出海助手-代码架构设计 / Codebase Design
> 本技能改造自开源技能 codebase-design（来源：mattpocock/skills，Matt Pocock 工程/生产力技能）。已完整保留原始运行文件（scripts/references/assets 与 LICENSE），并新增中文出海使用说明。原始英文说明见文末「English (Original)」与同目录 SKILL.original.md。
功能说明 / Functional Overview
设计与演进代码库结构，保持模块清晰、可维护、可扩展。
适用场景 / Use Cases
- 出海项目架构设计
- 模块边界划分
- 技术债治理规划
使用方法 / How to Use
- 在 WorkBuddy 中直接以自然语言描述需求，本技能会自动触发。
- 技能运行所需的全部脚本与资源已随目录附带（见本目录
scripts/、references/等），可离线运行。 - 涉及第三方服务（如 Notion / Slack / GitHub / X / WhatsApp 等）时，请按原始说明配置对应的 API Key 或授权。
示例 / Examples
- 「出海项目架构设计」——用自然语言把任务交给本技能即可。
限制说明 / Limitations
- 需要外部服务/凭证的技能，请先完成授权配置后使用。
- 本技能为开源技能的中文本地化版本，核心逻辑与原技能一致；如遇专业术语，正文保留英文原词（如 Shopify、SEO、GA4 等）。
English (Original) / 英文原文（完整保留）
> The section below is the original skill definition, preserved verbatim for traceability and full functionality.
Codebase Design
Design deep modules: a lot of behaviour behind a small interface, placed at a clean seam, testable through that interface. Use this language and these principles wherever code is being designed or restructured. The aim is leverage for callers, locality for maintainers, and testability for everyone.
Glossary
Use these terms exactly — don't substitute "component," "service," "API," or "boundary." Consistent language is the whole point.
Module — anything with an interface and an implementation. Deliberately scale-agnostic: a function, class, package, or tier-spanning slice. Avoid: unit, component, service.
Interface — everything a caller must know to use the module correctly: the type signature, but also invariants, ordering constraints, error modes, required configuration, and performance characteristics. Avoid: API, signature (too narrow — they refer only to the type-level surface).
Implementation — what's inside a module, its body of code. Distinct from Adapter: a thing can be a small adapter with a large implementation (a Postgres repo) or a large adapter with a small implementation (an in-memory fake). Reach for "adapter" when the seam is the topic; "implementation" otherwise.
Depth — leverage at the interface: the amount of behaviour a caller (or test) can exercise per unit of interface they have to learn. A module is deep when a large amount of behaviour sits behind a small interface, shallow when the interface is nearly as complex as the implementation.
Seam (Michael Feathers) — a place where you can alter behaviour without editing in that place; the location at which a module's interface lives. Where to put the seam is its own design decision, distinct from what goes behind it. Avoid: boundary (overloaded with DDD's bounded context).
Adapter — a concrete thing that satisfies an interface at a seam. Describes role (what slot it fills), not substance (what's inside).
Leverage — what callers get from depth: more capability per unit of interface they learn. One implementation pays back across N call sites and M tests.
Locality — what maintainers get from depth: change, bugs, knowledge, and verification concentrate in one place rather than spreading across callers. Fix once, fixed everywhere.
Deep vs shallow
Deep module = small interface + lots of implementation:
┌─────────────────────┐
│ Small Interface │ ← Few methods, simple params
├─────────────────────┤
│ │
│ Deep Implementation│ ← Complex logic hidden
│ │
└─────────────────────┘
Shallow module = large interface + little implementation (avoid):
┌─────────────────────────────────┐
│ Large Interface │ ← Many methods, complex params
├─────────────────────────────────┤
│ Thin Implementation │ ← Just passes through
└─────────────────────────────────┘
When designing an interface, ask:
- Can I reduce the number of methods?
- Can I simplify the parameters?
- Can I hide more complexity inside?
Principles
- Depth is a property of the interface, not the implementation. A deep module can be internally composed of small, mockable, swappable parts — they just aren't part of the interface. A module can have internal seams (private to its implementation, used by its own tests) as well as the external seam at its interface.
- The deletion test. Imagine deleting the module. If complexity vanishes, it was a pass-through. If complexity reappears across N callers, it was earning its keep.
- The interface is the test surface. Callers and tests cross the same seam. If you want to test past the interface, the module is probably the wrong shape.
- One adapter means a hypothetical seam. Two adapters means a real one. Don't introduce a seam unless something actually varies across it.
Designing for testability
Good interfaces make testing natural:
- Accept dependencies, don't create them.
```typescript
// Testable
function processOrder(order, paymentGateway) {}
// Hard to test
function processOrder(order) {
const gateway = new StripeGateway();
}
```
- Return results, don't produce side effects.
```typescript
// Testable
function calculateDiscount(cart): Discount {}
// Hard to test
function applyDiscount(cart): void {
cart.total -= discount;
}
```
- Small surface area. Fewer methods = fewer tests needed. Fewer params = simpler test setup.
Relationships
- A Module has exactly one Interface (the surface it presents to callers and tests).
- Depth is a property of a Module, measured against its Interface.
- A Seam is where a Module's Interface lives.
- An Adapter sits at a Seam and satisfies the Interface.
- Depth produces Leverage for callers and Locality for maintainers.
Rejected framings
- Depth as ratio of implementation-lines to interface-lines (Ousterhout): rewards padding the implementation. We use depth-as-leverage instead.
- "Interface" as the TypeScript
interfacekeyword or a class's public methods: too narrow — interface here includes every fact a caller must know. - "Boundary": overloaded with DDD's bounded context. Say seam or interface.
Going deeper
- Deepening a cluster given its dependencies — see DEEPENING.md: dependency categories, seam discipline, and replace-don't-layer testing.
- Exploring alternative interfaces — see DESIGN-IT-TWICE.md: spin up parallel sub-agents to design the interface several radically different ways, then compare on depth, locality, and seam placement.
