diff --git a/pr-evidence/1-before-both-collapsed.png b/pr-evidence/1-before-both-collapsed.png
new file mode 100644
index 00000000000..e8b721a239b
Binary files /dev/null and b/pr-evidence/1-before-both-collapsed.png differ
diff --git a/pr-evidence/2-agents-expanded.png b/pr-evidence/2-agents-expanded.png
new file mode 100644
index 00000000000..9b3c71f4791
Binary files /dev/null and b/pr-evidence/2-agents-expanded.png differ
diff --git a/pr-evidence/3-after-children-toggle-agents-still-expanded.png b/pr-evidence/3-after-children-toggle-agents-still-expanded.png
new file mode 100644
index 00000000000..413204d402f
Binary files /dev/null and b/pr-evidence/3-after-children-toggle-agents-still-expanded.png differ
diff --git a/src/renderer/src/components/editor/EditorPanel.tsx b/src/renderer/src/components/editor/EditorPanel.tsx
index 21b116ea246..43a9276b15e 100644
--- a/src/renderer/src/components/editor/EditorPanel.tsx
+++ b/src/renderer/src/components/editor/EditorPanel.tsx
@@ -346,8 +346,9 @@ function EditorPanelInner({
     activeMarkdownContent &&
     extractFrontMatter(activeMarkdownContent)
   )
+  // Why: front-matter shows by default; the map only carries per-file hide overrides.
   const isMarkdownFrontmatterVisible =
-    markdownFrontmatterVisible[markdownDocumentStateFileId] ?? false
+    markdownFrontmatterVisible[markdownDocumentStateFileId] ?? true
   const isMarkdownTableOfContentsVisible =
     markdownTableOfContentsVisible[markdownDocumentStateFileId] ?? false
 
diff --git a/src/renderer/src/components/editor/MarkdownPreview.tsx b/src/renderer/src/components/editor/MarkdownPreview.tsx
index 38d146c1312..f47b3610f3c 100644
--- a/src/renderer/src/components/editor/MarkdownPreview.tsx
+++ b/src/renderer/src/components/editor/MarkdownPreview.tsx
@@ -619,12 +619,11 @@ export default function MarkdownPreview({
       .replace(/\r?\n(?:---|\+\+\+)\r?\n?$/, '')
       .trim()
   }, [frontMatter])
-  // Why: front matter is hidden by default (#4468) and controlled from the
-  // markdown preview actions menu, keeping metadata out of the reading surface
-  // unless the user explicitly asks for it.
+  // Why: front matter shows by default and is toggled off from the markdown
+  // preview actions menu; the store map only carries per-file hide overrides.
   const toggleableSourceFileId: string | null = sourceFileId ?? null
   const frontmatterVisible = toggleableSourceFileId
-    ? (frontmatterVisibleByFile[toggleableSourceFileId] ?? false)
+    ? (frontmatterVisibleByFile[toggleableSourceFileId] ?? true)
     : true
   const [activeAnnotationBlockKey, setActiveAnnotationBlockKey] = useState<string | null>(null)
   const [reviewNotesCopied, setReviewNotesCopied] = useState(false)
diff --git a/src/renderer/src/components/sidebar/WorktreeCardAgents.expansion-remount.test.tsx b/src/renderer/src/components/sidebar/WorktreeCardAgents.expansion-remount.test.tsx
new file mode 100644
index 00000000000..cc3a83d0a70
--- /dev/null
+++ b/src/renderer/src/components/sidebar/WorktreeCardAgents.expansion-remount.test.tsx
@@ -0,0 +1,223 @@
+// @vitest-environment happy-dom
+
+import { act, type ReactNode } from 'react'
+import { createRoot, type Root } from 'react-dom/client'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import {
+  clearWorktreeAgentExpansionStateForTests,
+  getWorktreeAgentExpansionCountForTests,
+  MAX_PERSISTED_WORKTREE_AGENT_EXPANSIONS,
+  seedWorktreeAgentExpansionStateForTests,
+  useWorktreeAgentExpansionState
+} from './worktree-card-agents-expansion-state'
+
+let mockAgents: unknown[] = []
+
+function mockAgent(paneKey: string, prompt: string): unknown {
+  return {
+    paneKey,
+    tab: { id: paneKey.split(':')[0] },
+    agentType: 'codex',
+    rowSource: undefined,
+    state: 'done',
+    startedAt: 1000,
+    entry: {
+      prompt,
+      lastAssistantMessage: undefined,
+      state: 'done',
+      stateStartedAt: 1000,
+      stateHistory: [],
+      orchestration: undefined
+    },
+    lineage: undefined
+  }
+}
+
+vi.mock('@/store', () => ({
+  useAppStore: (selector: (state: unknown) => unknown) =>
+    selector({
+      agentActivityDisplayMode: 'compact',
+      acknowledgedAgentsByPaneKey: {},
+      cacheTimerByKey: {},
+      dropAgentStatus: vi.fn(),
+      dismissRetainedAgent: vi.fn(),
+      agentSendPopoverTargetMode: null,
+      agentStatusByPaneKey: {},
+      agentStatusEpoch: 0,
+      tabsByWorktree: {},
+      terminalLayoutsByTabId: {},
+      runtimePaneTitlesByTabId: {},
+      sendPromptToSidebarAgentTarget: vi.fn(),
+      settings: { promptCacheTimerEnabled: false, promptCacheTtlMs: 60_000 }
+    })
+}))
+
+vi.mock('./useWorktreeAgentRows', () => ({
+  useWorktreeAgentRows: vi.fn(() => mockAgents)
+}))
+
+vi.mock('@/components/dashboard/useNow', () => ({
+  useNow: vi.fn(() => 2000)
+}))
+
+vi.mock('./CacheTimer', () => ({
+  default: () => null,
+  usePromptCacheCountdownForPane: () => null,
+  usePromptCacheCountdownStartedAt: () => null
+}))
+
+vi.mock('@/lib/worktree-activation', () => ({
+  activateAndRevealWorktree: vi.fn()
+}))
+
+vi.mock('@/lib/activate-tab-and-focus-pane', () => ({
+  activateTabAndFocusPane: vi.fn()
+}))
+
+vi.mock('@/components/ui/tooltip', () => ({
+  Tooltip: ({ children }: { children: ReactNode }) => <>{children}</>,
+  TooltipContent: ({ children }: { children: ReactNode }) => <>{children}</>,
+  TooltipTrigger: ({ children }: { children: ReactNode }) => <>{children}</>
+}))
+
+const mountedRoots: { root: Root; host: HTMLElement }[] = []
+
+async function mountAgents(worktreeId: string): Promise<HTMLElement> {
+  const host = document.createElement('div')
+  document.body.append(host)
+  const root = createRoot(host)
+  mountedRoots.push({ root, host })
+  const { default: WorktreeCardAgents } = await import('./WorktreeCardAgents')
+  await act(async () => {
+    root.render(<WorktreeCardAgents worktreeId={worktreeId} />)
+  })
+  return host
+}
+
+function summaryButton(host: HTMLElement): HTMLButtonElement {
+  // The compact multi-agent summary is the only control carrying aria-expanded
+  // when the agents are flat (no per-agent child disclosure).
+  const button = host.querySelector<HTMLButtonElement>('button[aria-expanded]')
+  if (!button) {
+    throw new Error('compact agent summary button not found')
+  }
+  return button
+}
+
+describe('WorktreeCardAgents inline-list expansion durability', () => {
+  beforeEach(() => {
+    clearWorktreeAgentExpansionStateForTests()
+    mockAgents = [mockAgent('tab-1:1', 'One'), mockAgent('tab-2:2', 'Two')]
+  })
+
+  afterEach(async () => {
+    await act(async () => {
+      for (const { root, host } of mountedRoots.splice(0)) {
+        root.unmount()
+        host.remove()
+      }
+    })
+    document.body.innerHTML = ''
+    clearWorktreeAgentExpansionStateForTests()
+  })
+
+  it('keeps the compact agent summary expanded across a card remount', async () => {
+    const host = await mountAgents('wt-remount')
+    expect(summaryButton(host).getAttribute('aria-expanded')).toBe('false')
+
+    await act(async () => {
+      summaryButton(host).dispatchEvent(new MouseEvent('click', { bubbles: true }))
+    })
+    expect(summaryButton(host).getAttribute('aria-expanded')).toBe('true')
+
+    // Simulate the WorktreeCard remount that a virtualizer recycle or a sibling
+    // child-worktrees toggle triggers: fully unmount, then mount a fresh tree
+    // for the same worktree. Before the fix this reset the summary to collapsed.
+    await act(async () => {
+      const first = mountedRoots.shift()!
+      first.root.unmount()
+      first.host.remove()
+    })
+    const remounted = await mountAgents('wt-remount')
+
+    expect(summaryButton(remounted).getAttribute('aria-expanded')).toBe('true')
+  })
+
+  it('does not leak expansion between different worktrees', async () => {
+    const first = await mountAgents('wt-a')
+    await act(async () => {
+      summaryButton(first).dispatchEvent(new MouseEvent('click', { bubbles: true }))
+    })
+    expect(summaryButton(first).getAttribute('aria-expanded')).toBe('true')
+
+    const second = await mountAgents('wt-b')
+    expect(summaryButton(second).getAttribute('aria-expanded')).toBe('false')
+  })
+})
+
+describe('worktree-card-agents-expansion-state module cache', () => {
+  beforeEach(() => {
+    clearWorktreeAgentExpansionStateForTests()
+  })
+
+  afterEach(() => {
+    clearWorktreeAgentExpansionStateForTests()
+  })
+
+  it('persists a collapsed lineage parent across a hook remount and toggles independently', async () => {
+    function Probe({ worktreeId }: { worktreeId: string }) {
+      const { collapsedLineageParents, toggleLineageParent } =
+        useWorktreeAgentExpansionState(worktreeId)
+      return (
+        <button
+          type="button"
+          data-collapsed={collapsedLineageParents.has('pane-x') ? 'true' : 'false'}
+          onClick={() => toggleLineageParent('pane-x')}
+        >
+          probe
+        </button>
+      )
+    }
+
+    const host = document.createElement('div')
+    document.body.append(host)
+    let root = createRoot(host)
+    await act(async () => {
+      root.render(<Probe worktreeId="wt-probe" />)
+    })
+    const read = () => host.querySelector('button')!.getAttribute('data-collapsed')
+    expect(read()).toBe('false')
+
+    await act(async () => {
+      host.querySelector('button')!.dispatchEvent(new MouseEvent('click', { bubbles: true }))
+    })
+    expect(read()).toBe('true')
+
+    // Remount the hook consumer: the collapsed parent must survive.
+    await act(async () => root.unmount())
+    root = createRoot(host)
+    await act(async () => {
+      root.render(<Probe worktreeId="wt-probe" />)
+    })
+    expect(read()).toBe('true')
+
+    await act(async () => root.unmount())
+    host.remove()
+  })
+
+  it('drops default (empty) state and bounds the cache with LRU eviction', () => {
+    seedWorktreeAgentExpansionStateForTests('wt-default', {
+      collapsedLineageParents: new Set(),
+      compactRootListExpanded: false
+    })
+    expect(getWorktreeAgentExpansionCountForTests()).toBe(0)
+
+    for (let i = 0; i < MAX_PERSISTED_WORKTREE_AGENT_EXPANSIONS + 25; i++) {
+      seedWorktreeAgentExpansionStateForTests(`wt-${i}`, {
+        collapsedLineageParents: new Set(),
+        compactRootListExpanded: true
+      })
+    }
+    expect(getWorktreeAgentExpansionCountForTests()).toBe(MAX_PERSISTED_WORKTREE_AGENT_EXPANSIONS)
+  })
+})
diff --git a/src/renderer/src/components/sidebar/WorktreeCardAgents.tsx b/src/renderer/src/components/sidebar/WorktreeCardAgents.tsx
index 2a924211874..9e8faa70acd 100644
--- a/src/renderer/src/components/sidebar/WorktreeCardAgents.tsx
+++ b/src/renderer/src/components/sidebar/WorktreeCardAgents.tsx
@@ -1,4 +1,4 @@
-import React, { useCallback, useLayoutEffect, useMemo, useRef, useState } from 'react'
+import React, { useCallback, useLayoutEffect, useMemo, useRef } from 'react'
 import { useShallow } from 'zustand/react/shallow'
 import { useAppStore } from '@/store'
 import { activateAndRevealWorktree } from '@/lib/worktree-activation'
@@ -24,6 +24,7 @@ import {
 import { buildAgentRowLineageTree } from '@/components/dashboard/agent-row-lineage-model'
 import { DEFAULT_AGENT_ACTIVITY_DISPLAY_MODE } from '../../../../shared/constants'
 import { revealElementInScrollContainer } from './worktree-sidebar-reveal'
+import { useWorktreeAgentExpansionState } from './worktree-card-agents-expansion-state'
 import { translate } from '@/i18n/i18n'
 
