Overview
Agent skills can serve two different roles. A procedure is a skill the human deliberately invokes to make the agent follow a particular workflow. An ability is a skill the model can invoke for itself when it decides the capability is relevant.
Both forms can be useful, but they create different control and context costs. Procedure-oriented design keeps the human in charge of sequencing. Ability-oriented design gives the model more autonomy, but each available ability can expose descriptive text to the context window. A large catalogue of abilities can therefore consume context before useful work begins.