## What happened?

After upgrading LiteLLM proxy from `v1.83.14` to `v1.85.0`, Bedrock rerank requests fail with:

``` litellm.APIConnectionError: Unable to map Bedrock request to provider ```

The same configuration worked correctly on `v1.83.14`.

## Likely Root Cause

Based on changelog analysis between v1.83.14 and v1.85.0, the regression is most likely caused by:

1. **PR #25499** (`feat(vertex_ai): propagate metadata labels to embedding, Imagen, rerank`) — This PR modified `litellm/llms/base_llm/rerank/transformation.py` to add `litellm_params: Optional[dict] = None` to the abstract `transform_rerank_request` signature, and updated **all other rerank providers** (Cohere, Jina, DeepInfra, Fireworks, NVIDIA NIM, HuggingFace, hosted_vllm), but **did NOT update `litellm/llms/bedrock/rerank/transformation.py`**. Since Bedrock rerank uses its own handler (as noted in PR #22021: "All other rerank providers go through `base_llm_http_handler.rerank()`. Bedrock uses its own handler."), this mismatch likely breaks provider mapping.

2. **PR #27257** (`Refactor Bedrock response stream shape handling`) in v1.85.0 — may have reorganized Bedrock's internal provider registration/mapping and …