perf(ui): narrow session switch fanout

Keep sidebar rows independent from the active sync directory by moving export history loading behind an explicit-directory command.

Make active-project selection preserve project topology and remove activeProjectId from mounted group render props. Reuse a per-session-array ID index so subscription snapshots do not repeatedly scan session lists.

packages/ui/src/components/session/sidebar/list/SessionProjectCollection.tsx

@@ -286,7 +286,6 @@ const VisibleSessionProjects: React.FC<SessionProjectCollectionProps> = ({ topol
     hideDirectoryControls: view.hideDirectoryControls,
     mobileVariant: view.mobileVariant,
     alwaysShowActions,
-    activeProjectId: view.activeProjectId,
     notifyOnSubtasks,
     pinnedSessionIds: collection.pinnedSessionIds,
     sessionOrderIndex,
@@ -330,7 +329,6 @@ const VisibleSessionProjects: React.FC<SessionProjectCollectionProps> = ({ topol
     setCopiedSessionId,
     rowActions,
     toggleParent,
-    view.activeProjectId,
     view.hideDirectoryControls,
     view.hasSessionSearchQuery,
     view.mobileVariant,

packages/ui/src/components/session/sidebar/projects/SessionGroupSection.behavior.test.tsx

@@ -113,7 +113,6 @@ const createProps = (): SessionGroupSectionProps => ({
   resetGroupSessionLimit: () => undefined,
   mobileVariant: false,
   alwaysShowActions: false,
-  activeProjectId: 'project',
   setActiveProjectIdOnly: () => undefined,
   setActiveMainTab: () => undefined,
   setSessionSwitcherOpen: () => undefined,

packages/ui/src/components/session/sidebar/projects/SessionGroupSection.tsx

@@ -232,7 +232,6 @@ const areGroupPropsEqual = (prev: SessionGroupSectionProps, next: SessionGroupSe
     && prev.resetGroupSessionLimit === next.resetGroupSessionLimit
     && prev.mobileVariant === next.mobileVariant
     && prev.alwaysShowActions === next.alwaysShowActions
-    && prev.activeProjectId === next.activeProjectId
     && prev.setActiveProjectIdOnly === next.setActiveProjectIdOnly
     && prev.setSessionSwitcherOpen === next.setSessionSwitcherOpen
     && prev.openNewSessionDraft === next.openNewSessionDraft

packages/ui/src/components/session/sidebar/projects/SessionProjectScroller.tsx

@@ -58,7 +58,6 @@ type SessionProjectScrollerGroupProps = Pick<SessionGroupSectionProps,
   | 'startFolderRename'
   | 'setCopiedSessionId'
 > & {
-  activeProjectId: string | null;
   pinnedSessionIds: Set<string>;
   sessionOrderIndex: Map<string, number>;
 };

packages/ui/src/components/session/sidebar/sessions/SessionNodeItem.tsx

@@ -22,8 +22,8 @@ import { isSessionPinned, useSessionPinnedStore } from '@/stores/useSessionPinne
 import { Icon } from "@/components/icon/Icon";
 import { buildExportFilename, downloadAsMarkdown, formatSessionAsMarkdown, getExportRevealLabelKey, revealExportedMarkdown, saveAsMarkdownDesktop } from '@/lib/exportSession';
 import type { ChildSessionExport } from '@/lib/exportSession';
-import { buildSessionMessageRecordsSnapshot, useDirectoryStore, useGlobalSessionStatus, useSessionPermissions, useSessionQuestionCount } from '@/sync/sync-context';
-import { useSync } from '@/sync/use-sync';
+import { useGlobalSessionStatus, useSessionPermissions, useSessionQuestionCount } from '@/sync/sync-context';
+import { useSessionMessageRecordsForExport } from '@/sync/use-sync';
 import { useViewportStore, viewportSessionKey } from '@/sync/viewport-store';
 import { DraggableSessionRow } from '../folders/sessionFolderDnd';
 import { nodeContainsSessionId, nodeHasPinnedMembershipChange, selectQuestionBadgeSessionScopes } from './sessionNodeItemUtils';
@@ -383,10 +383,7 @@ function SessionNodeItemComponent(props: SessionNodeItemProps): React.ReactNode
   // project (falling back to the directory when no project is known) — a
   // selection must survive mixing sessions from different worktrees.
   const selectionScopeKey = projectId ?? sessionDirectory ?? null;
-  // Directory bootstrap is scheduled once at sidebar level. A row only needs
-  // the lightweight store reference for scoped state and export actions.
-  const directoryStore = useDirectoryStore(sessionDirectory ?? undefined, { bootstrap: false });
-  const sync = useSync();
+  const loadExportRecords = useSessionMessageRecordsForExport();
 
