[bugfix] catch xgrammar unsupported array constraints (#12210)

Signed-off-by: Jason Cheng <jasoncky96@gmail.com>

vllm/model_executor/guided_decoding/utils.py

@@ -20,6 +20,13 @@ def has_xgrammar_unsupported_json_features(schema: dict) -> bool:
                 ]):
             return True
 
+        # Check for array unsupported keywords
+        if obj.get("type") == "array" and any(key in obj for key in [
+                "uniqueItems", "contains", "minContains", "maxContains",
+                "minItems", "maxItems"
+        ]):
+            return True
+
         # Recursively check all nested objects and arrays
         for value in obj.values():
             if isinstance(value, dict):