fix(frontend): align usage APIs with Rust routes

frontend/src/api/__tests__/usage-contract.spec.ts

@@ -0,0 +1,117 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+const { getMock, cachedRequestMock, dedupedRequestMock, buildCacheKeyMock } = vi.hoisted(() => ({
+  getMock: vi.fn(),
+  cachedRequestMock: vi.fn(async (_key: string, fn: () => Promise<unknown>) => fn()),
+  dedupedRequestMock: vi.fn(async (_key: string, fn: () => Promise<unknown>) => fn()),
+  buildCacheKeyMock: vi.fn(() => 'cache-key'),
+}))
+
+vi.mock('@/api/client', () => ({
+  default: {
+    get: getMock,
+  },
+}))
+
+vi.mock('@/utils/cache', () => ({
+  cachedRequest: cachedRequestMock,
+  dedupedRequest: dedupedRequestMock,
+  buildCacheKey: buildCacheKeyMock,
+}))
+
+import { usageApi } from '@/api/usage'
+
+describe('usageApi contract alignment', () => {
+  beforeEach(() => {
+    getMock.mockReset()
+    cachedRequestMock.mockClear()
+    dedupedRequestMock.mockClear()
+    buildCacheKeyMock.mockClear()
+  })
+
+  it('loads current-user usage records from the Rust usage endpoint and normalizes pagination', async () => {
+    getMock.mockResolvedValueOnce({
+      data: {
+        records: [{ id: 'record-1' }],
+        pagination: {
+          total: 42,
+          limit: 10,
+          offset: 10,
+          has_more: true,
+        },
+      },
+    })
+
+    const result = await usageApi.getUsageRecords({
+      page: 2,
+      page_size: 10,
+      start_date: '2026-05-01',
+      end_date: '2026-05-16',
+    })
+
+    expect(getMock).toHaveBeenCalledWith('/api/users/me/usage', {
+      params: {
+        limit: 10,
+        offset: 10,
+        start_date: '2026-05-01',
+        end_date: '2026-05-16',
+      },
+    })
+    expect(result).toEqual({
+      records: [{ id: 'record-1' }],
+      total: 42,
+      page: 2,
+      page_size: 10,
+    })
+  })
+
+  it('loads admin usage for a specific user from admin usage endpoints', async () => {
+    getMock
+      .mockResolvedValueOnce({
+        data: {
+          total_requests: 7,
+          total_tokens: 99,
+          total_cost: 12.34,
+          avg_response_time: 456,
+        },
+      })
+      .mockResolvedValueOnce({
+        data: {
+          records: [{ id: 'record-2' }],
+          total: 1,
+          limit: 25,
+          offset: 0,
+        },
+      })
+
+    const result = await usageApi.getUserUsage('user-123', {
+      page: 1,
+      page_size: 25,
+      model: 'gpt-5.5',
+    })
+
+    expect(getMock).toHaveBeenNthCalledWith(1, '/api/admin/usage/stats', {
+      params: {
+        user_id: 'user-123',
+        model: 'gpt-5.5',
+      },
+    })
+    expect(getMock).toHaveBeenNthCalledWith(2, '/api/admin/usage/records', {
+      params: {
+        user_id: 'user-123',
+        limit: 25,
+        offset: 0,
+        model: 'gpt-5.5',
+      },
+    })
+    expect(result).toEqual({
+      records: [{ id: 'record-2' }],
+      stats: {
+        total_requests: 7,
+        total_tokens: 99,
+        total_cost: 12.34,
+        avg_response_time: 456,
+      },
+    })
+  })
+})