Developer outlines missing self-custody wallet design for AI agents using session keys and on-chain caveats

The article identifies a gap in the current market: custodial signing services (Coinbase CDP, Privy, Phantom, Turnkey) and local signing tools (mcp-wallet-signer, Frame.sh) exist separately, but no product bundles self-custody with agent-native signing. The author built an MCP server for CoW Protocol and encountered the problem directly when wiring it to a wallet.

The proposed solution uses session keys with on-chain caveats: a user holds the master key, signs once to grant a session key scoped permissions (only this protocol, only these tokens, only up to this amount, only for this duration), and the agent operates within those bounds without further prompts. EIP-7702 allows an EOA to delegate to a smart-account contract directly, removing bundler dependency from the signing path.

The required components already exist separately: MetaMask Smart Accounts Kit ships an audited EIP7702StatelessDeleGator on mainnet with caveat enforcers for target contracts, function selectors, value caps, and expiry; mcp-wallet-signer provides the transport and approval-routing pattern; passkeys backed by Secure Enclave or TPM provide hardware-backed signing verified on-chain via P-256 precompile. What is missing is an opinionated local daemon that exposes both an MCP signing surface and an EIP-1193 endpoint, mints ERC-7710 delegations to session keys, and broadcasts through any RPC without bundler dependency.