refactor: adopt createSingleton across the remaining stores

Replace the hand-rolled let _x / getX / __resetX boilerplate with the
createSingleton helper in all nine remaining singleton stores. Exposed
accessor names (getX, __resetX) are unchanged, so consumers and specs are
unaffected. Teardown wired to each stores destroy() where it has one
(fontCatalog, fontLifecycle, typography, availableFilter, theme, layout,
scrollBreadcrumbs); sort and appliedFilter have no teardown. Also merges
layoutStores duplicate $shared/lib imports.

src/entities/Font/model/store/fontCatalogStore/fontCatalogStore.svelte.ts

@@ -3,6 +3,7 @@ import {
     DEFAULT_QUERY_STALE_TIME_MS,
     getQueryClient,
 } from '$shared/api/queryClient';
+import { createSingleton } from '$shared/lib/helpers/createSingleton/createSingleton';
 import {
     type InfiniteData,
     InfiniteQueryObserver,
@@ -483,14 +484,12 @@ export class FontCatalogStore {
     }
 }
 
-let _catalog: FontCatalogStore | undefined;
+const catalog = createSingleton(
+    () => new FontCatalogStore({ limit: 50 }),
+    instance => instance.destroy(),
+);
 
-export function getFontCatalog(): FontCatalogStore {
+export const getFontCatalog = catalog.get;
-    return (_catalog ??= new FontCatalogStore({ limit: 50 }));
-}
 
 // test-only reset, so specs don't share a live observer
-export function __resetFontCatalog() {
+export const __resetFontCatalog = catalog.reset;
-    _catalog?.destroy();
-    _catalog = undefined;
-}

src/entities/Font/model/store/fontLifecycleManager/fontLifecycleManager.svelte.ts

@@ -1,3 +1,4 @@
+import { createSingleton } from '$shared/lib/helpers/createSingleton/createSingleton';
 import { SvelteMap } from 'svelte/reactivity';
 import {
     type FontLoadRequestConfig,
@@ -419,18 +420,16 @@ export class FontLifecycleManager {
     }
 }
 
-let _fontLifecycleManager: FontLifecycleManager | undefined;
-
 /**
  * App-wide font lifecycle manager, created on first access. Lazy so its
  * AbortController / FontFace bookkeeping isn't set up at module load.
  */
-export function getFontLifecycleManager(): FontLifecycleManager {
+const fontLifecycleManager = createSingleton(
-    return (_fontLifecycleManager ??= new FontLifecycleManager());
+    () => new FontLifecycleManager(),
-}
+    instance => instance.destroy(),
+);
+
+export const getFontLifecycleManager = fontLifecycleManager.get;
 
 // test-only reset, so specs don't share loaded-font/eviction state
-export function __resetFontLifecycleManager() {
+export const __resetFontLifecycleManager = fontLifecycleManager.reset;
-    _fontLifecycleManager?.destroy();
-    _fontLifecycleManager = undefined;
-}

src/features/AdjustTypography/model/store/typographySettingsStore/typographySettingsStore.svelte.ts

@@ -19,6 +19,7 @@ import {
 import {
     type PersistentStore,
     createPersistentStore,
+    createSingleton,
 } from '$shared/lib';
 import type { NumericControl } from '$shared/ui';
 import { SvelteMap } from 'svelte/reactivity';
@@ -349,22 +350,17 @@ export function createTypographySettingsStore(
 
 export type TypographySettingsStoreInstance = ReturnType<typeof createTypographySettingsStore>;
 
-let _typographySettingsStore: TypographySettingsStoreInstance | undefined;
-
 /**
  * App-wide typography settings store, keyed for the comparison view.
  * Created on first access so its persistent-store sync effects aren't set up
  * at module load.
  */
-export function getTypographySettingsStore(): TypographySettingsStoreInstance {
+const typographySettingsStore = createSingleton(
-    return (_typographySettingsStore ??= createTypographySettingsStore(
+    () => createTypographySettingsStore(DEFAULT_TYPOGRAPHY_CONTROLS_DATA, COMPARISON_STORAGE_KEY),
-        DEFAULT_TYPOGRAPHY_CONTROLS_DATA,
+    instance => instance.destroy(),
-        COMPARISON_STORAGE_KEY,
+);
-    ));
+
-}
+export const getTypographySettingsStore = typographySettingsStore.get;
 
