panic: runtime error: index out of range [-1] in gateway queue

### 🐛 Describe the bug

<img width="921" height="468" alt="Image" src="https://github.com/user-attachments/assets/1b98890e-851a-4712-a724-e3a5e8e1c7ea" />



### Steps to Reproduce

CICD ref: https://github.com/vllm-project/aibrix/actions/runs/16258376123/job/45898696940?pr=1283

### Expected behavior

should not be flaky

### Environment

nightly