This dependency was introduced by SERVER-92465 because the shard filterer now needs access to the ChunkManager::ChunkOwnership and ChunkMap::Direction enums, and they're defined in chunk_manager.h; transitively, op_observer depends on se value, which in turn depends on the shard filterer (and hence on chunk_manager, now that the shard-filterer needs these enums). It should be possible to fix this by moving the enums out into a separate header