Backplane Skill Protocol

Host-independent parsing, discovery, resolution, eligibility, complete tar+gzip bundle preparation, and a versioned Backplane read client for Agent Skills.

The library performs no Skill execution, directory scanning, network access, or database access at application startup. Hosts supply source roots, policies, destinations, and budgets explicitly.

Remote sources and one-shot preparation

Backplane.SkillProtocol.Client requires an HTTP origin, source ID, non-secret access-context ID, and credential supplier. It requests only the frozen /skill-protocol/v1/catalog, /resolve, and /artifact routes. All attempts share one deadline, responses are byte-bounded, and redirects are refused.

Backplane.SkillProtocol.Source.Backplane performs one verified download for each call. The caller supplies a fresh destination whose parent directory already exists:

source = Backplane.SkillProtocol.Source.Backplane.new!(client)

{:ok, prepared} =
  Backplane.SkillProtocol.Source.Backplane.prepare(source, skill_id, revision,
    destination: Path.join(task_root, "prepared-skill")
  )

Preparation resolves once, downloads that exact artifact, verifies it, and atomically publishes the complete files. Missing, invalid, or existing destinations fail without a network request. A later call downloads again, even for the same revision; remote failures never fall back to earlier files. The returned directory remains available until the host removes it. The library does not manage, scan, migrate, or clean caller-owned destinations.