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
2026-07-29 12:01:31 +00:00 · 2026-07-10 00:12:56 +02:00
parent b2c6476817
commit a743a22496
18 changed files with 445 additions and 262 deletions
--- a/packages/app/src/app/_layout.tsx
+++ b/packages/app/src/app/_layout.tsx
@@ -4,13 +4,7 @@ import { PortalProvider } from "@gorhom/portal";
 import { QueryClientProvider } from "@tanstack/react-query";
 import * as Linking from "expo-linking";
 import * as Notifications from "expo-notifications";
-import {
-  Stack,
-  useGlobalSearchParams,
-  useNavigationContainerRef,
-  usePathname,
-  useRouter,
-} from "expo-router";
+import { Stack, useNavigationContainerRef, usePathname, useRouter } from "expo-router";
 import {
  createContext,
  type ReactNode,
@@ -33,6 +27,7 @@ import { DownloadToast } from "@/components/download-toast";
 import { QuittingOverlay } from "@/components/quitting-overlay";
 import { KeyboardShortcutsDialog } from "@/components/keyboard-shortcuts-dialog";
 import { LeftSidebar } from "@/components/left-sidebar";
+import { SidebarModelProvider } from "@/components/sidebar/sidebar-model";
 import { CompactExplorerSidebarHost } from "@/components/compact-explorer-sidebar-host";
 import { ProjectPickerModal } from "@/components/project-picker-modal";
 import { ProviderSettingsHost } from "@/components/provider-settings-host";
@@ -93,12 +88,7 @@ import { usePanelStore } from "@/stores/panel-store";
 import { THEME_TO_UNISTYLES, type ThemeName } from "@/styles/theme";
 import type { HostProfile } from "@/types/host-connection";
 import { toggleDesktopSidebarsWithCheckoutIntent } from "@/utils/desktop-sidebar-toggle";
-import {
-  buildOpenProjectRoute,
-  parseHostAgentRouteFromPathname,
-  parseServerIdFromPathname,
-  parseWorkspaceOpenIntent,
-} from "@/utils/host-routes";
+import { buildOpenProjectRoute, parseServerIdFromPathname } from "@/utils/host-routes";
 import { buildNotificationRoute, resolveNotificationTarget } from "@/utils/notification-routing";
 import { navigateToAgent } from "@/utils/navigate-to-agent";
 import {
@@ -401,17 +391,12 @@ const MOBILE_WEB_GESTURE_TOUCH_ACTION = isWeb ? "auto" : "pan-y";

 interface AppContainerProps {
  children: ReactNode;
-  selectedAgentId?: string;
  chromeEnabled?: boolean;
 }

 const THEME_CYCLE_ORDER: ThemeName[] = ["dark", "zinc", "midnight", "claude", "ghostty", "light"];

-function AppContainer({
-  children,
-  selectedAgentId,
-  chromeEnabled: chromeEnabledOverride,
-}: AppContainerProps) {
+function AppContainer({ children, chromeEnabled: chromeEnabledOverride }: AppContainerProps) {
  const daemons = useHosts();
  const { settings, updateSettings } = useAppSettings();
  const toggleMobileAgentList = usePanelStore((state) => state.toggleMobileAgentList);
@@ -468,9 +453,7 @@ function AppContainer({

  const workspaceChrome = (
    <View style={rowStyle}>
-      {!isCompactLayout && chromeEnabled && !isFocusModeEnabled && (
-        <LeftSidebar selectedAgentId={selectedAgentId} />
-      )}
+      {!isCompactLayout && chromeEnabled && !isFocusModeEnabled && <LeftSidebar />}
      {isCompactLayout && chromeEnabled ? (
        <CompactExplorerSidebarHost enabled={chromeEnabled}>
          <View style={flexStyle}>{children}</View>
@@ -482,23 +465,25 @@ function AppContainer({
  );

  const content = (
-    <View style={layoutStyles.surfaceFill}>
-      {workspaceChrome}
-      <FloatingPanelPortalHost />
-      {isCompactLayout && chromeEnabled && <LeftSidebar selectedAgentId={selectedAgentId} />}
-      <DownloadToast />
-      <RosettaCalloutSource />
-      <UpdateCalloutSource />
-      <WorktreeSetupCalloutSource />
-      <CommandCenter />
-      <HostChooserModal />
-      <ProjectPickerModal />
-      <ProviderSettingsHost />
-      <WorkspaceShortcutTargetsSubscriber enabled={keyboardShortcutsEnabled} />
-      <WorkspaceSetupDialog />
-      <KeyboardShortcutsDialog />
-      <QuittingOverlay />
-    </View>
+    <SidebarModelProvider>
+      <View style={layoutStyles.surfaceFill}>
+        {workspaceChrome}
+        <FloatingPanelPortalHost />
+        {isCompactLayout && chromeEnabled && <LeftSidebar />}
+        <DownloadToast />
+        <RosettaCalloutSource />
+        <UpdateCalloutSource />
+        <WorktreeSetupCalloutSource />
+        <CommandCenter />
+        <HostChooserModal />
+        <ProjectPickerModal />
+        <ProviderSettingsHost />
+        <WorkspaceShortcutTargetsSubscriber enabled={keyboardShortcutsEnabled} />
+        <WorkspaceSetupDialog />
+        <KeyboardShortcutsDialog />
+        <QuittingOverlay />
+      </View>
+    </SidebarModelProvider>
  );

  if (!isCompactLayout) {
@@ -751,7 +736,6 @@ function OpenProjectListener() {

 function AppWithSidebar({ children }: { children: ReactNode }) {
  const pathname = usePathname();
-  const params = useGlobalSearchParams<{ open?: string | string[] }>();
  const hosts = useHosts();
  const storeReady = useStoreReady();
  const routeServerId = useMemo(() => parseServerIdFromPathname(pathname), [pathname]);
@@ -765,30 +749,7 @@ function AppWithSidebar({ children }: { children: ReactNode }) {
      pathname === "/schedules" ||
      routeHasKnownHost);

