Constant CLIENT_TOOL_CALL_TRIGGER 

const CLIENT_TOOL_CALL_TRIGGER: &str = "!MOCK_CLIENT_TOOL_CALL!";

Like TOOL_CALL_TRIGGER, but the call is one only the client can answer, so the chatbot suspends the turn instead of running anything. The turn is finished by the tool-response endpoint, whose request ends in the tool output and so gets the same text round.