FilteringMetadataCache::onCollectionPlacementVersionMismatch should only be used as a recovery path in the shard role loop when there has been a version mismatch. However, the codebase abuses it to force a refresh by passing boost::none as the router-received version.

We need to evaluate every use case and determine whether it will still work under authoritative shards.

Definition of done: every usage is either justified as-is or has a concrete plan for the authoritative world.