Business write + outbox_events INSERT (same transaction, atomic)
    ↓
Relay worker polls outbox_events every 1s
    ↓
Publishes to NATS JetStream
    ↓
Marks event as published (or increments retry counter)
    ↓
Cleanup: published events deleted after 7 days

// Writing to DB, then publishing directly — dual-write risk
db.Save(&user)
nats.Publish("user.created", event) // lost if NATS is down

db.Transaction(func(tx *gorm.DB) error {
    tx.Create(&user)
    return outboxRepo.Save(tx, OutboxEvent{
        EventType:   "user.created",
        AggregateID: user.ID,
        Payload:     mustMarshal(event),
    })
})
// Relay worker publishes asynchronously