fix(tasks): preserve GitHub list scroll restoration (#17547)

src/renderer/src/components/TaskPage.tsx

@@ -538,7 +538,10 @@ export default function TaskPage(): React.JSX.Element {
 
   useLayoutEffect(() => {
     const target = pendingGithubScrollRestoreRef.current
-    if (target === null || !pages[currentPage]) {
+    // Start observing as soon as the list mounts; its page rows may be committed
+    // by a later render, and the restore helper will retry when they appear.
+    // Keep the target armed while the detail route is transitioning and the list is still mounted.
+    if (target === null || pageData.openGitHubWorkItem) {
       return
     }
     return startGitHubListScrollRestore({
@@ -559,6 +562,7 @@ export default function TaskPage(): React.JSX.Element {
     currentPage,
     dialogWorkItem,
     githubResumeContextKey,
+    pageData.openGitHubWorkItem,
     pages,
     githubListScrollTopRef,
     pendingGithubScrollRestoreRef,

src/renderer/src/components/task-page-github-list-scroll-restore.test.ts

@@ -106,6 +106,28 @@ describe('GitHub task list scroll restore', () => {
     expect(applied.at(-1)).toBe(360)
   })
 
+  it('retries when the rows mount after the restore starts', async () => {
+    const list = createScrollList(0)
+    list.element.removeChild(list.rows)
+    const pendingRestoreRef = ref<number | null>(360)
+    const restoreWriteRef = ref<GitHubListRestoreWrite | null>(null)
+
+    startGitHubListScrollRestore({
+      target: 360,
+      scrollElementRef: ref<HTMLElement | null>(list.element),
+      pendingRestoreRef,
+      restoreWriteRef,
+      onScrollTopApplied: () => {}
+    })
+
+    list.setMaxScrollTop(900)
+    list.element.append(list.rows)
+    await Promise.resolve()
+
+    expect(list.element.scrollTop).toBe(360)
+    expect(pendingRestoreRef.current).toBeNull()
+  })
+
   it('keeps the remembered offset armed when the list never becomes tall enough', () => {
     const list = createScrollList(0)
     const pendingRestoreRef = ref<number | null>(360)

src/renderer/src/components/task-page/github/github-list-scroll-restore.ts

@@ -40,6 +40,7 @@ export function startGitHubListScrollRestore({
   restoreWriteRef.current = null
   let frame: number | null = null
   let observer: ResizeObserver | null = null
+  let mutationObserver: MutationObserver | null = null
   const stop = (): void => {
     if (frame !== null) {
       window.cancelAnimationFrame(frame)
@@ -47,6 +48,8 @@ export function startGitHubListScrollRestore({
     }
     observer?.disconnect()
     observer = null
+    mutationObserver?.disconnect()
+    mutationObserver = null
   }
   const restore = (): void => {
     const element = scrollElementRef.current
@@ -72,6 +75,10 @@ export function startGitHubListScrollRestore({
   for (const child of scrollElement.children) {
     observer.observe(child)
   }
+  // Rows can mount after this layout effect (for example when a cached page settles),
+  // so observe child-list changes to cover elements that were not present initially.
+  mutationObserver = new MutationObserver(restore)
+  mutationObserver.observe(scrollElement, { childList: true, subtree: true })
   restore()
   if (pendingRestoreRef.current === target) {
     frame = window.requestAnimationFrame(restore)