From a45376d58569a1ba293156325e87849a098f8b77 Mon Sep 17 00:00:00 2001
From: Bohdan Triapitsyn <artmore@protonmail.com>
Date: Mon, 15 Jun 2026 03:29:40 +0300
Subject: [PATCH] perf: migrate chat rendering to virtua (#1651)

* refactor: migrate chat history virtualization to virtua

* refactor: render loaded chat history directly

* refactor: finish virtua migration

* perf: defer tool body rendering

* perf: queue deferred tool body mounts

* perf: quiet and defer markdown file probes

* perf: defer markdown code highlighting

* perf: stabilize markdown plugin lists

* perf: defer mermaid markdown rendering

* perf: delay markdown file reference annotation

* perf: attach markdown table listeners on demand

* perf: trim markdown render overhead
---
 bun.lock                                      |   8 +-
 packages/ui/package.json                      |   2 +-
 packages/ui/src/apps/MobileFilesSurface.tsx   |   2 +-
 .../components/chat/MarkdownRendererImpl.tsx  | 343 +++++++++++++-----
 .../ui/src/components/chat/MessageList.tsx    | 261 +++++--------
 .../chat/hooks/useChatTimelineController.ts   | 127 +------
 .../components/chat/lib/turns/constants.ts    |   6 -
 .../components/chat/lib/turns/windowTurns.ts  |  44 ---
 .../components/chat/message/MessageBody.tsx   |   1 +
 .../chat/message/ToolOutputDialog.tsx         |   1 +
 .../chat/message/parts/ToolPart.tsx           |  93 +++--
 .../chat/message/parts/UserTextPart.tsx       |   3 +-
 .../message/parts/VirtualizedCodeBlock.tsx    |  59 +--
 .../components/sections/skills/SkillsPage.tsx |   1 +
 .../session/sidebar/SessionGroupSection.tsx   |  86 +----
 .../ui/src/components/ui/JsonTreeViewer.tsx   |  54 +--
 .../ui/src/components/ui/UpdateDialog.tsx     |   4 +-
 .../ui/src/components/views/FilesView.tsx     |  22 +-
 packages/ui/src/components/views/PlanView.tsx |   2 +-
 .../src/components/views/git/ChangesPanel.tsx |  87 ++---
 .../views/git/PullRequestSection.tsx          |   2 +
 .../src/bridge-localfs-proxy-runtime.test.js  |  59 +++
 .../src/bridge-localfs-proxy-runtime.ts       |  21 ++
 packages/web/server/lib/fs/routes.js          |   4 +
 24 files changed, 621 insertions(+), 671 deletions(-)
 create mode 100644 packages/vscode/src/bridge-localfs-proxy-runtime.test.js

diff --git a/bun.lock b/bun.lock
index 5cba7b78..b564331a 100644
--- a/bun.lock
+++ b/bun.lock
@@ -149,7 +149,6 @@
         "@pierre/diffs": "1.3.0-beta.4",
         "@replit/codemirror-vim": "^6.3.0",
         "@simplewebauthn/browser": "13.3.0",
-        "@tanstack/react-virtual": "^3.13.18",
         "@types/react-syntax-highlighter": "^15.5.13",
         "@xenova/transformers": "^2.17.2",
         "@zumer/snapdom": "^2.12.0",
@@ -183,6 +182,7 @@
         "sonner": "^2.0.7",
         "strip-json-comments": "^5.0.3",
         "tailwind-merge": "^3.3.1",
+        "virtua": "0.49.1",
         "yaml": "^2.8.1",
         "zod": "^4.3.6",
         "zustand": "^5.0.8",
@@ -1247,10 +1247,6 @@
 
     "@tailwindcss/postcss": ["@tailwindcss/postcss@4.2.1", "", { "dependencies": { "@alloc/quick-lru": "^5.2.0", "@tailwindcss/node": "4.2.1", "@tailwindcss/oxide": "4.2.1", "postcss": "^8.5.6", "tailwindcss": "4.2.1" } }, "sha512-OEwGIBnXnj7zJeonOh6ZG9woofIjGrd2BORfvE5p9USYKDCZoQmfqLcfNiRWoJlRWLdNPn2IgVZuWAOM4iTYMw=="],
 
-    "@tanstack/react-virtual": ["@tanstack/react-virtual@3.13.19", "", { "dependencies": { "@tanstack/virtual-core": "3.13.19" }, "peerDependencies": { "react": "^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0", "react-dom": "^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0" } }, "sha512-KzwmU1IbE0IvCZSm6OXkS+kRdrgW2c2P3Ho3NC+zZXWK6oObv/L+lcV/2VuJ+snVESRlMJ+w/fg4WXI/JzoNGQ=="],
-
-    "@tanstack/virtual-core": ["@tanstack/virtual-core@3.13.19", "", {}, "sha512-/BMP7kNhzKOd7wnDeB8NrIRNLwkf5AhCYCvtfZV2GXWbBieFm/el0n6LOAXlTi6ZwHICSNnQcIxRCWHrLzDY+g=="],
-
     "@textlint/ast-node-types": ["@textlint/ast-node-types@15.5.2", "", {}, "sha512-fCaOxoup5LIyBEo7R1oYWE7V4bSX0KQeHh66twon9e9usaLE3ijgF8QjYsR6joCssdeCHVd0wHm7ppsEyTr6vg=="],
 
     "@textlint/linter-formatter": ["@textlint/linter-formatter@15.5.2", "", { "dependencies": { "@azu/format-text": "^1.0.2", "@azu/style-format": "^1.0.1", "@textlint/module-interop": "15.5.2", "@textlint/resolver": "15.5.2", "@textlint/types": "15.5.2", "chalk": "^4.1.2", "debug": "^4.4.3", "js-yaml": "^4.1.1", "lodash": "^4.17.23", "pluralize": "^2.0.0", "string-width": "^4.2.3", "strip-ansi": "^6.0.1", "table": "^6.9.0", "text-table": "^0.2.0" } }, "sha512-jAw7jWM8+wU9cG6Uu31jGyD1B+PAVePCvnPKC/oov+2iBPKk3ao30zc/Itmi7FvXo4oPaL9PmzPPQhyniPVgVg=="],
@@ -3223,6 +3219,8 @@
 
     "vfile-message": ["vfile-message@4.0.3", "", { "dependencies": { "@types/unist": "^3.0.0", "unist-util-stringify-position": "^4.0.0" } }, "sha512-QTHzsGd1EhbZs4AsQ20JX1rC3cOlt/IWJruk893DfLRr57lcnOeMaWG4K0JrRta4mIJZKth2Au3mM3u03/JWKw=="],
 
