cable-sizing: max length, socket minimum, manual-entry warning, SVG icon

- Cross-section rows now include maxLengthForVoltageDropM, the inverse of
  the voltage-drop formula: the longest single run that stays within the
  requested max voltage drop at the given load/cosPhi/phase. Shown as a KPI
  and in the ok-summary alert.
- Added PRACTICAL_MINIMUM_CROSS_SECTION_MM2 (2.5 mm² for single_phase
  circuits) - a planning convention already named in this projects own
  docs/spec/06-future-sizing-and-calculations.md, not a thermal/
  voltage-drop requirement. Only ever raises a calculated recommendation,
  never lowers one that already needs more. circuitCategory is looked up
  from the circuits section and passed through from the editor.
- The manual cross-section field now warns (not blocks - manual override
  must stay possible per the same spec doc) when the typed value is not a
  standard cross-section, is smaller than the last calculation, or is
  below the practical minimum for single_phase circuits.
- Modal title now includes the circuit displayName next to the equipment
  identifier.
- Replaced the calculator emoji trigger icon with an inline SVG - the emoji
  did not render in at least one tested environment (missing font glyph),
  SVG has no such dependency.

src/frontend/components/cable-sizing-modal.tsx

@@ -3,6 +3,7 @@
 import { type FormEvent, useMemo, useState } from "react";
 import {
   CONDUCTOR_MATERIALS,
+  CROSS_SECTIONS_MM2,
   GROUPING_LABELS,
   GROUPING_OPTIONS,
   HARMONIC_NEUTRAL_LOAD_LABELS,
@@ -12,11 +13,13 @@ import {
   LAYING_METHODS,
   LAYING_METHOD_GROUP,
   LAYING_METHOD_LABELS,
+  PRACTICAL_MINIMUM_CROSS_SECTION_MM2,
   TEMPERATURE_FACTOR_AIR,
   TEMPERATURE_FACTOR_GROUND,
   type CableSizingAlert,
   type CableSizingInput,
   type CableSizingResult,
+  type CircuitCategory,
   type ConductorMaterial,
   type HarmonicNeutralLoad,
   type InsulationMaterial,
@@ -28,6 +31,7 @@ import { FormModal } from "./form-modal";
 
 interface CableSizingModalProps {
   circuit: CircuitTreeCircuitDto;
+  circuitCategory?: CircuitCategory;
   isSaving: boolean;
   projectId: string;
   onClose: () => void;
@@ -44,8 +48,19 @@ function temperatureOptions(method: LayingMethod) {
   return Object.keys(table).map(Number).sort((a, b) => a - b);
 }
 
+// Extracts the first decimal number from a free-text cross-section entry
+// like "2.5 mm²" or "2,5". Returns null if nothing parseable is found -
+// used only for the manual-entry sanity check below, never persisted.
+function parseCrossSectionMm2(text: string): number | null {
+  const match = text.match(/([0-9]+(?:[.,][0-9]+)?)/);
+  if (!match) return null;
+  const value = Number(match[1].replace(",", "."));
+  return Number.isFinite(value) ? value : null;
+}
+
 export function CableSizingModal({
   circuit,
+  circuitCategory,
   isSaving,
   projectId,
   onClose,
@@ -92,6 +107,7 @@ export function CableSizingModal({
       maxVoltageDropPercent,
       harmonicNeutralLoad,
       existingProtectionRatedCurrentA: circuit.protectionDevice?.ratedCurrentA,
+      circuitCategory,
     }),
     [
       phase,
@@ -107,9 +123,34 @@ export function CableSizingModal({
       maxVoltageDropPercent,
       harmonicNeutralLoad,
       circuit.protectionDevice?.ratedCurrentA,
+      circuitCategory,
     ]
   );
 
+  const manualCrossSectionWarning = useMemo(() => {
+    const trimmed = manualCrossSection.trim();
+    if (!trimmed) return null;
+    const parsed = parseCrossSectionMm2(trimmed);
+    if (parsed == null) return null;
+    if (!(CROSS_SECTIONS_MM2 as readonly number[]).includes(parsed)) {
+      return `${parsed} mm² ist kein Standard-Querschnitt (${CROSS_SECTIONS_MM2.join(", ")}).`;
+    }
+    if (
+      result?.dataVerified &&
+      result.recommendedCrossSectionMm2 != null &&
+      parsed < result.recommendedCrossSectionMm2
+    ) {
+      return `${parsed} mm² ist kleiner als die zuletzt berechnete Empfehlung (${result.recommendedCrossSectionMm2} mm²) - passt nicht zu Last${circuit.protectionDevice ? "/Sicherung" : ""} und Verlegeart.`;
+    }
+    const practicalMinimum = circuitCategory
+      ? PRACTICAL_MINIMUM_CROSS_SECTION_MM2[circuitCategory]
+      : undefined;
+    if (practicalMinimum != null && parsed < practicalMinimum) {
+      return `${parsed} mm² liegt unter dem Praxis-Mindestquerschnitt für 1-phasige Stromkreise (${practicalMinimum} mm²).`;
+    }
+    return null;
+  }, [manualCrossSection, result, circuit.protectionDevice, circuitCategory]);
+
   function handleLayingMethodChange(method: LayingMethod) {
     setLayingMethod(method);
     const options = temperatureOptions(method);
@@ -162,7 +203,9 @@ export function CableSizingModal({
       onSubmit={handleSubmit}
       submitDisabled={!manualCrossSection.trim()}
       submitLabel="Übernehmen"
-      title={`Kabel dimensionieren - ${circuit.equipmentIdentifier}`}
+      title={`Kabel dimensionieren - ${circuit.equipmentIdentifier}${
+        circuit.displayName ? ` (${circuit.displayName})` : ""
+      }`}
     >
       <div className="row g-3">
         <div className="col-12 col-md-4">
@@ -401,6 +444,16 @@ export function CableSizingModal({
               <div className="text-muted small">Korrekturfaktor</div>
               <div>{result.combinedDerationFactor.toFixed(2)}</div>
             </div>
+            <div className="col-6 col-md-3">
+              <div className="text-muted small">Max. Länge (ΔU-Grenze)</div>
+              <div>
+                {result.rows.find((row) => row.recommended)?.maxLengthForVoltageDropM != null
+                  ? `${result.rows
+                      .find((row) => row.recommended)!
+                      .maxLengthForVoltageDropM!.toFixed(0)} m`
+                  : "-"}
+              </div>
+            </div>
           </div>
           {alerts.map((alert, index) => (
             <div
@@ -459,6 +512,11 @@ export function CableSizingModal({
             value={manualCrossSection}
           />
         </div>
+        {manualCrossSectionWarning && (
+          <div className="col-12">
+            <div className="alert alert-warning mb-0">{manualCrossSectionWarning}</div>
+          </div>
+        )}
       </div>
     </FormModal>
   );