chore: fix TS alias resolution and SVG mocking for test setup

.gitea/workflows/workflow.yml

@@ -43,6 +43,12 @@ jobs:
       - name: Type Check
         run: yarn check
 
+      - name: Run Unit Tests
+        run: yarn test:unit
+
+      - name: Run Component Tests
+        run: yarn test:component
+
   publish:
     needs: build # Only runs if tests/lint pass
     runs-on: ubuntu-latest

dprint.json

@@ -33,10 +33,15 @@
     "exportDeclaration.forceMultiLine": "whenMultiple",
     "exportDeclaration.forceSingleLine": false,
     "ifStatement.useBraces": "always",
+    "ifStatement.singleBodyPosition": "nextLine",
     "whileStatement.useBraces": "always",
+    "whileStatement.singleBodyPosition": "nextLine",
     "forStatement.useBraces": "always",
+    "forStatement.singleBodyPosition": "nextLine",
     "forInStatement.useBraces": "always",
-    "forOfStatement.useBraces": "always"
+    "forInStatement.singleBodyPosition": "nextLine",
+    "forOfStatement.useBraces": "always",
+    "forOfStatement.singleBodyPosition": "nextLine"
   },
   "json": {
     "indentWidth": 2,

lefthook.yml

@@ -13,6 +13,10 @@ pre-commit:
 pre-push:
   parallel: true
   commands:
+    test-unit:
+      run: yarn test:unit
+    test-component:
+      run: yarn test:component
     type-check:
       run: yarn tsc --noEmit
 

src/entities/Font/model/const/const.ts

@@ -86,3 +86,9 @@ export const DEFAULT_TYPOGRAPHY_CONTROLS_DATA: ControlModel<ControlId>[] = [
 export const MULTIPLIER_S = 0.5;
 export const MULTIPLIER_M = 0.75;
 export const MULTIPLIER_L = 1;
+
+/**
+ * Index value for items not yet loaded in a virtualized list.
+ * Treated as being at the very bottom of the infinite scroll.
+ */
+export const VIRTUAL_INDEX_NOT_LOADED = Infinity;

src/entities/Font/model/store/fontStore/fontStore.svelte.spec.ts

@@ -561,4 +561,67 @@ describe('FontStore', () => {
             store.destroy();
         });
     });
+
+    describe('fetchAllPagesTo', () => {
+        beforeEach(() => {
+            fetch.mockReset();
+            queryClient.clear();
+        });
+
+        it('fetches all missing pages in parallel up to targetIndex', async () => {
+            // First page already loaded (offset 0, limit 10, total 50)
+            const firstFonts = generateMockFonts(10);
+            fetch.mockResolvedValueOnce(makeResponse(firstFonts, { total: 50, limit: 10, offset: 0 }));
+            const store = makeStore();
+            await store.refetch();
+            flushSync();
+
+            expect(store.fonts).toHaveLength(10);
+
+            // Mock remaining pages
+            for (let offset = 10; offset < 50; offset += 10) {
+                fetch.mockResolvedValueOnce(
+                    makeResponse(generateMockFonts(10), { total: 50, limit: 10, offset }),
+                );
+            }
+
+            await store.fetchAllPagesTo(40);
+            flushSync();
+
+            expect(store.fonts).toHaveLength(50);
+        });
+
+        it('skips pages that fail and still merges successful ones', async () => {
+            const firstFonts = generateMockFonts(10);
+            fetch.mockResolvedValueOnce(makeResponse(firstFonts, { total: 30, limit: 10, offset: 0 }));
+            const store = makeStore();
+            await store.refetch();
+            flushSync();
+
+            // offset=10 fails, offset=20 succeeds
+            fetch.mockRejectedValueOnce(new Error('network error'));
+            fetch.mockResolvedValueOnce(
+                makeResponse(generateMockFonts(10), { total: 30, limit: 10, offset: 20 }),
+            );
+
+            await store.fetchAllPagesTo(25);
+            flushSync();
+
+            // Page at offset=20 merged, page at offset=10 missing — 20 total
+            expect(store.fonts).toHaveLength(20);
+        });
+
+        it('is a no-op when target is within already-loaded data', async () => {
+            const firstFonts = generateMockFonts(10);
+            fetch.mockResolvedValueOnce(makeResponse(firstFonts, { total: 50, limit: 10, offset: 0 }));
+            const store = makeStore();
+            await store.refetch();
+            flushSync();
+
+            const callsBefore = fetch.mock.calls.length;
+            await store.fetchAllPagesTo(5);
+
+            expect(fetch.mock.calls.length).toBe(callsBefore);
+        });
+    });
 });

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

@@ -242,6 +242,80 @@ export class FontStore {
     async nextPage(): Promise<void> {
         await this.#observer.fetchNextPage();
     }
+
+    #isCatchingUp = false;
+    #inFlightOffsets = new Set<number>();
+
+    /**
+     * Fetch all pages between the current loaded count and targetIndex in parallel.
+     * Pages are merged into the cache as they arrive (sorted by offset).
+     * Failed pages are silently skipped — normal scroll will re-fetch them on demand.
+     */
+    async fetchAllPagesTo(targetIndex: number): Promise<void> {
+        if (this.#isCatchingUp) {
+            return;
+        }
+
+        const pageSize = typeof this.#params.limit === 'number' ? this.#params.limit : 50;
+        const key = this.buildQueryKey(this.#params);
+        const existing = this.#qc.getQueryData<InfiniteData<ProxyFontsResponse, PageParam>>(key);
+
+        if (!existing) {
+            return;
+        }
+
+        const loadedOffsets = new Set(existing.pageParams.map(p => p.offset));
+
+        // Collect offsets for all missing and not-in-flight pages
+        const missingOffsets: number[] = [];
+        for (let offset = 0; offset <= targetIndex; offset += pageSize) {
+            if (!loadedOffsets.has(offset) && !this.#inFlightOffsets.has(offset)) {
+                missingOffsets.push(offset);
+            }
+        }
+
+        if (missingOffsets.length === 0) {
+            return;
+        }
+
+        this.#isCatchingUp = true;
+
+        // Sorted merge buffer — flush in offset order as pages arrive
+        const buffer = new Map<number, ProxyFontsResponse>();
+        const failed = new Set<number>();
+        let nextFlushOffset = (existing.pageParams.at(-1)?.offset ?? -pageSize) + pageSize;
+
+        const flush = () => {
+            while (buffer.has(nextFlushOffset) || failed.has(nextFlushOffset)) {
+                if (buffer.has(nextFlushOffset)) {
+                    this.#appendPageToCache(buffer.get(nextFlushOffset)!);
+                    buffer.delete(nextFlushOffset);
+                }
+                failed.delete(nextFlushOffset);
+                nextFlushOffset += pageSize;
+            }
+        };
+
+        try {
+            await Promise.allSettled(
+                missingOffsets.map(async offset => {
+                    this.#inFlightOffsets.add(offset);
+                    try {
+                        const page = await this.fetchPage({ ...this.#params, offset });
+                        buffer.set(offset, page);
+                    } catch {
+                        failed.add(offset);
+                    } finally {
+                        this.#inFlightOffsets.delete(offset);
+                    }
+                    flush();
+                }),
+            );
+        } finally {
+            this.#isCatchingUp = false;
+        }
+    }
+
     /**
      * Backward pagination (no-op: infinite scroll accumulates forward only)
      */
@@ -289,6 +363,34 @@ export class FontStore {
         return this.fonts.filter(f => f.category === 'monospace');
     }
 
