We’re using NotificationCompat.MessagingStyle for some push-notifications in our Android app. Notifications are recieved via OneSignal SDK, and we implement INotificationServiceExtension to mutate them, including the aforementioned MessagingStyle.
When we receive a new message notification, we want to add the new message to an existing notification if it exists, otherwise display a new one.
Currently this requires fetching the old notification by its locusId, copying its style, canceling it and displaying a new one with the new message added. I am not sure if it’s the correct way. I should also mention that no notification ids are tracked, they a auto-generated by OneSignal.
Here’s a simplified implementation of INotificationServiceExtension:

class PushNotificationService : INotificationServiceExtension {
    override fun onNotificationReceived(event: INotificationReceivedEvent) {
        when (val type = event.notification.additionalData?.getString("type")) {
            "new_message" -> {
                // Can't be null if type exists
                val data: NewMessagePushData = event.notification.additionalData!!.let {
                    Json.decodeFromString(it.toString())
                }
                event.applyConversationStyle(data)
            }
            // ...
        }
    }

    private fun INotificationReceivedEvent.applyConversationStyle(
        data: NewMessagePushData
    ) {
        val notificationManager = context.getSystemService(FirebaseMessagingService.NOTIFICATION_SERVICE)
                as NotificationManager
        val previousNotification = notificationManager
            .activeNotifications
            .find {
                it.notification.locusId?.id == data.chatId.toString()
            }
        val usersDao = getService(context).usersDao()
        notification.setExtender { notification ->
            val (user, icon) = runBlocking {
                val user = /* Fetch user from local DB*/
                val icon = user?.let {/*Fetch user's avatar and process it for display*/}
                user to icon
            }
            if (user == null) return@setExtender notification

            val person = /*Build an androidx.core.app.Person from user data*/

            val style = previousNotification?.let {
                NotificationCompat.MessagingStyle.extractMessagingStyleFromNotification(it.notification)
            } ?: NotificationCompat.MessagingStyle(
                /*Build an androidx.core.app.Person for current user*/
            )
            
            // This is questionable!
            previousNotification?.id?.let {
                OneSignal.Notifications.removeNotification(it)
            }


            notification
                .setContentTitle(user.fullName.asString(context))
                .setStyle(
                    style
                        .addMessage(
                            NotificationCompat.MessagingStyle.Message(
                                data.body,
                                System.currentTimeMillis(),
                                person
                            )
                        )
                )
                .addPerson(person)
                .setLargeIcon(icon?.toIcon(context))
                .setCategory(Notification.CATEGORY_MESSAGE)
                .setLocusId(LocusIdCompat(data.chatId.toString()))
                .setShortcutInfo(context.createConversationShortcutIfNeeded(
                    data = data,
                    user = user,
                    person = person,
                    icon = icon
                ))
        }
    }
}

What is the correct and standard way of doing what I want? Should I bring my messages DAO into this service to fetch messages? Should I ask the backend team to keep track of notification ids and send the same ones for any particular conversation so the system auto-mutates them for me? Or should I keep track of those ids myself?