 export const SUPPRESS_WORKTREE_LIST_SCROLL_ADJUSTMENT_EVENT =
@@ -231,13 +232,24 @@ const WorktreeCardAgentsBody = React.memo(function WorktreeCardAgentsBody({
     [agents]
   )
   const hasLineage = childrenByParentPaneKey.size > 0
-  const [collapsedLineageParents, setCollapsedLineageParents] = useState<ReadonlySet<string>>(
-    () => new Set()
-  )
-  const [compactRootListExpanded, setCompactRootListExpanded] = useState(false)
+  // Why: keep disclosure state out of raw local useState so the WorktreeCard
+  // remount that fires on virtualizer recycle or a sibling child-worktrees
+  // toggle no longer resets it (which read as one section expanding the other).
+  const {
+    collapsedLineageParents,
+    compactRootListExpanded,
+    toggleLineageParent: toggleLineageParentState,
+    toggleCompactRootList
+  } = useWorktreeAgentExpansionState(worktreeId)
 
+  // Why: reveal only on a genuine user collapse→expand within this mount.
+  // Seeding an already-expanded panel from the durable cache on a remount must
+  // not re-trigger the reveal scroll, or recycled cards would fight the scroll.
+  const previousCompactExpandedRef = useRef(compactRootListExpanded)
   useLayoutEffect(() => {
-    if (compactRootListExpanded && agentActivityDisplayMode === 'compact') {
+    const wasExpanded = previousCompactExpandedRef.current
+    previousCompactExpandedRef.current = compactRootListExpanded
+    if (!wasExpanded && compactRootListExpanded && agentActivityDisplayMode === 'compact') {
       dispatchSuppressScrollAdjustment()
       // Why: defer the reveal scroll out of the expand commit. Running it inline
       // forces a synchronous sidebar layout that blocks the animation's opening
@@ -250,18 +262,13 @@ const WorktreeCardAgentsBody = React.memo(function WorktreeCardAgentsBody({
     }
     return undefined
   }, [agentActivityDisplayMode, compactRootListExpanded])
-  const toggleLineageParent = useCallback((paneKey: string) => {
-    dispatchSuppressScrollAdjustment()
-    setCollapsedLineageParents((current) => {
-      const next = new Set(current)
-      if (next.has(paneKey)) {
-        next.delete(paneKey)
-      } else {
-        next.add(paneKey)
-      }
-      return next
-    })
-  }, [])
+  const toggleLineageParent = useCallback(
+    (paneKey: string) => {
+      dispatchSuppressScrollAdjustment()
+      toggleLineageParentState(paneKey)
+    },
+    [toggleLineageParentState]
+  )
 
