The demo

@Entity
class Trip(
    var traveler: String,
    var destination: String,
    var startDate: LocalDate,
    var status: TripStatus = TripStatus.DRAFT,
    @OneToMany(cascade = [CascadeType.ALL])
    val hotels: MutableSet<HotelBooking> = linkedSetOf(),
    @OneToMany(cascade = [CascadeType.ALL])
    val flights: MutableSet<FlightBooking> = linkedSetOf(),
    @OneToMany(cascade = [CascadeType.ALL])
    val trains: MutableSet<TrainBooking> = linkedSetOf(),
)

Policy("Hotel budget",
    "Hotels may cost at most 180 EUR per night. " +
    "In London, Paris and Zurich the limit is 250 EUR per night.")

Policy("Rail first",
    "If the train journey takes 4 hours or less, the train must be used " +
    "instead of a flight. Second class only.")

@Service
@Transactional(readOnly = true)
class TravelFacts(private val trips: TripRepository, private val policies: PolicyRepository) {
    fun trip(tripId: Long): TripSnapshot
    fun policies(): List<PolicyText>
    fun costs(tripId: Long): CostBreakdown
}

@Serializable
data class ReviewOutcome(
    val verdict: Verdict,
    val summary: String,
    val violations: List<String> = emptyList(),
)

interface TripReviewer {
    val agent: ReviewAgent
    fun review(tripId: Long): ReviewOutcome
}

POST /api/trips/2/submit?agent=EMBABEL

@Async
@TransactionalEventListener
fun on(event: TripSubmitted) {
    val review = reviewers.getValue(event.agent).review(event.tripId)
    reviews.save(TripReview(event.tripId, event.agent, review))
}