Expose product length calculation through MCP

templates/roll_calculator.html

@@ -1080,6 +1080,16 @@ async function requestRollCalculation(calculationRequest) {
   return response.json();
 }
 
+async function requestProductLengthCalculation(calculationRequest) {
+  const response = await fetch('/api/calculations/product-length', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(calculationRequest)
+  });
+  if (!response.ok) throw new Error('Product-length calculation service failed');
+  return response.json();
+}
+
 document.getElementById('d-calc').addEventListener('click', async () => {
   invalidatePdfReport();
   const mode = document.querySelector('.mode-btn.active')?.dataset.mode || 'diameter';
@@ -1135,11 +1145,36 @@ document.getElementById('d-calc').addEventListener('click', async () => {
     renderAuthoritativeForkliftResult(authoritativeResult);
   } else if (mode === 'length') {
     if (!d || !t || !D) { alert('Please enter d, t, and D.'); return; }
-    const L_calc = (Math.PI / (4 * t)) * (D*D - d*d) / 1000;
+    try {
+      authoritativeResult = await requestProductLengthCalculation({
+        target_roll_diameter_mm: D,
+        core_diameter_mm: d,
+        thickness_mm: t,
+        thickness_stddev_mm: tol,
+        width_m: numericInput('d-wi'),
+        area_weight_g_m2: numericInput('d-aw')
+      });
+    } catch (error) {
+      alert(error.message);
+      return;
+    }
+    if (authoritativeResult.status !== 'success') {
+      const issue = authoritativeResult.invalid?.[0]?.message;
+      alert(issue || 'Product-length calculation failed.');
+      return;
+    }
+    const calculation = authoritativeResult.calculation;
+    const L_calc = calculation.average_product_length_m;
     resLabel.textContent = 'Product Length (L)';
     resVal.textContent = L_calc.toFixed(2) + ' m';
-    resRange.textContent = '';
+    if (tol) {
+      resRange.textContent = '−2σ: ' + calculation.minimum_product_length_m.toFixed(2) + ' m  |  +2σ: ' + calculation.maximum_product_length_m.toFixed(2) + ' m';
+    } else {
+      resRange.textContent = '';
+    }
     document.getElementById('d-le').value = L_calc.toFixed(2);
+    const materialWeight = calculation.material_weights_kg?.average_kg;
+    document.getElementById('d-wo').value = materialWeight === undefined ? '' : materialWeight.toFixed(1);
   } else if (mode === 'target') {
     const wi = parseFloat(document.getElementById('d-wi').value) || 0;
     const aw = parseFloat(document.getElementById('d-aw').value) || 0;