,15 +319,15 @@ export async function selectCourse(
      .where(eq(electiveCourses.id, courseId))
      .for("update")
      .limit(1)
-    if (!course) throw new Error("Course not found")
-    if (course.status !== "open") throw new Error("Course selection is not open")
+    if (!course) throw new ElectiveBusinessError("courseNotFound")
+    if (course.status !== "open") throw new ElectiveBusinessError("selectionNotOpen")

    const now = new Date()
    if (course.selectionStartAt && now < course.selectionStartAt) {
-      throw new Error("Selection has not started yet")
+      throw new ElectiveBusinessError("selectionNotStarted")
    }
    if (course.selectionEndAt && now > course.selectionEndAt) {
-      throw new Error("Selection has ended")
+      throw new ElectiveBusinessError("selectionEnded")
    }

    const [existing] = await tx
@@ -251,18 +341,21 @@ export async function selectCourse(
        )
      )
      .limit(1)
-    if (existing) throw new Error("Already selected this course")
+    if (existing) throw new ElectiveBusinessError("alreadySelected")

    // P2 建议：选课时间冲突检测
    const hasConflict = await checkScheduleConflict(tx, studentId, courseId)
    if (hasConflict) {
-      throw new Error("Schedule conflicts with your existing courses")
+      throw new ElectiveBusinessError("scheduleConflict")
    }

-    // P2 建议：学分上限校验
-    const creditCheck = await checkCreditLimit(tx, studentId, courseId)
+    // P2-4：学分上限校验（使用按年级配置的上限）
+    const creditCheck = await checkCreditLimit(tx, studentId, courseId, studentGradeId)
    if (creditCheck.exceeded) {
-      throw new Error(`Credit limit exceeded (${creditCheck.current}/${creditCheck.max})`)
+      throw new ElectiveBusinessError("creditExceeded", {
+        current: creditCheck.current,
+        max: creditCheck.max,
+      })
    }

    const id = createId()
@@ -272,13 +365,18 @@ export async function selectCourse(
    if (course.selectionMode === "fcfs" && course.enrolledCount < course.capacity) {
      status = "enrolled"
      enrolledAt = now
+      const newEnrolledCount = course.enrolledCount + 1
      await tx
        .update(electiveCourses)
        .set({
-          enrolledCount: course.enrolledCount + 1,
+          enrolledCount: newEnrolledCount,
          updatedAt: now,
        })
        .where(eq(electiveCourses.id, courseId))
+
+      // P2-4：容量阈值通知（fire-and-forget，不阻塞事务）
+      // 仅在跨过阈值时触发（避免每次选课都通知）
+      void notifyCapacityThresholdIfNeeded(course, newEnrolledCount)
    } else if (course.selectionMode === "fcfs") {
      status = "waitlist"
    }
@@ -293,21 +391,64 @@ export async function selectCourse(
      enrolledAt,
    })

-    return {
-      status,
-      message:
-        status === "enrolled"
-          ? "Enrolled successfully"
-          : status === "waitlist"
-            ? "Added to waitlist"
-            : "Selection submitted",
-    }
+    return { status }
  })
 }

