CATalog registrations are forever, which allows one to use uniqueness prelauncher to allow quick on-chain and off-chain validation that an NFT indeed represents the entry for a given CAT. XCHandles, on the other hand, has expiring handles - everyone is free to set the resolved launcher id to any singleton, and entries can expire. The oracle is a very simple action that will announce the value of a given slot on-chain. The announcement prefix, o, is concatenated with the slot's value hash. It's simple as that!