How could an inter-temporal banking system work?
(This question is meant to be an improvement and/or replacement for https://worldbuilding.stackexchange.com/questions/113986/how-would-you-bring-wealth-back-to-the-past, which some users have argued is off-topic for this group.)
Imagine a future world in which time travel is not uncommon. (Think of it as being like intercontinental travel today -- something that lots of people do, but it's pretty expensive, so most people can't afford to do it more than a few times in their lives, if ever.) In such a world, an entire infrastructure would eventually grow up around time travel: for example there might be temporal travel agents who would book your entire trip, complete with false identification papers and lodgings at your destination time. There would also presumably be some kind of inter-temporal law enforcement.
And, of course, there would probably need to be some kind of banking system. After all, the main users of time travel are the wealthy, and the wealthy are not going to want to travel back in time without access to their funds. An inter-temporal banking system would have to function as a bureau de change, exchanging currency from one point in time for currency from another. 205
Such a system would have to cope with the "exchange rate" produced by the effects of inflation over many years, and would have to grapple with the fundamental problem of transferring wealth across time without it losing value. How could such a system function?
In posing this question I am specifically not looking for "get rich by betting on sports or buying stocks" answers -- that kind of personal enrichment would, I assume, be prohibited by the inter-temporal law enforcement as a form of fraud. The question here is not "How could you make a lot of money in the past?", but rather "How could a banking system move money from future to past?"
Moving money from past to future is of course simple: you just deposit it in an account in the past and retrieve it when you return to your point of origin. Presumably the legal system would have to figure out some way of preventing everyone from enriching themselves via a long-term interest scheme -- it would be pretty disruptive to the economy if everyone who could afford a ticket to the past just invested their money in a savings account and came back to their point of departure a billionaire! -- but the basic problem of moving money forward in time seems easy to solve. How would a banking system handle the problem of moving money backward in time without disrupting the economy at either the point of origin or their destination, and without screwing up the timeline along the way? 205