[feat][Qwen3TTS] Simple dynamic TTFA based on Code2Wav load (#1714)

Signed-off-by: pablo <pablo@agigo.ai>
Co-authored-by: pablo <pablo@agigo.ai>

docs/design/feature/async_chunk_design.md

@@ -19,7 +19,7 @@ The `async_chunk` feature enables asynchronous, chunked processing of data acros
 
 For qwen3-omni:
 - **Thinker → Talker**: Per decode step (typically chunk_size=1)
-- **Talker → Code2Wav**: Accumulated to `codec_chunk_frames` (default=25) before sending. Set `initial_codec_chunk_frames` to emit smaller chunks during the initial phase for reduced TTFA
+- **Talker → Code2Wav**: Accumulated to `codec_chunk_frames` (default=25) before sending. During the initial phase, a dynamic initial chunk size (IC) is automatically selected based on server load to reduce TTFA. Use the per-request `initial_codec_chunk_frames` API field to override.
 - **Code2Wav**: Streaming decode with code2wav chunk_size
 
 With `async_chunk`:

docs/serving/speech_api.md

@@ -96,7 +96,7 @@ Content-Type: application/json
 | `language` | string | "Auto" | Language (see supported languages below) |
 | `instructions` | string | "" | Voice style/emotion instructions |
 | `max_new_tokens` | integer | 2048 | Maximum tokens to generate |
-| `initial_codec_chunk_frames` | integer | null | Initial chunk size for reduced TTFA (overrides stage config) |
+| `initial_codec_chunk_frames` | integer | null | Per-request initial chunk size override for TTFA tuning. When null, IC is computed dynamically based on server load. |
 
 **Supported languages:** Auto, Chinese, English, Japanese, Korean, German, French, Russian, Portuguese, Spanish, Italian
 

docs/user_guide/examples/offline_inference/qwen3_tts.md

@@ -99,7 +99,8 @@ python end2end.py --query-type CustomVoice --streaming --output-dir /tmp/out_str
 ```
 
 Each Code2Wav chunk is logged as it arrives (default 25 frames; configurable via `codec_chunk_frames`
-and `initial_codec_chunk_frames` in the stage config). The final WAV file is written once generation
+in the stage config). The initial chunk size is dynamically selected based on server load for reduced
+TTFA, and can be overridden per-request via the `initial_codec_chunk_frames` API field. The final WAV file is written once generation
 completes. This demonstrates that audio data is available progressively rather than only at the end.
 
 > **Note:** Streaming uses `AsyncOmni` internally. The non-streaming path (`Omni`) is unchanged.