+    /**
+     * Merge a single page into the InfiniteQuery cache in offset order.
+     * Called by fetchAllPagesTo as each parallel fetch resolves.
+     */
+    #appendPageToCache(page: ProxyFontsResponse): void {
+        const key = this.buildQueryKey(this.#params);
+        const existing = this.#qc.getQueryData<InfiniteData<ProxyFontsResponse, PageParam>>(key);
+        if (!existing) {
+            return;
+        }
+
+        // Guard against duplicates
+        const loadedOffsets = new Set(existing.pageParams.map(p => p.offset));
+        if (loadedOffsets.has(page.offset)) {
+            return;
+        }
+
+        const allPages = [...existing.pages, page].sort((a, b) => a.offset - b.offset);
+        const allParams = [...existing.pageParams, { offset: page.offset }].sort(
+            (a, b) => a.offset - b.offset,
+        );
+
+        this.#qc.setQueryData<InfiniteData<ProxyFontsResponse, PageParam>>(key, {
+            pages: allPages,
+            pageParams: allParams,
+        });
+    }
+
     private buildQueryKey(params: FontStoreParams): readonly unknown[] {
         const filtered: Record<string, any> = {};
 

src/entities/Font/ui/FontApplicator/FontApplicator.svelte

@@ -1,14 +1,11 @@
 <!--
     Component: FontApplicator
-    Loads fonts from fontshare with link tag
-    - Loads font only if it's not already applied
-    - Reacts to font load status to show/hide content
-    - Adds smooth transition when font appears
+    Applies a font to its children once the font file is loaded.
+    Shows the skeleton snippet while loading; falls back to system font if no skeleton is provided.
 -->
 <script lang="ts">
 import clsx from 'clsx';
 import type { Snippet } from 'svelte';
-import { prefersReducedMotion } from 'svelte/motion';
 import {
     DEFAULT_FONT_WEIGHT,
     type UnifiedFont,
@@ -33,6 +30,11 @@ interface Props {
      * Content snippet
      */
     children?: Snippet;
+    /**
+     * Shown while the font file is loading.
+     * When omitted, children render in system font until ready.
+     */
+    skeleton?: Snippet;
 }
 
 let {
@@ -40,6 +42,7 @@ let {
     weight = DEFAULT_FONT_WEIGHT,
     className,
     children,
+    skeleton,
 }: Props = $props();
 
 const status = $derived(
@@ -50,30 +53,16 @@ const status = $derived(
     ),
 );
 
-// The "Show" condition: Font is loaded OR it errored out OR it's a noTouch preview (like in search)
 const shouldReveal = $derived(status === 'loaded' || status === 'error');
-
-const transitionClasses = $derived(
-    prefersReducedMotion.current
-        ? 'transition-none' // Disable CSS transitions if motion is reduced
-        : 'transition-all duration-300 ease-[cubic-bezier(0.22,1,0.36,1)]',
-);
 </script>
 
-<div
-    style:font-family={shouldReveal
-    ? `'${font.name}'`
-    : 'system-ui, -apple-system, sans-serif'}
-    class={clsx(
-        transitionClasses,
-        // If reduced motion is on, we skip the transform/blur entirely
-        !shouldReveal
-            && !prefersReducedMotion.current
-            && 'opacity-50 scale-[0.95] blur-sm',
-        !shouldReveal && prefersReducedMotion.current && 'opacity-0', // Still hide until font is ready, but no movement
-        shouldReveal && 'opacity-100 scale-100 blur-0',
-        className,
-    )}
->
-    {@render children?.()}
-</div>
+{#if !shouldReveal && skeleton}
+    {@render skeleton()}
+{:else}
+    <div
+        style:font-family={shouldReveal ? `'${font.name}'` : 'system-ui, -apple-system, sans-serif'}
+        class={clsx(className)}
+    >
+        {@render children?.()}
+    </div>
+{/if}

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

@@ -4,6 +4,7 @@
     - Handles font registration with the manager
 -->
 <script lang="ts">
+import { debounce } from '$shared/lib/utils';
 import {
     Skeleton,
     VirtualList,
@@ -54,6 +55,10 @@ const isLoading = $derived(
 );
 
 let visibleFonts = $state<UnifiedFont[]>([]);
+let isCatchingUp = $state(false);
+
+const showInitialSkeleton = $derived(!!skeleton && isLoading && fontStore.fonts.length === 0);
+const showCatchupSkeleton = $derived(!!skeleton && isCatchingUp);
 
 function handleInternalVisibleChange(items: UnifiedFont[]) {
     visibleFonts = items;
@@ -61,8 +66,32 @@ function handleInternalVisibleChange(items: UnifiedFont[]) {
     onVisibleItemsChange?.(items);
 }
 
+/**
+ * Handle jump scroll — batch-load all missing pages then re-enable font loading.
+ * Suppresses appliedFontsManager.touch() during catch-up to avoid loading
+ * font files for thousands of intermediate fonts.
+ */
+async function handleJump(targetIndex: number) {
+    if (isCatchingUp || !fontStore.pagination.hasMore) {
+        return;
+    }
+    isCatchingUp = true;
+    try {
+        await fontStore.fetchAllPagesTo(targetIndex);
+    } finally {
+        isCatchingUp = false;
+    }
+}
+
+const debouncedTouch = debounce((configs: FontLoadRequestConfig[]) => {
+    appliedFontsManager.touch(configs);
+}, 150);
+
 // Re-touch whenever visible set or weight changes — fixes weight-change gap
 $effect(() => {
+    if (isCatchingUp) {
+        return;
+    }
     const configs: FontLoadRequestConfig[] = visibleFonts.flatMap(item => {
         const url = getFontUrl(item, weight);
         if (!url) {
@@ -71,7 +100,7 @@ $effect(() => {
         return [{ id: item.id, name: item.name, weight, url, isVariable: item.features?.isVariable }];
     });
     if (configs.length > 0) {
-        appliedFontsManager.touch(configs);
+        debouncedTouch(configs);
     }
 });
 
@@ -113,17 +142,19 @@ function loadMore() {
 function handleNearBottom(_lastVisibleIndex: number) {
     const { hasMore } = fontStore.pagination;
 
-    // VirtualList already checks if we're near the bottom of loaded items
-    if (hasMore && !fontStore.isFetching) {
+    // VirtualList already checks if we're near the bottom of loaded items.
+    // Guard isCatchingUp: fetchAllPagesTo bypasses TQ so isFetching stays false
+    // during batch catch-up, which would otherwise let nextPage() race with it.
+    if (hasMore && !fontStore.isFetching && !isCatchingUp) {
         loadMore();
     }
 }
 </script>
 
 <div class="relative w-full h-full">
-    {#if skeleton && isLoading && fontStore.fonts.length === 0}
+    {#if showInitialSkeleton && skeleton}
         <!-- Show skeleton only on initial load when no fonts are loaded yet -->
-        <div transition:fade={{ duration: 300 }}>
+        <div class="overflow-hidden h-full" transition:fade={{ duration: 300 }}>
             {@render skeleton()}
         </div>
     {:else}
@@ -131,14 +162,20 @@ function handleNearBottom(_lastVisibleIndex: number) {
         <VirtualList
             items={fontStore.fonts}
             total={fontStore.pagination.total}
-            isLoading={isLoading}
+            isLoading={isLoading || isCatchingUp}
             onVisibleItemsChange={handleInternalVisibleChange}
             onNearBottom={handleNearBottom}
+            onJump={handleJump}
             {...rest}
         >
             {#snippet children(scope)}
                 {@render children(scope)}
             {/snippet}
         </VirtualList>
+        {#if showCatchupSkeleton && skeleton}
+            <div class="absolute inset-0 overflow-hidden" transition:fade={{ duration: 150 }}>
+                {@render skeleton()}
+            </div>
+        {/if}
     {/if}
 </div>

src/features/GetFonts/index.ts

@@ -4,6 +4,7 @@ export {
     mapManagerToParams,
 } from './lib';
 
