fix: prevent ValueError when audio buffer is empty in STT (fixes openai#821) (openai#1934)

Author: gn00295120

src/agents/voice/models/openai_stt.py

@@ -122,7 +122,8 @@ def _end_turn(self, _transcript: str) -> None:
  return
 
  if self._tracing_span:
- if self._trace_include_sensitive_audio_data:
+ # Only encode audio if tracing is enabled AND buffer is not empty
+ if self._trace_include_sensitive_audio_data and self._turn_audio_buffer:
  self._tracing_span.span_data.input = _audio_to_base64(self._turn_audio_buffer)
 
  self._tracing_span.span_data.input_format = "pcm"