Jan 7, 2019

v3, but I realized it's not technically a double spend, it's just two unconfirmed transactions using the same outputs as input. Which is valid I believe. I was thinking, somehow, that maybe libbitcoin would track spending of an output as soon as it is added to a transaction, but that doesn't make too much sense in hindsight

This is certainly useful information, but can be expensive to index. We will eventually track this from startup in order to support fee increments for RBF.