code: func (b *Backend) updateState(signature *tasks.Signature, update bson.M) error {
  	update = bson.M{"$set": update}
  	_, err := b.tasksCollection.UpdateOne(context.Background(), bson.M{"_id": signature.UUID}, update, options.Update().SetUpsert(true))
  	return err
  }
docs: // updateState saves current task state