### What this PR does / why we need it?
- Fixes the bug that Multiple calls (maybe >100) to eagle3-qwen3-8b often incurs "attn_mask index out of range" error
### Does this PR introduce _any_ user-facing change?
N/A
### How was this patch tested?
```
python -m vllm.entrypoints.openai.api_server --host 0.0.0.0 --served-model-name Eagle3 --port 8000 --model Qwen/Qwen3-8B --seed 42 -tp 1 --speculative_config '{"model": "Tengyunw/qwen3_8b_eagle3", "draft_tensor_parallel_size": 1, "num_speculative_tokens": 5, "method": "eagle3"}'
```
Co-authored-by: liuruijin17
[ricklrj@outlook.com](mailto:ricklrj@outlook.com)
- vLLM version: v0.10.2
- vLLM main:
52d0cb8458
Signed-off-by: Icey <1790571317@qq.com>
68c5401ad6