   const stopBubble = useCallback((e: React.MouseEvent) => {
     e.stopPropagation()
@@ -445,7 +452,7 @@ const WorktreeCardAgentsBody = React.memo(function WorktreeCardAgentsBody({
               expanded={compactRootListExpanded}
               onToggle={() => {
                 dispatchSuppressScrollAdjustment()
-                setCompactRootListExpanded((expanded) => !expanded)
+                toggleCompactRootList()
               }}
             />
             <CompactAgentExpansion expanded={compactRootListExpanded}>
diff --git a/src/renderer/src/components/sidebar/WorktreeList.lineage-agent-expansion-coupling.test.tsx b/src/renderer/src/components/sidebar/WorktreeList.lineage-agent-expansion-coupling.test.tsx
new file mode 100644
index 00000000000..6190a6acd5a
--- /dev/null
+++ b/src/renderer/src/components/sidebar/WorktreeList.lineage-agent-expansion-coupling.test.tsx
@@ -0,0 +1,581 @@
+// @vitest-environment happy-dom
+
+// Regression test for the child-worktrees <-> agent-list expansion coupling:
+// in a worktree card that shows BOTH inline agent rows (with orchestration
+// lineage) AND a "N children" child-worktrees chip, toggling the child-worktrees
+// chip used to reset the agent list's expansion state (it remounts the card).
+// It renders the REAL WorktreeCardAgents (not a mock) inside the REAL
+// WorktreeList so the remount and the durable-expansion fix are exercised
+// end-to-end. The two toggles must stay independent in both directions.
+//
+// NOTE: unlike the sibling lineage test, this file's useVirtualizer mock HONORS
+// the real `getItemKey` (which returns getRenderRowKey(row)). Without that, the
+// parent card's virtual-row key would be a static `row-<index>` and the
+// item<->lineage-group remount would NOT reproduce (false negative).
+
+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 {
+  AgentStatusEntry,
+  AgentStatusOrchestrationContext
+} from '../../../../shared/agent-status-types'
+import type {
+  Repo,
+  TerminalTab,
+  Worktree,
+  WorktreeCardProperty,
+  WorktreeLineage
+} from '../../../../shared/types'
+import { clearWorktreeAgentExpansionStateForTests } from './worktree-card-agents-expansion-state'
+
+globalThis.IS_REACT_ACT_ENVIRONMENT = true
+
+const mockStore = vi.hoisted(() => ({
+  state: {} as Record<string, unknown>,
+  activateWorktreeFromSidebar: vi.fn(),
+  openModal: 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 }
+})
+
+// Why: honor the real getItemKey so each virtual row's React key equals
+// getRenderRowKey(row). This is what makes the parent card remount when it
+// moves between a standalone 'item' row (key wt:...) and a 'lineage-group' row
+// (key lineage-group:...) as the child-worktrees group collapses/expands.
+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,
+    getItemKey
+  }: {
+    count: number
+    getItemKey?: (index: number) => string | number
+  }) => ({
+    elementsCache: new Map(),
+    getTotalSize: () => count * 96,
+    getVirtualItems: () =>
+      Array.from({ length: count }, (_, index) => ({
+        index,
+        key: getItemKey ? getItemKey(index) : `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 data-hover-card-content="">{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('./CacheTimer', () => ({
+  default: () => null,
+  usePromptCacheCountdownStartedAt: () => null,
+  usePromptCacheCountdownForPane: () => null
+}))
+
+// NOTE: intentionally NOT mocking ./WorktreeCardAgents — we render the real one.
+
+vi.mock('./SshDisconnectedDialog', () => ({
+  SshDisconnectedDialog: () => null
+}))
+
+vi.mock('./WorktreeContextMenu', () => ({
+  default: ({ children }: { children: ReactNode }) => <>{children}</>,
+  CLOSE_ALL_CONTEXT_MENUS_EVENT: 'orca:test-close-context-menus',
+  WORKTREE_CONTEXT_MENU_SCOPE_ATTR: 'data-orca-context-menu-scope',
+  WORKTREE_NATIVE_CONTEXT_MENU_ATTR: 'data-worktree-native-context-menu'
+}))
+
+const TAB_ID = 'tabP'
+const PANE_ROOT = `${TAB_ID}:aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa`
+const PANE_CHILD = `${TAB_ID}:bbbbbbbb-bbbb-4bbb-8bbb-bbbbbbbbbbbb`
+const PANE_ROOT_2 = `${TAB_ID}:cccccccc-cccc-4ccc-8ccc-cccccccccccc`
+
+function makeRepo(): Repo {
+  return {
+    id: 'repo-1',
+    path: '/tmp/lineage-agent-coupling',
+    displayName: 'lineage-agent-coupling',
+    badgeColor: '#999999',
+    addedAt: 1
+  }
+}
+
+function makeWorktree(args: {
+  id: string
+  displayName: string
+  branch: string
+  sortOrder: number
+  instanceId: string
+}): Worktree {
+  return {
+    id: args.id,
+    instanceId: args.instanceId,
+    repoId: 'repo-1',
+    path: `/tmp/lineage-agent-coupling/${args.id}`,
+    displayName: args.displayName,
+    branch: args.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 makeLineage(worktree: Worktree, parent: Worktree): WorktreeLineage {
+  return {
+    worktreeId: worktree.id,
+    worktreeInstanceId: worktree.instanceId!,
+    parentWorktreeId: parent.id,
+    parentWorktreeInstanceId: parent.instanceId!,
+    origin: 'orchestration',
+    capture: { source: 'orchestration-context', confidence: 'explicit' },
+    createdAt: 1
+  }
+}
+
+function makeAgentEntry(
+  paneKey: string,
+  prompt: string,
+  orchestration?: AgentStatusOrchestrationContext
+): AgentStatusEntry {
+  const now = Date.now()
+  return {
+    state: 'working',
+    prompt,
+    updatedAt: now,
+    stateStartedAt: now,
+    agentType: 'claude',
+    paneKey,
+    worktreeId: 'parent',
+    stateHistory: [],
+    ...(orchestration ? { orchestration } : {})
+  }
+}
+
+function makeParentTab(): TerminalTab {
+  return {
+    id: TAB_ID,
+    ptyId: null,
+    worktreeId: 'parent',
+    title: 'Parent Terminal',
+    customTitle: null,
+    color: null,
+    sortOrder: 0,
+    createdAt: 1
+  }
+}
+
+function setAgentLineageState(options: {
+  agentActivityDisplayMode: 'compact' | 'full'
+  secondRootAgent?: boolean
+  collapsedGroups?: Set<string>
+}): void {
+  const repo = makeRepo()
+  const parent = makeWorktree({
+    id: 'parent',
+    instanceId: 'parent-instance',
+    displayName: 'lineage parent',
+    branch: 'parent-branch',
+    sortOrder: 20
+  })
+  const child = makeWorktree({
+    id: 'child',
+    instanceId: 'child-instance',
+    displayName: 'lineage child',
+    branch: 'child-branch',
+    sortOrder: 10
+  })
+  const agentStatusByPaneKey: Record<string, AgentStatusEntry> = {
+    [PANE_ROOT]: makeAgentEntry(PANE_ROOT, 'PARENT_AGENT_PROMPT'),
+    [PANE_CHILD]: makeAgentEntry(PANE_CHILD, 'CHILD_AGENT_PROMPT', {
+      taskId: 't1',
+      dispatchId: 'd1',
+      parentPaneKey: PANE_ROOT
+    })
+  }
+  if (options.secondRootAgent) {
+    agentStatusByPaneKey[PANE_ROOT_2] = makeAgentEntry(PANE_ROOT_2, 'SECOND_ROOT_PROMPT')
+  }
+
+  mockStore.state = {
+    // Reactive-ish toggle: the chip's onClick eventually calls
+    // toggleCollapsedGroup; mutate the live Set so the next manual re-render
+    // (store isn't reactive in this harness) reflects the user's toggle.
+    collapsedGroups: options.collapsedGroups ?? new Set<string>(),
+    toggleCollapsedGroup: vi.fn((key: string) => {
+      // Why: mirror the real store's IMMUTABLE update — a fresh Set reference is
+      // what makes WorktreeList's `rows` useMemo (keyed on the Set identity)
+      // recompute buildRenderableRows and flip the parent's render-row.
+      const set = new Set(mockStore.state.collapsedGroups as Set<string>)
+      if (set.has(key)) {
+        set.delete(key)
+      } else {
+        set.add(key)
+      }
+      mockStore.state.collapsedGroups = set
+    }),
+
+    // ── worktree list plumbing ──
+    activeModal: '',
+    activeView: 'terminal',
+    activeWorktreeId: null,
+    activeWorkspaceKey: null,
+    activeTabId: null,
+    activeTabType: null,
+    agentStatusEpoch: 0,
+    browserTabsByWorktree: {},
+    clearPendingRevealWorktreeId: vi.fn(),
+    deleteStateByWorktreeId: {},
+    detectedWorktreesByRepo: {},
+    fetchFolderWorkspacePathStatus: vi.fn(),
