[Feature] Graceful handling of non-existing lora_path in inference request

[lifuhuang]

Checklist

• 1. If the issue you raised is not a feature but a question, please raise a discussion at https://github.com/sgl-project/sglang/discussions/new/choose Otherwise, it will be closed.
• 2. Please use English, otherwise it will be closed.

Motivation

Creating an issue to track this TODO for myself (or anyone else who wants to help):

Currently when users call SGLang with a non-existing lora_path, SGLang server/engine would crash due to failed assertions in prepare_lora_batch. This is unideal as it imposes unnecessary burden for server owner to validate request params before they are passed to the SGLang backend.

Ideally, SGLang should have gracefully handled the exception and respond 4xx errors without crashing the server.

Related resources

No response

[lifuhuang]

Closing this issue as it is fixed by #7642