fix(desktop): virtualize channel member lists (#4991)

## Summary

- virtualize the unfiltered channel member roster instead of eagerly
mounting every member card
- retain the existing member search/add flow and archived-member
behavior
- cover a 500-member roster, bounded mounted rows, and scrolling to the
final member in E2E

## Cause

The members sidebar rendered every active member card at once. On large
channels this mounted hundreds or thousands of avatars, profile/presence
consumers, menus, and DOM rows, blocking the renderer even though
fetching the roster itself is fast.

## Testing

- `pnpm typecheck`
- `pnpm exec biome check src/features/channels/ui/MembersSidebar.tsx
tests/e2e/channels.spec.ts`
- `pnpm build:e2e`
- `pnpm exec playwright test tests/e2e/channels.spec.ts --grep 'members
sidebar (virtualizes large channel rosters|can invite relay-authorized
agents|can invite and remove managed agents|collapses same-persona
managed agents)'` (4 passed)
- pre-push: `desktop-check`, full `desktop-test` (4,371 passed),
branch-skew

Implemented by Carl on Wes's behalf.

Signed-off-by: Wes <wesbillman@users.noreply.github.com>
Co-authored-by: Carl <c7ebe626f000404285d3686e1dc74cc07cc60a9754a150041ba132e14bd3e2ec@buzz.block.builderlab.xyz>

desktop/src/features/channels/ui/MembersSidebar.tsx

@@ -30,6 +30,7 @@ import {
 import { formatOwnerLabel } from "@/features/profile/lib/identity";
 import { rankUserCandidatesBySearch } from "@/features/profile/lib/userCandidateSearch";
 import { usePresenceQuery } from "@/features/presence/hooks";
+import { VirtualizedList } from "@/shared/ui/VirtualizedList";
 import { useIdentityQuery } from "@/shared/api/hooks";
 import { changeChannelMemberRole } from "@/shared/api/tauri";
 import type {
@@ -199,7 +200,6 @@ export function MembersSidebar({
       ),
     [bots, currentPubkey, people],
   );
-
   const allMemberPubkeys = React.useMemo(
     () => rawMembers.map((member) => member.pubkey),
     [rawMembers],
@@ -217,9 +217,7 @@ export function MembersSidebar({
     if (!normalizedSearchQuery) {
       return activeMembers;
     }
-
     const profiles = memberProfilesQuery.data?.profiles ?? {};
-
     return activeMembers.filter((member) => {
       const normalizedPubkey = normalizePubkey(member.pubkey);
       const profile = profiles[normalizedPubkey] ?? null;
@@ -816,11 +814,14 @@ export function MembersSidebar({
                     ) : null}
                   </div>
                 ) : filteredActiveMembers.length > 0 ? (
-                  <div>
-                    {filteredActiveMembers.map((member) =>
-                      renderMemberCard(member, isBot(member)),
-                    )}
-                  </div>
+                  <VirtualizedList
+                    className="h-[calc(100%_-_2.25rem)]"
+                    getItemKey={(member) => member.pubkey}
+                    items={filteredActiveMembers}
+                    renderItem={(member) =>
+                      renderMemberCard(member, isBot(member))
+                    }
+                  />
                 ) : (
                   <p className="px-4 py-3 text-sm text-muted-foreground">
                     {membersQuery.isLoading

desktop/tests/e2e/channels.spec.ts

@@ -3394,6 +3394,40 @@ test("home inbox manage affordance opens management without leaving home", async
   await expect(page).not.toHaveURL(/#\/channels\//);
 });
 
+test("members sidebar virtualizes large channel rosters", async ({ page }) => {
+  await page.goto("/");
+  const channelId = await page
+    .getByTestId("channel-random")
+    .getAttribute("data-channel-id");
+  if (!channelId) {
+    throw new Error("Random channel id missing.");
+  }
+
+  const pubkeys = Array.from({ length: 500 }, (_, index) =>
+    (index + 1).toString(16).padStart(64, "0"),
+  );
+  await invokeMockCommand(page, "add_channel_members", {
+    channelId,
+    pubkeys,
+    role: "member",
+  });
+
+  await openMembersSidebar(page, "random");
+  const memberList = page.getByTestId("members-sidebar-people");
+  const memberRows = memberList.locator('[data-testid^="sidebar-member-"]');
+  await expect(memberRows.first()).toBeVisible();
+  expect(await memberRows.count()).toBeLessThan(50);
+
+  const virtualizedList = memberList.locator(".overflow-y-auto");
+  await virtualizedList.evaluate((element) => {
+    element.scrollTop = element.scrollHeight;
+    element.dispatchEvent(new Event("scroll"));
+  });
+  await expect(
+    memberList.getByTestId(`sidebar-member-${pubkeys.at(-1)}`),
+  ).toBeVisible();
+});
+
 test("members sidebar can invite relay-authorized agents", async ({ page }) => {
   await installMockBridge(page, {
     relayAgents: [