Type discriminator leaks from serialized value class to the next property

[huzvanec]

Describe the bug
When a @JvmInline value class implements a sealed interface, the polymorphic serialization does not correctly update its state after encoding the value class as a primitive. This causes the "type" discriminator to be injected into the next serializable property in the class.

To Reproduce

@Serializable
sealed interface Component

@Serializable
@JvmInline
value class TextComponent(val value: String) : Component

@Serializable
data class Behavior(val description: String)


@Serializable
data class Dog(
    val name: Component,    // value class implementing a sealed interface
    val behavior: Behavior  // the next object that incorrectly gets assigned the type discriminator during serialization
)

fun main(args: Array<String>) {
    val json = Json { prettyPrint = true }
    println(
        json.encodeToString(
            Dog(
                name = TextComponent("Daisy"),
                behavior = Behavior(description = "cuddly")
            )
        )
    )
}

outputs:

{
    "name": "Daisy",
    "behavior": {
        "type": "com.example.TextComponent",
        "description": "cuddly"
    }
}

Expected behavior
The name should either include its type or be a raw string, and behavior should not contain the type of the previous property.

Environment

• Kotlin version: 2.3.10
• Library version: 1.10.0
• Kotlin platforms: JVM
• Gradle version: 9.3.1
• IDE version: IntelliJ IDEA Ultimate 2025.3.3
• OS: Debian GNU/Linux 13 (trixie) x86_64
• JRE version: Temurin 21.0.10