perf: 加速语音转写缓存命中

迁移旧版语音转写缓存，并将补迁失败降级为一次性失败状态。

按账号和消息标识优先命中兼容缓存，未命中时才读取音频并计算哈希；导出缓存命中后合并异步刷新知识索引。

补充迁移、缓存快速路径、批量语音读取和导出流程测试。

tests/unit/voice-recognition-use-case.test.ts

@@ -72,7 +72,9 @@ describe('VoiceRecognitionUseCase transcript updates', () => {
 
   it('does not publish a transcript after the account generation changes mid-recognition', async () => {
     const useCase = createUseCase()
-    let finish: ((value: { transcript: string; durationMs: number; cached: boolean }) => void) | undefined
+    let finish:
+      | ((value: { transcript: string; durationMs: number; cached: boolean }) => void)
+      | undefined
     const state = useCase as unknown as {
       accountGeneration: number
       pipeline: { run: ReturnType<typeof vi.fn> }
@@ -98,4 +100,24 @@ describe('VoiceRecognitionUseCase transcript updates', () => {
     expect(listener).not.toHaveBeenCalled()
     await useCase.dispose()
   })
+
+  it('publishes an explicit cached transcript for a coalesced export index refresh', async () => {
+    const useCase = createUseCase()
+    const listener = vi.fn().mockResolvedValue(undefined)
+    useCase.onTranscriptUpdate(listener)
+    const reference = { sessionId: 'fixture-contact', localId: 11, createTime: 1_785_895_202 }
+
+    await useCase.publishTranscript(reference, '缓存导出文字', true)
+
+    expect(listener).toHaveBeenCalledWith(
+      expect.objectContaining({
+        accountIdentity: 'account-a',
+        reference,
+        state: 'transcribed',
+        transcript: '缓存导出文字',
+        cached: true
+      })
+    )
+    await useCase.dispose()
+  })
 })