Z-addresses usage analysis

[tromer]

@_eric

the amount of the transaction will be displayed on the blockchain, which is often helpful for showing the merchant proof of payment. IMO, until view keys are developed, z–>t is the ideal way to pay merchants.

Viewing keys won’t give us per-transaction proof of payment. For that, we need the payment disclosure feature, not yet available for Sapling.

(Oddly, payment disclosure are not mentioned in @nathan-at-least’s ECC R&D and Engineering Flight Plan or any recent GitHub updates I’ve noticed… I hope this is loose terminology rather than intentional omission.)