feat(dashboard): add per-user drill-down for group, model, and endpoint distributions

Click on a group name, model name, or endpoint name in the distribution
tables to expand and show per-user usage breakdown (requests, tokens,
actual cost, standard cost).

Backend: new GET /admin/dashboard/user-breakdown API with group_id,
model, endpoint, endpoint_type filters.
Frontend: clickable rows with expand/collapse sub-table in all three
distribution charts.

frontend/src/api/admin/dashboard.ts

@@ -12,6 +12,7 @@ import type {
   ApiKeyUsageTrendPoint,
   UserUsageTrendPoint,
   UserSpendingRankingResponse,
+  UserBreakdownItem,
   UsageRequestType
 } from '@/types'
 
@@ -156,6 +157,29 @@ export async function getGroupStats(params?: GroupStatsParams): Promise<GroupSta
   return data
 }
 
+export interface UserBreakdownParams {
+  start_date?: string
+  end_date?: string
+  group_id?: number
+  model?: string
+  endpoint?: string
+  endpoint_type?: 'inbound' | 'upstream' | 'path'
+  limit?: number
+}
+
+export interface UserBreakdownResponse {
+  users: UserBreakdownItem[]
+  start_date: string
+  end_date: string
+}
+
+export async function getUserBreakdown(params: UserBreakdownParams): Promise<UserBreakdownResponse> {
+  const { data } = await apiClient.get<UserBreakdownResponse>('/admin/dashboard/user-breakdown', {
+    params
+  })
+  return data
+}
+
 /**
  * Get dashboard snapshot v2 (aggregated response for heavy admin pages).
  */

frontend/src/components/charts/EndpointDistributionChart.vue

@@ -87,27 +87,40 @@
             </tr>
           </thead>
           <tbody>
-            <tr
-              v-for="item in displayEndpointStats"
-              :key="item.endpoint"
-              class="border-t border-gray-100 dark:border-gray-700"
-            >
-              <td class="max-w-[180px] truncate py-1.5 font-medium text-gray-900 dark:text-white" :title="item.endpoint">
-                {{ item.endpoint }}
-              </td>
-              <td class="py-1.5 text-right text-gray-600 dark:text-gray-400">
-                {{ formatNumber(item.requests) }}
-              </td>
-              <td class="py-1.5 text-right text-gray-600 dark:text-gray-400">
-                {{ formatTokens(item.total_tokens) }}
-              </td>
-              <td class="py-1.5 text-right text-green-600 dark:text-green-400">
-                ${{ formatCost(item.actual_cost) }}
-              </td>
-              <td class="py-1.5 text-right text-gray-400 dark:text-gray-500">
-                ${{ formatCost(item.cost) }}
-              </td>
-            </tr>
+            <template v-for="item in displayEndpointStats" :key="item.endpoint">
+              <tr
+                class="border-t border-gray-100 cursor-pointer transition-colors hover:bg-gray-50 dark:border-gray-700 dark:hover:bg-dark-700/40"
+                @click="toggleBreakdown(item.endpoint)"
+              >
+                <td class="max-w-[180px] truncate py-1.5 font-medium text-blue-600 hover:text-blue-800 dark:text-blue-400 dark:hover:text-blue-300" :title="item.endpoint">
+                  <span class="inline-flex items-center gap-1">
+                    <svg v-if="expandedKey === item.endpoint" class="h-3 w-3 shrink-0" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M19 9l-7 7-7-7"/></svg>
+                    <svg v-else class="h-3 w-3 shrink-0" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 5l7 7-7 7"/></svg>
+                    {{ item.endpoint }}
+                  </span>
+                </td>
+                <td class="py-1.5 text-right text-gray-600 dark:text-gray-400">
+                  {{ formatNumber(item.requests) }}
+                </td>
+                <td class="py-1.5 text-right text-gray-600 dark:text-gray-400">
+                  {{ formatTokens(item.total_tokens) }}
+                </td>
+                <td class="py-1.5 text-right text-green-600 dark:text-green-400">
+                  ${{ formatCost(item.actual_cost) }}
+                </td>
+                <td class="py-1.5 text-right text-gray-400 dark:text-gray-500">
+                  ${{ formatCost(item.cost) }}
+                </td>
+              </tr>
+              <tr v-if="expandedKey === item.endpoint">
+                <td colspan="5" class="p-0">
+                  <UserBreakdownSubTable
+                    :items="breakdownItems"
+                    :loading="breakdownLoading"
+                  />
+                </td>
+              </tr>
+            </template>
           </tbody>
         </table>
       </div>
@@ -119,12 +132,14 @@
 </template>
 
