fix: replace Price object in TransactionWasCreated with primitives

[josecarlospeer-cloud]

What

TransactionWasCreated was carrying a Price value object instead of primitive data. This couples the event schema to the Price class — a latent replay correctness bug.

Why it matters

Domain events are the durable record of what happened. They are serialized to the event store and replayed to rebuild aggregates. If Price ever changes (e.g., gains a taxRate field), old events deserialized from storage will be structurally inconsistent with the new class — silently producing wrong aggregate state on replay.

"Events are the durable record. They must be self-describing with primitive data."
— Young, CQRS Documents (2010)

Before

export default class TransactionWasCreated implements Domain.DomainEvent {
    constructor(
        public readonly aggregateId: string,
        public readonly product: string,
        public readonly price: Price,  // ← complex object, schema-coupled
        occurredAt?: Date,
    ) {}
}

After

export default class TransactionWasCreated implements Domain.DomainEvent {
    constructor(
        public readonly aggregateId: string,
        public readonly product: string,
        public readonly amount: number,    // ← primitive
        public readonly currency: string,  // ← primitive
        occurredAt?: Date,
    ) {}
}

Transaction.onTransactionWasCreated() reconstructs Price from primitives:

this.price = new Price(event.amount, event.currency);

Transactions.fromCreated() reads event.amount / event.currency directly (no change in semantics, removes property traversal through a domain class).

Transaction.test.ts updated to assert event.amount and event.currency individually.

Verification

yarn lint   ✅ 0 errors
yarn test   ✅ 13/13 passing

[jorge07]

this needs precision, not the best way to deal with money in the long run

[josecarlospeer-cloud]

Good call. Addressed in a second commit: Price.amount is now a string throughout.

What changed:

• Price.amount: number → string — no IEEE 754 anywhere in the domain or event
• TransactionWasCreated.amount: number → string — event carries exact decimal string
• CreateCommand: String(price.amount) converts the JSON number from the HTTP payload at the application boundary
• Transactions.fromCreated: Number(event.amount) for the TypeORM float column (read model precision is a separate concern; the event store record is now exact)
• All tests updated to pass string literals (new Price("12.5", "EUR"))

For a production system the next step would be accepting amount as string (or integer minor units) from the HTTP API too — but that's a breaking API change and Phase 4 territory.