+    fetchHostedReviewForBranch: vi.fn(),
+    fetchIssue: vi.fn(),
+    fetchLinearIssue: vi.fn(),
+    filterRepoIds: [],
+    folderWorkspaces: [],
+    folderWorkspacePathStatuses: {},
+    getFolderWorkspacePathStatusCacheKey: (request: unknown) => JSON.stringify(request),
+    getFreshFolderWorkspacePathStatus: () => null,
+    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: {},
+    runtimeAgentOrchestrationByPaneKey: {},
+    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(),
+    terminalLayoutsByTabId: {},
+    updateRepo: vi.fn(),
+    updateWorktreeMeta: vi.fn(),
+    updateWorktreesMeta: vi.fn(),
+    workspaceHostScope: 'all',
+    workspacePortScan: null,
+    workspaceStatuses: [],
+    worktreeCardProperties: [
+      'status',
+      'pr',
+      'comment',
+      'inline-agents'
+    ] satisfies WorktreeCardProperty[],
+    worktreeLineageById: { [child.id]: makeLineage(child, parent) },
+    worktreesByRepo: { [repo.id]: [parent, child] },
+
+    // ── agent-list specific state (real WorktreeCardAgents deps) ──
+    agentActivityDisplayMode: options.agentActivityDisplayMode,
+    agentSendPopoverTargetMode: null,
+    acknowledgedAgentsByPaneKey: {},
+    dropAgentStatus: vi.fn(),
+    dismissRetainedAgent: vi.fn(),
+    sendPromptToSidebarAgentTarget: vi.fn(),
+    tabsByWorktree: { parent: [makeParentTab()] },
+    agentStatusByPaneKey
+  }
+}
+
+const mountedRoots: Root[] = []
+
+async function renderWorktreeList(): Promise<{ container: HTMLDivElement; root: Root }> {
+  const container = document.createElement('div')
+  document.body.appendChild(container)
+  const root = createRoot(container)
+  mountedRoots.push(root)
+  await act(async () => {
+    root.render(
+      <WorktreeList scrollOffsetRef={{ current: 0 }} scrollAnchorRef={{ current: null }} />
+    )
+  })
+  return { container, root }
+}
+
+// Why: the mocked store isn't reactive. Re-render with FRESH ref props so
+// React.memo(WorktreeList) doesn't bail out, letting a collapsedGroups mutation
+// flow into buildRenderableRows (and thus flip the parent's virtual-row key).
+async function rerender(root: Root): Promise<void> {
+  await act(async () => {
+    root.render(
+      <WorktreeList scrollOffsetRef={{ current: 0 }} scrollAnchorRef={{ current: null }} />
+    )
+  })
+}
+
+function findButtonByAriaLabel(container: HTMLElement, pattern: RegExp): HTMLButtonElement | null {
+  return (
+    [...container.querySelectorAll<HTMLButtonElement>('button[aria-expanded]')].find((button) =>
+      pattern.test(button.getAttribute('aria-label') ?? '')
+    ) ?? null
+  )
+}
+
+function childWorktreeChip(container: HTMLElement): HTMLButtonElement | null {
+  return findButtonByAriaLabel(container, /child workspace/i)
+}
+
+function agentChildDisclosure(container: HTMLElement): HTMLButtonElement | null {
+  return findButtonByAriaLabel(container, /child agent/i)
+}
+
+function compactAgentSummary(container: HTMLElement): HTMLButtonElement | null {
+  return (
+    [...container.querySelectorAll<HTMLButtonElement>('button.compact-agent-summary-button')][0] ??
+    null
+  )
+}
+
+function childWorktreeCardPresent(container: HTMLElement): boolean {
+  return container.querySelector('[id="worktree-list-option-all%3Achild"]') !== null
+}
+
+function parentVirtualRowKey(container: HTMLElement): string | null {
+  return (
+    container
+      .querySelector('[data-worktree-id="parent"]')
+      ?.closest('[data-worktree-virtual-row]')
+      ?.getAttribute('data-worktree-virtual-row-key') ?? null
+  )
+}
+
+async function click(el: Element): Promise<void> {
+  await act(async () => {
+    el.dispatchEvent(new MouseEvent('click', { bubbles: true }))
+  })
+}
+
+describe('WorktreeCard agent-list <-> child-worktrees expansion coupling', () => {
+  beforeAll(async () => {
+    WorktreeList = (await import('./WorktreeList')).default as WorktreeListComponent
+  }, 60_000)
+
+  beforeEach(() => {
+    vi.clearAllMocks()
+    // Expansion now persists in a module-level cache that survives remounts, so
+    // it must be reset between cases or one test's collapse leaks into the next.
+    clearWorktreeAgentExpansionStateForTests()
+  })
+
+  afterEach(async () => {
+    await act(async () => {
+      for (const root of mountedRoots.splice(0)) {
+        root.unmount()
+      }
+    })
+    document.body.innerHTML = ''
+    clearWorktreeAgentExpansionStateForTests()
+  })
+
+  it('[full mode] both toggles render independently at mount', async () => {
+    setAgentLineageState({ agentActivityDisplayMode: 'full' })
+    const { container } = await renderWorktreeList()
+
+    // Sanity: real agent rows rendered (parent + its lineage child agent).
+    expect(container.textContent).toContain('PARENT_AGENT_PROMPT')
+    expect(container.textContent).toContain('CHILD_AGENT_PROMPT')
+
+    // Both controls exist and are independent DOM elements.
+    expect(childWorktreeChip(container)).not.toBeNull()
+    expect(agentChildDisclosure(container)).not.toBeNull()
+
+    // Defaults: child worktrees expanded (chip aria-expanded true) AND child
+    // agents expanded (disclosure aria-expanded true).
+    expect(childWorktreeChip(container)!.getAttribute('aria-expanded')).toBe('true')
+    expect(agentChildDisclosure(container)!.getAttribute('aria-expanded')).toBe('true')
+    expect(childWorktreeCardPresent(container)).toBe(true)
+  })
+
+  it('[full mode] toggling AGENTS does NOT change the child-worktrees chip (agents -> children uncoupled)', async () => {
+    setAgentLineageState({ agentActivityDisplayMode: 'full' })
+    const { container } = await renderWorktreeList()
+
+    expect(agentChildDisclosure(container)!.getAttribute('aria-expanded')).toBe('true')
+    expect(childWorktreeCardPresent(container)).toBe(true)
+
+    // Collapse the child AGENTS via the disclosure chevron.
+    await click(agentChildDisclosure(container)!)
+
+    // Agent children now collapsed (local state)...
+    expect(agentChildDisclosure(container)!.getAttribute('aria-expanded')).toBe('false')
+    expect(container.querySelector('.worktree-agent-lineage-children')).toBeNull()
+    // ...but the child WORKTREES are untouched: chip still expanded, child card present.
+    expect(childWorktreeChip(container)!.getAttribute('aria-expanded')).toBe('true')
+    expect(childWorktreeCardPresent(container)).toBe(true)
+    // And collapsedGroups was never mutated by an agent toggle.
+    expect((mockStore.state.collapsedGroups as Set<string>).size).toBe(0)
+  })
+
+  it('[full mode] toggling CHILD WORKTREES still remounts the card but PRESERVES agent expansion (regression)', async () => {
+    setAgentLineageState({ agentActivityDisplayMode: 'full' })
+    const { container, root } = await renderWorktreeList()
+
+    // Parent starts inside a lineage-group render row (children expanded).
+    expect(parentVirtualRowKey(container)).toBe('lineage-group:all:lineage:parent')
+
+    // User collapses the child AGENTS.
+    await click(agentChildDisclosure(container)!)
+    expect(agentChildDisclosure(container)!.getAttribute('aria-expanded')).toBe('false')
+
+    // User now clicks the CHILD-WORKTREES chip to collapse child worktrees.
+    await click(childWorktreeChip(container)!)
+    expect(mockStore.state.toggleCollapsedGroup).toHaveBeenCalledWith('lineage:parent')
+    // Store isn't reactive; flush the collapsedGroups change into a re-render.
+    await rerender(root)
+
+    // The remount still happens: the parent moved to a standalone 'item' render
+    // row with a DIFFERENT React key, and the child card is gone.
+    expect(parentVirtualRowKey(container)).toBe('wt:all:parent')
+    expect(childWorktreeCardPresent(container)).toBe(false)
+
+    // FIXED: the card remounted, but the durable expansion cache means the
+    // child AGENTS the user collapsed stay collapsed — the child-worktrees
+    // toggle no longer bleeds into the agent list.
