Keep large sidebars responsive (#1966)

* perf(app): keep large sidebars responsive

Sidebar rows rescanned every agent for each session update, multiplying work with both workspace and agent count. Build workspace activity once and share the derived sidebar model so updates scale with the underlying collections.

* test(app): use valid agent fixture for workspace restore

* refactor(app): keep sidebar model surface focused

packages/app/src/utils/sidebar-shortcuts.ts

@@ -1,9 +1,8 @@
 import type {
   SidebarProjectEntry,
-  SidebarStatusWorkspacePlacement,
   SidebarWorkspacePlacement,
 } from "@/hooks/use-sidebar-workspaces-list";
-import { buildStatusGroups } from "@/hooks/sidebar-status-view-model";
+import type { StatusGroup } from "@/hooks/sidebar-status-view-model";
 
 export interface SidebarShortcutWorkspaceTarget {
   serverId: string;
@@ -53,17 +52,15 @@ export function buildSidebarShortcutModel(input: {
 }
 
 export function buildStatusSidebarShortcutModel(input: {
-  workspaces: SidebarStatusWorkspacePlacement[];
-  projectNamesByKey: Map<string, string>;
+  groups: readonly StatusGroup[];
   collapsedStatusGroupKeys?: ReadonlySet<string>;
   shortcutLimit?: number;
 }): SidebarShortcutModel {
   const maxShortcuts = Math.max(0, Math.floor(input.shortcutLimit ?? 9));
-  const groups = buildStatusGroups(input.workspaces, input.projectNamesByKey);
   const shortcutTargets: SidebarShortcutWorkspaceTarget[] = [];
   const shortcutIndexByWorkspaceKey = new Map<string, number>();
 
-  for (const group of groups) {
+  for (const group of input.groups) {
     if (input.collapsedStatusGroupKeys?.has(group.bucket)) {
       continue;
     }