diff --git a/frontend-vue/tests/backoff-cap.test.ts b/frontend-vue/tests/backoff-cap.test.ts
new file mode 100644
index 00000000..478fa95c
--- /dev/null
+++ b/frontend-vue/tests/backoff-cap.test.ts
@@ -0,0 +1,110 @@
+import { test } from 'node:test'
+import assert from 'node:assert/strict'
+import {
+  getTaskPollBackoffMs,
+  configureTaskPolling,
+  resetTaskPollingConfig,
+} from '../src/shared/task-progress-config.ts'
+import { useTaskProgressLoop } from '../src/shared/composables/useTaskProgressLoop.ts'
+
+test('test_backoff_cap_reached', () => {
+  resetTaskPollingConfig()
+  assert.equal(getTaskPollBackoffMs(4), 8000)
+  assert.equal(getTaskPollBackoffMs(5), 10000, 'attempt 5 达到封顶')
+})
+
+test('test_backoff_stays_capped', () => {
+  resetTaskPollingConfig()
+  for (const attempt of [5, 6, 7, 10, 50]) {
+    assert.equal(getTaskPollBackoffMs(attempt), 10000, `attempt ${attempt} 保持 maxMs`)
+  }
+})
+
+test('test_cap_with_low_max', () => {
+  resetTaskPollingConfig()
+  configureTaskPolling({ backoffMaxMs: 1500 })
+  assert.equal(getTaskPollBackoffMs(0), 500)
+  assert.equal(getTaskPollBackoffMs(1), 1000)
+  assert.equal(getTaskPollBackoffMs(2), 1500, '低 maxMs 提前封顶')
+  assert.equal(getTaskPollBackoffMs(3), 1500)
+  resetTaskPollingConfig()
+})
+
+test('test_cap_with_high_factor', () => {
+  resetTaskPollingConfig()
+  configureTaskPolling({ backoffFactor: 5 })
+  assert.equal(getTaskPollBackoffMs(0), 500)
+  assert.equal(getTaskPollBackoffMs(1), 2500)
+  assert.equal(getTaskPollBackoffMs(2), 10000, '高 factor 快速封顶')
+  assert.equal(getTaskPollBackoffMs(3), 10000)
+  resetTaskPollingConfig()
+})
+
+test('test_cap_resets_after_success', () => {
+  resetTaskPollingConfig()
+  // 封顶只由 attempt 驱动：attempt 归 0 即从基数重新开始
+  assert.equal(getTaskPollBackoffMs(0), 500)
+  assert.equal(getTaskPollBackoffMs(50), 10000)
+  assert.equal(getTaskPollBackoffMs(0), 500, '成功后从 500 起')
+  assert.equal(getTaskPollBackoffMs(1), 1000)
+})
+
+test('test_cap_attempt_boundary', () => {
+  resetTaskPollingConfig()
+  configureTaskPolling({ backoffMaxMs: 2000 })
+  // 恰好等于封顶那一档：base × factor^1 = 1000 < 2000；^2 = 2000 = 封顶
+  assert.equal(getTaskPollBackoffMs(1), 1000)
+  assert.equal(getTaskPollBackoffMs(2), 2000, '恰等于 maxMs 不溢出')
+  assert.equal(getTaskPollBackoffMs(3), 2000)
+  resetTaskPollingConfig()
+})
+
+test('test_cap_integration_loop', async () => {
+  resetTaskPollingConfig()
+  const storage = new Map<string, string>()
+  ;(globalThis as Record<string, unknown>).window = {
+    localStorage: {
+      getItem: (k: string) => storage.get(k) ?? null,
+      setItem: (k: string, v: string) => { storage.set(k, v) },
+      removeItem: (k: string) => { storage.delete(k) },
+    },
+    setTimeout: (fn: () => void, ms: number) => globalThis.setTimeout(fn, ms),
+    clearTimeout: (id: unknown) => globalThis.clearTimeout(id as number),
+    setInterval: (fn: () => void, ms: number) => globalThis.setInterval(fn, ms),
+    clearInterval: (id: unknown) => globalThis.clearInterval(id as number),
+  }
+  const attempts: number[] = []
+  const loop = useTaskProgressLoop<{ taskId?: number; status?: string }>({
+    scope: 'cap-integration',
+    fetchProgress: async () => { throw new Error('net') },
+    extractTaskId: (d) => d?.taskId,
+    extractStatus: (d) => d?.status,
+    getIntervalMs: () => 60000,
+    onError: (_e, attempt) => attempts.push(attempt ?? -1),
+  })
+  loop.reset([1])
+  await new Promise<void>((r) => globalThis.setTimeout(r, 0))
+  for (let i = 0; i < 12; i++) {
+    await loop.refreshOnce()
+  }
+  const intervals = attempts.map((a) => getTaskPollBackoffMs(a))
+  assert.deepEqual(
+    intervals.slice(0, 7),
+    [500, 1000, 2000, 4000, 8000, 10000, 10000],
+    '失败计数映射到退避间隔，达到 maxMs 后保持',
+  )
+  const tail = intervals.slice(7)
+  assert.ok(tail.every((v) => v === 10000), '封顶后间隔恒等于 maxMs')
+  loop.dispose()
+  resetTaskPollingConfig()
+})
+
+test('test_cap_config_negative', () => {
+  resetTaskPollingConfig()
+  assert.throws(() => configureTaskPolling({ backoffMaxMs: 0 }), /退避上限必须为正数/)
+  assert.throws(() => configureTaskPolling({ backoffMaxMs: -5 }), /退避上限必须为正数/)
+  // 拒绝后退避仍按默认值工作，不产生非法间隔
+  assert.equal(getTaskPollBackoffMs(0), 500)
+  assert.equal(getTaskPollBackoffMs(50), 10000)
+  resetTaskPollingConfig()
+})