Merge pull request 'feature/test-coverage' (#27) from feature/test-coverage into main

Reviewed-on: #27

.storybook/Decorator.svelte

@@ -0,0 +1,29 @@
+<!--
+    Component: Decorator
+    Global Storybook decorator that wraps all stories with necessary providers.
+
+    This provides:
+    - ResponsiveManager context for breakpoint tracking
+    - TooltipProvider for shadcn Tooltip components
+-->
+<script lang="ts">
+import { createResponsiveManager } from '$shared/lib';
+import type { ResponsiveManager } from '$shared/lib';
+import { Provider as TooltipProvider } from '$shared/shadcn/ui/tooltip';
+import { setContext } from 'svelte';
+
+interface Props {
+    children: import('svelte').Snippet;
+}
+
+let { children }: Props = $props();
+
+// Create and provide responsive context
+const responsiveManager = createResponsiveManager();
+$effect(() => responsiveManager.init());
+setContext<ResponsiveManager>('responsive', responsiveManager);
+</script>
+
+<TooltipProvider delayDuration={200} skipDelayDuration={300}>
+    {@render children()}
+</TooltipProvider>

.storybook/StoryStage.svelte

@@ -7,9 +7,9 @@ interface Props {
 let { children, width = 'max-w-3xl' }: Props = $props();
 </script>
 
-<div class="flex min-h-screen w-full items-center justify-center bg-slate-50 p-8">
-    <div class="w-full bg-white shadow-xl ring-1 ring-slate-200 rounded-xl p-12 {width}">
-        <div class="relative flex justify-center items-center">
+<div class="flex min-h-screen w-full items-center justify-center bg-background p-8">
+    <div class="w-full bg-card shadow-lg ring-1 ring-border rounded-xl p-12 {width}">
+        <div class="relative flex justify-center items-center text-foreground">
             {@render children()}
         </div>
     </div>

.storybook/main.ts

@@ -21,7 +21,8 @@ const config: StorybookConfig = {
         {
             name: '@storybook/addon-svelte-csf',
             options: {
-                legacyTemplate: true, // Enables the legacy template syntax
+                // Use modern template syntax for better performance
+                legacyTemplate: false,
             },
         },
         '@chromatic-com/storybook',

.storybook/preview-head.html

@@ -0,0 +1,13 @@
+<link rel="preconnect" href="https://api.fontshare.com" />
+<link rel="preconnect" href="https://cdn.fontshare.com" crossorigin="anonymous" />
+<link rel="preconnect" href="https://fonts.googleapis.com" />
+<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin="anonymous" />
+<link
+    rel="stylesheet"
+    href="https://fonts.googleapis.com/css2?family=Barlow:ital,wght@0,100;0,200;1,100;1,200&family=Karla:wght@200..800&family=Major+Mono+Display&display=swap"
+/>
+<style>
+    body {
+        font-family: "Karla", system-ui, -apple-system, "Segoe UI", Inter, Roboto, Arial, sans-serif;
+    }
+</style>

.storybook/preview.ts

@@ -1,4 +1,5 @@
 import type { Preview } from '@storybook/svelte-vite';
+import Decorator from './Decorator.svelte';
 import StoryStage from './StoryStage.svelte';
 import '../src/app/styles/app.css';
 
@@ -23,25 +24,41 @@ const preview: Preview = {
             story: {
                 // This sets the default height for the iframe in Autodocs
                 iframeHeight: '400px',
-                // Ensure the story isn't forced into a tiny inline box
-                // inline: true,
             },
         },
+
+        head: `
+            <link rel="preconnect" href="https://api.fontshare.com" />
+            <link rel="preconnect" href="https://cdn.fontshare.com" crossorigin="anonymous" />
+            <link rel="preconnect" href="https://fonts.googleapis.com" />
+            <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin="anonymous" />
+            <link
+                rel="stylesheet"
+                href="https://fonts.googleapis.com/css2?family=Barlow:ital,wght@0,100;0,200;1,100;1,200&family=Karla:wght@200..800&family=Major+Mono+Display&display=swap"
+            />
+            <style>
+                body {
+                    font-family: "Karla", system-ui, -apple-system, "Segoe UI", Inter, Roboto, Arial, sans-serif;
+                }
+            </style>
+        `,
     },
+
     decorators: [
-        (storyFn, { parameters }) => {
-            const { Component, props } = storyFn();
-            return {
-                Component: StoryStage,
-                // We pass the actual story component into the Stage via a snippet/slot
-                // Svelte 5 Storybook handles this mapping internally when you return this structure
-                props: {
-                    children: Component,
-                    width: parameters.stageWidth || 'max-w-3xl',
-                    ...props,
-                },
-            };
-        },
+        // Wrap with providers (TooltipProvider, ResponsiveManager)
+        story => ({
+            Component: Decorator,
+            props: {
+                children: story(),
+            },
+        }),
+        // Wrap with StoryStage for presentation styling
+        story => ({
+            Component: StoryStage,
+            props: {
+                children: story(),
+            },
+        }),
     ],
 };
 

src/app/styles/app.css

@@ -167,7 +167,8 @@
   --color-gradient-from: var(--gradient-from);
   --color-gradient-via: var(--gradient-via);
   --color-gradient-to: var(--gradient-to);
-  --font-mono: var(--font-mono);
+  --font-mono: 'Major Mono Display', monospace;
+  --font-sans: 'Karla', system-ui, -apple-system, 'Segoe UI', Inter, Roboto, Arial, sans-serif;
 }
 
 @layer base {

src/entities/Font/index.ts

@@ -78,6 +78,56 @@ export {
     unifiedFontStore,
 } from './model';
 
+// Mock data helpers for Storybook and testing
+export {
+    createCategoriesFilter,
+    createErrorState,
+    createGenericFilter,
+    createLoadingState,
+    createMockComparisonStore,
+    // Filter mocks
+    createMockFilter,
+    createMockFontApiResponse,
+    createMockFontStoreState,
+    // Store mocks
+    createMockQueryState,
+    createMockReactiveState,
+    createMockStore,
+    createProvidersFilter,
+    createSubsetsFilter,
+    createSuccessState,
+    FONTHARE_FONTS,
+    generateMixedCategoryFonts,
+    generateMockFonts,
+    generatePaginatedFonts,
+    generateSequentialFilter,
+    GENERIC_FILTERS,
+    getAllMockFonts,
+    getFontsByCategory,
+    getFontsByProvider,
+    GOOGLE_FONTS,
+    MOCK_FILTERS,
+    MOCK_FILTERS_ALL_SELECTED,
+    MOCK_FILTERS_EMPTY,
+    MOCK_FILTERS_SELECTED,
+    MOCK_FONT_STORE_STATES,
+    MOCK_STORES,
+    type MockFilterOptions,
+    type MockFilters,
+    mockFontshareFont,
+    type MockFontshareFontOptions,
+    type MockFontStoreState,
+    // Font mocks
+    mockGoogleFont,
+    // Types
+    type MockGoogleFontOptions,
+    type MockQueryObserverResult,
+    type MockQueryState,
+    mockUnifiedFont,
+    type MockUnifiedFontOptions,
+    UNIFIED_FONTS,
+} from './lib/mocks';
+
 // UI elements
 export {
     FontApplicator,

src/entities/Font/lib/index.ts

@@ -6,3 +6,53 @@ export {
 } from './normalize/normalize';
 
 export { getFontUrl } from './getFontUrl/getFontUrl';
+
+// Mock data helpers for Storybook and testing
+export {
+    createCategoriesFilter,
+    createErrorState,
+    createGenericFilter,
+    createLoadingState,
+    createMockComparisonStore,
+    // Filter mocks
+    createMockFilter,
+    createMockFontApiResponse,
+    createMockFontStoreState,
+    // Store mocks
+    createMockQueryState,
+    createMockReactiveState,
+    createMockStore,
+    createProvidersFilter,
+    createSubsetsFilter,
+    createSuccessState,
+    FONTHARE_FONTS,
+    generateMixedCategoryFonts,
+    generateMockFonts,
+    generatePaginatedFonts,
+    generateSequentialFilter,
+    GENERIC_FILTERS,
+    getAllMockFonts,
+    getFontsByCategory,
+    getFontsByProvider,
+    GOOGLE_FONTS,
+    MOCK_FILTERS,
+    MOCK_FILTERS_ALL_SELECTED,
+    MOCK_FILTERS_EMPTY,
+    MOCK_FILTERS_SELECTED,
+    MOCK_FONT_STORE_STATES,
+    MOCK_STORES,
+    type MockFilterOptions,
+    type MockFilters,
+    mockFontshareFont,
+    type MockFontshareFontOptions,
+    type MockFontStoreState,
+    // Font mocks
+    mockGoogleFont,
+    // Types
+    type MockGoogleFontOptions,
+    type MockQueryObserverResult,
+    type MockQueryState,
+    mockUnifiedFont,
+    type MockUnifiedFontOptions,
+    UNIFIED_FONTS,
+} from './mocks';

src/entities/Font/lib/mocks/filters.mock.ts

@@ -0,0 +1,348 @@
+/**
+ * ============================================================================
+ * MOCK FONT FILTER DATA
+ * ============================================================================
+ *
+ * Factory functions and preset mock data for font-related filters.
+ * Used in Storybook stories for font filtering components.
+ *
+ * ## Usage
+ *
+ * ```ts
+ * import {
+ *     createMockFilter,
+ *     MOCK_FILTERS,
+ * } from '$entities/Font/lib/mocks';
+ *
+ * // Create a custom filter
+ * const customFilter = createMockFilter({
+ *     properties: [
+ *         { id: 'option1', name: 'Option 1', value: 'option1' },
+ *         { id: 'option2', name: 'Option 2', value: 'option2', selected: true },
+ *     ],
+ * });
+ *
+ * // Use preset filters
+ * const categoriesFilter = MOCK_FILTERS.categories;
+ * const subsetsFilter = MOCK_FILTERS.subsets;
+ * ```
+ */
+
+import type {
+    FontCategory,
+    FontProvider,
+    FontSubset,
+} from '$entities/Font/model/types';
+import type { Property } from '$shared/lib';
+import { createFilter } from '$shared/lib';
+
+// ============================================================================
+// TYPE DEFINITIONS
+// ============================================================================
+
+/**
+ * Options for creating a mock filter
+ */
+export interface MockFilterOptions {
+    /** Filter properties */
+    properties: Property<string>[];
+}
+
+/**
+ * Preset mock filters for font filtering
+ */
+export interface MockFilters {
+    /** Provider filter (Google, Fontshare) */
+    providers: ReturnType<typeof createFilter<'google' | 'fontshare'>>;
+    /** Category filter (sans-serif, serif, display, etc.) */
+    categories: ReturnType<typeof createFilter<FontCategory>>;
+    /** Subset filter (latin, latin-ext, cyrillic, etc.) */
+    subsets: ReturnType<typeof createFilter<FontSubset>>;
+}
+
+// ============================================================================
+// FONT CATEGORIES
+// ============================================================================
+
+/**
+ * Google Fonts categories
+ */
+export const GOOGLE_CATEGORIES: Property<'sans-serif' | 'serif' | 'display' | 'handwriting' | 'monospace'>[] = [
+    { id: 'sans-serif', name: 'Sans Serif', value: 'sans-serif' },
+    { id: 'serif', name: 'Serif', value: 'serif' },
+    { id: 'display', name: 'Display', value: 'display' },
+    { id: 'handwriting', name: 'Handwriting', value: 'handwriting' },
+    { id: 'monospace', name: 'Monospace', value: 'monospace' },
+];
+
+/**
+ * Fontshare categories (mapped to common naming)
+ */
+export const FONTHARE_CATEGORIES: Property<'sans' | 'serif' | 'slab' | 'display' | 'handwritten' | 'script'>[] = [
+    { id: 'sans', name: 'Sans', value: 'sans' },
+    { id: 'serif', name: 'Serif', value: 'serif' },
+    { id: 'slab', name: 'Slab', value: 'slab' },
+    { id: 'display', name: 'Display', value: 'display' },
+    { id: 'handwritten', name: 'Handwritten', value: 'handwritten' },
+    { id: 'script', name: 'Script', value: 'script' },
+];
+
+/**
+ * Unified categories (combines both providers)
+ */
+export const UNIFIED_CATEGORIES: Property<FontCategory>[] = [
+    { id: 'sans-serif', name: 'Sans Serif', value: 'sans-serif' },
+    { id: 'serif', name: 'Serif', value: 'serif' },
+    { id: 'display', name: 'Display', value: 'display' },
+    { id: 'handwriting', name: 'Handwriting', value: 'handwriting' },
+    { id: 'monospace', name: 'Monospace', value: 'monospace' },
+];
+
+// ============================================================================
+// FONT SUBSETS
+// ============================================================================
+
+/**
+ * Common font subsets
+ */
+export const FONT_SUBSETS: Property<FontSubset>[] = [
+    { id: 'latin', name: 'Latin', value: 'latin' },
+    { id: 'latin-ext', name: 'Latin Extended', value: 'latin-ext' },
+    { id: 'cyrillic', name: 'Cyrillic', value: 'cyrillic' },
+    { id: 'greek', name: 'Greek', value: 'greek' },
+    { id: 'arabic', name: 'Arabic', value: 'arabic' },
+    { id: 'devanagari', name: 'Devanagari', value: 'devanagari' },
+];
+
+// ============================================================================
+// FONT PROVIDERS
+// ============================================================================
+
+/**
+ * Font providers
+ */
+export const FONT_PROVIDERS: Property<FontProvider>[] = [
+    { id: 'google', name: 'Google Fonts', value: 'google' },
+    { id: 'fontshare', name: 'Fontshare', value: 'fontshare' },
+];
+
+// ============================================================================
+// FILTER FACTORIES
+// ============================================================================
+
+/**
+ * Create a mock filter from properties
+ */
+export function createMockFilter<TValue extends string>(
+    options: MockFilterOptions & { properties: Property<TValue>[] },
+) {
+    return createFilter<TValue>(options);
+}
+
+/**
+ * Create a mock filter for categories
+ */
+export function createCategoriesFilter(options?: { selected?: FontCategory[] }) {
+    const properties = UNIFIED_CATEGORIES.map(cat => ({
+        ...cat,
+        selected: options?.selected?.includes(cat.value) ?? false,
+    }));
+    return createFilter<FontCategory>({ properties });
+}
+
+/**
+ * Create a mock filter for subsets
+ */
+export function createSubsetsFilter(options?: { selected?: FontSubset[] }) {
+    const properties = FONT_SUBSETS.map(subset => ({
+        ...subset,
+        selected: options?.selected?.includes(subset.value) ?? false,
+    }));
+    return createFilter<FontSubset>({ properties });
+}
+
+/**
+ * Create a mock filter for providers
+ */
+export function createProvidersFilter(options?: { selected?: FontProvider[] }) {
+    const properties = FONT_PROVIDERS.map(provider => ({
+        ...provider,
+        selected: options?.selected?.includes(provider.value) ?? false,
+    }));
+    return createFilter<FontProvider>({ properties });
+}
+
+// ============================================================================
+// PRESET FILTERS
+// ============================================================================
+
+/**
+ * Preset mock filters - use these directly in stories
+ */
+export const MOCK_FILTERS: MockFilters = {
+    providers: createFilter({
+        properties: FONT_PROVIDERS,
+    }),
+    categories: createFilter({
+        properties: UNIFIED_CATEGORIES,
+    }),
+    subsets: createFilter({
+        properties: FONT_SUBSETS,
+    }),
+};
+
+/**
+ * Preset filters with some items selected
+ */
+export const MOCK_FILTERS_SELECTED: MockFilters = {
+    providers: createFilter({
+        properties: [
+            { ...FONT_PROVIDERS[0], selected: true },
+            { ...FONT_PROVIDERS[1] },
+        ],
+    }),
+    categories: createFilter({
+        properties: [
+            { ...UNIFIED_CATEGORIES[0], selected: true },
+            { ...UNIFIED_CATEGORIES[1], selected: true },
+            { ...UNIFIED_CATEGORIES[2] },
+            { ...UNIFIED_CATEGORIES[3] },
+            { ...UNIFIED_CATEGORIES[4] },
+        ],
+    }),
+    subsets: createFilter({
+        properties: [
+            { ...FONT_SUBSETS[0], selected: true },
+            { ...FONT_SUBSETS[1] },
+            { ...FONT_SUBSETS[2] },
+            { ...FONT_SUBSETS[3] },
+            { ...FONT_SUBSETS[4] },
+        ],
+    }),
+};
+
+/**
+ * Empty filters (all properties, none selected)
+ */
+export const MOCK_FILTERS_EMPTY: MockFilters = {
+    providers: createFilter({
+        properties: FONT_PROVIDERS.map(p => ({ ...p, selected: false })),
+    }),
+    categories: createFilter({
+        properties: UNIFIED_CATEGORIES.map(c => ({ ...c, selected: false })),
+    }),
+    subsets: createFilter({
+        properties: FONT_SUBSETS.map(s => ({ ...s, selected: false })),
+    }),
+};
+
+/**
+ * All selected filters
+ */
+export const MOCK_FILTERS_ALL_SELECTED: MockFilters = {
+    providers: createFilter({
+        properties: FONT_PROVIDERS.map(p => ({ ...p, selected: true })),
+    }),
+    categories: createFilter({
+        properties: UNIFIED_CATEGORIES.map(c => ({ ...c, selected: true })),
+    }),
+    subsets: createFilter({
+        properties: FONT_SUBSETS.map(s => ({ ...s, selected: true })),
+    }),
+};
+
+// ============================================================================
+// GENERIC FILTER MOCKS
+// ============================================================================
+
+/**
+ * Create a mock filter with generic string properties
+ * Useful for testing generic filter components
+ */
+export function createGenericFilter(
+    items: Array<{ id: string; name: string; selected?: boolean }>,
+    options?: { selected?: string[] },
+) {
+    const properties = items.map(item => ({
+        id: item.id,
+        name: item.name,
+        value: item.id,
+        selected: options?.selected?.includes(item.id) ?? item.selected ?? false,
+    }));
+    return createFilter({ properties });
+}
+
+/**
+ * Preset generic filters for testing
+ */
+export const GENERIC_FILTERS = {
+    /** Small filter with 3 items */
+    small: createFilter({
+        properties: [
+            { id: 'option-1', name: 'Option 1', value: 'option-1' },
+            { id: 'option-2', name: 'Option 2', value: 'option-2' },
+            { id: 'option-3', name: 'Option 3', value: 'option-3' },
+        ],
+    }),
+    /** Medium filter with 6 items */
+    medium: createFilter({
+        properties: [
+            { id: 'alpha', name: 'Alpha', value: 'alpha' },
+            { id: 'beta', name: 'Beta', value: 'beta' },
+            { id: 'gamma', name: 'Gamma', value: 'gamma' },
+            { id: 'delta', name: 'Delta', value: 'delta' },
+            { id: 'epsilon', name: 'Epsilon', value: 'epsilon' },
+            { id: 'zeta', name: 'Zeta', value: 'zeta' },
+        ],
+    }),
+    /** Large filter with 12 items */
+    large: createFilter({
+        properties: [
+            { id: 'jan', name: 'January', value: 'jan' },
+            { id: 'feb', name: 'February', value: 'feb' },
+            { id: 'mar', name: 'March', value: 'mar' },
+            { id: 'apr', name: 'April', value: 'apr' },
+            { id: 'may', name: 'May', value: 'may' },
+            { id: 'jun', name: 'June', value: 'jun' },
+            { id: 'jul', name: 'July', value: 'jul' },
+            { id: 'aug', name: 'August', value: 'aug' },
+            { id: 'sep', name: 'September', value: 'sep' },
+            { id: 'oct', name: 'October', value: 'oct' },
+            { id: 'nov', name: 'November', value: 'nov' },
+            { id: 'dec', name: 'December', value: 'dec' },
+        ],
+    }),
+    /** Filter with some pre-selected items */
+    partial: createFilter({
+        properties: [
+            { id: 'red', name: 'Red', value: 'red', selected: true },
+            { id: 'blue', name: 'Blue', value: 'blue', selected: false },
+            { id: 'green', name: 'Green', value: 'green', selected: true },
+            { id: 'yellow', name: 'Yellow', value: 'yellow', selected: false },
+        ],
+    }),
+    /** Filter with all items selected */
+    allSelected: createFilter({
+        properties: [
+            { id: 'cat', name: 'Cat', value: 'cat', selected: true },
+            { id: 'dog', name: 'Dog', value: 'dog', selected: true },
+            { id: 'bird', name: 'Bird', value: 'bird', selected: true },
+        ],
+    }),
+    /** Empty filter (no items) */
+    empty: createFilter({
+        properties: [],
+    }),
+};
+
+/**
+ * Generate a filter with sequential items
+ */
+export function generateSequentialFilter(count: number, prefix = 'Item ') {
+    const properties = Array.from({ length: count }, (_, i) => ({
+        id: `item-${i + 1}`,
+        name: `${prefix}${i + 1}`,
+        value: `item-${i + 1}`,
+    }));
+    return createFilter({ properties });
+}