+    "virtua": ["virtua@0.49.1", "", { "peerDependencies": { "react": ">=16.14.0", "react-dom": ">=16.14.0", "solid-js": ">=1.0", "svelte": ">=5.0", "vue": ">=3.2" }, "optionalPeers": ["react", "react-dom", "solid-js", "svelte", "vue"] }, "sha512-6f79msqg3jzNFdqJiS0FSzhRN1EHlDhR7EvW7emp6z5qQ22VdsReiDHflkpMEMhoAyUuYr69nwT0aagiM7NrUg=="],
+
     "vite": ["vite@7.3.1", "", { "dependencies": { "esbuild": "^0.27.0", "fdir": "^6.5.0", "picomatch": "^4.0.3", "postcss": "^8.5.6", "rollup": "^4.43.0", "tinyglobby": "^0.2.15" }, "optionalDependencies": { "fsevents": "~2.3.3" }, "peerDependencies": { "@types/node": "^20.19.0 || >=22.12.0", "jiti": ">=1.21.0", "less": "^4.0.0", "lightningcss": "^1.21.0", "sass": "^1.70.0", "sass-embedded": "^1.70.0", "stylus": ">=0.54.8", "sugarss": "^5.0.0", "terser": "^5.16.0", "tsx": "^4.8.1", "yaml": "^2.4.2" }, "optionalPeers": ["@types/node", "jiti", "less", "lightningcss", "sass", "sass-embedded", "stylus", "sugarss", "terser", "tsx", "yaml"], "bin": { "vite": "bin/vite.js" } }, "sha512-w+N7Hifpc3gRjZ63vYBXA56dvvRlNWRczTdmCBBa+CotUzAPf5b7YMdMR/8CQoeYE5LX3W4wj6RYTgonm1b9DA=="],
 
     "vite-plugin-pwa": ["vite-plugin-pwa@1.2.0", "", { "dependencies": { "debug": "^4.3.6", "pretty-bytes": "^6.1.1", "tinyglobby": "^0.2.10", "workbox-build": "^7.4.0", "workbox-window": "^7.4.0" }, "peerDependencies": { "@vite-pwa/assets-generator": "^1.0.0", "vite": "^3.1.0 || ^4.0.0 || ^5.0.0 || ^6.0.0 || ^7.0.0" }, "optionalPeers": ["@vite-pwa/assets-generator"] }, "sha512-a2xld+SJshT9Lgcv8Ji4+srFJL4k/1bVbd1x06JIkvecpQkwkvCncD1+gSzcdm3s+owWLpMJerG3aN5jupJEVw=="],
diff --git a/packages/ui/package.json b/packages/ui/package.json
index bec5fa1d..46d5b776 100644
--- a/packages/ui/package.json
+++ b/packages/ui/package.json
@@ -44,7 +44,6 @@
     "@pierre/diffs": "1.3.0-beta.4",
     "@replit/codemirror-vim": "^6.3.0",
     "@simplewebauthn/browser": "13.3.0",
-    "@tanstack/react-virtual": "^3.13.18",
     "@types/react-syntax-highlighter": "^15.5.13",
     "@xenova/transformers": "^2.17.2",
     "@zumer/snapdom": "^2.12.0",
@@ -78,6 +77,7 @@
     "sonner": "^2.0.7",
     "strip-json-comments": "^5.0.3",
     "tailwind-merge": "^3.3.1",
+    "virtua": "0.49.1",
     "yaml": "^2.8.1",
     "zod": "^4.3.6",
     "zustand": "^5.0.8"
diff --git a/packages/ui/src/apps/MobileFilesSurface.tsx b/packages/ui/src/apps/MobileFilesSurface.tsx
index f42d6378..e4080749 100644
--- a/packages/ui/src/apps/MobileFilesSurface.tsx
+++ b/packages/ui/src/apps/MobileFilesSurface.tsx
@@ -493,7 +493,7 @@ const MobileTextFile: React.FC<{ path: string; content: string }> = ({ path, con
   if (isMarkdownFile(path)) {
     return (
       <ScrollShadow className="h-full overflow-y-auto px-4 py-4">
-        <SimpleMarkdownRenderer content={content} />
+        <SimpleMarkdownRenderer content={content} enableFileReferences={false} />
       </ScrollShadow>
     );
   }
diff --git a/packages/ui/src/components/chat/MarkdownRendererImpl.tsx b/packages/ui/src/components/chat/MarkdownRendererImpl.tsx
index 57167371..2209caa9 100644
--- a/packages/ui/src/components/chat/MarkdownRendererImpl.tsx
+++ b/packages/ui/src/components/chat/MarkdownRendererImpl.tsx
@@ -2,7 +2,7 @@ import React from 'react';
 import 'katex/dist/katex.min.css';
 import { renderMermaidASCII, renderMermaidSVG } from 'beautiful-mermaid';
 import ReactMarkdown from 'react-markdown';
-import type { Components } from 'react-markdown';
+import type { Components, Options as ReactMarkdownOptions } from 'react-markdown';
 import remarkGfm from 'remark-gfm';
 import remarkMath from 'remark-math';
 import rehypeKatex from 'rehype-katex';
@@ -216,6 +216,10 @@ const TableCopyButton: React.FC<{ tableRef: React.RefObject<HTMLDivElement | nul
   const menuRef = React.useRef<HTMLDivElement>(null);
 
   React.useEffect(() => {
+    if (!showMenu) {
+      return;
+    }
+
     const handleClickOutside = (e: MouseEvent) => {
       if (menuRef.current && !menuRef.current.contains(e.target as Node)) {
         setShowMenu(false);
@@ -223,7 +227,7 @@ const TableCopyButton: React.FC<{ tableRef: React.RefObject<HTMLDivElement | nul
     };
     document.addEventListener('mousedown', handleClickOutside);
     return () => document.removeEventListener('mousedown', handleClickOutside);
-  }, []);
+  }, [showMenu]);
 
   const handleCopy = async (format: 'csv' | 'tsv' | 'markdown') => {
     const tableEl = tableRef.current?.querySelector('table');
@@ -308,6 +312,10 @@ const TableDownloadButton: React.FC<{ tableRef: React.RefObject<HTMLDivElement |
   const menuRef = React.useRef<HTMLDivElement>(null);
 
