/// <summary>
///     A single message in an AI conversation.
/// </summary>
public sealed class AiMessage
{
    /// <summary>Role of the message author.</summary>
    public required AiMessageRole Role { get; init; }
    /// <summary>Message content (may be streamed incrementally).</summary>
    public string Content { get; set; } = "";
    /// <summary>When the message was created.</summary>
    public DateTimeOffset Timestamp { get; init; } = DateTimeOffset.UtcNow;
    /// <summary>Whether this message is still being streamed.</summary>
    public bool IsStreaming { get; set; }
    /// <summary>Whether the user cancelled/stopped this response mid-stream.</summary>
    public bool IsCancelled { get; set; }
    /// <summary>Duration of the streaming response in milliseconds.</summary>
    public long DurationMs { get; set; }
    /// <summary>Estimated token count (approximate: chars / 4).</summary>
    public int EstimatedTokens { get; set; }
}