-  // Parse selectedAgentKey directly from pathname
-  // useLocalSearchParams doesn't update when navigating between same-pattern routes
-  const selectedAgentKey = useMemo(() => {
-    const workspaceMatch = pathname.match(/^\/h\/([^/]+)\/workspace\/[^/]+(?:\/|$)/);
-    const workspaceServerId = workspaceMatch?.[1]?.trim() ?? "";
-    const openValue = Array.isArray(params.open) ? params.open[0] : params.open;
-    const openIntent = parseWorkspaceOpenIntent(openValue);
-    if (workspaceServerId && openIntent?.kind === "agent") {
-      const agentId = openIntent.agentId.trim();
-      return agentId ? `${workspaceServerId}:${agentId}` : undefined;
-    }
-
-    const match = parseHostAgentRouteFromPathname(pathname);
-    return match ? `${match.serverId}:${match.agentId}` : undefined;
-  }, [params.open, pathname]);
-
-  return (
-    <AppContainer
-      selectedAgentId={shouldShowAppChrome ? selectedAgentKey : undefined}
-      chromeEnabled={shouldShowAppChrome}
-    >
-      {children}
-    </AppContainer>
-  );
+  return <AppContainer chromeEnabled={shouldShowAppChrome}>{children}</AppContainer>;
 }

 function FaviconStatusSync() {
--- a/packages/app/src/components/left-sidebar.tsx
+++ b/packages/app/src/components/left-sidebar.tsx
@@ -34,16 +34,12 @@ import { useIsCompactFormFactor } from "@/constants/layout";
 import { isWeb } from "@/constants/platform";
 import { useOpenProjectPicker } from "@/hooks/use-open-project-picker";
 import { useShortcutKeys } from "@/hooks/use-shortcut-keys";
-import { useSidebarShortcutModel } from "@/hooks/use-sidebar-shortcut-model";
 import { canCreateWorktreeForProjectKind } from "@/projects/host-projects";
 import { useHostFeature } from "@/runtime/host-features";
-import {
-  type SidebarProjectEntry,
-  type SidebarStatusWorkspacePlacement,
-  useSidebarWorkspacesList,
-} from "@/hooks/use-sidebar-workspaces-list";
-import { useStatusModeWorkspacePlacements } from "@/hooks/use-status-mode-workspaces";
-import { useSidebarViewStore, type SidebarGroupMode } from "@/stores/sidebar-view-store";
+import { type SidebarProjectEntry } from "@/hooks/use-sidebar-workspaces-list";
+import { useSidebarModel } from "@/components/sidebar/sidebar-model";
+import type { StatusGroup } from "@/hooks/sidebar-status-view-model";
+import { type SidebarGroupMode } from "@/stores/sidebar-view-store";
 import { useKeyboardShortcutsStore } from "@/stores/keyboard-shortcuts-store";
 import { useHosts } from "@/runtime/host-runtime";
 import { useActiveWorkspaceSelection } from "@/stores/navigation-active-workspace-store";
@@ -73,25 +69,20 @@ import { SidebarWorkspaceList } from "./sidebar-workspace-list";

 const MIN_CHAT_WIDTH = 400;

-type SidebarShortcutModel = ReturnType<typeof useSidebarShortcutModel>;
 type SidebarTheme = ReturnType<typeof useUnistyles>["theme"];

-interface LeftSidebarProps {
-  selectedAgentId?: string;
-}
-
 interface SidebarSharedProps {
  theme: SidebarTheme;
-  statusWorkspacePlacements: SidebarStatusWorkspacePlacement[];
+  statusGroups: StatusGroup[];
  projects: SidebarProjectEntry[];
  projectNamesByKey: Map<string, string>;
  isInitialLoad: boolean;
  isRevalidating: boolean;
  isManualRefresh: boolean;
  groupMode: SidebarGroupMode;
-  collapsedProjectKeys: SidebarShortcutModel["collapsedProjectKeys"];
-  shortcutIndexByWorkspaceKey: SidebarShortcutModel["shortcutIndexByWorkspaceKey"];
-  toggleProjectCollapsed: SidebarShortcutModel["toggleProjectCollapsed"];
+  collapsedProjectKeys: ReadonlySet<string>;
+  shortcutIndexByWorkspaceKey: Map<string, number>;
+  toggleProjectCollapsed: (projectKey: string) => void;
  handleRefresh: () => void;
  handleOpenProject: () => void;
  handleHome: () => void;
@@ -129,11 +120,7 @@ interface DesktopSidebarProps extends SidebarSharedProps {
  handleViewSchedules: () => void;
 }

-export const LeftSidebar = memo(function LeftSidebar({
-  selectedAgentId: _selectedAgentId,
-}: LeftSidebarProps) {
-  void _selectedAgentId;
-
+export const LeftSidebar = memo(function LeftSidebar() {
  const { theme } = useUnistyles();
  const { t } = useTranslation();
  const insets = useSafeAreaInsets();
@@ -144,22 +131,18 @@ export const LeftSidebar = memo(function LeftSidebar({
  const showMobileAgent = usePanelStore((state) => state.showMobileAgent);

  const {
-    workspacePlacements,
    projects,
    projectNamesByKey,
    isInitialLoad,
    isRevalidating,
    refreshAll,
-  } = useSidebarWorkspacesList({
-    enabled: isCompactLayout || isOpen,
-  });
-  const statusWorkspacePlacements = useStatusModeWorkspacePlacements({
-    placements: workspacePlacements,
-  });
-  const { collapsedProjectKeys, shortcutIndexByWorkspaceKey, toggleProjectCollapsed } =
-    useSidebarShortcutModel({ projects });
-
-  const groupMode = useSidebarViewStore((state) => state.groupMode);
+    statusGroups,
+    collapsedProjectKeys,
+    toggleProjectCollapsed,
+    groupMode,
+    shortcutModel,
+  } = useSidebarModel();
+  const { shortcutIndexByWorkspaceKey } = shortcutModel;

  const [isManualRefresh, setIsManualRefresh] = useState(false);

@@ -250,7 +233,7 @@ export const LeftSidebar = memo(function LeftSidebar({

  const sharedProps = {
    theme,
-    statusWorkspacePlacements,
+    statusGroups,
    projects,
    projectNamesByKey,
    isInitialLoad,
@@ -548,7 +531,7 @@ function SidebarFooter({

 function MobileSidebar({
  theme,
-  statusWorkspacePlacements,
+  statusGroups,
  projects,
  projectNamesByKey,
  isInitialLoad,
@@ -659,7 +642,7 @@ function MobileSidebar({
            onToggleProjectCollapsed={toggleProjectCollapsed}
            shortcutIndexByWorkspaceKey={shortcutIndexByWorkspaceKey}
            groupMode={groupMode}
-            statusWorkspacePlacements={statusWorkspacePlacements}
+            statusGroups={statusGroups}
            projects={projects}
            projectNamesByKey={projectNamesByKey}
            isRefreshing={isManualRefresh && isRevalidating}
@@ -686,7 +669,7 @@ function MobileSidebar({