+export { filtersStore } from './model/state/filters.svelte';
 export { filterManager } from './model/state/manager.svelte';
 
 export {

src/features/GetFonts/ui/Filters/Filters.svelte.test.ts

@@ -1,29 +1,40 @@
-import { filterManager } from '$features/GetFonts';
+import {
+    filterManager,
+    filtersStore,
+} from '$features/GetFonts';
 import {
     render,
     screen,
 } from '@testing-library/svelte';
+import { vi } from 'vitest';
 import Filters from './Filters.svelte';
 
 describe('Filters', () => {
     beforeEach(() => {
+        // Clear groups and mock filtersStore to be empty so the auto-sync effect doesn't overwrite us
         filterManager.setGroups([]);
+        vi.spyOn(filtersStore, 'filters', 'get').mockReturnValue([]);
+    });
+
+    afterEach(() => {
+        vi.restoreAllMocks();
     });
 
     describe('Rendering', () => {
         it('renders nothing when filter groups are empty', () => {
             const { container } = render(Filters);
-            expect(container.firstElementChild).toBeNull();
+            // It might render an empty container if the component has one, but we expect no children
+            expect(container.firstChild?.childNodes.length ?? 0).toBe(0);
         });
 
         it('renders a label for each filter group', () => {
             filterManager.setGroups([
-                { id: 'cat', label: 'Category', properties: [] },
-                { id: 'prov', label: 'Provider', properties: [] },
+                { id: 'cat', label: 'Categories', properties: [] },
+                { id: 'prov', label: 'Font Providers', properties: [] },
             ]);
             render(Filters);
-            expect(screen.getByText('Category')).toBeInTheDocument();
-            expect(screen.getByText('Provider')).toBeInTheDocument();
+            expect(screen.getByText('Categories')).toBeInTheDocument();
+            expect(screen.getByText('Font Providers')).toBeInTheDocument();
         });
 
         it('renders filter properties within groups', () => {

src/shared/lib/helpers/CharacterComparisonEngine/CharacterComparisonEngine.svelte.ts

@@ -95,11 +95,13 @@ export class CharacterComparisonEngine {
     #lastText = '';
     #lastFontA = '';
     #lastFontB = '';
+    #lastSpacing = 0;
+    #lastSize = 0;
 
     // Cached layout results
     #lastWidth = -1;
     #lastLineHeight = -1;
-    #lastResult: ComparisonResult | null = null;
+    #lastResult = $state<ComparisonResult | null>(null);
 
     constructor(locale?: string) {
         this.#segmenter = new Intl.Segmenter(locale, { granularity: 'grapheme' });
@@ -116,6 +118,8 @@ export class CharacterComparisonEngine {
      * @param fontB      CSS font string for the second font: `"weight sizepx \"family\""`.
      * @param width      Available line width in pixels.
      * @param lineHeight Line height in pixels (passed directly to pretext).
+     * @param spacing    Letter spacing in em (from typography settings).
+     * @param size       Current font size in pixels (used to convert spacing em to px).
      * @returns          Per-line grapheme data for both fonts. Empty `lines` when `text` is empty.
      */
     layout(
@@ -124,12 +128,21 @@ export class CharacterComparisonEngine {
         fontB: string,
         width: number,
         lineHeight: number,
+        spacing: number = 0,
+        size: number = 16,
     ): ComparisonResult {
         if (!text) {
             return { lines: [], totalHeight: 0 };
         }
 
-        const isFontChange = text !== this.#lastText || fontA !== this.#lastFontA || fontB !== this.#lastFontB;
+        const spacingPx = spacing * size;
+
+        const isFontChange = text !== this.#lastText
+            || fontA !== this.#lastFontA
+            || fontB !== this.#lastFontB
+            || spacing !== this.#lastSpacing
+            || size !== this.#lastSize;
+
         const isLayoutChange = width !== this.#lastWidth || lineHeight !== this.#lastLineHeight;
 
         if (!isFontChange && !isLayoutChange && this.#lastResult) {
@@ -140,11 +153,13 @@ export class CharacterComparisonEngine {
         if (isFontChange) {
             this.#preparedA = prepareWithSegments(text, fontA);
             this.#preparedB = prepareWithSegments(text, fontB);
-            this.#unifiedPrepared = this.#createUnifiedPrepared(this.#preparedA, this.#preparedB);
+            this.#unifiedPrepared = this.#createUnifiedPrepared(this.#preparedA, this.#preparedB, spacingPx);
 
             this.#lastText = text;
             this.#lastFontA = fontA;
             this.#lastFontB = fontB;
+            this.#lastSpacing = spacing;
+            this.#lastSize = size;
         }
 
         if (!this.#unifiedPrepared || !this.#preparedA || !this.#preparedB) {
@@ -175,7 +190,6 @@ export class CharacterComparisonEngine {
                     continue;
                 }
 
-                // PERFORMANCE: Reuse segmenter results if possible, but for now just optimize the loop
                 const graphemes = Array.from(this.#segmenter.segment(segmentText), s => s.segment);
 
                 const advA = intA.breakableFitAdvances[sIdx];
@@ -186,8 +200,12 @@ export class CharacterComparisonEngine {
 
                 for (let gIdx = gStart; gIdx < gEnd; gIdx++) {
                     const char = graphemes[gIdx];
-                    const wA = advA != null ? advA[gIdx]! : intA.widths[sIdx]!;
-                    const wB = advB != null ? advB[gIdx]! : intB.widths[sIdx]!;
+                    let wA = advA != null ? advA[gIdx]! : intA.widths[sIdx]!;
+                    let wB = advB != null ? advB[gIdx]! : intB.widths[sIdx]!;
+
+                    // Apply letter spacing (tracking) to the width of each character
+                    wA += spacingPx;
+                    wB += spacingPx;
 
                     chars.push({
                         char,
@@ -219,66 +237,92 @@ export class CharacterComparisonEngine {
     }
 
