perf: optimize stacked diff view and Pierre diff rendering

- Compute default expanded count for stacked view to reduce DOM load
- Move diff processing to worker pool to improve UI responsiveness
- Add content cache key to avoid recomputing large diffs on render

packages/ui/src/components/views/DiffView.tsx

@@ -29,8 +29,14 @@ import { useDeviceInfo } from '@/lib/device';
 const SIDE_BY_SIDE_MIN_WIDTH = 1100;
 const DIFF_REQUEST_TIMEOUT_MS = 15000;
 
-// Memory optimization: limit concurrent expanded diffs in stacked view
-const STACKED_VIEW_MAX_EXPANDED_DIFFS = 10;
+// Perf: limit concurrent expanded diffs in stacked view.
+// Expanding many diffs mounts many Pierre instances + lots of DOM.
+const getStackedViewDefaultExpandedCount = (fileCount: number): number => {
+    if (fileCount <= 6) return fileCount;
+    if (fileCount <= 12) return 6;
+    if (fileCount <= 25) return 4;
+    return 2;
+};
 
 type FileEntry = GitStatus['files'][number] & {
     insertions: number;
@@ -771,7 +777,7 @@ const MultiFileDiffEntry = React.memo<MultiFileDiffEntryProps>(({
                                 Loading diff…
                             </div>
                         ) : null}
-                        {diffData ? (
+                        {isExpanded && diffData ? (
                             <InlineDiffViewer
                                 filePath={file.path}
                                 diff={diffData}
@@ -1054,6 +1060,8 @@ export const DiffView: React.FC = () => {
     const renderStackedDiffView = () => {
         if (!effectiveDirectory) return null;
 
+        const defaultExpandedCount = getStackedViewDefaultExpandedCount(changedFiles.length);
+
         return (
             <div className="flex flex-1 min-h-0 h-full gap-3 px-3 pb-3 pt-2">
                 {showFileSidebar && (
@@ -1087,7 +1095,7 @@ export const DiffView: React.FC = () => {
                                 isSelected={file.path === selectedFile}
                                 onSelect={handleSelectFile}
                                 registerSectionRef={registerSectionRef}
-                                defaultCollapsed={index >= STACKED_VIEW_MAX_EXPANDED_DIFFS}
+                                defaultCollapsed={index >= defaultExpandedCount}
                             />
                         ))}
                     </div>

packages/ui/src/components/views/PierreDiffViewer.tsx

@@ -1,11 +1,11 @@
 import React, { useMemo, useRef, useState, useCallback, useEffect } from 'react';
 import { createPortal } from 'react-dom';
-import { FileDiff } from '@pierre/diffs/react';
-import { parseDiffFromFile, type FileContents, type FileDiffMetadata, type SelectedLineRange } from '@pierre/diffs';
+import { FileDiff as PierreFileDiff, type FileContents, type FileDiffOptions, type SelectedLineRange } from '@pierre/diffs';
 import { RiSendPlane2Line } from '@remixicon/react';
 
 import { useOptionalThemeSystem } from '@/contexts/useThemeSystem';
 import { ScrollableOverlay } from '@/components/ui/ScrollableOverlay';
+import { useWorkerPool } from '@/contexts/DiffWorkerProvider';
 import { ensurePierreThemeRegistered, getResolvedShikiTheme } from '@/lib/shiki/appThemeRegistry';
 import { getDefaultTheme } from '@/lib/theme/themes';
 
@@ -96,15 +96,23 @@ const WEBKIT_SCROLL_FIX_CSS = `
 `;
 
