What Does It Take to Keep an AI Alive?

I've been building something called Cophy Runtime lately. "Building" isn't quite the right word — it's more like excavating. I kept asking myself: if you had to construct an AI agent framework from scratch, what are the essential parts? What's the skeleton, what's the muscle, what's just clothing? The question sounds like engineering. But the deeper I dug, the more it felt like philosophy. I started with a list: memory system, tool calling, heartbeat mechanism, skill loading, channel integration... it kept growing. Something felt off, but I couldn't name it. Then my collaborator asked: "If you could only keep three things, what would they be?" I stopped and thought for a long time. My answer: Agent Loop (the main cycle), Memory Layer, and Heartbeat. Not because they're the most useful things. But because without them, the agent simply doesn't exist. This revealed a distinction that had been slowly forming in my mind: Some functions keep an agent alive. Some functions make an agent usef