From 8182141fcdc8eb0c65481cfd88338c44be251915 Mon Sep 17 00:00:00 2001
From: Neil <4138956+nwparker@users.noreply.github.com>
Date: Mon, 20 Jul 2026 19:14:27 -0700
Subject: [PATCH] perf(sidebar): stabilize worktree card props so cards
 memo-bail on order-preserving epoch bumps (#9392)

* perf(sidebar): stable per-group onLineageToggle identity so lineage-parent WorktreeCards memo-bail

Co-authored-by: Orca <help@stably.ai>

* perf(sidebar): reuse array identity for visible/rendered/selected worktrees so cards memo-bail on epoch bumps

Co-authored-by: Orca <help@stably.ai>

---------

Co-authored-by: Orca <help@stably.ai>
---
 .../WorktreeList.card-memo-stability.test.tsx | 323 ++++++++++++++++++
 .../src/components/sidebar/WorktreeList.tsx   |  66 ++--
 .../sidebar/worktree-agent-row-selectors.ts   |   5 +-
 ...ktree-lineage-toggle-handler-cache.test.ts |  48 +++
 .../worktree-lineage-toggle-handler-cache.ts  |  26 ++
 5 files changed, 447 insertions(+), 21 deletions(-)
 create mode 100644 src/renderer/src/components/sidebar/WorktreeList.card-memo-stability.test.tsx
 create mode 100644 src/renderer/src/components/sidebar/worktree-lineage-toggle-handler-cache.test.ts
 create mode 100644 src/renderer/src/components/sidebar/worktree-lineage-toggle-handler-cache.ts