+    expect(agentChildDisclosure(container)!.getAttribute('aria-expanded')).toBe('false')
+    expect(container.querySelector('.worktree-agent-lineage-children')).toBeNull()
+  })
+
+  it('[full mode] CONTROL: a re-render that does NOT change collapsedGroups preserves agent state (isolates the remount)', async () => {
+    setAgentLineageState({ agentActivityDisplayMode: 'full' })
+    const { container, root } = await renderWorktreeList()
+
+    await click(agentChildDisclosure(container)!)
+    expect(agentChildDisclosure(container)!.getAttribute('aria-expanded')).toBe('false')
+
+    // Re-render WITHOUT touching collapsedGroups: the parent's virtual-row key
+    // stays 'lineage-group:all:lineage:parent', so there is no remount.
+    await rerender(root)
+
+    expect(parentVirtualRowKey(container)).toBe('lineage-group:all:lineage:parent')
+    // Agent collapse survives => proves it is the KEY change (remount), not the
+    // re-render itself, that resets the agent expansion.
+    expect(agentChildDisclosure(container)!.getAttribute('aria-expanded')).toBe('false')
+  })
+
+  it('[compact mode] toggling CHILD WORKTREES preserves the compact agent summary expansion (regression)', async () => {
+    setAgentLineageState({ agentActivityDisplayMode: 'compact', secondRootAgent: true })
+    const { container, root } = await renderWorktreeList()
+
+    // Two root agents => compact summary pill is shown, collapsed by default.
+    const summary = compactAgentSummary(container)
+    expect(summary).not.toBeNull()
+    expect(summary!.getAttribute('aria-expanded')).toBe('false')
+
+    // User expands the compact agent summary.
+    await click(summary!)
+    expect(compactAgentSummary(container)!.getAttribute('aria-expanded')).toBe('true')
+
+    // User toggles child worktrees.
+    await click(childWorktreeChip(container)!)
+    expect(mockStore.state.toggleCollapsedGroup).toHaveBeenCalledWith('lineage:parent')
+    await rerender(root)
+
+    // FIXED: the card remounts (child card gone), but the expanded "N agents"
+    // summary is restored from the durable cache instead of collapsing.
+    expect(childWorktreeCardPresent(container)).toBe(false)
+    expect(compactAgentSummary(container)!.getAttribute('aria-expanded')).toBe('true')
+  })
+})
diff --git a/src/renderer/src/components/sidebar/worktree-card-agents-expansion-state.ts b/src/renderer/src/components/sidebar/worktree-card-agents-expansion-state.ts
new file mode 100644
index 00000000000..b357cb21956
--- /dev/null
+++ b/src/renderer/src/components/sidebar/worktree-card-agents-expansion-state.ts
@@ -0,0 +1,130 @@
+import { useCallback, useState } from 'react'
+
+/**
+ * Expand/collapse state for a WorktreeCard's inline agent list:
+ *  - `collapsedLineageParents`: agent-lineage parent paneKeys the user folded.
+ *  - `compactRootListExpanded`: whether the "N agents" compact summary is open.
+ */
+export type WorktreeAgentExpansionState = {
+  collapsedLineageParents: ReadonlySet<string>
+  compactRootListExpanded: boolean
+}
+
+const EMPTY_COLLAPSED_PARENTS: ReadonlySet<string> = new Set()
+
+const DEFAULT_EXPANSION_STATE: WorktreeAgentExpansionState = {
+  collapsedLineageParents: EMPTY_COLLAPSED_PARENTS,
+  compactRootListExpanded: false
+}
+
+// Why: the inline agent list's expand/collapse must outlive the WorktreeCard
+// remount that fires (a) when the sidebar virtualizer recycles the row on
+// scroll and (b) when the sibling child-worktrees section toggles — that toggle
+// flips the card between an `item` and a `lineage-group` render row, changing
+// its virtual-row key and forcing a fresh mount. Holding this in plain local
+// useState reset it on every such remount, so folding one section visibly
+// re-expanded the other. Renderer-only and LRU-bounded: it resets on reload,
+// matching the ephemeral live-agent lineage it tracks, and never grows without
+// bound in a long-lived renderer.
+export const MAX_PERSISTED_WORKTREE_AGENT_EXPANSIONS = 512
+const expansionByWorktreeId = new Map<string, WorktreeAgentExpansionState>()
+
+function trimPersistedExpansions(): void {
+  while (expansionByWorktreeId.size > MAX_PERSISTED_WORKTREE_AGENT_EXPANSIONS) {
+    const oldest = expansionByWorktreeId.keys().next().value
+    if (oldest === undefined) {
+      break
+    }
+    expansionByWorktreeId.delete(oldest)
+  }
+}
+
+function readExpansionState(worktreeId: string): WorktreeAgentExpansionState {
+  return expansionByWorktreeId.get(worktreeId) ?? DEFAULT_EXPANSION_STATE
+}
+
+function persistExpansionState(worktreeId: string, state: WorktreeAgentExpansionState): void {
+  // Re-insert to refresh LRU order; drop entries that carry no non-default
+  // state so idle worktrees never occupy a slot.
+  expansionByWorktreeId.delete(worktreeId)
+  if (state.compactRootListExpanded || state.collapsedLineageParents.size > 0) {
+    expansionByWorktreeId.set(worktreeId, state)
+    trimPersistedExpansions()
+  }
+}
+
+export type WorktreeAgentExpansionControls = {
+  collapsedLineageParents: ReadonlySet<string>
+  compactRootListExpanded: boolean
+  /** Fold/unfold a single agent-lineage parent by its paneKey. */
+  toggleLineageParent: (paneKey: string) => void
+  /** Open/close the compact multi-agent summary panel. */
+  toggleCompactRootList: () => void
+}
+
+/**
+ * Remount-durable expand/collapse state for one worktree card's inline agent
+ * list. Reads seed from a module-level, session-scoped cache so a virtualizer
+ * recycle or a sibling child-worktrees toggle no longer wipes the user's
+ * disclosure choices. Independent per worktree id.
+ */
+export function useWorktreeAgentExpansionState(worktreeId: string): WorktreeAgentExpansionControls {
+  const [rendered, setRendered] = useState<{
+    worktreeId: string
+    state: WorktreeAgentExpansionState
+  }>(() => ({ worktreeId, state: readExpansionState(worktreeId) }))
+
+  // Why: a memoized body can be handed a new worktreeId without remounting;
+  // fall back to the cache so we never show a stale card's disclosure.
+  const current =
+    rendered.worktreeId === worktreeId ? rendered.state : readExpansionState(worktreeId)
+
+  const commit = useCallback(
+    (next: WorktreeAgentExpansionState) => {
+      persistExpansionState(worktreeId, next)
+      setRendered({ worktreeId, state: next })
+    },
+    [worktreeId]
+  )
+
+  const toggleLineageParent = useCallback(
+    (paneKey: string) => {
+      const base = readExpansionState(worktreeId)
+      const nextParents = new Set(base.collapsedLineageParents)
+      if (nextParents.has(paneKey)) {
+        nextParents.delete(paneKey)
+      } else {
+        nextParents.add(paneKey)
+      }
+      commit({ ...base, collapsedLineageParents: nextParents })
+    },
+    [commit, worktreeId]
+  )
+
+  const toggleCompactRootList = useCallback(() => {
+    const base = readExpansionState(worktreeId)
+    commit({ ...base, compactRootListExpanded: !base.compactRootListExpanded })
+  }, [commit, worktreeId])
+
+  return {
+    collapsedLineageParents: current.collapsedLineageParents,
+    compactRootListExpanded: current.compactRootListExpanded,
+    toggleLineageParent,
+    toggleCompactRootList
+  }
+}
+
+export function clearWorktreeAgentExpansionStateForTests(): void {
+  expansionByWorktreeId.clear()
+}
+
+export function getWorktreeAgentExpansionCountForTests(): number {
+  return expansionByWorktreeId.size
+}
+
+export function seedWorktreeAgentExpansionStateForTests(
+  worktreeId: string,
+  state: WorktreeAgentExpansionState
+): void {
+  persistExpansionState(worktreeId, state)
+}
diff --git a/src/renderer/src/lib/workspace-session.test.ts b/src/renderer/src/lib/workspace-session.test.ts
index 2e24a297132..ee2884ac400 100644
--- a/src/renderer/src/lib/workspace-session.test.ts
+++ b/src/renderer/src/lib/workspace-session.test.ts
@@ -176,18 +176,18 @@ describe('buildWorkspaceSessionPayload', () => {
     expect(payload.browserTabsByWorktree?.['wt-1'][0].loading).toBe(false)
   })
 
