[Bugfix][Model] Fix Qwen3-TTS Code2Wav max_model_len validation (#2508)

Signed-off-by: greenhandzpx <px.tsang@foxmail.com>
Co-authored-by: greenhandzpx <px.tsang@foxmail.com>

tests/engine/test_arg_utils.py

@@ -139,6 +139,41 @@ def test_from_cli_args_picks_up_stage_configs_path():
     assert args.custom_pipeline_args is None
 
 
+def test_qwen3_tts_code2wav_injects_max_position_embeddings(monkeypatch):
+    """Ensure Code2Wav mirrors stage max_model_len into nested HF overrides.
+
+    Qwen3-TTS Code2Wav is a pure decoder stage whose runtime max_model_len can
+    legitimately exceed the base checkpoint's default text max length. Recent
+    vLLM validates these values during ModelConfig creation, so we inject
+    ``talker_config.max_position_embeddings`` before delegating to vLLM.
+    """
+    captured: dict[str, object] = {}
+    baseline_config = Mock()
+
+    def fake_create_model_config(self):
+        captured["hf_overrides"] = self.hf_overrides
+        return baseline_config
+
+    monkeypatch.setattr(EngineArgs, "create_model_config", fake_create_model_config)
+    monkeypatch.setattr(
+        OmniModelConfig,
+        "from_vllm_model_config",
+        classmethod(lambda cls, model_config, **omni_kwargs: model_config),
+    )
+
+    OmniEngineArgs(
+        model_arch="Qwen3TTSCode2Wav",
+        max_model_len=65536,
+    ).create_model_config()
+
+    assert captured["hf_overrides"] == {
+        "architectures": ["Qwen3TTSCode2Wav"],
+        "talker_config": {
+            "max_position_embeddings": 65536,
+        },
+    }
+
+
 def test_stage_specific_text_config_override():
     """Ensure dependent attributes are updated when using stage-specific config."""
     vllm_config = EngineArgs().create_model_config()

vllm_omni/engine/arg_utils.py

@@ -246,6 +246,13 @@ class OmniEngineArgs(EngineArgs):
                     if model_type is not None:
                         self.hf_overrides.setdefault("model_type", model_type)
 
+                # Stage wrappers (e.g. Code2Wav) may need max_model_len larger
+                # than the base checkpoint's text max_position_embeddings.
+                if self.model_arch == "Qwen3TTSCode2Wav" and self.max_model_len is not None:
+                    self.hf_overrides.setdefault("talker_config", {}).setdefault(
+                        "max_position_embeddings", int(self.max_model_len)
+                    )
+
             # For models whose HF config.json is empty or lacks model_type
             # (e.g. CosyVoice3), AutoConfig.from_pretrained fails because it
             # cannot determine which config class to use from the empty dict.