diff --git a/apps/api/src/routes/admin/analytics.ts b/apps/api/src/routes/admin/analytics.ts
new file mode 100644
index 0000000..6c3bf1e
--- /dev/null
+++ b/apps/api/src/routes/admin/analytics.ts
@@ -0,0 +1,367 @@
+/**
+ * 学情分析里的「卡点分析」和「历年概况」。
+ *
+ * 两边共用一个口径：**人 × 题**。原来的卡点数的是「错过一次的人」，全部时间、不分班 ——
+ * 阿福讲白搭显示 325 人卡住，交过的 782 人里其实 753 人后来做对了，排在前面的只是做的人多。
+ * 课堂驱动的题最后几乎都会做对（这学期「交过还没做对」最多的一道也就 10 人），真正卡人的是
+ * 「要交好几次才对」，所以这里给的是：第一次交就对的人、做对的人、做对之前交了几次。
+ *
+ * - 只算学生（STUDENT_ROLES），只算非比赛提交；没判完的、判题机自己崩了的（SYSTEM_ERROR）
+ *   不算一次「交」。
+ * - 选了时间段时，只算**第一次交**落在这段时间里的人题对，指标按这对的全部历史算 ——
+ *   否则「最近 7 天」会把上周错、这周对的人算成一次就对。
+ * - 「做对平均交几次」只数做对那次及之前的，做对以后又交的不算。
+ *
+ * 路径挂在 /problem-analytics 下，不放进 /problems：Hono 按注册顺序匹配，
+ * problem.ts 先注册的 `/problems/:id` 会把它整个吃掉（以前真发生过，见 git 历史）。
+ */
+
+import {
+  STUDENT_ROLES,
+  type StuckProblem,
+  type StuckProblemDetail,
+  type YearlyOverview,
+  type YearlySummary,
+} from "@oj2/contract"
+import { and, eq, inArray, sql, type SQL } from "drizzle-orm"
+import { Hono } from "hono"
+
+import { requireTeacher, type AppEnv } from "../../auth/middleware"
+import { db, schema } from "../../db"
+import { failure, success } from "../../http"
+import { JudgeStatus } from "../../judge/status"
+import { schoolYearOf, schoolYearStart, schoolYearStartOf, shiftMonthsByCalendar } from "../../time"
+import { queryInteger } from "../helpers"
+
+export const adminAnalyticsRoutes = new Hono<AppEnv>()
+
+const ACCEPTED = sql.join([JudgeStatus.ACCEPTED, JudgeStatus.AST_CHECK_FAILED], sql`, `)
+const NOT_COUNTED = sql.join(
+  [JudgeStatus.PENDING, JudgeStatus.JUDGING, JudgeStatus.SYSTEM_ERROR],
+  sql`, `,
+)
+const STUDENTS = sql.join(
+  STUDENT_ROLES.map((role) => sql`${role}`),
+  sql`, `,
+)
+
+/** `start` 是 ISO 时刻，解析不了就当没给（= 全部时间） */
+function parseStart(value: string | undefined) {
+  if (!value) return null
+  const time = Date.parse(value)
+  return Number.isNaN(time) ? null : new Date(time).toISOString()
+}
+
+/**
+ * 学生的非比赛提交，每条带上「这对人题」第一次做对的时刻和序号。
+ * 后面的查询都从这张表聚合成人题对。
+ */
+function studentSubmissions(where: SQL[]) {
+  return sql`
+    select s.id, s.user_id, s.problem_id, s.create_time, s.result, s.language, u.class_name,
+      min(s.create_time) filter (where s.result in (${ACCEPTED}))
+        over (partition by s.user_id, s.problem_id) as ac_at,
+      row_number() over (partition by s.user_id, s.problem_id order by s.create_time, s.id) as rn
+    from ${schema.submission} s
+    join ${schema.user} u on u.id = s.user_id
+    where s.contest_id is null
+      and s.result not in (${NOT_COUNTED})
+      and u.admin_type in (${STUDENTS})
+      ${sql.join(
+        where.map((condition) => sql`and ${condition}`),
+        sql` `,
+      )}
+  `
+}
+
+/** 班级精确匹配、时间段只留「在这段时间里交过」的人题对（第一次交在不在段里由 having 再卡） */
+function scope(className: string | undefined, start: string | null, problemId?: number) {
+  const where: SQL[] = []
+  if (problemId) where.push(sql`s.problem_id = ${problemId}`)
+  if (className) where.push(sql`u.class_name = ${className}`)
+  if (start)
+    where.push(sql`(s.user_id, s.problem_id) in (
+      select user_id, problem_id from ${schema.submission}
+      where contest_id is null and create_time >= ${start}
+      ${problemId ? sql`and problem_id = ${problemId}` : sql``}
+    )`)
+  return where
+}
+
+async function knowledgeTags(problemIds: number[]) {
+  const tags = new Map<number, string[]>()
+  if (!problemIds.length) return tags
+  const rows = await db
+    .select({ problemId: schema.problemTags.problemId, name: schema.problemTag.name })
+    .from(schema.problemTags)
+    .innerJoin(schema.problemTag, eq(schema.problemTag.id, schema.problemTags.problemtagId))
+    .where(
+      and(
+        inArray(schema.problemTags.problemId, problemIds),
+        eq(schema.problemTag.category, "knowledge"),
+      ),
+    )
+  for (const row of rows) tags.set(row.problemId, [...(tags.get(row.problemId) ?? []), row.name])
+  return tags
+}
+
+// ---------------------------------------------------------------- 卡点：每道题一行
+
+adminAnalyticsRoutes.get("/problem-analytics/stuck", requireTeacher, async (c) => {
+  const className = c.req.query("className")?.trim() || undefined