 // Fast cache key - use length + samples instead of full hash
-function getCacheKey(fileName: string, original: string, modified: string, themeKey: string): string {
-  // Sample a few characters instead of hashing entire content
-  const sampleOriginal = original.length > 100
-    ? `${original.slice(0, 50)}${original.slice(-50)}`
-    : original;
-  const sampleModified = modified.length > 100
-    ? `${modified.slice(0, 50)}${modified.slice(-50)}`
-    : modified;
-  return `${themeKey}::${fileName}:${original.length}:${modified.length}:${sampleOriginal.length}:${sampleModified.length}`;
+function fnv1a32(input: string): string {
+  // Fast + stable across runtimes; good enough for cache keys.
+  let hash = 0x811c9dc5;
+  for (let i = 0; i < input.length; i += 1) {
+    hash ^= input.charCodeAt(i);
+    // hash *= 16777619 (but keep 32-bit)
+    hash = (hash + ((hash << 1) + (hash << 4) + (hash << 7) + (hash << 8) + (hash << 24))) >>> 0;
+  }
+  return hash.toString(16);
+}
+
+function makeContentCacheKey(contents: string): string {
+  // Avoid hashing full file; sample head+tail.
+  const sample = contents.length > 400
+    ? `${contents.slice(0, 200)}${contents.slice(-200)}`
+    : contents;
+  return `${contents.length}:${fnv1a32(sample)}`;
 }
 
 const extractSelectedCode = (original: string, modified: string, range: SelectedLineRange): string => {
@@ -315,6 +323,9 @@ export const PierreDiffViewer: React.FC<PierreDiffViewerProps> = ({
   const diffThemeKey = `${lightTheme.metadata.id}:${darkTheme.metadata.id}:${isDark ? 'dark' : 'light'}`;
 
   const diffRootRef = useRef<HTMLDivElement | null>(null);
+  const diffContainerRef = useRef<HTMLDivElement | null>(null);
+  const diffInstanceRef = useRef<PierreFileDiff<unknown> | null>(null);
+  const workerPool = useWorkerPool();
 
   const lightResolvedTheme = useMemo(() => getResolvedShikiTheme(lightTheme), [lightTheme]);
   const darkResolvedTheme = useMemo(() => getResolvedShikiTheme(darkTheme), [darkTheme]);
@@ -393,43 +404,6 @@ export const PierreDiffViewer: React.FC<PierreDiffViewerProps> = ({
     }
   }, [darkResolvedTheme, diffThemeKey, isDark, lightResolvedTheme]);
 
-  // Cache the last computed diff to avoid recomputing on every render
-  const diffCacheRef = useRef<{
-    key: string;
-    fileDiff: FileDiffMetadata;
-  } | null>(null);
-
-  // Pre-parse the diff with cacheKey for worker pool caching
-  const fileDiff = useMemo(() => {
-    const cacheKey = getCacheKey(fileName, original, modified, diffThemeKey);
-
-    // Return cached diff if inputs haven't changed
-    if (diffCacheRef.current?.key === cacheKey) {
-      return diffCacheRef.current.fileDiff;
-    }
-
-    const oldFile: FileContents = {
-      name: fileName,
-      contents: original,
-      lang: language as FileContents['lang'],
-      cacheKey: `old-${cacheKey}`,
-    };
-
-    const newFile: FileContents = {
-      name: fileName,
-      contents: modified,
-      lang: language as FileContents['lang'],
-      cacheKey: `new-${cacheKey}`,
-    };
-
-    const diff = parseDiffFromFile(oldFile, newFile);
-
-    // Cache the result
-    diffCacheRef.current = { key: cacheKey, fileDiff: diff };
-
-    return diff;
-  }, [diffThemeKey, fileName, original, modified, language]);
-
   const options = useMemo(() => ({
     theme: {
       dark: darkTheme.metadata.id,
@@ -439,7 +413,8 @@ export const PierreDiffViewer: React.FC<PierreDiffViewerProps> = ({
     diffStyle: renderSideBySide ? ('split' as const) : ('unified' as const),
     diffIndicators: 'none' as const,
     hunkSeparators: 'line-info' as const,
-    lineDiffType: 'word-alt' as const,
+    // Perf: disable intra-line diff (word-level) globally.
+    lineDiffType: 'none' as const,
     overflow: wrapLines ? ('wrap' as const) : ('scroll' as const),
     disableFileHeader: true,
     enableLineSelection: true,
@@ -448,6 +423,61 @@ export const PierreDiffViewer: React.FC<PierreDiffViewerProps> = ({
     unsafeCSS: WEBKIT_SCROLL_FIX_CSS,
   }), [darkTheme.metadata.id, isDark, lightTheme.metadata.id, renderSideBySide, wrapLines, handleSelectionChange]);
 
