Harden MCP tool composition

roll_calculation.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 from dataclasses import asdict, dataclass
+from decimal import Decimal, ROUND_HALF_UP
 from difflib import SequenceMatcher
 import json
 import math
@@ -738,6 +739,56 @@ def calculate_roll(
     }
 
 
+def transport_roll_inputs_from_roll_calculation(
+    result: Any,
+) -> dict[str, float]:
+    """Derive browser-equivalent transport inputs from a roll calculation."""
+    if not isinstance(result, dict) or result.get("status") != "success":
+        raise ValueError("roll calculation result must have status success")
+
+    calculation = result.get("calculation")
+    effective_inputs = result.get("effective_inputs")
+    if not isinstance(calculation, dict) or not isinstance(effective_inputs, dict):
+        raise ValueError("successful roll calculation result is incomplete")
+
+    def calculation_number(field: str) -> float:
+        return _transport_roll_input_number(calculation.get(field), field)
+
+    def effective_number(field: str) -> float:
+        entry = effective_inputs.get(field)
+        if not isinstance(entry, dict):
+            raise ValueError(f"successful roll calculation result is missing {field}")
+        return _transport_roll_input_number(entry.get("value"), field)
+
+    return {
+        "roll_diameter_mm": _browser_one_decimal(
+            calculation_number("average_diameter_mm")
+        ),
+        "core_diameter_mm": effective_number("core_diameter_mm"),
+        "roll_width_m": effective_number("width_m"),
+        "roll_weight_kg": _browser_one_decimal(
+            calculation_number("roll_weight_kg")
+        ),
+        "product_length_m": calculation_number("effective_roll_length_m"),
+    }
+
+
+def _transport_roll_input_number(value: Any, field: str) -> float:
+    if isinstance(value, bool) or not isinstance(value, (int, float)):
+        raise ValueError(f"successful roll calculation result is missing {field}")
+    number = float(value)
+    if not math.isfinite(number) or number <= 0:
+        raise ValueError(f"successful roll calculation result has invalid {field}")
+    return number
+
+
+def _browser_one_decimal(value: float) -> float:
+    """Match the browser's positive-number ``toFixed(1)`` transport values."""
+    return float(
+        Decimal.from_float(value).quantize(Decimal("0.1"), rounding=ROUND_HALF_UP)
+    )
+
+
 def modify_calculation(
     state: CalculationState | dict[str, Any],
     changes: dict[str, Any],