[New Model] Devstral support

[JustinTong0323]

Serve with command:

python3 -m sglang.launch_server \
    --model-path mistralai/Devstral-Small-2505 \
    --tool-call-parser mistral

Motivation

• [Feature] support Devstral-Small-2505 #6523

Modifications

• Add auto chat template matching for devstral
• Add system prompt from model files (from here) to chat template
• Directly use mistral's tokenizer
• Add tool_call_separator to mistral and qwen25 tool call parser

Checklist

• Format your code according to the Code Formatting with Pre-Commit.
• Add unit tests as outlined in the Running Unit Tests.
• Update documentation / docstrings / example tutorials as needed, according to Writing Documentation.
• Provide throughput / latency benchmark results and accuracy evaluation results as needed, according to Benchmark and Profiling and Accuracy Results.
• For reviewers: If you haven't made any contributions to this PR and are only assisting with merging the main branch, please remove yourself as a co-author when merging the PR.
• Please feel free to join our Slack channel at https://slack.sglang.ai to discuss your PR.

[Copilot]

Pull Request Overview

Adds support for the new Devstral model by pulling in its system prompt, wiring up a conversation template, and handling its tokenizer.

• Introduces utilities to locate a local HF repo and read its SYSTEM_PROMPT.txt
• Registers a “devstral” conversation template and matching function
• Applies a temporary tokenizer fallback for Devstral in the HF Transformers helper

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
python/sglang/srt/utils.py	Added find_local_repo_dir and read_system_prompt_from_file utilities
python/sglang/srt/hf_transformers_utils.py	Mapped Devstral tokenizer to a Mistral Instruct tokenizer
python/sglang/srt/function_call/qwen25_detector.py	Added tool_call_separator argument in EBNF builder call
python/sglang/srt/function_call/mistral_detector.py	Added tool_call_separator argument in EBNF builder call
python/sglang/srt/conversation.py	Imported prompt reader; registered Devstral template and matcher

Comments suppressed due to low confidence (1)

python/sglang/srt/utils.py:2190

• Consider adding unit tests for find_local_repo_dir and read_system_prompt_from_file (including edge cases like missing cache or files) to ensure this logic remains robust.

def read_system_prompt_from_file(model_name: str) -> str:

[JustinTong0323]

Revert change with tool detector, which would be improved in #6597

[hnyls2002]

@JustinTong0323 Please fix lint error

[JustinTong0323]

@JustinTong0323 Please fix lint error

fixed, but it seems from main? Maybe a quick fix commit to main is better for all PRs