When performDeletes() and performUpdates() are called with a time-series source on a missing collection, the delete fails with the message "
Catalog changed during operation, could not find time series buckets collection for write," while the update path fails with NamespaceNotFound. It may be clearer to make the failure behavior of these functions (under the same conditions) more consistent (inserts and updates both fail with NamespaceNotFound).
For update, the collection acquisition lambda checks immediately after whether the collection exists and asserts if not.

For delete, the collection acquisition is passed to a checking function that asserts with a different message once it realizes the collection doesn't exist.

See the TODO(s) marked with this ticket number for anticipated test breakages should the failure behavior be changed.