+/**
+ * 容量阈值通知（P2-4 新增）。
+ *
+ * 触发条件：FCFS 模式下，录取后 `enrolledCount >= capacity * threshold`。
+ * 阈值来自 system_settings（`capacityNotifyThreshold`，默认 0.9）。
+ *
+ * 通知接收者：课程创建者/教师（teacherId）。
+ * 通知为 fire-and-forget，失败不影响选课流程。
+ *
+ * 防重复策略：仅当 `enrolledCount === Math.ceil(capacity * threshold)` 时触发，
+ * 即只在跨过阈值的瞬间触发一次。
+ */
+async function notifyCapacityThresholdIfNeeded(
+  course: { teacherId: string; id: string; name: string; capacity: number },
+  newEnrolledCount: number
+): Promise<void> {
+  try {
+    const threshold = await getCapacityNotifyThreshold()
+    const triggerPoint = Math.ceil(course.capacity * threshold)
+    // 仅在跨过阈值瞬间触发（避免每次选课都通知）
+    if (newEnrolledCount !== triggerPoint) return
+
+    // P2-4：通知文案使用 i18n 翻译键
+    const t = await getTranslations("elective")
+    const title = t("notifications.capacityWarningTitle", { courseName: course.name })
+    const content = t("notifications.capacityWarningContent", {
+      courseName: course.name,
+      enrolled: newEnrolledCount,
+      capacity: course.capacity,
+      percent: Math.round(threshold * 100),
+    })
+
+    await sendNotification({
+      userId: course.teacherId,
+      title,
+      content,
+      type: "warning",
+      actionUrl: `/admin/elective/${course.id}`,
+      metadata: {
+        courseId: course.id,
+        enrolledCount: newEnrolledCount,
+        capacity: course.capacity,
+        threshold,
+      },
+    })
+  } catch {
+    // fire-and-forget：通知失败不影响选课事务
+  }
+}
+
 export async function dropCourse(
  courseId: string,
-  studentId: string
+  studentId: string,
+  dropReason?: string
 ): Promise<void> {
  await db.transaction(async (tx) => {
    const [existing] = await tx
@@ -321,7 +462,7 @@ export async function dropCourse(
        )
      )
      .limit(1)
-    if (!existing) throw new Error("No active selection found")
+    if (!existing) throw new ElectiveBusinessError("noActiveSelection")

    // 锁定课程行，确保 enrolledCount 更新与候补递补的原子性
    const [course] = await tx
@@ -332,9 +473,20 @@ export async function dropCourse(
      .limit(1)

    const now = new Date()
+    // P2-4：退课截止时间校验
+    if (course?.dropDeadline && now > course.dropDeadline) {
+      throw new ElectiveBusinessError("dropDeadlinePassed")
+    }
+
    await tx
      .update(courseSelections)
-      .set({ status: "dropped", droppedAt: now, updatedAt: now })
+      .set({
+        status: "dropped",
+        droppedAt: now,
+        // P2-4：记录退课理由（trim 后存入，空字符串转为 null）
+        dropReason: dropReason && dropReason.trim().length > 0 ? dropReason.trim() : null,
+        updatedAt: now,
+      })
      .where(eq(courseSelections.id, existing.id))

    if (existing.status === "enrolled" && course && course.selectionMode === "fcfs") {
--- a/src/modules/elective/data-access-selections.ts
+++ b/src/modules/elective/data-access-selections.ts
@@ -37,6 +37,7 @@ type SelectionCoreRow = {
  courseCapacity: number | null
  courseEnrolledCount: number | null
  courseStatus: (typeof electiveCourses.status.enumValues)[number] | null
+  dropReason: string | null
 }

