Portable contract checklist

• The bundle is a directory containing a regular SKILL.md file.
• Frontmatter starts on the first line and has a closing delimiter.
• name is present, no longer than 64 characters, and uses lowercase letters, digits, and single hyphens.
• name matches the bundle directory.
• description is present, no longer than 1024 characters, and states when the skill is useful.
• Optional compatibility contains 1 to 500 characters when present.
• Optional metadata maps string keys to string values.
• Optional experimental allowed-tools is a non-empty space-separated string whose behavior is verified in the target host.
• Unknown runtime fields are separated from the portable package contract and handled by an explicit adapter.
• The Markdown body contains the procedure.
• Optional portable metadata and host-specific extensions remain distinguishable.

Passing this checklist makes the package structurally loadable. It does not grant filesystem, network, secret, subprocess, or tool authority.