   const selectionModeEnabled = useSessionMultiSelectStore((state) => state.enabled);
   const isRowSelected = useSessionMultiSelectStore(
@@ -478,8 +475,8 @@ function SessionNodeItemComponent(props: SessionNodeItemProps): React.ReactNode
     for (const child of children) {
       try {
         if (!sessionDirectory) throw new Error('Session directory is required for export');
-        await sync.loadCompleteHistory(child.session.id, sessionDirectory);
-        const childRecords = buildSessionMessageRecordsSnapshot(directoryStore.getState(), child.session.id).list;
+        const childRecords = await loadExportRecords({ directory: sessionDirectory, sessionID: child.session.id });
+        if (!childRecords) throw new Error('Session runtime changed during export');
         const childTitle = child.session.title || t('sessions.sidebar.session.export.untitledSubagent');
         // SAFETY: OpenCode session payloads may carry the optional agent label used by exports.
         const childAgent = (child.session as Session & { agent?: string }).agent;
@@ -496,7 +493,7 @@ function SessionNodeItemComponent(props: SessionNodeItemProps): React.ReactNode
       }
     }
     return { children: results, skipped };
-  }, [collectNodeDescendantIds, directoryStore, sessionDirectory, sync, t]);
+  }, [collectNodeDescendantIds, loadExportRecords, sessionDirectory, t]);
 
   const showSkippedSubtasksWarning = React.useCallback((count: number) => {
     if (count <= 0) return;
@@ -511,14 +508,11 @@ function SessionNodeItemComponent(props: SessionNodeItemProps): React.ReactNode
       return;
     }
 
-    try {
-      await sync.loadCompleteHistory(session.id, sessionDirectory);
-    } catch {
+    const records = await loadExportRecords({ directory: sessionDirectory, sessionID: session.id }).catch(() => null);
+    if (!records) {
       toast.error(t('sessions.sidebar.session.export.failedLoadHistory'));
       return;
     }
-
-    const records = buildSessionMessageRecordsSnapshot(directoryStore.getState(), session.id).list;
     if (records.length === 0) {
       toast.error(t('sessions.sidebar.session.export.nothingToExport'));
       return;
@@ -556,7 +550,7 @@ function SessionNodeItemComponent(props: SessionNodeItemProps): React.ReactNode
     downloadAsMarkdown(markdown, filename);
     toast.success(t('sessions.sidebar.session.export.success'));
     showSkippedSubtasksWarning(skippedSubtaskCount);
-  }, [collectChildExports, directoryStore, node.children, resolvedSession.title, session.id, sessionDirectory, showSkippedSubtasksWarning, sync, t]);
+  }, [collectChildExports, loadExportRecords, node.children, resolvedSession.title, session.id, sessionDirectory, showSkippedSubtasksWarning, t]);
   const handleExportSession = React.useCallback(async () => {
     if (node.children.length > 0) {
       setExportIncludeSubtasks(true);

packages/ui/src/stores/useProjectsStore.test.ts

@@ -20,6 +20,26 @@ describe("useProjectsStore settings synchronization", () => {
   })
 })
 
+describe("useProjectsStore selection identity", () => {
+  test("changes only the active project id", () => {
+    const first = { id: "project-a", path: "/repo-a", lastOpenedAt: 10 } as ProjectEntry
+    const second = { id: "project-b", path: "/repo-b", lastOpenedAt: 20 } as ProjectEntry
+    const projects = [first, second]
+    useProjectsStore.setState({
+      projects,
+      activeProjectId: first.id,
+      manualProjectOrder: projects.map((project) => project.id),
+    })
+
+    useProjectsStore.getState().setActiveProjectIdOnly(second.id)
+
+    const state = useProjectsStore.getState()
+    expect(state.activeProjectId).toBe(second.id)
+    expect(state.projects).toBe(projects)
+    expect(state.projects.map((project) => project.lastOpenedAt)).toEqual([10, 20])
+  })
+})
+
 describe("useProjectsStore default model and thinking level", () => {
   const seed = (project: ProjectEntry) => {
     useProjectsStore.setState({

packages/ui/src/stores/useProjectsStore.ts

@@ -357,13 +357,7 @@ const readPersistedActiveProjectId = (): string | null => {
   return null;
 };
 
-const cacheProjects = (projects: ProjectEntry[], activeProjectId: string | null) => {
-  try {
-    safeStorage.setItem(getProjectsStorageKey(), JSON.stringify(projects));
-  } catch {
-    // ignored
-  }
-
+const cacheActiveProjectId = (activeProjectId: string | null) => {
   try {
     const activeProjectStorageKey = getActiveProjectStorageKey();
     if (activeProjectId) {
@@ -376,6 +370,15 @@ const cacheProjects = (projects: ProjectEntry[], activeProjectId: string | null)
   }
 };
 
