Instruction file imported from xaligo/xaligo (.github/instructions/09-coding/09-01-01-coding-internal-usecase-root-contract.instructions.md). Copyright stays with the author.

09.01.01 Coding: internal/usecase root contract

internal/usecase root contract

Every non-test Go file directly below internal/usecase is one complete use-case component. Its declarations follow this order:

1. XxxUsecase interface;
2. unexported xxxUsecase concrete type;
3. NewXxxUsecase constructor returning the interface; and
4. receiver methods containing that component's orchestration.

Repository dependencies are constructor-injected fields on the concrete type. Do not leave declaration-free algorithm/wrapper/helper files such as a file containing only package functions. Calculation helpers belong in the versioned engine. A shared-source compatibility function may follow the receiver methods only when it is a thin, deprecated delegation with no independent logic.

Private orchestration helpers for a component stay in that component's file; do not create render_options.go, render_scene.go, or another root-level implementation fragment that lacks its own interface, concrete type, and constructor.