Core Design Principles (Operational Checklist)

Use when

• A task feels “easy to overbuild” (new helpers, new layers, new abstractions).
• You’re not sure where code should live.
• You need to choose between “quick fix” vs “correct boundary”.

Inputs (ask/confirm)

• What capability/bounded context owns this change?
• What is the smallest stable interface needed by the next layer?
• Where are the side effects (if any)?

Workflow (tool-first → assembly)

1. Identify the tool: the smallest reusable unit (pure function, port, adapter, store method).
2. Place it in the owner (capability / workspace / eventing / integration) without cross-context imports.
3. Add the assembly: facade/effect/component that wires it, preserving unidirectional flow.
4. Verify deletion path: removing the feature should be mostly deleting code, not untangling.

Hard checks (fail fast)

• No new cross-layer imports that violate Presentation → Application → Domain.
• No domain-side framework imports or side effects.
• No “god” utilities; prefer small, intention-revealing APIs.
• State stays centralized; UI binds to signals.

References

• .github/instructions/05-design-principles-copilot-instructions.md
• AGENTS.md and src/app/**/AGENTS.md