     /**
-     * Calculates character proximity and direction relative to a slider position.
+     * Calculates character states for an entire line in a single sequential pass.
      *
-     * Uses the most recent `layout()` result — must be called after `layout()`.
-     * No DOM calls are made; all geometry is derived from cached layout data.
+     * Walks characters left-to-right, accumulating the running x position using
+     * each character's actual rendered width: `widthB` for already-morphed characters
+     * (isPast=true) and `widthA` for upcoming ones. This ensures thresholds stay
+     * aligned with the visual DOM layout even when the two fonts have different widths.
      *
-     * @param lineIndex      Zero-based index of the line within the last layout result.
-     * @param charIndex      Zero-based index of the character within that line's `chars` array.
+     * @param line           A single laid-out line from the last layout result.
      * @param sliderPos      Current slider position as a percentage (0–100) of `containerWidth`.
-     * @param containerWidth Total container width in pixels, used to convert pixel offsets to %.
-     * @returns              `proximity` in [0, 1] (1 = slider exactly over char center) and
-     *                       `isPast` (true when the slider has already passed the char center).
+     * @param containerWidth Total container width in pixels.
+     * @returns              Per-character `proximity` and `isPast` in the same order as `line.chars`.
      */
-    getCharState(
-        lineIndex: number,
-        charIndex: number,
+    getLineCharStates(
+        line: ComparisonLine,
         sliderPos: number,
         containerWidth: number,
-    ): { proximity: number; isPast: boolean } {
-        if (!this.#lastResult || !this.#lastResult.lines[lineIndex]) {
-            return { proximity: 0, isPast: false };
+    ): Array<{ proximity: number; isPast: boolean }> {
+        if (!line) {
+            return [];
         }
-
-        const line = this.#lastResult.lines[lineIndex];
-        const char = line.chars[charIndex];
-
-        if (!char) {
-            return { proximity: 0, isPast: false };
-        }
-
-        // Center the comparison on the unified width
-        // In the UI, lines are centered. So we need to calculate the global X.
-        const lineXOffset = (containerWidth - line.width) / 2;
-        const charCenterX = lineXOffset + char.xA + (char.widthA / 2);
-
-        const charGlobalPercent = (charCenterX / containerWidth) * 100;
-
-        const distance = Math.abs(sliderPos - charGlobalPercent);
+        const chars = line.chars;
+        const n = chars.length;
+        const sliderX = (sliderPos / 100) * containerWidth;
         const range = 5;
-        const proximity = Math.max(0, 1 - distance / range);
-        const isPast = sliderPos > charGlobalPercent;
-
-        return { proximity, isPast };
+        // Prefix sums of widthA (left chars will be past → use widthA).
+        // Suffix sums of widthB (right chars will not be past → use widthB).
+        // This lets us compute, for each char i, what the total line width and
+        // char center would be at the exact moment the slider crosses that char:
+        //   left side (0..i-1) already past → font A widths
+        //   right side (i+1..n-1) not yet past → font B widths
+        const prefA = new Float64Array(n + 1);
+        const sufB = new Float64Array(n + 1);
+        for (let i = 0; i < n; i++) {
+            prefA[i + 1] = prefA[i] + chars[i].widthA;
+        }
+        for (let i = n - 1; i >= 0; i--) {
+            sufB[i] = sufB[i + 1] + chars[i].widthB;
+        }
+        // Per-char threshold: slider x at which this char should toggle isPast.
+        const thresholds = new Float64Array(n);
+        for (let i = 0; i < n; i++) {
+            const totalWidth = prefA[i] + chars[i].widthA + sufB[i + 1];
+            const xOffset = (containerWidth - totalWidth) / 2;
+            thresholds[i] = xOffset + prefA[i] + chars[i].widthA / 2;
+        }
+        // Determine isPast for each char at the current slider position.
+        const isPastArr = new Uint8Array(n);
+        for (let i = 0; i < n; i++) {
+            isPastArr[i] = sliderX > thresholds[i] ? 1 : 0;
+        }
+        // Compute visual positions based on actual rendered widths (font A if past, B if not).
+        const totalRendered = chars.reduce((s, c, i) => s + (isPastArr[i] ? c.widthA : c.widthB), 0);
+        const xOffset = (containerWidth - totalRendered) / 2;
+        let currentX = xOffset;
+        return chars.map((char, i) => {
+            const isPast = isPastArr[i] === 1;
+            const charWidth = isPast ? char.widthA : char.widthB;
+            const visualCenter = currentX + charWidth / 2;
+            const charGlobalPercent = (visualCenter / containerWidth) * 100;
+            const distance = Math.abs(sliderPos - charGlobalPercent);
+            const proximity = Math.max(0, 1 - distance / range);
+            currentX += charWidth;
+            return { proximity, isPast };
+        });
     }
 
     /**
      * Internal helper to merge two prepared texts into a "worst-case" unified version
      */
-    #createUnifiedPrepared(a: PreparedTextWithSegments, b: PreparedTextWithSegments): PreparedTextWithSegments {
+    #createUnifiedPrepared(
+        a: PreparedTextWithSegments,
+        b: PreparedTextWithSegments,
+        spacingPx: number = 0,
+    ): PreparedTextWithSegments {
         // Cast to `any`: accessing internal numeric arrays not in the public type signature.
         const intA = a as any;
         const intB = b as any;
 
         const unified = { ...intA };
 
-        unified.widths = intA.widths.map((w: number, i: number) => Math.max(w, intB.widths[i]));
+        unified.widths = intA.widths.map((w: number, i: number) => Math.max(w, intB.widths[i]) + spacingPx);
         unified.lineEndFitAdvances = intA.lineEndFitAdvances.map((w: number, i: number) =>
-            Math.max(w, intB.lineEndFitAdvances[i])
+            Math.max(w, intB.lineEndFitAdvances[i]) + spacingPx
         );
         unified.lineEndPaintAdvances = intA.lineEndPaintAdvances.map((w: number, i: number) =>
-            Math.max(w, intB.lineEndPaintAdvances[i])
+            Math.max(w, intB.lineEndPaintAdvances[i]) + spacingPx
         );
 
         unified.breakableFitAdvances = intA.breakableFitAdvances.map((advA: number[] | null, i: number) => {
@@ -287,13 +331,13 @@ export class CharacterComparisonEngine {
                 return null;
             }
             if (!advA) {
-                return advB;
+                return advB.map((w: number) => w + spacingPx);
             }
             if (!advB) {
-                return advA;
+                return advA.map((w: number) => w + spacingPx);
             }
 
-            return advA.map((w: number, j: number) => Math.max(w, advB[j]));
+            return advA.map((w: number, j: number) => Math.max(w, advB[j]) + spacingPx);
         });
 
         return unified;

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

@@ -109,56 +109,52 @@ describe('CharacterComparisonEngine', () => {
         expect(r2).not.toBe(r1);
     });
 
-    it('getCharState returns proximity 1 when slider is exactly over char center', () => {
-        // 'A' only: FontA width=10. Container=500px. Line centered.
-        // lineXOffset = (500 - maxWidth) / 2. maxWidth = max(10, 15) = 15 (FontB is wider).
-        // charCenterX = lineXOffset + xA + widthA/2.
-        // Using xA=0, widthA=10: charCenterX = (500-15)/2 + 0 + 5 = 247.5 + 5 = 252.5
-        // charGlobalPercent = (252.5 / 500) * 100 = 50.5
-        // distance = |50.5 - 50.5| = 0 => proximity = 1
+    it('getLineCharStates returns proximity 1 when slider is exactly over char center', () => {
         const containerWidth = 500;
-        engine.layout('A', '400 16px "FontA"', '400 16px "FontB"', containerWidth, 20);
-        // Recalculate expected percent manually:
-        const lineWidth = Math.max(FONT_A_WIDTH, FONT_B_WIDTH); // 15 (unified worst-case)
-        const lineXOffset = (containerWidth - lineWidth) / 2;
-        const charCenterX = lineXOffset + 0 + FONT_A_WIDTH / 2;
-        const charPercent = (charCenterX / containerWidth) * 100;
+        const result = engine.layout('A', '400 16px "FontA"', '400 16px "FontB"', containerWidth, 20);
+        // Single char: no neighbors → totalWidth = widthA, threshold = containerWidth/2.
+        // When isPast=false, visual center = (containerWidth - widthB)/2 + widthB/2 = containerWidth/2.
+        // So proximity=1 at exactly 50%.
+        const charPercent = 50;
 
-        const state = engine.getCharState(0, 0, charPercent, containerWidth);
-        expect(state.proximity).toBe(1);
-        expect(state.isPast).toBe(false);
+        const states = engine.getLineCharStates(result.lines[0], charPercent, containerWidth);
+        expect(states[0]?.proximity).toBe(1);
+        expect(states[0]?.isPast).toBe(false);
     });
 
