okay, apparently auto-buy of supplies is not broken. But it is also not really auto-buy. You must have buy set to true in the settings, but you also must have someone working the market job. And even then, they will only manage to buy a small amount of supplies daily regardless of what the number is set to. They will buy so long as your current supply is less than the set value to keep on hand. But they don't buy the amount to "reach" that amount. (so if you use more than they buy your supplies will continue to go down until you run out)