I was trying something like this but noticed that the exception is already unwrapped at this point.

coroutineContext[Job]?.invokeOnCompletion {
        if(it is CancellationException){
            call.cancel(it.message,it.cause ?: it)
        }
    }

That's not a cancellation handler @withoutclass. Cancellation exceptions are considered "normal".

Ah, my mistake.