   React.useEffect(() => {
+    if (!showMenu) {
+      return;
+    }
+
     const handleClickOutside = (e: MouseEvent) => {
       if (menuRef.current && !menuRef.current.contains(e.target as Node)) {
         setShowMenu(false);
@@ -315,7 +323,7 @@ const TableDownloadButton: React.FC<{ tableRef: React.RefObject<HTMLDivElement |
     };
     document.addEventListener('mousedown', handleClickOutside);
     return () => document.removeEventListener('mousedown', handleClickOutside);
-  }, []);
+  }, [showMenu]);
 
    const handleDownload = (format: 'csv' | 'markdown') => {
       const tableEl = tableRef.current?.querySelector('table');
@@ -364,16 +372,35 @@ const TableWrapper: React.FC<{ children?: React.ReactNode; className?: string }>
   const tableRef = React.useRef<HTMLDivElement>(null);
   const { isMobile, isTablet } = useDeviceInfo();
   const alwaysShowActions = isMobile || isTablet;
+  const [showActions, setShowActions] = React.useState(alwaysShowActions);
+
+  React.useEffect(() => {
+    if (alwaysShowActions) {
+      setShowActions(true);
+    }
+  }, [alwaysShowActions]);
 
   return (
-    <div className="group my-4 flex flex-col space-y-2" data-markdown="table-wrapper" ref={tableRef}>
-      <div className={cn(
-        "flex items-center justify-end gap-1 transition-opacity",
-        alwaysShowActions ? "opacity-100" : "opacity-0 group-hover:opacity-100"
-      )}>
-        <TableCopyButton tableRef={tableRef} />
-        <TableDownloadButton tableRef={tableRef} />
-      </div>
+    <div
+      className="group my-4 flex flex-col space-y-2"
+      data-markdown="table-wrapper"
+      ref={tableRef}
+      onMouseEnter={() => setShowActions(true)}
+      onMouseLeave={() => {
+        if (!alwaysShowActions) {
+          setShowActions(false);
+        }
+      }}
+      onFocusCapture={() => setShowActions(true)}
+    >
+      {showActions ? (
+        <div className="flex items-center justify-end gap-1 transition-opacity">
+          <TableCopyButton tableRef={tableRef} />
+          <TableDownloadButton tableRef={tableRef} />
+        </div>
+      ) : (
+        <div className="h-6" aria-hidden="true" />
+      )}
       <div className="overflow-x-auto rounded-lg border border-border/80 bg-[var(--surface-elevated)]">
         <table className={cn('w-full border-collapse text-sm', className)} data-markdown="table">
           {children}
@@ -383,40 +410,83 @@ const TableWrapper: React.FC<{ children?: React.ReactNode; className?: string }>
   );
 };
 
+const MERMAID_RENDER_DELAY_MS = 80;
+
 const MermaidBlock: React.FC<{ source: string; mode: 'svg' | 'ascii' }> = ({ source, mode }) => {
   const { t } = useI18n();
   const currentTheme = useCurrentMermaidTheme();
   const { isMobile, isTablet } = useDeviceInfo();
   const [copied, setCopied] = React.useState(false);
   const [downloaded, setDownloaded] = React.useState(false);
+  const [svg, setSvg] = React.useState('');
+  const [ascii, setAscii] = React.useState('');
 
-  const svg = React.useMemo(() => {
-    if (mode !== 'svg') return '';
-    try {
-      return renderMermaidSVG(source, {
-        bg: currentTheme.colors.surface.elevated,
-        fg: currentTheme.colors.surface.foreground,
-        line: currentTheme.colors.interactive.border,
-        accent: currentTheme.colors.primary.base,
-        muted: currentTheme.colors.surface.mutedForeground,
-        surface: currentTheme.colors.surface.muted,
-        border: currentTheme.colors.interactive.border,
-        transparent: true,
-        font: 'IBM Plex Sans, sans-serif',
+  React.useEffect(() => {
+    if (typeof window === 'undefined') {
+      try {
+        setSvg(mode === 'svg' ? renderMermaidSVG(source, {
+          bg: currentTheme.colors.surface.elevated,
+          fg: currentTheme.colors.surface.foreground,
+          line: currentTheme.colors.interactive.border,
+          accent: currentTheme.colors.primary.base,
+          muted: currentTheme.colors.surface.mutedForeground,
+          surface: currentTheme.colors.surface.muted,
+          border: currentTheme.colors.interactive.border,
+          transparent: true,
+          font: 'IBM Plex Sans, sans-serif',
+        }) : '');
+        setAscii(mode === 'ascii' ? renderMermaidASCII(source) : '');
+      } catch {
+        setSvg('');
+        setAscii('');
+      }
+      return;
+    }
+
+    let cancelled = false;
+    let frame: number | null = null;
+    setSvg('');
+    setAscii('');
+
+    const timer = window.setTimeout(() => {
+      frame = window.requestAnimationFrame(() => {
+        frame = null;
+        if (cancelled) {
+          return;
+        }
+
+        try {
+          if (mode === 'svg') {
+            setSvg(renderMermaidSVG(source, {
+              bg: currentTheme.colors.surface.elevated,
+              fg: currentTheme.colors.surface.foreground,
+              line: currentTheme.colors.interactive.border,
+              accent: currentTheme.colors.primary.base,
+              muted: currentTheme.colors.surface.mutedForeground,
+              surface: currentTheme.colors.surface.muted,
+              border: currentTheme.colors.interactive.border,
+              transparent: true,
+              font: 'IBM Plex Sans, sans-serif',
+            }));
+            return;
+          }
+
+          setAscii(renderMermaidASCII(source));
+        } catch {
+          setSvg('');
+          setAscii('');
+        }
       });
-    } catch {
-      return '';
-    }
-  }, [currentTheme, mode, source]);
+    }, MERMAID_RENDER_DELAY_MS);
 
-  const ascii = React.useMemo(() => {
-    if (mode !== 'ascii') return '';
-    try {
-      return renderMermaidASCII(source);
-    } catch {
-      return '';
-    }
-  }, [mode, source]);
+    return () => {
+      cancelled = true;
+      window.clearTimeout(timer);
+      if (frame !== null) {
+        window.cancelAnimationFrame(frame);
+      }
+    };
+  }, [currentTheme, mode, source]);
 
   const copyVisibilityClass = isMobile || isTablet ? 'opacity-100' : 'opacity-0 group-hover:opacity-100';
 
@@ -573,6 +643,10 @@ const stripLeadingFrontmatter = (markdown: string): string => {
 
 export type MarkdownVariant = 'assistant' | 'tool' | 'reasoning';
 
+const MARKDOWN_REMARK_PLUGINS: ReactMarkdownOptions['remarkPlugins'] = [remarkGfm, remarkMath];
+const MARKDOWN_REHYPE_PLUGINS: ReactMarkdownOptions['rehypePlugins'] = [[rehypeKatex, { throwOnError: false, errorColor: 'var(--destructive)' }]];
+const MARKDOWN_BLOCK_CACHE_MAX_ENTRIES = 240;
+
 type MarkdownStreamBlock = {
   key: string;
   raw: string;
@@ -613,14 +687,45 @@ const buildMarkdownCacheKey = (baseKey: string, raw: string, index: number, mode
   return `${baseKey}:${index}:${mode}:${raw.length}:${fnv1a32(sample)}`;
 };
 