 function DesktopSidebar({
  theme,
-  statusWorkspacePlacements,
+  statusGroups,
  projects,
  projectNamesByKey,
  isInitialLoad,
@@ -811,7 +794,7 @@ function DesktopSidebar({
            onToggleProjectCollapsed={toggleProjectCollapsed}
            shortcutIndexByWorkspaceKey={shortcutIndexByWorkspaceKey}
            groupMode={groupMode}
-            statusWorkspacePlacements={statusWorkspacePlacements}
+            statusGroups={statusGroups}
            projects={projects}
            projectNamesByKey={projectNamesByKey}
            isRefreshing={isManualRefresh && isRevalidating}
--- a/packages/app/src/components/sidebar-workspace-list.tsx
+++ b/packages/app/src/components/sidebar-workspace-list.tsx
@@ -68,7 +68,6 @@ import {
  shouldShowSidebarHostLabels,
  useSidebarWorkspaceEntry,
  type SidebarProjectEntry,
-  type SidebarStatusWorkspacePlacement,
  type SidebarWorkspaceEntry,
  type SidebarWorkspacePlacement,
 } from "@/hooks/use-sidebar-workspaces-list";
@@ -93,6 +92,7 @@ import { shouldRenderSyncedStatusLoader } from "@/utils/status-loader";
 import { isEmphasizedStatusDotBucket } from "@/utils/status-dot-color";
 import type { SidebarStateBucket } from "@/utils/sidebar-agent-state";
 import { SidebarStatusWorkspaceList } from "@/components/sidebar/sidebar-status-list";
+import type { StatusGroup } from "@/hooks/sidebar-status-view-model";
 import {
  SidebarWorkspaceRowFrame,
  SidebarWorkspaceRowContent,
@@ -228,7 +228,7 @@ function selectionForSelectedWorkspace(
 }

 interface SidebarWorkspaceListProps {
-  statusWorkspacePlacements: SidebarStatusWorkspacePlacement[];
+  statusGroups: StatusGroup[];
  projects: SidebarProjectEntry[];
  projectNamesByKey: Map<string, string>;
  collapsedProjectKeys: ReadonlySet<string>;
@@ -2166,7 +2166,7 @@ function areProjectBlockSelectionsEqual(
 const MemoProjectBlock = memo(ProjectBlock, areProjectBlockPropsEqual);

 export function SidebarWorkspaceList({
-  statusWorkspacePlacements,
+  statusGroups,
  projects,
  projectNamesByKey,
  collapsedProjectKeys,
@@ -2196,7 +2196,7 @@ export function SidebarWorkspaceList({
  const content =
    groupMode === "status" ? (
      <SidebarStatusModeWrapper
-        statusWorkspacePlacements={statusWorkspacePlacements}
+        statusGroups={statusGroups}
        projectNamesByKey={projectNamesByKey}
        shortcutIndexByWorkspaceKey={shortcutIndexByWorkspaceKey}
        onWorkspacePress={onWorkspacePress}
@@ -2224,14 +2224,14 @@ export function SidebarWorkspaceList({
 }

 function SidebarStatusModeWrapper({
-  statusWorkspacePlacements,
+  statusGroups,
  projectNamesByKey,
  shortcutIndexByWorkspaceKey: _projectShortcutIndex,
  onWorkspacePress,
  hostLabelByServerId,
  showHostLabels,
 }: {
-  statusWorkspacePlacements: SidebarStatusWorkspacePlacement[];
+  statusGroups: StatusGroup[];
  projectNamesByKey: Map<string, string>;
  shortcutIndexByWorkspaceKey: Map<string, number>;
  onWorkspacePress?: () => void;
@@ -2242,7 +2242,7 @@ function SidebarStatusModeWrapper({

  return (
    <SidebarStatusWorkspaceList
-      workspaces={statusWorkspacePlacements}
+      groups={statusGroups}
      projectNamesByKey={projectNamesByKey}
      shortcutIndexByWorkspaceKey={_projectShortcutIndex}
      showShortcutBadges={showShortcutBadges}
@@ -2268,7 +2268,7 @@ function ProjectModeList({
  supportsMultiplicityByServerId,
 }: Omit<
  SidebarWorkspaceListProps,
-  "statusWorkspacePlacements" | "projectNamesByKey" | "groupMode" | "isRefreshing" | "onRefresh"
+  "statusGroups" | "projectNamesByKey" | "groupMode" | "isRefreshing" | "onRefresh"
 > & {
  pathname: string;
  hostLabelByServerId: ReadonlyMap<string, string>;
--- a/packages/app/src/components/sidebar/sidebar-model.tsx
+++ b/packages/app/src/components/sidebar/sidebar-model.tsx
@@ -0,0 +1,76 @@
+import React, { createContext, useContext, useMemo, type ReactNode } from "react";
+import {
+  useSidebarWorkspacesList,
+  type SidebarWorkspacesListResult,
+} from "@/hooks/use-sidebar-workspaces-list";
+import { useStatusModeWorkspacePlacements } from "@/hooks/use-status-mode-workspaces";
+import { buildStatusGroups, type StatusGroup } from "@/hooks/sidebar-status-view-model";
+import { useSidebarCollapsedSectionsStore } from "@/stores/sidebar-collapsed-sections-store";
+import { useSidebarViewStore, type SidebarGroupMode } from "@/stores/sidebar-view-store";
+import {
+  buildSidebarShortcutModel,
+  buildStatusSidebarShortcutModel,
+  type SidebarShortcutModel,
+} from "@/utils/sidebar-shortcuts";
+
+interface SidebarModel extends SidebarWorkspacesListResult {
+  groupMode: SidebarGroupMode;
+  statusGroups: StatusGroup[];
+  collapsedProjectKeys: ReadonlySet<string>;
+  toggleProjectCollapsed: (projectKey: string) => void;
+  shortcutModel: SidebarShortcutModel;
+}
+
+const SidebarModelContext = createContext<SidebarModel | null>(null);
+
+export function SidebarModelProvider({ children }: { children: ReactNode }) {
+  const list = useSidebarWorkspacesList();
+  const groupMode = useSidebarViewStore((state) => state.groupMode);
+  const collapsedProjectKeys = useSidebarCollapsedSectionsStore(
+    (state) => state.collapsedProjectKeys,
+  );
+  const collapsedStatusGroupKeys = useSidebarCollapsedSectionsStore(
+    (state) => state.collapsedStatusGroupKeys,
+  );
+  const toggleProjectCollapsed = useSidebarCollapsedSectionsStore(
+    (state) => state.toggleProjectCollapsed,
+  );
+  const isStatusMode = groupMode === "status";
+  const statusWorkspacePlacements = useStatusModeWorkspacePlacements({
+    placements: list.workspacePlacements,
+    enabled: isStatusMode,
+  });
+  const statusGroups = useMemo(
+    () =>
+      isStatusMode ? buildStatusGroups(statusWorkspacePlacements, list.projectNamesByKey) : [],
+    [isStatusMode, list.projectNamesByKey, statusWorkspacePlacements],
+  );
+  const shortcutModel = useMemo(() => {
+    if (isStatusMode) {
+      return buildStatusSidebarShortcutModel({
+        groups: statusGroups,
+        collapsedStatusGroupKeys,
+      });
+    }
+    return buildSidebarShortcutModel({ projects: list.projects, collapsedProjectKeys });
+  }, [collapsedProjectKeys, collapsedStatusGroupKeys, isStatusMode, list.projects, statusGroups]);
+  const value = useMemo(
+    () => ({
+      ...list,
+      groupMode,
+      statusGroups,
+      collapsedProjectKeys,
+      toggleProjectCollapsed,
+      shortcutModel,
+    }),
+    [collapsedProjectKeys, groupMode, list, shortcutModel, statusGroups, toggleProjectCollapsed],
+  );
+
+  return <SidebarModelContext.Provider value={value}>{children}</SidebarModelContext.Provider>;
+}
+
+export function useSidebarModel(): SidebarModel {
+  const model = useContext(SidebarModelContext);
+  if (!model) throw new Error("SidebarModelProvider is required");
+  return model;
+}
--- a/packages/app/src/components/sidebar/sidebar-status-list.tsx
+++ b/packages/app/src/components/sidebar/sidebar-status-list.tsx
@@ -9,11 +9,7 @@ import {
  type SidebarStatusWorkspacePlacement,
  type SidebarWorkspaceEntry,
 } from "@/hooks/use-sidebar-workspaces-list";
-import {
-  buildStatusGroups,
-  buildStatusShortcutIndex,
-  type StatusGroup,
-} from "@/hooks/sidebar-status-view-model";
+import type { StatusGroup } from "@/hooks/sidebar-status-view-model";
 import { isWeb as platformIsWeb, isNative as platformIsNative } from "@/constants/platform";
 import { StyleSheet } from "react-native-unistyles";
 import type { Theme } from "@/styles/theme";
@@ -90,7 +86,7 @@ const archiveLeadingIcon = <ThemedArchive size={14} uniProps={foregroundMutedCol
 const renameLeadingIcon = <ThemedPencil size={14} uniProps={foregroundMutedColorMapping} />;

