PoS Upgrade Sharding

Once Ethereum upgrades to the PoS chain and implements sharding, are the shard chains or the Beacon Chain going to handle accounts and smart contracts. On Eth.org the descriptions of both say they won’t be able to handle accounts or smart contracts, but the Beacon chain has launched already and shard chains are still in development so I’m assuming it’ll be shard chains that are modified to handle accounts and smart contracts? Was just curious because someone has to execute and store them between the beacon chain and shard chains correct?