+  const start = parseStart(c.req.query("start"))
+  const rows = await db.execute<{
+    id: number
+    display_id: string
+    title: string
+    users: number
+    first_try: number
+    solved: number
+    solved_tries: number
+  }>(sql`
+    with s as (${studentSubmissions(scope(className, start))}),
+    pairs as (
+      select problem_id,
+        bool_or(rn = 1 and result in (${ACCEPTED})) as first_try,
+        min(ac_at) as ac_at,
+        count(*) filter (where ac_at is null or create_time <= ac_at) as tries
+      from s
+      group by user_id, problem_id
+      ${start ? sql`having min(create_time) >= ${start}` : sql``}
+    )
+    select p.id, p._id as display_id, p.title,
+      count(*)::int as users,
+      count(*) filter (where first_try)::int as first_try,
+      count(*) filter (where ac_at is not null)::int as solved,
+      coalesce(sum(tries) filter (where ac_at is not null), 0)::int as solved_tries
+    from pairs
+    join ${schema.problem} p on p.id = pairs.problem_id
+    group by p.id
+  `)
+  const tags = await knowledgeTags(rows.map((row) => row.id))
+  return success(
+    c,
+    rows.map(
+      (row) =>
+        ({
+          id: row.id,
+          displayId: row.display_id,
+          title: row.title,
+          tags: tags.get(row.id) ?? [],
+          users: row.users,
+          firstTry: row.first_try,
+          solved: row.solved,
+          solvedTries: row.solved_tries,
+        }) satisfies StuckProblem,
+    ),
+  )
+})
+
+// ---------------------------------------------------------------- 卡点：一道题
+
+adminAnalyticsRoutes.get("/problem-analytics/stuck/:id", requireTeacher, async (c) => {
+  const id = queryInteger(c.req.param("id"), 0, { min: 1 })
+  const [problem] = await db
+    .select({
+      id: schema.problem.id,
+      displayId: schema.problem.displayId,
+      title: schema.problem.title,
+    })
+    .from(schema.problem)
+    .where(eq(schema.problem.id, id))
+  if (!problem) return failure(c, 404, "problem-not-found", "题目不存在")
+
+  const className = c.req.query("className")?.trim() || undefined
+  const start = parseStart(c.req.query("start"))
+  const pairs = sql`
+    with s as (${studentSubmissions(scope(className, start, id))}),
+    pairs as (
+      select user_id, min(create_time) as first_at, min(ac_at) as ac_at,
+        bool_or(rn = 1 and result in (${ACCEPTED})) as first_try,
+        count(*) filter (where ac_at is null or create_time <= ac_at) as tries,
+        (array_agg(result order by create_time desc, id desc))[1] as last_result,
+        (array_agg(id order by create_time desc, id desc))[1] as last_id
+      from s
+      group by user_id
+      ${start ? sql`having min(create_time) >= ${start}` : sql``}
+    )
+  `
+  const [students, errors, history, tags] = await Promise.all([
+    db.execute<{
+      username: string
+      class_name: string | null
+      first_try: boolean
+      solved: boolean
+      tries: number
+      minutes: number | null
+      last_result: number
+      last_id: string
+    }>(sql`
+      ${pairs}
+      select u.username, u.class_name, pairs.first_try, pairs.ac_at is not null as solved,
+        pairs.tries::int as tries,
+        round(extract(epoch from pairs.ac_at - pairs.first_at) / 60)::int as minutes,
+        pairs.last_result, pairs.last_id
+      from pairs join ${schema.user} u on u.id = pairs.user_id
+    `),
+    db.execute<{ result: number; count: number }>(sql`
+      ${pairs}
+      select s.result, count(*)::int as count
+      from s join pairs using (user_id)
+      where s.result not in (${ACCEPTED})
+      group by s.result
+      order by count desc
+    `),
+    // 历年：全站、全部时间，按第一次交落在哪个学年分
+    db.execute<{ year: number; users: number; first_try: number }>(sql`
+      with s as (${studentSubmissions([sql`s.problem_id = ${id}`])}),
+      pairs as (
+        select min(create_time) as first_at, bool_or(rn = 1 and result in (${ACCEPTED})) as first_try
+        from s group by user_id
+      )
+      select ${schoolYearOf(sql`first_at`)} as year, count(*)::int as users,
+        count(*) filter (where first_try)::int as first_try
+      from pairs group by 1 order by 1
+    `),
