A cold wallet is key storage that has never touched a network: keys generated and held on an offline device, signatures made in isolation, transactions ferried by QR or USB. Nothing connected can steal what nothing connected ever saw.
The operational cost is friction: every cold signature is a ceremony. The pattern that works is tiered, hot for the float, cold for the reserve, with the split set by how much loss would hurt.
Merchants point checkouts at whichever wallet tier fits the exposure: the hot float settles daily, the cold reserve sweeps on a schedule, and the non-custodial architecture never forces funds into platform custody in between.
Every term behind the rails, the assets, and the settlement.