Function handle_vector_batch_upsert 

pub fn handle_vector_batch_upsert(
    vs: &VectorStore,
    _kg: &GraphHandle,
    args: Option<&Value>,
) -> Result<Value>

Bulk-ingest embeddings: { items: [{entityName, embedding, model?}, ...] }. Each item is upserted independently; per-item failures are reported rather than aborting the batch — the shape RAG ingestion pipelines expect.