+    knowledgeTags([id]),
+  ])
+  return success(c, {
+    problem: { ...problem, tags: tags.get(id) ?? [] },
+    students: students.map((row) => ({
+      username: row.username,
+      className: row.class_name,
+      firstTry: row.first_try,
+      solved: row.solved,
+      tries: row.tries,
+      minutes: row.minutes,
+      lastResult: row.last_result,
+      lastSubmissionId: row.last_id,
+    })),
+    errors: errors.map((row) => ({ result: row.result, count: row.count })),
+    history: history.map((row) => ({ year: row.year, users: row.users, firstTry: row.first_try })),
+  } satisfies StuckProblemDetail)
+})
+
+// ---------------------------------------------------------------- 历年概况
+
+/** 「在用的年级」：这段时间里至少这么多人交过题的年级才列 */
+const GRADE_MIN_USERS = 20
+
+adminAnalyticsRoutes.get("/problem-analytics/yearly", requireTeacher, async (c) => {
+  const now = new Date()
+  const current = schoolYearStart(now)
+  const [first] = await db.execute<{ year: number | null }>(sql`
+    select ${schoolYearOf(sql`min(create_time)`)} as year
+    from ${schema.submission} where contest_id is null
+  `)
+  const firstYear = Math.min(first?.year ?? current.year, current.year)
+
+  // 每个完整学年、进行中的学年（到现在），外加去年同期（上一学年开学到去年的今天）
+  const ranges: { key: number; year: number; from: string; to: string }[] = []
+  for (let year = firstYear; year <= current.year; year += 1) {
+    const to = year === current.year ? now.toISOString() : schoolYearStartOf(year + 1)
+    ranges.push({ key: year, year, from: schoolYearStartOf(year), to })
+  }
+  const hasLastYear = current.year - 1 >= firstYear
+  if (hasLastYear)
+    ranges.push({
+      key: -1,
+      year: current.year - 1,
+      from: schoolYearStartOf(current.year - 1),
+      to: shiftMonthsByCalendar(now, -12).toISOString(),
+    })
+
+  const values = sql.join(
+    ranges.map(
+      (range) => sql`(${range.key}::int, ${range.from}::timestamptz, ${range.to}::timestamptz)`,
+    ),
+    sql`, `,
+  )
+  const rows = await db.execute<{
+    key: number
+    users: number
+    submissions: number
+    problems: number
+    c_submissions: number
+    solved_pairs: number
+    started_pairs: number
+    first_try_pairs: number
+    solved_started: number
+    solved_tries: number
+    grades: string[] | null
+  }>(sql`
+    with ranges(key, f, t) as (values ${values}),
+    s as (${studentSubmissions([])}),
+    pairs as (
+      select min(create_time) as first_at, min(ac_at) as ac_at,
+        bool_or(rn = 1 and result in (${ACCEPTED})) as first_try,
+        count(*) filter (where ac_at is null or create_time <= ac_at) as tries
+      from s group by user_id, problem_id
+    ),
+    sub_stats as (
+      select r.key, count(distinct s.user_id)::int as users, count(*)::int as submissions,
+        count(distinct s.problem_id)::int as problems,
+        count(*) filter (where s.language in ('C', 'C++'))::int as c_submissions
+      from s join ranges r on s.create_time >= r.f and s.create_time < r.t
+      group by r.key
+    ),
+    pair_stats as (
+      select r.key,
+        count(*) filter (where p.ac_at >= r.f and p.ac_at < r.t)::int as solved_pairs,
+        count(*) filter (where p.first_at >= r.f and p.first_at < r.t)::int as started_pairs,
+        count(*) filter (where p.first_at >= r.f and p.first_at < r.t and p.first_try)::int
+          as first_try_pairs,
+        count(*) filter (where p.first_at >= r.f and p.first_at < r.t and p.ac_at is not null)::int
+          as solved_started,
+        coalesce(sum(p.tries) filter (
+          where p.first_at >= r.f and p.first_at < r.t and p.ac_at is not null
+        ), 0)::int as solved_tries
+      from pairs p join ranges r
+        on (p.first_at >= r.f and p.first_at < r.t) or (p.ac_at >= r.f and p.ac_at < r.t)
+      group by r.key
+    ),
+    grade_stats as (
+      select key, json_agg(grade order by grade) as grades from (
+        select r.key, left(s.class_name, 2) as grade
+        from s join ranges r on s.create_time >= r.f and s.create_time < r.t
+        where s.class_name ~ '^[0-9]{3,}$'
+        group by r.key, left(s.class_name, 2)
+        having count(distinct s.user_id) >= ${GRADE_MIN_USERS}
+      ) g group by key
