[Phase 2] Immutable registry and publishing CLI/CI

[mrgoonie]

Depends on

• Epic [Epic] SkillX Marketplace & Agent-Native Platform Roadmap #31

• Phase 0 [Phase 0] Foundations and protected data boundaries #32 (contracts and data boundaries)

• Phase 1 [Phase 1] Agent-native discovery and compatibility #33 (published contract surfaces)

Objective

Move SkillX from GitHub registration to immutable reproducible package releases.

Contracts come from Phase 0/1. Package-format work may begin after Phase 0.

Scope

• Deterministic artifact format.
• R2 artifact storage.
• Publisher namespace ownership.
• import vs publish semantics.
• validate, pack, publish, promote.
• CI trusted/scoped publishing.
• Quarantine/review/yank lifecycle.
• Entitlement-aware artifact resolution.

Implementation tasks

• Define archive layout and path safety constraints.
• Implement deterministic packer + SHA-256.
• Store immutable artifacts in R2.
• Add package/release registry APIs.
• Add publisher profiles/namespaces.
• Add namespace authorization.
• Rename/deprecate old GitHub publish semantics toward import.
• Implement skillx validate.
• Implement skillx pack.
• Implement release skillx publish.
• Implement skillx promote.
• Add publish idempotency keys.
• Add CI-scoped publisher credentials.
• Evaluate/implement GitHub OIDC trusted publishing.
• Add quarantine and review state.
• Add yanking and release-resolution policy.
• Add authorized signed/short-lived artifact download flow.
• Publish one standalone AgentKit skill manually.
• Publish same AgentKit artifact through CI.

Acceptance criteria

• Same version cannot receive different bytes.
• Manual/CI publish of same input resolves to same digest.
• Retried publish is safe.
• Publisher token cannot change commerce/account state.
• One AgentKit standalone skill is published without altering ak installer behavior.