refactor(view): extract canvas viewport hooks

view/canvas/useCanvasResize.ts

@@ -0,0 +1,20 @@
+import { useEffect, type RefObject } from "react";
+import type { Dispatch } from "@commands/dispatcher";
+
+export function useCanvasResize(canvasRef: RefObject<HTMLCanvasElement | null>, dispatch: Dispatch) {
+  useEffect(() => {
+    const canvas = canvasRef.current;
+    if (!canvas) return;
+
+    const resizeObserver = new ResizeObserver(([entry]) => {
+      if (!entry) return;
+
+      const width = Math.floor(entry.contentRect.width);
+      const height = Math.floor(entry.contentRect.height);
+      dispatch("viewport.setSize", { w: width, h: height });
+    });
+
+    resizeObserver.observe(canvas);
+    return () => resizeObserver.disconnect();
+  }, [canvasRef, dispatch]);
+}