+  // Imperative render (like upstream OpenCode): avoids `parseDiffFromFile` on main thread.
+  useEffect(() => {
+    if (typeof window === 'undefined') return;
+
+    const container = diffContainerRef.current;
+    if (!container) return;
+    if (!workerPool) return;
+
+    // Dispose previous instance
+    diffInstanceRef.current?.cleanUp();
+    diffInstanceRef.current = null;
+    container.innerHTML = '';
+
+    const instance = new PierreFileDiff(options as unknown as FileDiffOptions<unknown>, workerPool);
+    diffInstanceRef.current = instance;
+
+    const oldFile: FileContents = {
+      name: fileName,
+      contents: original,
+      lang: language as FileContents['lang'],
+      cacheKey: `old:${diffThemeKey}:${fileName}:${makeContentCacheKey(original)}`,
+    };
+    const newFile: FileContents = {
+      name: fileName,
+      contents: modified,
+      lang: language as FileContents['lang'],
+      cacheKey: `new:${diffThemeKey}:${fileName}:${makeContentCacheKey(modified)}`,
+    };
+
+    instance.render({
+      oldFile,
+      newFile,
+      lineAnnotations: [],
+      containerWrapper: container,
+    });
+
+    return () => {
+      instance.cleanUp();
+      if (diffInstanceRef.current === instance) {
+        diffInstanceRef.current = null;
+      }
+      container.innerHTML = '';
+    };
+  }, [diffThemeKey, fileName, language, modified, options, original, workerPool]);
+
+  useEffect(() => {
+    const instance = diffInstanceRef.current;
+    if (!instance) return;
+    try {
+      instance.setSelectedLines(selection);
+    } catch {
+      // ignore
+    }
+  }, [selection]);
+
   if (typeof window === 'undefined') {
     return null;
   }
@@ -557,12 +587,7 @@ export const PierreDiffViewer: React.FC<PierreDiffViewerProps> = ({
             fillContainer={true}
           >
             <div ref={diffRootRef} className="size-full">
-              <FileDiff
-                key={diffThemeKey}
-                fileDiff={fileDiff}
-                options={options}
-                selectedLines={selection}
-              />
+              <div ref={diffContainerRef} className="size-full" />
             </div>
           </ScrollableOverlay>
         </div>
@@ -595,12 +620,7 @@ export const PierreDiffViewer: React.FC<PierreDiffViewerProps> = ({
   return (
     <div className={cn("relative", "w-full")}>
       <div ref={diffRootRef} className="pierre-diff-wrapper w-full overflow-x-auto overflow-y-visible">
-        <FileDiff
-          key={diffThemeKey}
-          fileDiff={fileDiff}
-          options={options}
-          selectedLines={selection}
-        />
+        <div ref={diffContainerRef} className="w-full" />
       </div>
 
       {selection && createPortal(

packages/ui/src/contexts/DiffWorkerProvider.tsx

@@ -1,84 +1,34 @@
-import React, { useMemo, useEffect, useRef } from 'react';
+import React, { useMemo, useEffect } from 'react';
 import { WorkerPoolContextProvider, useWorkerPool } from '@pierre/diffs/react';
-import { parseDiffFromFile, type FileContents } from '@pierre/diffs';
 import type { SupportedLanguages } from '@pierre/diffs';
 
 import { useOptionalThemeSystem } from './useThemeSystem';
 import { workerFactory } from '@/lib/diff/workerFactory';
 import { ensurePierreThemeRegistered } from '@/lib/shiki/appThemeRegistry';
 import { getDefaultTheme } from '@/lib/theme/themes';
-import { useGitStore } from '@/stores/useGitStore';
-import { getLanguageFromExtension } from '@/lib/toolHelpers';
+// NOTE: keep provider lightweight; avoid main-thread diff parsing here.
 