 // test-only reset, so specs don't share persisted typography state or leak effects
-export function __resetTypographySettingsStore() {
+export const __resetTypographySettingsStore = typographySettingsStore.reset;
-    _typographySettingsStore?.destroy();
-    _typographySettingsStore = undefined;
-}

src/features/Breadcrumb/model/store/scrollBreadcrumbsStore.svelte.ts

@@ -1,3 +1,5 @@
+import { createSingleton } from '$shared/lib/helpers/createSingleton/createSingleton';
+
 /**
  * Scroll-based breadcrumb tracking store
  *
@@ -279,17 +281,15 @@ export function createScrollBreadcrumbsStore(): ScrollBreadcrumbsStore {
     return new ScrollBreadcrumbsStore();
 }
 
-let _scrollBreadcrumbsStore: ScrollBreadcrumbsStore | undefined;
-
 /**
  * App-wide scroll breadcrumbs store, created on first access.
  */
-export function getScrollBreadcrumbsStore(): ScrollBreadcrumbsStore {
+const scrollBreadcrumbsStore = createSingleton(
-    return (_scrollBreadcrumbsStore ??= createScrollBreadcrumbsStore());
+    () => createScrollBreadcrumbsStore(),
-}
+    instance => instance.destroy(),
+);
+
+export const getScrollBreadcrumbsStore = scrollBreadcrumbsStore.get;
 
 // test-only reset, so specs don't share observer/scroll state
-export function __resetScrollBreadcrumbsStore() {
+export const __resetScrollBreadcrumbsStore = scrollBreadcrumbsStore.reset;
-    _scrollBreadcrumbsStore?.destroy();
-    _scrollBreadcrumbsStore = undefined;
-}

src/features/ChangeAppTheme/model/store/ThemeManager/ThemeManager.svelte.ts

@@ -28,7 +28,10 @@
  * ```
  */
 
-import { createPersistentStore } from '$shared/lib';
+import {
+    createPersistentStore,
+    createSingleton,
+} from '$shared/lib';
 
 export const STORAGE_KEY = 'glyphdiff:theme';
 
@@ -195,23 +198,18 @@ class ThemeManager {
     }
 }
 
-let _themeManager: ThemeManager | undefined;
-
 /**
  * App-wide theme manager, created on first access.
  *
  * Lazy so its persistent-store subscription isn't set up at module load.
  * Call init() on mount and destroy() on unmount (see Layout).
  */
-export function getThemeManager(): ThemeManager {
+const themeManager = createSingleton(() => new ThemeManager(), instance => instance.destroy());
-    return (_themeManager ??= new ThemeManager());
+
-}
+export const getThemeManager = themeManager.get;
 
 // test-only reset, so specs don't share persisted theme state
-export function __resetThemeManager() {
+export const __resetThemeManager = themeManager.reset;
-    _themeManager?.destroy();
-    _themeManager = undefined;
-}
 
 /**
  * ThemeManager class exported for testing purposes

src/features/FilterAndSortFonts/model/store/appliedFilterStore/appliedFilterStore.svelte.ts

@@ -23,7 +23,10 @@
  * ```
  */
 
-import { createFilter } from '$shared/lib';
+import {
+    createFilter,
+    createSingleton,
+} from '$shared/lib';
 import { createDebouncedState } from '$shared/lib/helpers';
 import type {
     FilterConfig,
@@ -129,8 +132,6 @@ export function createAppliedFilterStore<TValue extends string>(config: FilterCo
 
 export type AppliedFilterStore = ReturnType<typeof createAppliedFilterStore>;
 
