[New Model] Devstral support (#6547)

Signed-off-by: Xinyuan Tong <justinning0323@outlook.com>

python/sglang/srt/utils.py

@@ -2169,3 +2169,51 @@ class Withable(Generic[T]):
         finally:
             assert self._value is new_value
             self._value = None
+
+
+def find_local_repo_dir(repo_id: str, revision: Optional[str] = None) -> Optional[str]:
+    import huggingface_hub as hf
+
+    # Build cache path
+    cache_path = os.path.join(
+        hf.constants.HF_HUB_CACHE,
+        hf.constants.REPO_ID_SEPARATOR.join(["models", *repo_id.split("/")]),
+    )
+
+    # Get revision from main ref if not specified
+    if not revision:
+        ref_path = os.path.join(cache_path, "refs", "main")
+        if os.path.isfile(ref_path):
+            with open(ref_path) as f:
+                revision = f.read().strip()
+
+    # List files from revision directory
+    if revision:
+        rev_dir = os.path.join(cache_path, "snapshots", revision)
+        if os.path.isdir(rev_dir):
+            return rev_dir
+
+    return None
+
+
+def read_system_prompt_from_file(model_name: str) -> str:
+    """Read system prompt from a file in the HuggingFace cache directory.
+
+    Args:
+        model_name: The model name to construct the file path
+
+    Returns:
+        The system prompt content from the file, or empty string if file not found
+    """
+    try:
+        local_repo_dir = find_local_repo_dir(model_name)
+        if local_repo_dir:
+            system_prompt_file = os.path.join(local_repo_dir, "SYSTEM_PROMPT.txt")
+            if os.path.exists(system_prompt_file):
+                with open(system_prompt_file, "r", encoding="utf-8") as f:
+                    return f.read()
+
+        return ""
+    except Exception:
+        # If anything fails, return empty string
+        return ""