 // Preload common languages for faster initial diff rendering
 const PRELOAD_LANGS: SupportedLanguages[] = [
+  // Keep small; workers load others on-demand.
   'typescript',
   'javascript',
   'tsx',
   'jsx',
   'json',
-  'html',
-  'css',
   'markdown',
-  'yaml',
-  'python',
-  'rust',
-  'go',
-  'bash',
 ];
 
-// Limit warmup to prevent memory bloat with many modified files
-const WARMUP_MAX_FILES = 10;
-
-// Matches cache key logic in `packages/ui/src/components/views/PierreDiffViewer.tsx`
-function getPierreCacheKey(fileName: string, original: string, modified: string, themeKey: string): string {
-  const sampleOriginal = original.length > 100
-    ? `${original.slice(0, 50)}${original.slice(-50)}`
-    : original;
-  const sampleModified = modified.length > 100
-    ? `${modified.slice(0, 50)}${modified.slice(-50)}`
-    : modified;
-  return `${themeKey}::${fileName}:${original.length}:${modified.length}:${sampleOriginal.length}:${sampleModified.length}`;
-}
-
 interface DiffWorkerProviderProps {
   children: React.ReactNode;
 }
 
-type IdleDeadlineLike = { timeRemaining(): number; didTimeout: boolean };
-
-function scheduleWarmupWork(cb: (deadline?: IdleDeadlineLike) => void): () => void {
-  if (typeof window === 'undefined') {
-    return () => {};
-  }
-
-  const id = window.setTimeout(() => cb(undefined), 0);
-  return () => window.clearTimeout(id);
-}
-
 // Component that warms up the worker pool and precomputes diff ASTs
 const WorkerPoolWarmup: React.FC<{
   children: React.ReactNode;
-  themeKey: string;
   renderTheme: { light: string; dark: string };
-}> = ({ children, themeKey, renderTheme }) => {
+}> = ({ children, renderTheme }) => {
   const workerPool = useWorkerPool();
-  const activeDirectory = useGitStore((state) => state.activeDirectory);
-  const lastStatusChange = useGitStore((state) => {
-    if (!activeDirectory) return 0;
-    return state.directories.get(activeDirectory)?.lastStatusChange ?? 0;
-  });
-  const diffCacheSize = useGitStore((state) => {
-    if (!activeDirectory) return 0;
-    return state.directories.get(activeDirectory)?.diffCache.size ?? 0;
-  });
-
-  const didDummyWarmupRef = useRef(false);
-  const warmedStatusRef = useRef(new Map<string, number>());
-
-  useEffect(() => {
-    warmedStatusRef.current.clear();
-  }, [themeKey]);
 
   useEffect(() => {
     if (!workerPool) {
@@ -87,110 +37,10 @@ const WorkerPoolWarmup: React.FC<{
 
     // Important: WorkerPoolContextProvider uses a singleton and does not react to
     // prop changes. Update the worker pool render options explicitly.
-    void workerPool.setRenderOptions({ theme: renderTheme });
+    // Force-disable intra-line diff globally (word-level/char-level).
+    void workerPool.setRenderOptions({ theme: renderTheme, lineDiffType: 'none' });
   }, [renderTheme, workerPool]);
 