 <script setup lang="ts">
-import { computed } from 'vue'
+import { computed, ref } from 'vue'
 import { useI18n } from 'vue-i18n'
 import { Chart as ChartJS, ArcElement, Tooltip, Legend } from 'chart.js'
 import { Doughnut } from 'vue-chartjs'
 import LoadingSpinner from '@/components/common/LoadingSpinner.vue'
-import type { EndpointStat } from '@/types'
+import UserBreakdownSubTable from './UserBreakdownSubTable.vue'
+import type { EndpointStat, UserBreakdownItem } from '@/types'
+import { getUserBreakdown } from '@/api/admin/dashboard'
 
 ChartJS.register(ArcElement, Tooltip, Legend)
 
@@ -144,6 +159,8 @@ const props = withDefaults(
     source?: EndpointSource
     showMetricToggle?: boolean
     showSourceToggle?: boolean
+    startDate?: string
+    endDate?: string
   }>(),
   {
     upstreamEndpointStats: () => [],
@@ -162,6 +179,33 @@ const emit = defineEmits<{
   'update:source': [value: EndpointSource]
 }>()
 
+const expandedKey = ref<string | null>(null)
+const breakdownItems = ref<UserBreakdownItem[]>([])
+const breakdownLoading = ref(false)
+
+const toggleBreakdown = async (endpoint: string) => {
+  if (expandedKey.value === endpoint) {
+    expandedKey.value = null
+    return
+  }
+  expandedKey.value = endpoint
+  breakdownLoading.value = true
+  breakdownItems.value = []
+  try {
+    const res = await getUserBreakdown({
+      start_date: props.startDate,
+      end_date: props.endDate,
+      endpoint,
+      endpoint_type: props.source,
+    })
+    breakdownItems.value = res.users || []
+  } catch {
+    breakdownItems.value = []
+  } finally {
+    breakdownLoading.value = false
+  }
+}
+
 const chartColors = [
   '#3b82f6',
   '#10b981',

frontend/src/components/charts/GroupDistributionChart.vue

@@ -37,7 +37,7 @@
       <div class="h-48 w-48">
         <Doughnut :data="chartData" :options="doughnutOptions" />
       </div>
-      <div class="max-h-48 flex-1 overflow-y-auto">
+      <div class="max-h-64 flex-1 overflow-y-auto">
         <table class="w-full text-xs">
           <thead>
             <tr class="text-gray-500 dark:text-gray-400">
@@ -49,30 +49,46 @@
             </tr>
           </thead>
           <tbody>
-            <tr
-              v-for="group in displayGroupStats"
-              :key="group.group_id"
-              class="border-t border-gray-100 dark:border-gray-700"
-            >
-              <td
-                class="max-w-[100px] truncate py-1.5 font-medium text-gray-900 dark:text-white"
-                :title="group.group_name || String(group.group_id)"
+            <template v-for="group in displayGroupStats" :key="group.group_id">
+              <tr
+                class="border-t border-gray-100 transition-colors dark:border-gray-700"
+                :class="group.group_id > 0 ? 'cursor-pointer hover:bg-gray-50 dark:hover:bg-dark-700/40' : ''"
+                @click="group.group_id > 0 && toggleBreakdown('group', group.group_id)"
               >
-                {{ group.group_name || t('admin.dashboard.noGroup') }}
-              </td>
-              <td class="py-1.5 text-right text-gray-600 dark:text-gray-400">
-                {{ formatNumber(group.requests) }}
-              </td>
-              <td class="py-1.5 text-right text-gray-600 dark:text-gray-400">
-                {{ formatTokens(group.total_tokens) }}
-              </td>
-              <td class="py-1.5 text-right text-green-600 dark:text-green-400">
-                ${{ formatCost(group.actual_cost) }}
-              </td>
-              <td class="py-1.5 text-right text-gray-400 dark:text-gray-500">
-                ${{ formatCost(group.cost) }}
-              </td>
-            </tr>
+                <td
+                  class="max-w-[100px] truncate py-1.5 font-medium"
+                  :class="group.group_id > 0 ? 'text-blue-600 hover:text-blue-800 dark:text-blue-400 dark:hover:text-blue-300' : 'text-gray-900 dark:text-white'"
+                  :title="group.group_name || String(group.group_id)"
+                >
+                  <span class="inline-flex items-center gap-1">
+                    <svg v-if="group.group_id > 0 && expandedKey === `group-${group.group_id}`" class="h-3 w-3 shrink-0" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M19 9l-7 7-7-7"/></svg>
+                    <svg v-else-if="group.group_id > 0" class="h-3 w-3 shrink-0" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 5l7 7-7 7"/></svg>
+                    {{ group.group_name || t('admin.dashboard.noGroup') }}
+                  </span>
+                </td>
+                <td class="py-1.5 text-right text-gray-600 dark:text-gray-400">
+                  {{ formatNumber(group.requests) }}
+                </td>
+                <td class="py-1.5 text-right text-gray-600 dark:text-gray-400">
+                  {{ formatTokens(group.total_tokens) }}
+                </td>
+                <td class="py-1.5 text-right text-green-600 dark:text-green-400">
+                  ${{ formatCost(group.actual_cost) }}
+                </td>
+                <td class="py-1.5 text-right text-gray-400 dark:text-gray-500">
+                  ${{ formatCost(group.cost) }}
+                </td>
+              </tr>
+              <!-- User breakdown sub-rows -->
+              <tr v-if="expandedKey === `group-${group.group_id}`">
+                <td colspan="5" class="p-0">
+                  <UserBreakdownSubTable
+                    :items="breakdownItems"
+                    :loading="breakdownLoading"
+                  />
+                </td>
+              </tr>
+            </template>
           </tbody>
         </table>
       </div>
@@ -87,12 +103,14 @@
 </template>
 
