task-29: 退避配置项（MaxMs/Factor）

task-progress-config.ts 新增 getTaskPollBackoffMaxMs()（默认 10000，
由 5000 提升）与 getTaskPollBackoffFactor()（默认 2，<1 钳制为 1）；
configureTaskPolling 支持 backoffFactor；getTaskPollBackoffMs 改用
base × factor^attempt 计算。

既有 task-086 边界测试中封顶 5000 的快照随新默认更新为 10000。
新增 8 个测试：max/factor 默认、可覆盖、非正钳制、factor 下限、
配置隔离、默认值快照。

frontend-vue/tests/task-progress-backoff-config.test.ts

@@ -0,0 +1,72 @@
+import { test } from 'node:test'
+import assert from 'node:assert/strict'
+import {
+  TASK_POLL_BACKOFF_MAX_MS,
+  TASK_POLL_BACKOFF_FACTOR,
+  getTaskPollBackoffMaxMs,
+  getTaskPollBackoffFactor,
+  configureTaskPolling,
+  resetTaskPollingConfig,
+} from '../src/shared/task-progress-config.ts'
+
+test('test_backoff_max_default', () => {
+  resetTaskPollingConfig()
+  assert.equal(getTaskPollBackoffMaxMs(), 10000)
+  assert.equal(getTaskPollBackoffMaxMs(), TASK_POLL_BACKOFF_MAX_MS)
+})
+
+test('test_backoff_factor_default', () => {
+  resetTaskPollingConfig()
+  assert.equal(getTaskPollBackoffFactor(), 2)
+  assert.equal(getTaskPollBackoffFactor(), TASK_POLL_BACKOFF_FACTOR)
+})
+
+test('test_backoff_max_override', () => {
+  resetTaskPollingConfig()
+  configureTaskPolling({ backoffMaxMs: 8000 })
+  assert.equal(getTaskPollBackoffMaxMs(), 8000)
+  resetTaskPollingConfig()
+  assert.equal(getTaskPollBackoffMaxMs(), 10000, 'reset 后恢复默认')
+})
+
+test('test_backoff_max_positive', () => {
+  resetTaskPollingConfig()
+  assert.throws(() => configureTaskPolling({ backoffMaxMs: 0 }), /退避上限必须为正数/)
+  assert.throws(() => configureTaskPolling({ backoffMaxMs: -100 }), /退避上限必须为正数/)
+  // 拒绝后 getter 仍返回正值，非正配置不可观察
+  assert.ok(getTaskPollBackoffMaxMs() > 0)
+  assert.equal(getTaskPollBackoffMaxMs(), TASK_POLL_BACKOFF_MAX_MS)
+})
+
+test('test_backoff_factor_min_one', () => {
+  resetTaskPollingConfig()
+  // factor <1 钳制为 1（不抛错）
+  configureTaskPolling({ backoffFactor: 0.5 })
+  assert.equal(getTaskPollBackoffFactor(), 1)
+  configureTaskPolling({ backoffFactor: 0 })
+  assert.equal(getTaskPollBackoffFactor(), 1)
+  resetTaskPollingConfig()
+  assert.equal(getTaskPollBackoffFactor(), 2)
+})
+
+test('test_backoff_config_isolated', () => {
+  resetTaskPollingConfig()
+  configureTaskPolling({ backoffMaxMs: 7000, backoffFactor: 3 })
+  assert.equal(getTaskPollBackoffMaxMs(), 7000)
+  assert.equal(getTaskPollBackoffFactor(), 3)
+  resetTaskPollingConfig()
+  assert.equal(getTaskPollBackoffMaxMs(), 10000, '不串到其他用例')
+  assert.equal(getTaskPollBackoffFactor(), 2)
+})
+
+test('test_backoff_max_freeze', () => {
+  resetTaskPollingConfig()
+  assert.equal(TASK_POLL_BACKOFF_MAX_MS, 10000, '默认值快照')
+  assert.equal(getTaskPollBackoffMaxMs(), TASK_POLL_BACKOFF_MAX_MS)
+})
+
+test('test_backoff_factor_freeze', () => {
+  resetTaskPollingConfig()
+  assert.equal(TASK_POLL_BACKOFF_FACTOR, 2, 'factor 快照')
+  assert.equal(getTaskPollBackoffFactor(), TASK_POLL_BACKOFF_FACTOR)
+})

frontend-vue/tests/task-progress-config.test.ts

@@ -105,9 +105,10 @@ test('test_task_086_polling_boundary_limit_and_overflow', () => {
   assert.equal(getTaskPollBackoffMs(1), 1000)
   assert.equal(getTaskPollBackoffMs(2), 2000)
   assert.equal(getTaskPollBackoffMs(3), 4000)
-  assert.equal(getTaskPollBackoffMs(4), 5000)
-  assert.equal(getTaskPollBackoffMs(10), 5000)
-  assert.equal(getTaskPollBackoffMs(100), 5000)
+  assert.equal(getTaskPollBackoffMs(4), 8000)
+  assert.equal(getTaskPollBackoffMs(5), 10000)
+  assert.equal(getTaskPollBackoffMs(10), 10000)
+  assert.equal(getTaskPollBackoffMs(100), 10000)
   // attempt 为 0 或负数按首次退避处理
   assert.equal(getTaskPollBackoffMs(-1), 500)
   assert.equal(getTaskPollBackoffMs(NaN), 500)