Where ACC Fits in the Agent Stack: Transport, Runtime Control, and Business Authority

Connecting an AI agent to a tool is becoming easier. Letting that agent operate a real business system responsibly is still a different problem. Imagine an existing commerce system with APIs for reading orders, changing inventory, creating refunds, and disabling staff accounts. OpenAPI can describe the endpoints. A tool protocol can make them discoverable. An agent framework can select an operation and generate arguments. But those pieces do not, by themselves, answer several business questions: Which operations may be exposed to an agent-facing surface? Which invocation must carry a trusted acting subject? Which operation is high consequence? When does an invocation express approval intent? Which calls need stronger audit handling? Which execution properties should a runtime know before it invokes the API? These questions sit between tool connectivity and final business authorization. That is the layer the Agent Capability Contract, or ACC, is designed to describe. Start with a concrete operation Consider this API operation: paths : /orders/{order_id}/refund : post : operationId : createRefund parameters : - in : path name : order_id required : true schema : type : string requestBody : required : true content : application/json : schema : type : object required : [ amount ] properties : amount : type : number minimum : 0 This is enough to describe how to call the operation. It is not enough to describe how an agent-facing system should treat it. ACC adds a small, machine-readable declaration next to the operation: x-agent-capability : version : 1 enabled : true scope : refund.create risk : level : high subject : required : true approval : required : true when : - param : amount op : " >" value : 1000 audit : sensitive : true execution : readonly : false idempotent : true timeout_ms : 10000 The declaration does not grant the refund. It tells a compatible runtime how the operation should be presented and governed before the business system receives the call. The miss