In cases where an aggregation on a sharded collection can be targeted to a single shard, we simply forward the pipeline to that shard and store the resulting cursor on the mongoS. Aggregations which start with $changeStream are targeted at all shards, but on a single-shard cluster this means that the entire pipeline will be forwarded, unsplit, to that shard. When we then attempt to lookup the post-change image, we hit the uassert here which prevents MongodProcessInterface from creating an internal pipeline on a collection that is sharded.