refactor(font): replace fontCatalogStore singleton with lazy getFontCatalog

Swap the eagerly-constructed fontCatalogStore singleton for a lazy
getFontCatalog() accessor (plus __resetFontCatalog for tests), so the
InfiniteQueryObserver is created on first use rather than at module load.
Update the model barrels and all consumers (FontVirtualList, SampleList,
SampleListSection) to the accessor.

Also extract createFontLoadRequestConfig from FontVirtualList: it resolves a
font's URL for a weight and returns a 0-or-1 element array, letting callers
flatMap over a list to build load requests and drop unresolvable fonts in one
pass.

src/entities/Font/lib/createFontLoadRequestContfig/createFontLoadRequestContfig.test.ts

@@ -0,0 +1,111 @@
+import {
+    describe,
+    expect,
+    it,
+} from 'vitest';
+import type { UnifiedFont } from '../../model/types';
+import { createFontLoadRequestContfig } from './createFontLoadRequestContfig';
+
+/**
+ * Minimal UnifiedFont mock — override only the fields a case exercises.
+ */
+function createMockFont(overrides: Partial<UnifiedFont> = {}): UnifiedFont {
+    const baseFont: UnifiedFont = {
+        id: 'test-font',
+        name: 'Test Font',
+        provider: 'google',
+        category: 'sans-serif',
+        subsets: ['latin'],
+        variants: [],
+        styles: {},
+        metadata: {
+            cachedAt: Date.now(),
+        },
+        features: {
+            isVariable: false,
+            tags: [],
+        },
+    };
+
+    return { ...baseFont, ...overrides };
+}
+
+describe('createFontLoadRequestContfig', () => {
+    it('builds a single-element config when a URL resolves', () => {
+        const font = createMockFont({
+            id: 'roboto',
+            name: 'Roboto',
+            styles: { variants: { '400': 'https://example.com/roboto-400.woff2' } },
+        });
+
+        const result = createFontLoadRequestContfig(font, 400);
+
+        expect(result).toEqual([
+            {
+                id: 'roboto',
+                name: 'Roboto',
+                weight: 400,
+                url: 'https://example.com/roboto-400.woff2',
+                isVariable: false,
+            },
+        ]);
+    });
+
+    it('returns an empty array when no URL resolves (flatMap drops the font)', () => {
+        const font = createMockFont({ styles: {} });
+
+        expect(createFontLoadRequestContfig(font, 400)).toEqual([]);
+    });
+
+    it('forwards isVariable from font features', () => {
+        const font = createMockFont({
+            features: { isVariable: true, tags: [] },
+            styles: { variants: { '700': 'https://example.com/inter-vf.woff2' } },
+        });
+
+        const [config] = createFontLoadRequestContfig(font, 700);
+
+        expect(config.isVariable).toBe(true);
+    });
+
+    it('sets isVariable to undefined when features is absent', () => {
+        // features is non-optional on UnifiedFont, but upstream data can be partial —
+        // the optional chain must not throw, and isVariable stays undefined.
+        const font = createMockFont({
+            styles: { variants: { '400': 'https://example.com/font.woff2' } },
+        });
+        // @ts-expect-error — deliberately drop the guaranteed field to exercise the optional chain
+        font.features = undefined;
+
+        const [config] = createFontLoadRequestContfig(font, 400);
+
+        expect(config.isVariable).toBeUndefined();
+    });
+
+    it('uses the resolved fallback URL, not just exact matches', () => {
+        // getFontUrl falls back to styles.regular when the exact weight is missing;
+        // the config must carry whatever URL actually resolved.
+        const font = createMockFont({
+            styles: { regular: 'https://example.com/font-regular.woff2' },
+        });
+
+        const [config] = createFontLoadRequestContfig(font, 900);
+
+        expect(config.url).toBe('https://example.com/font-regular.woff2');
+        expect(config.weight).toBe(900);
+    });
+
+    it('carries the requested weight even when the URL is a shared fallback', () => {
+        const font = createMockFont({
+            styles: { variants: { '400': 'https://example.com/shared.woff2' } },
+        });
+
+        expect(createFontLoadRequestContfig(font, 700)[0].weight).toBe(700);
+    });
+
+    it('propagates the invalid-weight error from getFontUrl', () => {
+        const font = createMockFont();
+
+        expect(() => createFontLoadRequestContfig(font, 450)).toThrow('Invalid weight: 450');
+    });
+});

src/entities/Font/lib/createFontLoadRequestContfig/createFontLoadRequestContfig.ts