+    )
+    select r.key, coalesce(sub.users, 0) as users, coalesce(sub.submissions, 0) as submissions,
+      coalesce(sub.problems, 0) as problems, coalesce(sub.c_submissions, 0) as c_submissions,
+      coalesce(ps.solved_pairs, 0) as solved_pairs, coalesce(ps.started_pairs, 0) as started_pairs,
+      coalesce(ps.first_try_pairs, 0) as first_try_pairs,
+      coalesce(ps.solved_started, 0) as solved_started,
+      coalesce(ps.solved_tries, 0) as solved_tries, gs.grades
+    from ranges r
+    left join sub_stats sub on sub.key = r.key
+    left join pair_stats ps on ps.key = r.key
+    left join grade_stats gs on gs.key = r.key
+  `)
+
+  const byKey = new Map(rows.map((row) => [row.key, row]))
+  const summary = (range: (typeof ranges)[number]): YearlySummary => {
+    const row = byKey.get(range.key)
+    return {
+      year: range.year,
+      until: range.to,
+      grades: row?.grades ?? [],
+      users: row?.users ?? 0,
+      submissions: row?.submissions ?? 0,
+      problems: row?.problems ?? 0,
+      solvedPairs: row?.solved_pairs ?? 0,
+      startedPairs: row?.started_pairs ?? 0,
+      firstTryPairs: row?.first_try_pairs ?? 0,
+      solvedStarted: row?.solved_started ?? 0,
+      solvedTries: row?.solved_tries ?? 0,
+      cSubmissions: row?.c_submissions ?? 0,
+    }
+  }
+  const lastYear = ranges.find((range) => range.key === -1)
+  return success(c, {
+    years: ranges.filter((range) => range.key !== -1).map(summary),
+    lastYearToDate: lastYear ? summary(lastYear) : null,
+  } satisfies YearlyOverview)
+})
diff --git a/apps/api/src/routes/admin/index.ts b/apps/api/src/routes/admin/index.ts
index c557c75..b77e1c7 100644
--- a/apps/api/src/routes/admin/index.ts
+++ b/apps/api/src/routes/admin/index.ts
@@ -4,6 +4,7 @@ import type { AppEnv } from "../../auth/middleware"
 import { adminAccountRoutes } from "./account"
 import { adminAchievementRoutes } from "./achievement"
 import { adminAiRoutes } from "./ai"
+import { adminAnalyticsRoutes } from "./analytics"
 import { adminConfRoutes } from "./conf"
 import { adminContestRoutes } from "./contest"
 import { adminLearnRoutes } from "./learn"
@@ -26,6 +27,7 @@ export const adminRoutes = new Hono<AppEnv>()
 adminRoutes.route("/", adminAccountRoutes)
 adminRoutes.route("/", adminAchievementRoutes)
 adminRoutes.route("/", adminAiRoutes)
+adminRoutes.route("/", adminAnalyticsRoutes)
 adminRoutes.route("/", adminConfRoutes)
 adminRoutes.route("/", adminContestRoutes)
 adminRoutes.route("/", adminLearnRoutes)
diff --git a/apps/api/src/routes/admin/tag.ts b/apps/api/src/routes/admin/tag.ts
index 1daad14..f86b4b0 100644
--- a/apps/api/src/routes/admin/tag.ts
+++ b/apps/api/src/routes/admin/tag.ts
@@ -3,45 +3,24 @@ import {
   generateFlowchartRequestSchema,
   renameTagRequestSchema,
   setTagCategoryRequestSchema,
-  type AcTrend,
   type AdminTag,
   type BatchProblemTagResponse,
   type GenerateFlowchartResponse,
   type RenameTagResponse,
-  type StuckProblem,
 } from "@oj2/contract"
-import {
-  and,
-  asc,
-  countDistinct,
-  count,
-  desc,
-  eq,
-  gte,
-  ilike,
-  inArray,
-  isNull,
-  lte,
-  ne,
-  sql,
-} from "drizzle-orm"
+import { and, asc, countDistinct, desc, eq, ilike, inArray, isNull, ne, sql } from "drizzle-orm"
 import { Hono } from "hono"
 
-import { requireProblemPermission, requireTeacher, type AppEnv } from "../../auth/middleware"
+import { requireProblemPermission, type AppEnv } from "../../auth/middleware"
 import type { AuthUser } from "../../auth/session"
 import { db, schema } from "../../db"
 import { failure, parseBody, success } from "../../http"
-import { JudgeStatus } from "../../judge/status"
 import { completeChat } from "../../services/ai"
-import { localTime, localYear } from "../../time"
-import { queryInteger, rounded } from "../helpers"
+import { queryInteger } from "../helpers"
 import { canEdit, findTagsByName, normalizeTagNames } from "./problem"
 
 export const adminTagRoutes = new Hono<AppEnv>()
 
-const ACCEPTED = [JudgeStatus.ACCEPTED, JudgeStatus.AST_CHECK_FAILED]
-const FAILED = [JudgeStatus.WRONG_ANSWER, JudgeStatus.COMPILE_ERROR, JudgeStatus.RUNTIME_ERROR]
-
 /** 能管所有题目：超管，或 problemPermission 为 All */