src/entities/Font/lib/mocks/fonts.mock.ts

@@ -0,0 +1,630 @@
+/**
+ * ============================================================================
+ * MOCK FONT DATA
+ * ============================================================================
+ *
+ * Factory functions and preset mock data for fonts.
+ * Used in Storybook stories, tests, and development.
+ *
+ * ## Usage
+ *
+ * ```ts
+ * import {
+ *     mockGoogleFont,
+ *     mockFontshareFont,
+ *     mockUnifiedFont,
+ *     GOOGLE_FONTS,
+ *     FONTHARE_FONTS,
+ *     UNIFIED_FONTS,
+ * } from '$entities/Font/lib/mocks';
+ *
+ * // Create a mock Google Font
+ * const roboto = mockGoogleFont({ family: 'Roboto', category: 'sans-serif' });
+ *
+ * // Create a mock Fontshare font
+ * const satoshi = mockFontshareFont({ name: 'Satoshi', slug: 'satoshi' });
+ *
+ * // Create a mock UnifiedFont
+ * const font = mockUnifiedFont({ id: 'roboto', name: 'Roboto' });
+ *
+ * // Use preset fonts
+ * import { UNIFIED_FONTS } from '$entities/Font/lib/mocks';
+ * ```
+ */
+
+import type {
+    FontCategory,
+    FontProvider,
+    FontSubset,
+    FontVariant,
+} from '$entities/Font/model/types';
+import type {
+    FontItem,
+    FontshareFont,
+    GoogleFontItem,
+} from '$entities/Font/model/types';
+import type {
+    FontFeatures,
+    FontMetadata,
+    FontStyleUrls,
+    UnifiedFont,
+} from '$entities/Font/model/types';
+
+// ============================================================================
+// GOOGLE FONTS MOCKS
+// ============================================================================
+
+/**
+ * Options for creating a mock Google Font
+ */
+export interface MockGoogleFontOptions {
+    /** Font family name (default: 'Mock Font') */
+    family?: string;
+    /** Font category (default: 'sans-serif') */
+    category?: 'sans-serif' | 'serif' | 'display' | 'handwriting' | 'monospace';
+    /** Font variants (default: ['regular', '700', 'italic', '700italic']) */
+    variants?: FontVariant[];
+    /** Font subsets (default: ['latin']) */
+    subsets?: string[];
+    /** Font version (default: 'v30') */
+    version?: string;
+    /** Last modified date (default: current ISO date) */
+    lastModified?: string;
+    /** Custom file URLs (if not provided, mock URLs are generated) */
+    files?: Partial<Record<FontVariant, string>>;
+    /** Popularity rank (1 = most popular) */
+    popularity?: number;
+}
+
+/**
+ * Default mock Google Font
+ */
+export function mockGoogleFont(options: MockGoogleFontOptions = {}): GoogleFontItem {
+    const {
+        family = 'Mock Font',
+        category = 'sans-serif',
+        variants = ['regular', '700', 'italic', '700italic'],
+        subsets = ['latin'],
+        version = 'v30',
+        lastModified = new Date().toISOString().split('T')[0],
+        files,
+        popularity = 1,
+    } = options;
+
+    const baseUrl = `https://fonts.gstatic.com/s/${family.toLowerCase().replace(/\s+/g, '')}/${version}`;
+
+    return {
+        family,
+        category,
+        variants: variants as FontVariant[],
+        subsets,
+        version,
+        lastModified,
+        files: files ?? {
+            regular: `${baseUrl}/KFOmCnqEu92Fr1Me4W.woff2`,
+            '700': `${baseUrl}/KFOlCnqEu92Fr1MmWUlfBBc9.woff2`,
+            italic: `${baseUrl}/KFOkCnqEu92Fr1Mu51xIIzI.woff2`,
+            '700italic': `${baseUrl}/KFOjCnqEu92Fr1Mu51TzBic6CsQ.woff2`,
+        },
+        menu: `https://fonts.googleapis.com/css2?family=${encodeURIComponent(family)}`,
+    };
+}
+
+/**
+ * Preset Google Font mocks
+ */
+export const GOOGLE_FONTS: Record<string, GoogleFontItem> = {
+    roboto: mockGoogleFont({
+        family: 'Roboto',
+        category: 'sans-serif',
+        variants: ['100', '300', '400', '500', '700', '900', 'italic', '700italic'],
+        subsets: ['latin', 'latin-ext', 'cyrillic', 'greek'],
+        popularity: 1,
+    }),
+    openSans: mockGoogleFont({
+        family: 'Open Sans',
+        category: 'sans-serif',
+        variants: ['300', '400', '500', '600', '700', '800', 'italic', '700italic'],
+        subsets: ['latin', 'latin-ext', 'cyrillic', 'greek'],
+        popularity: 2,
+    }),
+    lato: mockGoogleFont({
+        family: 'Lato',
+        category: 'sans-serif',
+        variants: ['100', '300', '400', '700', '900', 'italic', '700italic'],
+        subsets: ['latin', 'latin-ext'],
+        popularity: 3,
+    }),
+    playfairDisplay: mockGoogleFont({
+        family: 'Playfair Display',
+        category: 'serif',
+        variants: ['400', '500', '600', '700', '800', '900', 'italic', '700italic'],
+        subsets: ['latin', 'latin-ext', 'cyrillic'],
+        popularity: 10,
+    }),
+    montserrat: mockGoogleFont({
+        family: 'Montserrat',
+        category: 'sans-serif',
+        variants: ['100', '200', '300', '400', '500', '600', '700', '800', '900', 'italic', '700italic'],
+        subsets: ['latin', 'latin-ext', 'cyrillic', 'vietnamese'],
+        popularity: 4,
+    }),
+    sourceSansPro: mockGoogleFont({
+        family: 'Source Sans Pro',
+        category: 'sans-serif',
+        variants: ['200', '300', '400', '600', '700', '900', 'italic', '700italic'],
+        subsets: ['latin', 'latin-ext', 'cyrillic', 'greek', 'vietnamese'],
+        popularity: 5,
+    }),
+    merriweather: mockGoogleFont({
+        family: 'Merriweather',
+        category: 'serif',
+        variants: ['300', '400', '700', '900', 'italic', '700italic'],
+        subsets: ['latin', 'latin-ext', 'cyrillic', 'vietnamese'],
+        popularity: 15,
+    }),
+    robotoSlab: mockGoogleFont({
+        family: 'Roboto Slab',
+        category: 'serif',
+        variants: ['100', '300', '400', '500', '700', '900'],
+        subsets: ['latin', 'latin-ext', 'cyrillic', 'greek', 'vietnamese'],
+        popularity: 8,
+    }),
+    oswald: mockGoogleFont({
+        family: 'Oswald',
+        category: 'sans-serif',
+        variants: ['200', '300', '400', '500', '600', '700'],
+        subsets: ['latin', 'latin-ext', 'vietnamese'],
+        popularity: 6,
+    }),
+    raleway: mockGoogleFont({
+        family: 'Raleway',
+        category: 'sans-serif',
+        variants: ['100', '200', '300', '400', '500', '600', '700', '800', '900', 'italic'],
+        subsets: ['latin', 'latin-ext', 'cyrillic', 'vietnamese'],
+        popularity: 7,
+    }),
+};
+
+// ============================================================================
+// FONTHARE MOCKS
+// ============================================================================
+
+/**
+ * Options for creating a mock Fontshare font
+ */
+export interface MockFontshareFontOptions {
+    /** Font name (default: 'Mock Font') */
+    name?: string;
+    /** URL-friendly slug (default: derived from name) */
+    slug?: string;
+    /** Font category (default: 'sans') */
+    category?: 'sans' | 'serif' | 'slab' | 'display' | 'handwritten' | 'script' | 'mono';
+    /** Script (default: 'latin') */
+    script?: string;
+    /** Whether this is a variable font (default: false) */
+    isVariable?: boolean;
+    /** Font version (default: '1.0') */
+    version?: string;
+    /** Popularity/views count (default: 1000) */
+    views?: number;
+    /** Usage tags */
+    tags?: string[];
+    /** Font weights available */
+    weights?: number[];
+    /** Publisher name */
+    publisher?: string;
+    /** Designer name */
+    designer?: string;
+}
+
+/**
+ * Create a mock Fontshare style
+ */
+function mockFontshareStyle(
+    weight: number,
+    isItalic: boolean,
+    isVariable: boolean,
+    slug: string,
+): FontshareFont['styles'][number] {
+    const weightLabel = weight === 400 ? 'Regular' : weight === 700 ? 'Bold' : weight.toString();
+    const suffix = isItalic ? 'italic' : '';
+    const variablePrefix = isVariable ? 'variable-' : '';
+
+    return {
+        id: `style-${weight}${isItalic ? '-italic' : ''}`,
+        default: weight === 400 && !isItalic,
+        file: `//cdn.fontshare.com/wf/${slug}-${variablePrefix}${weight}${suffix}.woff2`,
+        is_italic: isItalic,
+        is_variable: isVariable,
+        properties: {},
+        weight: {
+            label: isVariable ? 'Variable' + (isItalic ? ' Italic' : '') : weightLabel,
+            name: isVariable ? 'Variable' + (isItalic ? 'Italic' : '') : weightLabel,
+            native_name: null,
+            number: isVariable ? 0 : weight,
+            weight: isVariable ? 0 : weight,
+        },
+    };
+}
+
+/**
+ * Default mock Fontshare font
+ */
+export function mockFontshareFont(options: MockFontshareFontOptions = {}): FontshareFont {
+    const {
+        name = 'Mock Font',
+        slug = name.toLowerCase().replace(/\s+/g, '-'),
+        category = 'sans',
+        script = 'latin',
+        isVariable = false,
+        version = '1.0',
+        views = 1000,
+        tags = [],
+        weights = [400, 700],
+        publisher = 'Mock Foundry',
+        designer = 'Mock Designer',
+    } = options;
+
+    // Generate styles based on weights and variable setting
+    const styles: FontshareFont['styles'] = isVariable
+        ? [
+            mockFontshareStyle(0, false, true, slug),
+            mockFontshareStyle(0, true, true, slug),
+        ]
+        : weights.flatMap(weight => [
+            mockFontshareStyle(weight, false, false, slug),
+            mockFontshareStyle(weight, true, false, slug),
+        ]);
+
+    return {
+        id: `mock-${slug}`,
+        name,
+        native_name: null,
+        slug,
+        category,
+        script,
+        publisher: {
+            bio: `Mock publisher bio for ${publisher}`,
+            email: null,
+            id: `pub-${slug}`,
+            links: [],
+            name: publisher,
+        },
+        designers: [
+            {
+                bio: `Mock designer bio for ${designer}`,
+                links: [],
+                name: designer,
+            },
+        ],
+        related_families: null,
+        display_publisher_as_designer: false,
+        trials_enabled: true,
+        show_latin_metrics: false,
+        license_type: 'ofl',
+        languages: 'English, Spanish, French, German',
+        inserted_at: '2021-03-12T20:49:05Z',
+        story: `<p>A mock font story for ${name}.</p>`,
+        version,
+        views,
+        views_recent: Math.floor(views * 0.1),
+        is_hot: views > 5000,
+        is_new: views < 500,
+        is_shortlisted: null,
+        is_top: views > 10000,
+        axes: isVariable
+            ? [
+                {
+                    name: 'Weight',
+                    property: 'wght',
+                    range_default: 400,
+                    range_left: 300,
+                    range_right: 700,
+                },
+            ]
+            : [],
+        font_tags: tags.map(name => ({ name })),
+        features: [],
+        styles,
+    };
+}
+
+/**
+ * Preset Fontshare font mocks
+ */
+export const FONTHARE_FONTS: Record<string, FontshareFont> = {
+    satoshi: mockFontshareFont({
+        name: 'Satoshi',
+        slug: 'satoshi',
+        category: 'sans',
+        isVariable: true,
+        views: 15000,
+        tags: ['Branding', 'Logos', 'Editorial'],
+        publisher: 'Indian Type Foundry',
+        designer: 'Denis Shelabovets',
+    }),
+    generalSans: mockFontshareFont({
+        name: 'General Sans',
+        slug: 'general-sans',
+        category: 'sans',
+        isVariable: true,
+        views: 12000,
+        tags: ['UI', 'Branding', 'Display'],
+        publisher: 'Indestructible Type',
+        designer: 'Eugene Tantsur',
+    }),
+    clashDisplay: mockFontshareFont({
+        name: 'Clash Display',
+        slug: 'clash-display',
+        category: 'display',
+        isVariable: false,
+        views: 8000,
+        tags: ['Headlines', 'Posters', 'Branding'],
+        weights: [400, 500, 600, 700],
+        publisher: 'Letterogika',
+        designer: 'Matěj Trnka',
+    }),
+    fonta: mockFontshareFont({
+        name: 'Fonta',
+        slug: 'fonta',
+        category: 'serif',
+        isVariable: false,
+        views: 5000,
+        tags: ['Editorial', 'Books', 'Magazines'],
+        weights: [300, 400, 500, 600, 700],
+        publisher: 'Fonta',
+        designer: 'Alexei Vanyashin',
+    }),
+    aileron: mockFontshareFont({
+        name: 'Aileron',
+        slug: 'aileron',
+        category: 'sans',
+        isVariable: false,
+        views: 3000,
+        tags: ['Display', 'Headlines'],
+        weights: [100, 200, 300, 400, 500, 600, 700, 800, 900],
+        publisher: 'Sorkin Type',
+        designer: 'Sorkin Type',
+    }),
+    beVietnamPro: mockFontshareFont({
+        name: 'Be Vietnam Pro',
+        slug: 'be-vietnam-pro',
+        category: 'sans',
+        isVariable: true,
+        views: 20000,
+        tags: ['UI', 'App', 'Web'],
+        publisher: 'ildefox',
+        designer: 'Manh Nguyen',
+    }),
+};
+
+// ============================================================================
+// UNIFIED FONT MOCKS
+// ============================================================================
+
+/**
+ * Options for creating a mock UnifiedFont
+ */
+export interface MockUnifiedFontOptions {
+    /** Unique identifier (default: derived from name) */
+    id?: string;
+    /** Font display name (default: 'Mock Font') */
+    name?: string;
+    /** Font provider (default: 'google') */
+    provider?: FontProvider;
+    /** Font category (default: 'sans-serif') */
+    category?: FontCategory;
+    /** Font subsets (default: ['latin']) */
+    subsets?: FontSubset[];
+    /** Font variants (default: ['regular', '700', 'italic', '700italic']) */
+    variants?: FontVariant[];
+    /** Style URLs (if not provided, mock URLs are generated) */
+    styles?: FontStyleUrls;
+    /** Metadata overrides */
+    metadata?: Partial<FontMetadata>;
+    /** Features overrides */
+    features?: Partial<FontFeatures>;
+}
+
+/**
+ * Default mock UnifiedFont
+ */
+export function mockUnifiedFont(options: MockUnifiedFontOptions = {}): UnifiedFont {
+    const {
+        id,
+        name = 'Mock Font',
+        provider = 'google',
+        category = 'sans-serif',
+        subsets = ['latin'],
+        variants = ['regular', '700', 'italic', '700italic'],
+        styles,
+        metadata,
+        features,
+    } = options;
+
+    const fontId = id ?? name.toLowerCase().replace(/\s+/g, '');
+    const baseUrl = provider === 'google'
+        ? `https://fonts.gstatic.com/s/${fontId}/v30`
+        : `//cdn.fontshare.com/wf/${fontId}`;
+
+    return {
+        id: fontId,
+        name,
+        provider,
+        category,
+        subsets,
+        variants: variants as FontVariant[],
+        styles: styles ?? {
+            regular: `${baseUrl}/regular.woff2`,
+            bold: `${baseUrl}/bold.woff2`,
+            italic: `${baseUrl}/italic.woff2`,
+            boldItalic: `${baseUrl}/bolditalic.woff2`,
+        },
+        metadata: {
+            cachedAt: Date.now(),
+            version: '1.0',
+            lastModified: new Date().toISOString().split('T')[0],
+            popularity: 1,
+            ...metadata,
+        },
+        features: {
+            isVariable: false,
+            ...features,
+        },
+    };
+}
+
+/**
+ * Preset UnifiedFont mocks
+ */
+export const UNIFIED_FONTS: Record<string, UnifiedFont> = {
+    roboto: mockUnifiedFont({
+        id: 'roboto',
+        name: 'Roboto',
+        provider: 'google',
+        category: 'sans-serif',
+        subsets: ['latin', 'latin-ext'],
+        variants: ['100', '300', '400', '500', '700', '900'],
+        metadata: { popularity: 1 },
+    }),
+    openSans: mockUnifiedFont({
+        id: 'open-sans',
+        name: 'Open Sans',
+        provider: 'google',
+        category: 'sans-serif',
+        subsets: ['latin', 'latin-ext'],
+        variants: ['300', '400', '500', '600', '700', '800'],
+        metadata: { popularity: 2 },
+    }),
+    lato: mockUnifiedFont({
+        id: 'lato',
+        name: 'Lato',
+        provider: 'google',
+        category: 'sans-serif',
+        subsets: ['latin', 'latin-ext'],
+        variants: ['100', '300', '400', '700', '900'],
+        metadata: { popularity: 3 },
+    }),
+    playfairDisplay: mockUnifiedFont({
+        id: 'playfair-display',
+        name: 'Playfair Display',
+        provider: 'google',
+        category: 'serif',
+        subsets: ['latin'],
+        variants: ['400', '700', '900'],
+        metadata: { popularity: 10 },
+    }),
+    montserrat: mockUnifiedFont({
+        id: 'montserrat',
+        name: 'Montserrat',
+        provider: 'google',
+        category: 'sans-serif',
+        subsets: ['latin', 'latin-ext'],
+        variants: ['100', '200', '300', '400', '500', '600', '700', '800', '900'],
+        metadata: { popularity: 4 },
+    }),
+    satoshi: mockUnifiedFont({
+        id: 'satoshi',
+        name: 'Satoshi',
+        provider: 'fontshare',
+        category: 'sans-serif',
+        subsets: ['latin'],
+        variants: ['regular', 'bold', 'italic', 'bolditalic'] as FontVariant[],
+        features: { isVariable: true, axes: [{ name: 'wght', property: 'wght', default: 400, min: 300, max: 700 }] },
+        metadata: { popularity: 15000 },
+    }),
+    generalSans: mockUnifiedFont({
+        id: 'general-sans',
+        name: 'General Sans',
+        provider: 'fontshare',
+        category: 'sans-serif',
+        subsets: ['latin'],
+        variants: ['regular', 'bold', 'italic', 'bolditalic'] as FontVariant[],
+        features: { isVariable: true },
+        metadata: { popularity: 12000 },
+    }),
+    clashDisplay: mockUnifiedFont({
+        id: 'clash-display',
+        name: 'Clash Display',
+        provider: 'fontshare',
+        category: 'display',
+        subsets: ['latin'],
+        variants: ['regular', '500', '600', 'bold'] as FontVariant[],
+        features: { tags: ['Headlines', 'Posters', 'Branding'] },
+        metadata: { popularity: 8000 },
+    }),
+    oswald: mockUnifiedFont({
+        id: 'oswald',
+        name: 'Oswald',
+        provider: 'google',
+        category: 'sans-serif',
+        subsets: ['latin'],
+        variants: ['200', '300', '400', '500', '600', '700'],
+        metadata: { popularity: 6 },
+    }),
+    raleway: mockUnifiedFont({
+        id: 'raleway',
+        name: 'Raleway',
+        provider: 'google',
+        category: 'sans-serif',
+        subsets: ['latin'],
+        variants: ['100', '200', '300', '400', '500', '600', '700', '800', '900'],
+        metadata: { popularity: 7 },
+    }),
+};
+
+/**
+ * Get an array of all preset UnifiedFonts
+ */
+export function getAllMockFonts(): UnifiedFont[] {
+    return Object.values(UNIFIED_FONTS);
+}
+
+/**
+ * Get fonts by provider
+ */
+export function getFontsByProvider(provider: FontProvider): UnifiedFont[] {
+    return getAllMockFonts().filter(font => font.provider === provider);
+}
+
+/**
+ * Get fonts by category
+ */
+export function getFontsByCategory(category: FontCategory): UnifiedFont[] {
+    return getAllMockFonts().filter(font => font.category === category);
+}
+
+/**
+ * Generate an array of mock fonts with sequential naming
+ */
+export function generateMockFonts(count: number, options?: Omit<MockUnifiedFontOptions, 'id' | 'name'>): UnifiedFont[] {
+    return Array.from({ length: count }, (_, i) =>
+        mockUnifiedFont({
+            ...options,
+            id: `mock-font-${i + 1}`,
+            name: `Mock Font ${i + 1}`,
+        }));
+}
+
+/**
+ * Generate an array of mock fonts with different categories
+ */
+export function generateMixedCategoryFonts(countPerCategory: number = 2): UnifiedFont[] {
+    const categories: FontCategory[] = ['sans-serif', 'serif', 'display', 'handwriting', 'monospace'];
+    const fonts: UnifiedFont[] = [];
+
+    categories.forEach(category => {
+        for (let i = 0; i < countPerCategory; i++) {
+            fonts.push(
+                mockUnifiedFont({
+                    id: `${category}-${i + 1}`,
+                    name: `${category.replace('-', ' ')} ${i + 1}`,
+                    category,
+                }),
+            );
+        }
+    });
+
+    return fonts;
+}

src/entities/Font/lib/mocks/index.ts

@@ -0,0 +1,84 @@
+/**
+ * ============================================================================
+ * MOCK DATA HELPERS - MAIN EXPORT
+ * ============================================================================
+ *
+ * Comprehensive mock data for Storybook stories, tests, and development.
+ *
+ * ## Quick Start
+ *
+ * ```ts
+ * import {
+ *     mockUnifiedFont,
+ *     UNIFIED_FONTS,
+ *     MOCK_FILTERS,
+ *     createMockFontStoreState,
+ * } from '$entities/Font/lib/mocks';
+ *
+ * // Use in stories
+ * const font = mockUnifiedFont({ name: 'My Font', category: 'serif' });
+ * const presets = UNIFIED_FONTS;
+ * const filter = MOCK_FILTERS.categories;
+ * ```
+ *
+ * @module
+ */
+
+// Font mocks
+export {
+    FONTHARE_FONTS,
+    generateMixedCategoryFonts,
+    generateMockFonts,
+    getAllMockFonts,
+    getFontsByCategory,
+    getFontsByProvider,
+    GOOGLE_FONTS,
+    mockFontshareFont,
+    type MockFontshareFontOptions,
+    mockGoogleFont,
+    type MockGoogleFontOptions,
+    mockUnifiedFont,
+    type MockUnifiedFontOptions,
+    UNIFIED_FONTS,
+} from './fonts.mock';
+
+// Filter mocks
+export {
+    createCategoriesFilter,
+    createGenericFilter,
+    createMockFilter,
+    createProvidersFilter,
+    createSubsetsFilter,
+    FONT_PROVIDERS,
+    FONT_SUBSETS,
+    FONTHARE_CATEGORIES,
+    generateSequentialFilter,
+    GENERIC_FILTERS,
+    GOOGLE_CATEGORIES,
+    MOCK_FILTERS,
+    MOCK_FILTERS_ALL_SELECTED,
+    MOCK_FILTERS_EMPTY,
+    MOCK_FILTERS_SELECTED,
+    type MockFilterOptions,
+    type MockFilters,
+    UNIFIED_CATEGORIES,
+} from './filters.mock';
+
+// Store mocks
+export {
+    createErrorState,
+    createLoadingState,
+    createMockComparisonStore,
+    createMockFontApiResponse,
+    createMockFontStoreState,
+    createMockQueryState,
+    createMockReactiveState,
+    createMockStore,
+    createSuccessState,
+    generatePaginatedFonts,
+    MOCK_FONT_STORE_STATES,
+    MOCK_STORES,
+    type MockFontStoreState,
+    type MockQueryObserverResult,
+    type MockQueryState,
+} from './stores.mock';

