ERC-4337 account (smart account)

ERC-4337 adds account abstraction without a consensus change. A user, or an agent, signs a UserOperation instead of a transaction; bundlers collect these from a separate mempool and submit them to a singleton EntryPoint contract, which calls each account's validateUserOp and then executes the call. A paymaster contract can agree to pay gas, so the account need not hold ETH.

For agents the interesting property is programmable validation: an account can accept a session key with a spending limit, require a second signature above a threshold, or rotate keys, all in contract code. Several wallet-infrastructure providers in the directory ship 4337 accounts or the bundler and paymaster services around them.

A 4337 account is not by itself a safety feature: the policy is whatever the account's code says, and a session key with no limit is a full key. Sato Hub measures the factories and EntryPoint activity, not the policies inside any account.