fix(CAD-13): double rendering - legacy canvas skips element rendering when pixi renderer is active (grid/background stay), defensive fallback if pixi fails

frontend/src/canvas/RenderEngine.ts

@@ -55,6 +55,8 @@ export class RenderEngine {
   /** src des zuletzt erfolgreich geladenen Hintergrundbilds. */
   private bgSrcLoaded = '';
   private dpr = 1;
+  /** CAD-13-fix: true = Legacy-Canvas zeichnet KEINE Elemente (Pixi-Overlay zeichnet sie). Grid/Hintergrund bleiben. */
+  skipElementRendering = false;
 
   constructor(
     canvas: HTMLCanvasElement,
@@ -161,6 +163,15 @@ export class RenderEngine {
     if (this.options.showGrid) this.drawGrid(w, h);
     if (this.options.backgroundSrc) this.drawBackground();
     this.drawRuler(w, h);
+
+    // CAD-13-fix: Wenn Pixi-Renderer aktiv ist (skipElementRendering=true),
+    // zeichnet das Legacy-Canvas KEINE Elemente mehr (sonst doppelt) —
+    // nur Grid/Hintergrund/Lineal bleiben hier.
+    if (this.skipElementRendering) {
+      this.ctx.restore();
+      return;
+    }
+
     const viewport = this.zoomPan.getViewport();
     const visibleElements = this.spatialIndex.search({
       minX: viewport.minX, minY: viewport.minY,

frontend/src/components/CanvasArea.tsx

@@ -82,6 +82,9 @@ const CanvasArea: React.FC<CanvasAreaProps> = ({
           pixi = new PixiRenderer();
           pixiRendererRef.current = pixi;
           pixi.init(pixiCanvas);
+          // CAD-13-fix: Pixi rendert jetzt die Elemente — Legacy-Canvas
+          // stellt nur noch Grid/Hintergrund/Lineal dar (sonst doppelt).
+          renderEngine.skipElementRendering = true;
           pixi.waitForReady().then(() => {
             // Task C4: Debug-Hook für Playwright-E2E-Assertions
             (window as unknown as { __v2Debug: unknown }).__v2Debug = {