FailedPreconditionObjectResult.cs

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;

public class FailedPreconditionObjectResult : ObjectResult
{
    public FailedPreconditionObjectResult(string detail)
        : base(detail)
        => StatusCode = StatusCodes.Status412PreconditionFailed;
}

public static class ControllerExtensions
{
    public static IActionResult FailedPrecondition(this Controller controller, string detail)
        => new FailedPreconditionObjectResult(detail);
}