 function canManageAllProblems(user: AuthUser) {
   return user.adminType === "Super Admin" || user.problemPermission === "All"
@@ -273,132 +252,6 @@ adminTagRoutes.put("/problems/:id/visibility", requireProblemPermission, async (
   return success(c, { visible: !problem.visible })
 })
 
-// ---------------------------------------------------------------- 卡点题目 / AC 趋势
-
-// 路径特意不放在 /problems 下：Hono 按**注册顺序**匹配（不是静态优先），
-// 而 problem.ts 的 `GET /problems/:id` 先注册，会把 `/problems/stuck` 整个吃掉 ——
-// 这两个 handler 曾经从未执行过，生效的还是那边的 requireProblemPermission 而非这里的
-// requireTeacher，而且完全没有报错。换个前缀，结构上就不可能再被遮蔽。
-adminTagRoutes.get("/problem-analytics/stuck", requireTeacher, async (c) => {
-  const failedFilter = sql`filter (where ${inArray(schema.submission.result, FAILED)})`
-  const rows = await db
-    .select({
-      displayId: schema.problem.displayId,
-      title: schema.problem.title,
-      total: count(),
-      accepted:
-        sql<number>`count(*) filter (where ${inArray(schema.submission.result, ACCEPTED)})`.mapWith(
-          Number,
-        ),
-      failed: sql<number>`count(*) ${failedFilter}`.mapWith(Number),
-      failedUsers: sql<number>`count(distinct ${schema.submission.userId}) ${failedFilter}`.mapWith(
-        Number,
-      ),
-    })
-    .from(schema.submission)
-    .innerJoin(schema.problem, eq(schema.submission.problemId, schema.problem.id))
-    /**
-     * 只看公共题，和隔壁 ac-trend 同一个口径。原来这里一个 where 都没有，比赛题
-     * 也进榜 —— 而比赛题的题号是每场比赛各自从 1 开始编的（快照里 61 道不同的题
-     * 都叫「1」），一旦挤进前 40，那一行显示的题号会指向一道根本不存在的公共题。
-     *
-     * 眼下还没发生：前 40 的门槛是 97 人卡住，比赛题最多的一道是 59 人。但两个班
-     * 一起考的场次有 95 人，撞上一道难题就够得着了。
-     *
-     * 加了这条对公共题的数字**没有任何影响**：比赛提交挂的是比赛自己的 problem 行
-     * （快照实测两个方向的交叉都是 0 条），公共题那一行本来就只统计自己的提交。
-     * 顺带让这条查询能用上 0013 的 submission_public_metrics_idx，173ms → 82ms。
-     */
-    .where(isNull(schema.submission.contestId))
-    .groupBy(schema.problem.id, schema.problem.displayId, schema.problem.title)
-    .having(sql`count(distinct ${schema.submission.userId}) ${failedFilter} > 0`)
-    .orderBy(desc(sql`count(distinct ${schema.submission.userId}) ${failedFilter}`))
-    .limit(40)
-  return success(
-    c,
-    rows.map(
-      (row) =>
-        ({
-          problemId: row.displayId,
-          problemTitle: row.title,
-          total: row.total,
-          failed: row.failed,
-          failedUsers: row.failedUsers,
-          acRate: row.total ? rounded((row.accepted / row.total) * 100, 1) : 0,
-        }) satisfies StuckProblem,
-    ),
-  )
-})
-
-adminTagRoutes.get("/problem-analytics/ac-trend", requireTeacher, async (c) => {
-  const currentYear = localYear()
-  // 参数按旧后端的口径夹逼：越界一律回落到默认值，不报错
-  let sinceYear = queryInteger(c.req.query("sinceYear"), 2023)
-  if (sinceYear < 2022 || sinceYear > currentYear) sinceYear = 2023
-  let untilYear = queryInteger(c.req.query("untilYear"), currentYear)
-  if (untilYear < sinceYear || untilYear > currentYear) untilYear = currentYear - 1
-  let minPerYear = queryInteger(c.req.query("minPerYear"), 100)
-  if (![50, 100, 200].includes(minPerYear)) minPerYear = 100
-
-  // 年份按东八区切，和上面 `currentYear` 的夹逼同口径
-  const year = sql<number>`extract(year from ${localTime(schema.submission.createTime)})`.mapWith(
-    Number,
-  )
-  const rows = await db
-    .select({
-      problemId: schema.problem.id,
-      displayId: schema.problem.displayId,
-      title: schema.problem.title,
-      year,
-      total: count(),
-      accepted:
-        sql<number>`count(*) filter (where ${inArray(schema.submission.result, ACCEPTED)})`.mapWith(
-          Number,
-        ),
-    })
-    .from(schema.submission)
-    .innerJoin(schema.problem, eq(schema.submission.problemId, schema.problem.id))
-    .where(and(isNull(schema.submission.contestId), gte(year, sinceYear), lte(year, untilYear)))
-    .groupBy(schema.problem.id, schema.problem.displayId, schema.problem.title, year)
-    .orderBy(asc(schema.problem.id), asc(year))
-
-  const required = new Set<number>()
-  for (let y = sinceYear; y <= untilYear; y += 1) required.add(y)
-
-  const grouped = new Map<number, { displayId: string; title: string; yearly: typeof rows }>()
-  for (const row of rows) {
