Six agent protocols launched in the last year. Everyone's obsessing over model selection. The operating surface around the model is what actually breaks.
Google I/O opened today with a flood of agent demos. Prompts becoming apps. Vibe coding going production. The spectacle is real. But the thing that determines whether any of this works isn't on stage. It's the quiet protocol stack underneath — MCP, A2A, AGUI, and their contested cousins.
Most teams can tell you which LLM they're using. Almost none can answer: which tools should the agent see? Who else can it delegate to? Where does the human approve or cancel?
Those three questions are the stack. Here's what sits at each layer.
MCP: tools are a security boundary, not a feature toggle
