feat(canvas): copy/paste nodes across designs

Clipboard now holds nodes + internal edges and survives design switches
(loadCanvas no longer clears it), so a selection copied in one design can
be pasted into another. Copy pulls in children of selected groups/
containers; paste remaps node/edge/parent IDs and lands the bounding-box
center under the cursor (or viewport center). Shortcut handling moved into
CanvasContainer for flow-coordinate projection.

ha-relevant: yes

frontend/src/stores/__tests__/canvasStore.test.ts

@@ -30,7 +30,7 @@ describe('canvasStore', () => {
       editingTextId: null,
       past: [],
       future: [],
-      clipboard: [],
+      clipboard: { nodes: [], edges: [] },
     })
   })
 
@@ -690,25 +690,112 @@ describe('canvasStore', () => {
     })
     useCanvasStore.getState().copySelectedNodes()
     const { clipboard } = useCanvasStore.getState()
-    expect(clipboard).toHaveLength(1)
-    expect(clipboard[0].id).toBe('a')
+    expect(clipboard.nodes).toHaveLength(1)
+    expect(clipboard.nodes[0].id).toBe('a')
   })
 
-  it('pasteNodes creates new nodes with new IDs and offset position', () => {
-    const node = { ...makeNode('src'), position: { x: 100, y: 100 }, selected: true }
-    useCanvasStore.setState({ nodes: [node], edges: [], clipboard: [node] })
+  it('copySelectedNodes captures edges whose endpoints are both selected', () => {
+    useCanvasStore.setState({
+      nodes: [
+        { ...makeNode('a'), selected: true },
+        { ...makeNode('b'), selected: true },
+        { ...makeNode('c'), selected: false },
+      ],
+      edges: [makeEdge('e-ab', 'a', 'b'), makeEdge('e-bc', 'b', 'c')],
+    })
+    useCanvasStore.getState().copySelectedNodes()
+    const { clipboard } = useCanvasStore.getState()
+    expect(clipboard.nodes.map((n) => n.id).sort()).toEqual(['a', 'b'])
+    expect(clipboard.edges).toHaveLength(1)
+    expect(clipboard.edges[0].id).toBe('e-ab')
+  })
+
+  it('copySelectedNodes pulls in children of a selected group', () => {
+    useCanvasStore.setState({
+      nodes: [
+        { ...makeNode('g', { type: 'group' }), type: 'group', selected: true },
+        { ...makeNode('child', { parent_id: 'g' }), parentId: 'g', selected: false },
+      ],
+      edges: [],
+    })
+    useCanvasStore.getState().copySelectedNodes()
+    expect(useCanvasStore.getState().clipboard.nodes.map((n) => n.id).sort()).toEqual(['child', 'g'])
+  })
+
+  it('pasteNodes creates new nodes with new IDs and a cascade offset by default', () => {
+    const node = { ...makeNode('src'), position: { x: 100, y: 100 } }
+    useCanvasStore.setState({ nodes: [], edges: [], clipboard: { nodes: [node], edges: [] } })
     useCanvasStore.getState().pasteNodes()
     const { nodes } = useCanvasStore.getState()
-    expect(nodes).toHaveLength(2)
-    const pasted = nodes.find((n) => n.id !== 'src')!
-    expect(pasted).toBeDefined()
-    expect(pasted.position.x).toBe(150)
-    expect(pasted.position.y).toBe(150)
-    expect(pasted.selected).toBe(false)
+    expect(nodes).toHaveLength(1)
+    const pasted = nodes[0]
+    expect(pasted.id).not.toBe('src')
+    expect(pasted.position).toEqual({ x: 150, y: 150 })
+    expect(pasted.selected).toBe(true)
+  })
+
+  it('pasteNodes centers the pasted bounding box on the target point', () => {
+    const node = { ...makeNode('src'), position: { x: 0, y: 0 }, width: 100, height: 100 }
+    useCanvasStore.setState({ nodes: [], edges: [], clipboard: { nodes: [node], edges: [] } })
+    useCanvasStore.getState().pasteNodes({ x: 500, y: 300 })
+    const pasted = useCanvasStore.getState().nodes[0]
+    // bbox center (50,50) shifted onto (500,300) → top-left at (450,250)
+    expect(pasted.position).toEqual({ x: 450, y: 250 })
+  })
+
+  it('pasteNodes remaps edge endpoints to the new node IDs', () => {
+    const a = { ...makeNode('a') }
+    const b = { ...makeNode('b') }
+    useCanvasStore.setState({
+      nodes: [],
+      edges: [],
+      clipboard: { nodes: [a, b], edges: [makeEdge('e-ab', 'a', 'b')] },
+    })
+    useCanvasStore.getState().pasteNodes()
+    const { nodes, edges } = useCanvasStore.getState()
+    expect(edges).toHaveLength(1)
+    const ids = nodes.map((n) => n.id)
+    expect(ids).toContain(edges[0].source)
+    expect(ids).toContain(edges[0].target)
+    expect(edges[0].source).not.toBe('a')
+    expect(edges[0].id).not.toBe('e-ab')
+  })
+
+  it('pasteNodes preserves parent-child relationship under remapped IDs', () => {
+    const group = { ...makeNode('g', { type: 'group' }), type: 'group', position: { x: 0, y: 0 } }
+    const child = { ...makeNode('child', { parent_id: 'g' }), parentId: 'g', extent: 'parent' as const, position: { x: 20, y: 30 } }
+    useCanvasStore.setState({ nodes: [], edges: [], clipboard: { nodes: [group, child], edges: [] } })
+    useCanvasStore.getState().pasteNodes()
+    const { nodes } = useCanvasStore.getState()
+    const newGroup = nodes.find((n) => n.data.type === 'group')!
+    const newChild = nodes.find((n) => n.id !== newGroup.id)!
+    expect(newChild.parentId).toBe(newGroup.id)
+    expect(newChild.data.parent_id).toBe(newGroup.id)
+    // Child keeps its parent-relative position (no offset applied to children)
+    expect(newChild.position).toEqual({ x: 20, y: 30 })
+    // Group (the root) precedes its child in the array
+    expect(nodes.findIndex((n) => n.id === newGroup.id)).toBeLessThan(
+      nodes.findIndex((n) => n.id === newChild.id),
+    )
+  })
+
+  it('clipboard survives loadCanvas so nodes can be pasted into another design', () => {
+    useCanvasStore.setState({
+      nodes: [{ ...makeNode('a'), selected: true }],
+      edges: [],
+    })
+    useCanvasStore.getState().copySelectedNodes()
+    // Switch to another design: loadCanvas replaces nodes/edges.
+    useCanvasStore.getState().loadCanvas([makeNode('other')], [])
+    expect(useCanvasStore.getState().clipboard.nodes).toHaveLength(1)
+    useCanvasStore.getState().pasteNodes()
+    const ids = useCanvasStore.getState().nodes.map((n) => n.id)
+    expect(ids).toContain('other')
+    expect(ids).toHaveLength(2)
   })
 
   it('pasteNodes does nothing when clipboard is empty', () => {
-    useCanvasStore.setState({ nodes: [makeNode('n1')], edges: [], clipboard: [] })
+    useCanvasStore.setState({ nodes: [makeNode('n1')], edges: [], clipboard: { nodes: [], edges: [] } })
     useCanvasStore.getState().pasteNodes()
     expect(useCanvasStore.getState().nodes).toHaveLength(1)
   })
@@ -867,7 +954,7 @@ describe('canvasStore — custom style apply', () => {
       editingTextId: null,
       past: [],
       future: [],
-      clipboard: [],
+      clipboard: { nodes: [], edges: [] },
     })
   })