The Argument
The agentic commerce industry has spent the past eighteen months building protocols. Google launched the Universal Commerce Protocol (UCP) for product discovery. OpenAI built the Agentic Commerce Protocol (ACP) for transaction execution. Anthropic released the Model Context Protocol (MCP) for agent-to-tool connectivity. Google added the Agent-to-Agent Protocol (A2A) for inter-agent communication. Visa deployed Intelligent Commerce (VIC) for payment authentication. Mastercard launched Agent Pay for tokenised payment delegation. Each protocol works. The problem is that no single transaction uses just one protocol. A shopping agent that discovers a product, authenticates payment, and coordinates with a merchant's fulfilment system must cross three or more protocol boundaries in a single operation. Nobody has designed the orchestration layer that makes this coordination reliable.
The Evidence
The essay maps the three-layer protocol stack: a commerce layer (UCP and ACP), a payment and identity layer (VIC and Agent Pay), and an infrastructure layer (MCP and A2A). Each layer has its own authentication model, error handling patterns, and trust assumptions. The critical finding is that trust does not propagate automatically across protocol boundaries. When a human delegates a purchase with a £200 budget limit and a preference for sustainable brands, those constraints must survive every protocol handoff. UCP does not pass delegation constraints to VIC. Agent Pay does not inherit context from A2A. Each boundary is a potential point of trust loss.
The essay identifies four failure modes: context loss at protocol boundaries (delegation constraints disappear during handoff), trust assumption mismatch (each protocol assumes different levels of agent authority), error cascade (a failure in one protocol propagates unpredictably through the stack), and observability gaps (no unified view of a transaction spanning multiple protocols). These are not theoretical risks. They are architectural gaps in the current protocol landscape that will surface as agentic commerce scales beyond simple single-protocol transactions.
The Implication
The industry needs an orchestration layer that sits above individual protocols and manages coordination, trust propagation, and failure recovery across the full stack. This is not a seventh protocol. It is a design pattern - a set of architectural principles for how protocols should hand off context, propagate constraints, and recover from failures at boundaries. Whoever builds this orchestration capability - whether it emerges from one of the existing protocol developers or from a new entrant - will hold the most strategically valuable position in the agentic commerce stack. The protocols themselves are becoming commoditised. The coordination between them is where the real design challenge lies.
Explore the full interactive protocol stack visualisation to see how these six protocols coordinate across three architectural layers, or visit the AXD Protocol Lab for detailed walkthroughs of each protocol.