-let _appliedFilterStore: AppliedFilterStore | undefined;
-
 /**
  * App-wide filter manager, created on first access.
  *
@@ -138,14 +139,14 @@ let _appliedFilterStore: AppliedFilterStore | undefined;
  * lives in `./bindings.svelte` and populates groups once backend filter
  * metadata arrives.
  */
-export function getAppliedFilterStore(): AppliedFilterStore {
+const appliedFilterStore = createSingleton(() =>
-    return (_appliedFilterStore ??= createAppliedFilterStore<string>({
+    createAppliedFilterStore<string>({
         queryValue: '',
         groups: [],
-    }));
+    })
-}
+);
+
+export const getAppliedFilterStore = appliedFilterStore.get;
 
 // test-only reset, so specs don't share filter/selection state
-export function __resetAppliedFilterStore() {
+export const __resetAppliedFilterStore = appliedFilterStore.reset;
-    _appliedFilterStore = undefined;
-}

src/features/FilterAndSortFonts/model/store/availableFilterStore/availableFilterStore.svelte.ts

@@ -22,6 +22,7 @@ import {
     DEFAULT_QUERY_STALE_TIME_MS,
     getQueryClient,
 } from '$shared/api/queryClient';
+import { createSingleton } from '$shared/lib/helpers/createSingleton/createSingleton';
 import {
     type QueryKey,
     QueryObserver,
@@ -126,18 +127,16 @@ export class AvailableFilterStore {
     }
 }
 
-let _availableFilterStore: AvailableFilterStore | undefined;
-
 /**
  * App-wide filter-metadata store, created on first access. Lazy so the
  * QueryObserver isn't constructed at module load.
  */
-export function getAvailableFilterStore(): AvailableFilterStore {
+const availableFilterStore = createSingleton(
-    return (_availableFilterStore ??= new AvailableFilterStore());
+    () => new AvailableFilterStore(),
-}
+    instance => instance.destroy(),
+);
+
+export const getAvailableFilterStore = availableFilterStore.get;
 
 // test-only reset, so specs don't share a live observer
-export function __resetAvailableFilterStore() {
+export const __resetAvailableFilterStore = availableFilterStore.reset;
-    _availableFilterStore?.destroy();
-    _availableFilterStore = undefined;
-}

src/features/FilterAndSortFonts/model/store/sortStore/sortStore.svelte.ts

@@ -1,3 +1,5 @@
+import { createSingleton } from '$shared/lib/helpers/createSingleton/createSingleton';
+
 /**
  * Sort store — manages the current sort option for font listings.
  *
@@ -46,16 +48,12 @@ export function createSortStore(initial: SortOption = 'Popularity') {
 
 export type SortStore = ReturnType<typeof createSortStore>;
 
-let _sortStore: SortStore | undefined;
-
 /**
  * App-wide sort store, created on first access.
  */
-export function getSortStore(): SortStore {
+const sortStore = createSingleton(() => createSortStore());
-    return (_sortStore ??= createSortStore());
+
-}
+export const getSortStore = sortStore.get;
 
 // test-only reset, so specs don't share selection state
-export function __resetSortStore() {
+export const __resetSortStore = sortStore.reset;
-    _sortStore = undefined;
-}

src/widgets/SampleList/model/stores/layoutStore/layoutStore.svelte.ts

@@ -16,8 +16,11 @@
  * - Desktop Large (>= 1280px): 4 columns
  */
 
-import { createPersistentStore } from '$shared/lib';
+import {
-import { responsiveManager } from '$shared/lib';
+    createPersistentStore,
+    createSingleton,
+    responsiveManager,
+} from '$shared/lib';
 
 export type LayoutMode = 'list' | 'grid';
 
@@ -153,20 +156,16 @@ class LayoutManager {
     }
 }
 
-let _layoutManager: LayoutManager | undefined;
-
 /**
  * App-wide layout manager, created on first access. Lazy so its persisted
  * layout preference isn't read at module load.
  */
-export function getLayoutManager(): LayoutManager {
+const layoutManager = createSingleton(() => new LayoutManager(), instance => instance.destroy());
-    return (_layoutManager ??= new LayoutManager());
+
-}
+export const getLayoutManager = layoutManager.get;
 
 // test-only reset, so specs don't share persisted layout state
-export function __resetLayoutManager() {
+export const __resetLayoutManager = layoutManager.reset;
-    _layoutManager = undefined;
-}
 
 // Export class for testing purposes
 export { LayoutManager };