-    it('getCharState returns proximity 0 when slider is far from char', () => {
-        engine.layout('A', '400 16px "FontA"', '400 16px "FontB"', 500, 20);
-        // Slider at 0%, char is near 50% — distance > 5 range => proximity = 0
-        const state = engine.getCharState(0, 0, 0, 500);
-        expect(state.proximity).toBe(0);
+    it('getLineCharStates returns proximity 0 when slider is far from char', () => {
+        const result = engine.layout('A', '400 16px "FontA"', '400 16px "FontB"', 500, 20);
+        const states = engine.getLineCharStates(result.lines[0], 0, 500);
+        expect(states[0]?.proximity).toBe(0);
     });
 
-    it('getCharState isPast is true when slider has passed char center', () => {
-        engine.layout('A', '400 16px "FontA"', '400 16px "FontB"', 500, 20);
-        const state = engine.getCharState(0, 0, 100, 500);
-        expect(state.isPast).toBe(true);
+    it('getLineCharStates isPast is true when slider has passed char center', () => {
+        const result = engine.layout('A', '400 16px "FontA"', '400 16px "FontB"', 500, 20);
+        const states = engine.getLineCharStates(result.lines[0], 100, 500);
+        expect(states[0]?.isPast).toBe(true);
     });
 
-    it('getCharState returns safe default for out-of-range lineIndex', () => {
-        engine.layout('A', '400 16px "FontA"', '400 16px "FontB"', 500, 20);
-        const state = engine.getCharState(99, 0, 50, 500);
-        expect(state.proximity).toBe(0);
-        expect(state.isPast).toBe(false);
+    it('getLineCharStates returns empty array for out-of-range lineIndex', () => {
+        const result = engine.layout('A', '400 16px "FontA"', '400 16px "FontB"', 500, 20);
+        // Passing an undefined object because the index doesn't exist.
+        const states = engine.getLineCharStates(result.lines[99], 50, 500);
+        expect(states).toEqual([]);
     });
 
-    it('getCharState returns safe default for out-of-range charIndex', () => {
-        engine.layout('A', '400 16px "FontA"', '400 16px "FontB"', 500, 20);
-        const state = engine.getCharState(0, 99, 50, 500);
-        expect(state.proximity).toBe(0);
-        expect(state.isPast).toBe(false);
+    it('getLineCharStates returns empty array before layout() has been called', () => {
+        // Passing an undefined object because layout() hasn't been called.
+        const states = engine.getLineCharStates(undefined as any, 50, 500);
+        expect(states).toEqual([]);
     });
 
-    it('getCharState returns safe default before layout() has been called', () => {
-        const state = engine.getCharState(0, 0, 50, 500);
-        expect(state.proximity).toBe(0);
-        expect(state.isPast).toBe(false);
+    it('getLineCharStates returns safe defaults for all chars', () => {
+        const result = engine.layout('A', '400 16px "FontA"', '400 16px "FontB"', 500, 20);
+        const states = engine.getLineCharStates(result.lines[0], 50, 500);
+        expect(states.length).toBeGreaterThan(0);
+        for (const s of states) {
+            expect(s.proximity).toBeGreaterThanOrEqual(0);
+            expect(s.proximity).toBeLessThanOrEqual(1);
+            expect(typeof s.isPast).toBe('boolean');
+        }
     });
 });

src/shared/lib/utils/getSkeletonWidth/getSkeletonWidth.ts

@@ -0,0 +1,13 @@
+/**
+ * Generates a consistent but varied width for skeleton placeholders.
+ * Uses a predefined sequence to ensure stability between renders.
+ *
+ * @param index - Index of the item in a list to pick a width from the sequence
+ * @param multiplier - Multiplier to apply to the base sequence values (default: 4)
+ * @returns CSS width value (e.g., "128px")
+ */
+export function getSkeletonWidth(index: number, multiplier = 4): string {
+    const sequence = [32, 48, 40, 56, 36, 44, 52, 38, 46, 42, 34, 50];
+    const base = sequence[index % sequence.length];
+    return `${base * multiplier}px`;
+}

src/shared/lib/utils/index.ts

@@ -17,6 +17,7 @@ export {
 export { clampNumber } from './clampNumber/clampNumber';
 export { debounce } from './debounce/debounce';
 export { getDecimalPlaces } from './getDecimalPlaces/getDecimalPlaces';
+export { getSkeletonWidth } from './getSkeletonWidth/getSkeletonWidth';
 export { roundToStepPrecision } from './roundToStepPrecision/roundToStepPrecision';
 export { smoothScroll } from './smoothScroll/smoothScroll';
 export { splitArray } from './splitArray/splitArray';

src/shared/ui/ComboControl/ComboControl.svelte.test.ts

@@ -114,7 +114,7 @@ describe('ComboControl', () => {
         it('opens popover with vertical slider on trigger click', async () => {
             render(ComboControl, { control: makeControl(50), controlLabel: 'Size control' });
             expect(screen.queryByRole('slider')).not.toBeInTheDocument();
-            await fireEvent.click(screen.getByLabelText('Size control'));
+            await fireEvent.click(screen.getByText('Size control'));
             await waitFor(() => expect(screen.getByRole('slider')).toBeInTheDocument());
         });
     });

src/shared/ui/VirtualList/VirtualList.svelte

@@ -62,6 +62,10 @@ interface Props extends
      * Near bottom callback
      */
     onNearBottom?: (lastVisibleIndex: number) => void;
+    /**
+     * Fires when scroll position exceeds loaded content — user jumped beyond data
+     */
+    onJump?: (targetIndex: number) => void;
     /**
      * Item render snippet
      */
@@ -95,6 +99,7 @@ let {
     class: className,
     onVisibleItemsChange,
     onNearBottom,
+    onJump,
     children,
     useWindowScroll = false,
     isLoading = false,
@@ -170,6 +175,10 @@ const throttledNearBottom = throttle((lastVisibleIndex: number) => {
     onNearBottom?.(lastVisibleIndex);
 }, 200); // 200ms throttle
 
+const throttledOnJump = throttle((targetIndex: number) => {
+    onJump?.(targetIndex);
+}, 200);
+
 // Calculate top/bottom padding for spacer elements
 // In CSS Grid, gap creates space BETWEEN elements.
 // The top spacer should place the first row at its virtual offset.
@@ -227,6 +236,26 @@ $effect(() => {
         }
     }
 });
+
+$effect(() => {
+    // Fire onJump when scroll is beyond the loaded content boundary.
+    // Target index estimates which item the user scrolled to.
+    if (!onJump || !virtualizer.containerHeight || virtualizer.scrollOffset <= 0) {
+        return;
+    }
+
+    const isAhead = virtualizer.scrollOffset > virtualizer.totalSize;
+    if (!isAhead) {
+        return;
+    }
+
+    const estimatedItemHeight = typeof itemHeight === 'number' ? itemHeight : 80;
+    // Include visible rows + overscan so the bottom of the viewport is fully covered
+    const topItemIndex = Math.floor(virtualizer.scrollOffset / estimatedItemHeight) * columns;
+    const visibleRows = Math.ceil(virtualizer.containerHeight / estimatedItemHeight);
+    const targetIndex = topItemIndex + (visibleRows + overscan) * columns;
+    throttledOnJump(targetIndex);
+});
 </script>
 