-    const bucket = grouped.get(row.problemId)
-    if (bucket) bucket.yearly.push(row)
-    else
-      grouped.set(row.problemId, {
-        displayId: row.displayId,
-        title: row.title,
-        yearly: [row],
-      })
-  }
-
-  const result = []
-  for (const entry of grouped.values()) {
-    const years = new Set(entry.yearly.map((row) => row.year))
-    // 每一年都得有数据，且每年提交量都超过门槛 —— 否则趋势没有可比性
-    if (![...required].every((y) => years.has(y))) continue
-    if (!entry.yearly.every((row) => row.total > minPerYear)) continue
-    result.push({
-      problemId: entry.displayId,
-      problemTitle: entry.title,
-      yearly: entry.yearly
-        .map((row) => ({
-          year: row.year,
-          total: row.total,
-          accepted: row.accepted,
-          acRate: row.total ? rounded((row.accepted / row.total) * 100, 1) : 0,
-        }))
-        .sort((left, right) => left.year - right.year),
-    } satisfies AcTrend)
-  }
-  return success(c, result)
-})
-
 // ---------------------------------------------------------------- Python → 流程图
 
 adminTagRoutes.post("/problems/flowchart", requireProblemPermission, async (c) => {
diff --git a/apps/api/src/time.ts b/apps/api/src/time.ts
index dde0762..8e3193d 100644
--- a/apps/api/src/time.ts
+++ b/apps/api/src/time.ts
@@ -95,6 +95,21 @@ export function termStart(now: Date | number | string = new Date()): string {
   return fromWallClock(new Date(Date.UTC(termYear, termMonth - 1, 1))).toISOString()
 }
 
+/**
+ * 学年从哪天零点（东八区）算起：9 月 1 日。返回 `{ year, start }`，`year` 是起始年
+ * （2025 = 25–26 学年），`start` 是 ISO 字符串。SQL 里按学年分组用 `schoolYearOf()`，两边同一个口径。
+ */
+export function schoolYearStart(now: Date | number | string = new Date()) {
+  const wall = toWallClock(now)
+  const year = wall.getUTCMonth() + 1 >= 9 ? wall.getUTCFullYear() : wall.getUTCFullYear() - 1
+  return { year, start: schoolYearStartOf(year) }
+}
+
+/** 某个学年起始年的 9 月 1 日零点（东八区），ISO 字符串 */
+export function schoolYearStartOf(year: number): string {
+  return fromWallClock(new Date(Date.UTC(year, 8, 1))).toISOString()
+}
+
 /** 按北京时间的日历做月份平移，日号超出目标月长度时截到月末，时分秒毫秒原样保留 */
 export function shiftMonthsByCalendar(instant: Date, months: number): Date {
   const wall = toWallClock(instant)
@@ -121,3 +136,8 @@ const TIME_ZONE_SQL = sql.raw(`'${TIME_ZONE}'`)
 export function localTime(column: SQLWrapper) {
   return sql`(${column} at time zone ${TIME_ZONE_SQL})`
 }
+
+/** 时刻所在学年的起始年（9 月起算），和 `schoolYearStart()` 同一个口径 */
+export function schoolYearOf(column: SQLWrapper) {
+  return sql<number>`extract(year from ${localTime(column)} - interval '8 months')::int`
+}
diff --git a/apps/web/src/admin/problem/TopACTrend.vue b/apps/web/src/admin/problem/TopACTrend.vue
deleted file mode 100644
index fef4ae0..0000000
--- a/apps/web/src/admin/problem/TopACTrend.vue
+++ /dev/null
@@ -1,189 +0,0 @@
-<script setup lang="ts">
-import PageHeader from "admin/components/PageHeader.vue"
-import type { AcTrend } from "utils/types"
-import { Line } from "vue-chartjs"
-import {
-  Chart as ChartJS,
-  CategoryScale,
-  Filler,
-  LinearScale,
-  LineElement,
-  PointElement,
-  Title,
-  Tooltip,
-} from "chart.js"
-import { getTopACTrend } from "admin/api"
-import { zonedYear } from "utils/functions"
-
-ChartJS.register(CategoryScale, Filler, LinearScale, LineElement, PointElement, Title, Tooltip)
-
-type ProblemTrend = AcTrend
-
-// 年份按东八区取，和后端 ac-trend 的夹逼口径（`localYear()`）对齐。
-// 用 `new Date().getFullYear()` 的话，跨年那几个小时里浏览器年份可能比后端认定的
-// 年份晚一年，默认的 untilYear 会被后端夹掉、图表悄悄变成另一个区间。
-const currentYear = zonedYear()
-const yearOptions = Array.from({ length: currentYear - 2022 + 1 }, (_, i) => ({
-  label: String(2022 + i),
-  value: 2022 + i,
-}))
-const minPerYearOptions = [
-  { label: "50", value: 50 },
-  { label: "100", value: 100 },
-  { label: "200", value: 200 },
-]
-
-const sinceYear = ref(2023)
-const untilYear = ref(currentYear - 1)
-const minPerYear = ref(100)
-const loading = ref(false)
-const data = ref<ProblemTrend[]>([])
-
-const acLabelPlugin = {
-  id: "acLabel",
-  afterDatasetsDraw(chart: any) {
-    const ctx = chart.ctx
-    chart.data.datasets.forEach((_: any, i: number) => {
-      const meta = chart.getDatasetMeta(i)
