Do not alter paths data when loading through d3js (#7026)

* d3-sankey alters the object passed into it. we must copy the object we pass to it

* save a path in a test

* don't rely on being able to query the toast when testing if paths saved

cypress/integration/paths.js

@@ -14,4 +14,10 @@ describe('Paths', () => {
 
         cy.get('[data-attr=paths-viz]').should('exist')
     })
+
+    it('can save paths', () => {
+        cy.get('[data-attr="insight-edit-button"]').should('not.exist')
+        cy.get('[data-attr="insight-save-button"]').click()
+        cy.get('[data-attr="insight-edit-button"]').should('exist')
+    })
 })

frontend/src/scenes/paths/NewPaths.tsx

@@ -271,7 +271,10 @@ export function NewPaths({ dashboardItemId = null, color = 'white' }: PathsProps
 
         const svg = createCanvas(width, height)
         const sankey = createSankey(width, height)
-        const { nodes, links } = sankey(paths)
+        const { nodes, links } = sankey({
+            nodes: paths.nodes.map((d) => ({ ...d })),
+            links: paths.links.map((d) => ({ ...d })),
+        })
 
         setPathItemCards(
             nodes.map((node: PathNodeData) => ({ ...node, visible: node.y1 - node.y0 > HIDE_PATH_CARD_HEIGHT }))