 const toIso = (d: Date | null | undefined): string | null =>
@@ -56,6 +57,7 @@ const mapSelectionRow = (
  selectedAt: toIsoRequired(r.selectedAt),
  enrolledAt: toIso(r.enrolledAt),
  droppedAt: toIso(r.droppedAt),
+  dropReason: r.dropReason,
  lotteryRank: r.lotteryRank,
  createdAt: toIsoRequired(r.createdAt),
  updatedAt: toIsoRequired(r.updatedAt),
@@ -77,6 +79,7 @@ const buildSelectionCoreSelect = () =>
      selectedAt: courseSelections.selectedAt,
      enrolledAt: courseSelections.enrolledAt,
      droppedAt: courseSelections.droppedAt,
+      dropReason: courseSelections.dropReason,
      lotteryRank: courseSelections.lotteryRank,
      createdAt: courseSelections.createdAt,
      updatedAt: courseSelections.updatedAt,
--- a/src/modules/elective/data-access-settings.ts
+++ b/src/modules/elective/data-access-settings.ts
@@ -0,0 +1,97 @@
+import "server-only"
+
+import { cache } from "react"
+import { eq, and } from "drizzle-orm"
+
+import { db } from "@/shared/db"
+import { systemSettings } from "@/shared/db/schema"
+
+/**
+ * 选课模块配置化设置（P2-4 新增）。
+ *
+ * 设计原则：
+ * - 复用全局 `system_settings` 表（category="elective"），避免新增独立表
+ * - 支持按年级覆盖（key=`creditLimit:grade:<gradeId>`），fallback 到全局（key=`creditLimit:default`）
+ * - 用 React `cache()` 包装，单次请求内去重
+ * - 配置缺失时使用默认值（向后兼容）
+ *
+ * 配置项：
+ * - `creditLimit:default` / `creditLimit:grade:<gradeId>`：学期学分上限（默认 10）
+ * - `capacityNotifyThreshold`：容量阈值通知比例 0-1（默认 0.9）
+ */
+
+const SETTINGS_CATEGORY = "elective"
+
+/** 默认学期学分上限（K12 选修课） */
+const DEFAULT_MAX_CREDIT_PER_TERM = 10
+/** 默认容量阈值通知比例（90%） */
+const DEFAULT_CAPACITY_NOTIFY_THRESHOLD = 0.9
+
+/**
+ * 读取 system_settings 中指定 key 的值。
+ * 失败或未配置时返回 null（不抛错，保证向后兼容）。
+ */
+async function readSettingValue(key: string): Promise<string | null> {
+  const [row] = await db
+    .select({ value: systemSettings.value, valueType: systemSettings.valueType })
+    .from(systemSettings)
+    .where(
+      and(
+        eq(systemSettings.category, SETTINGS_CATEGORY),
+        eq(systemSettings.key, key)
+      )
+    )
+    .limit(1)
+  return row?.value ?? null
+}
+
+/**
+ * 获取学期学分上限（P2-4 新增）。
+ *
+ * 查询顺序：
+ * 1. 若传入 gradeId，先查 `creditLimit:grade:<gradeId>`
+ * 2. 若未配置或未传入 gradeId，fallback 到 `creditLimit:default`
+ * 3. 都未配置则返回默认值 10
+ *
+ * @param gradeId 学生所在年级 ID（可选）
+ */
+export const getElectiveCreditLimit = cache(
+  async (gradeId?: string | null): Promise<number> => {
+    if (gradeId) {
+      const gradeValue = await readSettingValue(`creditLimit:grade:${gradeId}`)
+      if (gradeValue !== null) {
+        const parsed = Number(gradeValue)
+        if (!Number.isNaN(parsed) && parsed > 0) return parsed
+      }
+    }
+    const defaultValue = await readSettingValue("creditLimit:default")
+    if (defaultValue !== null) {
+      const parsed = Number(defaultValue)
+      if (!Number.isNaN(parsed) && parsed > 0) return parsed
+    }
+    return DEFAULT_MAX_CREDIT_PER_TERM
+  }
+)
+
+/**
+ * 获取容量阈值通知比例（P2-4 新增）。
+ *
+ * 当课程 `enrolledCount >= capacity * threshold` 时触发管理员通知。
+ * 默认 0.9（90%）。
+ */
+export const getCapacityNotifyThreshold = cache(
+  async (): Promise<number> => {
+    const value = await readSettingValue("capacityNotifyThreshold")
+    if (value !== null) {
+      const parsed = Number(value)
+      if (!Number.isNaN(parsed) && parsed > 0 && parsed <= 1) return parsed
+    }
+    return DEFAULT_CAPACITY_NOTIFY_THRESHOLD
+  }
+)
+
+/** 导出默认值常量（供测试与文档引用） */
+export const ELECTIVE_DEFAULTS = {
+  MAX_CREDIT_PER_TERM: DEFAULT_MAX_CREDIT_PER_TERM,
+  CAPACITY_NOTIFY_THRESHOLD: DEFAULT_CAPACITY_NOTIFY_THRESHOLD,
+} as const
--- a/src/modules/elective/data-access-stats.ts
+++ b/src/modules/elective/data-access-stats.ts
@@ -0,0 +1,88 @@
+import "server-only"
+
+import { cache } from "react"
+import { count, eq, sql } from "drizzle-orm"
+
+import { db } from "@/shared/db"
+import { courseSelections, electiveCourses } from "@/shared/db/schema"
+
+/**
+ * 选课模块管理员概览统计（P1-13 新增）。
+ * 用于 admin/teacher 列表页顶部展示关键指标。
+ */
+
+export interface ElectiveOverviewStats {
+  /** 课程总数 */
+  totalCourses: number
+  /** 总选课人数（已录取 + 候补 + 已选） */
+  totalEnrolled: number
+  /** 平均容量使用率（百分比，0-100） */
+  avgUtilization: number
+  /** 待抽签的课程数（selectionMode=lottery 且 status=open 且存在 selected 记录） */
+  pendingLottery: number
+}
+
+/**
+ * 获取选修课全局概览统计（admin 视角）。
+ *
+ * 实现要点：
+ * - 4 个独立查询合并为 3 个 SQL（pendingLottery 需 join），避免 N+1
+ * - 使用 SQL 聚合而非拉全表后 reduce，避免大数据量内存峰值
+ * - admin 不做 scope 过滤（统计全部课程）
+ */
+export const getElectiveOverviewStats = cache(
+  async (): Promise<ElectiveOverviewStats> => {
+    // 并行执行聚合查询
+    const [totalRow, enrolledRow, utilizationRow, pendingRow] = await Promise.all([
+      // 1. 课程总数
+      db