@@ -0,0 +1,33 @@
+import type {
+    FontLoadRequestConfig,
+    UnifiedFont,
+} from '../../model';
+import { getFontUrl } from '../getFontUrl/getFontUrl';
+
+/**
+ * Build the font-lifecycle load request for a single font at a given weight.
+ *
+ * Returns a 0-or-1 element array rather than `FontLoadRequestConfig | undefined`
+ * so call sites can `flatMap` over a font list — resolve the URL and drop fonts
+ * that have none in a single pass, with no separate filter step. An empty array
+ * means the font has no loadable asset for this weight (or its fallbacks) and is
+ * silently skipped.
+ *
+ * `isVariable` is forwarded from the font's features so the lifecycle manager can
+ * dedupe variable fonts per ID (they load once regardless of weight) while still
+ * loading static fonts per weight.
+ *
+ * @param font - Unified font to load
+ * @param weight - Numeric weight (100-900)
+ * @returns Single-element config array, or `[]` when no URL resolves
+ * @throws Error when weight is outside the valid 100-900 range (propagated from `getFontUrl`)
+ */
+export function createFontLoadRequestContfig(font: UnifiedFont, weight: number): FontLoadRequestConfig[] {
+    const url = getFontUrl(font, weight);
+
+    if (!url) {
+        return [];
+    }
+
+    return [{ id: font.id, name: font.name, weight, url, isVariable: font.features?.isVariable }];
+}

src/entities/Font/model/index.ts

@@ -1,3 +1,6 @@
 export * from './const/const';
+
+export { getFontCatalog } from './store';
+
 export * from './store';
 export * from './types';

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

@@ -483,8 +483,14 @@ export class FontCatalogStore {
     }
 }
 
-export function createFontCatalogStore(params: FontStoreParams = {}): FontCatalogStore {
-    return new FontCatalogStore(params);
+let _catalog: FontCatalogStore | undefined;
+
+export function getFontCatalog(): FontCatalogStore {
+    return (_catalog ??= new FontCatalogStore({ limit: 50 }));
 }
 
-export const fontCatalogStore = new FontCatalogStore({ limit: 50 });
+// test-only reset, so specs don't share a live observer
+export function __resetFontCatalog() {
+    _catalog?.destroy();
+    _catalog = undefined;
+}

src/entities/Font/model/store/index.ts

@@ -2,11 +2,9 @@
 export * from './fontLifecycleManager/fontLifecycleManager.svelte';
 
 // Paginated catalog
-export {
-    createFontCatalogStore,
-    FontCatalogStore,
-    fontCatalogStore,
-} from './fontCatalogStore/fontCatalogStore.svelte';
+export { getFontCatalog } from './fontCatalogStore/fontCatalogStore.svelte';
+
+export type { FontCatalogStore } from './fontCatalogStore/fontCatalogStore.svelte';
 
 // Batch fetch by IDs (detail-cache seeding)
 export { FontsByIdsStore } from './fontsByIdsStore/fontsByIdsStore.svelte';

src/entities/Font/ui/FontVirtualList/FontVirtualList.svelte

@@ -5,21 +5,18 @@
 -->
 <script lang="ts">
 import { debounce } from '$shared/lib/utils';
-import {
-    Skeleton,
-    VirtualList,
-} from '$shared/ui';
+import { VirtualList } from '$shared/ui';
 import type {
     ComponentProps,
     Snippet,
 } from 'svelte';
 import { fade } from 'svelte/transition';
-import { getFontUrl } from '../../lib';
+import { createFontLoadRequestContfig } from '../../lib/createFontLoadRequestContfig/createFontLoadRequestContfig';
 import {
     type FontLoadRequestConfig,
     type UnifiedFont,
-    fontCatalogStore,
     fontLifecycleManager,
+    getFontCatalog,
 } from '../../model';
 
 interface Props extends
@@ -55,17 +52,27 @@ let {
     ...rest
 }: Props = $props();
 