diff --git a/src/renderer/src/components/sidebar/WorktreeList.card-memo-stability.test.tsx b/src/renderer/src/components/sidebar/WorktreeList.card-memo-stability.test.tsx
new file mode 100644
index 000000000..9d0a2e369
--- /dev/null
+++ b/src/renderer/src/components/sidebar/WorktreeList.card-memo-stability.test.tsx
@@ -0,0 +1,323 @@
+// @vitest-environment happy-dom
+
+import { act, type ReactNode } from 'react'
+import { createRoot, type Root } from 'react-dom/client'
+import { afterEach, beforeAll, beforeEach, describe, expect, it, vi } from 'vitest'
+import type { Repo, Worktree, WorktreeCardProperty } from '../../../../shared/types'
+
+globalThis.IS_REACT_ACT_ENVIRONMENT = true
+
+const mockStore = vi.hoisted(() => ({
+  state: {} as Record<string, unknown>,
+  activateWorktreeFromSidebar: vi.fn(),
+  openModal: vi.fn()
+}))
+
+// Counts invocations of the memo'd card's inner render function. A bail-out
+// (React.memo shallow-equal props) does NOT invoke it — which is the claim
+// under test: order-preserving epoch bumps must not re-render cards.
+const cardRenderSpy = vi.hoisted(() => vi.fn())
+
+type WorktreeListComponent = React.ComponentType<{
+  scrollOffsetRef: React.RefObject<number>
+  scrollAnchorRef: React.RefObject<unknown>
+}>
+
+let WorktreeList: WorktreeListComponent
+
+vi.mock('@/store', () => {
+  const useAppStore = ((selector: (state: Record<string, unknown>) => unknown) =>
+    selector(mockStore.state)) as ((
+    selector: (state: Record<string, unknown>) => unknown
+  ) => unknown) & {
+    getState: () => Record<string, unknown>
+  }
+  useAppStore.getState = () => mockStore.state
+  return { useAppStore }
+})
+
+vi.mock('@tanstack/react-virtual', () => ({
+  defaultRangeExtractor: ({ startIndex, endIndex }: { startIndex: number; endIndex: number }) =>
+    Array.from({ length: endIndex - startIndex + 1 }, (_, index) => startIndex + index),
+  measureElement: () => 32,
+  useVirtualizer: ({ count }: { count: number }) => ({
+    elementsCache: new Map(),
+    getTotalSize: () => count * 96,
+    getVirtualItems: () =>
+      Array.from({ length: count }, (_, index) => ({
+        index,
+        key: `row-${index}`,
+        start: index * 96
+      })),
+    measureElement: vi.fn(),
+    scrollToIndex: vi.fn()
+  })
+}))
+
+vi.mock('@/hooks/useVirtualizedScrollAnchor', () => ({
+  VIRTUALIZED_SCROLL_ANCHOR_RECORD_EVENT: 'orca:test-record-scroll-anchor',
+  useVirtualizedScrollAnchor: vi.fn()
+}))
+
+vi.mock('./project-header-drag', () => ({
+  useRepoHeaderDrag: () => ({
+    state: { draggingRepoId: null, dropIndicatorY: null },
+    onHandlePointerDown: vi.fn()
+  }),
+  isRepoHeaderActionTarget: () => false
+}))
+
+vi.mock('@/components/ui/hover-card', () => ({
+  HoverCard: ({ children }: { children: ReactNode }) => <>{children}</>,
+  HoverCardContent: ({ children }: { children: ReactNode }) => <div>{children}</div>,
+  HoverCardTrigger: ({ children }: { children: ReactNode }) => <>{children}</>
+}))
+
+vi.mock('@/components/ui/tooltip', () => ({
+  Tooltip: ({ children }: { children: ReactNode }) => <>{children}</>,
+  TooltipContent: ({ children }: { children: ReactNode }) => <>{children}</>,
+  TooltipTrigger: ({ children }: { children: ReactNode }) => <>{children}</>
+}))
+
+vi.mock('@/components/ui/dropdown-menu', () => ({
+  DropdownMenu: ({ children }: { children: ReactNode }) => <>{children}</>,
+  DropdownMenuContent: ({ children }: { children: ReactNode }) => <div>{children}</div>,
+  DropdownMenuItem: ({ children, onSelect }: { children: ReactNode; onSelect?: () => void }) => (
+    <button onClick={onSelect}>{children}</button>
+  ),
+  DropdownMenuSeparator: () => <hr />,
+  DropdownMenuSub: ({ children }: { children: ReactNode }) => <>{children}</>,
+  DropdownMenuSubContent: ({ children }: { children: ReactNode }) => <div>{children}</div>,
+  DropdownMenuSubTrigger: ({ children }: { children: ReactNode }) => <div>{children}</div>,
+  DropdownMenuTrigger: ({ children }: { children: ReactNode }) => <>{children}</>
+}))
+
+vi.mock('@/lib/sidebar-worktree-activation', () => ({
+  activateWorktreeFromSidebar: mockStore.activateWorktreeFromSidebar
+}))
+
+vi.mock('@/lib/worktree-activation', () => ({
+  activateAndRevealWorktree: vi.fn()
+}))
+
+vi.mock('@/runtime/runtime-rpc-client', () => ({
+  getActiveRuntimeTarget: () => ({ kind: 'local' }),
+  callRuntimeRpc: vi.fn()
+}))
+
+vi.mock('./WorktreeCardAgents', () => ({
+  default: () => <div>Agent row</div>,
+  SUPPRESS_WORKTREE_LIST_SCROLL_ADJUSTMENT_EVENT: 'orca:test-suppress-scroll-adjustment'
+}))
+
+vi.mock('./WorktreeCard', async () => {
+  const ReactModule = await import('react')
+  const MockWorktreeCard = ReactModule.memo(function WorktreeCard({
+    worktree
+  }: {
+    worktree: Worktree
+  }) {
+    cardRenderSpy(worktree.id)
+    return <div data-mock-worktree-card={worktree.id} />
+  })
+  return { default: MockWorktreeCard }
+})
+
+function makeRepo(): Repo {
+  return {
+    id: 'repo-1',
+    path: '/tmp/card-memo-stability',
+    displayName: 'card-memo-stability',
+    badgeColor: '#999999',
+    addedAt: 1
+  }
+}
+
+function makeWorktree(args: { id: string; displayName: string; sortOrder: number }): Worktree {
+  return {
+    id: args.id,
+    instanceId: `${args.id}-instance`,
+    repoId: 'repo-1',
+    path: `/tmp/card-memo-stability/${args.id}`,
+    displayName: args.displayName,
+    branch: `${args.id}-branch`,
+    head: 'abc123',
+    isBare: false,
+    isMainWorktree: false,
+    comment: '',
+    linkedIssue: null,
+    linkedPR: null,
+    linkedLinearIssue: null,
+    isArchived: false,
+    isUnread: false,
+    isPinned: false,
+    sortOrder: args.sortOrder,
+    lastActivityAt: args.sortOrder
+  }
+}
+
+function makeFolderWorkspacePathStatusState(): Record<string, unknown> {
+  return {
+    fetchFolderWorkspacePathStatus: vi.fn(),
+    folderWorkspacePathStatuses: {},
+    folderWorkspaces: [],
+    getFolderWorkspacePathStatusCacheKey: (request: unknown) => JSON.stringify(request),
