feat(registry): add OAuth provider detection logic

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

tests/test_registry_oauth.py

@@ -0,0 +1,21 @@
+"""Test OAuth detection in provider registry."""
+import pytest
+from nanobot.providers.registry import should_use_oauth_provider
+
+
+def test_should_use_oauth_for_oat_token():
+    """OAuth provider should be used for sk-ant-oat tokens."""
+    assert should_use_oauth_provider("sk-ant-oat01-xxx", "anthropic/claude-opus-4-5") is True
+    assert should_use_oauth_provider("sk-ant-oat01-xxx", "claude-sonnet-4") is True
+
+
+def test_should_not_use_oauth_for_regular_key():
+    """Regular API keys should not use OAuth provider."""
+    assert should_use_oauth_provider("sk-ant-api03-xxx", "claude-opus-4-5") is False
+    assert should_use_oauth_provider("sk-or-v1-xxx", "anthropic/claude-opus-4-5") is False
+
+
+def test_should_not_use_oauth_for_non_anthropic():
+    """Non-Anthropic models should not use OAuth provider."""
+    assert should_use_oauth_provider("sk-ant-oat01-xxx", "gpt-4") is False
+    assert should_use_oauth_provider("sk-ant-oat01-xxx", "deepseek/deepseek-chat") is False