model: support Step3V (#8583)

Signed-off-by: Xinyuan Tong <justinning0323@outlook.com>
Co-authored-by: nnnobody-code <nnnobody@foxmail.com>
Co-authored-by: ispobock <ispobaoke@gmail.com>
Co-authored-by: Qiaolin-Yu <qy254@cornell.edu>
Co-authored-by: Qiaolin-Yu <liin1211@outlook.com>
Co-authored-by: Xinyuan Tong <justinning0323@outlook.com>
Co-authored-by: Xinyuan Tong <115166877+JustinTong0323@users.noreply.github.com>

python/sglang/srt/jinja_template_utils.py

@@ -165,7 +165,7 @@ def process_content_for_template_format(
         new_msg["content"] = processed_content_parts
         return new_msg
 
-    else:  # content_format == "string"
+    elif content_format == "string":
         # String format: flatten to text only (for templates like DeepSeek)
         text_parts = []
         for chunk in msg_dict["content"]:
@@ -179,3 +179,6 @@ def process_content_for_template_format(
         new_msg["content"] = " ".join(text_parts) if text_parts else ""
         new_msg = {k: v for k, v in new_msg.items() if v is not None}
         return new_msg
+
+    else:
+        raise ValueError(f"Invalid content format: {content_format}")