CartesiaTTSService: reset context id when flushing audio

CHANGELOG.md

@@ -52,6 +52,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- Fixed a `CartesiaTTSService` issue that could cause audio overlapping in some
+  cases.
+
 - Fixed an issue that was causing `AudioBufferProcessor` to not record
   synchronized audio.
 

src/pipecat/services/cartesia.py

@@ -239,6 +239,7 @@ class CartesiaTTSService(WordTTSService, WebsocketService):
         logger.trace(f"{self}: flushing audio")
         msg = self._build_msg(text="", continue_transcript=False)
         await self._websocket.send(msg)
+        self._context_id = None
 
     async def _receive_messages(self):
         async for message in self._get_websocket():