fix(app): reject stale timeline range indexes (#33488)

packages/app/test-browser/solid-virtual.test.ts

@@ -1,6 +1,7 @@
 import { expect, test } from "bun:test"
-import { createVirtualizer } from "@tanstack/solid-virtual"
+import { createVirtualizer, defaultRangeExtractor } from "@tanstack/solid-virtual"
 import { createRoot, createSignal } from "solid-js"
+import { filterVirtualIndexes } from "@/pages/session/timeline/virtual-items"
 
 test("reactive count updates preserve measured row sizes", () => {
   createRoot((dispose) => {
@@ -44,3 +45,26 @@ test("logical scroll offset includes pending measurement adjustments", () => {
     dispose()
   })
 })
+
+test("stale pinned indexes do not produce missing virtual items after count shrinks", () => {
+  createRoot((dispose) => {
+    const [count, setCount] = createSignal(2)
+    const pinned = [1]
+    const virtualizer = createVirtualizer<HTMLDivElement, HTMLDivElement>({
+      get count() {
+        return count()
+      },
+      getScrollElement: () => null,
+      estimateSize: () => 60,
+      initialRect: { width: 800, height: 600 },
+      rangeExtractor: (range) =>
+        filterVirtualIndexes([...new Set([...defaultRangeExtractor(range), ...pinned])], range.count),
+    })
+
+    expect(virtualizer.getVirtualItems().map((item) => item.index)).toEqual([0, 1])
+    setCount(1)
+    expect(virtualizer.getVirtualItems().map((item) => item.index)).toEqual([0])
+    expect(() => new Map(virtualizer.getVirtualItems().map((item) => [item.key, item]))).not.toThrow()
+    dispose()
+  })
+})