 {#snippet content()}

src/widgets/ComparisonView/lib/index.ts

@@ -0,0 +1,2 @@
+export * from './utils/dotTransition';
+export * from './utils/getPretextFontString';

src/widgets/ComparisonView/lib/utils/dotTransition.ts

@@ -0,0 +1,99 @@
+import { VIRTUAL_INDEX_NOT_LOADED } from '$entities/Font';
+import { cubicOut } from 'svelte/easing';
+import {
+    type CrossfadeParams,
+    type TransitionConfig,
+    crossfade,
+} from 'svelte/transition';
+
+/**
+ * Custom parameters for dot transitions in virtualized lists.
+ */
+export interface DotTransitionParams extends CrossfadeParams {
+    /**
+     * Unique key for crossfade pairing
+     */
+    key: any;
+    /**
+     * Current index of the item in the list
+     */
+    index: number;
+    /**
+     * Target index to move towards (e.g. counterpart side index)
+     */
+    otherIndex: number;
+}
+
+/**
+ * Type-safe helper to create dot transition parameters.
+ */
+export function getDotTransitionParams(
+    key: 'active-dot' | 'inactive-dot',
+    index: number,
+    otherIndex: number,
+): DotTransitionParams {
+    return { key, index, otherIndex };
+}
+
+/**
+ * Type guard for DotTransitionParams.
+ */
+function isDotTransitionParams(p: CrossfadeParams): p is DotTransitionParams {
+    return (
+        p !== null
+        && typeof p === 'object'
+        && 'index' in p
+        && 'otherIndex' in p
+    );
+}
+
+/**
+ * Creates a crossfade transition pair optimized for virtualized font lists.
+ *
+ * It uses the 'index' and 'otherIndex' params to calculate the direction
+ * of the slide animation when a matching pair cannot be found in the DOM
+ * (e.g. because it was virtualized out).
+ */
+export function createDotCrossfade() {
+    return crossfade({
+        duration: 300,
+        easing: cubicOut,
+        fallback(node: Element, params: CrossfadeParams, _intro: boolean): TransitionConfig {
+            if (!isDotTransitionParams(params)) {
+                return {
+                    duration: 300,
+                    easing: cubicOut,
+                    css: t => `opacity: ${t};`,
+                };
+            }
+
+            const { index, otherIndex } = params;
+
+            // If the other target is unknown, just fade in place
+            if (otherIndex === undefined || otherIndex === -1) {
+                return {
+                    duration: 300,
+                    easing: cubicOut,
+                    css: t => `opacity: ${t};`,
+                };
+            }
+
+            const diff = otherIndex - index;
+            const sign = diff > 0 ? 1 : (diff < 0 ? -1 : 0);
+
+            // Use container height for a full-height slide
+            const listEl = node.closest('[data-font-list]');
+            const h = listEl?.clientHeight ?? 300;
+            const fromY = sign * h;
+
+            return {
+                duration: 300,
+                easing: cubicOut,
+                css: (t, u) => `
+                    transform: translateY(${fromY * u}px);
+                    opacity: ${t};
+                `,
+            };
+        },
+    });
+}

src/widgets/ComparisonView/lib/utils/getPretextFontString.test.ts

@@ -0,0 +1,35 @@
+import {
+    describe,
+    expect,
+    it,
+} from 'vitest';
+import { getPretextFontString } from './getPretextFontString';
+
+describe('getPretextFontString', () => {
+    it('correctly formats the font string for pretext', () => {
+        const weight = 400;
+        const sizePx = 16;
+        const fontName = 'Inter';
+        const expected = '400 16px "Inter"';
+
+        expect(getPretextFontString(weight, sizePx, fontName)).toBe(expected);
+    });
+
+    it('works with different weight and size', () => {
+        const weight = 700;
+        const sizePx = 32;
+        const fontName = 'Roboto';
+        const expected = '700 32px "Roboto"';
+
+        expect(getPretextFontString(weight, sizePx, fontName)).toBe(expected);
+    });
+
+    it('handles font names with spaces', () => {
+        const weight = 400;
+        const sizePx = 16;
+        const fontName = 'Open Sans';
+        const expected = '400 16px "Open Sans"';
+
+        expect(getPretextFontString(weight, sizePx, fontName)).toBe(expected);
+    });
+});

src/widgets/ComparisonView/lib/utils/getPretextFontString.ts

@@ -0,0 +1,11 @@
+/**
+ * Formats a font configuration into a string format required by @chenglou/pretext.
+ *
+ * @param weight - Numeric font weight (e.g., 400).
+ * @param sizePx - Font size in pixels.
+ * @param fontName - The font family name.
+ * @returns A formatted font string: `"weight sizepx \"fontName\""`.
+ */
+export function getPretextFontString(weight: number, sizePx: number, fontName: string): string {
+    return `${weight} ${sizePx}px "${fontName}"`;
+}

src/widgets/ComparisonView/model/stores/comparisonStore.svelte.ts

@@ -24,6 +24,7 @@ import {
 import { typographySettingsStore } from '$features/SetupFont/model';
 import { createPersistentStore } from '$shared/lib';
 import { untrack } from 'svelte';
+import { getPretextFontString } from '../../lib';
 
 /**
  * Storage schema for comparison state
@@ -205,8 +206,8 @@ export class ComparisonStore {
             return;
         }
 
-        const fontAString = `${weight} ${size}px "${fontAName}"`;
-        const fontBString = `${weight} ${size}px "${fontBName}"`;
+        const fontAString = getPretextFontString(weight, size, fontAName);
+        const fontBString = getPretextFontString(weight, size, fontBName);
 
         // Check if already loaded to avoid UI flash
         const isALoaded = document.fonts.check(fontAString);

src/widgets/ComparisonView/ui/Character/Character.svelte

@@ -48,6 +48,7 @@ $effect(() => {
     <span
         class="char-wrap"
         style:font-size="{typography.renderedSize}px"
+        style:margin-right="{typography.spacing}em"
         style:will-change={proximity > 0 ? 'transform' : 'auto'}
     >
         {#each [0, 1] as s (s)}

src/widgets/ComparisonView/ui/FontList/FontList.svelte

@@ -8,65 +8,86 @@ import {
     FontApplicator,
     FontVirtualList,
     type UnifiedFont,
+    VIRTUAL_INDEX_NOT_LOADED,
+    appliedFontsManager,
+    fontStore,
 } from '$entities/Font';
+import { getSkeletonWidth } from '$shared/lib/utils';
 import {
     Button,
     Label,
+    Skeleton,
 } from '$shared/ui';
 import DotIcon from '@lucide/svelte/icons/dot';
-import { cubicOut } from 'svelte/easing';
-import { crossfade } from 'svelte/transition';
-import { comparisonStore } from '../../model';
+import { fade } from 'svelte/transition';
+import {
+    createDotCrossfade,
+    getDotTransitionParams,
+} from '../../lib';
+import {
+    type Side,
+    comparisonStore,
+} from '../../model';
 
 const side = $derived(comparisonStore.side);
-let prevIndexA: number | null = null;
-let prevIndexB: number | null = null;
-let selectedIndexA: number | null = null;
-let selectedIndexB: number | null = null;
-let pendingDirection: 1 | -1 = 1;
 
