[luvadlamudi/tamuhack26 + tarun-swastya-ai/rag-pipeline-llamaindex]: the $vectorSearch aggregation stage is Atlas-only; running it against local MongoDB raises the '$vectorSearch is only valid for Atlas' error, so update the connection string to the Atlas cluster. Index Building Failed has three usual causes: the cluster tier must be M10 or higher for full Vector Search, the cluster version must be 6.0.11+ or 7.0.2+, and the collection needs at least one document. A new index takes 1-2 minutes to reach Active status; queries before that fail.

Context: Pointing a vector-search app at a local or self-hosted MongoDB fails at runtime. The stage only exists on Atlas.