}
	existingRoot.merge(*otherRoot)
	eHash := d.rootHash()
	for key := range otherRoot.Children {
		entry := other.Cache[key]
		flat := other.flatten(entry)
		existing := d.Cache[key]
		// If not found, merging simply adds.
		existing.merge(flat)
		d.replaceHashed(dataUsageHash(key), &eHash, existing)
	}
}

type objectIO interface {