+const MARKDOWN_BLOCK_CACHE = new Map<string, MarkdownStreamBlock[]>();
+
+const getMarkdownBlockCacheEntry = (key: string): MarkdownStreamBlock[] | undefined => {
+  const cached = MARKDOWN_BLOCK_CACHE.get(key);
+  if (!cached) {
+    return undefined;
+  }
+  MARKDOWN_BLOCK_CACHE.delete(key);
+  MARKDOWN_BLOCK_CACHE.set(key, cached);
+  return cached;
+};
+
+const setMarkdownBlockCacheEntry = (key: string, blocks: MarkdownStreamBlock[]): void => {
+  while (MARKDOWN_BLOCK_CACHE.size >= MARKDOWN_BLOCK_CACHE_MAX_ENTRIES) {
+    const oldest = MARKDOWN_BLOCK_CACHE.keys().next().value;
+    if (typeof oldest !== 'string') {
+      break;
+    }
+    MARKDOWN_BLOCK_CACHE.delete(oldest);
+  }
+  MARKDOWN_BLOCK_CACHE.set(key, blocks);
+};
+
 const streamMarkdownBlocks = (text: string, live: boolean, baseKey: string): MarkdownStreamBlock[] => {
   if (!live) {
-    return [{
+    const cacheKey = `${baseKey}:final:${text.length}:${fnv1a32(text.length > 800 ? `${text.slice(0, 400)}${text.slice(-400)}` : text)}`;
+    const cached = getMarkdownBlockCacheEntry(cacheKey);
+    if (cached) {
+      return cached;
+    }
+
+    const blocks: MarkdownStreamBlock[] = [{
       key: buildMarkdownCacheKey(baseKey, text, 0, 'full'),
       raw: text,
       src: text,
       mode: 'full',
     }];
+    setMarkdownBlockCacheEntry(cacheKey, blocks);
+    return blocks;
   }
 
   const healed = healMarkdown(text);
@@ -742,6 +847,7 @@ const normalizeCodeBlockText = (code: string, language: string): string => {
 };
 
 const CODE_HIGHLIGHT_SETTLE_MS = 300;
+const CODE_HIGHLIGHT_INITIAL_DELAY_MS = 80;
 const CODE_HIGHLIGHT_LINE_LIMIT = 1200;
 const VSCODE_CODE_HIGHLIGHT_LINE_LIMIT = 200;
 const CODE_SHARED_STYLE: React.CSSProperties = {
@@ -795,23 +901,57 @@ const MarkdownCodeBlock: React.FC<{
   syntaxTheme: { [key: string]: React.CSSProperties };
 }> = ({ code, language, syntaxTheme }) => {
   const [copied, setCopied] = React.useState(false);
-  const [highlight, setHighlight] = React.useState(true);
+  const [highlight, setHighlight] = React.useState(false);
   const [viewMode, setViewMode] = React.useState<'code' | 'preview'>('code');
   const prevCodeRef = React.useRef<string>(code);
   const timerRef = React.useRef<ReturnType<typeof setTimeout> | null>(null);
   const { isMobile, isTablet } = useDeviceInfo();
+  const alwaysShowControls = isMobile || isTablet;
+  const [showControls, setShowControls] = React.useState(alwaysShowControls);
   const skipHighlight = exceedsLineLimit(code, getCodeHighlightLineLimit());
 
   const canPreview = language === 'html' || language === 'htm';
 
+  React.useEffect(() => {
+    if (alwaysShowControls) {
+      setShowControls(true);
+    }
+  }, [alwaysShowControls]);
+
   React.useEffect(() => {
     if (!canPreview && viewMode !== 'code') {
       setViewMode('code');
     }
   }, [canPreview, viewMode]);
 
+  React.useEffect(() => {
+    if (skipHighlight) {
+      setHighlight(false);
+      return;
+    }
+
+    if (typeof window === 'undefined') {
+      setHighlight(true);
+      return;
+    }
+
+    let frame: number | null = null;
+    const timer = window.setTimeout(() => {
+      frame = window.requestAnimationFrame(() => {
+        frame = null;
+        setHighlight(true);
+      });
+    }, CODE_HIGHLIGHT_INITIAL_DELAY_MS);
+
+    return () => {
+      window.clearTimeout(timer);
+      if (frame !== null) {
+        window.cancelAnimationFrame(frame);
+      }
+    };
+  }, [skipHighlight]);
+
   // Defer Prism highlighting while code is actively streaming.
-  // Initial mount renders highlighted immediately (plays nice with finalized blocks).
   React.useEffect(() => {
     if (prevCodeRef.current === code) return;
     prevCodeRef.current = code;
@@ -848,46 +988,57 @@ const MarkdownCodeBlock: React.FC<{
   }, [canPreview, code]);
 
