### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

## Bug description

When using a Responses API compatible provider in streaming mode (Azure OpenAI), LiteLLM does not handle the `response.incomplete` event in: `litellm/completion_extras/litellm_responses_transformation/transformation.py`

Instead it falls through to: ```python verbose_logger.debug( f"Chat provider: Unhandled event type '{event_type}', creating empty chunk" ) ```

This causes terminal metadata like `response.content_filters` to be dropped before downstream callbacks / guardrails (e.g. `async_post_call_streaming_iterator_hook()` in CustomLogger) can inspect it.

Expected behavior: - `response.incomplete` should be explicitly handled - `content_filters` / `incomplete_details` should be forwarded on the streamed `ModelResponseStream`, ideally via `provider_specific_fields`

## Relevant code path

Current unhandled-event fallback is in:

`litellm/completion_extras/litellm_responses_transformation/transformation.py`

The transform in this version handles events: - `response.created` - `response.output_item.added` - `response.fu…