Use Modular Wallets

This gets you building ERC-4337 smart contract wallets with Circle's SDK. Users log in with passkeys instead of seed phrases, transactions can be gasless through Circle's paymaster, and you can batch multiple calls into one operation. The skill covers the full flow from WebAuthn registration to sending user ops, plus passkey recovery via BIP-39 if someone loses device access. Works across Arbitrum, Base, Polygon and other L2s, but not Ethereum mainnet or non-EVM chains. The two-transport pattern (passkey transport for auth, modular transport for chain ops) takes a minute to grasp, but the references walk through it. Useful if you're building onchain apps where wallet UX actually matters.