Reference

OctopusWallet (the borrowed code)

What each arm runs. Nothing else.

Functions

Function	Notes
`execute(Call[] calls, uint256 deadline, bytes signature)`	Anyone may submit. Runs the calls if the wallet's own key signed them. All or nothing.
`digestFor(calls, nonce, deadline) view`	The 32 bytes the wallet key must sign.
`domainSeparator() view`	EIP-712 domain bound to the wallet's address and the chain.
`nonce() view`	The next nonce for this wallet.
`receive()`, ERC-721 and ERC-1155 receivers	The wallet can still receive anything.

Digest

EIP712Domain: name "Octopus Wallet", version "1", chainId, verifyingContract = the wallet
Execute(bytes32 callsHash, uint256 nonce, uint256 deadline)
callsHash = keccak256(concat(keccak256(abi.encode(to, value, keccak256(data))) for each call))

Storage

The nonce lives at slot keccak256("octopus.wallet.nonce.v1"), not at slot 0. A wallet's own storage may be used by other delegations, so Octo never uses the low slots.

Errors

Expired()
BadSignature()
CallFailed(uint256 index, bytes reason)

The signature must be a 65-byte ECDSA signature by the wallet's own key. There is no owner and no upgrade.