fix: preserve provider-specific tool call metadata for Gemini

nanobot/agent/loop.py

@@ -208,14 +208,7 @@ class AgentLoop:
                     await on_progress(self._tool_hint(response.tool_calls), tool_hint=True)
 
                 tool_call_dicts = [
-                    {
-                        "id": tc.id,
-                        "type": "function",
-                        "function": {
-                            "name": tc.name,
-                            "arguments": json.dumps(tc.arguments, ensure_ascii=False)
-                        }
-                    }
+                    self._build_tool_call_message(tc)
                     for tc in response.tool_calls
                 ]
                 messages = self.context.add_assistant_message(
@@ -256,6 +249,22 @@ class AgentLoop:
 
         return final_content, tools_used, messages
 
+    @staticmethod
+    def _build_tool_call_message(tc: Any) -> dict[str, Any]:
+        tool_call = {
+                        "id": tc.id,
+                        "type": "function",
+                        "function": {
+                            "name": tc.name,
+                            "arguments": json.dumps(tc.arguments, ensure_ascii=False)
+                        }
+                    }
+        if getattr(tc, "provider_specific_fields", None):
+            tool_call["provider_specific_fields"] = tc.provider_specific_fields
+        if getattr(tc, "function_provider_specific_fields", None):
+            tool_call["function"]["provider_specific_fields"] = tc.function_provider_specific_fields
+        return tool_call
+
     async def run(self) -> None:
         """Run the agent loop, dispatching messages as tasks to stay responsive to /stop."""
         self._running = True