 interface StatusWorkspaceListProps {
-  workspaces: SidebarStatusWorkspacePlacement[];
+  groups: StatusGroup[];
  projectNamesByKey: Map<string, string>;
  shortcutIndexByWorkspaceKey: Map<string, number>;
  showShortcutBadges: boolean;
@@ -100,31 +96,19 @@ interface StatusWorkspaceListProps {
 }

 export function SidebarStatusWorkspaceList({
-  workspaces,
+  groups,
  projectNamesByKey,
-  shortcutIndexByWorkspaceKey: _projectShortcutIndex,
+  shortcutIndexByWorkspaceKey,
  showShortcutBadges,
  onWorkspacePress,
  hostLabelByServerId,
  showHostLabels,
 }: StatusWorkspaceListProps) {
-  const groups = useMemo(
-    () => buildStatusGroups(workspaces, projectNamesByKey),
-    [workspaces, projectNamesByKey],
-  );
  const collapsedStatusGroupKeys = useSidebarCollapsedSectionsStore(
    (state) => state.collapsedStatusGroupKeys,
  );

-  const statusShortcutIndex = useMemo(
-    () =>
-      showShortcutBadges
-        ? buildStatusShortcutIndex(
-            groups.filter((group) => !collapsedStatusGroupKeys.has(group.bucket)),
-          )
-        : new Map<string, number>(),
-    [collapsedStatusGroupKeys, groups, showShortcutBadges],
-  );
+  const statusShortcutIndex = showShortcutBadges ? shortcutIndexByWorkspaceKey : new Map();

  return (
    <View style={styles.container}>
--- a/packages/app/src/components/workspace-shortcut-targets-subscriber.test.tsx
+++ b/packages/app/src/components/workspace-shortcut-targets-subscriber.test.tsx
@@ -14,6 +14,7 @@ import { useSidebarOrderStore } from "@/stores/sidebar-order-store";
 import { useSidebarViewStore } from "@/stores/sidebar-view-store";
 import type { HostProfile } from "@/types/host-connection";
 import { WorkspaceShortcutTargetsSubscriber } from "./workspace-shortcut-targets-subscriber";
+import { SidebarModelProvider } from "./sidebar/sidebar-model";

 vi.hoisted(() => {
  (globalThis as unknown as { __DEV__: boolean }).__DEV__ = false;
@@ -122,7 +123,11 @@ describe("WorkspaceShortcutTargetsSubscriber", () => {

  it("publishes workspace shortcut targets without rendering the sidebar", async () => {
    await act(async () => {
-      root?.render(<WorkspaceShortcutTargetsSubscriber enabled={true} />);
+      root?.render(
+        <SidebarModelProvider>
+          <WorkspaceShortcutTargetsSubscriber enabled={true} />
+        </SidebarModelProvider>,
+      );
    });

    expect(useKeyboardShortcutsStore.getState().sidebarShortcutWorkspaceTargets).toEqual([
@@ -186,7 +191,11 @@ describe("WorkspaceShortcutTargetsSubscriber", () => {
    });

    await act(async () => {
-      root?.render(<WorkspaceShortcutTargetsSubscriber enabled={true} />);
+      root?.render(
+        <SidebarModelProvider>
+          <WorkspaceShortcutTargetsSubscriber enabled={true} />
+        </SidebarModelProvider>,
+      );
    });

    expect(useKeyboardShortcutsStore.getState().sidebarShortcutWorkspaceTargets).toEqual([
@@ -220,7 +229,11 @@ describe("WorkspaceShortcutTargetsSubscriber", () => {
    });

    await act(async () => {
-      root?.render(<WorkspaceShortcutTargetsSubscriber enabled={true} />);
+      root?.render(
+        <SidebarModelProvider>
+          <WorkspaceShortcutTargetsSubscriber enabled={true} />
+        </SidebarModelProvider>,
+      );
    });

    expect(useKeyboardShortcutsStore.getState().sidebarShortcutWorkspaceTargets).toEqual([
@@ -238,11 +251,19 @@ describe("WorkspaceShortcutTargetsSubscriber", () => {

  it("clears targets when disabled", async () => {
    await act(async () => {
-      root?.render(<WorkspaceShortcutTargetsSubscriber enabled={true} />);
+      root?.render(
+        <SidebarModelProvider>
+          <WorkspaceShortcutTargetsSubscriber enabled={true} />
+        </SidebarModelProvider>,
+      );
    });

