feat(moss-tts-nano): add single-stage MOSS-TTS-Nano TTS support

Integrates OpenMOSS-Team/MOSS-TTS-Nano (0.1B) as a single
GPUGenerationWorker stage.  Both the AR LM and MOSS-Audio-Tokenizer-Nano
codec run inside MossTTSNanoForGeneration.forward(), removing the need for
an inter-stage connector.

Key design choices:
- Weights loaded in load_weights() not __init__ (avoids pre-CUDA alloc)
- trust_remote_code delegates to upstream HF model classes
- codec path read from config.audio_tokenizer_pretrained_name_or_path
- inference_stream() collects progressive audio chunks for low latency
- 48 kHz stereo output; voice clone + continuation modes supported


Signed-off-by: Yueqian Lin <linyueqian@outlook.com>

tests/e2e/offline_inference/test_moss_tts_nano.py

@@ -0,0 +1,132 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""E2E offline inference tests for MOSS-TTS-Nano single-stage pipeline."""
+
+from __future__ import annotations
+
+import pytest
+import torch
+from vllm import SamplingParams
+
+from tests.utils import hardware_test
+from vllm_omni import Omni
+
+MODEL_NAME = "OpenMOSS-Team/MOSS-TTS-Nano"
+STAGE_CONFIG = "vllm_omni/model_executor/stage_configs/moss_tts_nano.yaml"
+SAMPLE_RATE = 48000
+
+DEFAULT_SAMPLING = SamplingParams(
+    temperature=1.0,
+    top_p=1.0,
+    top_k=50,
+    max_tokens=4096,
+    seed=42,
+    detokenize=False,
+)
+
+
+def _build_request(
+    text: str,
+    voice: str = "Junhao",
+    mode: str = "voice_clone",
+    max_new_frames: int = 100,  # short for tests
+    seed: int = 42,
+) -> dict:
+    return {
+        "prompt": "<|im_start|>assistant\n",
+        "additional_information": {
+            "text": [text],
+            "voice": [voice],
+            "mode": [mode],
+            "max_new_frames": [max_new_frames],
+            "seed": [seed],
+        },
+    }
+
+
+def _collect_audio(omni: Omni, request: dict) -> tuple[torch.Tensor, int]:
+    """Run a single request and return (waveform, sample_rate)."""
+    for stage_outputs in omni.generate(request, DEFAULT_SAMPLING):
+        for req_output in stage_outputs.request_output:
+            mm = req_output.outputs[0].multimodal_output
+            assert mm is not None, "Expected multimodal_output to be non-None"
+            audio = mm.get("audio")
+            sr = mm.get("sr")
+            assert audio is not None, "Expected 'audio' key in multimodal_output"
+            assert isinstance(audio, torch.Tensor), f"audio should be Tensor, got {type(audio)}"
+            return audio.cpu(), int(sr.item()) if sr is not None else SAMPLE_RATE
+    raise AssertionError("No stage outputs received")
+
+
+@pytest.fixture(scope="module")
+def omni_engine():
+    """Module-scoped Omni engine to avoid re-loading the model for each test."""
+    return Omni(model=MODEL_NAME, stage_configs_path=STAGE_CONFIG, stage_init_timeout=180)
+
+
+@pytest.mark.omni
+@hardware_test(res={"cuda": "L4"})
+def test_moss_tts_nano_english(omni_engine):
+    """English TTS produces non-empty 48 kHz stereo audio."""
+    req = _build_request("Hello, this is a test of MOSS-TTS-Nano.", voice="Ava")
+    audio, sr = _collect_audio(omni_engine, req)
+
+    assert sr == SAMPLE_RATE, f"Expected sample_rate={SAMPLE_RATE}, got {sr}"
+    assert audio.numel() > 0, "Audio tensor should not be empty"
+    assert not torch.all(audio == 0), "Audio should not be all-zeros (silence)"
+
+
+@pytest.mark.omni
+@hardware_test(res={"cuda": "L4"})
+def test_moss_tts_nano_chinese(omni_engine):
+    """Chinese TTS produces non-empty audio."""
+    req = _build_request("你好，这是语音合成测试。", voice="Junhao")
+    audio, sr = _collect_audio(omni_engine, req)
+
+    assert sr == SAMPLE_RATE
+    assert audio.numel() > 0
+    assert not torch.all(audio == 0)
+
+
+@pytest.mark.omni
+@hardware_test(res={"cuda": "L4"})
+def test_moss_tts_nano_deterministic(omni_engine):
+    """Same seed produces identical waveforms."""
+    req = _build_request("Reproducible output test.", voice="Adam", seed=123)
+    audio1, _ = _collect_audio(omni_engine, req)
+    audio2, _ = _collect_audio(omni_engine, req)
+
+    assert audio1.shape == audio2.shape, "Waveform shapes should match with same seed"
+    assert torch.allclose(audio1, audio2, atol=1e-4), "Waveforms should match with same seed"
+
+
+@pytest.mark.omni
+@hardware_test(res={"cuda": "L4"})
+def test_moss_tts_nano_batch(omni_engine):
+    """Batch of two requests returns audio for each."""
+    requests = [
+        _build_request("First request.", voice="Ava"),
+        _build_request("Second request.", voice="Bella"),
+    ]
+    results = []
+    for stage_outputs in omni_engine.generate(requests, [DEFAULT_SAMPLING] * 2):
+        for req_output in stage_outputs.request_output:
+            mm = req_output.outputs[0].multimodal_output
+            assert mm is not None
+            results.append(mm["audio"].cpu())
+
+    assert len(results) == 2, f"Expected 2 outputs, got {len(results)}"
+    for i, audio in enumerate(results):
+        assert audio.numel() > 0, f"Audio {i} is empty"
+
+
+@pytest.mark.omni
+@hardware_test(res={"cuda": "L4"})
+def test_moss_tts_nano_voice_presets(omni_engine):
+    """Multiple built-in voice presets all produce valid audio."""
+    voices = ["Junhao", "Ava", "Bella"]
+    for voice in voices:
+        req = _build_request(f"Testing voice {voice}.", voice=voice)
+        audio, sr = _collect_audio(omni_engine, req)
+        assert audio.numel() > 0, f"Voice {voice} produced empty audio"
+        assert sr == SAMPLE_RATE