HSDD Contract: First-Class Versioned Interfaces

A contract is the only thing one HSDD node may know about another. It is a standalone, versioned file, not prose buried in a spec.

Core principle: A contract has two parts with two jobs. The YAML frontmatter is machine-readable metadata projected into the registry. The body is the human-facing interface injected into a consuming phase's context. A consumer reads exactly one of those, never the producing node's internals.

When to Use

• A node spec (hsdd-spec) named a contract id under Consumes/Produces and the body needs writing.
• A contract must change: bump the version, add a guarantee, deprecate.
• The registry (hsdd/contract/INDEX.md) needs regenerating after a change.

Do NOT use for node decomposition (hsdd-spec) or phase planning (hsdd-phase-plan).