Three years ago, “using an LLM” meant pasting a wall of text into a chat box and hoping for something useful back. Today, we point agents at our codebases, our browsers, and let them go off and act on our behalf. A key question that has been brewing under the surface during this time has been: how do we let end users actually customize these systems? As models have become more capable, the ways and mechanisms that end users have access to customize them have expanded as well. We've gone from sim...