Skill-in-Skill: Agent Skills That Carry Their Own Execution Conditions Across Domains

Agent skills provide LLMs with reusable procedural knowledge, but existing skills typically specify what to do without carrying the conditions that govern valid use. As a result, activation scope, authorization, and execution evidence remain external to the skill and may be lost when the skill is transferred or reused. We introduce Skill-in-Skill (SIS), a portable skill architecture that binds a reusable capability with its governance contract as a single self-contained unit. SIS carries activation, authorization, execution, and verification conditions with the skill, and records runtime evidence to support independent validation of governed execution. We compare SIS with an External Governance Sidecar (SIDECAR) that keeps equivalent governance outside the skill package. Across open-weight models, SIS consistently reduces context-access and tool-use overhead, with up to 90.3% fewer repeated task-context reads and 13.2% lower end-to-end latency. In cross-boundary transfer tests, SIS preserves authorized execution after site or principal changes while blocking effects when destination governance is absent. These results show that binding governance to the capability improves the portability and efficiency of governed skill execution without weakening enforcement.