-const [send, receive] = crossfade({
-    duration: 300,
-    easing: cubicOut,
-    fallback(node) {
-        // Read pendingDirection synchronously — no reactive timing issues
-        const fromY = pendingDirection * (node.closest('[data-font-list]')?.clientHeight ?? 300);
-        return {
-            duration: 300,
-            easing: cubicOut,
-            css: t => `transform: translateY(${fromY * (1 - t)}px);`,
-        };
-    },
+// Treat -1 (not loaded) as being at the very bottom of the infinite list
+function getVirtualIndex(fontId: string | undefined): number {
+    if (!fontId) {
+        return -1;
+    }
+    const idx = fontStore.fonts.findIndex(f => f.id === fontId);
+    if (idx === -1) {
+        return VIRTUAL_INDEX_NOT_LOADED;
+    }
+    return idx;
+}
+
+// Reactive indices of the currently selected fonts in the full list
+const indexA = $derived(getVirtualIndex(comparisonStore.fontA?.id));
+const indexB = $derived(getVirtualIndex(comparisonStore.fontB?.id));
+
+// Track previous state for directional fallback transitions.
+// We use plain variables here. In Svelte 5, updates to these in an $effect
+// happen AFTER the render/DOM update, so transitions starting as a result
+// of that update will see the "old" values of these variables.
+let prevIndexA = indexA;
+let prevIndexB = indexB;
+let prevSide: Side = side;
+
+const [send, receive] = createDotCrossfade();
+
+$effect(() => {
+    // This effect runs after every change to indexA, indexB, or side.
+    // It captures the "current" values which will serve as "previous" values
+    // for the NEXT transition.
+    prevIndexA = indexA;
+    prevIndexB = indexB;
+    prevSide = side;
 });
 
-function handleSelect(font: UnifiedFont, index: number) {
+function handleSelect(font: UnifiedFont) {
     if (side === 'A') {
-        if (prevIndexA !== null) {
-            pendingDirection = index > prevIndexA ? -1 : 1;
-        }
-        prevIndexA = index;
-        selectedIndexA = index;
         comparisonStore.fontA = font;
-    } else if (side === 'B') {
-        if (prevIndexB !== null) {
-            pendingDirection = index > prevIndexB ? -1 : 1;
-        }
-        prevIndexB = index;
-        selectedIndexB = index;
+    } else {
         comparisonStore.fontB = font;
     }
 }
 
-// When side switches, compute direction from relative positions of A vs B
-$effect(() => {
-    const _ = side; // track side
-    if (selectedIndexA !== null && selectedIndexB !== null) {
-        // Switching TO B means dot moves toward B's position relative to A
-        pendingDirection = side === 'B'
-            ? (selectedIndexB > selectedIndexA ? 1 : -1)
-            : (selectedIndexA > selectedIndexB ? 1 : -1);
-    }
-});
+/**
+ * Returns true once the font file is loaded (or errored) and safe to render.
+ * Called inside the template — Svelte 5 tracks the $state reads inside
+ * appliedFontsManager.getFontStatus(), so each row re-renders reactively
+ * when its file arrives.
+ */
+function isFontReady(font: UnifiedFont): boolean {
+    const status = appliedFontsManager.getFontStatus(
+        font.id,
+        DEFAULT_FONT_WEIGHT,
+        font.features?.isVariable,
+    );
+    return status === 'loaded' || status === 'error';
+}
 </script>
 
 <div class="flex-1 min-h-0 h-full">
@@ -79,41 +100,93 @@ $effect(() => {
         <FontVirtualList
             data-font-list
             weight={DEFAULT_FONT_WEIGHT}
-            itemHeight={45}
+            itemHeight={44}
             class="bg-transparent min-h-0 h-full scroll-stable py-2 pl-6 pr-4"
         >
+            {#snippet skeleton()}
+                <div class="py-2.5 md:py-3 px-7">
+                    {#each { length: 50 } as _, index (index)}
+                        <div class="w-full px-3 py-3 flex items-center justify-between">
+                            <div class="flex-1 flex items-center gap-3">
+                                <Skeleton
+                                    class="h-4 w-32 bg-neutral-200/70 dark:bg-neutral-800/70"
+                                    style="width: {getSkeletonWidth(index)}"
+                                />
+                            </div>
+                            <Skeleton class="w-1.5 h-1.5 rounded-full bg-neutral-200/70 dark:bg-neutral-800/70" />
+                        </div>
+                    {/each}
+                </div>
+            {/snippet}
+
             {#snippet children({ item: font, index })}
-                {@const isSelectedA = font.id === comparisonStore.fontA?.id}
-                {@const isSelectedB = font.id === comparisonStore.fontB?.id}
-                {@const active = (side === 'A' && isSelectedA) || (side === 'B' && isSelectedB)}
+                <div class="relative h-[44px] w-full">
+                    {#if !isFontReady(font)}
+                        <div
+                            class="absolute inset-0 px-3 md:px-4 flex items-center justify-between border border-transparent"
+                            transition:fade={{ duration: 300 }}
+                        >
+                            <Skeleton
+                                class="h-4 bg-neutral-200/70 dark:bg-neutral-800/70"
+                                style="width: {getSkeletonWidth(index)}"
+                            />
+                            <Skeleton class="w-1.5 h-1.5 rounded-full bg-neutral-200/70 dark:bg-neutral-800/70" />
+                        </div>
+                    {:else}
+                        {@const isSelectedA = font.id === comparisonStore.fontA?.id}
+                        {@const isSelectedB = font.id === comparisonStore.fontB?.id}
+                        {@const active = (side === 'A' && isSelectedA) || (side === 'B' && isSelectedB)}
 
-                <Button
-                    variant="tertiary"
-                    {active}
-                    onclick={() => handleSelect(font, index)}
-                    class="w-full px-3 md:px-4 py-2.5 md:py-3 flex !justify-between text-left text-sm"
-                    iconPosition="right"
-                >
-                    <FontApplicator {font}>{font.name}</FontApplicator>
+                        <div transition:fade={{ duration: 300 }} class="h-full">
+                            <Button
+                                variant="tertiary"
+                                {active}
+                                onclick={() => handleSelect(font)}
+                                class="w-full h-full px-3 md:px-4 py-2.5 md:py-3 flex !justify-between text-left text-sm"
+                                iconPosition="right"
+                            >
+                                <FontApplicator {font}>
+                                    {font.name}
+                                </FontApplicator>
 
-                    {#snippet icon()}
-                        {#if active}
-                            <div
-                                in:receive={{ key: 'active-dot' }}
-                                out:send={{ key: 'active-dot' }}
-                            >
-                                <DotIcon class="size-8 stroke-brand" />
-                            </div>
-                        {:else if isSelectedA || isSelectedB}
-                            <div
-                                in:receive={{ key: 'inactive-dot' }}
-                                out:send={{ key: 'inactive-dot' }}
-                            >
-                                <DotIcon class="size-8 stroke-neutral-300 dark:stroke-neutral-600" />
-                            </div>
-                        {/if}
-                    {/snippet}
-                </Button>
+                                {#snippet icon()}
+                                    {#if active}
+                                        <div
+                                            in:receive={getDotTransitionParams(
+                                                'active-dot',
+                                                index,
+                                                prevSide === 'A' ? prevIndexA : prevIndexB,
+                                            )}
+                                            out:send={getDotTransitionParams(
+                                                'active-dot',
+                                                index,
+                                                side === 'A' ? indexA : indexB,
+                                            )}
+                                        >
+                                            <DotIcon class="size-8 stroke-brand" />
+                                        </div>
+                                    {:else if isSelectedA || isSelectedB}
+                                        {@const isA = isSelectedA}
+                                        <div
+                                            in:receive={getDotTransitionParams(
+                                                'inactive-dot',
+                                                index,
+                                                isA ? prevIndexB : prevIndexA,
+                                            )}
+                                            out:send={getDotTransitionParams(
+                                                'inactive-dot',
+                                                index,
+                                                isA ? indexB : indexA,
+                                            )}
+                                        >
+                                            <DotIcon class="size-8 stroke-neutral-300 dark:stroke-neutral-600" />
+                                        </div>
+                                    {/if}
+                                {/snippet}
+                            </Button>
+                        </div>
+                    {/if}
+                </div>
             {/snippet}
         </FontVirtualList>
     </div>

src/widgets/ComparisonView/ui/Line/Line.svelte

@@ -33,8 +33,8 @@ let { chars, character }: Props = $props();
 
