Is it possible to keep type-safty with kotlinx.serialization of a 3rd-party sealed class?

Question

There is an Event sealed interface with UserConnected and EstimationSent implementations.

data class User(
  val id: String,
  val displayName: String,
)

sealed interface Event {
  val id: String
}

data class UserConnected(
  override val id: String,
  val user: User,
) : Event


data class EstimationSent(
  override val id: String,
  val userId: String,
  val estimation: Int,
) : Event

These classes living in a 3rd-party module, thus cannot be annotated or modified.

Is it possible to make the Event sealed interface with its implementations serializable producing the following JSON?

UserConnected:

{
  "eventId": "string",
  "data": {
    "userId": "string",
    "userDisplayName": "string"
  }
}

EstimationSent:

{
  "eventId": "string",
  "data": {
    "userId": "string",
    "estimation": 42
  }
}

The goal would be to have a polymorphic serialization which possibly type-safe.

---

I have tried to implement a custom KSerializer and register it like this:

val format = Json {
  serializersModule = SerializersModule {
    polymorphic(Event::class) {
      subclass(UserConnected::class, UserConnectedSerializer)
      subclass(EstimationSent::class, EstimationSentSerializer)
    }
  }
}

However, this solution does not provide compile-time error if there is a missing KSerializer for an Event implementation.