fix: add clear error message for invalid thinking_style values

Widen thinking_style from Literal to str | None and add a
@field_validator that produces a helpful error message listing
valid options when an invalid value is provided.

Addresses the review feedback on #4482.

nanobot/config/schema.py

@@ -2,9 +2,9 @@
 from __future__ import annotations
 
 from pathlib import Path
-from typing import TYPE_CHECKING, Any, Literal
+from typing import TYPE_CHECKING, Any, ClassVar, Literal
 
-from pydantic import AliasChoices, ConfigDict, Field, model_validator
+from pydantic import AliasChoices, ConfigDict, Field, field_validator, model_validator
 from pydantic_settings import BaseSettings
 
 from nanobot.config_base import Base
@@ -182,7 +182,29 @@ class ProviderConfig(Base):
     extra_headers: dict[str, str] | None = None  # Custom headers (e.g. APP-Code for AiHubMix)
     extra_body: dict[str, Any] | None = None  # Extra provider request fields; shape depends on provider/API surface
     extra_query: dict[str, str] | None = None  # Extra query params (e.g. api-version for Azure-style gateways)
-    thinking_style: Literal["thinking_type", "enable_thinking", "reasoning_split"] | None = None  # Thinking/reasoning style for custom providers
+    thinking_style: str | None = None  # Thinking/reasoning style for custom providers
+
+    # Valid values mirror the keys of _THINKING_STYLE_MAP in
+    # nanobot/providers/openai_compat_provider.py. Kept duplicated here to
+    # avoid an import cycle (schema.py must not import from providers/).
+    _VALID_THINKING_STYLES: ClassVar[tuple[str, ...]] = (
+        "thinking_type",
+        "enable_thinking",
+        "reasoning_split",
+    )
+
+    @field_validator("thinking_style")
+    @classmethod
+    def _validate_thinking_style(cls, v: str | None) -> str | None:
+        if not v:  # None or "" -> no injection, valid (backwards compatible)
+            return v
+        if v not in cls._VALID_THINKING_STYLES:
+            raise ValueError(
+                f"Invalid thinking_style {v!r}. "
+                f"Must be one of: {', '.join(repr(s) for s in cls._VALID_THINKING_STYLES)} "
+                f"(or empty/omitted)."
+            )
+        return v
 
 
 class BedrockProviderConfig(ProviderConfig):

tests/providers/test_custom_thinking_style.py

@@ -45,3 +45,18 @@ class TestCustomProviderThinkingStyle:
         }
         pc = ProvidersConfig.model_validate(data)
         assert pc.custom.thinking_style == "enable_thinking"
+
+    def test_invalid_thinking_style_raises_with_clear_message(self) -> None:
+        """An invalid thinking_style must raise a ValidationError whose message
+        lists the valid options (not just Pydantic's generic Literal error)."""
+        import pytest
+        from pydantic import ValidationError
+
+        with pytest.raises(ValidationError) as exc_info:
+            ProviderConfig.model_validate({"thinkingStyle": "thinking_typ"})
+
+        message = str(exc_info.value)
+        assert "Invalid thinking_style" in message
+        assert "thinking_type" in message
+        assert "enable_thinking" in message
+        assert "reasoning_split" in message