EnumeratorExtensions.cs

using System;
using System.Collections.Generic;

public static class EnumeratorExtensions
{
    public static IEnumerable<T> TakeNextUntil<T>(this IEnumerator<T> enumerator, Predicate<T> predicate)
    {
        while(enumerator.MoveNext())
        {
            var item = enumerator.Current;
            if (predicate(item))
                break;
            yield return item;
        }
    }
    
    public static T TakeNextItem<T>(this IEnumerator<T> enumerator) => 
            enumerator.MoveNext()? enumerator.Current : throw new Exception("Cannot retrieve next item");
}