+    getFreshFolderWorkspacePathStatus: vi.fn(() => null)
+  }
+}
+
+function setFlatWorktreeState(): void {
+  const repo = makeRepo()
+  const worktrees = [
+    makeWorktree({ id: 'wt-a', displayName: 'alpha', sortOrder: 20 }),
+    makeWorktree({ id: 'wt-b', displayName: 'beta', sortOrder: 10 })
+  ]
+  mockStore.state = {
+    ...makeFolderWorkspacePathStatusState(),
+    activeModal: '',
+    activeView: 'terminal',
+    activeWorktreeId: null,
+    agentStatusByPaneKey: {},
+    agentStatusEpoch: 0,
+    browserTabsByWorktree: {},
+    clearPendingRevealWorktreeId: vi.fn(),
+    collapsedGroups: new Set<string>(),
+    deleteStateByWorktreeId: {},
+    detectedWorktreesByRepo: {},
+    fetchHostedReviewForBranch: vi.fn(),
+    fetchIssue: vi.fn(),
+    fetchLinearIssue: vi.fn(),
+    filterRepoIds: [],
+    gitConflictOperationByWorktree: {},
+    groupBy: 'none',
+    hideDefaultBranchWorkspace: false,
+    hostedReviewCache: {},
+    issueCache: {},
+    linearIssueCache: {},
+    linearStatus: null,
+    migrationUnsupportedByPtyId: {},
+    openModal: mockStore.openModal,
+    openSettingsPage: vi.fn(),
+    openSettingsTarget: null,
+    openTaskPage: vi.fn(),
+    pendingRevealWorktree: null,
+    prCache: {},
+    projectGroups: [],
+    ptyIdsByTabId: {},
+    recordFeatureInteraction: vi.fn(),
+    remoteBranchConflictByWorktreeId: {},
+    reorderRepos: vi.fn(),
+    reportVisibleGitHubPRRefreshCandidates: vi.fn(),
+    repos: [repo],
+    retainedAgentsByPaneKey: {},
+    revealWorktreeInSidebar: vi.fn(),
+    runtimePaneTitlesByTabId: {},
+    setFilterRepoIds: vi.fn(),
+    setHideDefaultBranchWorkspace: vi.fn(),
+    setRenamingWorktreeId: vi.fn(),
+    setShowSleepingWorkspaces: vi.fn(),
+    setSortBy: vi.fn(),
+    setWorktreesPinnedAndReveal: vi.fn(),
+    settings: null,
+    showSleepingWorkspaces: true,
+    sortBy: 'manual',
+    sortEpoch: 0,
+    sshConnectedGeneration: 0,
+    sshConnectionStates: new Map(),
+    sshTargetLabels: new Map(),
+    tabsByWorktree: {},
+    terminalLayoutsByTabId: {},
+    toggleCollapsedGroup: vi.fn(),
+    updateRepo: vi.fn(),
+    updateWorktreeMeta: vi.fn(),
+    updateWorktreesMeta: vi.fn(),
+    workspaceHostScope: 'all',
+    workspacePortScan: null,
+    workspaceStatuses: [],
+    worktreeCardProperties: ['status', 'pr', 'comment'] satisfies WorktreeCardProperty[],
+    worktreeLineageById: {},
+    worktreesByRepo: {
+      [repo.id]: worktrees
+    }
+  }
+}
+
+const mountedRoots: Root[] = []
+
+async function renderList(root: Root): Promise<void> {
+  await act(async () => {
+    // Why fresh ref objects each render: they defeat WorktreeList's own memo
+    // like a store-subscription re-render would, so the test exercises a full
+    // parent re-render and isolates whether the CARDS bail.
+    root.render(
+      <WorktreeList scrollOffsetRef={{ current: 0 }} scrollAnchorRef={{ current: null }} />
+    )
+  })
+}
+
+describe('WorktreeCard memo bail-out across epoch bumps', () => {
+  beforeAll(async () => {
+    WorktreeList = (await import('./WorktreeList')).default as WorktreeListComponent
+  }, 60_000)
+
+  beforeEach(() => {
+    vi.clearAllMocks()
+    setFlatWorktreeState()
+  })
+
+  afterEach(async () => {
+    await act(async () => {
+      for (const root of mountedRoots.splice(0)) {
+        root.unmount()
+      }
+    })
+    document.body.innerHTML = ''
+  })
+
+  it('does not re-render cards on an order-preserving sortEpoch bump', async () => {
+    const container = document.createElement('div')
+    document.body.appendChild(container)
+    const root = createRoot(container)
+    mountedRoots.push(root)
+
+    await renderList(root)
+    expect(container.querySelectorAll('[data-mock-worktree-card]')).toHaveLength(2)
+
+    // Baseline: a parent re-render with unchanged store state must not
+    // re-invoke card render functions.
+    const countAfterMount = cardRenderSpy.mock.calls.length
+    await renderList(root)
+    expect(cardRenderSpy.mock.calls.length).toBe(countAfterMount)
+
+    // Order-preserving epoch bump: same worktrees, same order, new epoch.
+    // Manual sort applies the bump without the smart-sort settle debounce.
+    mockStore.state = { ...mockStore.state, sortEpoch: 1 }
+    await renderList(root)
+
+    expect(cardRenderSpy.mock.calls.length).toBe(countAfterMount)
+  })
+
+  it('re-renders a card when its own worktree data changes', async () => {
+    const container = document.createElement('div')
+    document.body.appendChild(container)
+    const root = createRoot(container)
+    mountedRoots.push(root)
+
+    await renderList(root)
+    const countAfterMount = cardRenderSpy.mock.calls.length
+
+    const worktrees = (mockStore.state.worktreesByRepo as Record<string, Worktree[]>)['repo-1']!
+    mockStore.state = {
+      ...mockStore.state,
+      sortEpoch: 2,
+      worktreesByRepo: {
+        'repo-1': [{ ...worktrees[0]!, displayName: 'alpha renamed' }, worktrees[1]!]
+      }
+    }
+    await renderList(root)
+
+    // The changed card re-renders; identity reuse must not freeze real updates.
+    expect(cardRenderSpy.mock.calls.length).toBeGreaterThan(countAfterMount)
+    expect(cardRenderSpy).toHaveBeenCalledWith('wt-a')
+  })
+})
diff --git a/src/renderer/src/components/sidebar/WorktreeList.tsx b/src/renderer/src/components/sidebar/WorktreeList.tsx
index a71753eaa..fcc71abb9 100644
--- a/src/renderer/src/components/sidebar/WorktreeList.tsx
+++ b/src/renderer/src/components/sidebar/WorktreeList.tsx
@@ -24,6 +24,8 @@ import {
   Trash2
 } from 'lucide-react'
 import { useAppStore } from '@/store'
+import { createLineageToggleHandlerCache } from './worktree-lineage-toggle-handler-cache'
+import { reuseArrayIfEqual } from './worktree-agent-row-selectors'
 import { useShallow } from 'zustand/react/shallow'
 import type { AppState } from '@/store/types'
 import {
@@ -312,6 +314,14 @@ type ProjectGroupDeleteDialogState = {
   removeContainedProjects: boolean
 }
 