    await act(async () => {
-      root?.render(<WorkspaceShortcutTargetsSubscriber enabled={false} />);
+      root?.render(
+        <SidebarModelProvider>
+          <WorkspaceShortcutTargetsSubscriber enabled={false} />
+        </SidebarModelProvider>,
+      );
    });

    expect(useKeyboardShortcutsStore.getState().sidebarShortcutWorkspaceTargets).toEqual([]);
--- a/packages/app/src/components/workspace-shortcut-targets-subscriber.tsx
+++ b/packages/app/src/components/workspace-shortcut-targets-subscriber.tsx
@@ -1,56 +1,13 @@
-import { useEffect, useMemo } from "react";
-import { useSidebarWorkspacesList } from "@/hooks/use-sidebar-workspaces-list";
-import { useStatusModeWorkspacePlacements } from "@/hooks/use-status-mode-workspaces";
+import { useEffect } from "react";
+import { useSidebarModel } from "@/components/sidebar/sidebar-model";
 import { useKeyboardShortcutsStore } from "@/stores/keyboard-shortcuts-store";
-import { useSidebarCollapsedSectionsStore } from "@/stores/sidebar-collapsed-sections-store";
-import { useSidebarViewStore } from "@/stores/sidebar-view-store";
-import {
-  buildSidebarShortcutModel,
-  buildStatusSidebarShortcutModel,
-} from "@/utils/sidebar-shortcuts";

 export function WorkspaceShortcutTargetsSubscriber({ enabled }: { enabled: boolean }) {
-  const { workspacePlacements, projects, projectNamesByKey } = useSidebarWorkspacesList({
-    enabled,
-  });
-  const groupMode = useSidebarViewStore((state) => state.groupMode);
-  const isStatusMode = enabled && groupMode === "status";
-  const statusWorkspacePlacements = useStatusModeWorkspacePlacements({
-    placements: workspacePlacements,
-    enabled: isStatusMode,
-  });
-  const collapsedProjectKeys = useSidebarCollapsedSectionsStore(
-    (state) => state.collapsedProjectKeys,
-  );
-  const collapsedStatusGroupKeys = useSidebarCollapsedSectionsStore(
-    (state) => state.collapsedStatusGroupKeys,
-  );
+  const { shortcutModel } = useSidebarModel();
  const setSidebarShortcutWorkspaceTargets = useKeyboardShortcutsStore(
    (state) => state.setSidebarShortcutWorkspaceTargets,
  );

-  const shortcutModel = useMemo(() => {
-    if (groupMode === "status") {
-      return buildStatusSidebarShortcutModel({
-        workspaces: statusWorkspacePlacements,
-        projectNamesByKey,
-        collapsedStatusGroupKeys,
-      });
-    }
-
-    return buildSidebarShortcutModel({
-      projects,
-      collapsedProjectKeys,
-    });
-  }, [
-    collapsedProjectKeys,
-    collapsedStatusGroupKeys,
-    groupMode,
-    projectNamesByKey,
-    projects,
-    statusWorkspacePlacements,
-  ]);
-
  useEffect(() => {
    if (!enabled) {
      setSidebarShortcutWorkspaceTargets([]);
--- a/packages/app/src/hooks/sidebar-workspaces-view-model.test.ts
+++ b/packages/app/src/hooks/sidebar-workspaces-view-model.test.ts
@@ -231,6 +231,7 @@ describe("shared sidebar workspace model", () => {
      sessions: [
        {
          serverId: "host-a",
+          workspaceAgentActivity: new Map(),
          workspaces: new Map([
            [
              "main",
@@ -246,6 +247,7 @@ describe("shared sidebar workspace model", () => {
        },
        {
          serverId: "host-b",
+          workspaceAgentActivity: new Map(),
          workspaces: new Map([
            [
              "feature",
--- a/packages/app/src/hooks/sidebar-workspaces-view-model.ts
+++ b/packages/app/src/hooks/sidebar-workspaces-view-model.ts
@@ -2,13 +2,13 @@ import type { PrHint } from "@/git/pr-hint";
 import { selectPrHintFromStatus } from "@/git/pr-hint";
 import { type HostProjectListItem } from "@/projects/host-project-model";
 import type { PendingCreateAttempt } from "@/stores/create-flow-store";
-import type { Agent, WorkspaceDescriptor } from "@/stores/session-store";
+import type { WorkspaceDescriptor } from "@/stores/session-store";
 import type {
  WorkspaceStructureHostPlacement,
  WorkspaceStructureProject,
 } from "@/projects/workspace-structure";
 import { projectDisplayNameFromProjectId } from "@/utils/project-display-name";
-import { deriveSidebarStateBucket } from "@/utils/sidebar-agent-state";
+import type { WorkspaceAgentActivity } from "@/utils/workspace-agent-activity";
 import { resolveWorkspaceMapKeyByIdentity } from "@/utils/workspace-identity";

 const EMPTY_PROJECTS: SidebarProjectEntry[] = [];
@@ -66,7 +66,7 @@ export interface SidebarWorkspacePlacementModel {
 export interface SidebarStatusWorkspaceSession {
  serverId: string;
  workspaces: Map<string, WorkspaceDescriptor>;
-  agents?: Map<string, Agent>;
+  workspaceAgentActivity: Map<string, WorkspaceAgentActivity>;
 }

 interface EffectiveWorkspaceStatus {
@@ -74,8 +74,6 @@ interface EffectiveWorkspaceStatus {
  enteredAt: Date | null;
 }

-interface WorkspaceAgentActivity extends EffectiveWorkspaceStatus {}
-
 function projectNameForWorkspace(workspace: WorkspaceDescriptor, projectKey: string): string {
  return (
    workspace.projectCustomName ??
@@ -96,7 +94,7 @@ export function createSidebarWorkspaceEntry(input: {
  serverId: string;
  workspace: WorkspaceDescriptor;
  pendingCreateAttempts?: Record<string, PendingCreateAttempt>;
-  agents?: Map<string, Agent>;
+  workspaceAgentActivity?: ReadonlyMap<string, WorkspaceAgentActivity>;
 }): SidebarWorkspaceEntry {
  const projectKey = input.workspace.project?.projectKey ?? input.workspace.projectId;
  const effectiveStatus = deriveEffectiveWorkspaceStatus(input);
@@ -129,7 +127,7 @@ function deriveEffectiveWorkspaceStatus(input: {
  serverId: string;
  workspace: WorkspaceDescriptor;
  pendingCreateAttempts?: Record<string, PendingCreateAttempt>;
-  agents?: Map<string, Agent>;
+  workspaceAgentActivity?: ReadonlyMap<string, WorkspaceAgentActivity>;
 }): EffectiveWorkspaceStatus {
  if (input.workspace.status !== "done") {
    return { status: input.workspace.status, enteredAt: input.workspace.statusEnteredAt };
@@ -144,10 +142,7 @@ function deriveEffectiveWorkspaceStatus(input: {
    return { status: "running", enteredAt: pendingStartedAt };
  }

