C# monad class for handling outcome

Result.cs

public abstract record Result
{
    #region Helper methods

    public static Success Ok() => new();
    public static Success.WithValue<T> Ok<T>(T value) => new(value);
    public static Failure Fail(string reason) => new(Codes.Unprocessable, reason);
    public static Failure Error(Exception exception) => new(Codes.Unknown, exception.Message);
    public static Failure NotFound(string entity) => new(Codes.NotFound, $"{entity} is not found.");
    public static Failure.Invalid Reject(IDictionary<string, string[]> errors) => new(errors);

    #endregion

    #region Type definitions

    public abstract record SuccessBase : Result;
    public sealed record Success : SuccessBase
    {
        public sealed record WithValue<T>(T Value) : SuccessBase;
    }

    public abstract record FailureBase(int Code, string Reason) : Result;
    public sealed record Failure(int Code, string Reason) : FailureBase(Code, Reason)
    {
        public sealed record Unknown(Exception Exception) : FailureBase(Codes.Unknown, Exception.Message);
        public sealed record Invalid(IDictionary<string, string[]> Errors) : FailureBase(
            Codes.BadRequest, "One or more validation failures have occured.");
    }

    #endregion
}

file struct Codes
{
    public const int BadRequest = 400;
    public const int NotFound = 404;
    public const int Unprocessable = 422;
    public const int Unknown = 500;
}