Fix ContentVariantTool to implement required SimpleTool abstract methods

- Add get_tool_fields() stub method (required by SimpleTool ABC)
- Add prepare_prompt() implementation using chat-style prompt
- Tool now successfully instantiates and can be registered
- All 4 tools (chat, contentvariant, listmodels, version) working

tools/contentvariant.py

@@ -72,8 +72,22 @@ class ContentVariantTool(SimpleTool):
     def get_request_model(self):
         return ContentVariantRequest
 
-    def format_request_for_model(self, request: ContentVariantRequest) -> dict:
-        """Format the content variant request for the AI model"""
+    def get_tool_fields(self) -> dict:
+        """
+        Tool-specific field definitions for ContentVariant.
+
+        Note: This method isn't used since we override get_input_schema(),
+        but it's required by the SimpleTool abstract base class.
+        """
+        return {
+            "content": {
+                "type": "string",
+                "description": "Base content or topic to create variations from",
+            }
+        }
+
+    async def prepare_prompt(self, request: ContentVariantRequest) -> str:
+        """Prepare the content variant prompt"""
         prompt_parts = [f"Generate {request.variation_count} variations of this content:"]
         prompt_parts.append(f"\n**Base Content:**\n{request.content}")
 
@@ -94,18 +108,9 @@ class ContentVariantTool(SimpleTool):
             "testing angles, and predicted audience responses."
         )
 
-        formatted_request = {
-            "prompt": "\n".join(prompt_parts),
-            "files": request.files or [],
-            "images": request.images or [],
-            "continuation_id": request.continuation_id,
-            "model": request.model,
-            "temperature": request.temperature,
-            "thinking_mode": request.thinking_mode,
-            "use_websearch": request.use_websearch,
-        }
-
-        return formatted_request
+        # Use SimpleTool's chat-style prompt preparation
+        request.prompt = "\n".join(prompt_parts)
+        return self.prepare_chat_style_prompt(request)
 
     def get_input_schema(self) -> dict:
         """Return the JSON schema for this tool's input"""