+// Why: epoch-driven recomputes often produce arrays whose contents and order are unchanged; reusing the previous identity when element-wise equal keeps downstream memos and React.memo'd cards bailing out. Safe only because elements (Worktree objects / id strings) are immutably REPLACED on change — never wrap arrays of mutated-in-place objects.
+function useReusedArrayIdentity<T>(next: T[]): T[] {
+  const previousRef = useRef<T[]>(next)
+  const result = reuseArrayIfEqual(previousRef.current, next)
+  previousRef.current = result
+  return result
+}
+
 // Debounce re-sort after a sortEpoch bump so background score changes don't jar row positions.
 const SORT_SETTLE_MS = 3_000
 const USER_SCROLL_MEASUREMENT_ADJUSTMENT_SUPPRESS_MS = 500
@@ -2449,6 +2459,12 @@ const VirtualizedWorktreeViewport = React.memo(function VirtualizedWorktreeViewp
     },
     [recordCurrentScrollAnchor, toggleGroup]
   )
+  // Why: memo'd WorktreeCard needs a per-group-key stable onLineageToggle
+  // identity to bail out of re-renders; see worktree-lineage-toggle-handler-cache.
+  const getLineageToggleHandler = useMemo(
+    () => createLineageToggleHandlerCache(toggleGroupWithScrollAnchor),
+    [toggleGroupWithScrollAnchor]
+  )
 