-  const rootAgentActivity = getRootAgentWorkspaceActivity({
-    workspace: input.workspace,
-    agents: input.agents,
-  });
+  const rootAgentActivity = input.workspaceAgentActivity?.get(input.workspace.id);
  if (rootAgentActivity && rootAgentActivity.status !== "done") {
    return rootAgentActivity;
  }
@@ -173,28 +168,6 @@ function getPendingInitialAgentCreateStartedAt(input: {
  return latestStartedAt;
 }

-function getRootAgentWorkspaceActivity(input: {
-  workspace: WorkspaceDescriptor;
-  agents?: Map<string, Agent>;
-}): WorkspaceAgentActivity | null {
-  let latest: WorkspaceAgentActivity | null = null;
-  for (const agent of input.agents?.values() ?? []) {
-    if (agent.archivedAt || agent.parentAgentId) continue;
-    if (agent.workspaceId !== input.workspace.id) continue;
-    const status = deriveSidebarStateBucket({
-      status: agent.status,
-      pendingPermissionCount: agent.pendingPermissions.length,
-      requiresAttention: agent.requiresAttention,
-      attentionReason: agent.attentionReason,
-    });
-    const enteredAt = agent.attentionTimestamp ?? agent.updatedAt;
-    if (!latest || enteredAt > (latest.enteredAt ?? new Date(0))) {
-      latest = { status, enteredAt };
-    }
-  }
-  return latest;
-}
-
 export function buildSidebarWorkspacePlacementModel(input: {
  projects: readonly HostProjectListItem[];
 }): SidebarWorkspacePlacementModel {
@@ -298,7 +271,7 @@ export function buildSidebarStatusWorkspacePlacements(input: {
      serverId: placement.serverId,
      workspace,
      pendingCreateAttempts: input.pendingCreateAttempts,
-      agents: session.agents,
+      workspaceAgentActivity: session.workspaceAgentActivity,
    });

    rows.push({
--- a/packages/app/src/hooks/use-sidebar-workspaces-list.ts
+++ b/packages/app/src/hooks/use-sidebar-workspaces-list.ts
@@ -61,12 +61,14 @@ export function useSidebarWorkspaceEntry(
    (state) => {
      const workspace = selectWorkspace(state, serverId, workspaceId);
      if (!workspace) return null;
-      const agents = serverId ? state.sessions[serverId]?.agents : undefined;
+      const workspaceAgentActivity = serverId
+        ? state.sessions[serverId]?.workspaceAgentActivity
+        : undefined;
      return createSidebarWorkspaceEntry({
        serverId: serverId ?? "",
        workspace,
        pendingCreateAttempts,
-        agents,
+        workspaceAgentActivity,
      });
    },
    equal,
--- a/packages/app/src/hooks/use-status-mode-workspaces.test.ts
+++ b/packages/app/src/hooks/use-status-mode-workspaces.test.ts
@@ -4,20 +4,21 @@ import {
  selectStatusModeSessions,
  type StatusModeSession,
 } from "./use-status-mode-workspaces";
-import type { Agent, WorkspaceDescriptor } from "@/stores/session-store";
+import type { WorkspaceAgentActivity } from "@/utils/workspace-agent-activity";
+import type { WorkspaceDescriptor } from "@/stores/session-store";

 function workspaceMap(): Map<string, WorkspaceDescriptor> {
  return new Map();
 }

-function agentMap(): Map<string, Agent> {
+function activityMap(): Map<string, WorkspaceAgentActivity> {
  return new Map();
 }

 function statusSession(input?: Partial<Omit<StatusModeSession, "serverId">>) {
  return {
    workspaces: input?.workspaces ?? workspaceMap(),
-    agents: input?.agents ?? agentMap(),
+    workspaceAgentActivity: input?.workspaceAgentActivity ?? activityMap(),
  };
 }

@@ -37,34 +38,44 @@ describe("status mode session selection", () => {
        ["host-b", "missing", "host-a"],
      ),
    ).toEqual([
-      { serverId: "host-b", workspaces: hostB.workspaces, agents: hostB.agents },
-      { serverId: "host-a", workspaces: hostA.workspaces, agents: hostA.agents },
+      {
+        serverId: "host-b",
+        workspaces: hostB.workspaces,
+        workspaceAgentActivity: hostB.workspaceAgentActivity,
+      },
+      {
+        serverId: "host-a",
+        workspaces: hostA.workspaces,
+        workspaceAgentActivity: hostA.workspaceAgentActivity,
+      },
    ]);
  });

  it("keeps selector output equal when only wrapper objects change", () => {
    const workspaces = workspaceMap();
-    const agents = agentMap();
+    const workspaceAgentActivity = activityMap();

-    const previous = selectStatusModeSessions({ "host-a": statusSession({ workspaces, agents }) }, [
-      "host-a",
-    ]);
-    const next = selectStatusModeSessions({ "host-a": statusSession({ workspaces, agents }) }, [
-      "host-a",
-    ]);
+    const previous = selectStatusModeSessions(
+      { "host-a": statusSession({ workspaces, workspaceAgentActivity }) },
+      ["host-a"],
+    );
+    const next = selectStatusModeSessions(
+      { "host-a": statusSession({ workspaces, workspaceAgentActivity }) },
+      ["host-a"],
+    );

    expect(previous).not.toBe(next);
    expect(areStatusModeSessionsEqual(previous, next)).toBe(true);
  });

-  it("detects workspace or agent map changes for selected hosts", () => {
-    const agents = agentMap();
+  it("detects workspace or activity index changes for selected hosts", () => {
+    const workspaceAgentActivity = activityMap();
    const previous = selectStatusModeSessions(
-      { "host-a": statusSession({ agents, workspaces: workspaceMap() }) },
+      { "host-a": statusSession({ workspaceAgentActivity, workspaces: workspaceMap() }) },
      ["host-a"],
    );
    const next = selectStatusModeSessions(
-      { "host-a": statusSession({ agents, workspaces: workspaceMap() }) },
+      { "host-a": statusSession({ workspaceAgentActivity, workspaces: workspaceMap() }) },
      ["host-a"],
    );

