feat(engine): canvas panning, wheel zoom and link editing tools

Drag empty space to pan, mouse-wheel to zoom, and selecting a link now
shows vertex/segment/arrowhead/remove tools so connectors can be rerouted
and deleted interactively.

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

src/renderer/diagram/controller.ts

@@ -3,7 +3,7 @@
  * framework-agnostic API for the React shell: add nodes, edit properties,
  * select/delete/copy, undo/redo, configure, save/load and run the mock flow.
  */
-import { dia, shapes, highlighters, g } from '@joint/core'
+import { dia, shapes, highlighters, linkTools, g } from '@joint/core'
 import {
   PipelineNode,
   createNode,
@@ -113,10 +113,47 @@ export class DiagramController {
       }
     })
 
+    // Pan the canvas by dragging empty space.
+    let pan: { tx: number; ty: number; x: number; y: number } | null = null
+    paper.on('blank:pointerdown', (evt: dia.Event) => {
+      const t = paper.translate()
+      pan = { tx: t.tx, ty: t.ty, x: evt.clientX ?? 0, y: evt.clientY ?? 0 }
+    })
+    paper.on('blank:pointermove', (evt: dia.Event) => {
+      if (!pan) return
+      paper.translate(pan.tx + ((evt.clientX ?? 0) - pan.x), pan.ty + ((evt.clientY ?? 0) - pan.y))
+    })
+    paper.on('blank:pointerup', () => (pan = null))
+
+    // Wheel to zoom toward the cursor.
+    paper.on('blank:mousewheel', (evt: dia.Event, _x, _y, delta: number) => {
+      evt.preventDefault?.()
+      this.zoom(delta > 0 ? 1.1 : 1 / 1.1)
+    })
+    paper.on('cell:mousewheel', (_v, evt: dia.Event, _x, _y, delta: number) => {
+      evt.preventDefault?.()
+      this.zoom(delta > 0 ? 1.1 : 1 / 1.1)
+    })
+
     this.graph.on('remove', () => !this.restoring && this.fire('change'))
     this.graph.on('add', () => !this.restoring && this.fire('change'))
   }
 
+  private addLinkTools(link: dia.Link): void {
+    const view = this.paper?.findViewByModel(link)
+    if (!view) return
+    view.addTools(
+      new dia.ToolsView({
+        tools: [
+          new linkTools.Vertices(),
+          new linkTools.Segments(),
+          new linkTools.TargetArrowhead(),
+          new linkTools.Remove({ distance: 20 })
+        ]
+      })
+    )
+  }
+
   private validateConnection = (
     sourceView: dia.CellView,
     sourceMagnet: SVGElement | null,
@@ -197,6 +234,7 @@ export class DiagramController {
         padding: 4,
         attrs: { stroke: '#f0c000', 'stroke-width': 2 }
       })
+      if (cell.isLink()) this.addLinkTools(cell as dia.Link)
     }
   }
 
@@ -206,7 +244,10 @@ export class DiagramController {
       if (!cell) continue
       if (!cell.isLink()) this.setPortsVisible(cell as dia.Element, false)
       const view = this.paper?.findViewByModel(cell)
-      if (view) highlighters.mask.remove(view, 'sel')
+      if (view) {
+        highlighters.mask.remove(view, 'sel')
+        if (cell.isLink()) view.removeTools()
+      }
     }
   }