aggrivated-
I don't think money is a claim on energy at all. As I said - its just a marker for foregone consumption, which could have happened at a given time and place, but you decided instead that you weren't going to consume.
As time passes you decide to cash in the marker, you may be able to consume more or you may be able to consume less, depending on the conditions of the system at that moment in time, and the item you want to consume.
If you forego consumption prior to peak oil, your implicit exchange rate includes an oil price of $3.00/bbl. If you then cash the marker in 20 years later and you are looking for an energy product when oil is at $40/bbl, you won't get the same experience.
Exchange rates change depending on circumstance. That's just how it is. Expecting any monetary system to fix the exchange rates in stone for everything in perpetuity is just an exercise in fantasy. Things are always changing. Sometimes there is a glut, sometimes a shortage - for wheat, for energy, for money, for property - for everything.
Some stuff will get cheaper, some stuff more expensive. Did anyone expect oil to drop to $27/bbl in 2015? I sure didn't. But it happened. You just never know.
So what is money a claim on? Whatever happens to be available, at the current exchange rate, which changes over time. And the only way you can save money is to forego consumption.
Even if we had "sound money", 100% reserved, with everyone using little gold coins for every transaction, there is no guarantee that if you save a gold coin now, you'll be able to buy the same amount of oil in the future that you can buy today. It might be more, it might be less. (Didn't 2015-2016 teach us any humility at all about how energy prices can surprise us?)