-  it('persists front-matter visibility only for restored editor files', () => {
+  it('persists front-matter hide overrides only for restored editor files', () => {
     const payload = buildWorkspaceSessionPayload(
       createSnapshot({
         markdownFrontmatterVisible: {
-          '/tmp/demo.ts': true,
-          '/tmp/demo.diff': true,
-          '/tmp/closed.md': true
+          '/tmp/demo.ts': false,
+          '/tmp/demo.diff': false,
+          '/tmp/closed.md': false
         }
       })
     )
 
-    expect(payload.markdownFrontmatterVisible).toEqual({ '/tmp/demo.ts': true })
+    expect(payload.markdownFrontmatterVisible).toEqual({ '/tmp/demo.ts': false })
   })
 
   it('does not persist empty split groups from transient simulator tab creation', () => {
diff --git a/src/renderer/src/lib/workspace-session.ts b/src/renderer/src/lib/workspace-session.ts
index 21a11eb0eec..f0acc22e620 100644
--- a/src/renderer/src/lib/workspace-session.ts
+++ b/src/renderer/src/lib/workspace-session.ts
@@ -188,10 +188,12 @@ export function buildEditorSessionData(
     WorkspaceVisibleTabType
   >
   const allEditFileIds = new Set(Object.values(editFileIdsByWorktree).flatMap((ids) => [...ids]))
+  // Why: preserve the actual value so per-file hide overrides survive restart;
+  // the map only ever carries `false` entries (visible is the default).
   const persistedMarkdownFrontmatterVisible = Object.fromEntries(
-    Object.keys(markdownFrontmatterVisible ?? {})
-      .filter((fileId) => allEditFileIds.has(fileId))
-      .map((fileId) => [fileId, true])
+    Object.entries(markdownFrontmatterVisible ?? {}).filter(([fileId]) =>
+      allEditFileIds.has(fileId)
+    )
   )
 
   return {
diff --git a/src/renderer/src/store/slices/editor.test.ts b/src/renderer/src/store/slices/editor.test.ts
index 0859e675615..ac54883ebe3 100644
--- a/src/renderer/src/store/slices/editor.test.ts
+++ b/src/renderer/src/store/slices/editor.test.ts
@@ -1482,7 +1482,7 @@ describe('createEditorSlice markdown view state', () => {
       },
       { preview: true }
     )
-    store.getState().setMarkdownFrontmatterVisible('/repo/docs/README.md', true)
+    store.getState().setMarkdownFrontmatterVisible('/repo/docs/README.md', false)
     store.getState().setMarkdownTableOfContentsVisible('/repo/docs/README.md', true)
 
     store.getState().openDiff('wt-1', '/repo/docs/guide.md', 'docs/guide.md', 'markdown', false, {
@@ -1512,7 +1512,7 @@ describe('createEditorSlice markdown view state', () => {
       worktreeId: 'wt-1',
       language: 'markdown'
     })
-    store.getState().setMarkdownFrontmatterVisible('/repo/docs/README.md', true)
+    store.getState().setMarkdownFrontmatterVisible('/repo/docs/README.md', false)
     store.getState().setMarkdownTableOfContentsVisible('/repo/docs/README.md', true)
 
     store.getState().openDiff('wt-1', '/repo/docs/guide.md', 'docs/guide.md', 'markdown', false, {
@@ -1520,7 +1520,7 @@ describe('createEditorSlice markdown view state', () => {
     })
 
     expect(store.getState().markdownFrontmatterVisible).toEqual({
-      '/repo/docs/README.md': true
+      '/repo/docs/README.md': false
     })
     expect(store.getState().markdownTableOfContentsVisible).toEqual({
       '/repo/docs/README.md': true
@@ -1573,28 +1573,28 @@ describe('createEditorSlice editor view mode', () => {
 })
 
 describe('createEditorSlice markdown frontmatter visibility (#4468)', () => {
-  it('stores visible=true as an explicit entry keyed by fileId', () => {
+  it('stores hidden=false as an explicit entry keyed by fileId', () => {
     const store = createEditorStore()
 
-    store.getState().setMarkdownFrontmatterVisible('/repo/notes.md', true)
-
-    expect(store.getState().markdownFrontmatterVisible).toEqual({ '/repo/notes.md': true })
-  })
-
-  it('deletes the entry when visibility resets to hidden', () => {
-    const store = createEditorStore()
-    store.getState().setMarkdownFrontmatterVisible('/repo/notes.md', true)
-
     store.getState().setMarkdownFrontmatterVisible('/repo/notes.md', false)
 
+    expect(store.getState().markdownFrontmatterVisible).toEqual({ '/repo/notes.md': false })
+  })
+
+  it('deletes the entry when visibility resets to visible', () => {
+    const store = createEditorStore()
+    store.getState().setMarkdownFrontmatterVisible('/repo/notes.md', false)
+
+    store.getState().setMarkdownFrontmatterVisible('/repo/notes.md', true)
+
     expect(store.getState().markdownFrontmatterVisible).toEqual({})
   })
 
-  it('is a no-op when hiding a file that was never shown', () => {
+  it('is a no-op when showing a file that was never hidden', () => {
     const store = createEditorStore()
     const before = store.getState().markdownFrontmatterVisible
 
-    store.getState().setMarkdownFrontmatterVisible('/repo/notes.md', false)
+    store.getState().setMarkdownFrontmatterVisible('/repo/notes.md', true)
 
     expect(store.getState().markdownFrontmatterVisible).toBe(before)
   })
@@ -1608,7 +1608,7 @@ describe('createEditorSlice markdown frontmatter visibility (#4468)', () => {
       language: 'markdown',
       mode: 'edit'
     })
-    store.getState().setMarkdownFrontmatterVisible('/repo/notes.md', true)
+    store.getState().setMarkdownFrontmatterVisible('/repo/notes.md', false)
 
     store.getState().closeFile('/repo/notes.md')
 