src/entities/Font/lib/mocks/stores.mock.ts

@@ -0,0 +1,590 @@
+/**
+ * ============================================================================
+ * MOCK FONT STORE HELPERS
+ * ============================================================================
+ *
+ * Factory functions and preset mock data for TanStack Query stores and state management.
+ * Used in Storybook stories for components that use reactive stores.
+ *
+ * ## Usage
+ *
+ * ```ts
+ * import {
+ *     createMockQueryState,
+ *     MOCK_STORES,
+ * } from '$entities/Font/lib/mocks';
+ *
+ * // Create a mock query state
+ * const loadingState = createMockQueryState({ status: 'pending' });
+ * const errorState = createMockQueryState({ status: 'error', error: 'Failed to load' });
+ * const successState = createMockQueryState({ status: 'success', data: mockFonts });
+ *
+ * // Use preset stores
+ * const mockFontStore = MOCK_STORES.unifiedFontStore();
+ * ```
+ */
+
+import type { UnifiedFont } from '$entities/Font/model/types';
+import type {
+    QueryKey,
+    QueryObserverResult,
+    QueryStatus,
+} from '@tanstack/svelte-query';
+import {
+    UNIFIED_FONTS,
+    generateMockFonts,
+} from './fonts.mock';
+
+// ============================================================================
+// TANSTACK QUERY MOCK TYPES
+// ============================================================================
+
+/**
+ * Mock TanStack Query state
+ */
+export interface MockQueryState<TData = unknown, TError = Error> {
+    status: QueryStatus;
+    data?: TData;
+    error?: TError;
+    isLoading?: boolean;
+    isFetching?: boolean;
+    isSuccess?: boolean;
+    isError?: boolean;
+    isPending?: boolean;
+    dataUpdatedAt?: number;
+    errorUpdatedAt?: number;
+    failureCount?: number;
+    failureReason?: TError;
+    errorUpdateCount?: number;
+    isRefetching?: boolean;
+    isRefetchError?: boolean;
+    isPaused?: boolean;
+}
+
+/**
+ * Mock TanStack Query observer result
+ */
+export interface MockQueryObserverResult<TData = unknown, TError = Error> {
+    status?: QueryStatus;
+    data?: TData;
+    error?: TError;
+    isLoading?: boolean;
+    isFetching?: boolean;
+    isSuccess?: boolean;
+    isError?: boolean;
+    isPending?: boolean;
+    dataUpdatedAt?: number;
+    errorUpdatedAt?: number;
+    failureCount?: number;
+    failureReason?: TError;
+    errorUpdateCount?: number;
+    isRefetching?: boolean;
+    isRefetchError?: boolean;
+    isPaused?: boolean;
+}
+
+// ============================================================================
+// TANSTACK QUERY MOCK FACTORIES
+// ============================================================================
+
+/**
+ * Create a mock query state for TanStack Query
+ */
+export function createMockQueryState<TData = unknown, TError = Error>(
+    options: MockQueryState<TData, TError>,
+): MockQueryObserverResult<TData, TError> {
+    const {
+        status,
+        data,
+        error,
+    } = options;
+
+    return {
+        status: status ?? 'success',
+        data,
+        error,
+        isLoading: status === 'pending' ? true : false,
+        isFetching: status === 'pending' ? true : false,
+        isSuccess: status === 'success',
+        isError: status === 'error',
+        isPending: status === 'pending',
+        dataUpdatedAt: status === 'success' ? Date.now() : undefined,
+        errorUpdatedAt: status === 'error' ? Date.now() : undefined,
+        failureCount: status === 'error' ? 1 : 0,
+        failureReason: status === 'error' ? error : undefined,
+        errorUpdateCount: status === 'error' ? 1 : 0,
+        isRefetching: false,
+        isRefetchError: false,
+        isPaused: false,
+    };
+}
+
+/**
+ * Create a loading query state
+ */
+export function createLoadingState<TData = unknown>(): MockQueryObserverResult<TData> {
+    return createMockQueryState<TData>({ status: 'pending', data: undefined, error: undefined });
+}
+
+/**
+ * Create an error query state
+ */
+export function createErrorState<TError = Error>(
+    error: TError,
+): MockQueryObserverResult<unknown, TError> {
+    return createMockQueryState<unknown, TError>({ status: 'error', data: undefined, error });
+}
+
+/**
+ * Create a success query state
+ */
+export function createSuccessState<TData>(data: TData): MockQueryObserverResult<TData> {
+    return createMockQueryState<TData>({ status: 'success', data, error: undefined });
+}
+
+// ============================================================================
+// FONT STORE MOCKS
+// ============================================================================
+
+/**
+ * Mock UnifiedFontStore state
+ */
+export interface MockFontStoreState {
+    /** All cached fonts */
+    fonts: Record<string, UnifiedFont>;
+    /** Current page */
+    page: number;
+    /** Total pages available */
+    totalPages: number;
+    /** Items per page */
+    limit: number;
+    /** Total font count */
+    total: number;
+    /** Loading state */
+    isLoading: boolean;
+    /** Error state */
+    error: Error | null;
+    /** Search query */
+    searchQuery: string;
+    /** Selected provider */
+    provider: 'google' | 'fontshare' | 'all';
+    /** Selected category */
+    category: string | null;
+    /** Selected subset */
+    subset: string | null;
+}
+
+/**
+ * Create a mock font store state
+ */
+export function createMockFontStoreState(
+    options: Partial<MockFontStoreState> = {},
+): MockFontStoreState {
+    const {
+        page = 1,
+        limit = 24,
+        isLoading = false,
+        error = null,
+        searchQuery = '',
+        provider = 'all',
+        category = null,
+        subset = null,
+    } = options;
+
+    // Generate mock fonts if not provided
+    const mockFonts = options.fonts ?? Object.fromEntries(
+        Object.values(UNIFIED_FONTS).map(font => [font.id, font]),
+    );
+
+    const fontArray = Object.values(mockFonts);
+    const total = options.total ?? fontArray.length;
+    const totalPages = options.totalPages ?? Math.ceil(total / limit);
+
+    return {
+        fonts: mockFonts,
+        page,
+        totalPages,
+        limit,
+        total,
+        isLoading,
+        error,
+        searchQuery,
+        provider,
+        category,
+        subset,
+    };
+}
+
+/**
+ * Preset font store states
+ */
+export const MOCK_FONT_STORE_STATES = {
+    /** Initial loading state */
+    loading: createMockFontStoreState({
+        isLoading: true,
+        fonts: {},
+        total: 0,
+        page: 1,
+    }),
+
+    /** Empty state (no fonts found) */
+    empty: createMockFontStoreState({
+        fonts: {},
+        total: 0,
+        page: 1,
+        isLoading: false,
+    }),
+
+    /** First page with fonts */
+    firstPage: createMockFontStoreState({
+        fonts: Object.fromEntries(
+            Object.values(UNIFIED_FONTS).slice(0, 10).map(font => [font.id, font]),
+        ),
+        total: 50,
+        page: 1,
+        limit: 10,
+        totalPages: 5,
+        isLoading: false,
+    }),
+
+    /** Second page with fonts */
+    secondPage: createMockFontStoreState({
+        fonts: Object.fromEntries(
+            Object.values(UNIFIED_FONTS).slice(10, 20).map(font => [font.id, font]),
+        ),
+        total: 50,
+        page: 2,
+        limit: 10,
+        totalPages: 5,
+        isLoading: false,
+    }),
+
+    /** Last page with fonts */
+    lastPage: createMockFontStoreState({
+        fonts: Object.fromEntries(
+            Object.values(UNIFIED_FONTS).slice(0, 5).map(font => [font.id, font]),
+        ),
+        total: 25,
+        page: 3,
+        limit: 10,
+        totalPages: 3,
+        isLoading: false,
+    }),
+
+    /** Error state */
+    error: createMockFontStoreState({
+        fonts: {},
+        error: new Error('Failed to load fonts'),
+        total: 0,
+        page: 1,
+        isLoading: false,
+    }),
+
+    /** With search query */
+    withSearch: createMockFontStoreState({
+        fonts: Object.fromEntries(
+            Object.values(UNIFIED_FONTS).slice(0, 3).map(font => [font.id, font]),
+        ),
+        total: 3,
+        page: 1,
+        isLoading: false,
+        searchQuery: 'Roboto',
+    }),
+
+    /** Filtered by category */
+    filteredByCategory: createMockFontStoreState({
+        fonts: Object.fromEntries(
+            Object.values(UNIFIED_FONTS)
+                .filter(f => f.category === 'serif')
+                .slice(0, 5)
+                .map(font => [font.id, font]),
+        ),
+        total: 5,
+        page: 1,
+        isLoading: false,
+        category: 'serif',
+    }),
+
+    /** Filtered by provider */
+    filteredByProvider: createMockFontStoreState({
+        fonts: Object.fromEntries(
+            Object.values(UNIFIED_FONTS)
+                .filter(f => f.provider === 'google')
+                .slice(0, 5)
+                .map(font => [font.id, font]),
+        ),
+        total: 5,
+        page: 1,
+        isLoading: false,
+        provider: 'google',
+    }),
+
+    /** Large dataset */
+    largeDataset: createMockFontStoreState({
+        fonts: Object.fromEntries(
+            generateMockFonts(50).map(font => [font.id, font]),
+        ),
+        total: 500,
+        page: 1,
+        limit: 50,
+        totalPages: 10,
+        isLoading: false,
+    }),
+};
+
+// ============================================================================
+// MOCK STORE OBJECT
+// ============================================================================
+
+/**
+ * Create a mock store object that mimics TanStack Query behavior
+ * Useful for components that subscribe to store properties
+ */
+export function createMockStore<T>(config: {
+    data?: T;
+    isLoading?: boolean;
+    isError?: boolean;
+    error?: Error;
+    isFetching?: boolean;
+}) {
+    const {
+        data,
+        isLoading = false,
+        isError = false,
+        error,
+        isFetching = false,
+    } = config;
+
+    return {
+        get data() {
+            return data;
+        },
+        get isLoading() {
+            return isLoading;
+        },
+        get isError() {
+            return isError;
+        },
+        get error() {
+            return error;
+        },
+        get isFetching() {
+            return isFetching;
+        },
+        get isSuccess() {
+            return !isLoading && !isError && data !== undefined;
+        },
+        get status() {
+            if (isLoading) return 'pending';
+            if (isError) return 'error';
+            return 'success';
+        },
+    };
+}
+
+/**
+ * Preset mock stores
+ */
+export const MOCK_STORES = {
+    /** Font store in loading state */
+    loadingFontStore: createMockStore<UnifiedFont[]>({
+        isLoading: true,
+        data: undefined,
+    }),
+
+    /** Font store with fonts loaded */
+    successFontStore: createMockStore<UnifiedFont[]>({
+        data: Object.values(UNIFIED_FONTS),
+        isLoading: false,
+        isError: false,
+    }),
+
+    /** Font store with error */
+    errorFontStore: createMockStore<UnifiedFont[]>({
+        data: undefined,
+        isLoading: false,
+        isError: true,
+        error: new Error('Failed to load fonts'),
+    }),
+
+    /** Font store with empty results */
+    emptyFontStore: createMockStore<UnifiedFont[]>({
+        data: [],
+        isLoading: false,
+        isError: false,
+    }),
+
+    /**
+     * Create a mock UnifiedFontStore-like object
+     * Note: This is a simplified mock for Storybook use
+     */
+    unifiedFontStore: (state: Partial<MockFontStoreState> = {}) => {
+        const mockState = createMockFontStoreState(state);
+        return {
+            // State properties
+            get fonts() {
+                return mockState.fonts;
+            },
+            get page() {
+                return mockState.page;
+            },
+            get totalPages() {
+                return mockState.totalPages;
+            },
+            get limit() {
+                return mockState.limit;
+            },
+            get total() {
+                return mockState.total;
+            },
+            get isLoading() {
+                return mockState.isLoading;
+            },
+            get error() {
+                return mockState.error;
+            },
+            get searchQuery() {
+                return mockState.searchQuery;
+            },
+            get provider() {
+                return mockState.provider;
+            },
+            get category() {
+                return mockState.category;
+            },
+            get subset() {
+                return mockState.subset;
+            },
+            // Methods (no-op for Storybook)
+            nextPage: () => {},
+            prevPage: () => {},
+            goToPage: (_page: number) => {},
+            setLimit: (_limit: number) => {},
+            setProvider: (_provider: typeof mockState.provider) => {},
+            setCategory: (_category: string | null) => {},
+            setSubset: (_subset: string | null) => {},
+            setSearch: (_query: string) => {},
+            resetFilters: () => {},
+        };
+    },
+};
+
+// ============================================================================
+// REACTIVE STATE MOCKS
+// ============================================================================
+
+/**
+ * Create a reactive state object using Svelte 5 runes pattern
+ * Useful for stories that need reactive state
+ *
+ * Note: This uses plain JavaScript objects since Svelte runes
+ * only work in .svelte files. For Storybook, this provides
+ * a similar API for testing.
+ */
+export function createMockReactiveState<T>(initialValue: T) {
+    let value = initialValue;
+
+    return {
+        get value() {
+            return value;
+        },
+        set value(newValue: T) {
+            value = newValue;
+        },
+        update(fn: (current: T) => T) {
+            value = fn(value);
+        },
+    };
+}
+
+/**
+ * Mock comparison store for ComparisonSlider component
+ */
+export function createMockComparisonStore(config: {
+    fontA?: UnifiedFont;
+    fontB?: UnifiedFont;
+    text?: string;
+} = {}) {
+    const { fontA, fontB, text = 'The quick brown fox jumps over the lazy dog.' } = config;
+
+    return {
+        get fontA() {
+            return fontA ?? UNIFIED_FONTS.roboto;
+        },
+        get fontB() {
+            return fontB ?? UNIFIED_FONTS.openSans;
+        },
+        get text() {
+            return text;
+        },
+        // Methods (no-op for Storybook)
+        setFontA: (_font: UnifiedFont | undefined) => {},
+        setFontB: (_font: UnifiedFont | undefined) => {},
+        setText: (_text: string) => {},
+        swapFonts: () => {},
+    };
+}
+
+// ============================================================================
+// MOCK DATA GENERATORS
+// ============================================================================
+
+/**
+ * Generate paginated font data
+ */
+export function generatePaginatedFonts(
+    totalCount: number,
+    page: number,
+    limit: number,
+): {
+    fonts: UnifiedFont[];
+    page: number;
+    totalPages: number;
+    total: number;
+    hasNextPage: boolean;
+    hasPrevPage: boolean;
+} {
+    const totalPages = Math.ceil(totalCount / limit);
+    const startIndex = (page - 1) * limit;
+    const endIndex = Math.min(startIndex + limit, totalCount);
+
+    return {
+        fonts: generateMockFonts(endIndex - startIndex).map((font, i) => ({
+            ...font,
+            id: `font-${startIndex + i + 1}`,
+            name: `Font ${startIndex + i + 1}`,
+        })),
+        page,
+        totalPages,
+        total: totalCount,
+        hasNextPage: page < totalPages,
+        hasPrevPage: page > 1,
+    };
+}
+
+/**
+ * Create mock API response for fonts
+ */
+export function createMockFontApiResponse(config: {
+    fonts?: UnifiedFont[];
+    total?: number;
+    page?: number;
+    limit?: number;
+} = {}) {
+    const fonts = config.fonts ?? Object.values(UNIFIED_FONTS);
+    const total = config.total ?? fonts.length;
+    const page = config.page ?? 1;
+    const limit = config.limit ?? fonts.length;
+
+    return {
+        data: fonts,
+        meta: {
+            total,
+            page,
+            limit,
+            totalPages: Math.ceil(total / limit),
+            hasNextPage: page < Math.ceil(total / limit),
+            hasPrevPage: page > 1,
+        },
+    };
+}

src/entities/Font/model/store/appliedFontsStore/appliedFontStore.test.ts

@@ -12,9 +12,12 @@ import { AppliedFontsManager } from './appliedFontsStore.svelte';
 describe('AppliedFontsManager', () => {
     let manager: AppliedFontsManager;
     let mockFontFaceSet: any;
+    let mockFetch: any;
+    let failUrls: Set<string>;
 
     beforeEach(() => {
         vi.useFakeTimers();
+        failUrls = new Set();
 
         mockFontFaceSet = {
             add: vi.fn(),
@@ -22,11 +25,13 @@ describe('AppliedFontsManager', () => {
         };
 
         // 1. Properly mock FontFace as a constructor function
-        const MockFontFace = vi.fn(function(this: any, name: string, url: string) {
+        // The actual implementation passes buffer (ArrayBuffer) as second arg, not URL string
+        const MockFontFace = vi.fn(function(this: any, name: string, bufferOrUrl: ArrayBuffer | string) {
             this.name = name;
-            this.url = url;
+            this.bufferOrUrl = bufferOrUrl;
             this.load = vi.fn().mockImplementation(() => {
-                if (url.includes('fail')) return Promise.reject(new Error('Load failed'));
+                // For error tests, we track which URLs should fail via failUrls
+                // The fetch mock will have already rejected for those URLs
                 return Promise.resolve(this);
             });
         });
@@ -44,18 +49,37 @@ describe('AppliedFontsManager', () => {
             randomUUID: () => '11111111-1111-1111-1111-111111111111' as any,
         });
 
+        // 3. Mock fetch to return fake ArrayBuffer data
+        mockFetch = vi.fn((url: string) => {
+            if (failUrls.has(url)) {
+                return Promise.reject(new Error('Network error'));
+            }
+            return Promise.resolve({
+                ok: true,
+                status: 200,
+                arrayBuffer: () => Promise.resolve(new ArrayBuffer(8)),
+                clone: () => ({
+                    ok: true,
+                    status: 200,
+                    arrayBuffer: () => Promise.resolve(new ArrayBuffer(8)),
+                }),
+            } as Response);
+        });
+        vi.stubGlobal('fetch', mockFetch);
+
         manager = new AppliedFontsManager();
     });
 
     afterEach(() => {
         vi.clearAllTimers();
         vi.useRealTimers();
+        vi.unstubAllGlobals();
     });
 
     it('should batch multiple font requests into a single process', async () => {
         const configs = [
-            { id: 'lato-400', name: 'Lato', url: 'lato.ttf', weight: 400 },
-            { id: 'lato-700', name: 'Lato', url: 'lato-bold.ttf', weight: 700 },
+            { id: 'lato-400', name: 'Lato', url: 'https://example.com/lato.ttf', weight: 400 },
+            { id: 'lato-700', name: 'Lato', url: 'https://example.com/lato-bold.ttf', weight: 700 },
         ];
 
         manager.touch(configs);
@@ -71,7 +95,10 @@ describe('AppliedFontsManager', () => {
         // Suppress expected console error for clean test logs
         const spy = vi.spyOn(console, 'error').mockImplementation(() => {});
 
