Use shared clock for active usage timers

frontend/src/features/usage/components/__tests__/ElapsedTimeText.spec.ts

@@ -0,0 +1,56 @@
+import { afterEach, describe, expect, it } from 'vitest'
+import { createApp, type App } from 'vue'
+import ElapsedTimeText from '../ElapsedTimeText.vue'
+
+const mountedApps: Array<{ app: App, root: HTMLElement }> = []
+
+function mountElapsedTimeText(props: Record<string, unknown>) {
+  const root = document.createElement('div')
+  document.body.appendChild(root)
+
+  const app = createApp(ElapsedTimeText, props)
+  app.mount(root)
+  mountedApps.push({ app, root })
+  return root
+}
+
+afterEach(() => {
+  for (const { app, root } of mountedApps.splice(0)) {
+    app.unmount()
+    root.remove()
+  }
+})
+
+describe('ElapsedTimeText', () => {
+  it('uses the supplied display clock for active requests', () => {
+    const root = mountElapsedTimeText({
+      createdAt: '2026-05-28T12:00:00Z',
+      status: 'streaming',
+      responseTimeMs: 10_000,
+      displayNowMs: Date.parse('2026-05-28T12:00:40Z'),
+    })
+
+    expect(root.textContent).toBe('40.00s')
+  })
+
+  it('keeps terminal requests pinned to the backend final duration', () => {
+    const root = mountElapsedTimeText({
+      createdAt: '2026-05-28T12:00:00Z',
+      status: 'completed',
+      responseTimeMs: 42_340,
+      displayNowMs: Date.parse('2026-05-28T12:01:30Z'),
+    })
+
+    expect(root.textContent).toBe('42.34s')
+  })
+
+  it('clamps active elapsed time at zero when the display clock is behind', () => {
+    const root = mountElapsedTimeText({
+      createdAt: '2026-05-28T12:00:40Z',
+      status: 'pending',
+      displayNowMs: Date.parse('2026-05-28T12:00:00Z'),
+    })
+
+    expect(root.textContent).toBe('0.00s')
+  })
+})

frontend/src/features/usage/components/__tests__/UsageRecordsTable.spec.ts

@@ -91,8 +91,16 @@ vi.mock('lucide-vue-next', async () => {
 vi.mock('../ElapsedTimeText.vue', () => ({
   default: defineComponent({
     name: 'ElapsedTimeTextStub',
-    setup() {
-      return () => h('span', 'elapsed')
+    props: {
+      displayNowMs: {
+        type: Number,
+        default: null,
+      },
+    },
+    setup(props) {
+      return () => h('span', {
+        'data-display-now-ms': props.displayNowMs == null ? '' : String(props.displayNowMs),
+      }, 'elapsed')
     },
   }),
 }))
@@ -243,6 +251,16 @@ describe('UsageRecordsTable', () => {
     expect(root.querySelector('[data-active-latency-state="waiting-first-byte"]')).toBeNull()
   })
 
+  it('passes the shared display clock to active elapsed text', () => {
+    const root = mountUsageRecordsTable([buildRecord({
+      status: 'streaming',
+      response_time_ms: null,
+      first_byte_time_ms: 500,
+    })], { displayNowMs: 1_779_999_000_000 })
+
+    expect(root.querySelector('[data-display-now-ms="1779999000000"]')).not.toBeNull()
+  })
+
   it('shows failed when Codex image progress fails before the usage record finalizes', () => {
     const root = mountUsageRecordsTable([buildRecord({
       status: 'pending',