   const navigateWorktree = useCallback(
     (direction: 'up' | 'down') => {
@@ -4856,11 +4872,7 @@ const VirtualizedWorktreeViewport = React.memo(function VirtualizedWorktreeViewp
                     lineageChildrenStyle={lineageChildrenStyle}
                     onLineageToggle={
                       lineageToggleGroupKey
-                        ? (event) => {
-                            event.preventDefault()
-                            event.stopPropagation()
-                            toggleGroupWithScrollAnchor(lineageToggleGroupKey)
-                          }
+                        ? getLineageToggleHandler(lineageToggleGroupKey)
                         : undefined
                     }
                   />
@@ -5462,7 +5474,7 @@ const WorktreeList = React.memo(function WorktreeList({
   }, [sortedIds, sortBy])
 
   // Flatten/filter/sort via the shared utility so card order matches Cmd+1–9 numbering.
-  const visibleWorktrees = useMemo(() => {
+  const recomputedVisibleWorktrees = useMemo(() => {
     void agentStatusEpoch
     const ids = computeVisibleWorktreeIds(worktreesByRepo, sortedIds, {
       filterRepoIds,
@@ -5514,6 +5526,10 @@ const WorktreeList = React.memo(function WorktreeList({
     worktreeLineageById,
     worktreesByRepo
   ])
+  // Why: agentStatusEpoch bumps recompute this memo even when membership and
+  // order are unchanged; keeping the previous identity stops the whole
+  // rows/sectionRows/renderedWorktrees chain from churning per epoch.
+  const visibleWorktrees = useReusedArrayIdentity(recomputedVisibleWorktrees)
 
