Builder Vault is Blockdaemon’s production MPC threshold-signing platform (powered by the Sepior TSM). Its developer documentation explains that each presignature contains shares of a random signing nonce, and that an MPC node enforces single-use by deleting the presignature in the same transaction in which it consumes its share. The docs additionally warn that backup-and-restore can reintroduce a previously-consumed presignature, turning a routine ops procedure into a key-extraction vector if mishandled. Operators are therefore instructed to delete all presignatures either before taking a database backup or upon restoring.