The problem campus-escrow-app solves

Campus marketplace groups — Facebook, Telegram, WhatsApp — run entirely on trust. A buyer sends payment first and just hopes the seller ships; there's no recourse if they don't, and no way to verify a stranger's reputation.

Vault fixes this with an escrow smart contract on Sui. The buyer's payment locks on-chain the moment they pay. The seller ships, the buyer confirms receipt, and only then does the money move — or, if the buyer goes silent past a deadline, the seller can claim the funds directly, so they're never left holding an unpaid item either. zkLogin means a buyer can do all of this signing in with a Google account, no wallet experience required, and sponsored transactions mean they never need to hold SUI just to pay gas.

Challenges we ran into

Sui's SDK moved out from under us. Partway through the build we discovered @mysten/dapp-kit had just been superseded by a new architecture (dapp-kit-core plus a gRPC client) — most tutorials online still reference the old one. We ended up reading the installed package's own TypeScript definitions directly rather than trust outdated examples.

A real bug in our first contract draft. An early version of the escrow module had @0xS as a placeholder address — S isn't a valid hex digit, so it failed to even compile. sui move test caught it immediately, a good reminder to run the actual compiler early.

Environment setup ate real time. Getting the Sui CLI running meant discovering Windows PowerShell isn't a Unix shell, setting up WSL, and learning that a Windows username and a WSL username aren't the same thing — small things, but each cost a debugging round before we could start building.