   return (
-    <div data-component="markdown-code" className="my-4 group overflow-hidden rounded-2xl border border-border/80 bg-[var(--surface-elevated)]">
+    <div
+      data-component="markdown-code"
+      className="my-4 group overflow-hidden rounded-2xl border border-border/80 bg-[var(--surface-elevated)]"
+      onMouseEnter={() => setShowControls(true)}
+      onMouseLeave={() => {
+        if (!alwaysShowControls) {
+          setShowControls(false);
+        }
+      }}
+      onFocusCapture={() => setShowControls(true)}
+    >
       <div className="flex items-center justify-between border-b border-border/70 px-3 py-1.5">
         <span className="font-mono text-[13px] text-muted-foreground">{language}</span>
-        <div className={cn(
-          "flex items-center gap-1 transition-opacity",
-          isMobile || isTablet ? "opacity-100" : "opacity-100 md:opacity-0 md:group-hover:opacity-100"
-        )}>
-          {canPreview ? (
+        {showControls ? (
+          <div className="flex min-h-6 items-center gap-1 transition-opacity">
+            {canPreview ? (
+              <button
+                type="button"
+                onClick={() => setViewMode((mode) => (mode === 'preview' ? 'code' : 'preview'))}
+                className="p-1 rounded hover:bg-interactive-hover/60 text-muted-foreground hover:text-foreground transition-colors"
+                title={viewMode === 'preview' ? 'Show code' : 'Preview'}
+                aria-pressed={viewMode === 'preview'}
+                aria-label={viewMode === 'preview' ? 'Show code' : 'Preview HTML'}
+              >
+                {viewMode === 'preview' ? <Icon name="code" className="size-3.5" /> : <Icon name="eye" className="size-3.5" />}
+              </button>
+            ) : null}
+            {canPreview ? (
+              <button
+                type="button"
+                onClick={handleDownload}
+                className="p-1 rounded hover:bg-interactive-hover/60 text-muted-foreground hover:text-foreground transition-colors"
+                title="Download HTML"
+                aria-label="Download HTML"
+              >
+                <Icon name="download" className="size-3.5" />
+              </button>
+            ) : null}
             <button
               type="button"
-              onClick={() => setViewMode((mode) => (mode === 'preview' ? 'code' : 'preview'))}
+              onClick={() => { void handleCopy(); }}
               className="p-1 rounded hover:bg-interactive-hover/60 text-muted-foreground hover:text-foreground transition-colors"
-              title={viewMode === 'preview' ? 'Show code' : 'Preview'}
-              aria-pressed={viewMode === 'preview'}
-              aria-label={viewMode === 'preview' ? 'Show code' : 'Preview HTML'}
+              title={copied ? 'Copied' : 'Copy code'}
+              aria-label={copied ? 'Copied' : 'Copy code'}
             >
-              {viewMode === 'preview' ? <Icon name="code" className="size-3.5" /> : <Icon name="eye" className="size-3.5" />}
+              {copied ? <Icon name="check" className="size-3.5" /> : <Icon name="file-copy" className="size-3.5" />}
             </button>
-          ) : null}
-          {canPreview ? (
-            <button
-              type="button"
-              onClick={handleDownload}
-              className="p-1 rounded hover:bg-interactive-hover/60 text-muted-foreground hover:text-foreground transition-colors"
-              title="Download HTML"
-              aria-label="Download HTML"
-            >
-              <Icon name="download" className="size-3.5" />
-            </button>
-          ) : null}
-          <button
-            type="button"
-            onClick={() => { void handleCopy(); }}
-            className="p-1 rounded hover:bg-interactive-hover/60 text-muted-foreground hover:text-foreground transition-colors"
-            title={copied ? 'Copied' : 'Copy code'}
-            aria-label={copied ? 'Copied' : 'Copy code'}
-          >
-            {copied ? <Icon name="check" className="size-3.5" /> : <Icon name="file-copy" className="size-3.5" />}
-          </button>
-        </div>
+          </div>
+        ) : (
+          <div className="min-h-6 min-w-6" aria-hidden="true" />
+        )}
       </div>
       {canPreview && viewMode === 'preview' ? (
         <div className="h-[320px] md:h-[420px] bg-background">
@@ -1078,7 +1229,7 @@ const MarkdownBlockView: React.FC<{
   components: Components;
 }> = React.memo(({ block, components }) => {
   return (
-    <ReactMarkdown remarkPlugins={[remarkGfm, remarkMath]} rehypePlugins={[[rehypeKatex, { throwOnError: false, errorColor: 'var(--destructive)' }]]} components={components}>
+    <ReactMarkdown remarkPlugins={MARKDOWN_REMARK_PLUGINS} rehypePlugins={MARKDOWN_REHYPE_PLUGINS} components={components}>
       {block.src}
     </ReactMarkdown>
   );
@@ -1119,8 +1270,9 @@ const MAX_BLOCK_CODE_SCAN_LENGTH = 200_000;
 const FILE_REFERENCE_STAT_CONCURRENCY = 4;
 const FILE_REFERENCE_STAT_CACHE_MAX = 1000;
 const VSCODE_FILE_REFERENCE_STAT_CACHE_MAX = 200;
-const FILE_REFERENCE_LINK_LIMIT = 200;
+const FILE_REFERENCE_LINK_LIMIT = 80;
 const VSCODE_FILE_REFERENCE_LINK_LIMIT = 40;
+const FILE_REFERENCE_ANNOTATION_DELAY_MS = 160;
 const FILE_REFERENCE_STAT_CACHE = new Map<string, Promise<boolean>>();
 let activeFileReferenceStatCount = 0;
 const pendingFileReferenceStats: Array<() => void> = [];
@@ -1462,11 +1614,18 @@ const fileReferenceExists = (resolvedPath: string): Promise<boolean> => {
   const request = new Promise<boolean>((resolve) => {
     const run = () => {
       activeFileReferenceStatCount += 1;
-      void runtimeFetch(`/api/fs/stat?path=${encodeURIComponent(normalizedPath)}`, {
+      void runtimeFetch(`/api/fs/stat?path=${encodeURIComponent(normalizedPath)}&optional=true`, {
         method: 'GET',
         cache: 'no-store',
       })
-        .then((response) => resolve(response.ok))
+        .then(async (response) => {
+          if (!response.ok) {
+            resolve(false);
+            return;
+          }
+          const payload = await response.json().catch(() => null) as { exists?: unknown } | null;
+          resolve(payload?.exists !== false);
+        })
         .catch(() => resolve(false))
         .finally(() => {
           activeFileReferenceStatCount = Math.max(0, activeFileReferenceStatCount - 1);
@@ -1547,6 +1706,24 @@ const useFileReferenceInteractions = ({
       return;
     }
 
+    const scheduleAnnotation = (delayMs = 0) => {
+      if (annotationDebounceRef.current !== null && typeof window !== 'undefined') {
+        window.clearTimeout(annotationDebounceRef.current);
+      }
+      if (typeof window === 'undefined') {
+        annotateFileLinks();
+        return;
+      }
+      annotationDebounceRef.current = window.setTimeout(() => {
+        annotationDebounceRef.current = null;
+        window.requestAnimationFrame(() => {
+          if (!cancelled) {
+            annotateFileLinks();
+          }
+        });
+      }, delayMs);
+    };
+
     const annotateFileLinks = () => {
       if (enabled) {
         wrapBlockCodePathTokens(container);
@@ -1674,20 +1851,10 @@ const useFileReferenceInteractions = ({
       void openFileReference(target);
     };
 