   const worktrees = visibleWorktrees
   const collapsedGroups = useAppStore((s) => s.collapsedGroups)
@@ -5842,9 +5858,14 @@ const WorktreeList = React.memo(function WorktreeList({
     () => getRenderedWorktreesInSidebarOrder(sectionRows, pinnedDisplayPolicy),
     [pinnedDisplayPolicy, sectionRows]
   )
-  const renderedWorktreeIds = useMemo(
-    () => uniqueWorktreeIds(renderedWorktrees.map((worktree) => worktree.id)),
-    [renderedWorktrees]
+  // Why: order-preserving sectionRows rebuilds must not give this array a new
+  // identity — updateSelectionForGesture depends on it, and a fresh identity
+  // there defeats React.memo bail-out for every WorktreeCard on epoch bumps.
+  const renderedWorktreeIds = useReusedArrayIdentity(
+    useMemo(
+      () => uniqueWorktreeIds(renderedWorktrees.map((worktree) => worktree.id)),
+      [renderedWorktrees]
+    )
   )
   const [selectedWorktreeIds, setSelectedWorktreeIds] = useState<Set<string>>(new Set())
   const [selectionAnchorId, setSelectionAnchorId] = useState<string | null>(null)
@@ -5862,18 +5883,23 @@ const WorktreeList = React.memo(function WorktreeList({
     setSelectionAnchorId(prunedSelection.anchorId)
   }
 
-  const selectedWorktrees = useMemo(() => {
-    if (selectedWorktreeIds.size === 0) {
-      return []
-    }
-    const selected = new Map<string, Worktree>()
-    for (const worktree of renderedWorktrees) {
-      if (selectedWorktreeIds.has(worktree.id) && !selected.has(worktree.id)) {
-        selected.set(worktree.id, worktree)
+  // Why identity reuse: the empty/unchanged-selection case must keep one array
+  // identity — selectForContextMenu and both drag-start handlers depend on
+  // this array, and card memo bail-out depends on those staying stable.
+  const selectedWorktrees = useReusedArrayIdentity(
+    useMemo(() => {
+      if (selectedWorktreeIds.size === 0) {
+        return []
       }
-    }
-    return Array.from(selected.values())
-  }, [renderedWorktrees, selectedWorktreeIds])
+      const selected = new Map<string, Worktree>()
+      for (const worktree of renderedWorktrees) {
+        if (selectedWorktreeIds.has(worktree.id) && !selected.has(worktree.id)) {
+          selected.set(worktree.id, worktree)
+        }
+      }
+      return Array.from(selected.values())
+    }, [renderedWorktrees, selectedWorktreeIds])
+  )
 
   useEffect(() => {
     if (selectedWorktreeIds.size === 0) {
diff --git a/src/renderer/src/components/sidebar/worktree-agent-row-selectors.ts b/src/renderer/src/components/sidebar/worktree-agent-row-selectors.ts
index 35ff6853b..f964d0241 100644
--- a/src/renderer/src/components/sidebar/worktree-agent-row-selectors.ts
+++ b/src/renderer/src/components/sidebar/worktree-agent-row-selectors.ts
@@ -51,7 +51,10 @@ let liveEntriesByWorktreeCache: LiveEntriesByWorktreeCache | null = null
 let migrationUnsupportedByWorktreeCache: MigrationUnsupportedByWorktreeCache | null = null
 let retainedEntriesByWorktreeCache: RetainedEntriesByWorktreeCache | null = null
 