-        const config = { id: 'broken', name: 'Broken', url: 'fail.ttf', weight: 400 };
+        const failUrl = 'https://example.com/fail.ttf';
+        failUrls.add(failUrl);
+
+        const config = { id: 'broken', name: 'Broken', url: failUrl, weight: 400 };
 
         manager.touch([config]);
         await vi.advanceTimersByTimeAsync(50);
@@ -81,7 +108,7 @@ describe('AppliedFontsManager', () => {
     });
 
     it('should purge fonts after TTL expires', async () => {
-        const config = { id: 'ephemeral', name: 'Temp', url: 'temp.ttf', weight: 400 };
+        const config = { id: 'ephemeral', name: 'Temp', url: 'https://example.com/temp.ttf', weight: 400 };
 
         manager.touch([config]);
         await vi.advanceTimersByTimeAsync(50);
@@ -96,7 +123,7 @@ describe('AppliedFontsManager', () => {
     });
 
     it('should NOT purge fonts that are still being "touched"', async () => {
-        const config = { id: 'active', name: 'Active', url: 'active.ttf', weight: 400 };
+        const config = { id: 'active', name: 'Active', url: 'https://example.com/active.ttf', weight: 400 };
 
         manager.touch([config]);
         await vi.advanceTimersByTimeAsync(50);

src/shared/lib/helpers/createEntityStore/createEntityStore.test.ts

@@ -0,0 +1,420 @@
+import {
+    beforeEach,
+    describe,
+    expect,
+    it,
+} from 'vitest';
+import {
+    type Entity,
+    EntityStore,
+    createEntityStore,
+} from './createEntityStore.svelte';
+
+interface TestEntity {
+    id: string;
+    name: string;
+    value: number;
+}
+
+describe('createEntityStore', () => {
+    describe('Construction and Initialization', () => {
+        it('should create an empty store when no initial entities are provided', () => {
+            const store = createEntityStore<TestEntity>();
+
+            expect(store.all).toEqual([]);
+        });
+
+        it('should create a store with initial entities', () => {
+            const initialEntities: TestEntity[] = [
+                { id: '1', name: 'First', value: 1 },
+                { id: '2', name: 'Second', value: 2 },
+            ];
+            const store = createEntityStore(initialEntities);
+
+            expect(store.all).toHaveLength(2);
+            expect(store.all).toEqual(initialEntities);
+        });
+
+        it('should create EntityStore instance', () => {
+            const store = createEntityStore<TestEntity>();
+
+            expect(store).toBeInstanceOf(EntityStore);
+        });
+    });
+
+    describe('Selectors', () => {
+        let store: EntityStore<TestEntity>;
+        let entities: TestEntity[];
+
+        beforeEach(() => {
+            entities = [
+                { id: '1', name: 'First', value: 10 },
+                { id: '2', name: 'Second', value: 20 },
+                { id: '3', name: 'Third', value: 30 },
+            ];
+            store = createEntityStore(entities);
+        });
+
+        it('should return all entities as an array', () => {
+            const all = store.all;
+
+            expect(all).toEqual(entities);
+            expect(all).toHaveLength(3);
+        });
+
+        it('should get a single entity by ID', () => {
+            const entity = store.getById('2');
+
+            expect(entity).toEqual({ id: '2', name: 'Second', value: 20 });
+        });
+
+        it('should return undefined for non-existent ID', () => {
+            const entity = store.getById('999');
+
+            expect(entity).toBeUndefined();
+        });
+
+        it('should get multiple entities by IDs', () => {
+            const entities = store.getByIds(['1', '3']);
+
+            expect(entities).toEqual([
+                { id: '1', name: 'First', value: 10 },
+                { id: '3', name: 'Third', value: 30 },
+            ]);
+        });
+
+        it('should filter out undefined results when getting by IDs', () => {
+            const entities = store.getByIds(['1', '999', '3']);
+
+            expect(entities).toEqual([
+                { id: '1', name: 'First', value: 10 },
+                { id: '3', name: 'Third', value: 30 },
+            ]);
+            expect(entities).toHaveLength(2);
+        });
+
+        it('should return empty array when no IDs match', () => {
+            const entities = store.getByIds(['999', '888']);
+
+            expect(entities).toEqual([]);
+        });
+
+        it('should check if entity exists by ID', () => {
+            expect(store.has('1')).toBe(true);
+            expect(store.has('999')).toBe(false);
+        });
+    });
+
+    describe('CRUD Operations - Create', () => {
+        it('should add a single entity', () => {
+            const store = createEntityStore<TestEntity>();
+
+            store.addOne({ id: '1', name: 'First', value: 1 });
+
+            expect(store.all).toHaveLength(1);
+            expect(store.getById('1')).toEqual({ id: '1', name: 'First', value: 1 });
+        });
+
+        it('should add multiple entities at once', () => {
+            const store = createEntityStore<TestEntity>();
+
+            store.addMany([
+                { id: '1', name: 'First', value: 1 },
+                { id: '2', name: 'Second', value: 2 },
+                { id: '3', name: 'Third', value: 3 },
+            ]);
+
+            expect(store.all).toHaveLength(3);
+        });
+
+        it('should replace entity when adding with existing ID', () => {
+            const store = createEntityStore<TestEntity>([{ id: '1', name: 'Original', value: 1 }]);
+
+            store.addOne({ id: '1', name: 'Updated', value: 2 });
+
+            expect(store.all).toHaveLength(1);
+            expect(store.getById('1')).toEqual({ id: '1', name: 'Updated', value: 2 });
+        });
+    });
+
+    describe('CRUD Operations - Update', () => {
+        it('should update an existing entity', () => {
+            const store = createEntityStore<TestEntity>([{ id: '1', name: 'Original', value: 1 }]);
+
+            store.updateOne('1', { name: 'Updated' });
+
+            expect(store.getById('1')).toEqual({ id: '1', name: 'Updated', value: 1 });
+        });
+
+        it('should update multiple properties at once', () => {
+            const store = createEntityStore<TestEntity>([{ id: '1', name: 'Original', value: 1 }]);
+
+            store.updateOne('1', { name: 'Updated', value: 2 });
+
+            expect(store.getById('1')).toEqual({ id: '1', name: 'Updated', value: 2 });
+        });
+
+        it('should do nothing when updating non-existent entity', () => {
+            const store = createEntityStore<TestEntity>([{ id: '1', name: 'Original', value: 1 }]);
+
+            store.updateOne('999', { name: 'Updated' });
+
+            expect(store.all).toHaveLength(1);
+            expect(store.getById('1')).toEqual({ id: '1', name: 'Original', value: 1 });
+        });
+
+        it('should preserve entity when no changes are provided', () => {
+            const store = createEntityStore<TestEntity>([{ id: '1', name: 'Original', value: 1 }]);
+
+            store.updateOne('1', {});
+
+            expect(store.getById('1')).toEqual({ id: '1', name: 'Original', value: 1 });
+        });
+    });
+
+    describe('CRUD Operations - Delete', () => {
+        it('should remove a single entity', () => {
+            const store = createEntityStore<TestEntity>([
+                { id: '1', name: 'First', value: 1 },
+                { id: '2', name: 'Second', value: 2 },
+            ]);
+
+            store.removeOne('1');
+
+            expect(store.all).toHaveLength(1);
+            expect(store.getById('1')).toBeUndefined();
+            expect(store.getById('2')).toEqual({ id: '2', name: 'Second', value: 2 });
+        });
+
+        it('should remove multiple entities', () => {
+            const store = createEntityStore<TestEntity>([
+                { id: '1', name: 'First', value: 1 },
+                { id: '2', name: 'Second', value: 2 },
+                { id: '3', name: 'Third', value: 3 },
+            ]);
+
+            store.removeMany(['1', '3']);
+
+            expect(store.all).toHaveLength(1);
+            expect(store.getById('2')).toEqual({ id: '2', name: 'Second', value: 2 });
+        });
+
+        it('should do nothing when removing non-existent entity', () => {
+            const store = createEntityStore<TestEntity>([{ id: '1', name: 'First', value: 1 }]);
+
+            store.removeOne('999');
+
+            expect(store.all).toHaveLength(1);
+        });
+
+        it('should handle empty array when removing many', () => {
+            const store = createEntityStore<TestEntity>([{ id: '1', name: 'First', value: 1 }]);
+
+            store.removeMany([]);
+
+            expect(store.all).toHaveLength(1);
+        });
+    });
+
+    describe('Bulk Operations', () => {
+        it('should set all entities, replacing existing', () => {
+            const store = createEntityStore<TestEntity>([
+                { id: '1', name: 'First', value: 1 },
+                { id: '2', name: 'Second', value: 2 },
+            ]);
+
+            store.setAll([{ id: '3', name: 'Third', value: 3 }]);
+
+            expect(store.all).toHaveLength(1);
+            expect(store.getById('1')).toBeUndefined();
+            expect(store.getById('3')).toEqual({ id: '3', name: 'Third', value: 3 });
+        });
+
+        it('should clear all entities', () => {
+            const store = createEntityStore<TestEntity>([
+                { id: '1', name: 'First', value: 1 },
+                { id: '2', name: 'Second', value: 2 },
+            ]);
+
+            store.clear();
+
+            expect(store.all).toEqual([]);
+            expect(store.all).toHaveLength(0);
+        });
+    });
+
+    describe('Reactivity with SvelteMap', () => {
+        it('should return reactive arrays', () => {
+            const store = createEntityStore<TestEntity>([{ id: '1', name: 'First', value: 1 }]);
+
+            // The all getter should return a fresh array (or reactive state)
+            const first = store.all;
+            const second = store.all;
+
+            // Both should have the same content
+            expect(first).toEqual(second);
+        });
+
+        it('should reflect changes in subsequent calls', () => {
+            const store = createEntityStore<TestEntity>([{ id: '1', name: 'First', value: 1 }]);
+
+            expect(store.all).toHaveLength(1);
+
+            store.addOne({ id: '2', name: 'Second', value: 2 });
+
+            expect(store.all).toHaveLength(2);
+        });
+    });
+
+    describe('Edge Cases', () => {
+        it('should handle empty initial array', () => {
+            const store = createEntityStore<TestEntity>([]);
+
+            expect(store.all).toEqual([]);
+        });
+
+        it('should handle single entity', () => {
+            const store = createEntityStore<TestEntity>([{ id: '1', name: 'First', value: 1 }]);
+
+            expect(store.all).toHaveLength(1);
+            expect(store.getById('1')).toEqual({ id: '1', name: 'First', value: 1 });
+        });
+
+        it('should handle entities with complex objects', () => {
+            interface ComplexEntity extends Entity {
+                id: string;
+                data: {
+                    nested: {
+                        value: string;
+                    };
+                };
+                tags: string[];
+            }
+
+            const entity: ComplexEntity = {
+                id: '1',
+                data: { nested: { value: 'test' } },
+                tags: ['a', 'b', 'c'],
+            };
+
+            const store = createEntityStore<ComplexEntity>([entity]);
+
+            expect(store.getById('1')).toEqual(entity);
+        });
+
+        it('should handle numeric string IDs', () => {
+            const store = createEntityStore<TestEntity>([
+                { id: '123', name: 'First', value: 1 },
+                { id: '456', name: 'Second', value: 2 },
+            ]);
+
+            expect(store.getById('123')).toEqual({ id: '123', name: 'First', value: 1 });
+            expect(store.getById('456')).toEqual({ id: '456', name: 'Second', value: 2 });
+        });
+
+        it('should handle UUID-like IDs', () => {
+            const uuid1 = '550e8400-e29b-41d4-a716-446655440000';
+            const uuid2 = '550e8400-e29b-41d4-a716-446655440001';
+
+            const store = createEntityStore<TestEntity>([
+                { id: uuid1, name: 'First', value: 1 },
+                { id: uuid2, name: 'Second', value: 2 },
+            ]);
+
+            expect(store.getById(uuid1)).toEqual({ id: uuid1, name: 'First', value: 1 });
+        });
+    });
+
+    describe('Type Safety', () => {
+        it('should enforce Entity type with id property', () => {
+            // This test verifies type checking at compile time
+            const validEntity: TestEntity = { id: '1', name: 'Test', value: 1 };
+
+            const store = createEntityStore<TestEntity>([validEntity]);
+
+            expect(store.getById('1')).toEqual(validEntity);
+        });
+
+        it('should work with different entity types', () => {
+            interface User extends Entity {
+                id: string;
+                name: string;
+                email: string;
+            }
+
+            interface Product extends Entity {
+                id: string;
+                title: string;
+                price: number;
+            }
+
+            const userStore = createEntityStore<User>([
+                { id: 'u1', name: 'John', email: 'john@example.com' },
+            ]);
+
+            const productStore = createEntityStore<Product>([
+                { id: 'p1', title: 'Widget', price: 9.99 },
+            ]);
+
+            expect(userStore.getById('u1')?.email).toBe('john@example.com');
+            expect(productStore.getById('p1')?.price).toBe(9.99);
+        });
+    });
+
+    describe('Large Datasets', () => {
+        it('should handle large number of entities efficiently', () => {
+            const entities: TestEntity[] = Array.from({ length: 1000 }, (_, i) => ({
+                id: `id-${i}`,
+                name: `Entity ${i}`,
+                value: i,
+            }));
+
+            const store = createEntityStore(entities);
+
+            expect(store.all).toHaveLength(1000);
+            expect(store.getById('id-500')).toEqual({
+                id: 'id-500',
+                name: 'Entity 500',
+                value: 500,
+            });
+        });
+
+        it('should efficiently check existence in large dataset', () => {
+            const entities: TestEntity[] = Array.from({ length: 1000 }, (_, i) => ({
+                id: `id-${i}`,
+                name: `Entity ${i}`,
+                value: i,
+            }));
+
+            const store = createEntityStore(entities);
+
+            expect(store.has('id-999')).toBe(true);
+            expect(store.has('id-1000')).toBe(false);
+        });
+    });
+
+    describe('Method Chaining', () => {
+        it('should support chaining add operations', () => {
+            const store = createEntityStore<TestEntity>();
+
+            store.addOne({ id: '1', name: 'First', value: 1 });
+            store.addOne({ id: '2', name: 'Second', value: 2 });
+            store.addOne({ id: '3', name: 'Third', value: 3 });
+
+            expect(store.all).toHaveLength(3);
+        });
+
+        it('should support chaining update operations', () => {
+            const store = createEntityStore<TestEntity>([
+                { id: '1', name: 'First', value: 1 },
+                { id: '2', name: 'Second', value: 2 },
+            ]);
+
+            store.updateOne('1', { value: 10 });
+            store.updateOne('2', { value: 20 });
+
+            expect(store.getById('1')?.value).toBe(10);
+            expect(store.getById('2')?.value).toBe(20);
+        });
+    });
+});

src/shared/lib/helpers/createPersistentStore/createPersistentStore.test.ts

@@ -0,0 +1,377 @@
+/** @vitest-environment jsdom */
+import {
+    afterEach,
+    beforeEach,
+    describe,
+    expect,
+    it,
+    vi,
+} from 'vitest';
+import { createPersistentStore } from './createPersistentStore.svelte';
+
+describe('createPersistentStore', () => {
+    let mockLocalStorage: Storage;
+    const testKey = 'test-store-key';
+
+    beforeEach(() => {
+        // Mock localStorage
+        const storeMap = new Map<string, string>();
+
+        mockLocalStorage = {
+            get length() {
+                return storeMap.size;
+            },
+            clear() {
+                storeMap.clear();
+            },
+            getItem(key: string) {
+                return storeMap.get(key) ?? null;
+            },
+            setItem(key: string, value: string) {
+                storeMap.set(key, value);
+            },
+            removeItem(key: string) {
+                storeMap.delete(key);
+            },
+            key(index: number) {
+                return Array.from(storeMap.keys())[index] ?? null;
+            },
+        };
+
+        vi.stubGlobal('localStorage', mockLocalStorage);
+    });
+
+    afterEach(() => {
+        vi.unstubAllGlobals();
+    });
+
+    describe('Initialization', () => {
+        it('should create store with default value when localStorage is empty', () => {
+            const store = createPersistentStore(testKey, 'default');
+
+            expect(store.value).toBe('default');
+        });
+
+        it('should create store with value from localStorage', () => {
+            mockLocalStorage.setItem(testKey, JSON.stringify('stored value'));
+
+            const store = createPersistentStore(testKey, 'default');
+
+            expect(store.value).toBe('stored value');
+        });
+
+        it('should parse JSON from localStorage', () => {
+            const storedValue = { name: 'Test', count: 42 };
+            mockLocalStorage.setItem(testKey, JSON.stringify(storedValue));
+
+            const store = createPersistentStore(testKey, { name: 'Default', count: 0 });
+
+            expect(store.value).toEqual(storedValue);
+        });
+
+        it('should use default value when localStorage has invalid JSON', () => {
+            const consoleSpy = vi.spyOn(console, 'warn').mockImplementation(() => {});
+            mockLocalStorage.setItem(testKey, 'invalid json{');
+
+            const store = createPersistentStore(testKey, 'default');
+
+            expect(store.value).toBe('default');
+            expect(consoleSpy).toHaveBeenCalled();
+            consoleSpy.mockRestore();
+        });
+    });
+
+    describe('Reading Values', () => {
+        it('should return current value via getter', () => {
+            const store = createPersistentStore(testKey, 'default');
+
+            expect(store.value).toBe('default');
+        });
+
+        it('should return updated value after setter', () => {
+            const store = createPersistentStore(testKey, 'default');
+
+            store.value = 'updated';
+
+            expect(store.value).toBe('updated');
+        });
+
+        it('should preserve type information', () => {
+            interface TestObject {
+                name: string;
+                count: number;
+            }
+            const defaultValue: TestObject = { name: 'Test', count: 0 };
+            const store = createPersistentStore<TestObject>(testKey, defaultValue);
+
+            expect(store.value.name).toBe('Test');
+            expect(store.value.count).toBe(0);
+        });
+    });
+
+    describe('Writing Values', () => {
+        it('should update value when set via setter', () => {
+            const store = createPersistentStore(testKey, 'default');
+
+            store.value = 'new value';
+
+            expect(store.value).toBe('new value');
+        });
+
+        it('should serialize objects to JSON', () => {
+            const store = createPersistentStore(testKey, { name: 'Default', count: 0 });
+
+            store.value = { name: 'Updated', count: 42 };
+
+            // The value is updated in the store
+            expect(store.value).toEqual({ name: 'Updated', count: 42 });
+        });
+
+        it('should handle arrays', () => {
+            const store = createPersistentStore<number[]>(testKey, []);
+
+            store.value = [1, 2, 3];
+
+            expect(store.value).toEqual([1, 2, 3]);
+        });
+
+        it('should handle booleans', () => {
+            const store = createPersistentStore<boolean>(testKey, false);
+
+            store.value = true;
+
+            expect(store.value).toBe(true);
+        });
+
+        it('should handle null values', () => {
+            const store = createPersistentStore<string | null>(testKey, null);
+
+            store.value = 'not null';
+
+            expect(store.value).toBe('not null');
+        });
+    });
+
+    describe('Clear Function', () => {
+        it('should reset value to default when clear is called', () => {
+            const store = createPersistentStore(testKey, 'default');
+
+            store.value = 'modified';
+            store.clear();
+
+            expect(store.value).toBe('default');
+        });
+
+        it('should work with object defaults', () => {
+            const defaultValue = { name: 'Default', count: 0 };
+            const store = createPersistentStore(testKey, defaultValue);
+
+            store.value = { name: 'Modified', count: 42 };
+            store.clear();
+
+            expect(store.value).toEqual(defaultValue);
+        });
+
+        it('should work with array defaults', () => {
+            const defaultValue = [1, 2, 3];
+            const store = createPersistentStore<number[]>(testKey, defaultValue);
+
+            store.value = [4, 5, 6];
+            store.clear();
+
+            expect(store.value).toEqual(defaultValue);
+        });
+    });
+
+    describe('Type Support', () => {
+        it('should work with string type', () => {
+            const store = createPersistentStore<string>(testKey, 'default');
+
+            store.value = 'test string';
+
+            expect(store.value).toBe('test string');
+        });
+
+        it('should work with number type', () => {
+            const store = createPersistentStore<number>(testKey, 0);
+
+            store.value = 42;
+
+            expect(store.value).toBe(42);
+        });
+
+        it('should work with boolean type', () => {
+            const store = createPersistentStore<boolean>(testKey, false);
+
+            store.value = true;
+
+            expect(store.value).toBe(true);
+        });
+
+        it('should work with object type', () => {
+            interface TestObject {
+                name: string;
+                value: number;
+            }
+            const defaultValue: TestObject = { name: 'Test', value: 0 };
+            const store = createPersistentStore<TestObject>(testKey, defaultValue);
+
+            store.value = { name: 'Updated', value: 42 };
+
+            expect(store.value.name).toBe('Updated');
+            expect(store.value.value).toBe(42);
+        });
+
+        it('should work with array type', () => {
+            const store = createPersistentStore<string[]>(testKey, []);
+
+            store.value = ['a', 'b', 'c'];
+
+            expect(store.value).toEqual(['a', 'b', 'c']);
+        });
+
+        it('should work with null type', () => {
+            const store = createPersistentStore<string | null>(testKey, null);
+
+            expect(store.value).toBeNull();
+
+            store.value = 'not null';
+
+            expect(store.value).toBe('not null');
+        });
+    });
+
+    describe('Edge Cases', () => {
+        it('should handle empty string', () => {
+            const store = createPersistentStore(testKey, 'default');
+
+            store.value = '';
+
+            expect(store.value).toBe('');
+        });
+
+        it('should handle zero number', () => {
+            const store = createPersistentStore<number>(testKey, 100);
+
+            store.value = 0;
+
+            expect(store.value).toBe(0);
+        });
+
+        it('should handle false boolean', () => {
+            const store = createPersistentStore<boolean>(testKey, true);
+
+            store.value = false;
+
+            expect(store.value).toBe(false);
+        });
+
+        it('should handle empty array', () => {
+            const store = createPersistentStore<number[]>(testKey, [1, 2, 3]);
+
+            store.value = [];
+
+            expect(store.value).toEqual([]);
+        });
+
+        it('should handle empty object', () => {
+            const store = createPersistentStore<Record<string, unknown>>(testKey, { a: 1 });
+
+            store.value = {};
+
+            expect(store.value).toEqual({});
+        });
+
+        it('should handle special characters in string', () => {
+            const store = createPersistentStore(testKey, '');
+
+            const specialString = 'Hello "world"\nNew line\tTab';
+            store.value = specialString;
+
+            expect(store.value).toBe(specialString);
+        });
+
+        it('should handle unicode characters', () => {
+            const store = createPersistentStore(testKey, '');
+
+            store.value = 'Hello 世界 🌍';
+
+            expect(store.value).toBe('Hello 世界 🌍');
+        });
+    });
+
+    describe('Multiple Instances', () => {
+        it('should handle multiple stores with different keys', () => {
+            const store1 = createPersistentStore('key1', 'value1');
+            const store2 = createPersistentStore('key2', 'value2');
+
+            store1.value = 'updated1';
+            store2.value = 'updated2';
+
+            expect(store1.value).toBe('updated1');
+            expect(store2.value).toBe('updated2');
+        });
+
+        it('should keep stores independent', () => {
+            const store1 = createPersistentStore('key1', 'default1');
+            const store2 = createPersistentStore('key2', 'default2');
+
+            store1.clear();
+
+            expect(store1.value).toBe('default1');
+            expect(store2.value).toBe('default2');
+        });
+    });
+
+    describe('Complex Scenarios', () => {
+        it('should handle nested objects', () => {
+            interface NestedObject {
+                user: {
+                    name: string;
+                    settings: {
+                        theme: string;
+                        notifications: boolean;
+                    };
+                };
+            }
+            const defaultValue: NestedObject = {
+                user: {
+                    name: 'Test',
+                    settings: { theme: 'light', notifications: true },
+                },
+            };
+            const store = createPersistentStore<NestedObject>(testKey, defaultValue);
+
+            store.value = {
+                user: {
+                    name: 'Updated',
+                    settings: { theme: 'dark', notifications: false },
+                },
+            };
+
+            expect(store.value).toEqual({
+                user: {
+                    name: 'Updated',
+                    settings: { theme: 'dark', notifications: false },
+                },
+            });
+        });
+
+        it('should handle arrays of objects', () => {
+            interface Item {
+                id: number;
+                name: string;
+            }
+            const store = createPersistentStore<Item[]>(testKey, []);
+
+            store.value = [
+                { id: 1, name: 'First' },
+                { id: 2, name: 'Second' },
+                { id: 3, name: 'Third' },
+            ];
+
+            expect(store.value).toHaveLength(3);
+            expect(store.value[0].name).toBe('First');
+        });
+    });
+});