+const cacheProjects = (projects: ProjectEntry[], activeProjectId: string | null) => {
+  try {
+    safeStorage.setItem(getProjectsStorageKey(), JSON.stringify(projects));
+  } catch {
+    // ignored
+  }
+  cacheActiveProjectId(activeProjectId);
+};
+
 const persistProjects = (projects: ProjectEntry[], activeProjectId: string | null, manualOrder?: string[]) => {
   cacheProjects(projects, activeProjectId);
   if (manualOrder) {
@@ -693,18 +696,13 @@ export const useProjectsStore = create<ProjectsStore>()(
       if (activeProjectId === id) {
         return;
       }
-      const target = projects.find((project) => project.id === id);
-      if (!target) {
+      if (!projects.some((project) => project.id === id)) {
         return;
       }
 
-      const now = Date.now();
-      const nextProjects = projects.map((project) =>
-        project.id === id ? { ...project, lastOpenedAt: now } : project
-      );
-
-      set({ projects: nextProjects, activeProjectId: id });
-      persistProjects(nextProjects, id, get().manualProjectOrder);
+      set({ activeProjectId: id });
+      cacheActiveProjectId(id);
+      void updateDesktopSettings({ activeProjectId: id });
     },
 
     renameProject: (id: string, label: string) => {

packages/ui/src/sync/sync-context.tsx

@@ -2845,13 +2845,25 @@ export function useScopedBlockingQuestions(sessionID: string | null, directory?:
   return useScopedBlockingRequests(sessionID, directory, selectQuestionRequestsBySession, EMPTY_QUESTION_REQUESTS)
 }
 
+const sessionsByIdCache = new WeakMap<State["session"], Map<string, Session>>()
+
+const getSessionById = (sessions: State["session"], sessionID?: string | null): Session | undefined => {
+  if (!sessionID) return undefined
+  let sessionsById = sessionsByIdCache.get(sessions)
+  if (!sessionsById) {
+    sessionsById = new Map(sessions.map((session) => [session.id, session]))
+    sessionsByIdCache.set(sessions, sessionsById)
+  }
+  return sessionsById.get(sessionID)
+}
+
 export function useParentSession(sessionID: string | null, directory?: string): Session | null {
   return useDirectorySync(
     useCallback((state: State) => {
       if (!sessionID) return null
-      const current = state.session.find((s) => s.id === sessionID)
+      const current = getSessionById(state.session, sessionID)
       if (!current?.parentID) return null
-      return state.session.find((s) => s.id === current.parentID)
+      return getSessionById(state.session, current.parentID)
         ?? getAllSyncSessions().find((s) => s.id === current.parentID)
         ?? null
     }, [sessionID]),
@@ -2864,7 +2876,8 @@ export function useSession(sessionID?: string | null, directory?: string) {
   const { childStores } = useSyncSystem()
   const getSnapshot = useCallback(() => {
     if (directory) {
-      return childStores.getChild(directory)?.getState().session.find((session) => session.id === sessionID)
+      const sessions = childStores.getChild(directory)?.getState().session
+      return sessions ? getSessionById(sessions, sessionID) : undefined
     }
     return findLiveSession(getLiveStates(childStores), sessionID)
   }, [childStores, directory, sessionID])

packages/ui/src/sync/use-sync.ts

@@ -14,6 +14,7 @@ import {
   useSyncSDK,
   useSyncRuntime,
   resyncBlockingRequestsForDirectory,
+  buildSessionMessageRecordsSnapshot,
 } from "./sync-context"
 import { stripSessionDiffSnapshots } from "./sanitize"
 import { isVSCodeRuntime } from "@/lib/desktop"
@@ -412,3 +413,17 @@ export function usePrefetchSessionMessages() {
     touch(sessionID, directory)
   }, [messageLoader, runtimeKey, touch])
 }
+
+export function useSessionMessageRecordsForExport() {
+  const { childStores, messageLoader, runtimeKey } = useSyncRuntime()
+  const touch = useSessionCacheTouch()
+
+  return useCallback(async ({ directory, sessionID }: { directory: string; sessionID: string }) => {
+    if (getRuntimeKey() !== runtimeKey) return null
+    const store = childStores.ensureChild(directory, { bootstrap: false })
+    touch(sessionID, directory)
+    await messageLoader.loadComplete({ directory, sessionID })
+    if (getRuntimeKey() !== runtimeKey) return null
+    return buildSessionMessageRecordsSnapshot(store.getState(), sessionID).list
+  }, [childStores, messageLoader, runtimeKey, touch])
+}