[Core] Retain structured configs through runtime startup (#6849)

Signed-off-by: maithilijoshi20 <97733343+maithilijoshi20@users.noreply.github.com>

tests/entrypoints/openai_api/test_tts_adapter.py

@@ -22,6 +22,7 @@ from vllm_omni.entrypoints.openai.tts_adapters import (
     detect_tts_model_type,
     resolve_adapter,
 )
+from vllm_omni.entrypoints.openai.tts_adapters.base import resolve_stage_model_path
 from vllm_omni.entrypoints.openai.tts_adapters.covo_audio import CovoAudioAdapter
 from vllm_omni.entrypoints.openai.tts_adapters.higgs_audio_v2 import HiggsAudioV2Adapter
 from vllm_omni.entrypoints.openai.tts_adapters.indextts2 import (
@@ -99,6 +100,31 @@ def test_resolve_unknown_returns_none():
     assert resolve_adapter(None) is None
 
 
+def test_stage_model_path_prefers_typed_override():
+    engine_client = SimpleNamespace(
+        stage_configs=[
+            SimpleNamespace(engine_args=SimpleNamespace(model="legacy-stage-model")),
+            SimpleNamespace(
+                model_config=SimpleNamespace(model="typed-stage-model"),
+            ),
+        ],
+        model="served-model",
+    )
+
+    assert resolve_stage_model_path(engine_client) == "typed-stage-model"
+
+
+def test_stage_model_path_falls_back_to_legacy_then_served_model():
+    legacy_client = SimpleNamespace(
+        stage_configs=[SimpleNamespace(engine_args=SimpleNamespace(model="legacy-stage-model"))],
+        model="served-model",
+    )
+    served_client = SimpleNamespace(stage_configs=[SimpleNamespace()], model="served-model")
+
+    assert resolve_stage_model_path(legacy_client) == "legacy-stage-model"
+    assert resolve_stage_model_path(served_client) == "served-model"
+
+
 def test_voxcpm2_resolves():
     """VoxCPM2 (the served ``latent_generator`` model) resolves cleanly.