--- a/packages/app/src/hooks/use-status-mode-workspaces.ts
+++ b/packages/app/src/hooks/use-status-mode-workspaces.ts
@@ -16,13 +16,13 @@ const EMPTY_PENDING_CREATE_ATTEMPTS: ReturnType<

 interface StatusModeSessionSource {
  workspaces: SessionState["workspaces"];
-  agents: SessionState["agents"];
+  workspaceAgentActivity: SessionState["workspaceAgentActivity"];
 }

 export interface StatusModeSession {
  serverId: string;
  workspaces: SessionState["workspaces"];
-  agents: SessionState["agents"];
+  workspaceAgentActivity: SessionState["workspaceAgentActivity"];
 }

 export function selectStatusModeSessions(
@@ -38,7 +38,7 @@ export function selectStatusModeSessions(
    statusSessions.push({
      serverId,
      workspaces: session.workspaces,
-      agents: session.agents,
+      workspaceAgentActivity: session.workspaceAgentActivity,
    });
  }
  return statusSessions;
@@ -59,7 +59,7 @@ export function areStatusModeSessionsEqual(
      !rightSession ||
      leftSession.serverId !== rightSession.serverId ||
      leftSession.workspaces !== rightSession.workspaces ||
-      leftSession.agents !== rightSession.agents
+      leftSession.workspaceAgentActivity !== rightSession.workspaceAgentActivity
    ) {
      return false;
    }
--- a/packages/app/src/stores/session-store.ts
+++ b/packages/app/src/stores/session-store.ts
@@ -37,6 +37,10 @@ import {
  createAgentLastActivityCoalescer,
  type AgentLastActivityCommitter,
 } from "@/runtime/activity";
+import {
+  buildWorkspaceAgentActivityIndex,
+  type WorkspaceAgentActivity,
+} from "@/utils/workspace-agent-activity";

 // Re-export types that were in session-context
 export type MessageEntry =
@@ -353,6 +357,7 @@ export interface SessionState {

  // Agents
  agents: Map<string, Agent>;
+  workspaceAgentActivity: Map<string, WorkspaceAgentActivity>;
  agentDetails: Map<string, Agent>;
  workspaces: Map<string, WorkspaceDescriptor>;
  // Project parents with no active workspaces, keyed by projectId. The
@@ -560,6 +565,7 @@ function createInitialSessionState(serverId: string, client: DaemonClient): Sess
    agentAuthoritativeHistoryApplied: new Map(),
    initializingAgents: new Map(),
    agents: new Map(),
+    workspaceAgentActivity: new Map(),
    agentDetails: new Map(),
    workspaces: new Map(),
    emptyProjects: new Map(),
@@ -1194,7 +1200,11 @@ export const useSessionStore = create<SessionStore>()(
            ...prev,
            sessions: {
              ...prev.sessions,
-              [serverId]: { ...session, agents: nextAgents },
+              [serverId]: {
+                ...session,
+                agents: nextAgents,
+                workspaceAgentActivity: buildWorkspaceAgentActivityIndex(nextAgents),
+              },
            },
          };
        });
--- a/packages/app/src/utils/navigate-to-agent/restore-archived-workspace.test.ts
+++ b/packages/app/src/utils/navigate-to-agent/restore-archived-workspace.test.ts
@@ -27,6 +27,39 @@ const SERVER_ID = "server-1";
 const AGENT_ID = "agent-1";
 const WORKSPACE_ID = "workspace-1";

+function agent(archivedAt: Date | null): Agent {
+  const createdAt = new Date("2026-01-01T00:00:00.000Z");
+  return {
+    serverId: SERVER_ID,
+    id: AGENT_ID,
+    provider: "codex",
+    status: "idle",
+    createdAt,
+    updatedAt: createdAt,
+    lastUserMessageAt: null,
+    lastActivityAt: createdAt,
+    capabilities: {
+      supportsStreaming: true,
+      supportsSessionPersistence: true,
+      supportsDynamicModes: true,
+      supportsMcpServers: true,
+      supportsReasoningStream: true,
+      supportsToolInvocations: true,
+    },
+    currentModeId: null,
+    availableModes: [],
+    pendingPermissions: [],
+    persistence: null,
+    title: null,
+    cwd: "/repo",
+    workspaceId: WORKSPACE_ID,
+    model: null,
+    archivedAt,
+    parentAgentId: null,
+    labels: {},
+  };
+}
+
 function status(): "restoring" | "failed" | "needs-host-upgrade" | null {
  return (
    useSessionStore.getState().sessions[SERVER_ID]?.restoringWorkspaces.get(WORKSPACE_ID) ?? null
@@ -44,11 +77,7 @@ function seedArchivedAgent(options?: { worktreeRestore?: boolean }): void {
  } as unknown as Parameters<typeof store.updateSessionServerInfo>[1]);
  store.setAgents(SERVER_ID, (prev) => {
    const next = new Map(prev);
-    next.set(AGENT_ID, {
-      id: AGENT_ID,
-      workspaceId: WORKSPACE_ID,
-      archivedAt: new Date(),
-    } as unknown as Agent);
+    next.set(AGENT_ID, agent(new Date("2026-01-02T00:00:00.000Z")));
    return next;
  });
 }
@@ -95,11 +124,7 @@ describe("restoreArchivedWorkspace via navigateToAgent", () => {
    const store = useSessionStore.getState();
    store.setAgents(SERVER_ID, (prev) => {
      const next = new Map(prev);
-      next.set(AGENT_ID, {
-        id: AGENT_ID,
-        workspaceId: WORKSPACE_ID,
-        archivedAt: undefined,
-      } as unknown as Agent);
+      next.set(AGENT_ID, agent(null));
      return next;
    });
    refreshAgent.mockImplementation(() => new Promise(() => {}));
--- a/packages/app/src/utils/sidebar-shortcuts.test.ts
+++ b/packages/app/src/utils/sidebar-shortcuts.test.ts
@@ -3,6 +3,7 @@ import type {
  SidebarProjectEntry,
  SidebarWorkspaceEntry,
 } from "@/hooks/use-sidebar-workspaces-list";
+import { buildStatusGroups } from "@/hooks/sidebar-status-view-model";

 import {
  buildSidebarShortcutModel,
@@ -202,11 +203,13 @@ describe("buildStatusSidebarShortcutModel", () => {
    ];

    const model = buildStatusSidebarShortcutModel({
-      workspaces,
-      projectNamesByKey: new Map([
-        ["p1", "Project 1"],
-        ["p2", "Project 2"],
-      ]),
+      groups: buildStatusGroups(
+        workspaces,
+        new Map([
+          ["p1", "Project 1"],
+          ["p2", "Project 2"],
+        ]),
+      ),
    });

    expect(model.shortcutTargets).toEqual([
@@ -242,8 +245,7 @@ describe("buildStatusSidebarShortcutModel", () => {
    ];

    const model = buildStatusSidebarShortcutModel({
-      workspaces,
-      projectNamesByKey: new Map([["p1", "Project 1"]]),
+      groups: buildStatusGroups(workspaces, new Map([["p1", "Project 1"]])),
      collapsedStatusGroupKeys: new Set(["needs_input"]),
    });