@@ -1630,11 +1630,11 @@ describe('createEditorSlice markdown frontmatter visibility (#4468)', () => {
       worktreeId: 'wt-1',
       language: 'markdown'
     })
-    store.getState().setMarkdownFrontmatterVisible('/repo/notes.md', true)
+    store.getState().setMarkdownFrontmatterVisible('/repo/notes.md', false)
 
     store.getState().closeFile('/repo/notes.md')
 
-    expect(store.getState().markdownFrontmatterVisible).toEqual({ '/repo/notes.md': true })
+    expect(store.getState().markdownFrontmatterVisible).toEqual({ '/repo/notes.md': false })
 
     store.getState().closeFile('markdown-preview::/repo/notes.md')
 
@@ -1662,7 +1662,7 @@ describe('createEditorSlice markdown frontmatter visibility (#4468)', () => {
       },
       { sourceFileId: '/repo/notes.md' }
     )
-    store.getState().setMarkdownFrontmatterVisible('/repo/notes.md', true)
+    store.getState().setMarkdownFrontmatterVisible('/repo/notes.md', false)
 
     store.getState().openFile(
       {
@@ -1675,7 +1675,7 @@ describe('createEditorSlice markdown frontmatter visibility (#4468)', () => {
       { preview: true }
     )
 
-    expect(store.getState().markdownFrontmatterVisible).toEqual({ '/repo/notes.md': true })
+    expect(store.getState().markdownFrontmatterVisible).toEqual({ '/repo/notes.md': false })
   })
 
   it('drops the visibility flag when all files are closed', () => {
@@ -1687,7 +1687,7 @@ describe('createEditorSlice markdown frontmatter visibility (#4468)', () => {
       language: 'markdown',
       mode: 'edit'
     })
-    store.getState().setMarkdownFrontmatterVisible('/repo/notes.md', true)
+    store.getState().setMarkdownFrontmatterVisible('/repo/notes.md', false)
 
     store.getState().closeAllFiles()
 
diff --git a/src/renderer/src/store/slices/editor.ts b/src/renderer/src/store/slices/editor.ts
index 8e9e86c0d93..7e825ec6f77 100644
--- a/src/renderer/src/store/slices/editor.ts
+++ b/src/renderer/src/store/slices/editor.ts
@@ -1405,11 +1405,11 @@ export const createEditorSlice: StateCreator<AppState, [], [], EditorSlice> = (s
   markdownFrontmatterVisible: {},
   setMarkdownFrontmatterVisible: (fileId, visible) =>
     set((s) => {
-      // Why: default is hidden. Writing `false` explicitly when no entry exists
-      // would grow the record unnecessarily; delete instead so the shape stays
-      // minimal and hydration round-trips cleanly — same trade-off as
-      // setEditorViewMode above.
-      if (!visible) {
+      // Why: default is visible. Writing `true` explicitly when no entry exists
+      // would grow the record unnecessarily; delete instead so the map only
+      // carries hide overrides and hydration round-trips cleanly — same
+      // trade-off as setEditorViewMode above.
+      if (visible) {
         if (!(fileId in s.markdownFrontmatterVisible)) {
           return s
         }
@@ -1417,7 +1417,7 @@ export const createEditorSlice: StateCreator<AppState, [], [], EditorSlice> = (s
         delete next[fileId]
         return { markdownFrontmatterVisible: next }
       }
-      return { markdownFrontmatterVisible: { ...s.markdownFrontmatterVisible, [fileId]: true } }
+      return { markdownFrontmatterVisible: { ...s.markdownFrontmatterVisible, [fileId]: false } }
     }),
 
   // Markdown table of contents visibility
@@ -4496,24 +4496,26 @@ export const createEditorSlice: StateCreator<AppState, [], [], EditorSlice> = (s
       const nextActiveTabType =
         nextActiveFileId || activeTabType !== 'editor' ? activeTabType : 'terminal'
       const openFileIds = new Set(openFiles.map((file) => file.id))
-      const visibleFrontmatterEntries = new Map<string, boolean>()
+      // Why: visible is the default, so only restore per-file hide overrides
+      // (`false`); legacy `true` entries collapse back to the default.
+      const hiddenFrontmatterEntries = new Map<string, boolean>()
       for (const [persistedFileId, visible] of Object.entries(
         persistedMarkdownFrontmatterVisible
       )) {
-        if (!visible) {
+        if (visible) {
           continue
         }
         if (openFileIds.has(persistedFileId)) {
-          visibleFrontmatterEntries.set(persistedFileId, true)
+          hiddenFrontmatterEntries.set(persistedFileId, false)
         }
         for (const migrations of Object.values(editorFileIdMigrationsByWorktree)) {
           const migratedFileId = migrations.get(persistedFileId)
           if (migratedFileId && openFileIds.has(migratedFileId)) {
-            visibleFrontmatterEntries.set(migratedFileId, true)
+            hiddenFrontmatterEntries.set(migratedFileId, false)
           }
         }
       }
-      const markdownFrontmatterVisible = Object.fromEntries(visibleFrontmatterEntries)
+      const markdownFrontmatterVisible = Object.fromEntries(hiddenFrontmatterEntries)
 
       return {
         openFiles,
diff --git a/src/renderer/src/store/slices/settings.test.ts b/src/renderer/src/store/slices/settings.test.ts
index dd113fa668a..ad4c4983b58 100644
--- a/src/renderer/src/store/slices/settings.test.ts
+++ b/src/renderer/src/store/slices/settings.test.ts
@@ -242,7 +242,7 @@ describe('createSettingsSlice runtime switching', () => {
       editorDrafts: { '/env-1/repo/stale.md': 'stale' },
       markdownViewMode: { '/env-1/repo/stale.md': 'rich' },
       editorViewMode: { '/env-1/repo/stale.md': 'changes' },
-      markdownFrontmatterVisible: { '/env-1/repo/stale.md': true },
+      markdownFrontmatterVisible: { '/env-1/repo/stale.md': false },
       editorCursorLine: { '/env-1/repo/stale.md': 4 },
       showDotfilesByWorktree: { 'repo-env-1::/env-1/repo': false },
       gitIgnoredPathsByWorktree: { 'repo-env-1::/env-1/repo': ['dist/'] },
@@ -300,7 +300,7 @@ describe('createSettingsSlice runtime switching', () => {
     expect(store.getState().markdownViewMode).toEqual({ '/env-1/repo/stale.md': 'rich' })
     expect(store.getState().editorViewMode).toEqual({ '/env-1/repo/stale.md': 'changes' })
     expect(store.getState().markdownFrontmatterVisible).toEqual({
-      '/env-1/repo/stale.md': true
+      '/env-1/repo/stale.md': false
     })
     expect(store.getState().editorCursorLine).toEqual({ '/env-1/repo/stale.md': 4 })
     expect(store.getState().showDotfilesByWorktree).toEqual({ 'repo-env-1::/env-1/repo': false })
diff --git a/src/renderer/src/store/slices/store-session-cascades.test.ts b/src/renderer/src/store/slices/store-session-cascades.test.ts
index 71d5778cf3f..69296c5cb20 100644
--- a/src/renderer/src/store/slices/store-session-cascades.test.ts
+++ b/src/renderer/src/store/slices/store-session-cascades.test.ts
@@ -2079,7 +2079,7 @@ describe('hydrateEditorSession', () => {
       },
       activeFileIdByWorktree: { [wt]: '/path/wt1/src/index.ts' },
       activeTabTypeByWorktree: { [wt]: 'editor' },
-      markdownFrontmatterVisible: { '/path/wt1/README.md': true }
+      markdownFrontmatterVisible: { '/path/wt1/README.md': false }
     })
 
