[真实链路自测]：完成完整流程自测和ACK缓冲修正，包含真实Provider验收、播放回声清理和回归测试

src/owner_voice_pet/assistant_pipeline.py

@@ -227,7 +227,6 @@ class TurnController:
     def _acknowledge_wake(self, turn_id: int) -> ProviderError | None:
         text = self.config.wake_ack_text.strip()
         if not text:
-            self._drain_input_after_playback()
             return None
         try:
             self._event(ACK_STARTED, PipelineState.SPEAKING, f"应答中：{text}", turn_id=turn_id)
@@ -278,9 +277,9 @@ class TurnController:
         self._drain_input_after_playback()
 
     def _drain_input_after_playback(self) -> None:
+        self.transport.flush_input()
         if self.config.post_playback_drain_ms <= 0:
             return
-        self.transport.flush_input()
         remaining_ms = self.config.post_playback_drain_ms
         while remaining_ms > 0:
             timeout_ms = min(50, remaining_ms)