gm casters, any recommendations for a simple, secure, and extensible smart contract wallet?

(I’m looking for solidity code I can extend, not an app)

building /hatsprotocol | 
proudly mid-curving it since 1995

currently under consideration:

- the contract formerly known as gnosis safe
- DS-proxy

what else?

Authereum may still be good. https://docs.authereum.com/integration

you can look into implementations of EIP-4337. BLS wallet is a project that has open-sourced contracts, off-chain infra, and a wallet chrome extenstion https://github.com/web3well/bls-wallet

Argent - https://github.com/argentlabs/argent-contracts