-const isLoading = $derived(
-    fontCatalogStore.isFetching || fontCatalogStore.isLoading,
-);
+const fontCatalog = getFontCatalog();
+
+const isLoading = $derived<boolean>(fontCatalog?.isLoading);
+const isFetching = $derived<boolean>(fontCatalog.isFetching);
+const hasMore = $derived<boolean>(fontCatalog?.pagination?.hasMore);
+const fonts = $derived<UnifiedFont[]>(fontCatalog.fonts);
+const total = $derived<number>(fontCatalog?.pagination.total);
 
 let visibleFonts = $state<UnifiedFont[]>([]);
-let isCatchingUp = $state(false);
+let isCatchingUp = $state<boolean>(false);
 
-const showInitialSkeleton = $derived(!!skeleton && isLoading && fontCatalogStore.fonts.length === 0);
-const showCatchupSkeleton = $derived(!!skeleton && isCatchingUp);
+const showInitialSkeleton = $derived.by(() => (
+    !!skeleton && (isLoading || isFetching) && fontCatalog.fonts.length === 0
+));
+const showCatchupSkeleton = $derived.by(() => (
+    !!skeleton && isCatchingUp
+));
 // Settled query with no matches — empty state replaces the (otherwise blank) list.
-const showEmpty = $derived(!!empty && !isLoading && !isCatchingUp && fontCatalogStore.fonts.length === 0);
+const showEmpty = $derived.by(() => (
+    !!empty && !(isLoading || isFetching) && !isCatchingUp && fontCatalog.fonts.length === 0
+));
 
 function handleInternalVisibleChange(items: UnifiedFont[]) {
     visibleFonts = items;
@@ -79,12 +86,12 @@ function handleInternalVisibleChange(items: UnifiedFont[]) {
  * font files for thousands of intermediate fonts.
  */
 async function handleJump(targetIndex: number) {
-    if (isCatchingUp || !fontCatalogStore.pagination.hasMore) {
+    if (isCatchingUp || !hasMore) {
         return;
     }
     isCatchingUp = true;
     try {
-        await fontCatalogStore.fetchAllPagesTo(targetIndex);
+        await fontCatalog.fetchAllPagesTo(targetIndex);
     } finally {
         isCatchingUp = false;
     }
@@ -105,13 +112,7 @@ $effect(() => {
     if (isCatchingUp) {
         return;
     }
-    const configs: FontLoadRequestConfig[] = visibleFonts.flatMap(item => {
-        const url = getFontUrl(item, weight);
-        if (!url) {
-            return [];
-        }
-        return [{ id: item.id, name: item.name, weight, url, isVariable: item.features?.isVariable }];
-    });
+    const configs = visibleFonts.flatMap(item => createFontLoadRequestContfig(item, weight));
     if (configs.length > 0) {
         debouncedTouch(configs);
     }
@@ -137,13 +138,11 @@ $effect(() => {
  * Load more fonts by moving to the next page
  */
 function loadMore() {
-    if (
-        !fontCatalogStore.pagination.hasMore
-        || fontCatalogStore.isFetching
-    ) {
+    if (!hasMore || isFetching) {
         return;
     }
-    fontCatalogStore.nextPage();
+
+    fontCatalog.nextPage();
 }
 
