Add machine-aware maximum product length

roll_calculation.py

@@ -425,6 +425,54 @@ def calculate_material_weight(
     }
 
 
+def calculate_material_length_for_weight(
+    *,
+    target_material_weight_kg: Any,
+    width_m: Any,
+    area_weight_g_m2: Any,
+) -> dict[str, Any]:
+    """Calculate material length for a target material-only roll weight."""
+    values = {
+        "target_material_weight_kg": target_material_weight_kg,
+        "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}
+
+    length_m = (
+        normalized["target_material_weight_kg"]
+        * 1000
+        / normalized["width_m"]
+        / normalized["area_weight_g_m2"]
+    )
+    if not math.isfinite(length_m) or length_m <= 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_length_m": length_m,
+    }
+
+
 def _material_weight_kg(
     roll_length_m: float, width_m: float, area_weight_g_m2: float
 ) -> float: