Skill: backend/domain-logic-module

Purpose

Create or refactor domain logic so that business rules live in:

• a testable module boundary
• with explicit invariants
• and deterministic error behavior

This skill prevents domain rules from leaking into controllers, jobs, or adapters.

Inputs

• Domain concept to implement or change (1–3 sentences)
• Invariants that must always hold (must/must-not list)
• Entry points that will call this module:
  • endpoint handler / job / integration adapter
• Repo profile (preferred): <repo>/REPO_PROFILE.json