-    annotateFileLinks();
+    scheduleAnnotation(FILE_REFERENCE_ANNOTATION_DELAY_MS);
 
     const observer = new MutationObserver(() => {
-      if (annotationDebounceRef.current !== null && typeof window !== 'undefined') {
-        window.clearTimeout(annotationDebounceRef.current);
-      }
-      if (typeof window === 'undefined') {
-        annotateFileLinks();
-        return;
-      }
-      annotationDebounceRef.current = window.setTimeout(() => {
-        annotationDebounceRef.current = null;
-        annotateFileLinks();
-      }, 120);
+      scheduleAnnotation(FILE_REFERENCE_ANNOTATION_DELAY_MS);
     });
     observer.observe(container, {
       childList: true,
diff --git a/packages/ui/src/components/chat/MessageList.tsx b/packages/ui/src/components/chat/MessageList.tsx
index cc3d58fa..2489c2a4 100644
--- a/packages/ui/src/components/chat/MessageList.tsx
+++ b/packages/ui/src/components/chat/MessageList.tsx
@@ -1,6 +1,6 @@
 import React from 'react';
 import type { Part } from '@opencode-ai/sdk/v2';
-import { measureElement as measureVirtualElement, type VirtualItem, useVirtualizer } from '@tanstack/react-virtual';
+import { Virtualizer, type CacheSnapshot, type VirtualizerHandle } from 'virtua';
 
 import ChatMessage from './ChatMessage';
 import { areOptionalRenderRelevantMessagesEqual, areRelevantTurnGroupingContextsEqual, areRenderRelevantMessagesEqual } from './message/renderCompare';
@@ -21,10 +21,10 @@ import { getReviewTransferDirection, type ReviewTransferDirection } from '@/lib/
 import { getOriginalSessionID, getReviewSessionID } from '@/lib/sessionReviewMetadata';
 
 const MESSAGE_LIST_VIRTUALIZE_THRESHOLD = 5;
-const MESSAGE_LIST_OVERSCAN = 6;
 const EMPTY_STATIC_ENTRY_MESSAGES: ChatMessageEntry[] = [];
 const EMPTY_UNGROUPED_MESSAGE_IDS = new Set<string>();
-const EMPTY_VIRTUAL_ROWS: VirtualItem[] = [];
+const MESSAGE_LIST_BUFFER_SIZE = 900;
+const TIMELINE_CACHE_LIMIT = 16;
 
 const estimateHistoryEntryHeight = (entry: RenderEntry | undefined): number => {
     if (!entry) {
@@ -38,6 +38,38 @@ const estimateHistoryEntryHeight = (entry: RenderEntry | undefined): number => {
     return 140;
 };
 
+const sameKeys = (a: readonly string[] | undefined, b: readonly string[] | undefined): boolean => {
+    if (a === b) return true;
+    if (!a || !b) return false;
+    if (a.length !== b.length) return false;
+    return a.every((key, index) => key === b[index]);
+};
+
+const timelineCache = new Map<string, { keys: readonly string[]; cache: CacheSnapshot }>();
+
+const readTimelineCache = (sessionKey: string, keys: readonly string[]): CacheSnapshot | undefined => {
+    const entry = timelineCache.get(sessionKey);
+    if (!entry) return undefined;
+    if (sameKeys(entry.keys, keys)) return entry.cache;
+    timelineCache.delete(sessionKey);
+    return undefined;
+};
+
+const writeTimelineCache = (
+    sessionKey: string,
+    keys: readonly string[],
+    handle: VirtualizerHandle | null | undefined,
+): void => {
+    if (!handle || keys.length === 0) return;
+    timelineCache.delete(sessionKey);
+    timelineCache.set(sessionKey, { keys: keys.slice(), cache: handle.cache });
+    while (timelineCache.size > TIMELINE_CACHE_LIMIT) {
+        const oldest = timelineCache.keys().next().value;
+        if (typeof oldest !== 'string') break;
+        timelineCache.delete(oldest);
+    }
+};
+
 const useStableEvent = <TArgs extends unknown[], TResult>(handler: (...args: TArgs) => TResult) => {
     const handlerRef = React.useRef(handler);
     React.useEffect(() => {
@@ -959,10 +991,12 @@ MessageListEntry.displayName = 'MessageListEntry';
 type StaticHistoryListProps = {
     entries: RenderEntry[];
     shouldVirtualize: boolean;
-    virtualRows: VirtualItem[];
-    totalSize: number;
-    measureElement: (element: HTMLDivElement | null) => void;
     contentRef: React.RefObject<HTMLDivElement | null>;
+    scrollRef?: React.RefObject<HTMLDivElement | null>;
+    virtualizerRef: React.Ref<VirtualizerHandle>;
+    virtualizerKey: string;
+    virtualCache?: CacheSnapshot;
+    shift: boolean;
     onMessageContentChange: (reason?: ContentChangeReason) => void;
     getAnimationHandlers: (messageId: string) => AnimationHandlers;
     scrollToBottom?: () => void;
@@ -977,7 +1011,7 @@ type StaticHistoryListProps = {
     reviewTransferDirection?: ReviewTransferDirection | null;
 };
 
-const StaticHistoryList = React.memo(({ entries, shouldVirtualize, virtualRows, totalSize, measureElement, contentRef, onMessageContentChange, getAnimationHandlers, scrollToBottom, stickyUserHeader, defaultActivityExpanded, turnUiStates, onToggleTurnGroup, chatRenderMode, shouldAnimateUserMessage, onUserAnimationConsumed, activeStreamingPhase, reviewTransferDirection }: StaticHistoryListProps) => {
+const StaticHistoryList = React.memo(({ entries, shouldVirtualize, contentRef, scrollRef, virtualizerRef, virtualizerKey, virtualCache, shift, onMessageContentChange, getAnimationHandlers, scrollToBottom, stickyUserHeader, defaultActivityExpanded, turnUiStates, onToggleTurnGroup, chatRenderMode, shouldAnimateUserMessage, onUserAnimationConsumed, activeStreamingPhase, reviewTransferDirection }: StaticHistoryListProps) => {
     const renderEntry = React.useCallback((entry: RenderEntry) => {
         return (
             <MessageListEntry
@@ -1001,13 +1035,6 @@ const StaticHistoryList = React.memo(({ entries, shouldVirtualize, virtualRows,
         );
     }, [activeStreamingPhase, chatRenderMode, defaultActivityExpanded, getAnimationHandlers, onMessageContentChange, onToggleTurnGroup, onUserAnimationConsumed, reviewTransferDirection, scrollToBottom, shouldAnimateUserMessage, stickyUserHeader, turnUiStates]);
 
-    const paddingTop = shouldVirtualize && virtualRows.length > 0
-        ? virtualRows[0]?.start ?? 0
-        : 0;
-    const paddingBottom = shouldVirtualize && virtualRows.length > 0
-        ? Math.max(0, totalSize - (virtualRows[virtualRows.length - 1]?.end ?? 0))
-        : 0;
-
     if (!shouldVirtualize) {
         return (
             <div ref={contentRef} className="relative w-full">
@@ -1023,43 +1050,23 @@ const StaticHistoryList = React.memo(({ entries, shouldVirtualize, virtualRows,
         );
     }
 
