Spec design for shared Go contract kit

[aryeko]

Story

• Shared Contract Kit for Go Variants #69

Motivation

Agree on shared API surface before implementation and adoption.

Scope

In:

• Shared helper API
• Adoption boundaries
• Compatibility expectations

Out:

• Target-specific business logic

Requirements

• Define helper functions and payload schema ownership
• Define variant integration points

Acceptance criteria

• Shared contract design captures required helper API and adoption plan

Verification

Commands:

• go list ./...

CI checks:

• (none)

Evidence:

• Shared contract API design

Artifacts

• Design consumed by T-021..T-024

Spec reference

• .sisyphus/plans/apps-implementation-roadmap.md
• Section: ST-006
• Quote: Shared Contract Kit for Go Variants

Dependencies

Blocked by:

• (none)