src/shared/lib/helpers/createVirtualizer/createVirtualizer.test.ts

@@ -0,0 +1,550 @@
+/** @vitest-environment jsdom */
+import {
+    afterEach,
+    describe,
+    expect,
+    it,
+    vi,
+} from 'vitest';
+import { createVirtualizer } from './createVirtualizer.svelte';
+
+/**
+ * NOTE: Svelte 5 Runes Testing Limitations
+ *
+ * The createVirtualizer helper uses Svelte 5 runes ($state, $derived, $derived.by)
+ * which require a full Svelte runtime environment to work correctly. In unit tests
+ * with jsdom, these runes are stubbed and don't provide actual reactivity.
+ *
+ * These tests focus on:
+ * 1. API surface verification (methods, getters exist)
+ * 2. Initial state calculation
+ * 3. DOM integration (event listeners are attached)
+ * 4. Edge case handling
+ *
+ * For full reactivity testing, use browser-based tests with @vitest/browser-playwright
+ */
+
+// Mock ResizeObserver globally since it's not available in jsdom
+class MockResizeObserver {
+    observe = vi.fn();
+    unobserve = vi.fn();
+    disconnect = vi.fn();
+}
+
+globalThis.ResizeObserver = MockResizeObserver as any;
+
+// Mock requestAnimationFrame
+globalThis.requestAnimationFrame =
+    ((cb: FrameRequestCallback) =>
+        setTimeout(() => cb(performance.now()), 16) as unknown) as typeof requestAnimationFrame;
+globalThis.cancelAnimationFrame = vi.fn();
+
+/**
+ * Helper to create test data array
+ */
+function createTestData(count: number): string[] {
+    return Array.from({ length: count }, (_, i) => `Item ${i}`);
+}
+
+/**
+ * Helper to create a mock scrollable container element
+ */
+function createMockContainer(height = 500, scrollTop = 0): any {
+    const container = document.createElement('div');
+    Object.defineProperty(container, 'offsetHeight', {
+        value: height,
+        configurable: true,
+        writable: true,
+    });
+    Object.defineProperty(container, 'scrollTop', {
+        value: scrollTop,
+        writable: true,
+        configurable: true,
+    });
+    // Add scrollTo method for testing
+    container.scrollTo = vi.fn();
+    return container;
+}
+
+describe('createVirtualizer - Basic API and State', () => {
+    describe('Basic Initialization and API Surface', () => {
+        it('should initialize and return expected API surface', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 0,
+                data: [],
+                estimateSize: () => 50,
+            }));
+
+            // Verify API surface exists
+            expect(virtualizer).toHaveProperty('items');
+            expect(virtualizer).toHaveProperty('totalSize');
+            expect(virtualizer).toHaveProperty('scrollOffset');
+            expect(virtualizer).toHaveProperty('containerHeight');
+            expect(virtualizer).toHaveProperty('container');
+            expect(virtualizer).toHaveProperty('measureElement');
+            expect(virtualizer).toHaveProperty('scrollToIndex');
+            expect(virtualizer).toHaveProperty('scrollToOffset');
+
+            // Verify initial values
+            expect(virtualizer.items).toEqual([]);
+            expect(virtualizer.totalSize).toBe(0);
+            expect(virtualizer.scrollOffset).toBe(0);
+            expect(virtualizer.containerHeight).toBe(0);
+        });
+
+        it('should calculate correct totalSize for uniform item sizes', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 10,
+                data: createTestData(10),
+                estimateSize: () => 50,
+            }));
+
+            // 10 items * 50px each = 500px total
+            expect(virtualizer.totalSize).toBe(500);
+        });
+
+        it('should calculate correct totalSize for varying item sizes', () => {
+            const sizes = [50, 100, 150, 75, 125]; // Sum = 500
+            const virtualizer = createVirtualizer(() => ({
+                count: 5,
+                data: createTestData(5),
+                estimateSize: (i: number) => sizes[i],
+            }));
+
+            expect(virtualizer.totalSize).toBe(500);
+        });
+
+        it('should handle empty list (count = 0)', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 0,
+                data: [],
+                estimateSize: () => 50,
+            }));
+
+            expect(virtualizer.totalSize).toBe(0);
+            expect(virtualizer.items).toEqual([]);
+        });
+
+        it('should handle very large lists', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 100000,
+                data: createTestData(100000),
+                estimateSize: () => 50,
+            }));
+
+            expect(virtualizer.totalSize).toBe(5000000); // 100000 * 50
+        });
+
+        it('should handle zero estimated size', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 10,
+                data: createTestData(10),
+                estimateSize: () => 0,
+            }));
+
+            expect(virtualizer.totalSize).toBe(0);
+        });
+    });
+
+    describe('Container Action', () => {
+        let cleanupHandlers: (() => void)[] = [];
+
+        afterEach(() => {
+            cleanupHandlers.forEach(cleanup => cleanup());
+            cleanupHandlers = [];
+        });
+
+        it('should attach container action and set up listeners', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 100,
+                data: createTestData(100),
+                estimateSize: () => 50,
+            }));
+
+            const container = createMockContainer(500, 0);
+            const addEventListenerSpy = vi.spyOn(container, 'addEventListener');
+
+            const cleanup = virtualizer.container(container);
+            cleanupHandlers.push(() => cleanup?.destroy?.());
+
+            // Verify scroll listener was attached
+            expect(addEventListenerSpy).toHaveBeenCalledWith(
+                'scroll',
+                expect.any(Function),
+                { passive: true },
+            );
+        });
+
+        it('should update containerHeight when container is attached', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 100,
+                data: createTestData(100),
+                estimateSize: () => 50,
+            }));
+
+            const container = createMockContainer(500, 0);
+            const cleanup = virtualizer.container(container);
+            cleanupHandlers.push(() => cleanup?.destroy?.());
+
+            expect(virtualizer.containerHeight).toBe(500);
+        });
+
+        it('should clean up listeners on destroy', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 100,
+                data: createTestData(100),
+                estimateSize: () => 50,
+            }));
+
+            const container = createMockContainer(500, 0);
+            const removeEventListenerSpy = vi.spyOn(container, 'removeEventListener');
+
+            const cleanup = virtualizer.container(container);
+            cleanup?.destroy?.();
+
+            expect(removeEventListenerSpy).toHaveBeenCalled();
+        });
+
+        it('should support window scrolling mode', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 100,
+                data: createTestData(100),
+                estimateSize: () => 50,
+                useWindowScroll: true,
+            }));
+
+            const container = createMockContainer(500, 0);
+            const windowAddSpy = vi.spyOn(window, 'addEventListener');
+
+            const cleanup = virtualizer.container(container);
+            cleanupHandlers.push(() => cleanup?.destroy?.());
+
+            // Should attach to window scroll
+            expect(windowAddSpy).toHaveBeenCalledWith('scroll', expect.any(Function), expect.any(Object));
+            expect(windowAddSpy).toHaveBeenCalledWith('resize', expect.any(Function));
+
+            windowAddSpy.mockRestore();
+        });
+    });
+
+    describe('scrollToIndex Method', () => {
+        let cleanupHandlers: (() => void)[] = [];
+
+        afterEach(() => {
+            cleanupHandlers.forEach(cleanup => cleanup());
+            cleanupHandlers = [];
+        });
+
+        it('should have scrollToIndex method that does not throw without container', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 100,
+                data: createTestData(100),
+                estimateSize: () => 50,
+            }));
+
+            // Should not throw when container is not attached
+            expect(() => virtualizer.scrollToIndex(50)).not.toThrow();
+        });
+
+        it('should scroll to specific index with container attached', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 100,
+                data: createTestData(100),
+                estimateSize: () => 50,
+            }));
+
+            const container = createMockContainer(500, 0);
+            const scrollToSpy = vi.spyOn(container, 'scrollTo');
+
+            const cleanup = virtualizer.container(container);
+            cleanupHandlers.push(() => cleanup?.destroy?.());
+
+            virtualizer.scrollToIndex(10);
+
+            expect(scrollToSpy).toHaveBeenCalledWith({
+                top: expect.any(Number),
+                behavior: 'smooth',
+            });
+        });
+
+        it('should handle center alignment', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 100,
+                data: createTestData(100),
+                estimateSize: () => 50,
+            }));
+
+            const container = createMockContainer(500, 0);
+            const scrollToSpy = vi.spyOn(container, 'scrollTo');
+
+            const cleanup = virtualizer.container(container);
+            cleanupHandlers.push(() => cleanup?.destroy?.());
+
+            virtualizer.scrollToIndex(10, 'center');
+
+            expect(scrollToSpy).toHaveBeenCalled();
+        });
+
+        it('should handle end alignment', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 100,
+                data: createTestData(100),
+                estimateSize: () => 50,
+            }));
+
+            const container = createMockContainer(500, 0);
+            const scrollToSpy = vi.spyOn(container, 'scrollTo');
+
+            const cleanup = virtualizer.container(container);
+            cleanupHandlers.push(() => cleanup?.destroy?.());
+
+            virtualizer.scrollToIndex(10, 'end');
+
+            expect(scrollToSpy).toHaveBeenCalled();
+        });
+
+        it('should not scroll for out of bounds indices', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 100,
+                data: createTestData(100),
+                estimateSize: () => 50,
+            }));
+
+            const container = createMockContainer(500, 0);
+            const scrollToSpy = vi.spyOn(container, 'scrollTo');
+
+            const cleanup = virtualizer.container(container);
+            cleanupHandlers.push(() => cleanup?.destroy?.());
+
+            // Negative index
+            virtualizer.scrollToIndex(-1);
+
+            // Index >= count
+            virtualizer.scrollToIndex(100);
+
+            // Should not have been called
+            expect(scrollToSpy).not.toHaveBeenCalled();
+        });
+    });
+
+    describe('scrollToOffset Method', () => {
+        let cleanupHandlers: (() => void)[] = [];
+
+        afterEach(() => {
+            cleanupHandlers.forEach(cleanup => cleanup());
+            cleanupHandlers = [];
+        });
+
+        it('should scroll to specific pixel offset', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 100,
+                data: createTestData(100),
+                estimateSize: () => 50,
+            }));
+
+            const container = createMockContainer(500, 0);
+            const scrollToSpy = vi.spyOn(container, 'scrollTo');
+
+            const cleanup = virtualizer.container(container);
+            cleanupHandlers.push(() => cleanup?.destroy?.());
+
+            virtualizer.scrollToOffset(1000);
+
+            expect(scrollToSpy).toHaveBeenCalledWith({ top: 1000, behavior: 'auto' });
+        });
+
+        it('should support smooth behavior', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 100,
+                data: createTestData(100),
+                estimateSize: () => 50,
+            }));
+
+            const container = createMockContainer(500, 0);
+            const scrollToSpy = vi.spyOn(container, 'scrollTo');
+
+            const cleanup = virtualizer.container(container);
+            cleanupHandlers.push(() => cleanup?.destroy?.());
+
+            virtualizer.scrollToOffset(1000, 'smooth');
+
+            expect(scrollToSpy).toHaveBeenCalledWith({ top: 1000, behavior: 'smooth' });
+        });
+    });
+
+    describe('measureElement Action', () => {
+        it('should attach measureElement action to DOM element', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 10,
+                data: createTestData(10),
+                estimateSize: () => 50,
+            }));
+
+            const element = document.createElement('div');
+            element.dataset.index = '0';
+
+            // Should not throw when attaching measureElement
+            expect(() => {
+                const cleanup = virtualizer.measureElement(element);
+                cleanup?.destroy?.();
+            }).not.toThrow();
+        });
+
+        it('should clean up observer on destroy', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 10,
+                data: createTestData(10),
+                estimateSize: () => 50,
+            }));
+
+            const element = document.createElement('div');
+            element.dataset.index = '0';
+
+            const cleanup = virtualizer.measureElement(element);
+
+            // Should not throw when destroying
+            expect(() => cleanup?.destroy?.()).not.toThrow();
+        });
+
+        it('should handle multiple elements being measured', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 10,
+                data: createTestData(10),
+                estimateSize: () => 50,
+            }));
+
+            const elements = Array.from({ length: 5 }, (_, i) => {
+                const el = document.createElement('div');
+                el.dataset.index = String(i);
+                return el;
+            });
+
+            const cleanups = elements.map(el => virtualizer.measureElement(el));
+
+            // Should not throw when measuring multiple elements
+            expect(() => {
+                cleanups.forEach(cleanup => cleanup?.destroy?.());
+            }).not.toThrow();
+        });
+    });
+
+    describe('Options Handling', () => {
+        it('should use default overscan of 5', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 100,
+                data: createTestData(100),
+                estimateSize: () => 50,
+            }));
+
+            // Options with default overscan should work
+            expect(virtualizer).toHaveProperty('items');
+        });
+
+        it('should use custom overscan value', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 100,
+                data: createTestData(100),
+                estimateSize: () => 50,
+                overscan: 10,
+            }));
+
+            expect(virtualizer).toHaveProperty('items');
+        });
+
+        it('should use index as default key when getItemKey is not provided', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 10,
+                data: createTestData(10),
+                estimateSize: () => 50,
+            }));
+
+            expect(virtualizer).toHaveProperty('items');
+        });
+
+        it('should use custom getItemKey when provided', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 10,
+                data: createTestData(10),
+                estimateSize: () => 50,
+                getItemKey: (i: number) => `custom-key-${i}`,
+            }));
+
+            expect(virtualizer).toHaveProperty('items');
+        });
+
+        it('should use custom scrollMargin when provided', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 100,
+                data: createTestData(100),
+                estimateSize: () => 50,
+                scrollMargin: 100,
+            }));
+
+            expect(virtualizer).toHaveProperty('items');
+        });
+    });
+
+    describe('Edge Cases', () => {
+        it('should handle single item list', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 1,
+                data: ['Item 0'],
+                estimateSize: () => 100,
+            }));
+
+            expect(virtualizer.totalSize).toBe(100);
+        });
+
+        it('should handle items larger than viewport', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 5,
+                data: createTestData(5),
+                estimateSize: () => 200, // Each item is 200px
+            }));
+
+            // Total size should still be calculated correctly
+            expect(virtualizer.totalSize).toBe(1000); // 5 * 200
+        });
+
+        it('should handle overscan larger than viewport', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 10,
+                data: createTestData(10),
+                estimateSize: () => 50,
+                overscan: 100, // Very large overscan
+            }));
+
+            expect(virtualizer).toHaveProperty('items');
+        });
+
+        it('should handle negative estimated size (graceful degradation)', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 10,
+                data: createTestData(10),
+                estimateSize: () => -10,
+            }));
+
+            // Should calculate total size (may be negative, but shouldn't crash)
+            expect(virtualizer.totalSize).toBeLessThanOrEqual(0);
+        });
+    });
+
+    describe('Virtual Item Structure', () => {
+        it('should return items with correct structure when container is attached', () => {
+            const virtualizer = createVirtualizer(() => ({
+                count: 100,
+                data: createTestData(100),
+                estimateSize: () => 50,
+            }));
+
+            const container = createMockContainer(500, 0);
+            const cleanup = virtualizer.container(container);
+
+            // Items may be empty in test environment due to reactivity limitations
+            // but we verify the structure exists
+            expect(Array.isArray(virtualizer.items)).toBe(true);
+
+            cleanup?.destroy?.();
+        });
+    });
+});

src/shared/lib/storybook/MockIcon.svelte

@@ -0,0 +1,41 @@
+<!--
+    Component: MockIcon
+    Wrapper component for Lucide icons to properly handle className in Storybook.
+
+    Lucide Svelte icons from @lucide/svelte/icons/* don't properly handle
+    the className prop directly. This wrapper ensures the class is applied
+    correctly via the HTML element's class attribute.
+-->
+<script lang="ts">
+import { cn } from '$shared/shadcn/utils/shadcn-utils';
+import type {
+    Component,
+    Snippet,
+} from 'svelte';
+
+interface Props {
+    /**
+     * The Lucide icon component
+     */
+    icon: Component;
+    /**
+     * CSS classes to apply to the icon
+     */
+    class?: string;
+    /**
+     * Additional icon-specific attributes
+     */
+    attrs?: Record<string, unknown>;
+}
+
+let { icon: Icon, class: className, attrs = {} }: Props = $props();
+</script>
+
+{#if Icon}
+    {@const __iconClass__ = cn('size-4', className)}
+    <!-- Render icon component dynamically with class prop -->
+    <Icon
+        class={__iconClass__}
+        {...attrs}
+    />
+{/if}

src/shared/lib/storybook/Providers.svelte

@@ -0,0 +1,64 @@
+<!--
+    Component: Providers
+    Storybook wrapper that provides required contexts for components.
+
+    Provides:
+    - responsive: ResponsiveManager context for breakpoint tracking
+    - tooltip: Tooltip.Provider context for shadcn Tooltip components
+    - Additional Radix UI providers can be added here as needed
+-->
+<script lang="ts">
+import { createResponsiveManager } from '$shared/lib';
+import type { ResponsiveManager } from '$shared/lib';
+import { Provider as TooltipProvider } from '$shared/shadcn/ui/tooltip';
+import { setContext } from 'svelte';
+import type { Snippet } from 'svelte';
+
+interface Props {
+    children: Snippet;
+    /**
+     * Initial viewport width for the responsive context (default: 1280)
+     */
+    initialWidth?: number;
+    /**
+     * Initial viewport height for the responsive context (default: 720)
+     */
+    initialHeight?: number;
+    /**
+     * Tooltip provider options
+     */
+    tooltipDelayDuration?: number;
+    /**
+     * Tooltip skip delay duration
+     */
+    tooltipSkipDelayDuration?: number;
+}
+
+let {
+    children,
+    initialWidth = 1280,
+    initialHeight = 720,
+    tooltipDelayDuration = 200,
+    tooltipSkipDelayDuration = 300,
+}: Props = $props();
+
+// Create a responsive manager with default breakpoints
+const responsiveManager = createResponsiveManager();
+
+// Initialize the responsive manager to set up resize listeners
+$effect(() => {
+    return responsiveManager.init();
+});
+
+// Provide the responsive context
+setContext<ResponsiveManager>('responsive', responsiveManager);
+</script>
+
+<div class="storybook-providers" style:width="100%" style:height="100%">
+    <TooltipProvider
+        delayDuration={tooltipDelayDuration}
+        skipDelayDuration={tooltipSkipDelayDuration}
+    >
+        {@render children()}
+    </TooltipProvider>
+</div>

src/shared/lib/storybook/index.ts

@@ -0,0 +1,24 @@
+/**
+ * ============================================================================
+ * STORYBOOK HELPERS
+ * ============================================================================
+ *
+ * Helper components and utilities for Storybook stories.
+ *
+ * ## Usage
+ *
+ * ```svelte
+ * <script lang="ts">
+ * import { Providers, MockIcon } from '$shared/lib/storybook';
+ * </script>
+ *
+ * <Providers>
+ *   <YourComponent />
+ * </Providers>
+ * ```
+ *
+ * @module
+ */
+
+export { default as MockIcon } from './MockIcon.svelte';
+export { default as Providers } from './Providers.svelte';

