Cursor rule

1---
2description: Business rules and domain logic
3globs: web/src/domain/**/*.ts
4alwaysApply: false
5---
6 
7# Business Rules (Domain Layer)
8 
9## Principles
10 
11- **Total isolation**: zero imports from `infrastructure/`, `presentation/`, or external libs
12- **Immutability**: value entities (`Money`, `StockQuantity`) must be immutable
13- **Pure methods**: given the same input, always the same output
14- **Self-validation**: entities validate their own invariants in the constructor
15 
16```typescript
17// ✅ Value entity with validation
18class Money {
19  constructor(
20    readonly amount: number,
21    readonly currency: Currency,
22  ) {
23    if (amount < 0) throw new Error('Amount cannot be negative');
24  }
25 
26  add(other: Money): Money {
27    if (this.currency !== other.currency) throw new Error('Currency mismatch');
28    return new Money(this.amount + other.amount, this.currency);
29  }
30}
31```
32 
33## Domain Services
34 
35- `PortfolioCalculationService`: position calculations, gain/loss, average cost
36- `PortfolioAnalyticsService`: snapshots and analytical aggregations
37- Receive dependencies via interface (e.g., `IExchangeRateService`)
38 
39## Operations
40 
41- `VestingOperation`: represents RSU/ESPP vesting
42- `TradeOperation`: represents stock buy/sell
43- Each operation is an immutable record with all required data
44 
45## When Modifying Business Rules
46 
471. Change only in `domain/` — never in presentation
482. Write unit tests for every scenario
493. Validate against the business guide (`docs/guia_negocio.md`)
50