test(app): reproduce settings sidebar scroll reset on section select (#1532)

Selecting a settings section mounts a new settings screen, so the
desktop sidebar's scroll body starts again at offset 0. This test
scrolls the sidebar to its end and selects two host sections; it fails
on main with the offset dropping from 236 to 0.

packages/app/e2e/browser/settings-navigation.spec.ts

@@ -40,6 +40,8 @@ import {
   expectSettingsHostPickerLabel,
   openSettingsHostSection,
   removeCurrentHostFromSettings,
+  scrollSettingsSidebarToEnd,
+  expectSettingsSidebarScrollOffset,
 } from "../support/helpers/settings";
 import { getServerId } from "../support/helpers/server-id";
 import { expectAppRoute } from "../support/helpers/route-assertions";
@@ -77,6 +79,23 @@ test.describe("Settings sidebar navigation", () => {
     await expect(page).not.toHaveURL(/\/settings(\/|$)/);
   });
 
+  test.describe("in a short window", () => {
+    test.use({ viewport: { width: 1280, height: 480 } });
+
+    test("selecting a section keeps the sidebar scroll position", async ({ page }) => {
+      const serverId = getServerId();
+      await gotoAppShell(page);
+      await openSettings(page);
+      const offset = await scrollSettingsSidebarToEnd(page);
+
+      await openSettingsHostSection(page, serverId, "plugins");
+      await expectSettingsSidebarScrollOffset(page, offset);
+
+      await openSettingsHostSection(page, serverId, "terminals");
+      await expectSettingsSidebarScrollOffset(page, offset);
+    });
+  });
+
   test("/h/[serverId]/settings redirects to the host connections section", async ({ page }) => {
     await gotoAppShell(page);
     await verifyLegacyHostSettingsRedirect(page);

packages/app/e2e/support/helpers/settings.ts

@@ -453,3 +453,21 @@ export async function expectHostOnlineWithoutError(page: Page): Promise<void> {
   await expect(page.getByTestId("host-page-identity")).toContainText("Online");
   await expect(page.getByTestId("host-connection-error")).toHaveCount(0);
 }
+
+export async function scrollSettingsSidebarToEnd(page: Page): Promise<number> {
+  const scrollBody = page.getByTestId("settings-sidebar-scroll-body");
+  await expect(scrollBody).toBeVisible();
+  await scrollBody.hover();
+  await page.mouse.wheel(0, 10_000);
+  const readOffset = () => scrollBody.evaluate((node) => node.scrollTop);
+  await expect
+    .poll(readOffset, { message: "settings sidebar must overflow for this check" })
+    .toBeGreaterThan(0);
+  await expect.poll(async () => (await readOffset()) - (await readOffset())).toBe(0);
+  return readOffset();
+}
+
+export async function expectSettingsSidebarScrollOffset(page: Page, offset: number): Promise<void> {
+  const scrollBody = page.getByTestId("settings-sidebar-scroll-body");
+  await expect.poll(() => scrollBody.evaluate((node) => node.scrollTop)).toBe(offset);
+}