I think you have gotten some great advice! My 10-year-old often behaves similarly at home (but rarely at school--I'm grateful for that!) and it really, really wears on his dad and me. Stormborn's description, "She didn't throw screaming fits (except bedtime) as much as argue and debate over every.single.thing. with all the hyperbole and tenacity of a defense attorney." also sounds very familiar! We had started out being very flexible with our son and appreciating his intelligence when he would debate things and try to come to a mutually agreeable solution...but over time, his focus was more on winning or just on prolonging the inevitable by arguing, and he began to insult us and use a very unpleasant and disrespectful tone, so it's just gotten terrible!
"Finding his currency" is a great approach. We had a
treasure chest at one point, and we've generally used screen time (computer or TV) as his reward for reasonable behavior. After a major crisis at the beginning of third grade, we worked much harder on setting up very clear and very agreed-upon-by-child-and-both-parents rules and schedule and responsibilities for fourth grade and now fifth grade. We were happy with the way things were going on school days, but during the weekend he tended to be on the computer every moment we didn't forbid it, and then when he finally got off he would be nasty with us and demand constant amusement. This past weekend, we tried a new rule that he has to earn his weekend screen time by doing tasks that he chooses from a list we make. That worked pretty well.
I highly recommend the book
Kids, Parents, and Power Struggles by Mary Sheedy Kurcinka. It's not a one-size-fits-all approach but helps you figure out what's going on with your individual kid and your individual self (and co-parent if you have one) and why you clash, and what to do about it.
In the specific example that you gave, I can see a couple of places where you might be able to change your thinking or approach. I mean this very gently. I know you are aching from years of struggle. I don't want you to feel criticized. What I'm trying to say is that my experience has shown me some approaches that work better than others, so although I am far from perfect at even thinking of them in the moment let alone applying them, I want to share them in case they might help you.
I was cleaning and dropped an cherry from Hi Ho Cherrio. I asked him to pick it up and hand it back to me. He stomped around. He said it was too hard. He told me to have his brother do it. He took off to see what his older brother was doing. He declared that he was not the one to drop it there. Then, finally, he succumbed to having to do it. He started with moving furniture, even though no furniture needed to be moved to pick it up. Finally, while nursing the baby, I bent over and picked it up.
YOU dropped something, but you asked HIM to pick it up. Why? Do you feel it was unreasonable for him to complain that he was not the one who dropped it? Could it be that he said it was too hard because he could see that you felt YOU should not have to do it? I'm not saying that it was wrong for you to ask for his help. I'm asking you to clarify in your own mind why this was an important issue, what it means to you to have him comply with this type of request. How do you respond if he drops something and asks you to pick it up and give it to him?
What was your goal? I mean, obviously you wanted the cherry picked up, but did you want this simple task over with as quickly as possible so you could get on with cleaning and not worry about the baby choking on the cherry--or did you want to have this kid do something for you because he was hanging around being unhelpful while you were working hard cleaning up after his ungrateful messiness? If you just want it done, it's fine to ask, but at the first resistance say calmly, "Oh, that's hard for you? Seems easy to me!" as you scoop it up and (go ahead and feel very noble about this) get on with your life instead of getting drawn into a power struggle!
At the point when he accepted that he would have to do it...what made that happen? (I don't think I've ever seen that with my son when the task was something I wanted done that did not affect him.) Look for clues as to what brings him to the idea that a task is inevitable, and see if you can nudge him to that point earlier in the process.
When he started moving furniture that you felt didn't need to be moved to reach the cherry...did you say so? I've found that if my son is finally doing something I want him to do, and I tell him he's "doing it wrong" in any way, he will stop and argue--and frankly, I will do that too if put in that situation! Nobody likes to feel like the result of compliance is criticism, and being told that you're making a task harder than necessary can make you feel stupid. So it's better not to mention it but just stay out of the way of his doing the task the way he's doing it.
So he was moving the furniture, and then what happened--why did YOU pick up the cherry after all that? I feel like there's something missing from the story. Did he give up and go away without getting the job done? Did you lose patience with his making the job more difficult than necessary and go, "Fine! I'll do it myself!"? What happened?
If it's really important to you that he do something instead of your doing it, then it is absolutely crucial that you NOT do it and hold firm on his doing it. If you say he needs to do it but then do it yourself, you're teaching him that you don't really mean it, so he's going to delay and complain next time in hopes of getting out of it again. (I have a lot of trouble with this! But the evidence is clear.)
Friday, we decided to take the kids to a special pizza making thing. It involved going to a place he had not been before, and he got to go through an assembly line like thing and make his own pizza at a restaurant and then they baked it for him. Fun! So, I said no one goes who has not put away his own laundry. So, he put it away! No problem. He has to put it away in months because the suggestion he put it away is met with the dramatic incapable act. I cannot pay him with a special event every time he needs to so much as put away his own laundry.
No, you cannot take him out to dinner every time you do the laundry. But you can apply this general approach to the smaller rewards of life. My son enjoys coming shopping with me, so, "When you have put away your laundry, then we can go to Costco." is often effective--especially if I then walk away and gather my things for shopping, and if I come back and find that he's playing and ignoring the laundry, I say, "I see you decided not to go to Costco. Bye!"
My son does his own laundry every Thursday after school. Unlike his tasks for the other days, laundry has multiple steps. He needs reminders to do the next step. I'm at work at that time, and his dad also has poor laundry memory. So if I find my son's clothes in the dryer after I get home, I tell him it's time to put away his laundry NOW, and if doing so reduces the time available for his bedtime story, oh well, he should have remembered to do it before. If I find his clothes after he's in bed, I put them in his basket (so that I can use the machine) and leave a note on the computer chair: "Put away laundry before screen time."