Investment is circulation though. They are no longer holding the $10 you spent to buy 10 Libra but $10 worth of Apple stock say that definitely isn't always worth $10 and Apple or whoever sold that stock now has $10.
There's nothing binding about that proposed setup though. It wouldn't affect the function from the chain side so there's no real way to validate that that is what their doing outside of independent audits.
They could instead deposit it into their own bank, i.e. full reserve, and let the bank do the investing/recirculation itself which it is accredited to do.
