feat(canvas): blank-drag panning and Ctrl/Cmd+wheel zoom-to-cursor

- Pan the viewport by dragging empty canvas
- Ctrl/Cmd + mouse wheel zooms toward the pointer; handler cleaned up on destroy
- Make PropertiesPanel's selectionRev dependency explicit for the linter

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/canvas/CanvasController.ts

@@ -200,15 +200,36 @@ export class CanvasController {
       this.selectCell(link, false);
       this.commit();
     });
-    p.on("blank:pointerdown", () => {
+    // Blank drag pans the canvas.
+    p.on("blank:pointerdown", (evt: dia.Event) => {
       this.clearSelection();
+      const t = this.paper.translate();
+      this.panStart = { x: (evt.clientX ?? 0) - t.tx, y: (evt.clientY ?? 0) - t.ty };
+    });
+    p.on("blank:pointermove", (evt: dia.Event) => {
+      if (!this.panStart) return;
+      this.paper.translate((evt.clientX ?? 0) - this.panStart.x, (evt.clientY ?? 0) - this.panStart.y);
+    });
+    p.on("blank:pointerup", () => {
+      this.panStart = null;
     });
     p.on("cell:pointerdblclick", (view) => {
       // double-click focuses without toggling multi-select
       this.selectCell(view.model, false);
     });
+
+    // Ctrl/⌘ + wheel zooms toward the cursor.
+    this.wheelHandler = (e: WheelEvent) => {
+      if (!(e.ctrlKey || e.metaKey)) return;
+      e.preventDefault();
+      this.zoom(e.deltaY < 0 ? 1.1 : 1 / 1.1, { x: e.clientX, y: e.clientY });
+    };
+    this.paper.el.addEventListener("wheel", this.wheelHandler, { passive: false });
   }
 
+  private panStart: { x: number; y: number } | null = null;
+  private wheelHandler: ((e: WheelEvent) => void) | null = null;
+
   private snapElement(el: dia.Element): void {
     const g = this.config.gridSize;
     const { x, y } = el.position();
@@ -720,6 +741,7 @@ export class CanvasController {
 
   destroy(): void {
     this.stopFlow();
+    if (this.wheelHandler) this.paper.el.removeEventListener("wheel", this.wheelHandler);
     this.paper.remove();
   }
 }

src/ui/PropertiesPanel.tsx

@@ -29,6 +29,7 @@ export function PropertiesPanel() {
   const cell = selection && controller ? controller.getPrimary() : null;
 
   const model = useMemo(() => {
+    void rev; // recompute when the selected cell's props change externally
     if (!cell || !selection) return null;
     const props = (cell.prop("props") ?? {}) as Record<string, PropertyValue>;
     if (selection.kind === "node") {