When max_tokens >= max_model_len, vLLM engine rejects the request.
Clamp to (max_model_len - prompt_tokens) in both to_sampling_params
and to_beam_search_params so oversized max_tokens values degrade
gracefully instead of returning HTTP 400.
CCCL logical.cu pattern: handle boundary conditions (empty range,
overflow) gracefully instead of hard-failing.