src/shared/lib/utils/smoothScroll/smoothScroll.test.ts

@@ -0,0 +1,368 @@
+/** @vitest-environment jsdom */
+import {
+    afterEach,
+    beforeEach,
+    describe,
+    expect,
+    it,
+    vi,
+} from 'vitest';
+import { smoothScroll } from './smoothScroll';
+
+describe('smoothScroll', () => {
+    let mockAnchor: HTMLAnchorElement;
+    let mockTarget: HTMLElement;
+    let mockScrollIntoView: ReturnType<typeof vi.fn>;
+    let mockPushState: ReturnType<typeof vi.fn>;
+
+    beforeEach(() => {
+        // Mock scrollIntoView
+        mockScrollIntoView = vi.fn();
+        HTMLElement.prototype.scrollIntoView = mockScrollIntoView as (arg?: boolean | ScrollIntoViewOptions) => void;
+
+        // Mock history.pushState
+        mockPushState = vi.fn();
+        vi.stubGlobal('history', {
+            pushState: mockPushState,
+        });
+
+        // Create mock elements
+        mockAnchor = document.createElement('a');
+        mockAnchor.setAttribute('href', '#section-1');
+
+        mockTarget = document.createElement('div');
+        mockTarget.id = 'section-1';
+        document.body.appendChild(mockTarget);
+    });
+
+    afterEach(() => {
+        vi.clearAllMocks();
+        vi.unstubAllGlobals();
+        document.body.innerHTML = '';
+    });
+
+    describe('Basic Functionality', () => {
+        it('should be a function that returns an object with destroy method', () => {
+            const action = smoothScroll(mockAnchor);
+
+            expect(typeof action).toBe('object');
+            expect(typeof action.destroy).toBe('function');
+        });
+
+        it('should add click event listener to the anchor element', () => {
+            const addEventListenerSpy = vi.spyOn(mockAnchor, 'addEventListener');
+            smoothScroll(mockAnchor);
+
+            expect(addEventListenerSpy).toHaveBeenCalledWith('click', expect.any(Function));
+            addEventListenerSpy.mockRestore();
+        });
+
+        it('should remove click event listener when destroy is called', () => {
+            const action = smoothScroll(mockAnchor);
+            const removeEventListenerSpy = vi.spyOn(mockAnchor, 'removeEventListener');
+
+            action.destroy();
+
+            expect(removeEventListenerSpy).toHaveBeenCalledWith('click', expect.any(Function));
+            removeEventListenerSpy.mockRestore();
+        });
+    });
+
+    describe('Click Handling', () => {
+        it('should prevent default behavior on click', () => {
+            const mockEvent = new MouseEvent('click', {
+                bubbles: true,
+                cancelable: true,
+            });
+            const preventDefaultSpy = vi.spyOn(mockEvent, 'preventDefault');
+
+            smoothScroll(mockAnchor);
+            mockAnchor.dispatchEvent(mockEvent);
+
+            expect(preventDefaultSpy).toHaveBeenCalled();
+            preventDefaultSpy.mockRestore();
+        });
+
+        it('should scroll to target element when clicked', () => {
+            const mockEvent = new MouseEvent('click', { bubbles: true, cancelable: true });
+
+            smoothScroll(mockAnchor);
+            mockAnchor.dispatchEvent(mockEvent);
+
+            expect(mockScrollIntoView).toHaveBeenCalledWith({
+                behavior: 'smooth',
+                block: 'start',
+            });
+        });
+
+        it('should update URL hash without jumping when clicked', () => {
+            const mockEvent = new MouseEvent('click', { bubbles: true, cancelable: true });
+
+            smoothScroll(mockAnchor);
+            mockAnchor.dispatchEvent(mockEvent);
+
+            expect(mockPushState).toHaveBeenCalledWith(null, '', '#section-1');
+        });
+    });
+
+    describe('Edge Cases', () => {
+        it('should do nothing when href attribute is missing', () => {
+            mockAnchor.removeAttribute('href');
+            const mockEvent = new MouseEvent('click', { bubbles: true, cancelable: true });
+
+            smoothScroll(mockAnchor);
+            mockAnchor.dispatchEvent(mockEvent);
+
+            expect(mockScrollIntoView).not.toHaveBeenCalled();
+            expect(mockPushState).not.toHaveBeenCalled();
+        });
+
+        it('should do nothing when href is just "#"', () => {
+            mockAnchor.setAttribute('href', '#');
+            const mockEvent = new MouseEvent('click', { bubbles: true, cancelable: true });
+
+            smoothScroll(mockAnchor);
+            mockAnchor.dispatchEvent(mockEvent);
+
+            expect(mockScrollIntoView).not.toHaveBeenCalled();
+            expect(mockPushState).not.toHaveBeenCalled();
+        });
+
+        it('should do nothing when target element does not exist', () => {
+            mockAnchor.setAttribute('href', '#non-existent');
+            const mockEvent = new MouseEvent('click', { bubbles: true, cancelable: true });
+
+            smoothScroll(mockAnchor);
+            mockAnchor.dispatchEvent(mockEvent);
+
+            expect(mockScrollIntoView).not.toHaveBeenCalled();
+            expect(mockPushState).not.toHaveBeenCalled();
+        });
+
+        it('should handle empty href attribute', () => {
+            mockAnchor.setAttribute('href', '');
+            const mockEvent = new MouseEvent('click', { bubbles: true, cancelable: true });
+
+            smoothScroll(mockAnchor);
+            mockAnchor.dispatchEvent(mockEvent);
+
+            expect(mockScrollIntoView).not.toHaveBeenCalled();
+        });
+    });
+
+    describe('Multiple Anchors', () => {
+        it('should work correctly with multiple anchor elements', () => {
+            const anchor1 = document.createElement('a');
+            anchor1.setAttribute('href', '#section-1');
+            const target1 = document.createElement('div');
+            target1.id = 'section-1';
+            document.body.appendChild(target1);
+
+            const anchor2 = document.createElement('a');
+            anchor2.setAttribute('href', '#section-2');
+            const target2 = document.createElement('div');
+            target2.id = 'section-2';
+            document.body.appendChild(target2);
+
+            const action1 = smoothScroll(anchor1);
+            const action2 = smoothScroll(anchor2);
+
+            const event1 = new MouseEvent('click', { bubbles: true, cancelable: true });
+            anchor1.dispatchEvent(event1);
+
+            expect(mockScrollIntoView).toHaveBeenCalledTimes(1);
+
+            const event2 = new MouseEvent('click', { bubbles: true, cancelable: true });
+            anchor2.dispatchEvent(event2);
+
+            expect(mockScrollIntoView).toHaveBeenCalledTimes(2);
+            expect(mockPushState).toHaveBeenCalledWith(null, '', '#section-2');
+
+            // Cleanup
+            action1.destroy();
+            action2.destroy();
+        });
+    });
+
+    describe('Cleanup', () => {
+        it('should not trigger clicks after destroy is called', () => {
+            const action = smoothScroll(mockAnchor);
+
+            action.destroy();
+
+            const mockEvent = new MouseEvent('click', { bubbles: true, cancelable: true });
+            mockAnchor.dispatchEvent(mockEvent);
+
+            expect(mockScrollIntoView).not.toHaveBeenCalled();
+            expect(mockPushState).not.toHaveBeenCalled();
+        });
+
+        it('should allow multiple destroy calls without errors', () => {
+            const action = smoothScroll(mockAnchor);
+
+            expect(() => {
+                action.destroy();
+                action.destroy();
+                action.destroy();
+            }).not.toThrow();
+        });
+    });
+
+    describe('Scroll Options', () => {
+        it('should always use smooth behavior', () => {
+            const mockEvent = new MouseEvent('click', { bubbles: true, cancelable: true });
+
+            smoothScroll(mockAnchor);
+            mockAnchor.dispatchEvent(mockEvent);
+
+            expect(mockScrollIntoView).toHaveBeenCalledWith(
+                expect.objectContaining({
+                    behavior: 'smooth',
+                }),
+            );
+        });
+
+        it('should always use block: start', () => {
+            const mockEvent = new MouseEvent('click', { bubbles: true, cancelable: true });
+
+            smoothScroll(mockAnchor);
+            mockAnchor.dispatchEvent(mockEvent);
+
+            expect(mockScrollIntoView).toHaveBeenCalledWith(
+                expect.objectContaining({
+                    block: 'start',
+                }),
+            );
+        });
+    });
+
+    describe('Different Hash Formats', () => {
+        it('should handle simple hash like "#section"', () => {
+            const target = document.createElement('div');
+            target.id = 'section';
+            document.body.appendChild(target);
+
+            mockAnchor.setAttribute('href', '#section');
+            const mockEvent = new MouseEvent('click', { bubbles: true, cancelable: true });
+
+            smoothScroll(mockAnchor);
+            mockAnchor.dispatchEvent(mockEvent);
+
+            expect(mockScrollIntoView).toHaveBeenCalled();
+            expect(mockPushState).toHaveBeenCalledWith(null, '', '#section');
+        });
+
+        it('should handle hash with multiple words like "#my-section"', () => {
+            const target = document.createElement('div');
+            target.id = 'my-section';
+            document.body.appendChild(target);
+
+            mockAnchor.setAttribute('href', '#my-section');
+            const mockEvent = new MouseEvent('click', { bubbles: true, cancelable: true });
+
+            smoothScroll(mockAnchor);
+            mockAnchor.dispatchEvent(mockEvent);
+
+            expect(mockScrollIntoView).toHaveBeenCalled();
+            expect(mockPushState).toHaveBeenCalledWith(null, '', '#my-section');
+        });
+
+        it('should handle hash with numbers like "#section-1-2"', () => {
+            const target = document.createElement('div');
+            target.id = 'section-1-2';
+            document.body.appendChild(target);
+
+            mockAnchor.setAttribute('href', '#section-1-2');
+            const mockEvent = new MouseEvent('click', { bubbles: true, cancelable: true });
+
+            smoothScroll(mockAnchor);
+            mockAnchor.dispatchEvent(mockEvent);
+
+            expect(mockScrollIntoView).toHaveBeenCalled();
+            expect(mockPushState).toHaveBeenCalledWith(null, '', '#section-1-2');
+        });
+    });
+
+    describe('Special Cases', () => {
+        it('should gracefully handle missing history.pushState', () => {
+            // Create a fresh test environment
+            const testAnchor = document.createElement('a');
+            testAnchor.href = '#test';
+            const testTarget = document.createElement('div');
+            testTarget.id = 'test';
+            document.body.appendChild(testTarget);
+
+            // Don't stub history - the action should still work without it
+            const action = smoothScroll(testAnchor);
+            const mockEvent = new MouseEvent('click', { bubbles: true, cancelable: true });
+
+            // Should not throw even if history.pushState might not exist
+            expect(() => testAnchor.dispatchEvent(mockEvent)).not.toThrow();
+
+            action.destroy();
+            testTarget.remove();
+        });
+    });
+
+    describe('Return Value', () => {
+        it('should return an action object compatible with Svelte use directive', () => {
+            const action = smoothScroll(mockAnchor);
+
+            expect(action).toHaveProperty('destroy');
+            expect(typeof action.destroy).toBe('function');
+        });
+
+        it('should allow chaining destroy calls', () => {
+            const action = smoothScroll(mockAnchor);
+
+            const result = action.destroy();
+
+            expect(result).toBeUndefined();
+        });
+    });
+
+    describe('Real-World Scenarios', () => {
+        it('should handle table of contents navigation', () => {
+            const sections = ['intro', 'features', 'pricing', 'contact'];
+            sections.forEach(id => {
+                const section = document.createElement('section');
+                section.id = id;
+                document.body.appendChild(section);
+
+                const link = document.createElement('a');
+                link.href = `#${id}`;
+                document.body.appendChild(link);
+
+                const action = smoothScroll(link);
+
+                const event = new MouseEvent('click', { bubbles: true, cancelable: true });
+                link.dispatchEvent(event);
+
+                expect(mockScrollIntoView).toHaveBeenCalled();
+
+                action.destroy();
+            });
+
+            expect(mockScrollIntoView).toHaveBeenCalledTimes(sections.length);
+        });
+
+        it('should work with back-to-top button', () => {
+            const topAnchor = document.createElement('a');
+            topAnchor.href = '#top';
+            document.body.appendChild(topAnchor);
+
+            const topElement = document.createElement('div');
+            topElement.id = 'top';
+            document.body.prepend(topElement);
+
+            const action = smoothScroll(topAnchor);
+
+            const event = new MouseEvent('click', { bubbles: true, cancelable: true });
+            topAnchor.dispatchEvent(event);
+
+            expect(mockScrollIntoView).toHaveBeenCalled();
+
+            action.destroy();
+        });
+    });
+});

src/shared/lib/utils/splitArray/splitArray.test.ts

@@ -0,0 +1,405 @@
+import {
+    describe,
+    expect,
+    it,
+} from 'vitest';
+import { splitArray } from './splitArray';
+
+describe('splitArray', () => {
+    describe('Basic Functionality', () => {
+        it('should split an array into two arrays based on callback', () => {
+            const input = [1, 2, 3, 4, 5];
+            const [pass, fail] = splitArray(input, n => n > 2);
+
+            expect(pass).toEqual([3, 4, 5]);
+            expect(fail).toEqual([1, 2]);
+        });
+
+        it('should return two arrays', () => {
+            const result = splitArray([1, 2, 3], () => true);
+
+            expect(Array.isArray(result)).toBe(true);
+            expect(result).toHaveLength(2);
+            expect(Array.isArray(result[0])).toBe(true);
+            expect(Array.isArray(result[1])).toBe(true);
+        });
+
+        it('should preserve original array', () => {
+            const input = [1, 2, 3, 4, 5];
+            const original = [...input];
+
+            splitArray(input, n => n % 2 === 0);
+
+            expect(input).toEqual(original);
+        });
+    });
+
+    describe('Empty Array', () => {
+        it('should return two empty arrays for empty input', () => {
+            const [pass, fail] = splitArray([], () => true);
+
+            expect(pass).toEqual([]);
+            expect(fail).toEqual([]);
+        });
+
+        it('should handle empty array with falsy callback', () => {
+            const [pass, fail] = splitArray([], () => false);
+
+            expect(pass).toEqual([]);
+            expect(fail).toEqual([]);
+        });
+    });
+
+    describe('All Pass', () => {
+        it('should put all elements in pass array when callback returns true for all', () => {
+            const input = [1, 2, 3, 4, 5];
+            const [pass, fail] = splitArray(input, () => true);
+
+            expect(pass).toEqual([1, 2, 3, 4, 5]);
+            expect(fail).toEqual([]);
+        });
+
+        it('should put all elements in pass array using always-true condition', () => {
+            const input = ['a', 'b', 'c'];
+            const [pass, fail] = splitArray(input, s => s.length > 0);
+
+            expect(pass).toEqual(['a', 'b', 'c']);
+            expect(fail).toEqual([]);
+        });
+    });
+
+    describe('All Fail', () => {
+        it('should put all elements in fail array when callback returns false for all', () => {
+            const input = [1, 2, 3, 4, 5];
+            const [pass, fail] = splitArray(input, () => false);
+
+            expect(pass).toEqual([]);
+            expect(fail).toEqual([1, 2, 3, 4, 5]);
+        });
+
+        it('should put all elements in fail array using always-false condition', () => {
+            const input = ['a', 'b', 'c'];
+            const [pass, fail] = splitArray(input, s => s.length > 10);
+
+            expect(pass).toEqual([]);
+            expect(fail).toEqual(['a', 'b', 'c']);
+        });
+    });
+
+    describe('Mixed Results', () => {
+        it('should split even and odd numbers', () => {
+            const input = [1, 2, 3, 4, 5, 6];
+            const [even, odd] = splitArray(input, n => n % 2 === 0);
+
+            expect(even).toEqual([2, 4, 6]);
+            expect(odd).toEqual([1, 3, 5]);
+        });
+
+        it('should split positive and negative numbers', () => {
+            const input = [-3, -2, -1, 0, 1, 2, 3];
+            const [positive, negative] = splitArray(input, n => n >= 0);
+
+            expect(positive).toEqual([0, 1, 2, 3]);
+            expect(negative).toEqual([-3, -2, -1]);
+        });
+
+        it('should split strings by length', () => {
+            const input = ['a', 'ab', 'abc', 'abcd'];
+            const [long, short] = splitArray(input, s => s.length >= 3);
+
+            expect(long).toEqual(['abc', 'abcd']);
+            expect(short).toEqual(['a', 'ab']);
+        });
+
+        it('should split objects by property', () => {
+            interface Item {
+                id: number;
+                active: boolean;
+            }
+            const input: Item[] = [
+                { id: 1, active: true },
+                { id: 2, active: false },
+                { id: 3, active: true },
+                { id: 4, active: false },
+            ];
+            const [active, inactive] = splitArray(input, item => item.active);
+
+            expect(active).toEqual([
+                { id: 1, active: true },
+                { id: 3, active: true },
+            ]);
+            expect(inactive).toEqual([
+                { id: 2, active: false },
+                { id: 4, active: false },
+            ]);
+        });
+    });
+
+    describe('Type Safety', () => {
+        it('should work with number arrays', () => {
+            const [pass, fail] = splitArray([1, 2, 3], n => n > 1);
+
+            expect(pass).toEqual([2, 3]);
+            expect(fail).toEqual([1]);
+
+            // Type check - should be numbers
+            const sum = pass[0] + pass[1];
+            expect(sum).toBe(5);
+        });
+
+        it('should work with string arrays', () => {
+            const [pass, fail] = splitArray(['a', 'bb', 'ccc'], s => s.length > 1);
+
+            expect(pass).toEqual(['bb', 'ccc']);
+            expect(fail).toEqual(['a']);
+
+            // Type check - should be strings
+            const concatenated = pass.join('');
+            expect(concatenated).toBe('bbccc');
+        });
+
+        it('should work with boolean arrays', () => {
+            const [pass, fail] = splitArray([true, false, true], b => b);
+
+            expect(pass).toEqual([true, true]);
+            expect(fail).toEqual([false]);
+        });
+
+        it('should work with generic objects', () => {
+            interface Person {
+                name: string;
+                age: number;
+            }
+            const people: Person[] = [
+                { name: 'Alice', age: 25 },
+                { name: 'Bob', age: 30 },
+                { name: 'Charlie', age: 20 },
+            ];
+            const [adults, minors] = splitArray(people, p => p.age >= 21);
+
+            expect(adults).toEqual([
+                { name: 'Alice', age: 25 },
+                { name: 'Bob', age: 30 },
+            ]);
+            expect(minors).toEqual([{ name: 'Charlie', age: 20 }]);
+        });
+
+        it('should work with null and undefined', () => {
+            const input = [null, undefined, 1, 0, ''];
+            const [truthy, falsy] = splitArray(input, item => !!item);
+
+            expect(truthy).toEqual([1]);
+            expect(falsy).toEqual([null, undefined, 0, '']);
+        });
+    });
+
+    describe('Callback Functions', () => {
+        it('should support arrow function syntax', () => {
+            const [pass, fail] = splitArray([1, 2, 3, 4], x => x % 2 === 0);
+
+            expect(pass).toEqual([2, 4]);
+            expect(fail).toEqual([1, 3]);
+        });
+
+        it('should support regular function syntax', () => {
+            const [pass, fail] = splitArray([1, 2, 3, 4], function(x) {
+                return x % 2 === 0;
+            });
+
+            expect(pass).toEqual([2, 4]);
+            expect(fail).toEqual([1, 3]);
+        });
+
+        it('should support inline conditions', () => {
+            const input = [1, 2, 3, 4, 5];
+            const [greaterThan3, others] = splitArray(input, x => x > 3);
+
+            expect(greaterThan3).toEqual([4, 5]);
+            expect(others).toEqual([1, 2, 3]);
+        });
+    });
+
+    describe('Order Preservation', () => {
+        it('should maintain order within each resulting array', () => {
+            const input = [5, 1, 4, 2, 3];
+            const [greaterThan2, lessOrEqual] = splitArray(input, n => n > 2);
+
+            expect(greaterThan2).toEqual([5, 4, 3]);
+            expect(lessOrEqual).toEqual([1, 2]);
+        });
+
+        it('should preserve relative order for complex objects', () => {
+            interface Item {
+                id: number;
+                value: string;
+            }
+            const input: Item[] = [
+                { id: 1, value: 'a' },
+                { id: 2, value: 'b' },
+                { id: 3, value: 'c' },
+                { id: 4, value: 'd' },
+            ];
+            const [evenIds, oddIds] = splitArray(input, item => item.id % 2 === 0);
+
+            expect(evenIds).toEqual([
+                { id: 2, value: 'b' },
+                { id: 4, value: 'd' },
+            ]);
+            expect(oddIds).toEqual([
+                { id: 1, value: 'a' },
+                { id: 3, value: 'c' },
+            ]);
+        });
+    });
+
+    describe('Edge Cases', () => {
+        it('should handle single element array (truthy)', () => {
+            const [pass, fail] = splitArray([1], () => true);
+
+            expect(pass).toEqual([1]);
+            expect(fail).toEqual([]);
+        });
+
+        it('should handle single element array (falsy)', () => {
+            const [pass, fail] = splitArray([1], () => false);
+
+            expect(pass).toEqual([]);
+            expect(fail).toEqual([1]);
+        });
+
+        it('should handle two element array', () => {
+            const [pass, fail] = splitArray([1, 2], n => n === 1);
+
+            expect(pass).toEqual([1]);
+            expect(fail).toEqual([2]);
+        });
+
+        it('should handle array with duplicate values', () => {
+            const [pass, fail] = splitArray([1, 1, 2, 2, 1, 1], n => n === 1);
+
+            expect(pass).toEqual([1, 1, 1, 1]);
+            expect(fail).toEqual([2, 2]);
+        });
+
+        it('should handle zero values', () => {
+            const [truthy, falsy] = splitArray([0, 1, 0, 2], Boolean);
+
+            expect(truthy).toEqual([1, 2]);
+            expect(falsy).toEqual([0, 0]);
+        });
+
+        it('should handle NaN values', () => {
+            const input = [1, NaN, 2, NaN, 3];
+            const [numbers, nans] = splitArray(input, n => !Number.isNaN(n));
+
+            expect(numbers).toEqual([1, 2, 3]);
+            expect(nans).toEqual([NaN, NaN]);
+        });
+    });
+
+    describe('Large Arrays', () => {
+        it('should handle large arrays efficiently', () => {
+            const largeArray = Array.from({ length: 10000 }, (_, i) => i);
+            const [even, odd] = splitArray(largeArray, n => n % 2 === 0);
+
+            expect(even).toHaveLength(5000);
+            expect(odd).toHaveLength(5000);
+            expect(even[0]).toBe(0);
+            expect(even[9999]).toBeUndefined();
+            expect(even[4999]).toBe(9998);
+        });
+
+        it('should maintain correct results for all elements in large array', () => {
+            const input = Array.from({ length: 1000 }, (_, i) => i);
+            const [multiplesOf3, others] = splitArray(input, n => n % 3 === 0);
+
+            // Verify counts
+            expect(multiplesOf3).toHaveLength(334); // 0, 3, 6, ..., 999
+            expect(others).toHaveLength(666);
+
+            // Verify all multiples of 3 are in correct array
+            multiplesOf3.forEach(n => {
+                expect(n % 3).toBe(0);
+            });
+
+            // Verify no multiples of 3 are in others
+            others.forEach(n => {
+                expect(n % 3).not.toBe(0);
+            });
+        });
+    });
+
+    describe('Real-World Use Cases', () => {
+        it('should separate valid from invalid emails', () => {
+            const emails = [
+                'valid@example.com',
+                'invalid',
+                'another@test.org',
+                'not-an-email',
+                'user@domain.co.uk',
+            ];
+            const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
+            const [valid, invalid] = splitArray(emails, email => emailRegex.test(email));
+
+            expect(valid).toEqual([
+                'valid@example.com',
+                'another@test.org',
+                'user@domain.co.uk',
+            ]);
+            expect(invalid).toEqual(['invalid', 'not-an-email']);
+        });
+
+        it('should separate completed from pending tasks', () => {
+            interface Task {
+                id: number;
+                title: string;
+                completed: boolean;
+            }
+            const tasks: Task[] = [
+                { id: 1, title: 'Task 1', completed: true },
+                { id: 2, title: 'Task 2', completed: false },
+                { id: 3, title: 'Task 3', completed: true },
+                { id: 4, title: 'Task 4', completed: false },
+            ];
+            const [completed, pending] = splitArray(tasks, task => task.completed);
+
+            expect(completed).toHaveLength(2);
+            expect(pending).toHaveLength(2);
+            expect(completed.every(t => t.completed)).toBe(true);
+            expect(pending.every(t => !t.completed)).toBe(true);
+        });
+
+        it('should separate adults from minors by age', () => {
+            interface Person {
+                name: string;
+                age: number;
+            }
+            const people: Person[] = [
+                { name: 'Alice', age: 17 },
+                { name: 'Bob', age: 25 },
+                { name: 'Charlie', age: 16 },
+                { name: 'Diana', age: 30 },
+                { name: 'Eve', age: 18 },
+            ];
+            const [adults, minors] = splitArray(people, person => person.age >= 18);
+
+            expect(adults).toEqual([
+                { name: 'Bob', age: 25 },
+                { name: 'Diana', age: 30 },
+                { name: 'Eve', age: 18 },
+            ]);
+            expect(minors).toEqual([
+                { name: 'Alice', age: 17 },
+                { name: 'Charlie', age: 16 },
+            ]);
+        });
+
+        it('should separate truthy from falsy values', () => {
+            const mixed = [0, 1, false, true, '', 'hello', null, undefined, [], [0]];
+            const [truthy, falsy] = splitArray(mixed, Boolean);
+
+            expect(truthy).toEqual([1, true, 'hello', [], [0]]);
+            expect(falsy).toEqual([0, false, '', null, undefined]);
+        });
+    });
+});