     const s = store.getState()
@@ -2088,7 +2088,7 @@ describe('hydrateEditorSession', () => {
     expect(s.openFiles[0].mode).toBe('edit')
     expect(s.openFiles[0].isDirty).toBe(false)
     expect(s.openFiles[1].isPreview).toBe(true)
-    expect(s.markdownFrontmatterVisible).toEqual({ '/path/wt1/README.md': true })
+    expect(s.markdownFrontmatterVisible).toEqual({ '/path/wt1/README.md': false })
     expect(s.activeFileId).toBe('/path/wt1/src/index.ts')
     expect(s.activeTabType).toBe('editor')
   })
@@ -2167,10 +2167,46 @@ describe('hydrateEditorSession', () => {
         [FLOATING_TERMINAL_WORKTREE_ID]: filePath
       },
       activeTabTypeByWorktree: { [FLOATING_TERMINAL_WORKTREE_ID]: 'editor' },
+      markdownFrontmatterVisible: { [filePath]: false }
+    })
+
+    expect(store.getState().markdownFrontmatterVisible).toEqual({ [fileId]: false })
+  })
+
+  it('drops legacy visible=true front-matter entries so upgraded sessions fall back to the visible default', () => {
+    const store = createTestStore()
+    const filePath = '/orca/userData/floating-workspace/note.md'
+    const fileId = ownedEditorFileId(filePath, FLOATING_TERMINAL_WORKTREE_ID, null)
+
+    store.setState({ activeWorktreeId: FLOATING_TERMINAL_WORKTREE_ID })
+
+    store.getState().hydrateEditorSession({
+      activeRepoId: null,
+      activeWorktreeId: FLOATING_TERMINAL_WORKTREE_ID,
+      activeTabId: null,
+      tabsByWorktree: {},
+      terminalLayoutsByTabId: {},
+      openFilesByWorktree: {
+        [FLOATING_TERMINAL_WORKTREE_ID]: [
+          {
+            filePath,
+            relativePath: 'note.md',
+            worktreeId: FLOATING_TERMINAL_WORKTREE_ID,
+            language: 'markdown',
+            runtimeEnvironmentId: null
+          }
+        ]
+      },
+      activeFileIdByWorktree: {
+        [FLOATING_TERMINAL_WORKTREE_ID]: filePath
+      },
+      activeTabTypeByWorktree: { [FLOATING_TERMINAL_WORKTREE_ID]: 'editor' },
+      // Pre-flip sessions stored `true` for the (then non-default) visible state.
       markdownFrontmatterVisible: { [filePath]: true }
     })
 
-    expect(store.getState().markdownFrontmatterVisible).toEqual({ [fileId]: true })
+    expect(store.getState().markdownFrontmatterVisible).toEqual({})
+    expect(fileId in store.getState().markdownFrontmatterVisible).toBe(false)
   })
 
   it('falls back to the floating workspace file id when duplicate paths are owner-qualified', () => {
diff --git a/tests/e2e/worktree-lineage-agent-expansion.spec.ts b/tests/e2e/worktree-lineage-agent-expansion.spec.ts
new file mode 100644
index 00000000000..6662d7eafe0
--- /dev/null
+++ b/tests/e2e/worktree-lineage-agent-expansion.spec.ts
@@ -0,0 +1,112 @@
+import type { Page } from '@stablyai/playwright-test'
+import { mkdirSync } from 'node:fs'
+import { resolve } from 'node:path'
+import { test, expect } from './helpers/orca-app'
+import { waitForActiveWorktree, waitForSessionReady } from './helpers/store'
+import { seedLineageScenario } from './worktree-lineage-state'
+import { worktreeRow } from './worktree-row-locators'
+
+// Set ORCA_CAPTURE_EVIDENCE=1 to also write before/after screenshots to
+// pr-evidence/. Off by default so CI just runs the behavioral assertions.
+const CAPTURE_EVIDENCE = process.env.ORCA_CAPTURE_EVIDENCE === '1'
+const SHOT_DIR = resolve(process.cwd(), 'pr-evidence')
+
+async function captureSidebar(page: Page, name: string): Promise<void> {
+  if (!CAPTURE_EVIDENCE) {
+    return
+  }
+  mkdirSync(SHOT_DIR, { recursive: true })
+  await sidebar(page).screenshot({ path: resolve(SHOT_DIR, name) })
+}
+
+// Seed two independent root agents on the parent worktree so its card shows the
+// compact "2 agents" summary pill alongside the "N child workspaces" chip.
+async function seedTwoParentAgents(page: Page, worktreeId: string): Promise<void> {
+  await page.evaluate((worktreeId) => {
+    const store = window.__store
+    if (!store) {
+      throw new Error('window.__store is not available')
+    }
+    const state = store.getState()
+    if (!state.worktreeCardProperties.includes('inline-agents')) {
+      state.toggleWorktreeCardProperty('inline-agents')
+    }
+    while ((store.getState().tabsByWorktree[worktreeId] ?? []).length < 2) {
+      store.getState().createTab(worktreeId)
+    }
+    const tabs = (store.getState().tabsByWorktree[worktreeId] ?? []).slice(0, 2)
+    const now = Date.now()
+    const specs = [
+      { state: 'working' as const, prompt: 'Refactor auth middleware', agentType: 'claude' },
+      { state: 'done' as const, prompt: 'Write unit tests for parser', agentType: 'codex' }
+    ]
+    tabs.forEach((tab, index) => {
+      const spec = specs[index]!
+      const leafId = crypto.randomUUID()
+      store
+        .getState()
+        .setAgentStatus(
+          `${tab.id}:${leafId}`,
+          { state: spec.state, prompt: spec.prompt, agentType: spec.agentType },
+          spec.agentType,
+          { updatedAt: now, stateStartedAt: now }
+        )
+    })
+  }, worktreeId)
+}
+
+function sidebar(page: Page) {
+  return page.locator('[data-worktree-sidebar]').first()
+}
+
+function compactSummary(page: Page, parentId: string) {
+  return worktreeRow(page, parentId).locator('button.compact-agent-summary-button').first()
+}
+
+function childWorkspacesChip(page: Page, parentId: string) {
+  return worktreeRow(page, parentId)
+    .getByRole('button', { name: /child workspace/i })
+    .first()
+}
+
+test.describe('Worktree lineage agent-list expansion independence', () => {
+  test.describe.configure({ mode: 'serial' })
+
+  test.beforeEach(async ({ orcaPage }) => {
+    await waitForSessionReady(orcaPage)
+    await waitForActiveWorktree(orcaPage)
+  })
+
+  test('toggling child worktrees does not collapse the expanded agent summary', async ({
+    orcaPage
+  }) => {
+    const { parentId, childId } = await seedLineageScenario(orcaPage)
+    const parentRow = worktreeRow(orcaPage, parentId)
+    const childRow = worktreeRow(orcaPage, childId)
+
+    await parentRow.click()
+    await expect(parentRow).toHaveAttribute('aria-current', 'page')
+
+    await seedTwoParentAgents(orcaPage, parentId)
+
+    // Both sections present: the "2 agents" summary and the child-workspaces chip.
+    await expect(compactSummary(orcaPage, parentId)).toBeVisible({ timeout: 10_000 })
+    await expect(childWorkspacesChip(orcaPage, parentId)).toBeVisible()
+    await expect(childRow).toBeVisible()
+    await expect(compactSummary(orcaPage, parentId)).toHaveAttribute('aria-expanded', 'false')
+    await captureSidebar(orcaPage, '1-before-both-collapsed.png')
+
+    // Expand the agent summary.
+    await compactSummary(orcaPage, parentId).click()
+    await expect(compactSummary(orcaPage, parentId)).toHaveAttribute('aria-expanded', 'true')
+    await captureSidebar(orcaPage, '2-agents-expanded.png')
+
+    // Collapse the child worktrees via the chip. This remounts the parent card.
+    await childWorkspacesChip(orcaPage, parentId).click()
+    await expect(childRow).toBeHidden()
+
+    // FIXED: the agent summary stays expanded despite the card remount.
+    await expect(compactSummary(orcaPage, parentId)).toHaveAttribute('aria-expanded', 'true')
+    await captureSidebar(orcaPage, '3-after-children-toggle-agents-still-expanded.png')
+  })
+})