Previously @traced_tts scoped the span to the lifetime of run_tts(). For
streaming TTS services run_tts() returns as soon as the synthesis request
is sent, long before audio chunks arrive, so:
- The span duration measured the WebSocket-send time, not synthesis time.
- The first synthesis recorded the WS-send duration as metrics.ttfb (via
the in-progress fallback in FrameProcessorMetrics.ttfb).
- Subsequent syntheses recorded the previous call's TTFB on the current
span (off-by-one).
The decorator now uses a __set_name__ descriptor to wrap the owning
class's setup() at class definition time. setup() installs per-instance
patches on create_audio_context, append_to_audio_context,
remove_audio_context, on_audio_context_completed, and
reset_active_audio_context. These patches own the span lifetime:
- create_audio_context: open span, set baseline attributes.
- append_to_audio_context: record metrics.ttfb on the first
TTSAudioRawFrame (when stop_ttfb_metrics has produced a real value),
end span on appended TTSStoppedFrame.
- on_audio_context_completed: end span on natural completion (handles
services that auto-push TTSStoppedFrame via push_frame, bypassing
append_to_audio_context).
- remove_audio_context: safety net for explicit removal paths.
- reset_active_audio_context: interruption hook (always reached from
_handle_interruption); marks the span tts.interrupted=true only when
nothing else has closed it.
The run_tts wrapper now only attaches per-call attributes (text,
metrics.character_count) to the already-open span. No changes required
in tts_service.py or in any of the per-service files.
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