+        .select({ total: count() })
+        .from(electiveCourses),
+
+      // 2. 总选课人数（活跃选课记录数）
+      db
+        .select({ total: count() })
+        .from(courseSelections)
+        .where(
+          sql`${courseSelections.status} IN ('selected', 'enrolled', 'waitlist')`
+        ),
+
+      // 3. 平均容量使用率（capacity > 0 时计算 enrolledCount/capacity 平均值）
+      db
+        .select({
+          avg: sql<number>`COALESCE(
+            AVG(
+              CASE
+                WHEN ${electiveCourses.capacity} > 0
+                THEN ${electiveCourses.enrolledCount}::float / ${electiveCourses.capacity}
+                ELSE 0
+              END
+            ) * 100,
+            0
+          )`,
+        })
+        .from(electiveCourses),
+
+      // 4. 待抽签课程数：lottery 模式且 status=open 且有 selected 状态的选课记录
+      db
+        .select({ total: sql<number>`count(distinct ${electiveCourses.id})` })
+        .from(electiveCourses)
+        .innerJoin(
+          courseSelections,
+          eq(courseSelections.courseId, electiveCourses.id)
+        )
+        .where(
+          sql`${electiveCourses.selectionMode} = 'lottery'
+            AND ${electiveCourses.status} = 'open'
+            AND ${courseSelections.status} = 'selected'`
+        ),
+    ])
+
+    return {
+      totalCourses: totalRow[0]?.total ?? 0,
+      totalEnrolled: enrolledRow[0]?.total ?? 0,
+      avgUtilization: Math.round(Number(utilizationRow[0]?.avg ?? 0)),
+      pendingLottery: pendingRow[0]?.total ?? 0,
+    }
+  }
+)
--- a/src/modules/elective/data-access.ts
+++ b/src/modules/elective/data-access.ts
@@ -62,6 +62,7 @@ export const mapCourseRow = (
  endDate: r.endDate ? new Date(r.endDate).toISOString().slice(0, 10) : null,
  selectionStartAt: toIso(r.selectionStartAt),
  selectionEndAt: toIso(r.selectionEndAt),
+  dropDeadline: toIso(r.dropDeadline),
  status: r.status,
  selectionMode: r.selectionMode,
  credit: String(r.credit),
@@ -89,6 +90,7 @@ export const buildCourseSelect = () =>
      endDate: electiveCourses.endDate,
      selectionStartAt: electiveCourses.selectionStartAt,
      selectionEndAt: electiveCourses.selectionEndAt,
+      dropDeadline: electiveCourses.dropDeadline,
      status: electiveCourses.status,
      selectionMode: electiveCourses.selectionMode,
      credit: electiveCourses.credit,
@@ -133,51 +135,41 @@ export const getElectiveCourses = cache(
  async (
    params?: GetElectiveCoursesParams & { scope?: DataScope; currentUserId?: string }
  ): Promise<ElectiveCourseWithDetails[]> => {
-    try {
-      const conditions: SQL[] = []
-      if (params?.status)
-        conditions.push(
-          eq(electiveCourses.status, params.status)
-        )
-      if (params?.gradeId) conditions.push(eq(electiveCourses.gradeId, params.gradeId))
-      if (params?.subjectId)
-        conditions.push(eq(electiveCourses.subjectId, params.subjectId))
-      if (params?.teacherId)
-        conditions.push(eq(electiveCourses.teacherId, params.teacherId))
-      if (params?.scope) {
-        const scopeFilter = buildScopeFilter(params.scope, params.currentUserId)
-        if (scopeFilter) conditions.push(scopeFilter)
-      }
-
-      const query = buildCourseSelect()
-      const rows = await (conditions.length > 0
-        ? query.where(and(...conditions))
-        : query
-      ).orderBy(desc(electiveCourses.createdAt))
-
-      if (rows.length === 0) return []
-      const displayMaps = await resolveCourseDisplayNames(rows)
-      return rows.map((r) => mapCourseRow(r, displayMaps.teacherNames, displayMaps.subjectNames, displayMaps.gradeNames))
-    } catch (error) {
-      console.error("getElectiveCourses failed:", error)
-      return []
+    const conditions: SQL[] = []
+    if (params?.status)
+      conditions.push(
+        eq(electiveCourses.status, params.status)
+      )
+    if (params?.gradeId) conditions.push(eq(electiveCourses.gradeId, params.gradeId))
+    if (params?.subjectId)
+      conditions.push(eq(electiveCourses.subjectId, params.subjectId))
+    if (params?.teacherId)
+      conditions.push(eq(electiveCourses.teacherId, params.teacherId))
+    if (params?.scope) {
+      const scopeFilter = buildScopeFilter(params.scope, params.currentUserId)
+      if (scopeFilter) conditions.push(scopeFilter)
    }
+
+    const query = buildCourseSelect()
+    const rows = await (conditions.length > 0
+      ? query.where(and(...conditions))
+      : query
+    ).orderBy(desc(electiveCourses.createdAt))
+
+    if (rows.length === 0) return []
+    const displayMaps = await resolveCourseDisplayNames(rows)
+    return rows.map((r) => mapCourseRow(r, displayMaps.teacherNames, displayMaps.subjectNames, displayMaps.gradeNames))
  }
 )