 <script setup lang="ts">
-import { computed } from 'vue'
+import { computed, ref } from 'vue'
 import { useI18n } from 'vue-i18n'
 import { Chart as ChartJS, ArcElement, Tooltip, Legend } from 'chart.js'
 import { Doughnut } from 'vue-chartjs'
 import LoadingSpinner from '@/components/common/LoadingSpinner.vue'
-import type { GroupStat } from '@/types'
+import UserBreakdownSubTable from './UserBreakdownSubTable.vue'
+import type { GroupStat, UserBreakdownItem } from '@/types'
+import { getUserBreakdown } from '@/api/admin/dashboard'
 
 ChartJS.register(ArcElement, Tooltip, Legend)
 
@@ -105,6 +123,8 @@ const props = withDefaults(defineProps<{
   loading?: boolean
   metric?: DistributionMetric
   showMetricToggle?: boolean
+  startDate?: string
+  endDate?: string
 }>(), {
   loading: false,
   metric: 'tokens',
@@ -115,6 +135,33 @@ const emit = defineEmits<{
   'update:metric': [value: DistributionMetric]
 }>()
 
+const expandedKey = ref<string | null>(null)
+const breakdownItems = ref<UserBreakdownItem[]>([])
+const breakdownLoading = ref(false)
+
+const toggleBreakdown = async (type: string, id: number | string) => {
+  const key = `${type}-${id}`
+  if (expandedKey.value === key) {
+    expandedKey.value = null
+    return
+  }
+  expandedKey.value = key
+  breakdownLoading.value = true
+  breakdownItems.value = []
+  try {
+    const res = await getUserBreakdown({
+      start_date: props.startDate,
+      end_date: props.endDate,
+      group_id: Number(id),
+    })
+    breakdownItems.value = res.users || []
+  } catch {
+    breakdownItems.value = []
+  } finally {
+    breakdownLoading.value = false
+  }
+}
+
 const chartColors = [
   '#3b82f6',
   '#10b981',

