ChatResponse

data class ChatResponse(
    val id: String,
    val role: String,
    val parts: List<Part>,
    val metadata: ResponseMetadata
)

enum class Role {
    USER,       // serialized as "user"
    ASSISTANT   // serialized as "assistant"
}

enum class FinishReason {
    STOP,       // serialized as "stop" — normal completion
    ERROR,      // serialized as "error" — an error occurred
    TOOL_CALLS, // serialized as "tool-calls" — waiting for tool results
    UNKNOWN     // serialized as "unknown" — unrecognized finish reason
}