 export const getElectiveCourseById = cache(
  async (id: string): Promise<ElectiveCourseWithDetails | null> => {
-    try {
-      const [row] = await buildCourseSelect()
-        .where(eq(electiveCourses.id, id))
-        .limit(1)
-      if (!row) return null
-      const displayMaps = await resolveCourseDisplayNames([row])
-      return mapCourseRow(row, displayMaps.teacherNames, displayMaps.subjectNames, displayMaps.gradeNames)
-    } catch (error) {
-      console.error("getElectiveCourseById failed:", error)
-      return null
-    }
+    const [row] = await buildCourseSelect()
+      .where(eq(electiveCourses.id, id))
+      .limit(1)
+    if (!row) return null
+    const displayMaps = await resolveCourseDisplayNames([row])
+    return mapCourseRow(row, displayMaps.teacherNames, displayMaps.subjectNames, displayMaps.gradeNames)
  }
 )

@@ -201,6 +193,8 @@ export async function createElectiveCourse(
    endDate: data.endDate ? safeParseDate(data.endDate, "结束日期") : null,
    selectionStartAt: data.selectionStartAt ? safeParseDate(data.selectionStartAt, "选课开始时间") : null,
    selectionEndAt: data.selectionEndAt ? safeParseDate(data.selectionEndAt, "选课结束时间") : null,
+    // P2-4：退课截止时间
+    dropDeadline: data.dropDeadline ? safeParseDate(data.dropDeadline, "退课截止时间") : null,
    status: "draft",
    selectionMode: data.selectionMode,
    credit: data.credit,
@@ -229,6 +223,9 @@ export async function updateElectiveCourse(
    update.selectionStartAt = data.selectionStartAt ? safeParseDate(data.selectionStartAt, "选课开始时间") : null
  if (data.selectionEndAt !== undefined)
    update.selectionEndAt = data.selectionEndAt ? safeParseDate(data.selectionEndAt, "选课结束时间") : null
+  // P2-4：退课截止时间
+  if (data.dropDeadline !== undefined)
+    update.dropDeadline = data.dropDeadline ? safeParseDate(data.dropDeadline, "退课截止时间") : null
  if (data.status !== undefined) update.status = data.status
  if (data.selectionMode !== undefined) update.selectionMode = data.selectionMode
  if (data.credit !== undefined) update.credit = data.credit
--- a/src/modules/elective/export.ts
+++ b/src/modules/elective/export.ts
@@ -6,10 +6,15 @@ import { exportToExcel } from "@/shared/lib/excel"

 import { getElectiveCourses } from "./data-access"
 import { getCourseSelections } from "./data-access-selections"
+import {
+  ElectiveCourseStatusEnum,
+} from "./schema"

