Custody determines who controls signing authority and how that authority is protected, recovered, revoked, or shared. A custodial service may hold keys for the user, while self-custody places direct key responsibility with the owner; programmable agent systems can isolate signing behind policy-controlled services.
Custody design affects theft risk, recovery, availability, compliance, and the blast radius of an agent error. Keys should remain outside model context, and the signing boundary should verify the exact transaction and policy rather than accepting arbitrary agent-generated payloads.
ELI5
Wallet custody means keeping control of the secret keys that can move funds. Whoever has that control can authorize payments, so the keys need strong protection, recovery rules, and clear ownership.
For example, an AI agent can ask a wallet service to pay for data without ever seeing the private key. The service checks the exact amount and recipient, then signs only if the request fits the owner's policy.
