fix(app): optimize large review panes (#35375)

packages/app/src/components/virtual-scroll-element.test.ts

@@ -0,0 +1,18 @@
+import { expect, test } from "bun:test"
+import { virtualScrollElement } from "./virtual-scroll-element"
+
+test("resolves the connected viewport that owns the virtual root", () => {
+  const stale = document.createElement("div")
+  stale.className = "scroll-view__viewport"
+  const viewport = document.createElement("div")
+  viewport.className = "scroll-view__viewport"
+  const root = document.createElement("div")
+  viewport.append(root)
+  document.body.append(viewport)
+
+  expect(virtualScrollElement(root)).toBe(viewport)
+  expect(virtualScrollElement(root)).not.toBe(stale)
+
+  viewport.remove()
+  expect(virtualScrollElement(root)).toBeNull()
+})