In calculi for modelling communication jinsoon+coupons protocols, internal and external choices play dual roles.Two external choices can be viewed naturally as dual too, as they represent an agreement between the communicating parties.If the interaction fails, the past agreements are good candidates as points where to toyota tarago 1985 roll back, in order to take a different agreement.We propose a variant of contracts with synchronous rollbacks to agreement points in case of deadlock.The new calculus is equipped with a compliance relation which is shown to be decidable.