--- a/packages/app/src/utils/sidebar-shortcuts.ts
+++ b/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;
    }
--- a/packages/app/src/utils/workspace-agent-activity.test.ts
+++ b/packages/app/src/utils/workspace-agent-activity.test.ts
@@ -0,0 +1,142 @@
+import { describe, expect, it } from "vitest";
+import type { Agent } from "@/stores/session-store";
+import { buildWorkspaceAgentActivityIndex } from "./workspace-agent-activity";
+
+function agent(input: {
+  id: string;
+  workspaceId?: string;
+  status?: Agent["status"];
+  updatedAt: string;
+  attentionTimestamp?: string | null;
+  requiresAttention?: boolean;
+  attentionReason?: Agent["attentionReason"];
+  pendingPermissionCount?: number;
+  archivedAt?: string | null;
+  parentAgentId?: string | null;
+}): Agent {
+  return {
+    serverId: "host-a",
+    id: input.id,
+    provider: "codex",
+    status: input.status ?? "idle",
+    createdAt: new Date("2026-01-01T00:00:00.000Z"),
+    updatedAt: new Date(input.updatedAt),
+    lastUserMessageAt: null,
+    lastActivityAt: new Date(input.updatedAt),
+    capabilities: {
+      supportsStreaming: true,
+      supportsSessionPersistence: true,
+      supportsDynamicModes: true,
+      supportsMcpServers: true,
+      supportsReasoningStream: true,
+      supportsToolInvocations: true,
+    },
+    currentModeId: null,
+    availableModes: [],
+    pendingPermissions: Array.from({ length: input.pendingPermissionCount ?? 0 }, (_, index) => ({
+      id: `permission-${index}`,
+      provider: "codex",
+      name: "shell",
+      kind: "tool",
+      input: {},
+    })),
+    persistence: null,
+    title: null,
+    cwd: "/repo",
+    workspaceId: input.workspaceId,
+    model: null,
+    requiresAttention: input.requiresAttention,
+    attentionReason: input.attentionReason,
+    attentionTimestamp: input.attentionTimestamp ? new Date(input.attentionTimestamp) : null,
+    archivedAt: input.archivedAt ? new Date(input.archivedAt) : null,
+    parentAgentId: input.parentAgentId ?? null,
+    labels: {},
+  };
+}
+
+describe("workspace agent activity index", () => {
+  it("keeps the latest active root agent for each workspace", () => {
+    const index = buildWorkspaceAgentActivityIndex(
+      new Map([
+        [
+          "older",
+          agent({
+            id: "older",
+            workspaceId: "workspace-a",
+            status: "running",
+            updatedAt: "2026-06-01T10:00:00.000Z",
+          }),
+        ],
+        [
+          "permission",
+          agent({
+            id: "permission",
+            workspaceId: "workspace-a",
+            updatedAt: "2026-06-01T10:01:00.000Z",
+            pendingPermissionCount: 1,
+          }),
+        ],
+        [
+          "attention",
+          agent({
+            id: "attention",
+            workspaceId: "workspace-b",
+            updatedAt: "2026-06-01T10:00:00.000Z",
+            attentionTimestamp: "2026-06-01T10:02:00.000Z",
+            requiresAttention: true,
+            attentionReason: "finished",
+          }),
+        ],
+      ]),
+    );
+
+    expect(index).toEqual(
+      new Map([
+        ["workspace-a", { status: "needs_input", enteredAt: new Date("2026-06-01T10:01:00.000Z") }],
+        ["workspace-b", { status: "attention", enteredAt: new Date("2026-06-01T10:02:00.000Z") }],
+      ]),
+    );
+  });
+
+  it("does not let archived or child agents change root workspace activity", () => {
+    const index = buildWorkspaceAgentActivityIndex(
+      new Map([
+        [
+          "root",
+          agent({
+            id: "root",
+            workspaceId: "workspace-a",
+            status: "running",
+            updatedAt: "2026-06-01T10:00:00.000Z",
+          }),
+        ],
+        [
+          "child",
+          agent({
+            id: "child",
+            workspaceId: "workspace-a",
+            updatedAt: "2026-06-01T10:03:00.000Z",
+            pendingPermissionCount: 1,
+            parentAgentId: "root",
+          }),
+        ],
+        [
+          "archived",
+          agent({
+            id: "archived",
+            workspaceId: "workspace-a",
+            updatedAt: "2026-06-01T10:04:00.000Z",
+            requiresAttention: true,
+            attentionReason: "error",
+            archivedAt: "2026-06-01T10:04:00.000Z",
+          }),
+        ],
+      ]),
+    );
+
+    expect(index.get("workspace-a")).toEqual({
+      status: "running",
+      enteredAt: new Date("2026-06-01T10:00:00.000Z"),
+    });
+  });
+});
--- a/packages/app/src/utils/workspace-agent-activity.ts
+++ b/packages/app/src/utils/workspace-agent-activity.ts
@@ -0,0 +1,37 @@
+import type { Agent, WorkspaceDescriptor } from "@/stores/session-store";
+import { deriveSidebarStateBucket } from "./sidebar-agent-state";
+
+export interface WorkspaceAgentActivity {
+  status: WorkspaceDescriptor["status"];
+  enteredAt: Date | null;
+}
+
+export function buildWorkspaceAgentActivityIndex(
+  agents: ReadonlyMap<string, Agent>,
+): Map<string, WorkspaceAgentActivity> {
+  const activityByWorkspaceId = new Map<string, WorkspaceAgentActivity>();
+
+  for (const agent of agents.values()) {
+    if (agent.archivedAt || agent.parentAgentId || !agent.workspaceId) {
+      continue;
+    }
+
+    const enteredAt = agent.attentionTimestamp ?? agent.updatedAt;
+    const current = activityByWorkspaceId.get(agent.workspaceId);
+    if (current && enteredAt <= (current.enteredAt ?? new Date(0))) {
+      continue;
+    }
+
+    activityByWorkspaceId.set(agent.workspaceId, {
+      status: deriveSidebarStateBucket({
+        status: agent.status,
+        pendingPermissionCount: agent.pendingPermissions.length,
+        requiresAttention: agent.requiresAttention,
+        attentionReason: agent.attentionReason,
+      }),
+      enteredAt,
+    });
+  }
+
+  return activityByWorkspaceId;
+}