Harden MCP article and weight workflows

roll_calculation.py

@@ -374,6 +374,63 @@ def get_article(
     return repository.resolve(article_number, article_name_hint)
 
 
+def calculate_material_weight(
+    *,
+    roll_length_m: Any,
+    width_m: Any,
+    area_weight_g_m2: Any,
+) -> dict[str, Any]:
+    """Calculate material-only roll weight without a core or diameter assumption."""
+    values = {
+        "roll_length_m": roll_length_m,
+        "width_m": width_m,
+        "area_weight_g_m2": area_weight_g_m2,
+    }
+    invalid = []
+    normalized = {}
+    for field, value in values.items():
+        if isinstance(value, bool) or not isinstance(value, (int, float)):
+            invalid.append({"field": field, "message": "must be a number"})
+            continue
+        number = float(value)
+        if not math.isfinite(number) or number <= 0:
+            invalid.append(
+                {"field": field, "message": "must be greater than zero"}
+            )
+            continue
+        normalized[field] = number
+    if invalid:
+        return {"status": "invalid_parameter", "invalid": invalid}
+
+    material_weight = _material_weight_kg(
+        normalized["roll_length_m"],
+        normalized["width_m"],
+        normalized["area_weight_g_m2"],
+    )
+    if not math.isfinite(material_weight) or material_weight <= 0:
+        return {
+            "status": "invalid_parameter",
+            "invalid": [
+                {
+                    "field": "request",
+                    "message": "values are outside the supported calculation range",
+                }
+            ],
+        }
+    return {
+        "status": "success",
+        "weight_scope": "material_only",
+        "inputs": normalized,
+        "material_weight_kg": material_weight,
+    }
+
+
+def _material_weight_kg(
+    roll_length_m: float, width_m: float, area_weight_g_m2: float
+) -> float:
+    return area_weight_g_m2 * roll_length_m * width_m / 1000
+
+
 def _canonical_name(value: str) -> str:
     value = value.casefold().replace("×", " x ")
     tokens = re.findall(r"\d+(?:[.,]\d+)?|[^\W\d_]+", value)
@@ -746,7 +803,7 @@ def calculate_roll(
         )
         roll_weight = None
         if request.include_roll_weight:
-            roll_weight = area_weight * length * width / 1000
+            roll_weight = _material_weight_kg(length, width, area_weight)
     except OverflowError:
         return _issue_result(
             "invalid_parameter",