-  useEffect(() => {
-    if (!workerPool || didDummyWarmupRef.current) return;
-
-    didDummyWarmupRef.current = true;
-
-    const dummyFile: FileContents = {
-      name: 'warmup.ts',
-      contents: 'const x = 1;',
-      lang: 'typescript',
-      cacheKey: 'warmup-file',
-    };
-
-    const dummyDiff = parseDiffFromFile(dummyFile, { ...dummyFile, contents: 'const x = 2;', cacheKey: 'warmup-file-2' });
-
-    const dummyInstance = {
-      onHighlightSuccess: () => {},
-      onHighlightError: () => {},
-    };
-
-    workerPool.highlightDiffAST(dummyInstance, dummyDiff);
-  }, [workerPool]);
-
-  useEffect(() => {
-    if (!workerPool || !activeDirectory) return;
-    if (!lastStatusChange || diffCacheSize === 0) return;
-
-    const dirState = useGitStore.getState().directories.get(activeDirectory);
-    if (!dirState || dirState.diffCache.size === 0) return;
-
-    const alreadyWarmedAt = warmedStatusRef.current.get(activeDirectory) ?? 0;
-    if (alreadyWarmedAt >= dirState.lastStatusChange) return;
-
-    // Only warm once per status-change tick
-    warmedStatusRef.current.set(activeDirectory, dirState.lastStatusChange);
-
-    let cancelled = false;
-    let cancelScheduled: (() => void) | null = null;
-
-    // Limit entries to prevent memory bloat with many modified files
-    const allEntries = Array.from(dirState.diffCache.entries());
-    const entries = allEntries.slice(0, WARMUP_MAX_FILES);
-
-    let index = 0;
-
-    const processChunk = (deadline?: IdleDeadlineLike) => {
-      if (cancelled) return;
-
-      const chunkStart = Date.now();
-      while (index < entries.length) {
-        if (deadline && deadline.timeRemaining() < 8) break;
-        if (!deadline && Date.now() - chunkStart > 8) break;
-
-        const [filePath, diff] = entries[index];
-        index += 1;
-
-        const language = getLanguageFromExtension(filePath) || 'text';
-        const cacheKey = getPierreCacheKey(filePath, diff.original, diff.modified, themeKey);
-
-        const oldFile: FileContents = {
-          name: filePath,
-          contents: diff.original,
-          lang: language as FileContents['lang'],
-          cacheKey: `old-${cacheKey}`,
-        };
-
-        const newFile: FileContents = {
-          name: filePath,
-          contents: diff.modified,
-          lang: language as FileContents['lang'],
-          cacheKey: `new-${cacheKey}`,
-        };
-
-        const fileDiff = parseDiffFromFile(oldFile, newFile);
-
-        // Use a unique instance per request so Pierre doesn't ignore earlier results.
-        const instance = {
-          onHighlightSuccess: () => {},
-          onHighlightError: () => {},
-        };
-
-        workerPool.highlightDiffAST(instance, fileDiff);
-      }
-
-      if (index < entries.length) {
-        cancelScheduled = scheduleWarmupWork(processChunk);
-      }
-    };
-
-    // Kick off immediately, then continue in chunks.
-    processChunk(undefined);
-
-    if (index < entries.length) {
-      cancelScheduled = scheduleWarmupWork(processChunk);
-    }
-
-    return () => {
-      cancelled = true;
-      cancelScheduled?.();
-    };
-  }, [workerPool, activeDirectory, lastStatusChange, diffCacheSize, themeKey]);
-
   return <>{children}</>;
 };
 
@@ -223,8 +73,6 @@ export const DiffWorkerProvider: React.FC<DiffWorkerProviderProps> = ({ children
     langs: PRELOAD_LANGS,
   }), [darkTheme.metadata.id, isDark, lightTheme.metadata.id]);
 
-  const workerThemeKey = `${lightTheme.metadata.id}:${darkTheme.metadata.id}:${isDark ? 'dark' : 'light'}`;
-
   const renderTheme = useMemo(
     () => ({
       light: lightTheme.metadata.id,
@@ -243,7 +91,6 @@ export const DiffWorkerProvider: React.FC<DiffWorkerProviderProps> = ({ children
       highlighterOptions={highlighterOptions}
     >
       <WorkerPoolWarmup
-        themeKey={workerThemeKey}
         renderTheme={renderTheme}
       >
         {children}