fix: add input validation and cpu() guard in OmniVoiceGenerate

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_generator.py

@@ -1,5 +1,5 @@
 # tests/test_generator.py
-from unittest.mock import patch, MagicMock, call
+from unittest.mock import patch, MagicMock
 import torch
 import pytest
 from nodes.generator import OmniVoiceGenerate
@@ -92,6 +92,32 @@ def test_generate_voice_cloning():
     assert "ref_audio" in call_kwargs
 
 
+def test_voice_cloning_without_ref_audio_raises():
+    node = OmniVoiceGenerate()
+    mock_model = make_mock_model()
+    with pytest.raises(ValueError, match="ref_audio"):
+        node.generate(
+            model=mock_model,
+            text="Hello",
+            mode="voice_cloning",
+            speed=1.0,
+            num_step=32,
+        )
+
+
+def test_voice_design_without_instruct_raises():
+    node = OmniVoiceGenerate()
+    mock_model = make_mock_model()
+    with pytest.raises(ValueError, match="instruct"):
+        node.generate(
+            model=mock_model,
+            text="Hello",
+            mode="voice_design",
+            speed=1.0,
+            num_step=32,
+        )
+
+
 def test_output_waveform_shape():
     node = OmniVoiceGenerate()
     # Simulate two chunks returned by OmniVoice