decodeJsonElement incorrectly returns the full array when decoding an array element via decodeFromJsonElement

[JBeet]

Describe the bug
In a custom deserialization for a JSON array I want to use JsonDecoder.decodeJsonElement(). I call decodeElementIndex, and expect it to return the next item in the JSON array. This works when decoding from a string (Json.decodeFromString), but doesn't work when decoding from a JsonElement (Json.decodeFromJsonElement)

To Reproduce

fun main() {
    val str = """[1,2]"""
    val json: JsonArray = Json.parseToJsonElement(str) as JsonArray
    val fromString: List<JsonElement> = Json.decodeFromString(JsonElementListSerializer, str)
    val fromJsonElement: List<JsonElement> = Json.decodeFromJsonElement(JsonElementListSerializer, json)
    println("$fromJsonElement should equal $fromString")
    // OUTPUT: [[1,2], [1,2]] should equal [1, 2]
}

object JsonElementListSerializer : DeserializationStrategy<List<JsonElement>> {
    override val descriptor: SerialDescriptor = ListSerializer(JsonElement.serializer()).descriptor
    override fun deserialize(decoder: Decoder): List<JsonElement> = buildList {
        decoder.decodeStructure(descriptor) {
            while (true) {
                val index = decodeElementIndex(descriptor)
                if (index == CompositeDecoder.DECODE_DONE) break
                add((this as JsonDecoder).decodeJsonElement())
            }
        }
    }
}

Expected behavior
The resulting list with both methods should be the same, and contain only JsonPrimitives, never JsonArrays.

Environment

• Kotlin version: 2.2.0
• Library version: 1.9.0
• Kotlin platforms: JVM
• Gradle version: tested with 8.13