chore: OpenAIMixin implements ModelsProtocolPrivate (#3662)

# What does this PR do?

add ModelsProtocolPrivate methods to OpenAIMixin

this will allow providers using OpenAIMixin to use a common interface


## Test Plan

ci w/ new tests

llama_stack/providers/remote/inference/cerebras/cerebras.py

@@ -25,9 +25,6 @@ from llama_stack.apis.inference import (
     ToolPromptFormat,
     TopKSamplingStrategy,
 )
-from llama_stack.providers.utils.inference.model_registry import (
-    ModelRegistryHelper,
-)
 from llama_stack.providers.utils.inference.openai_compat import (
     get_sampling_options,
     process_chat_completion_response,
@@ -44,7 +41,6 @@ from .config import CerebrasImplConfig
 
 class CerebrasInferenceAdapter(
     OpenAIMixin,
-    ModelRegistryHelper,
     Inference,
 ):
     def __init__(self, config: CerebrasImplConfig) -> None:

llama_stack/providers/remote/inference/fireworks/fireworks.py

@@ -44,7 +44,7 @@ from .config import FireworksImplConfig
 logger = get_logger(name=__name__, category="inference::fireworks")
 
 
-class FireworksInferenceAdapter(OpenAIMixin, ModelRegistryHelper, Inference, NeedsRequestProviderData):
+class FireworksInferenceAdapter(OpenAIMixin, Inference, NeedsRequestProviderData):
     embedding_model_metadata = {
         "nomic-ai/nomic-embed-text-v1.5": {"embedding_dimension": 768, "context_length": 8192},
         "accounts/fireworks/models/qwen3-embedding-8b": {"embedding_dimension": 4096, "context_length": 40960},

llama_stack/providers/remote/inference/tgi/tgi.py

@@ -29,7 +29,6 @@ from llama_stack.apis.models import Model
 from llama_stack.apis.models.models import ModelType
 from llama_stack.log import get_logger
 from llama_stack.models.llama.sku_list import all_registered_models
-from llama_stack.providers.datatypes import ModelsProtocolPrivate
 from llama_stack.providers.utils.inference.model_registry import (
     ModelRegistryHelper,
     build_hf_repo_model_entry,
@@ -65,7 +64,6 @@ def build_hf_repo_model_entries():
 class _HfAdapter(
     OpenAIMixin,
     Inference,
-    ModelsProtocolPrivate,
 ):
     url: str
     api_key: SecretStr

llama_stack/providers/remote/inference/together/together.py

@@ -47,7 +47,7 @@ from .config import TogetherImplConfig
 logger = get_logger(name=__name__, category="inference::together")
 
 
-class TogetherInferenceAdapter(OpenAIMixin, ModelRegistryHelper, Inference, NeedsRequestProviderData):
+class TogetherInferenceAdapter(OpenAIMixin, Inference, NeedsRequestProviderData):
     embedding_model_metadata = {
         "togethercomputer/m2-bert-80M-32k-retrieval": {"embedding_dimension": 768, "context_length": 32768},
         "BAAI/bge-large-en-v1.5": {"embedding_dimension": 1024, "context_length": 512},

llama_stack/providers/utils/inference/openai_mixin.py

@@ -26,14 +26,14 @@ from llama_stack.apis.inference import (
 from llama_stack.apis.models import ModelType
 from llama_stack.core.request_headers import NeedsRequestProviderData
 from llama_stack.log import get_logger
-from llama_stack.providers.utils.inference.model_registry import ModelRegistryHelper
+from llama_stack.providers.datatypes import ModelsProtocolPrivate
 from llama_stack.providers.utils.inference.openai_compat import prepare_openai_completion_params
 from llama_stack.providers.utils.inference.prompt_adapter import localize_image_content
 
 logger = get_logger(name=__name__, category="providers::utils")
 
 
-class OpenAIMixin(ModelRegistryHelper, NeedsRequestProviderData, ABC):
+class OpenAIMixin(ModelsProtocolPrivate, NeedsRequestProviderData, ABC):
     """
     Mixin class that provides OpenAI-specific functionality for inference providers.
     This class handles direct OpenAI API calls using the AsyncOpenAI client.
@@ -73,6 +73,9 @@ class OpenAIMixin(ModelRegistryHelper, NeedsRequestProviderData, ABC):
     # Optional field name in provider data to look for API key, which takes precedence
     provider_data_api_key_field: str | None = None
 
+    # automatically set by the resolver when instantiating the provider
+    __provider_id__: str
+
     @abstractmethod
     def get_api_key(self) -> str:
         """
@@ -356,6 +359,24 @@ class OpenAIMixin(ModelRegistryHelper, NeedsRequestProviderData, ABC):
             usage=usage,
         )
 
+    ###
+    # ModelsProtocolPrivate implementation - provide model management functionality
+    #
+    #  async def register_model(self, model: Model) -> Model: ...
+    #  async def unregister_model(self, model_id: str) -> None: ...
+    #
+    #  async def list_models(self) -> list[Model] | None: ...
+    #  async def should_refresh_models(self) -> bool: ...
+    ##
+
+    async def register_model(self, model: Model) -> Model:
+        if not await self.check_model_availability(model.provider_model_id):
+            raise ValueError(f"Model {model.provider_model_id} is not available from provider {self.__provider_id__}")
+        return model
+
+    async def unregister_model(self, model_id: str) -> None:
+        return None
+
     async def list_models(self) -> list[Model] | None:
         """
         List available models from the provider's /v1/models endpoint augmented with static embedding model metadata.
@@ -400,5 +421,7 @@ class OpenAIMixin(ModelRegistryHelper, NeedsRequestProviderData, ABC):
         """
         if not self._model_cache:
             await self.list_models()
-
         return model in self._model_cache
+
+    async def should_refresh_models(self) -> bool:
+        return False