Package Relay (BIP331) Package = a set of related transactions (typically parent + child) that mempool evaluates atomically . Until BIP331, mempool processed one tx at a time, which broke CPFP when a parent was below mempool min fee rate. Activation - BIP331 mempool policy in Bitcoin Core 28.0 (Sept 2024). - Companion: TRUC v3 transactions (BIP431) for stricter Lightning-class packages. Why packages Pre-package relay: - Parent tx P with fee rate X submitted; if X < mempool min, P is rejected. - Child C spending P's output, even at high fee rate, cannot rescue P because mempool evaluates C alo…