-    if (virtualRows.length === 0 && entries.length > 0) {
-        return (
-            <div ref={contentRef} className="relative w-full">
-                {entries.map((entry) => (
-                    <div
-                        key={entry.key}
-                        data-turn-entry={entry.key}
-                    >
-                        {renderEntry(entry)}
-                    </div>
-                ))}
-            </div>
-        );
-    }
-
     return (
-        <div ref={contentRef} className="relative w-full">
-            {paddingTop > 0 ? <div aria-hidden="true" style={{ height: `${paddingTop}px` }} /> : null}
-            {virtualRows.map((virtualRow) => {
-                const entry = entries[virtualRow.index];
-                if (!entry) {
-                    return null;
-                }
-
-                return (
-                    <div
-                        key={virtualRow.key}
-                        ref={measureElement}
-                        data-index={virtualRow.index}
-                        data-turn-entry={entry.key}
-                    >
-                        {renderEntry(entry)}
-                    </div>
-                );
-            })}
-            {paddingBottom > 0 ? <div aria-hidden="true" style={{ height: `${paddingBottom}px` }} /> : null}
-        </div>
+        <Virtualizer
+            key={virtualizerKey}
+            ref={virtualizerRef}
+            data={entries}
+            cache={virtualCache}
+            itemSize={virtualCache ? undefined : estimateHistoryEntryHeight(undefined)}
+            bufferSize={MESSAGE_LIST_BUFFER_SIZE}
+            shift={shift}
+            scrollRef={scrollRef}
+        >
+            {(entry) => (
+                <div key={entry.key} data-turn-entry={entry.key}>
+                    {renderEntry(entry)}
+                </div>
+            )}
+        </Virtualizer>
     );
 });
 
@@ -1229,7 +1236,7 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
     }), [messages]);
 
     const historyContentRef = React.useRef<HTMLDivElement | null>(null);
-    const pendingVirtualMeasureFrameRef = React.useRef<number | null>(null);
+    const historyVirtualizerRef = React.useRef<VirtualizerHandle | null>(null);
     const resolveScrollContainer = React.useCallback((): HTMLDivElement | null => {
         if (scrollRef?.current) {
             return scrollRef.current;
@@ -1332,120 +1339,44 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
 
     const historyEntries = staticRenderEntries;
     const shouldVirtualizeHistory = historyEntries.length >= MESSAGE_LIST_VIRTUALIZE_THRESHOLD;
-
-    const previousHistoryLenRef = React.useRef(historyEntries.length);
-    const previousFirstEntryKeyRef = React.useRef(historyEntries[0]?.key);
-
-    React.useLayoutEffect(() => {
-        const previousLen = previousHistoryLenRef.current;
-        const currentLen = historyEntries.length;
-        const previousFirstKey = previousFirstEntryKeyRef.current;
-        const currentFirstKey = historyEntries[0]?.key;
-
-        previousHistoryLenRef.current = currentLen;
-        previousFirstEntryKeyRef.current = currentFirstKey;
-
-        const grew = currentLen > previousLen;
-        const firstChanged = previousFirstKey !== currentFirstKey;
-        if (!shouldVirtualizeHistory || isLoadingOlder || disableStaging || !grew || !firstChanged || previousLen === 0) {
+    const historyEntryKeys = React.useMemo(() => historyEntries.map((entry) => entry.key), [historyEntries]);
+    const virtualCache = React.useMemo(
+        () => (shouldVirtualizeHistory ? readTimelineCache(sessionKey, historyEntryKeys) : undefined),
+        [historyEntryKeys, sessionKey, shouldVirtualizeHistory],
+    );
+    const virtualCacheSessionRef = React.useRef(sessionKey);
+    const virtualCacheKeysRef = React.useRef(historyEntryKeys);
+    const setHistoryVirtualizer = React.useCallback((handle: VirtualizerHandle | null) => {
+        if (!handle) {
+            writeTimelineCache(
+                virtualCacheSessionRef.current,
+                virtualCacheKeysRef.current,
+                historyVirtualizerRef.current,
+            );
+            historyVirtualizerRef.current = null;
             return;
         }
 
-        const prependedCount = currentLen - previousLen;
-        const shiftedOldFirst = historyEntries[prependedCount]?.key;
-        if (shiftedOldFirst !== previousFirstKey) {
-            return;
-        }
-
-        // Prepend detected: new entries added at the beginning of the list.
-        // The virtualizer renders based on the current scroll offset which
-        // now maps to different items. Compensate so the user sees the
-        // prepended content (scroll to top) or stays on the same content.
-        let prependedHeight = 0;
-        for (let i = 0; i < prependedCount; i++) {
-            prependedHeight += estimateHistoryEntryHeight(historyEntries[i]);
-        }
-
-        const scrollEl = resolveScrollContainer();
-        if (!scrollEl || prependedHeight <= 0) return;
-
-        scrollEl.scrollTop += prependedHeight;
-    });
-
-    const historyVirtualizer = useVirtualizer({
-        count: historyEntries.length,
-        getScrollElement: resolveScrollContainer,
-        estimateSize: (index) => estimateHistoryEntryHeight(historyEntries[index]),
-        getItemKey: (index) => historyEntries[index]?.key ?? String(index),
-        measureElement: measureVirtualElement,
-        useAnimationFrameWithResizeObserver: true,
-        overscan: MESSAGE_LIST_OVERSCAN,
-        enabled: shouldVirtualizeHistory,
-    });
-
-    React.useLayoutEffect(() => {
-        const historyContent = historyContentRef.current;
-        if (!historyContent || !shouldVirtualizeHistory) {
-            return;
-        }
-
-        if (typeof ResizeObserver === 'undefined') {
-            return;
-        }
-
-        const observer = new ResizeObserver(() => {
-            historyVirtualizer.measure();
-        });
-        observer.observe(historyContent);
-        return () => {
-            observer.disconnect();
-        };
-    }, [historyEntries.length, shouldVirtualizeHistory, historyVirtualizer]);
-
-    React.useEffect(() => {
-        if (!shouldVirtualizeHistory) {
-            return;
-        }
-
-        historyVirtualizer.measure();
-    }, [historyEntries.length, historyVirtualizer, shouldVirtualizeHistory]);
-
-    const scheduleVirtualMeasure = React.useCallback(() => {
-        if (!shouldVirtualizeHistory) {
-            return;
-        }
-        if (typeof window === 'undefined') {
-            historyVirtualizer.measure();
-            return;
-        }
-        if (pendingVirtualMeasureFrameRef.current !== null) {
-            return;
-        }
-        pendingVirtualMeasureFrameRef.current = window.requestAnimationFrame(() => {
-            pendingVirtualMeasureFrameRef.current = null;
-            historyVirtualizer.measure();
-        });
-    }, [historyVirtualizer, shouldVirtualizeHistory]);
-
-    React.useEffect(() => {
-        return () => {
-            if (pendingVirtualMeasureFrameRef.current !== null && typeof window !== 'undefined') {
-                window.cancelAnimationFrame(pendingVirtualMeasureFrameRef.current);
-            }
-        };
+        historyVirtualizerRef.current = handle;
     }, []);
 
