Function pool_upgrade 

pub fn pool_upgrade(pool: ShieldedPool) -> NetworkUpgrade

The network upgrade at which a shielded pool begins to exist.

This is the workspace’s single pool-to-upgrade mapping: upstream zcash_protocol deliberately ships ShieldedPool and NetworkUpgrade as unrelated enums, so the mapping is defined exactly once, here. Every height clamp involving a pool’s existence derives from it. A second mapping anywhere in the workspace is a defect.