Curb

Curb is a wallet with a daily spending limit — the seatbelt your bank card has and your crypto wallet doesn't. You set a daily limit and deposit. Sending under it works normally and confirms in a few hundred milliseconds. Sending over it is rejected by the contract — not by a dialog you can click through. The vault custodies the funds, so your own key can't exceed your own limit: money leaves through send() or not at all. Lowering the limit is instant; raising it is timelocked, so a stolen key can't widen it and drain you in one move. What I learned: 1. EIP-7702 is the obvious tool for this and it does not work. A delegated EOA keeps its key — delegated code runs when the account is CALLED, not when the key signs a plain transaction, and delegation can be cleared at will. A 7702 spending limit is a switch the attacker flips off. You cannot limit a key you still hold; you have to not hold the money. That one finding reshaped the whole design. 2. Speed isn't the feature, it's the reason the feature survives. A limit works on any chain. But Curb puts a contract hop in front of every send, and on a 12-second chain you'd feel that tax and switch it off within a week. eth_sendRawTransactionSync returns the receipt in the same request, so the protection is invisible. That's what Monad bought. 3. Writing the honest threat model made the project better. A stolen key still takes a day's limit — and ~2x across a window boundary, which I pinned with a test rather than hiding. A security review found that lowerCap (the obvious panic move) didn't clear a pending raise, so the safe-looking action failed exactly when you'd need it. Fixed. Native MON only. One feature that genuinely works beats five that don't. Prior art credited: Argent v1 had daily limits; Safe has allowance modules. This is a missing default, not a new idea.