[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.

## Matched source
Source: Source: https://github.com/luvadlamudi/tamuhack26/blob/HEAD/backend/rag/VECTOR_INDEX_SETUP.md
Original query: "MongoDB Atlas Vector Search: '$vectorSearch is only valid for Atlas'"
Key terms: atlas, mongodb, only, search, valid, vector, vectorsearch