feat(providers): add create_provider factory with OAuth detection

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

nanobot/providers/__init__.py

@@ -1,6 +1,43 @@
-"""LLM provider abstraction module."""
+"""Provider module exports."""
 
-from nanobot.providers.base import LLMProvider, LLMResponse
+from nanobot.providers.base import LLMProvider, LLMResponse, ToolCallRequest
 from nanobot.providers.litellm_provider import LiteLLMProvider
+from nanobot.providers.anthropic_oauth import AnthropicOAuthProvider
+from nanobot.providers.registry import should_use_oauth_provider
 
-__all__ = ["LLMProvider", "LLMResponse", "LiteLLMProvider"]
+__all__ = [
+    "LLMProvider",
+    "LLMResponse",
+    "ToolCallRequest",
+    "LiteLLMProvider",
+    "AnthropicOAuthProvider",
+    "create_provider",
+]
+
+
+def create_provider(
+    api_key: str,
+    model: str,
+    api_base: str | None = None,
+    extra_headers: dict[str, str] | None = None,
+    provider_name: str | None = None,
+) -> LLMProvider:
+    """Factory function to create appropriate provider.
+
+    Automatically selects AnthropicOAuthProvider for OAuth tokens,
+    LiteLLMProvider for everything else.
+    """
+    if should_use_oauth_provider(api_key, model):
+        return AnthropicOAuthProvider(
+            oauth_token=api_key,
+            default_model=model,
+            api_base=api_base,
+        )
+
+    return LiteLLMProvider(
+        api_key=api_key,
+        api_base=api_base,
+        default_model=model,
+        extra_headers=extra_headers,
+        provider_name=provider_name,
+    )

tests/test_provider_factory.py

@@ -0,0 +1,32 @@
+"""Test provider factory with OAuth support."""
+import pytest
+from nanobot.providers import create_provider
+from nanobot.providers.anthropic_oauth import AnthropicOAuthProvider
+from nanobot.providers.litellm_provider import LiteLLMProvider
+
+
+def test_create_provider_oauth_token():
+    """OAuth tokens should create AnthropicOAuthProvider."""
+    provider = create_provider(
+        api_key="sk-ant-oat01-test-token",
+        model="anthropic/claude-opus-4-5"
+    )
+    assert isinstance(provider, AnthropicOAuthProvider)
+
+
+def test_create_provider_regular_key():
+    """Regular API keys should create LiteLLMProvider."""
+    provider = create_provider(
+        api_key="sk-ant-api03-regular-key",
+        model="anthropic/claude-opus-4-5"
+    )
+    assert isinstance(provider, LiteLLMProvider)
+
+
+def test_create_provider_openrouter():
+    """OpenRouter keys should create LiteLLMProvider."""
+    provider = create_provider(
+        api_key="sk-or-v1-xxx",
+        model="anthropic/claude-opus-4-5"
+    )
+    assert isinstance(provider, LiteLLMProvider)