feat: load config class when doing variable substitution

When using bash style substitution env variable in distribution
template, we are processing the string and convert it to the type
associated with the provider's config class. This allows us to return
the proper type. This is crucial for api key since they are not strings
anymore but SecretStr. If the key is unset we will get an empty string
which will result in a Pydantic error like:

```
ERROR    2025-09-25 21:40:44,565 __main__:527 core::server: Error creating app: 1 validation error for AnthropicConfig
         api_key
           Input should be a valid string
             For further information visit
             https://errors.pydantic.dev/2.11/v/string_type
```

Signed-off-by: Sébastien Han <seb@redhat.com>

llama_stack/providers/inline/scoring/braintrust/__init__.py

@@ -5,15 +5,16 @@
 # the root directory of this source tree.
 from typing import Any
 
-from pydantic import BaseModel, SecretStr
+from pydantic import BaseModel
 
 from llama_stack.core.datatypes import Api
+from llama_stack.core.secret_types import MySecretStr
 
 from .config import BraintrustScoringConfig
 
 
 class BraintrustProviderDataValidator(BaseModel):
-    openai_api_key: SecretStr
+    openai_api_key: MySecretStr
 
 
 async def get_provider_impl(

llama_stack/providers/inline/scoring/braintrust/braintrust.py

@@ -17,7 +17,7 @@ from autoevals.ragas import (
     ContextRelevancy,
     Faithfulness,
 )
-from pydantic import BaseModel, SecretStr
+from pydantic import BaseModel
 
 from llama_stack.apis.datasetio import DatasetIO
 from llama_stack.apis.datasets import Datasets
@@ -31,6 +31,7 @@ from llama_stack.apis.scoring import (
 from llama_stack.apis.scoring_functions import ScoringFn, ScoringFnParams
 from llama_stack.core.datatypes import Api
 from llama_stack.core.request_headers import NeedsRequestProviderData
+from llama_stack.core.secret_types import MySecretStr
 from llama_stack.providers.datatypes import ScoringFunctionsProtocolPrivate
 from llama_stack.providers.utils.common.data_schema_validator import (
     get_valid_schemas,
@@ -152,7 +153,7 @@ class BraintrustScoringImpl(
                 raise ValueError(
                     'Pass OpenAI API Key in the header X-LlamaStack-Provider-Data as { "openai_api_key": <your api key>}'
                 )
-            self.config.openai_api_key = SecretStr(provider_data.openai_api_key)
+            self.config.openai_api_key = MySecretStr(provider_data.openai_api_key)
 
         os.environ["OPENAI_API_KEY"] = self.config.openai_api_key.get_secret_value()
 

llama_stack/providers/inline/scoring/braintrust/config.py

@@ -5,12 +5,13 @@
 # the root directory of this source tree.
 from typing import Any
 
-from pydantic import BaseModel, Field, SecretStr
+from pydantic import BaseModel, Field
+
+from llama_stack.core.secret_types import MySecretStr
 
 
 class BraintrustScoringConfig(BaseModel):
-    openai_api_key: SecretStr = Field(
-        default=SecretStr(""),
+    openai_api_key: MySecretStr = Field(
         description="The OpenAI API Key",
     )
 

llama_stack/providers/inline/telemetry/meta_reference/console_span_processor.py

@@ -65,8 +65,7 @@ class ConsoleSpanProcessor(SpanProcessor):
                     if key.startswith("__") or key in ["message", "severity"]:
                         continue
 
-                    str_value = str(value)
-                    logger.info(f"[dim]{key}[/dim]: {str_value}")
+                    logger.info(f"[dim]{key}[/dim]: {value}")
 
     def shutdown(self) -> None:
         """Shutdown the processor."""