When RavenDB runs resharding to balance the data load between shards, it copies
documents from one shard to another and then removes their original copy.
If a change occurs in the original data after some of it was copied to its
new location (e.g. a time series has updated entries in the original bucket after
its parent document was copied), RavenDB will not remove the original
document and its extensions from their original location until the new/modified
data is relocated as well.
In all other respects, we handle the original document as if it had already moved,
including reading from and writing to only the new document in its new bucket and shard.