Your question is Codebase Structure, Dependency Direction, and Testing. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Describe how you ensure your code is maintainable and scalable for long-term projects.
Give a practical codebase structure with clear layers, dependency direction, state ownership, dependency injection, and testing practices. Explain at least one trade-off against an alternative approach.