frontend/src/components/charts/ModelDistributionChart.vue

@@ -71,7 +71,7 @@
       <div class="h-48 w-48">
         <Doughnut :data="chartData" :options="doughnutOptions" />
       </div>
-      <div class="max-h-48 flex-1 overflow-y-auto">
+      <div class="max-h-64 flex-1 overflow-y-auto">
         <table class="w-full text-xs">
           <thead>
             <tr class="text-gray-500 dark:text-gray-400">
@@ -83,30 +83,43 @@
             </tr>
           </thead>
           <tbody>
-            <tr
-              v-for="model in displayModelStats"
-              :key="model.model"
-              class="border-t border-gray-100 dark:border-gray-700"
-            >
-              <td
-                class="max-w-[100px] truncate py-1.5 font-medium text-gray-900 dark:text-white"
-                :title="model.model"
+            <template v-for="model in displayModelStats" :key="model.model">
+              <tr
+                class="border-t border-gray-100 cursor-pointer transition-colors hover:bg-gray-50 dark:border-gray-700 dark:hover:bg-dark-700/40"
+                @click="toggleBreakdown('model', model.model)"
               >
-                {{ model.model }}
-              </td>
-              <td class="py-1.5 text-right text-gray-600 dark:text-gray-400">
-                {{ formatNumber(model.requests) }}
-              </td>
-              <td class="py-1.5 text-right text-gray-600 dark:text-gray-400">
-                {{ formatTokens(model.total_tokens) }}
-              </td>
-              <td class="py-1.5 text-right text-green-600 dark:text-green-400">
-                ${{ formatCost(model.actual_cost) }}
-              </td>
-              <td class="py-1.5 text-right text-gray-400 dark:text-gray-500">
-                ${{ formatCost(model.cost) }}
-              </td>
-            </tr>
+                <td
+                  class="max-w-[100px] truncate py-1.5 font-medium text-blue-600 hover:text-blue-800 dark:text-blue-400 dark:hover:text-blue-300"
+                  :title="model.model"
+                >
+                  <span class="inline-flex items-center gap-1">
+                    <svg v-if="expandedKey === `model-${model.model}`" class="h-3 w-3 shrink-0" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M19 9l-7 7-7-7"/></svg>
+                    <svg v-else class="h-3 w-3 shrink-0" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 5l7 7-7 7"/></svg>
+                    {{ model.model }}
+                  </span>
+                </td>
+                <td class="py-1.5 text-right text-gray-600 dark:text-gray-400">
+                  {{ formatNumber(model.requests) }}
+                </td>
+                <td class="py-1.5 text-right text-gray-600 dark:text-gray-400">
+                  {{ formatTokens(model.total_tokens) }}
+                </td>
+                <td class="py-1.5 text-right text-green-600 dark:text-green-400">
+                  ${{ formatCost(model.actual_cost) }}
+                </td>
+                <td class="py-1.5 text-right text-gray-400 dark:text-gray-500">
+                  ${{ formatCost(model.cost) }}
+                </td>
+              </tr>
+              <tr v-if="expandedKey === `model-${model.model}`">
+                <td colspan="5" class="p-0">
+                  <UserBreakdownSubTable
+                    :items="breakdownItems"
+                    :loading="breakdownLoading"
+                  />
+                </td>
+              </tr>
+            </template>
           </tbody>
         </table>
       </div>
@@ -193,7 +206,9 @@ import { useI18n } from 'vue-i18n'
 import { Chart as ChartJS, ArcElement, Tooltip, Legend } from 'chart.js'
 import { Doughnut } from 'vue-chartjs'
 import LoadingSpinner from '@/components/common/LoadingSpinner.vue'
-import type { ModelStat, UserSpendingRankingItem } from '@/types'
+import UserBreakdownSubTable from './UserBreakdownSubTable.vue'
+import type { ModelStat, UserSpendingRankingItem, UserBreakdownItem } from '@/types'
+import { getUserBreakdown } from '@/api/admin/dashboard'
 
 ChartJS.register(ArcElement, Tooltip, Legend)
 
@@ -213,6 +228,8 @@ const props = withDefaults(defineProps<{
   showMetricToggle?: boolean
   rankingLoading?: boolean
   rankingError?: boolean
+  startDate?: string
+  endDate?: string
 }>(), {
   enableRankingView: false,
   rankingItems: () => [],
@@ -226,6 +243,33 @@ const props = withDefaults(defineProps<{
   rankingError: false
 })
 
+const expandedKey = ref<string | null>(null)
+const breakdownItems = ref<UserBreakdownItem[]>([])
+const breakdownLoading = ref(false)
+
+const toggleBreakdown = async (type: string, id: string) => {
+  const key = `${type}-${id}`
+  if (expandedKey.value === key) {
+    expandedKey.value = null
+    return
+  }
+  expandedKey.value = key
+  breakdownLoading.value = true
+  breakdownItems.value = []
+  try {
+    const res = await getUserBreakdown({
+      start_date: props.startDate,
+      end_date: props.endDate,
+      model: id,
+    })
+    breakdownItems.value = res.users || []
+  } catch {
+    breakdownItems.value = []
+  } finally {
+    breakdownLoading.value = false
+  }
+}
+
 const emit = defineEmits<{
   'update:metric': [value: DistributionMetric]
   'ranking-click': [item: UserSpendingRankingItem]

