Expose product length calculation through MCP

app.py

@@ -32,7 +32,11 @@ from pdf_report import (
     render_roll_report,
     safe_report_filename,
 )
-from roll_calculation import calculate_roll, modify_calculation
+from roll_calculation import (
+    calculate_product_length,
+    calculate_roll,
+    modify_calculation,
+)
 from transport_calculation import analyze_transport, transport_presets
 
 app = Flask(__name__)
@@ -199,6 +203,40 @@ def create_roll_calculation():
     return jsonify(result), 200
 
 
+@app.route("/api/calculations/product-length", methods=["POST"])
+@auth.login_required
+def create_product_length_calculation():
+    """Calculate deterministic product length for a target roll diameter."""
+    payload = request.get_json(silent=True)
+    if not isinstance(payload, dict):
+        result = {
+            "status": "invalid_parameter",
+            "invalid": [{"field": "request", "message": "JSON object required"}],
+        }
+    else:
+        allowed = {
+            "target_roll_diameter_mm",
+            "core_diameter_mm",
+            "thickness_mm",
+            "thickness_stddev_mm",
+            "width_m",
+            "area_weight_g_m2",
+        }
+        unknown = sorted(set(payload) - allowed)
+        if unknown:
+            result = {
+                "status": "invalid_parameter",
+                "invalid": [{
+                    "field": "request",
+                    "message": "unknown request fields: " + ", ".join(unknown),
+                }],
+            }
+        else:
+            result = calculate_product_length(**payload)
+    log_access(auth.current_user(), "/api/calculations/product-length", "POST")
+    return jsonify(result), 200
+
+
 @app.route("/api/calculations/roll/modify", methods=["POST"])
 @auth.login_required
 def modify_roll_calculation():