-      meta.data.forEach((point: any, j: number) => {
-        const value = chart.data.datasets[i].data[j]
-        if (value === null || value === undefined) return
-        ctx.save()
-        ctx.font = "bold 11px sans-serif"
-        ctx.fillStyle = "rgba(99, 179, 237, 1)"
-        ctx.textAlign = "center"
-        ctx.textBaseline = "bottom"
-        ctx.fillText(`${value}%`, point.x, point.y - 6)
-        ctx.restore()
-      })
-    })
-  },
-}
-
-function getChartData(problem: ProblemTrend) {
-  return {
-    labels: problem.yearly.map((y) => String(y.year)),
-    datasets: [
-      {
-        label: "AC 率",
-        data: problem.yearly.map((y) => y.acRate),
-        fill: true,
-        tension: 0.3,
-        backgroundColor: "rgba(99, 179, 237, 0.2)",
-        borderColor: "rgba(99, 179, 237, 1)",
-        pointBackgroundColor: "rgba(99, 179, 237, 1)",
-        pointRadius: 4,
-      },
-    ],
-  }
-}
-
-function getChartOptions(problem: ProblemTrend) {
-  return {
-    responsive: true,
-    maintainAspectRatio: false,
-    plugins: {
-      title: {
-        display: true,
-        text: `${problem.problemId} · ${problem.problemTitle}`,
-        font: { size: 14 },
-      },
-      tooltip: {
-        callbacks: {
-          label: (ctx: any) => {
-            const entry = problem.yearly[ctx.dataIndex]
-            return `AC 率: ${entry.acRate}% (${entry.accepted}/${entry.total})`
-          },
-        },
-      },
-    },
-    scales: {
-      y: {
-        min: 0,
-        max: 100,
-        ticks: { callback: (v: any) => `${v}%` },
-      },
-      x: {
-        title: { display: true, text: "年份" },
-      },
-    },
-  }
-}
-
-async function fetchData() {
-  loading.value = true
-  try {
-    const res = await getTopACTrend({
-      sinceYear: sinceYear.value,
-      untilYear: untilYear.value,
-      minPerYear: minPerYear.value,
-    })
-    data.value = res
-  } finally {
-    loading.value = false
-  }
-}
-
-onMounted(fetchData)
-</script>
-
-<template>
-  <PageHeader title="年度趋势">
-    <template #extra>
-      <n-tag type="info" size="small" round>共 {{ data.length }} 题</n-tag>
-    </template>
-    <template #filters>
-      <span>年份范围</span>
-      <n-select
-        v-model:value="sinceYear"
-        :options="yearOptions"
-        style="width: 100px"
-        @update:value="fetchData"
-      />
-      <span>—</span>
-      <n-select
-        v-model:value="untilYear"
-        :options="yearOptions"
-        style="width: 100px"
-        @update:value="fetchData"
-      />
-      <span>年提交下限</span>
-      <n-select
-        v-model:value="minPerYear"
-        :options="minPerYearOptions"
-        style="width: 90px"
-        @update:value="fetchData"
-      />
-    </template>
-  </PageHeader>
-  <n-spin :show="loading">
-    <div v-if="!loading && data.length === 0" style="text-align: center; padding: 40px">
-      暂无数据
-    </div>
-    <div v-else class="grid">
-      <div v-for="problem in data" :key="problem.problemId" class="chart-card">
-        <Line
-          :data="getChartData(problem)"
-          :options="getChartOptions(problem)"
-          :plugins="[acLabelPlugin]"
-        />
-      </div>
-    </div>
-  </n-spin>
-</template>
-
-<style scoped>
-.grid {
-  display: grid;
-  grid-template-columns: repeat(2, 1fr);
-  gap: 24px;
-  padding: 8px 0;
-}
-
-.chart-card {
-  height: 260px;
-  border-radius: 8px;
-  padding: 8px;
-  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.08);
-}
-</style>
diff --git a/packages/contract/src/admin.ts b/packages/contract/src/admin.ts
index f0fadb1..490e274 100644
--- a/packages/contract/src/admin.ts
+++ b/packages/contract/src/admin.ts
@@ -534,26 +534,81 @@ export const batchProblemTagResponseSchema = z.object({
   tagCount: z.number().int(),
 })
 
+/**
+ * 卡点分析的一道题（一行）。口径是「人 × 题」：只算**第一次交**落在所选时间段里的那些
+ * 人题对，指标按这对的全部历史算（做没做对、交了几次才对）。比率由前端按人数算，
+ * 这样知识点的汇总能按所选门槛过滤后再加权。
+ */
 export const stuckProblemSchema = z.object({
-  problemId: z.string(),
-  problemTitle: z.string(),
-  total: z.number().int(),
-  failed: z.number().int(),
-  failedUsers: z.number().int(),
-  acRate: z.number(),
+  id: z.number().int(),
