config.provider doesn't load builtin providers

[jeffscottward]

Summary

When using factory.ModelConfig with an explicit provider parameter, the builtin providers are not loaded first, causing the provider resolution to fail.

Steps to Reproduce

from langextract import factory
import langextract as lx

config = factory.ModelConfig(
    model_id="llama-3.3-70b-versatile",
    provider="openai",  # or "OpenAI" or "OpenAILanguageModel"
    provider_kwargs={
        "api_key": "...",
        "base_url": "https://api.groq.com/openai/v1",
    }
)

result = lx.extract(
    text_or_documents="Some text",
    prompt_description="Extract info",
    examples=[...],
    config=config,
)

Error

langextract.core.exceptions.InferenceConfigError: No provider found matching: 'openai'. Available providers can be listed with list_providers()

Root Cause

In factory.py line 223-228, providers.load_builtins_once() is only called when config.provider is NOT set:

if config.provider:
    provider_class = router.resolve_provider(config.provider)
else:
    providers.load_builtins_once()  # Only called here!
    providers.load_plugins_once()
    provider_class = router.resolve(config.model_id)

Workaround

Import and instantiate the provider directly:

from langextract.providers.openai import OpenAILanguageModel

model = OpenAILanguageModel(
    model_id="llama-3.3-70b-versatile",
    api_key="...",
    base_url="https://api.groq.com/openai/v1",
)

result = lx.extract(
    text_or_documents="...",
    model=model,  # Pass model directly instead of config
    ...
)

Expected Behavior

providers.load_builtins_once() should be called regardless of whether config.provider is set.

Use Case

This bug blocks using OpenAI-compatible APIs like Groq, Together, Anyscale, etc. where:

1. The model ID doesn't match the default OpenAI patterns (^gpt-4, ^gpt-5)
2. Users need to explicitly specify provider="openai" with a custom base_url

Environment

• langextract version: 1.1.1
• Python: 3.12