 /**
@@ -153,12 +152,10 @@ function loadMore() {
  * of the loaded items. Only fetches if there are more pages available.
  */
 function handleNearBottom(_lastVisibleIndex: number) {
-    const { hasMore } = fontCatalogStore.pagination;
-
     // VirtualList already checks if we're near the bottom of loaded items.
     // Guard isCatchingUp: fetchAllPagesTo bypasses TQ so isFetching stays false
     // during batch catch-up, which would otherwise let nextPage() race with it.
-    if (hasMore && !fontCatalogStore.isFetching && !isCatchingUp) {
+    if (hasMore && !isFetching && !isCatchingUp) {
         loadMore();
     }
 }
@@ -177,9 +174,9 @@ function handleNearBottom(_lastVisibleIndex: number) {
     {:else}
         <!-- VirtualList persists during pagination - no destruction/recreation -->
         <VirtualList
-            items={fontCatalogStore.fonts}
-            total={fontCatalogStore.pagination.total}
-            isLoading={isLoading || isCatchingUp}
+            items={fonts}
+            {total}
+            isLoading={isLoading || isFetching || isCatchingUp}
             onVisibleItemsChange={handleInternalVisibleChange}
             onNearBottom={handleNearBottom}
             onJump={handleJump}

src/widgets/SampleList/ui/SampleList/SampleList.svelte

@@ -10,8 +10,8 @@ import {
     createFontRowSizeResolver,
 } from '$entities/Font';
 import {
-    fontCatalogStore,
     fontLifecycleManager,
+    getFontCatalog,
 } from '$entities/Font/model';
 import {
     TypographyMenu,
@@ -22,6 +22,8 @@ import { throttle } from '$shared/lib/utils';
 import { Skeleton } from '$shared/ui';
 import { layoutManager } from '../../model';
 
+const fontCatalog = getFontCatalog();
+
 // FontSampler chrome heights — derived from Tailwind classes in FontSampler.svelte.
 // Header: py-3 (12+12px padding) + ~32px content row ≈ 56px.
 // Only the header is counted; the mobile footer (md:hidden) is excluded because
@@ -44,14 +46,16 @@ const SAMPLER_FALLBACK_HEIGHT = 220;
  */
 const CHECK_POSITION_THROTTLE_MS = 100;
 
-let text = $state('The quick brown fox jumps over the lazy dog...');
+const fonts = $derived(fontCatalog?.fonts);
+
+let text = $state<string>('The quick brown fox jumps over the lazy dog...');
 let wrapper = $state<HTMLDivElement | null>(null);
 // Binds to the actual window height
-let innerHeight = $state(0);
+let innerHeight = $state<number>(0);
 // Is the component above the middle of the viewport?
-let isAboveMiddle = $state(false);
+let isAboveMiddle = $state<boolean>(false);
 // Inner width of the wrapper div — updated by bind:clientWidth on mount and resize.
-let containerWidth = $state(0);
+let containerWidth = $state<number>(0);
 
 const checkPosition = throttle(() => {
     if (!wrapper) {
@@ -69,7 +73,7 @@ const checkPosition = throttle(() => {
 // change triggers a full offsets recompute in createVirtualizer — no DOM snap.
 const fontRowHeight = $derived.by(() =>
     createFontRowSizeResolver({
-        getFonts: () => fontCatalogStore.fonts,
+        getFonts: () => fonts,
         getWeight: () => typographySettingsStore.weight,
         getPreviewText: () => text,
         getContainerWidth: () => containerWidth,

src/widgets/SampleList/ui/SampleListSection/SampleListSection.svelte

@@ -3,7 +3,7 @@
     Wraps SampleList with a Section component
 -->
 <script lang="ts">
-import { fontCatalogStore } from '$entities/Font/model';
+import { getFontCatalog } from '$entities/Font/model';
 import { NavigationWrapper } from '$features/Breadcrumb';
 import type { ResponsiveManager } from '$shared/lib';
 import { cn } from '$shared/lib';
@@ -26,6 +26,9 @@ interface Props {
 const { index }: Props = $props();
 
 const responsive = getContext<ResponsiveManager>('responsive');
+
+const fontCatalog = getFontCatalog();
+const total = $derived<number>(fontCatalog?.pagination?.total);
 </script>
 
 <NavigationWrapper index={2} title="Samples">
@@ -36,7 +39,7 @@ const responsive = getContext<ResponsiveManager>('responsive');
             id="sample_set"
             title="Sample Set"
             headerTitle="visual_output"
-            headerSubtitle="items_total: {fontCatalogStore.pagination.total ?? 0}"
+            headerSubtitle="items_total: {total ?? 0}"
             headerAction={registerAction}
         >
             {#snippet headerContent()}