The canonical three-package capability seam for reusable agent instructions: a provider registry, a local implementation, and the model-facing catalog/loader consumer. All are product packages.

Package	Role	ctx key
`skill/`	Provider registry, precedence resolution, stable catalog snapshots, and full-definition lookup	`ctx.skills`
`skill-local/`	Project/custom/user filesystem provider	(registers on `ctx.skills`)
`tool-skill/`	Session-prefix catalog and model-facing `skill` loader	(registers on `ctx.tools`)

The interface lives at skill/skill/. Providers register synchronously and perform asynchronous discovery through ctx.skills; tool-skill consumes only that interface, so an embedded or remote provider can replace or complement skill-local without changing the model-facing contract. agent-core loads this family by default, but it remains a capability outside the core control spine, parallel to bash/, fs/, web/, and subagent/.