Relayer

The relayer is a backend service that sits between users and the blockchain. It sponsors gas fees and submits transactions on behalf of users, so that users don't need to reveal their identity by transacting from their own address. For L3 operations, the relayer also maintains the nullifier IMT state and provides insertion witnesses needed for unstake proofs.

The reference implementation has no gas protection — anyone can burn relayer funds by submitting bogus proofs (see flaw #3). The relayer is also a single point of failure for L3: if it loses its IMT state, staked funds become unrecoverable (see flaw #4).