frontend/src/components/charts/UserBreakdownSubTable.vue

@@ -0,0 +1,71 @@
+<template>
+  <div class="bg-gray-50/50 dark:bg-dark-700/30">
+    <div v-if="loading" class="flex items-center justify-center py-3">
+      <LoadingSpinner />
+    </div>
+    <div v-else-if="items.length === 0" class="py-2 text-center text-xs text-gray-400">
+      {{ t('admin.dashboard.noDataAvailable') }}
+    </div>
+    <table v-else class="w-full text-xs">
+      <thead>
+        <tr class="text-gray-400 dark:text-gray-500">
+          <th class="py-1 pl-6 text-left">{{ t('admin.dashboard.spendingRankingUser') }}</th>
+          <th class="py-1 text-right">{{ t('admin.dashboard.requests') }}</th>
+          <th class="py-1 text-right">{{ t('admin.dashboard.tokens') }}</th>
+          <th class="py-1 text-right">{{ t('admin.dashboard.actual') }}</th>
+          <th class="py-1 pr-1 text-right">{{ t('admin.dashboard.standard') }}</th>
+        </tr>
+      </thead>
+      <tbody>
+        <tr
+          v-for="user in items"
+          :key="user.user_id"
+          class="border-t border-gray-100/50 dark:border-gray-700/50"
+        >
+          <td class="max-w-[120px] truncate py-1 pl-6 text-gray-600 dark:text-gray-300" :title="user.email">
+            {{ user.email || `User #${user.user_id}` }}
+          </td>
+          <td class="py-1 text-right text-gray-500 dark:text-gray-400">
+            {{ user.requests.toLocaleString() }}
+          </td>
+          <td class="py-1 text-right text-gray-500 dark:text-gray-400">
+            {{ formatTokens(user.total_tokens) }}
+          </td>
+          <td class="py-1 text-right text-green-600 dark:text-green-400">
+            ${{ formatCost(user.actual_cost) }}
+          </td>
+          <td class="py-1 pr-1 text-right text-gray-400 dark:text-gray-500">
+            ${{ formatCost(user.cost) }}
+          </td>
+        </tr>
+      </tbody>
+    </table>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { useI18n } from 'vue-i18n'
+import LoadingSpinner from '@/components/common/LoadingSpinner.vue'
+import type { UserBreakdownItem } from '@/types'
+
+const { t } = useI18n()
+
+defineProps<{
+  items: UserBreakdownItem[]
+  loading?: boolean
+}>()
+
+const formatTokens = (value: number): string => {
+  if (value >= 1_000_000_000) return `${(value / 1_000_000_000).toFixed(2)}B`
+  if (value >= 1_000_000) return `${(value / 1_000_000).toFixed(2)}M`
+  if (value >= 1_000) return `${(value / 1_000).toFixed(2)}K`
+  return value.toLocaleString()
+}
+
+const formatCost = (value: number): string => {
+  if (value >= 1000) return (value / 1000).toFixed(2) + 'K'
+  if (value >= 1) return value.toFixed(2)
+  if (value >= 0.01) return value.toFixed(3)
+  return value.toFixed(4)
+}
+</script>

frontend/src/types/index.ts

@@ -1202,6 +1202,15 @@ export interface GroupStat {
   actual_cost: number // 实际扣除
 }
 
+export interface UserBreakdownItem {
+  user_id: number
+  email: string
+  requests: number
+  total_tokens: number
+  cost: number
+  actual_cost: number
+}
+
 export interface UserUsageTrendPoint {
   date: string
   user_id: number

frontend/src/views/admin/DashboardView.vue

@@ -246,6 +246,8 @@
               :loading="chartsLoading"
               :ranking-loading="rankingLoading"
               :ranking-error="rankingError"
+              :start-date="startDate"
+              :end-date="endDate"
               @ranking-click="goToUserUsage"
             />
             <TokenUsageTrend :trend-data="trendData" :loading="chartsLoading" />

frontend/src/views/admin/UsageView.vue

@@ -18,12 +18,16 @@
             :model-stats="modelStats"
             :loading="chartsLoading"
             :show-metric-toggle="true"
+            :start-date="startDate"
+            :end-date="endDate"
           />
           <GroupDistributionChart
             v-model:metric="groupDistributionMetric"
             :group-stats="groupStats"
             :loading="chartsLoading"
             :show-metric-toggle="true"
+            :start-date="startDate"
+            :end-date="endDate"
           />
         </div>
         <div class="grid grid-cols-1 gap-6 lg:grid-cols-2">
@@ -37,6 +41,8 @@
             :show-source-toggle="true"
             :show-metric-toggle="true"
             :title="t('usage.endpointDistribution')"
+            :start-date="startDate"
+            :end-date="endDate"
           />
           <TokenUsageTrend :trend-data="trendData" :loading="chartsLoading" />
         </div>