fix: iterate pre-computed chars array in Line.svelte to fix unicode grapheme splitting bug

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

@@ -6,15 +6,21 @@
 import type { Snippet } from 'svelte';
 import { comparisonStore } from '../../model';
 
+interface LineChar {
+    char: string;
+    xA: number;
+    widthA: number;
+    xB: number;
+    widthB: number;
+}
+
 interface Props {
     /**
-     * Line text
+     * Pre-computed grapheme array from CharacterComparisonEngine.
+     * Using the engine's chars array (rather than splitting line.text) ensures
+     * correct grapheme-cluster boundaries for emoji and multi-codepoint characters.
      */
-    text: string;
-    /**
-     * DOM element reference
-     */
-    element?: HTMLElement;
+    chars: LineChar[];
     /**
      * Character render snippet
      */
@@ -22,18 +28,15 @@ interface Props {
 }
 const typography = $derived(comparisonStore.typography);
 
-let { text, element = $bindable<HTMLElement>(), character }: Props = $props();
-
-const characters = $derived(text.split(''));
+let { chars, character }: Props = $props();
 </script>
 
 <div
-    bind:this={element}
     class="relative flex w-full justify-center items-center whitespace-nowrap"
     style:height="{typography.height}em"
     style:line-height="{typography.height}em"
 >
-    {#each characters as char, index}
-        {@render character?.({ char, index })}
+    {#each chars as c, index}
+        {@render character?.({ char: c.char, index })}
     {/each}
 </div>

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

@@ -9,11 +9,12 @@
 -->
 <script lang="ts">
 import {
-    type CharacterComparison,
     type ResponsiveManager,
-    createCharacterComparison,
     debounce,
 } from '$shared/lib';
+import {
+    CharacterComparisonEngine,
+} from '$shared/lib/helpers/CharacterComparisonEngine/CharacterComparisonEngine.svelte';
 import { cn } from '$shared/shadcn/utils/shadcn-utils';
 import { Loader } from '$shared/ui';
 import { getContext } from 'svelte';
@@ -44,22 +45,16 @@ const isLoading = $derived(comparisonStore.isLoading || !comparisonStore.isReady
 const typography = $derived(comparisonStore.typography);
 
 let container = $state<HTMLElement>();
-let measureCanvas = $state<HTMLCanvasElement>();
 
 const responsive = getContext<ResponsiveManager>('responsive');
 const isMobile = $derived(responsive?.isMobile ?? false);
 
 let isDragging = $state(false);
 
-const charComparison: CharacterComparison = createCharacterComparison(
-    () => comparisonStore.text,
-    () => fontA,
-    () => fontB,
-    () => typography.weight,
-    () => typography.renderedSize,
-);
+// New high-performance layout engine
+const comparisonEngine = new CharacterComparisonEngine();
 
-let lineElements = $state<(HTMLElement | undefined)[]>([]);
+let layoutResult = $state<ReturnType<typeof comparisonEngine.layout>>({ lines: [], totalHeight: 0 });
 
 const sliderSpring = new Spring(50, {
     stiffness: 0.2,
@@ -123,18 +118,41 @@ $effect(() => {
     const _weight = typography.weight;
     const _size = typography.renderedSize;
     const _height = typography.height;
-    if (container && measureCanvas && fontA && fontB) {
-        requestAnimationFrame(() => {
-            charComparison.breakIntoLines(container, measureCanvas);
-        });
+
+    if (container && fontA && fontB) {
+        // PRETEXT API strings: "weight sizepx family"
+        const fontAStr = `${_weight} ${_size}px "${fontA.name}"`;
+        const fontBStr = `${_weight} ${_size}px "${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
+
+        layoutResult = comparisonEngine.layout(
+            _text,
+            fontAStr,
+            fontBStr,
+            availableWidth,
+            lineHeight,
+        );
     }
 });
 
 $effect(() => {
     if (typeof window === 'undefined') return;
     const handleResize = () => {
-        if (container && measureCanvas) {
-            charComparison.breakIntoLines(container, measureCanvas);
+        if (container && fontA && fontB) {
+            const width = container.offsetWidth;
+            const padding = isMobile ? 48 : 96;
+            layoutResult = comparisonEngine.layout(
+                comparisonStore.text,
+                `${typography.weight} ${typography.renderedSize}px "${fontA.name}"`,
+                `${typography.weight} ${typography.renderedSize}px "${fontB.name}"`,
+                width - padding,
+                typography.renderedSize * 1.2,
+            );
         }
     };
     window.addEventListener('resize', handleResize);
@@ -156,9 +174,6 @@ const scaleClass = $derived(
 );
 </script>
 
-<!-- Hidden measurement canvas -->
-<canvas bind:this={measureCanvas} class="hidden" width="1" height="1"></canvas>
-
 <!--
     Outer flex container — fills parent.
     The paper div inside scales down when the sidebar opens on desktop.
@@ -218,10 +233,10 @@ const scaleClass = $derived(
                             my-auto
                         "
                     >
-                        {#each charComparison.lines as line, lineIndex}
-                            <Line bind:element={lineElements[lineIndex]} text={line.text}>
+                        {#each layoutResult.lines as line, lineIndex}
+                            <Line chars={line.chars}>
                                 {#snippet character({ char, index })}
-                                    {@const { proximity, isPast } = charComparison.getCharState(index, sliderPos, lineElements[lineIndex], container)}
+                                    {@const { proximity, isPast } = comparisonEngine.getCharState(lineIndex, index, sliderPos, container?.offsetWidth ?? 0)}
                                     <Character {char} {proximity} {isPast} />
                                 {/snippet}
                             </Line>