### What happened?

On LiteLLM Proxy **v1.91.0**, with a vector store created via `POST /v1/rag/ingest` (backend `s3_vectors`) and present in the registry with valid `litellm_params` (including `embedding_model`), the emulated `file_search` on `POST /v1/responses` (Anthropic model, `stream: false`) always returns **no results**:

- the `file_search_call` output item reports `status: "completed"` and shows generated `queries`, - but `results` is `null` — even with `"include": ["file_search_call.results"]`, - and the assistant answers that nothing was found in the knowledge base.

A **direct search on the exact same store id succeeds** with the correct chunk (score ~0.55), so the index and query-time embedding work. The emulation's internal search appears to fail and be silently swallowed — no error is surfaced anywhere.

### Reproduction

1. Ingest: ```bash curl -sS "$PROXY/v1/rag/ingest" -H "Authorization: Bearer $KEY" -H "Content-Type: application/json" -d '{ "file": {"filename": "probe.txt", "content": "<base64 of: Acme WiFi plans: Basic plan costs 10 dollars for 100Mbps. Premium plan costs 25 dollars for 1Gbps fiber.>", "content_type": "text/plain"}, "ingest_options": { …