src/shared/lib/utils/throttle/throttle.test.ts

@@ -0,0 +1,319 @@
+import {
+    afterEach,
+    beforeEach,
+    describe,
+    expect,
+    it,
+    vi,
+} from 'vitest';
+import { throttle } from './throttle';
+
+describe('throttle', () => {
+    beforeEach(() => {
+        vi.useFakeTimers();
+    });
+
+    afterEach(() => {
+        vi.restoreAllMocks();
+        vi.useRealTimers();
+    });
+
+    describe('Basic Functionality', () => {
+        it('should execute function immediately on first call', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 300);
+
+            throttled('arg1', 'arg2');
+
+            expect(mockFn).toHaveBeenCalledTimes(1);
+            expect(mockFn).toHaveBeenCalledWith('arg1', 'arg2');
+        });
+
+        it('should throttle subsequent calls within wait period', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 300);
+
+            throttled('first');
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            // Call again within wait period - should not execute
+            throttled('second');
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            // Advance time past wait period
+            vi.advanceTimersByTime(300);
+
+            // Now trailing call executes
+            expect(mockFn).toHaveBeenCalledTimes(2);
+            expect(mockFn).toHaveBeenLastCalledWith('second');
+        });
+
+        it('should allow execution after wait period expires', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            throttled('first');
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            vi.advanceTimersByTime(100);
+            throttled('second');
+
+            expect(mockFn).toHaveBeenCalledTimes(2);
+        });
+    });
+
+    describe('Trailing Edge Execution', () => {
+        it('should execute throttled call after wait period', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 300);
+
+            throttled('first');
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            throttled('second');
+            throttled('third');
+            // Still 1 because these are throttled
+
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            vi.advanceTimersByTime(300);
+
+            // Trailing call executes
+            expect(mockFn).toHaveBeenCalledTimes(2);
+            expect(mockFn).toHaveBeenLastCalledWith('third');
+        });
+
+        it('should cancel previous trailing call on new invocation', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            throttled('first');
+            vi.advanceTimersByTime(50);
+            throttled('second');
+            vi.advanceTimersByTime(30);
+            throttled('third');
+
+            // At this point only first call executed
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            // Advance to trigger trailing call
+            vi.advanceTimersByTime(70);
+
+            // First call + trailing (third)
+            expect(mockFn).toHaveBeenCalledTimes(2);
+            expect(mockFn).toHaveBeenLastCalledWith('third');
+        });
+    });
+
+    describe('Arguments and Context', () => {
+        it('should pass the correct arguments from the last throttled call', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            throttled('arg1', 'arg2');
+            vi.advanceTimersByTime(50);
+            throttled('arg3', 'arg4');
+            vi.advanceTimersByTime(100);
+
+            expect(mockFn).toHaveBeenCalledTimes(2);
+            expect(mockFn).toHaveBeenLastCalledWith('arg3', 'arg4');
+        });
+
+        it('should handle no arguments', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            throttled();
+
+            expect(mockFn).toHaveBeenCalledTimes(1);
+        });
+
+        it('should handle single argument', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            throttled('single');
+
+            expect(mockFn).toHaveBeenCalledTimes(1);
+            expect(mockFn).toHaveBeenCalledWith('single');
+        });
+
+        it('should handle multiple arguments', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            throttled(1, 2, 3, 'four', { five: 5 });
+
+            expect(mockFn).toHaveBeenCalledTimes(1);
+            expect(mockFn).toHaveBeenCalledWith(1, 2, 3, 'four', { five: 5 });
+        });
+    });
+
+    describe('Timing', () => {
+        it('should handle very short wait times (1ms)', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 1);
+
+            throttled('first');
+            vi.advanceTimersByTime(1);
+            throttled('second');
+
+            expect(mockFn).toHaveBeenCalledTimes(2);
+        });
+
+        it('should handle longer wait times (1000ms)', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 1000);
+
+            throttled('first');
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            vi.advanceTimersByTime(500);
+            throttled('second');
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            vi.advanceTimersByTime(500);
+            expect(mockFn).toHaveBeenCalledTimes(2);
+        });
+    });
+
+    describe('Rapid Calls', () => {
+        it('should handle rapid successive calls correctly', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            throttled('call1');
+            vi.advanceTimersByTime(10);
+            throttled('call2');
+            vi.advanceTimersByTime(10);
+            throttled('call3');
+            vi.advanceTimersByTime(10);
+
+            expect(mockFn).toHaveBeenCalledTimes(1);
+            expect(mockFn).toHaveBeenCalledWith('call1');
+
+            vi.advanceTimersByTime(100);
+
+            expect(mockFn).toHaveBeenCalledTimes(2);
+            expect(mockFn).toHaveBeenLastCalledWith('call3');
+        });
+
+        it('should execute function at most once per wait period plus trailing', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            // Make many rapid calls
+            for (let i = 0; i < 10; i++) {
+                vi.advanceTimersByTime(5);
+                throttled(`call${i}`);
+            }
+
+            // Should execute immediately
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            vi.advanceTimersByTime(100);
+
+            // Plus trailing call
+            expect(mockFn).toHaveBeenCalledTimes(2);
+        });
+    });
+
+    describe('Edge Cases', () => {
+        it('should handle zero wait time', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 0);
+
+            throttled('first');
+
+            // With zero wait time, function may execute synchronously
+            // but the internal timing may still prevent immediate re-execution
+            expect(mockFn).toHaveBeenCalledTimes(1);
+        });
+
+        it('should handle being called at exactly wait boundary', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            throttled('first');
+            vi.advanceTimersByTime(100);
+            throttled('second');
+
+            expect(mockFn).toHaveBeenCalledTimes(2);
+        });
+    });
+
+    describe('Return Value', () => {
+        it('should not return anything (void)', () => {
+            const mockFn = vi.fn().mockReturnValue('result');
+            const throttled = throttle(mockFn, 100);
+
+            const result = throttled('arg');
+
+            expect(result).toBeUndefined();
+        });
+    });
+
+    describe('Real-World Scenarios', () => {
+        it('should throttle scroll-like events', () => {
+            const mockFn = vi.fn();
+            const throttledScroll = throttle(mockFn, 100);
+
+            throttledScroll();
+            vi.advanceTimersByTime(10);
+            throttledScroll();
+            vi.advanceTimersByTime(10);
+            throttledScroll();
+            vi.advanceTimersByTime(10);
+
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            vi.advanceTimersByTime(100);
+            expect(mockFn).toHaveBeenCalledTimes(2);
+        });
+
+        it('should throttle resize-like events', () => {
+            const mockFn = vi.fn();
+            const throttledResize = throttle(mockFn, 200);
+
+            throttledResize();
+            for (let i = 1; i <= 10; i++) {
+                vi.advanceTimersByTime(10);
+                throttledResize();
+            }
+
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            vi.advanceTimersByTime(200);
+            expect(mockFn).toHaveBeenCalledTimes(2);
+        });
+    });
+
+    describe('Comparison Characteristics', () => {
+        it('should execute immediately on first call', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 300);
+
+            throttled('first');
+
+            // Throttle executes immediately (unlike debounce)
+            expect(mockFn).toHaveBeenCalledTimes(1);
+        });
+
+        it('should allow execution during continuous calls at intervals', () => {
+            const mockFn = vi.fn();
+            const waitTime = 100;
+            const throttled = throttle(mockFn, waitTime);
+
+            throttled('call1');
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            vi.advanceTimersByTime(waitTime);
+            throttled('call2');
+            expect(mockFn).toHaveBeenCalledTimes(2);
+
+            vi.advanceTimersByTime(waitTime);
+            throttled('call3');
+            expect(mockFn).toHaveBeenCalledTimes(3);
+        });
+    });
+});

src/shared/ui/ComboControlV2/ComboControlV2.stories.svelte

@@ -10,7 +10,8 @@ const { Story } = defineMeta({
     parameters: {
         docs: {
             description: {
-                component: 'ComboControl with input field and slider',
+                component:
+                    'ComboControl with input field and slider. Simplified version without increase/decrease buttons.',
             },
             story: { inline: false }, // Render stories in iframe for state isolation
         },
@@ -26,18 +27,85 @@ const { Story } = defineMeta({
             control: 'text',
             description: 'Label for the ComboControl',
         },
+        control: {
+            control: 'object',
+            description: 'TypographyControl instance managing the value and bounds',
+        },
     },
 });
 </script>
 
 <script lang="ts">
-const control = createTypographyControl({ min: 0, max: 100, step: 1, value: 50 });
+const horizontalControl = createTypographyControl({ min: 0, max: 100, step: 1, value: 50 });
+const verticalControl = createTypographyControl({ min: 0, max: 100, step: 1, value: 50 });
+const floatControl = createTypographyControl({ min: 0, max: 1, step: 0.01, value: 0.5 });
+const atMinControl = createTypographyControl({ min: 0, max: 100, step: 1, value: 0 });
+const atMaxControl = createTypographyControl({ min: 0, max: 100, step: 1, value: 100 });
+const largeRangeControl = createTypographyControl({ min: 0, max: 1000, step: 10, value: 500 });
 </script>
 
-<Story name="Horizontal" args={{ orientation: 'horizontal', control }}>
-    <ComboControlV2 control={control} orientation="horizontal" />
+<Story
+    name="Horizontal"
+    args={{
+        control: horizontalControl,
+        orientation: 'horizontal',
+        label: 'Size',
+    }}
+>
+    <ComboControlV2 control={horizontalControl} orientation="horizontal" label="Size" />
 </Story>
 
-<Story name="Vertical" args={{ orientation: 'vertical', control, class: 'h-48' }}>
-    <ComboControlV2 control={control} orientation="vertical" />
+<Story
+    name="Vertical"
+    args={{
+        control: verticalControl,
+        orientation: 'vertical',
+        label: 'Size',
+    }}
+>
+    <ComboControlV2 control={verticalControl} orientation="vertical" class="h-48" label="Size" />
+</Story>
+
+<Story
+    name="With Float Values"
+    args={{
+        control: floatControl,
+        orientation: 'vertical',
+        label: 'Opacity',
+    }}
+>
+    <ComboControlV2 control={floatControl} orientation="vertical" class="h-48" label="Opacity" />
+</Story>
+
+<Story
+    name="At Minimum"
+    args={{
+        control: atMinControl,
+        orientation: 'horizontal',
+        label: 'Size',
+    }}
+>
+    <ComboControlV2 control={atMinControl} orientation="horizontal" label="Size" />
+</Story>
+
+<Story
+    name="At Maximum"
+    args={{
+        control: atMaxControl,
+        orientation: 'horizontal',
+        label: 'Size',
+    }}
+>
+    <ComboControlV2 control={atMaxControl} orientation="horizontal" label="Size" />
+</Story>
+
+<Story
+    name="Large Range"
+    args={{
+        control: largeRangeControl,
+        orientation: 'horizontal',
+        label: 'Scale',
+    }}
+>
+    <ComboControlV2 control={largeRangeControl} orientation="horizontal" label="Scale" />
 </Story>

src/shared/ui/IconButton/IconButton.stories.svelte

@@ -0,0 +1,101 @@
+<script module>
+import { defineMeta } from '@storybook/addon-svelte-csf';
+import IconButton from './IconButton.svelte';
+
+const { Story } = defineMeta({
+    title: 'Shared/IconButton',
+    component: IconButton,
+    tags: ['autodocs'],
+    parameters: {
+        docs: {
+            description: {
+                component:
+                    'Icon button with rotation animation on click. Features clockwise/counterclockwise rotation options and icon snippet support for flexible icon rendering.',
+            },
+            story: { inline: false },
+        },
+        layout: 'centered',
+    },
+    argTypes: {
+        rotation: {
+            control: 'select',
+            options: ['clockwise', 'counterclockwise'],
+            description: 'Direction of rotation animation on click',
+        },
+        icon: {
+            control: 'object',
+            description: 'Icon snippet to render (required)',
+        },
+        disabled: {
+            control: 'boolean',
+            description: 'Disable the button',
+        },
+        onclick: {
+            action: 'clicked',
+            description: 'Click handler',
+        },
+    },
+});
+</script>
+
+<script lang="ts">
+import ChevronLeft from '@lucide/svelte/icons/chevron-left';
+import ChevronRight from '@lucide/svelte/icons/chevron-right';
+import MinusIcon from '@lucide/svelte/icons/minus';
+import PlusIcon from '@lucide/svelte/icons/plus';
+import SettingsIcon from '@lucide/svelte/icons/settings';
+import XIcon from '@lucide/svelte/icons/x';
+</script>
+
+{#snippet chevronRightIcon({ className }: { className: string })}
+    <ChevronRight class={className} />
+{/snippet}
+
+{#snippet chevronLeftIcon({ className }: { className: string })}
+    <ChevronLeft class={className} />
+{/snippet}
+
+{#snippet plusIcon({ className }: { className: string })}
+    <PlusIcon class={className} />
+{/snippet}
+
+{#snippet minusIcon({ className }: { className: string })}
+    <MinusIcon class={className} />
+{/snippet}
+
+{#snippet settingsIcon({ className }: { className: string })}
+    <SettingsIcon class={className} />
+{/snippet}
+
+{#snippet xIcon({ className }: { className: string })}
+    <XIcon class={className} />
+{/snippet}
+
+<Story
+    name="Default"
+    args={{
+        icon: chevronRightIcon,
+    }}
+>
+    <IconButton onclick={() => console.log('Default clicked')}>
+        {#snippet icon({ className })}
+            <ChevronRight class={className} />
+        {/snippet}
+    </IconButton>
+</Story>
+
+<Story
+    name="Disabled"
+    args={{
+        icon: chevronRightIcon,
+        disabled: true,
+    }}
+>
+    <div class="flex flex-col gap-4 items-center">
+        <IconButton disabled>
+            {#snippet icon({ className })}
+                <ChevronRight class={className} />
+            {/snippet}
+        </IconButton>
+    </div>
+</Story>

src/shared/ui/IconButton/IconButton.svelte

@@ -41,7 +41,7 @@ let { rotation = 'clockwise', icon, ...rest }: Props = $props();
     size="icon"
     {...rest}
 >
-    {@render icon({
+    {@render icon?.({
     className: cn(
         'size-4 transition-all duration-200 stroke-[1.5] stroke-text-muted group-hover:stroke-foreground group-hover:scale-110 group-hover:stroke-2 group-active:scale-90 group-disabled:stroke-transparent',
         rotation === 'clockwise'

src/shared/ui/Section/Section.stories.svelte

@@ -0,0 +1,475 @@
+<script module>
+import { cn } from '$shared/shadcn/utils/shadcn-utils';
+import { defineMeta } from '@storybook/addon-svelte-csf';
+import Section from './Section.svelte';
+
+const { Story } = defineMeta({
+    title: 'Shared/Section',
+    component: Section,
+    tags: ['autodocs'],
+    parameters: {
+        docs: {
+            description: {
+                component:
+                    'Page layout component with optional sticky title feature. Provides a container for page widgets with title, icon, description snippets. The title can remain fixed while scrolling through content.',
+            },
+            story: { inline: false },
+        },
+        layout: 'fullscreen',
+    },
+    argTypes: {
+        id: {
+            control: 'text',
+            description: 'ID of the section',
+        },
+        index: {
+            control: 'number',
+            description: 'Index of the section (used for default description)',
+        },
+        stickyTitle: {
+            control: 'boolean',
+            description: 'When true, title stays fixed while scrolling through content',
+        },
+        stickyOffset: {
+            control: 'text',
+            description: 'Top offset for sticky title (e.g. "60px")',
+        },
+        class: {
+            control: 'text',
+            description: 'Additional CSS classes',
+        },
+        onTitleStatusChange: {
+            action: 'titleStatusChanged',
+            description: 'Callback when title visibility status changes',
+        },
+    },
+});
+</script>
+
+<script lang="ts">
+import ListIcon from '@lucide/svelte/icons/list';
+import SearchIcon from '@lucide/svelte/icons/search';
+import SettingsIcon from '@lucide/svelte/icons/settings';
+</script>
+
+{#snippet searchIcon({ className }: { className?: string })}
+    <SearchIcon class={className} />
+{/snippet}
+
+{#snippet welcomeTitle({ className }: { className?: string })}
+    <h2 class={className}>Welcome</h2>
+{/snippet}
+
+{#snippet welcomeContent({ className }: { className?: string })}
+    <div class={cn(className, 'min-w-128')}>
+        <p class="text-lg text-text-muted">
+            This is the default section layout with a title and content area. The section uses a 2-column grid layout
+            with the title on the left and content on the right.
+        </p>
+    </div>
+{/snippet}
+
+{#snippet stickyTitle({ className }: { className?: string })}
+    <h2 class={className}>Sticky Title</h2>
+{/snippet}
+
+{#snippet stickyContent({ className }: { className?: string })}
+    <div class={cn(className, 'min-w-128')}>
+        <p class="text-lg text-text-muted mb-4">
+            This section has a sticky title that stays fixed while you scroll through the content. Try scrolling down to
+            see the effect.
+        </p>
+        <div class="space-y-4">
+            <p class="text-text-muted">
+                Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor incididunt ut labore et
+                dolore magna aliqua.
+            </p>
+            <p class="text-text-muted">
+                Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo
+                consequat.
+            </p>
+            <p class="text-text-muted">
+                Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur.
+            </p>
+            <p class="text-text-muted">
+                Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollim anim id est
+                laborum.
+            </p>
+            <p class="text-text-muted">
+                Sed ut perspiciatis unde omnis iste natus error sit voluptatem accusantium doloremque laudantium.
+            </p>
+        </div>
+    </div>
+{/snippet}
+
+{#snippet searchFontsTitle({ className }: { className?: string })}
+    <h2 class={className}>Search Fonts</h2>
+{/snippet}
+
+{#snippet searchFontsDescription({ className }: { className?: string })}
+    <span class={className}>Find your perfect typeface</span>
+{/snippet}
+
+{#snippet searchFontsContent({ className }: { className?: string })}
+    <div class={cn(className, 'min-w-128')}>
+        <p class="text-lg text-text-muted">
+            Use the search bar to find fonts by name, or use the filters to browse by category, subset, or provider.
+        </p>
+    </div>
+{/snippet}
+
+{#snippet longContentTitle({ className }: { className?: string })}
+    <h2 class={className}>Long Content</h2>
+{/snippet}
+
+{#snippet longContent({ className }: { className?: string })}
+    <div class={cn(className, 'min-w-128')}>
+        <div class="space-y-6">
+            <p class="text-lg text-text-muted">
+                This section demonstrates how the sticky title behaves with longer content. As you scroll through this
+                content, the title remains visible at the top of the viewport.
+            </p>
+            <div class="h-64 bg-background-40 rounded-lg flex items-center justify-center">
+                <span class="text-text-muted">Content block 1</span>
+            </div>
+            <p class="text-text-muted">
+                The sticky position is achieved using CSS position: sticky with a configurable top offset. This is
+                useful for long sections where you want to maintain context while scrolling.
+            </p>
+            <div class="h-64 bg-background-40 rounded-lg flex items-center justify-center">
+                <span class="text-text-muted">Content block 2</span>
+            </div>
+            <p class="text-text-muted">
+                The Intersection Observer API is used to detect when the section title scrolls out of view, triggering
+                the optional onTitleStatusChange callback.
+            </p>
+            <div class="h-64 bg-background-40 rounded-lg flex items-center justify-center">
+                <span class="text-text-muted">Content block 3</span>
+            </div>
+        </div>
+    </div>
+{/snippet}
+
+{#snippet minimalTitle({ className }: { className?: string })}
+    <h2 class={className}>Minimal Section</h2>
+{/snippet}
+
+{#snippet minimalContent({ className }: { className?: string })}
+    <div class={cn(className, 'min-w-128')}>
+        <p class="text-text-muted">
+            A minimal section without index, icon, or description. Just the essentials.
+        </p>
+    </div>
+{/snippet}
+
+{#snippet customTitle({ className }: { className?: string })}
+    <h2 class={className}>Custom Content</h2>
+{/snippet}
+
+{#snippet customDescription({ className }: { className?: string })}
+    <span class={className}>With interactive elements</span>
+{/snippet}
+
+{#snippet customContent({ className }: { className?: string })}
+    <div class={cn(className, 'min-w-128')}>
+        <div class="grid grid-cols-2 gap-4">
+            <div class="p-4 bg-background-40 rounded-lg">
+                <h3 class="font-semibold mb-2">Card 1</h3>
+                <p class="text-sm text-text-muted">Some content here</p>
+            </div>
+            <div class="p-4 bg-background-40 rounded-lg">
+                <h3 class="font-semibold mb-2">Card 2</h3>
+                <p class="text-sm text-text-muted">More content here</p>
+            </div>
+        </div>
+    </div>
+{/snippet}
+
+<Story
+    name="Default"
+    args={{
+        title: welcomeTitle,
+        content: welcomeContent,
+    }}
+>
+    <div class="grid grid-cols-1 lg:grid-cols-[auto_1fr] gap-x-6 sm:gap-x-8 md:gap-x-10 lg:gap-x-12 p-8 max-w-6xl mx-auto">
+        <Section index={1}>
+            {#snippet title({ className })}
+                <h2 class={className}>Welcome</h2>
+            {/snippet}
+            {#snippet content({ className })}
+                <div class={cn(className, 'min-w-128')}>
+                    <p class="text-lg text-text-muted">
+                        This is the default section layout with a title and content area. The section uses a 2-column
+                        grid layout with the title on the left and content on the right.
+                    </p>
+                </div>
+            {/snippet}
+        </Section>
+    </div>
+</Story>
+
+<Story
+    name="With Sticky Title"
+    args={{
+        title: stickyTitle,
+        content: stickyContent,
+    }}
+>
+    <div class="h-[200vh]">
+        <div class="grid grid-cols-1 lg:grid-cols-[auto_1fr] gap-x-6 sm:gap-x-8 md:gap-x-10 lg:gap-x-12 p-8 max-w-6xl mx-auto">
+            <Section
+                id="sticky-section"
+                index={1}
+                stickyTitle={true}
+                stickyOffset="20px"
+            >
+                {#snippet title({ className })}
+                    <h2 class={className}>Sticky Title</h2>
+                {/snippet}
+                {#snippet content({ className })}
+                    <div class={cn(className, 'min-w-128')}>
+                        <p class="text-lg text-text-muted mb-4">
+                            This section has a sticky title that stays fixed while you scroll through the content. Try
+                            scrolling down to see the effect.
+                        </p>
+                        <div class="space-y-4">
+                            <p class="text-text-muted">
+                                Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor
+                                incididunt ut labore et dolore magna aliqua.
+                            </p>
+                            <p class="text-text-muted">
+                                Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea
+                                commodo consequat.
+                            </p>
+                            <p class="text-text-muted">
+                                Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat
+                                nulla pariatur.
+                            </p>
+                            <p class="text-text-muted">
+                                Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt
+                                mollim anim id est laborum.
+                            </p>
+                            <p class="text-text-muted">
+                                Sed ut perspiciatis unde omnis iste natus error sit voluptatem accusantium doloremque
+                                laudantium.
+                            </p>
+                        </div>
+                    </div>
+                {/snippet}
+            </Section>
+        </div>
+    </div>
+</Story>
+
+<Story
+    name="With Icon and Description"
+    args={{
+        icon: searchIcon,
+        title: searchFontsTitle,
+        description: searchFontsDescription,
+        content: searchFontsContent,
+    }}
+>
+    <div class="grid grid-cols-1 lg:grid-cols-[auto_1fr] gap-x-6 sm:gap-x-8 md:gap-x-10 lg:gap-x-12 p-8 max-w-6xl mx-auto">
+        <Section index={1}>
+            {#snippet title({ className })}
+                <h2 class={className}>Search Fonts</h2>
+            {/snippet}
+            {#snippet icon({ className })}
+                <SearchIcon class={className} />
+            {/snippet}
+            {#snippet description({ className })}
+                <span class={className}>Find your perfect typeface</span>
+            {/snippet}
+            {#snippet content({ className })}
+                <div class={cn(className, 'min-w-128')}>
+                    <p class="text-lg text-text-muted">
+                        Use the search bar to find fonts by name, or use the filters to browse by category, subset, or
+                        provider.
+                    </p>
+                </div>
+            {/snippet}
+        </Section>
+    </div>
+</Story>
+
+<Story name="Multiple Sections" tags={['!autodocs']}>
+    <div class="grid grid-cols-1 lg:grid-cols-[auto_1fr] gap-x-6 sm:gap-x-8 md:gap-x-10 lg:gap-x-12 p-8 max-w-6xl mx-auto">
+        <Section
+            id="section-1"
+            index={1}
+            stickyTitle={true}
+        >
+            {#snippet title({ className })}
+                <h2 class={className}>Typography</h2>
+            {/snippet}
+            {#snippet icon({ className })}
+                <SettingsIcon class={className} />
+            {/snippet}
+            {#snippet description({ className })}
+                <span class={className}>Adjust text appearance</span>
+            {/snippet}
+            {#snippet content({ className })}
+                <div class={cn(className, 'min-w-128')}>
+                    <p class="text-lg text-text-muted">
+                        Control the size, weight, and line height of your text. These settings apply across the
+                        comparison view.
+                    </p>
+                </div>
+            {/snippet}
+        </Section>
+
+        <Section
+            id="section-2"
+            index={2}
+            stickyTitle={true}
+        >
+            {#snippet title({ className })}
+                <h2 class={className}>Font Search</h2>
+            {/snippet}
+            {#snippet icon({ className })}
+                <SearchIcon class={className} />
+            {/snippet}
+            {#snippet description({ className })}
+                <span class={className}>Browse available typefaces</span>
+            {/snippet}
+            {#snippet content({ className })}
+                <div class={cn(className, 'min-w-128')}>
+                    <p class="text-lg text-text-muted">
+                        Search through our collection of fonts from Google Fonts and Fontshare. Use filters to narrow
+                        down your selection.
+                    </p>
+                </div>
+            {/snippet}
+        </Section>
+
+        <Section
+            id="section-3"
+            index={3}
+            stickyTitle={true}
+        >
+            {#snippet title({ className })}
+                <h2 class={className}>Sample List</h2>
+            {/snippet}
+            {#snippet icon({ className })}
+                <ListIcon class={className} />
+            {/snippet}
+            {#snippet description({ className })}
+                <span class={className}>Preview font samples</span>
+            {/snippet}
+            {#snippet content({ className })}
+                <div class={cn(className, 'min-w-128')}>
+                    <p class="text-lg text-text-muted">
+                        Browse through font samples with your custom text. The list is virtualized for optimal
+                        performance.
+                    </p>
+                </div>
+            {/snippet}
+        </Section>
+    </div>
+</Story>
+
+<Story
+    name="With Long Content"
+    args={{
+        title: longContentTitle,
+        content: longContent,
+    }}
+>
+    <div class="grid grid-cols-1 lg:grid-cols-[auto_1fr] gap-x-6 sm:gap-x-8 md:gap-x-10 lg:gap-x-12 p-8 max-w-6xl mx-auto">
+        <Section
+            index={1}
+            stickyTitle={true}
+            stickyOffset="0px"
+        >
+            {#snippet title({ className })}
+                <h2 class={className}>Long Content</h2>
+            {/snippet}
+            {#snippet content({ className })}
+                <div class={cn(className, 'min-w-128')}>
+                    <div class="space-y-6">
+                        <p class="text-lg text-text-muted">
+                            This section demonstrates how the sticky title behaves with longer content. As you scroll
+                            through this content, the title remains visible at the top of the viewport.
+                        </p>
+                        <div class="h-64 bg-background-40 rounded-lg flex items-center justify-center">
+                            <span class="text-text-muted">Content block 1</span>
+                        </div>
+                        <p class="text-text-muted">
+                            The sticky position is achieved using CSS position: sticky with a configurable top offset.
+                            This is useful for long sections where you want to maintain context while scrolling.
+                        </p>
+                        <div class="h-64 bg-background-40 rounded-lg flex items-center justify-center">
+                            <span class="text-text-muted">Content block 2</span>
+                        </div>
+                        <p class="text-text-muted">
+                            The Intersection Observer API is used to detect when the section title scrolls out of view,
+                            triggering the optional onTitleStatusChange callback.
+                        </p>
+                        <div class="h-64 bg-background-40 rounded-lg flex items-center justify-center">
+                            <span class="text-text-muted">Content block 3</span>
+                        </div>
+                    </div>
+                </div>
+            {/snippet}
+        </Section>
+    </div>
+</Story>
+
+<Story
+    name="Minimal"
+    args={{
+        title: minimalTitle,
+        content: minimalContent,
+    }}
+>
+    <div class="grid grid-cols-1 lg:grid-cols-[auto_1fr] gap-x-6 sm:gap-x-8 md:gap-x-10 lg:gap-x-12 p-8 max-w-6xl mx-auto">
+        <Section>
+            {#snippet title({ className })}
+                <h2 class={className}>Minimal Section</h2>
+            {/snippet}
+            {#snippet content({ className })}
+                <div class={cn(className, 'min-w-128')}>
+                    <p class="text-text-muted">
+                        A minimal section without index, icon, or description. Just the essentials.
+                    </p>
+                </div>
+            {/snippet}
+        </Section>
+    </div>
+</Story>
+
+<Story
+    name="Custom Content"
+    args={{
+        title: customTitle,
+        description: customDescription,
+        content: customContent,
+    }}
+>
+    <div class="grid grid-cols-1 lg:grid-cols-[auto_1fr] gap-x-6 sm:gap-x-8 md:gap-x-10 lg:gap-x-12 p-8 max-w-6xl mx-auto">
+        <Section index={42}>
+            {#snippet title({ className })}
+                <h2 class={className}>Custom Content</h2>
+            {/snippet}
+            {#snippet description({ className })}
+                <span class={className}>With interactive elements</span>
+            {/snippet}
+            {#snippet content({ className })}
+                <div class={cn(className, 'min-w-128')}>
+                    <div class="grid grid-cols-2 gap-4">
+                        <div class="p-4 bg-background-40 rounded-lg">
+                            <h3 class="font-semibold mb-2">Card 1</h3>
+                            <p class="text-sm text-text-muted">Some content here</p>
+                        </div>
+                        <div class="p-4 bg-background-40 rounded-lg">
+                            <h3 class="font-semibold mb-2">Card 2</h3>
+                            <p class="text-sm text-text-muted">More content here</p>
+                        </div>
+                    </div>
+                </div>
+            {/snippet}
+        </Section>
+    </div>
+</Story>

