task(C4): use_pixi_renderer flag on by default with e2e proof

frontend/src/components/CanvasArea.tsx

@@ -17,7 +17,7 @@ import { logger } from '../utils/logger';
 import { CADDocument } from '../kernel/document/CADDocument';
 import { YjsDocument } from '../crdt/YjsDocument';
 import { setActiveDocument, getActiveDocument } from '../kernel/document/documentService';
-import { V2_TOOLS_ENABLED } from '../kernel/featureFlags';
+import { V2_TOOLS_ENABLED, USE_PIXI_RENDERER } from '../kernel/featureFlags';
 import { PixiRenderer } from '../render/pixi/PixiRenderer';
 import { pluginRegistry } from '../plugins';
 
@@ -71,18 +71,24 @@ const CanvasArea: React.FC<CanvasAreaProps> = ({
       // App-Level-Zugriffspunkt für HistoryPanel/Tastenkürzel (Task A4.11):
       setActiveDocument(v2Doc);
 
-      // ── Task C2: PixiJS-Renderer parallel schalten ──
+      // ── Task C2/C4: PixiJS-Renderer parallel schalten ──
       // DEFENSIV: Ein Ausfall von Pixi (z.B. WebGL im Headless-Browser)
       // darf NIEMALS den kompletten Editor-Mount brechen. Im Fehlerfall
       // läuft weiter ohne Overlay.
       let pixi: PixiRenderer | null = null;
       const pixiCanvas = pixiCanvasRef.current;
-      if (pixiCanvas) {
+      if (pixiCanvas && USE_PIXI_RENDERER) {
         try {
           pixi = new PixiRenderer();
           pixiRendererRef.current = pixi;
           pixi.init(pixiCanvas);
-          pixi.waitForReady().catch((err) => {
+          pixi.waitForReady().then(() => {
+            // Task C4: Debug-Hook für Playwright-E2E-Assertions
+            (window as unknown as { __v2Debug: unknown }).__v2Debug = {
+              renderer: pixi,
+              info: () => pixiRendererRef.current?.getDebugInfo() ?? null,
+            };
+          }).catch((err) => {
             logger.warn('Pixi init failed — V2-Overlay deaktiviert:', err);
             pixi = null;
             pixiRendererRef.current = null;

frontend/src/kernel/featureFlags.ts

@@ -13,3 +13,11 @@
 /** Ist der V2-Werkzeugpfad (Dispatcher/CADDocument) aktiv? Default: ja. */
 export const V2_TOOLS_ENABLED: boolean =
   import.meta.env.VITE_TOOL_DISPATCHER !== 'legacy';
+
+/**
+ * Task C4: Pixi als Primär-Renderer für V2-Elemente (Overlay über Legacy).
+ * Default: ja (durch phase-a-verify E2E abgesichert).
+ * Opt-out: VITE_USE_PIXI=false.
+ */
+export const USE_PIXI_RENDERER: boolean =
+  import.meta.env.VITE_USE_PIXI !== 'false';

frontend/src/render/pixi/PixiRenderer.ts

@@ -48,6 +48,9 @@ export class PixiRenderer implements RenderAdapter {
     await this.ready;
   }
 
+  /** Task C4: true sobald setupApp fertig ist (via readyResolve gesetzt). */
+  private initialized = false;
+
   // ── Lifecycle ────────────────────────────────────────────
 
   init(canvas: HTMLCanvasElement): void {
@@ -89,6 +92,7 @@ export class PixiRenderer implements RenderAdapter {
       this.overlayLayer = overlay;
       this.app.stage.addChild(overlay);
       this.applyViewportTransform();
+      this.initialized = true;              // Task C4: fuer getDebugInfo
     });
   }
 
@@ -252,6 +256,17 @@ export class PixiRenderer implements RenderAdapter {
     return null;
   }
 
+  /**
+   * Task C4: Debug-Info für Playwright-E2E-Assertions.
+   * Ermöglicht Testabfragen wie 'wie viele Elemente sind gerendert?'
+   */
+  getDebugInfo(): { cachedElements: number; ready: boolean } {
+    return {
+      cachedElements: this.graphicsCache.size,
+      ready: this.initialized,
+    };
+  }
+
   // ── Internes ─────────────────────────────────────────────
 
   private applyViewportTransform(): void {