+  displayId: z.string(),
+  title: z.string(),
+  /** 知识点（category = knowledge 的标签） */
+  tags: z.array(z.string()),
+  /** 做过的人 */
+  users: z.number().int(),
+  /** 第一次交就对的人 */
+  firstTry: z.number().int(),
+  /** 做对了的人 */
+  solved: z.number().int(),
+  /** 做对的人「做对那次及之前」一共交了几次，加总 —— 除以 solved 就是平均 */
+  solvedTries: z.number().int(),
 })
 
-export const acTrendYearSchema = z.object({
+export const stuckStudentSchema = z.object({
+  username: z.string(),
+  className: z.string().nullable(),
+  firstTry: z.boolean(),
+  solved: z.boolean(),
+  /** 做对了：做对那次及之前交了几次；没做对：一共交了几次 */
+  tries: z.number().int(),
+  /** 第一次交到做对隔了几分钟，没做对是 null */
+  minutes: z.number().int().nullable(),
+  lastResult: z.number().int(),
+  lastSubmissionId: z.string(),
+})
+
+export const stuckProblemDetailSchema = z.object({
+  problem: z.object({
+    id: z.number().int(),
+    displayId: z.string(),
+    title: z.string(),
+    tags: z.array(z.string()),
+  }),
+  students: z.array(stuckStudentSchema),
+  /** 这些人错的那些次，按判题结果分 */
+  errors: z.array(z.object({ result: z.number().int(), count: z.number().int() })),
+  /** 全站历年（学年按 9 月起算，`year` 是起始年），不受班级和时间段影响 */
+  history: z.array(
+    z.object({ year: z.number().int(), users: z.number().int(), firstTry: z.number().int() }),
+  ),
+})
+
+export const yearlySummarySchema = z.object({
+  /** 学年起始年，2025 = 25–26 学年 */
   year: z.number().int(),
-  total: z.number().int(),
-  accepted: z.number().int(),
-  acRate: z.number(),
+  /** 统计到哪天为止（不含），进行中的学年和去年同期才有意义 */
+  until: z.string(),
+  grades: z.array(z.string()),
+  users: z.number().int(),
+  submissions: z.number().int(),
+  problems: z.number().int(),
+  /** 这段时间里第一次做对的人题对 */
+  solvedPairs: z.number().int(),
+  /** 第一次交在这段时间里的人题对，和其中第一次就对的 */
+  startedPairs: z.number().int(),
+  firstTryPairs: z.number().int(),
+  /** 上面那批里做对了的，以及它们做对那次及之前一共交了几次 */
+  solvedStarted: z.number().int(),
+  solvedTries: z.number().int(),
+  cSubmissions: z.number().int(),
 })
 
-export const acTrendSchema = z.object({
-  problemId: z.string(),
-  problemTitle: z.string(),
-  yearly: z.array(acTrendYearSchema),
+export const yearlyOverviewSchema = z.object({
+  /** 从最早的学年到现在这个学年（最后一个是进行中的，只算到今天） */
+  years: z.array(yearlySummarySchema),
+  /** 去年同期：上一个学年开学到「去年的今天」 */
+  lastYearToDate: yearlySummarySchema.nullable(),
 })
 
 // ---------------------------------------------------------------- 自学情况
@@ -943,12 +998,15 @@ export type AdminAiReportListItem = z.infer<typeof adminAiReportListItemSchema>
 export type AdminAiReport = z.infer<typeof adminAiReportSchema>
 export type AdminAiReportList = z.infer<typeof adminAiReportListSchema>
 export type StuckProblem = z.infer<typeof stuckProblemSchema>
+export type StuckStudent = z.infer<typeof stuckStudentSchema>
+export type StuckProblemDetail = z.infer<typeof stuckProblemDetailSchema>
+export type YearlySummary = z.infer<typeof yearlySummarySchema>
+export type YearlyOverview = z.infer<typeof yearlyOverviewSchema>
 export type LearnBoard = z.infer<typeof learnBoardSchema>
 export type LearnBoardStudent = z.infer<typeof learnBoardStudentSchema>
 export type LearnExerciseProgress = z.infer<typeof learnExerciseProgressSchema>
 export type LearnExerciseProgressList = z.infer<typeof learnExerciseProgressListSchema>
 export type LearnExerciseAttempt = z.infer<typeof learnExerciseAttemptSchema>
-export type AcTrend = z.infer<typeof acTrendSchema>
 
 export type AdminTag = z.infer<typeof adminTagSchema>
 export type RenameTagResponse = z.infer<typeof renameTagResponseSchema>
@@ -1010,7 +1068,6 @@ export type CreateProblemSetBadgeRequest = z.infer<typeof createProblemSetBadgeR
 export type UpdateProblemSetBadgeRequest = z.infer<typeof updateProblemSetBadgeRequestSchema>
 export type RenameTagRequest = z.infer<typeof renameTagRequestSchema>
 export type BatchProblemTagRequest = z.infer<typeof batchProblemTagRequestSchema>
-export type AcTrendYear = z.infer<typeof acTrendYearSchema>
 export type GenerateFlowchartRequest = z.infer<typeof generateFlowchartRequestSchema>
 export type GenerateFlowchartResponse = z.infer<typeof generateFlowchartResponseSchema>
 export type UpdateProblemRequest = z.infer<typeof updateProblemRequestSchema>