For thirty years, the person at the keyboard was the one who acted. Software waited for a click, a keystroke, a confirmed intent, then executed exactly what was asked. The entire discipline of interface design grew up around that fact: reduce friction, clarify affordances, make the right action obvious, because a human being was going to press the button and live with what happened next.

That chain is changing shape. The person at the keyboard is becoming the person who delegates. They describe an outcome, hand it to an agent, and the agent decides which tools to call, which data to touch, and in what order, often without a human reviewing any individual step. The click is still there. It now authorises a chain of decisions rather than a single one.

This changes the actual design question. “Is it usable” assumes the human is the one doing the acting, and asks whether they can do it correctly. It is a question about interface. “Is it containable” assumes the agent is the one doing the acting, and asks whether it can do something the human never intended, given the tools and data it has been handed. It is a question about the boundary of the system, not the clarity of its buttons.

Usability failures are recoverable: a confusing screen wastes a few minutes and gets fixed in the next release. Containment failures are not the same shape of problem. An agent that can route protected data to an undeclared sink, or exceed its authority under some input nobody tested, does not fail gracefully. It fails once, silently, and the cost lands wherever the data or the authority ended up.

This is the problem KERN is built to answer directly: not by watching an agent’s behaviour and raising an alarm when something looks wrong, but by compiling its declared tools, data labels and authority boundaries into a bounded system and proving, for every input, what it can and cannot reach. Usable is still worth having. Containable is now the precondition for shipping anything that acts on your behalf.