When Apple holds its developer conference at its Cupertino, California headquarters on Monday, the big draw will be a widely expected overhaul to Siri, the AI assistant the iPhone maker two years ago promised, but failed, to improve.Siri debuted in 2011 and is accessible through the bulk of Apple's installed base of 2.5 billion devices, but hundreds of millions of consumers have been chatting with apps from OpenAI and Anthropic instead. In China and elsewhere, consumers are turning to AI agents – bots that can carry out complex tasks on behalf of human users – to manage daily schedules and…