fix(ui): close review findings from the switch-and-scroll integration

- Markdown DOM cache: key includes a content-length fingerprint so an
  edited or reverted part re-materializing under the same id cannot
  restore stale DOM, memoization uses scalar identities instead of the
  part object (store reducers recreate part objects on unrelated updates,
  which re-ran the async render pipeline for identical content), and a
  probe with a mismatched locale/directory no longer destroys the entry
  it failed to claim.
- Sidebar bootstrap: the layout-level sync owner only knows known
  directories, so expanded projects bootstrapped serialized at background
  priority. The visible collection now publishes a second, expansion-
  aware demand owner, restoring concurrent hydration for expanded
  projects and worktree groups.
- Settings: local changes still sitting in the debounce buffer are not
  yet tracked as mutations, so a settings GET racing the debounce window
  briefly reverted them; reconciled results now reapply the pending
  buffer.

packages/ui/src/lib/persistence.ts

@@ -1884,12 +1884,22 @@ export const syncDesktopSettings = async (): Promise<void> => {
   // Each step is wrapped in try/catch so a failure in one side-effect (e.g.
   // a TypeError from writing to a contextBridge-protected global) doesn't
   // prevent server settings from reaching the Zustand store.
+  // Local changes sitting in the debounce buffer are not yet tracked as
+  // mutations (record() only stores while a request is in flight), so a GET
+  // racing the debounce window would briefly revert them. Reapply the
+  // pending buffer over every reconciled result.
+  const overlayPendingChanges = (settings: DesktopSettings): DesktopSettings => {
+    if (!_pendingSettingsChanges || !_pendingSettingsContext) return settings;
+    if (!isSettingsRuntimeContextCurrent(_pendingSettingsContext)) return settings;
+    return { ...settings, ..._pendingSettingsChanges };
+  };
+
   const applySettings = async (loadedSettings: DesktopSettings) => {
     if (!isSettingsRuntimeContextCurrent(context)) return;
-    let settings = _settingsMutationTracker.reconcile(loadedSettings, operation);
+    let settings = overlayPendingChanges(_settingsMutationTracker.reconcile(loadedSettings, operation));
     await waitForHydration();
     if (!isSettingsRuntimeContextCurrent(context)) return;
-    settings = _settingsMutationTracker.reconcile(loadedSettings, operation);
+    settings = overlayPendingChanges(_settingsMutationTracker.reconcile(loadedSettings, operation));
     const shouldPersistCraftGoalMigration = settings.draftStartersCraftGoalAdded !== true
       || settings.draftStartersScheduleTaskAdded !== true;
     // `autoSaveEnabled` is new to the settings backend. Until the server has a