fix: preserve provider-specific tool call metadata for Gemini

nanobot/agent/subagent.py

@@ -135,14 +135,7 @@ class SubagentManager:
                 if response.has_tool_calls:
                     # Add assistant message with tool calls
                     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.append({
@@ -230,6 +223,22 @@ Stay focused on the assigned task. Your final response will be reported back to
             parts.append(f"## Skills\n\nRead SKILL.md with read_file to use a skill.\n\n{skills_summary}")
 
         return "\n\n".join(parts)
+
+    @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 cancel_by_session(self, session_key: str) -> int:
         """Cancel all subagents for the given session. Returns count cancelled."""