Produce a deconflicted list of form values across layers
        as a *copy* to avoid iter vs edit issues in the indexes.

async def getFormTodo(self, name):
        '''
        Produce a deconflicted list of form values across layers
        as a *copy* to avoid iter vs edit issues in the indexes.
        '''
        size = 0
        logger.warning(f'MIGRATION: calculating form todo: {name}')
        async with self.getTempSlab() as slab:

            for layr in self.layers:

                async for buid, valu in layr.iterFormRows(name):
                    slab.put(buid, s_msgpack.en(valu), overwrite=False)
                    size += 1

            logger.warning(f'MIGRATION: {name} todo size: {size}')

            for buid, byts in slab.scanByFull():
                yield buid, s_msgpack.un(byts)