### Check for existing issues

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

### What happened?

When using [dynamic_rate_limiter_v3](https://docs.litellm.ai/docs/proxy/dynamic_rate_limit) for priority-based rate limiting alongside configured fallbacks, rate-limited requests return 429 to the client instead of falling back to the configured fallback model. This is because the rate limiter raises `HTTPException(429)` in `async_pre_call_hook`, which executes before the router's fallback logic.

My goal is to: - Reserve capacity for high-priority requests (key tagged "priority":"high") - Automatically redirect low-priority requests to Fallback when model TPM is saturated.

This example setup is designed for a PTU reservation scenario with Pay-As-You-Go fallback on Azure OpenAI / vertex ai

### Current Setup

**Models:** ```yaml model_list: - model_name: gpt-4.1-ptu-20250414 litellm_params: model: azure/gpt-4.1-ptu api_base: ... tpm: 40000

- model_name: gpt-4.1-20250414 litellm_params: model: azure/gpt-4.1 api_base: ... ```

**LiteLLM Settings:** ```yaml litellm_settings: callbacks: ["dynamic_rate_…