Cursor rule

1---
2alwaysApply: true
3---
4# Implementing New Features
5 
6## Checklist Before Coding
7 
81. Identify which layer the feature belongs to
92. Define interfaces/contracts before implementations
103. Start with the domain if business rules are involved
114. Write tests alongside the implementation
12 
13## Implementation Order
14 
15```
161. Domain (entities, services)          → Unit tests
172. Application (interfaces, use cases)  → Tests with mocks
183. Infrastructure (repositories, APIs)  → Integration tests
194. Presentation (UI, formatters)        → Visual verification
20```
21 
22## Patterns to Follow
23 
24- Single responsibility per class/function
25- Prefer composition over inheritance
26- Use discriminated unions to represent states
27- Inject dependencies — never instantiate services internally
28- Side-effect-free code in the domain
29 
30## What to Avoid
31 
32- Classes with more than 200 lines
33- Functions with more than 5 parameters (use a config object)
34- Circular imports between layers
35- Complex conditional logic (extract into strategy/policy)
36- Magic strings (use enums or constants)
37- Comments explaining "what" — the code should be clear
38