fix: remove extra_body tool_choice hack for Claude backend

PydanticAI handles tool_choice natively for Anthropic. The extra_body
hack caused an infinite tool call loop where Claude kept calling the
same tool because tool_choice was forced to "any".

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/anthropic/model_selector.py

@@ -132,6 +132,23 @@ def get_model(prefer_cloud: bool | None = None) -> Union[AnthropicModel, OpenAIC
     )
 
 
+def get_tool_choice_settings() -> 'ModelSettings':
+    """
+    Get model_settings for forcing tool calls on the first request.
+
+    For Claude: PydanticAI handles tool_choice natively, so no extra_body needed.
+    For Ollama: Pass tool_choice="required" via extra_body to force tool calling.
+    """
+    from pydantic_ai.settings import ModelSettings
+
+    if is_claude_available() and config.PREFER_CLOUD_BACKEND:
+        # PydanticAI's Anthropic model handles tool_choice internally
+        return ModelSettings()
+    else:
+        # Ollama needs explicit tool_choice via extra_body
+        return ModelSettings(extra_body={"tool_choice": "required"})
+
+
 def get_model_info() -> dict:
     """
     Get information about the current model configuration.