 <div
     class="relative flex w-full justify-center items-center whitespace-nowrap"
-    style:height="{typography.height}em"
-    style:line-height="{typography.height}em"
+    style:height="{typography.height * typography.renderedSize}px"
+    style:line-height="{typography.height * typography.renderedSize}px"
 >
     {#each chars as c, index}
         {@render character?.({ char: c.char, index })}

src/widgets/ComparisonView/ui/SliderArea/SliderArea.svelte

@@ -22,6 +22,7 @@ import clsx from 'clsx';
 import { getContext } from 'svelte';
 import { Spring } from 'svelte/motion';
 import { fade } from 'svelte/transition';
+import { getPretextFontString } from '../../lib';
 import { comparisonStore } from '../../model';
 import Character from '../Character/Character.svelte';
 import Line from '../Line/Line.svelte';
@@ -53,6 +54,7 @@ const isMobile = $derived(responsive?.isMobile ?? false);
 
 let isDragging = $state(false);
 let isTypographyMenuOpen = $state(false);
+let containerWidth = $state(0);
 
 // New high-performance layout engine
 const comparisonEngine = new CharacterComparisonEngine();
@@ -127,24 +129,28 @@ $effect(() => {
     const _weight = typography.weight;
     const _size = typography.renderedSize;
     const _height = typography.height;
+    const _spacing = typography.spacing;
 
     if (container && fontA && fontB) {
         // PRETEXT API strings: "weight sizepx family"
-        const fontAStr = `${_weight} ${_size}px "${fontA.name}"`;
-        const fontBStr = `${_weight} ${_size}px "${fontB.name}"`;
+        const fontAStr = getPretextFontString(_weight, _size, fontA.name);
+        const fontBStr = getPretextFontString(_weight, _size, fontB.name);
 
         // Use offsetWidth to avoid transform scaling issues
         const width = container.offsetWidth;
         const padding = isMobile ? 48 : 96;
         const availableWidth = width - padding;
-        const lineHeight = _size * 1.2; // Approximate
+        const lineHeight = _size * _height;
 
+        containerWidth = width;
         layoutResult = comparisonEngine.layout(
             _text,
             fontAStr,
             fontBStr,
             availableWidth,
             lineHeight,
+            _spacing,
+            _size,
         );
     }
 });
@@ -157,12 +163,15 @@ $effect(() => {
         if (container && fontA && fontB) {
             const width = container.offsetWidth;
             const padding = isMobile ? 48 : 96;
+            containerWidth = width;
             layoutResult = comparisonEngine.layout(
                 comparisonStore.text,
-                `${typography.weight} ${typography.renderedSize}px "${fontA.name}"`,
-                `${typography.weight} ${typography.renderedSize}px "${fontB.name}"`,
+                getPretextFontString(typography.weight, typography.renderedSize, fontA.name),
+                getPretextFontString(typography.weight, typography.renderedSize, fontB.name),
                 width - padding,
-                typography.renderedSize * 1.2,
+                typography.renderedSize * typography.height,
+                typography.spacing,
+                typography.renderedSize,
             );
         }
     };
@@ -239,11 +248,15 @@ const scaleClass = $derived(
                             my-auto
                         "
                     >
-                        {#each layoutResult.lines as line, lineIndex}
+                        {#each layoutResult.lines as line}
+                            {@const lineStates = comparisonEngine.getLineCharStates(line, sliderPos, containerWidth)}
                             <Line chars={line.chars}>
                                 {#snippet character({ char, index })}
-                                    {@const { proximity, isPast } = comparisonEngine.getCharState(lineIndex, index, sliderPos, container?.offsetWidth ?? 0)}
-                                    <Character {char} {proximity} {isPast} />
+                                    <Character
+                                        {char}
+                                        proximity={lineStates[index]?.proximity ?? 0}
+                                        isPast={lineStates[index]?.isPast ?? false}
+                                    />
                                 {/snippet}
                             </Line>
                         {/each}

tsconfig.json

@@ -38,6 +38,8 @@
     "src/**/*.js",
     "src/**/*.svelte",
     "src/**/*.d.ts",
+    "vitest.config*.ts",
+    "vitest.setup*.ts",
     "vitest.types.d.ts"
   ],
   "exclude": [

vitest.config.component.ts

@@ -0,0 +1,29 @@
+import { svelte } from '@sveltejs/vite-plugin-svelte';
+import path from 'node:path';
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+    plugins: [svelte()],
+
+    test: {
+        environment: 'jsdom',
+        include: ['src/**/*.svelte.test.ts'],
+        exclude: ['node_modules', 'dist', 'e2e', '.storybook'],
+        restoreMocks: true,
+        setupFiles: ['./vitest.setup.component.ts', './vitest.setup.jsdom.ts'],
+        globals: true,
+    },
+
+    resolve: {
+        conditions: ['browser'],
+        alias: {
+            $lib: path.resolve(__dirname, './src/lib'),
+            $app: path.resolve(__dirname, './src/app'),
+            $shared: path.resolve(__dirname, './src/shared'),
+            $entities: path.resolve(__dirname, './src/entities'),
+            $features: path.resolve(__dirname, './src/features'),
+            $routes: path.resolve(__dirname, './src/routes'),
+            $widgets: path.resolve(__dirname, './src/widgets'),
+        },
+    },
+});

vitest.setup.component.ts

@@ -1,3 +1,4 @@
+import { queryClient } from '$shared/api/queryClient';
 import * as matchers from '@testing-library/jest-dom/matchers';
 import { cleanup } from '@testing-library/svelte';
 import {
@@ -13,6 +14,7 @@ expect.extend(matchers);
 
 afterEach(() => {
     cleanup();
+    queryClient.clear();
 });
 
 // Mock window.matchMedia for components that use it

vitest.setup.jsdom.ts

@@ -0,0 +1,46 @@
+import { vi } from 'vitest';
+
+// jsdom lacks ResizeObserver
+global.ResizeObserver = class {
+    observe = vi.fn();
+    unobserve = vi.fn();
+    disconnect = vi.fn();
+} as unknown as typeof ResizeObserver;
+
+// jsdom lacks Web Animations API
+Element.prototype.animate = vi.fn().mockReturnValue({
+    onfinish: null,
+    cancel: vi.fn(),
+    finish: vi.fn(),
+    pause: vi.fn(),
+    play: vi.fn(),
+});
+
+// jsdom lacks SVG geometry methods
+(SVGElement.prototype as any).getTotalLength = vi.fn(() => 0);
+
+// Robust localStorage mock for jsdom environment
+const localStorageMock = (() => {
+    let store: Record<string, string> = {};
+    return {
+        getItem: vi.fn((key: string) => store[key] || null),
+        setItem: vi.fn((key: string, value: string) => {
+            store[key] = value.toString();
+        }),
+        removeItem: vi.fn((key: string) => {
+            delete store[key];
+        }),
+        clear: vi.fn(() => {
+            store = {};
+        }),
+        key: vi.fn((index: number) => Object.keys(store)[index] || null),
+        get length() {
+            return Object.keys(store).length;
+        },
+    };
+})();
+
+Object.defineProperty(window, 'localStorage', {
+    value: localStorageMock,
+    writable: true,
+});