fix: preserve dynamic custom provider semantics

maintainer edit: treat arbitrary custom provider names as direct OpenAI-compatible providers, validate their api_type consistently, and avoid Pydantic instance-field warnings in fallback routing.

nanobot/config/schema.py

@@ -241,6 +241,15 @@ class ProvidersConfig(Base):
     qianfan: ProviderConfig = Field(default_factory=ProviderConfig)  # Qianfan (百度千帆)
     nvidia: ProviderConfig = Field(default_factory=ProviderConfig)  # NVIDIA NIM (nvapi- keys)
 
+    @model_validator(mode="after")
+    def convert_extra_providers(self):
+        """Convert extra fields (custom providers) to ProviderConfig objects."""
+        if self.model_extra:
+            for key, value in self.model_extra.items():
+                if isinstance(value, dict):
+                    self.model_extra[key] = ProviderConfig.model_validate(value)
+        return self
+
     @model_validator(mode="after")
     def _validate_api_type_scope(self) -> "ProvidersConfig":
         for name in self.__class__.model_fields:
@@ -249,15 +258,9 @@ class ProvidersConfig(Base):
             provider = getattr(self, name, None)
             if isinstance(provider, ProviderConfig) and provider.api_type != "auto":
                 raise ValueError("providers.<name>.api_type is only supported for providers.openai")
-        return self
-
-    @model_validator(mode="after")
-    def convert_extra_providers(self):
-        """Convert extra fields (custom providers) to ProviderConfig objects."""
-        if self.model_extra:
-            for key, value in self.model_extra.items():
-                if isinstance(value, dict):
-                    self.model_extra[key] = ProviderConfig.model_validate(value)
+        for provider in (self.model_extra or {}).values():
+            if isinstance(provider, ProviderConfig) and provider.api_type != "auto":
+                raise ValueError("providers.<name>.api_type is only supported for providers.openai")
         return self
 
 
@@ -478,10 +481,7 @@ class Config(BaseSettings):
                 return p, spec.name
 
         # Final fallback: check for any configured custom provider
-        for attr_name in dir(self.providers):
-            if attr_name.startswith("_"):
-                continue
-            p = getattr(self.providers, attr_name, None)
+        for attr_name, p in (self.providers.model_extra or {}).items():
             if isinstance(p, ProviderConfig) and p.api_base:
                 return p, attr_name
 

nanobot/providers/factory.py

@@ -8,7 +8,7 @@ from pathlib import Path
 from nanobot.config.schema import Config, InlineFallbackConfig, ModelPresetConfig
 from nanobot.providers.base import LLMProvider
 from nanobot.providers.fallback_provider import FallbackProvider
-from nanobot.providers.registry import find_by_name
+from nanobot.providers.registry import create_dynamic_spec, find_by_name
 
 
 @dataclass(frozen=True)
@@ -41,6 +41,8 @@ def _make_provider_core(
     provider_name = config.get_provider_name(model, preset=resolved)
     p = config.get_provider(model, preset=resolved)
     spec = find_by_name(provider_name) if provider_name else None
+    if provider_name and not spec and p:
+        spec = create_dynamic_spec(provider_name)
     if spec and spec.is_transcription_only:
         raise ValueError(f"Provider '{provider_name}' only supports transcription.")
     backend = spec.backend if spec else "openai_compat"

tests/cli/test_commands.py

@@ -664,6 +664,30 @@ def test_make_provider_passes_extra_headers_to_custom_provider():
     assert kwargs["default_headers"]["x-session-affinity"] == "sticky-session"
 
 
+def test_make_provider_treats_dynamic_custom_provider_as_direct():
+    config = Config.model_validate(
+        {
+            "agents": {"defaults": {"provider": "my-company-api", "model": "gpt-4o-mini"}},
+            "providers": {
+                "my-company-api": {
+                    "apiBase": "https://example.com/v1",
+                }
+            },
+        }
+    )
+
+    with patch("nanobot.providers.openai_compat_provider.AsyncOpenAI") as mock_async_openai:
+        provider = make_provider(config)
+        asyncio.run(provider._ensure_client())
+
+    assert provider.get_default_model() == "gpt-4o-mini"
+    assert provider._spec.name == "my_company_api"
+    assert provider._spec.is_direct is True
+    kwargs = mock_async_openai.call_args.kwargs
+    assert kwargs["api_key"] == "no-key"
+    assert kwargs["base_url"] == "https://example.com/v1"
+
+
 @pytest.fixture
 def mock_agent_runtime(tmp_path):
     """Mock agent command dependencies for focused CLI tests."""

tests/config/test_model_presets.py

@@ -1,3 +1,5 @@
+import warnings
+
 import pytest
 
 from nanobot.config.schema import Config
@@ -47,6 +49,35 @@ def test_provider_api_type_is_openai_only() -> None:
             }
         })
 
+    with pytest.raises(ValueError, match="only supported"):
+        Config.model_validate({
+            "providers": {
+                "my-company-api": {
+                    "apiBase": "https://example.test/v1",
+                    "apiType": "responses",
+                }
+            }
+        })
+
+
+def test_custom_provider_fallback_uses_model_extra_without_pydantic_warnings() -> None:
+    config = Config.model_validate({
+        "agents": {
+            "defaults": {
+                "model": "unmatched-model",
+            }
+        },
+        "providers": {
+            "my-company-api": {
+                "apiBase": "https://example.test/v1",
+            }
+        },
+    })
+
+    with warnings.catch_warnings():
+        warnings.simplefilter("error")
+        assert config.get_provider_name() == "my-company-api"
+
 
 def test_legacy_defaults_config_without_presets_still_resolves() -> None:
     config = Config.model_validate({