src/shared/ui/Slider/Slider.stories.svelte

@@ -31,21 +31,26 @@ const { Story } = defineMeta({
             control: 'number',
             description: 'Step size for value increments',
         },
+        label: {
+            control: 'text',
+            description: 'Optional label displayed inline on the track',
+        },
     },
 });
 </script>
 
 <script lang="ts">
-let minValue = 0;
-let maxValue = 100;
-let stepValue = 1;
 let value = $state(50);
 </script>
 
-<Story name="Horizontal" args={{ orientation: 'horizontal', min: minValue, max: maxValue, step: stepValue, value }}>
-    <Slider bind:value min={minValue} max={maxValue} step={stepValue} />
+<Story name="Horizontal" args={{ orientation: 'horizontal', min: 0, max: 100, step: 1, value }}>
+    <Slider bind:value />
 </Story>
 
-<Story name="Vertical" args={{ orientation: 'vertical', min: minValue, max: maxValue, step: stepValue, value }}>
-    <Slider bind:value min={minValue} max={maxValue} step={stepValue} orientation="vertical" />
+<Story name="Vertical" args={{ orientation: 'vertical', min: 0, max: 100, step: 1, value }}>
+    <Slider bind:value />
+</Story>
+
+<Story name="With Label" args={{ orientation: 'horizontal', min: 0, max: 100, step: 1, value, label: 'SIZE' }}>
+    <Slider bind:value />
 </Story>

src/shared/ui/VirtualList/VirtualList.stories.svelte

@@ -38,27 +38,31 @@ const { Story } = defineMeta({
 
 <script lang="ts">
 const smallDataSet = Array.from({ length: 20 }, (_, i) => `${i + 1}) I will not waste chalk.`);
-const largeDataSet = Array.from(
-    { length: 10000 },
+const mediumDataSet = Array.from(
+    { length: 200 },
     (_, i) => `${i + 1}) I will not skateboard in the halls.`,
 );
 const emptyDataSet: string[] = [];
 </script>
 
 <Story name="Small Dataset">
-    <VirtualList items={smallDataSet} itemHeight={40}>
-        {#snippet children({ item })}
-            <div class="p-2 m-0.5 rounded-sm hover:bg-accent">{item}</div>
-        {/snippet}
-    </VirtualList>
+    <div class="h-[400px]">
+        <VirtualList items={smallDataSet} itemHeight={40}>
+            {#snippet children({ item })}
+                <div class="p-2 m-0.5 rounded-sm hover:bg-accent">{item}</div>
+            {/snippet}
+        </VirtualList>
+    </div>
 </Story>
 
-<Story name="Large Dataset">
-    <VirtualList items={largeDataSet} itemHeight={40}>
-        {#snippet children({ item })}
-            <div class="p-2 m-0.5 rounded-sm hover:bg-accent">{item}</div>
-        {/snippet}
-    </VirtualList>
+<Story name="Medium Dataset (200 items)">
+    <div class="h-[400px]">
+        <VirtualList items={mediumDataSet} itemHeight={40}>
+            {#snippet children({ item })}
+                <div class="p-2 m-0.5 rounded-sm hover:bg-accent">{item}</div>
+            {/snippet}
+        </VirtualList>
+    </div>
 </Story>
 
 <Story name="Empty Dataset">

src/widgets/ComparisonSlider/ui/ComparisonSlider/ComparisonSlider.stories.svelte

@@ -0,0 +1,136 @@
+<script module>
+import Providers from '$shared/lib/storybook/Providers.svelte';
+import { defineMeta } from '@storybook/addon-svelte-csf';
+import ComparisonSlider from './ComparisonSlider.svelte';
+
+const { Story } = defineMeta({
+    title: 'Widgets/ComparisonSlider',
+    component: ComparisonSlider,
+    tags: ['autodocs'],
+    parameters: {
+        docs: {
+            description: {
+                component:
+                    'A multiline text comparison slider that morphs between two fonts. Features character-level morphing, responsive layout, and performance optimization using offscreen canvas. Switch between slider mode (interactive text) and settings mode (controls panel).',
+            },
+            story: { inline: false },
+        },
+        layout: 'fullscreen',
+    },
+    argTypes: {
+        // This component uses internal stores, so no direct props to document
+    },
+});
+</script>
+
+<script lang="ts">
+import type { UnifiedFont } from '$entities/Font';
+import { comparisonStore } from '$widgets/ComparisonSlider/model';
+
+// Mock fonts for testing - using web-safe fonts that are always available
+const mockArial: UnifiedFont = {
+    id: 'arial',
+    name: 'Arial',
+    provider: 'google',
+    category: 'sans-serif',
+    subsets: ['latin'],
+    variants: ['400', '700'],
+    styles: {
+        regular: '',
+        bold: '',
+    },
+    metadata: {
+        cachedAt: Date.now(),
+        version: '1.0',
+        popularity: 1,
+    },
+    features: {
+        isVariable: false,
+    },
+};
+
+const mockGeorgia: UnifiedFont = {
+    id: 'georgia',
+    name: 'Georgia',
+    provider: 'google',
+    category: 'serif',
+    subsets: ['latin'],
+    variants: ['400', '700'],
+    styles: {
+        regular: '',
+        bold: '',
+    },
+    metadata: {
+        cachedAt: Date.now(),
+        version: '1.0',
+        popularity: 2,
+    },
+    features: {
+        isVariable: false,
+    },
+};
+
+const mockVerdana: UnifiedFont = {
+    id: 'verdana',
+    name: 'Verdana',
+    provider: 'google',
+    category: 'sans-serif',
+    subsets: ['latin'],
+    variants: ['400', '700'],
+    styles: {
+        regular: '',
+        bold: '',
+    },
+    metadata: {
+        cachedAt: Date.now(),
+        version: '1.0',
+        popularity: 3,
+    },
+    features: {
+        isVariable: false,
+    },
+};
+
+const mockCourier: UnifiedFont = {
+    id: 'courier-new',
+    name: 'Courier New',
+    provider: 'google',
+    category: 'monospace',
+    subsets: ['latin'],
+    variants: ['400', '700'],
+    styles: {
+        regular: '',
+        bold: '',
+    },
+    metadata: {
+        cachedAt: Date.now(),
+        version: '1.0',
+        popularity: 10,
+    },
+    features: {
+        isVariable: false,
+    },
+};
+</script>
+
+<Story name="Default">
+    {@const _ = (comparisonStore.fontA = mockArial, comparisonStore.fontB = mockGeorgia)}
+    <Providers>
+        <div class="min-h-screen flex items-center justify-center p-8">
+            <div class="w-full max-w-5xl">
+                <ComparisonSlider />
+            </div>
+        </div>
+    </Providers>
+</Story>
+
+<Story name="Loading State">
+    {@const _ = (comparisonStore.fontA = undefined, comparisonStore.fontB = undefined)}
+    <Providers>
+        <div class="min-h-screen flex items-center justify-center p-8">
+            <div class="w-full max-w-5xl">
+                <ComparisonSlider />
+            </div>
+        </div>
+    </Providers>
+</Story>

src/widgets/ComparisonSlider/ui/ComparisonSlider/FontShifter.svelte

@@ -1,52 +0,0 @@
-<script lang="ts">
-import { cn } from '$shared/shadcn/utils/shadcn-utils';
-
-interface Props {
-    text: string;
-    fontName: string;
-    isAnimating: boolean;
-    onAnimationComplete?: () => void;
-}
-
-let { text, fontName, isAnimating, onAnimationComplete }: Props = $props();
-
-// Split text into characters, preserving spaces
-const chars = $derived(text.split('').map(c => c === ' ' ? '\u00A0' : c));
-
-let completedCount = 0;
-
-function handleTransitionEnd() {
-    completedCount++;
-    if (completedCount === chars.length) {
-        onAnimationComplete?.();
-        completedCount = 0;
-    }
-}
-</script>
-
-<div class="relative inline-flex flex-wrap leading-tight">
-    {#each chars as char, i}
-        <span
-            class={cn(
-                'inline-block transition-all duration-500 ease-[cubic-bezier(0.34,1.56,0.64,1)]',
-                isAnimating ? 'opacity-0 -translate-y-4 rotate-x-90' : 'opacity-100 translate-y-0 rotate-x-0',
-            )}
-            style:font-family={fontName}
-            style:transition-delay="{i * 25}ms"
-            ontransitionend={i === chars.length - 1 ? handleTransitionEnd : null}
-        >
-            {char}
-        </span>
-    {/each}
-</div>
-
-<style>
-/* Necessary for the "Flip" feel */
-div {
-	perspective: 1000px;
-}
-span {
-	transform-style: preserve-3d;
-	backface-visibility: hidden;
-}
-</style>

src/widgets/FontSearch/ui/FontSearch/FontSearch.stories.svelte

@@ -0,0 +1,102 @@
+<script module>
+import { defineMeta } from '@storybook/addon-svelte-csf';
+import FontSearch from './FontSearch.svelte';
+
+const { Story } = defineMeta({
+    title: 'Widgets/FontSearch',
+    component: FontSearch,
+    tags: ['autodocs'],
+    parameters: {
+        docs: {
+            description: {
+                component:
+                    'Primary search interface with filter panel. Provides a search input and filtering for fonts by provider, category, and subset. Filters can be toggled open/closed with an animated transition.',
+            },
+            story: { inline: false },
+        },
+        layout: 'centered',
+    },
+    argTypes: {
+        showFilters: {
+            control: 'boolean',
+            description: 'Controllable flag to show/hide filters (bindable)',
+        },
+    },
+});
+</script>
+
+<script lang="ts">
+let showFiltersDefault = $state(true);
+let showFiltersClosed = $state(false);
+let showFiltersOpen = $state(true);
+</script>
+
+<Story name="Default">
+    <div class="w-full max-w-2xl">
+        <FontSearch bind:showFilters={showFiltersDefault} />
+    </div>
+</Story>
+
+<Story name="Filters Open">
+    <div class="w-full max-w-2xl">
+        <FontSearch bind:showFilters={showFiltersOpen} />
+        <div class="mt-8 text-center">
+            <p class="text-text-muted text-sm">Filters panel is open and visible</p>
+        </div>
+    </div>
+</Story>
+
+<Story name="Filters Closed">
+    <div class="w-full max-w-2xl">
+        <FontSearch bind:showFilters={showFiltersClosed} />
+        <div class="mt-8 text-center">
+            <p class="text-text-muted text-sm">Filters panel is closed - click the slider icon to open</p>
+        </div>
+    </div>
+</Story>
+
+<Story name="Full Width">
+    <div class="w-full px-8">
+        <FontSearch />
+    </div>
+</Story>
+
+<Story name="In Context" tags={['!autodocs']}>
+    <div class="w-full max-w-3xl p-8 space-y-6">
+        <div class="text-center mb-8">
+            <h1 class="text-4xl font-bold mb-2">Font Browser</h1>
+            <p class="text-text-muted">Search and filter through our collection of fonts</p>
+        </div>
+
+        <div class="bg-background-20 rounded-2xl p-6">
+            <FontSearch />
+        </div>
+
+        <div class="mt-8 p-6 bg-background-40 rounded-xl">
+            <p class="text-text-muted text-center">Font results will appear here...</p>
+        </div>
+    </div>
+</Story>
+
+<Story name="With Filters Demo">
+    <div class="w-full max-w-2xl">
+        <div class="mb-4 p-4 bg-background-40 rounded-lg">
+            <p class="text-sm text-text-muted">
+                <strong class="text-foreground">Demo Note:</strong> Click the slider icon to toggle filters. Use the
+                filter categories to select options. Use the filter controls to reset or apply your selections.
+            </p>
+        </div>
+        <FontSearch />
+    </div>
+</Story>
+
+<Story name="Responsive Behavior">
+    <div class="w-full">
+        <div class="mb-4 text-center">
+            <p class="text-text-muted text-sm">Resize browser to see responsive layout</p>
+        </div>
+        <div class="px-4 sm:px-8 md:px-12">
+            <FontSearch />
+        </div>
+    </div>
+</Story>

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

@@ -0,0 +1,89 @@
+<script module>
+import { defineMeta } from '@storybook/addon-svelte-csf';
+import SampleList from './SampleList.svelte';
+
+const { Story } = defineMeta({
+    title: 'Widgets/SampleList',
+    component: SampleList,
+    tags: ['autodocs'],
+    parameters: {
+        docs: {
+            description: {
+                component:
+                    'Virtualized font list with pagination. Renders a list of fonts with auto-loading when scrolling near the bottom. Includes a typography menu for font setup that appears when scrolling past the middle of the viewport.',
+            },
+            story: { inline: false },
+        },
+        layout: 'fullscreen',
+    },
+    argTypes: {
+        // This component uses internal stores, so no direct props to document
+    },
+});
+</script>
+
+<Story name="Default">
+    <div class="min-h-screen bg-background">
+        <div class="max-w-4xl mx-auto py-12 px-4 sm:px-6 lg:px-8">
+            <div class="mb-8 text-center">
+                <h1 class="text-4xl font-bold mb-2">Font Samples</h1>
+                <p class="text-text-muted">Scroll to see more fonts and load additional pages</p>
+            </div>
+            <SampleList />
+        </div>
+    </div>
+</Story>
+
+<Story name="Full Page">
+    <div class="min-h-screen bg-background">
+        <SampleList />
+    </div>
+</Story>
+
+<Story name="With Typography Controls">
+    <div class="min-h-screen bg-background">
+        <div class="max-w-4xl mx-auto py-12 px-4 sm:px-6 lg:px-8">
+            <div class="mb-8 text-center">
+                <h1 class="text-4xl font-bold mb-2">Typography Controls</h1>
+                <p class="text-text-muted">Scroll down to see the typography menu appear</p>
+            </div>
+            <SampleList />
+        </div>
+    </div>
+</Story>
+
+<Story name="Custom Text">
+    <div class="min-h-screen bg-background">
+        <div class="max-w-4xl mx-auto py-12 px-4 sm:px-6 lg:px-8">
+            <div class="mb-8 text-center">
+                <h1 class="text-4xl font-bold mb-2">Custom Sample Text</h1>
+                <p class="text-text-muted">Edit the text in any card to change all samples</p>
+            </div>
+            <SampleList />
+        </div>
+    </div>
+</Story>
+
+<Story name="Pagination Info">
+    <div class="min-h-screen bg-background">
+        <div class="max-w-4xl mx-auto py-12 px-4 sm:px-6 lg:px-8">
+            <div class="mb-8 text-center">
+                <h1 class="text-4xl font-bold mb-2">Paginated List</h1>
+                <p class="text-text-muted">Fonts load automatically as you scroll</p>
+            </div>
+            <SampleList />
+        </div>
+    </div>
+</Story>
+
+<Story name="Responsive Layout">
+    <div class="min-h-screen bg-background">
+        <div class="max-w-6xl mx-auto py-12 px-4 sm:px-6 lg:px-8">
+            <div class="mb-8 text-center">
+                <h1 class="text-4xl font-bold mb-2">Responsive Sample List</h1>
+                <p class="text-text-muted">Resize browser to see responsive behavior</p>
+            </div>
+            <SampleList />
+        </div>
+    </div>
+</Story>