 /**
 * 导出选修课课程列表到 Excel
 * Sheet 1: 课程明细
+ *
+ * 注意：通过 Zod 枚举做类型守卫，避免 `as` 类型断言。
 */
 export async function exportElectiveCoursesToExcel(params: {
  status?: string
@@ -17,8 +22,14 @@ export async function exportElectiveCoursesToExcel(params: {
 }): Promise<Buffer> {
  const t = await getTranslations("elective")

+  // 用 Zod 枚举校验 status，通过则类型收窄为 ElectiveCourseStatus
+  const statusParsed = params.status
+    ? ElectiveCourseStatusEnum.safeParse(params.status)
+    : undefined
+  const status = statusParsed?.success ? statusParsed.data : undefined
+
  const courses = await getElectiveCourses({
-    status: params.status as "draft" | "open" | "closed" | "cancelled" | undefined,
+    status,
    teacherId: params.teacherId,
  })

@@ -33,7 +44,7 @@ export async function exportElectiveCoursesToExcel(params: {
    [t("fields.schedule")]: c.schedule ?? "",
    [t("fields.credit")]: c.credit,
    [t("fields.selectionMode")]: t(`selectionMode.${c.selectionMode}`),
-    status: t(`status.${c.status}`),
+    [t("export.statusHeader")]: t(`status.${c.status}`),
    [t("fields.startDate")]: c.startDate ?? "",
    [t("fields.endDate")]: c.endDate ?? "",
  }))
@@ -41,7 +52,7 @@ export async function exportElectiveCoursesToExcel(params: {
  return exportToExcel({
    sheets: [
      {
-        name: t("title.adminList"),
+        name: t("export.courseSheetName"),
        columns: [
          { header: t("fields.name"), key: t("fields.name"), width: 24 },
          { header: t("fields.teacher"), key: t("fields.teacher"), width: 16 },
@@ -53,7 +64,7 @@ export async function exportElectiveCoursesToExcel(params: {
          { header: t("fields.schedule"), key: t("fields.schedule"), width: 20 },
          { header: t("fields.credit"), key: t("fields.credit"), width: 8 },
          { header: t("fields.selectionMode"), key: t("fields.selectionMode"), width: 16 },
-          { header: "Status", key: "status", width: 12 },
+          { header: t("export.statusHeader"), key: t("export.statusHeader"), width: 12 },
          { header: t("fields.startDate"), key: t("fields.startDate"), width: 14 },
          { header: t("fields.endDate"), key: t("fields.endDate"), width: 14 },
        ],
@@ -75,25 +86,25 @@ export async function exportCourseSelectionsToExcel(params: {
  const selections = await getCourseSelections(params.courseId)

  const rows = selections.map((s, idx) => ({
-    "#": idx + 1,
+    [t("export.indexHeader")]: idx + 1,
    [t("fields.name")]: s.studentName ?? "",
-    status: t(`selectionStatus.${s.status}`),
-    priority: s.priority ?? 1,
-    selectedAt: s.selectedAt.split("T")[0],
-    enrolledAt: s.enrolledAt ? s.enrolledAt.split("T")[0] : "",
+    [t("export.statusHeader")]: t(`selectionStatus.${s.status}`),
+    [t("export.priorityHeader")]: s.priority ?? 1,
+    [t("export.selectedAtHeader")]: s.selectedAt.split("T")[0],
+    [t("export.enrolledAtHeader")]: s.enrolledAt ? s.enrolledAt.split("T")[0] : "",
  }))

