code: func (r *Registrar) ConsensusMigrationStart(context uint64) error {
  	r.lock.Lock()
  	defer r.lock.Unlock()
  
  	for id, chain := range r.chains {
  		if id != r.systemChannel.ChainID() && chain.MigrationStatus().IsPending() {
  			return errors.Errorf("cannot start new consensus-type migration because standard channel %s, still pending", id)
  		}
  	}
  
  	for _, chain := range r.chains {
  		chain.MigrationStatus().SetStateContext(ab.ConsensusType_MIG_STATE_START, context)
  	}
  	logger.Debugf("Consensus-type migration: all standard channels marked as started, context=%d", context)
  
  	return nil
  }
docs: // ConsensusMigrationStart checks whether consensus-type migration had started,
  // and then marks all standard channels as started.