Optimizing 3D model preview rendering during artifact streaming to prevent visual flickering and state loss.

**content**: The viewer tears down and rebuilds its entire Three.js scene whenever the `artifact` prop identity changes, which can happen multiple times per agent run when `streamAgent` emits `artifacts` events. **file**: src/components/CadViewer.tsx **code**: ```ts useEffect(() => { // full scene / renderer / controls setup return () => { disposed = true; controller.abort(); cancelAnimationFrame(frame); observer.disconnect(); controls.removeEventListener('change', draw); controls.dispose(); if (model) disposeTree(model); renderer.dispose(); controllerRef.current = undefined; }; }, [artifact]); ``` **description**: Each `artifacts` event in CadWorkbench replaces `previewArtifact` with a new object reference, so the heavy effect re-runs mid-run: WebGLRenderer is disposed and recreated, OrbitControls is rebuilt, and the model is re-fetched from disk. The visible symptom is the canvas flashing blank and the camera resetting to the isometric fit. Hidden risks include GPU memory churn under rapid events, lost orbit/zoom state during user interaction, and aborted in-flight fetches that may surface as transient errors. Is a keyed/scene-caching layer or stable artifact identity (e.g., path-based memoization) intended? Suggested fix: memoize `previewArtifact` by `path`/`modifiedAt` and split scene lifecycle from model swap so only the mesh is replaced.