$lookup doesn't include any details about its subpipeline in the explain output. More concretely, its serialize function returns the stored _userPipeline which is the pipeline prior to any optimizations/view resolution. In other words, $search will not be desugared and therefore DocumentSourceInternalSearchIdLookup::serialize(), which publicizies the view transforms for mongot pipelines, will never be invoked. This is relevant for testing SPM-3672 because we cannot examine the explain output for the view transforms for $lookup.$search when the inner coll is a view - because again, the view transforms will not be present.

If we can show the desugared/parsed subpipeline, like we do for unionWith's subpipeline, that would be beneficial for testing and probably for our customers as well.