An escrow contract with disputes and deadlines

#Brief

Escrow is a classic contract: a buyer pays, a seller delivers, an arbiter settles disputes. The hard part is making sure every possible sequence of actions ends somewhere safe. Use a local Anvil chain and, when you deploy publicly, a testnet such as Sepolia with free test ether from a faucet. Never use real funds or a wallet that holds any, and never paste a private key into code or a website.

#What to build

1. Design the state machine on paper first, with who may trigger each transition and when

2. Implement it with custom errors, events and pull-based withdrawals

3. Add deadlines: automatic refund if the seller does not deliver, and a default resolution if the arbiter does not act

4. Write unit tests for each transition and fuzz tests for random sequences of actions

5. Write invariant tests: the contract balance equals what is owed, and after the deadline some party can always withdraw

#Deliverables

• Repository with src/, test/, docs/state-diagram.md and README.md

#How it is graded

Reviewers call transitions out of order, as the wrong party and after deadlines, and read your invariants.

#Stretch

Support ERC-20 payments as well as ether, including tokens that take a fee on transfer.