revert: remove usage elapsed clock calibration

frontend/src/api/__tests__/serverTiming.spec.ts

@@ -1,62 +0,0 @@
-import { describe, expect, it } from 'vitest'
-import {
-  SERVER_NOW_UNIX_MS_HEADER,
-  buildServerTimingMetadata,
-  readServerNowUnixMsFromHeaders,
-  withServerTiming,
-} from '../serverTiming'
-
-describe('serverTiming', () => {
-  it('reads server time from response headers', () => {
-    expect(readServerNowUnixMsFromHeaders({
-      [SERVER_NOW_UNIX_MS_HEADER]: '1779999000123',
-    })).toBe(1_779_999_000_123)
-    expect(readServerNowUnixMsFromHeaders({
-      'X-Aether-Server-Now-Unix-Ms': '1779999000456',
-    })).toBe(1_779_999_000_456)
-  })
-
-  it('does not fall back to body fields', () => {
-    const timing = buildServerTimingMetadata({
-      headers: {},
-      data: {
-        server_now_unix_ms: 1_779_999_000_123,
-      },
-    }, 1_000, 1_100)
-
-    expect(timing).toBeUndefined()
-  })
-
-  it('builds metadata with round trip duration', () => {
-    const timing = buildServerTimingMetadata({
-      headers: {
-        [SERVER_NOW_UNIX_MS_HEADER]: '1050',
-      },
-    }, 1_000, 1_125)
-
-    expect(timing).toEqual({
-      server_now_unix_ms: 1_050,
-      client_send_unix_ms: 1_000,
-      client_receive_unix_ms: 1_125,
-      round_trip_ms: 125,
-    })
-  })
-
-  it('returns the original payload when the header is missing or invalid', () => {
-    const payload = { records: [] }
-
-    expect(withServerTiming({ data: payload, headers: {} }, 1_000)).toBe(payload)
-    expect(withServerTiming({
-      data: payload,
-      headers: { [SERVER_NOW_UNIX_MS_HEADER]: 'not-a-number' },
-    }, 1_000)).toBe(payload)
-    expect(withServerTiming({
-      data: payload,
-      headers: { [SERVER_NOW_UNIX_MS_HEADER]: '0' },
-    }, 1_000)).toBe(payload)
-    expect(withServerTiming({
-      data: payload,
-      headers: { [SERVER_NOW_UNIX_MS_HEADER]: '1050.5' },
-    }, 1_000)).toBe(payload)
-  })
-})

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

@@ -1,4 +1,4 @@
-import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
 
 const { getMock, cachedRequestMock, dedupedRequestMock, buildCacheKeyMock } = vi.hoisted(() => ({
   getMock: vi.fn(),
@@ -29,10 +29,6 @@ describe('usageApi contract alignment', () => {
     buildCacheKeyMock.mockClear()
   })
 
-  afterEach(() => {
-    vi.restoreAllMocks()
-  })
-
   it('loads current-user usage records from the Rust usage endpoint and normalizes pagination', async () => {
     getMock.mockResolvedValueOnce({
       data: {
@@ -119,56 +115,6 @@ describe('usageApi contract alignment', () => {
     })
   })
 
-  it('captures admin user usage server timing when the records request resolves', async () => {
-    let now = 1_000
-    vi.spyOn(Date, 'now').mockImplementation(() => now)
-
-    let resolveStats: ((value: unknown) => void) | null = null
-    getMock.mockImplementation((url: string) => {
-      if (url === '/api/admin/usage/stats') {
-        return new Promise(resolve => {
-          resolveStats = resolve
-        })
-      }
-      if (url === '/api/admin/usage/records') {
-        return Promise.resolve({
-          headers: {
-            'x-aether-server-now-unix-ms': '10050',
-          },
-          data: {
-            records: [{ id: 'record-3' }],
-            total: 1,
-            limit: 25,
-            offset: 0,
-          },
-        })
-      }
-      return Promise.reject(new Error(`unexpected url: ${url}`))
-    })
-
-    const resultPromise = usageApi.getUserUsage('user-123', { page: 1, page_size: 25 })
-    now = 1_100
-    await Promise.resolve()
-    now = 20_000
-    resolveStats?.({
-      data: {
-        total_requests: 1,
-        total_tokens: 10,
-        total_cost: 0.1,
-        avg_response_time: 500,
-      },
-    })
-
-    const result = await resultPromise
-
-    expect(result.server_timing).toEqual({
-      server_now_unix_ms: 10_050,
-      client_send_unix_ms: 1_000,
-      client_receive_unix_ms: 1_100,
-      round_trip_ms: 100,
-    })
-  })
-
   it('uses an extended timeout and cache bypass option for admin analytics', async () => {
     getMock
       .mockResolvedValueOnce({