  return exportToExcel({
    sheets: [
      {
-        name: t("student.mySelections"),
+        name: t("export.selectionSheetName"),
        columns: [
-          { header: "#", key: "#", width: 6 },
+          { header: t("export.indexHeader"), key: t("export.indexHeader"), width: 6 },
          { header: t("fields.name"), key: t("fields.name"), width: 18 },
-          { header: "Status", key: "status", width: 12 },
-          { header: "Priority", key: "priority", width: 10 },
-          { header: "Selected At", key: "selectedAt", width: 14 },
-          { header: "Enrolled At", key: "enrolledAt", width: 14 },
+          { header: t("export.statusHeader"), key: t("export.statusHeader"), width: 12 },
+          { header: t("export.priorityHeader"), key: t("export.priorityHeader"), width: 10 },
+          { header: t("export.selectedAtHeader"), key: t("export.selectedAtHeader"), width: 14 },
+          { header: t("export.enrolledAtHeader"), key: t("export.enrolledAtHeader"), width: 14 },
        ],
        rows,
      },
--- a/src/modules/elective/schema.ts
+++ b/src/modules/elective/schema.ts
@@ -63,6 +63,13 @@ export const CreateElectiveCourseSchema = z
      .optional()
      .nullable()
      .refine(isValidDateString, "选课结束时间格式无效"),
+    /** 退课截止时间（P2-4 新增）：超过此时间学生不可退课 */
+    dropDeadline: z
+      .string()
+      .trim()
+      .optional()
+      .nullable()
+      .refine(isValidDateString, "退课截止时间格式无效"),
    selectionMode: ElectiveSelectionModeEnum.optional(),
    credit: z.string().trim().optional().nullable(),
  })
@@ -79,6 +86,7 @@ export const CreateElectiveCourseSchema = z
    endDate: optionalStringToNull(v.endDate),
    selectionStartAt: optionalStringToNull(v.selectionStartAt),
    selectionEndAt: optionalStringToNull(v.selectionEndAt),
+    dropDeadline: optionalStringToNull(v.dropDeadline),
    selectionMode: v.selectionMode ?? "fcfs",
    credit: v.credit && v.credit.length > 0 ? v.credit : "1.0",
  }))
@@ -119,6 +127,13 @@ export const UpdateElectiveCourseSchema = z
      .optional()
      .nullable()
      .refine(isValidDateString, "选课结束时间格式无效"),
+    /** 退课截止时间（P2-4 新增）：超过此时间学生不可退课 */
+    dropDeadline: z
+      .string()
+      .trim()
+      .optional()
+      .nullable()
+      .refine(isValidDateString, "退课截止时间格式无效"),
    status: ElectiveCourseStatusEnum.optional(),
    selectionMode: ElectiveSelectionModeEnum.optional(),
    credit: z.string().trim().optional().nullable(),
@@ -149,6 +164,10 @@ export const UpdateElectiveCourseSchema = z
      v.selectionEndAt !== undefined
        ? optionalStringToNull(v.selectionEndAt)
        : undefined,
+    dropDeadline:
+      v.dropDeadline !== undefined
+        ? optionalStringToNull(v.dropDeadline)
+        : undefined,
    credit:
      v.credit !== undefined
        ? v.credit && v.credit.length > 0
@@ -168,6 +187,8 @@ export type SelectCourseInput = z.infer<typeof SelectCourseSchema>

 export const DropCourseSchema = z.object({
  courseId: z.string().trim().min(1),
+  /** 退课理由（P2-4 新增）：可选，最长 255 字符 */
+  dropReason: z.string().trim().max(255).optional(),
 })

 export type DropCourseInput = z.infer<typeof DropCourseSchema>
--- a/src/modules/elective/types.ts
+++ b/src/modules/elective/types.ts
@@ -24,6 +24,8 @@ export interface ElectiveCourse {
  endDate: string | null
  selectionStartAt: string | null
  selectionEndAt: string | null
+  /** 退课截止时间（P2-4 新增）：ISO 字符串，为 null 表示不限制 */
+  dropDeadline: string | null
  status: ElectiveCourseStatus
  selectionMode: ElectiveSelectionMode
  credit: string
@@ -46,6 +48,8 @@ export interface CourseSelection {
  selectedAt: string
  enrolledAt: string | null
  droppedAt: string | null
+  /** 退课理由（P2-4 新增）：学生退课时可选填写 */
+  dropReason: string | null
  lotteryRank: number | null
  createdAt: string
  updatedAt: string