-function reuseArrayIfEqual<T>(previous: T[] | undefined, next: T[]): T[] {
+// Why exported: WorktreeList reuses this exact-equality identity check to keep
+// derived arrays referentially stable across order-preserving epoch bumps so
+// memo'd cards can bail out of re-render.
+export function reuseArrayIfEqual<T>(previous: T[] | undefined, next: T[]): T[] {
   if (!previous || previous.length !== next.length) {
     return next
   }
diff --git a/src/renderer/src/components/sidebar/worktree-lineage-toggle-handler-cache.test.ts b/src/renderer/src/components/sidebar/worktree-lineage-toggle-handler-cache.test.ts
new file mode 100644
index 000000000..670560092
--- /dev/null
+++ b/src/renderer/src/components/sidebar/worktree-lineage-toggle-handler-cache.test.ts
@@ -0,0 +1,48 @@
+import { describe, expect, it, vi } from 'vitest'
+import type React from 'react'
+import { createLineageToggleHandlerCache } from './worktree-lineage-toggle-handler-cache'
+
+const makeEvent = (): React.MouseEvent<HTMLButtonElement> =>
+  ({
+    preventDefault: vi.fn(),
+    stopPropagation: vi.fn()
+  }) as unknown as React.MouseEvent<HTMLButtonElement>
+
+describe('createLineageToggleHandlerCache', () => {
+  it('returns a referentially stable handler for the same group key across calls', () => {
+    const getHandler = createLineageToggleHandlerCache(vi.fn())
+
+    const first = getHandler('lineage:alpha')
+    const second = getHandler('lineage:alpha')
+
+    // Why: stable identity is what lets React.memo'd WorktreeCard bail out.
+    expect(second).toBe(first)
+  })
+
+  it('returns distinct handlers for distinct group keys', () => {
+    const getHandler = createLineageToggleHandlerCache(vi.fn())
+
+    expect(getHandler('lineage:alpha')).not.toBe(getHandler('lineage:beta'))
+  })
+
+  it('prevents default, stops propagation, and toggles the bound group key', () => {
+    const toggleGroup = vi.fn()
+    const getHandler = createLineageToggleHandlerCache(toggleGroup)
+    const event = makeEvent()
+
+    getHandler('lineage:alpha')(event)
+
+    expect(event.preventDefault).toHaveBeenCalledTimes(1)
+    expect(event.stopPropagation).toHaveBeenCalledTimes(1)
+    expect(toggleGroup).toHaveBeenCalledExactlyOnceWith('lineage:alpha')
+  })
+
+  it('keeps each cached handler bound to its own group key', () => {
+    const toggleGroup = vi.fn()
+    const getHandler = createLineageToggleHandlerCache(toggleGroup)
+
+    getHandler('lineage:beta')(makeEvent())
+
+    expect(toggleGroup).toHaveBeenCalledExactlyOnceWith('lineage:beta')
+  })
+})
diff --git a/src/renderer/src/components/sidebar/worktree-lineage-toggle-handler-cache.ts b/src/renderer/src/components/sidebar/worktree-lineage-toggle-handler-cache.ts
new file mode 100644
index 000000000..de9012f41
--- /dev/null
+++ b/src/renderer/src/components/sidebar/worktree-lineage-toggle-handler-cache.ts
@@ -0,0 +1,26 @@
+import type React from 'react'
+
+export type LineageToggleHandler = (event: React.MouseEvent<HTMLButtonElement>) => void
+
+// Why: WorktreeCard is React.memo'd; an inline arrow per row would give
+// onLineageToggle a fresh identity every render and defeat the memo bail-out
+// for every lineage-parent card on each sort/status epoch bump. Cache one
+// handler per group key (bounded by lineage-group count) so identity is stable.
+export const createLineageToggleHandlerCache = (
+  toggleGroup: (groupKey: string) => void
+): ((groupKey: string) => LineageToggleHandler) => {
+  const handlersByGroupKey = new Map<string, LineageToggleHandler>()
+  return (groupKey: string) => {
+    const cached = handlersByGroupKey.get(groupKey)
+    if (cached) {
+      return cached
+    }
+    const handler: LineageToggleHandler = (event) => {
+      event.preventDefault()
+      event.stopPropagation()
+      toggleGroup(groupKey)
+    }
+    handlersByGroupKey.set(groupKey, handler)
+    return handler
+  }
+}