-    const historyVirtualRows = React.useMemo(
-        () => (shouldVirtualizeHistory ? historyVirtualizer.getVirtualItems() : EMPTY_VIRTUAL_ROWS),
-        [historyVirtualizer, shouldVirtualizeHistory],
-    );
+    React.useEffect(() => {
+        virtualCacheSessionRef.current = sessionKey;
+        virtualCacheKeysRef.current = historyEntryKeys;
+    }, [historyEntryKeys, sessionKey]);
+
+    React.useEffect(() => {
+        const virtualizerForCleanup = historyVirtualizerRef.current;
+        return () => {
+            writeTimelineCache(virtualCacheSessionRef.current, virtualCacheKeysRef.current, virtualizerForCleanup);
+        };
+    }, []);
 
     const allEntries = React.useMemo(() => {
         return trailingStreamingEntry ? [...historyEntries, trailingStreamingEntry] : historyEntries;
     }, [historyEntries, trailingStreamingEntry]);
 
     const stableHistoryContentChange = useStableEvent((reason?: ContentChangeReason) => {
-        scheduleVirtualMeasure();
         onMessageContentChange(reason);
     });
 
@@ -1540,10 +1471,14 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
             return false;
         }
 
-        const virtualizerBehavior = behavior === 'smooth' ? 'smooth' : 'auto';
-        historyVirtualizer.scrollToIndex(index, { align: 'start', behavior: virtualizerBehavior });
+        const virtualizer = historyVirtualizerRef.current;
+        if (!virtualizer) {
+            return false;
+        }
+
+        virtualizer.scrollToIndex(index, { align: 'start', smooth: behavior === 'smooth' });
         return true;
-    }, [historyEntries.length, historyVirtualizer, shouldVirtualizeHistory]);
+    }, [historyEntries.length, shouldVirtualizeHistory]);
 
     const scrollMessageElementIntoView = React.useCallback((messageId: string, behavior: ScrollBehavior = 'auto') => {
         const container = resolveScrollContainer();
@@ -1682,7 +1617,7 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
 
             scrollToBottom: () => {
                 if (shouldVirtualizeHistory && historyEntries.length > 0) {
-                    historyVirtualizer.scrollToIndex(historyEntries.length - 1, { align: 'end' });
+                    historyVirtualizerRef.current?.scrollToIndex(historyEntries.length - 1, { align: 'end' });
                     return;
                 }
                 const container = resolveScrollContainer();
@@ -1703,7 +1638,7 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
         return () => {
             objectRef.current = null;
         };
-    }, [findMessageElement, historyEntries.length, historyVirtualizer, messageIndexMap, resolveScrollContainer, scrollHistoryIndexIntoView, scrollMessageElementIntoView, shouldVirtualizeHistory, trailingStreamingEntry, turnIndexMap, ref]);
+    }, [findMessageElement, historyEntries.length, messageIndexMap, resolveScrollContainer, scrollHistoryIndexIntoView, scrollMessageElementIntoView, shouldVirtualizeHistory, trailingStreamingEntry, turnIndexMap, ref]);
 
     const disableFadeIn = false;
 
@@ -1714,10 +1649,12 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
                         <StaticHistoryList
                             entries={historyEntries}
                             shouldVirtualize={shouldVirtualizeHistory}
-                            virtualRows={historyVirtualRows}
-                            totalSize={historyVirtualizer.getTotalSize()}
-                            measureElement={historyVirtualizer.measureElement}
                             contentRef={historyContentRef}
+                            scrollRef={scrollRef}
+                            virtualizerRef={setHistoryVirtualizer}
+                            virtualizerKey={sessionKey}
+                            virtualCache={virtualCache}
+                            shift={isLoadingOlder || disableStaging}
                             onMessageContentChange={stableHistoryContentChange}
                             getAnimationHandlers={stableGetAnimationHandlers}
                             scrollToBottom={stableScrollToBottom}
diff --git a/packages/ui/src/components/chat/hooks/useChatTimelineController.ts b/packages/ui/src/components/chat/hooks/useChatTimelineController.ts
index 41befabc..5af98f8f 100644
--- a/packages/ui/src/components/chat/hooks/useChatTimelineController.ts
+++ b/packages/ui/src/components/chat/hooks/useChatTimelineController.ts
@@ -2,13 +2,9 @@ import React from 'react';
 
 import type { ChatMessageEntry } from '../lib/turns/types';
 import type { MessageListHandle } from '../MessageList';
-import { TURN_WINDOW_DEFAULTS } from '../lib/turns/constants';
 import {
     buildTurnWindowModel,
-    clampTurnStart,
-    getInitialTurnStart,
     updateTurnWindowModelIncremental,
-    windowMessagesByTurn,
     type TurnWindowModel,
 } from '../lib/turns/windowTurns';
 import type { TurnHistorySignals } from '../lib/turns/historySignals';
@@ -152,20 +148,17 @@ export const useChatTimelineController = ({
         return nextModel;
     }, [messages, sessionId]);
 
-    const [turnStart, setTurnStart] = React.useState(() => getInitialTurnStart(turnWindowModel.turnCount));
     const [isLoadingOlder, setIsLoadingOlder] = React.useState(false);
     const [pendingRevealWork, setPendingRevealWork] = React.useState(false);
     const [activeTurnId, setActiveTurnId] = React.useState<string | null>(null);
 
     const turnModelRef = React.useRef(turnWindowModel);
-    const turnStartRef = React.useRef(turnStart);
     const isPinnedRef = React.useRef(isPinned);
     const isLoadingOlderRef = React.useRef(isLoadingOlder);
     const pendingRevealWorkRef = React.useRef(pendingRevealWork);
     const sessionIdRef = React.useRef<string | null>(sessionId);
     const messagesRef = React.useRef(messages);
     const historyMetaRef = React.useRef<SessionHistoryMeta | null>(historyMeta);
-    const previousTurnCountRef = React.useRef(turnWindowModel.turnCount);
     const initializedSessionRef = React.useRef<string | null>(null);
     const pendingRenderResolversRef = React.useRef<Array<() => void>>([]);
     const pendingScrollRequestRef = React.useRef<PendingScrollRequest | null>(null);
@@ -174,7 +167,7 @@ export const useChatTimelineController = ({
 
     const historySignals = React.useMemo(() => {
         const defaultLimit = getMemoryLimits().HISTORICAL_MESSAGES;
-        const hasBufferedTurns = turnStart > 0;
+        const hasBufferedTurns = false;
         const hasMoreAboveTurns = historyMeta
             ? !historyMeta.complete
             : messages.length >= defaultLimit;
@@ -183,14 +176,13 @@ export const useChatTimelineController = ({
             hasBufferedTurns,
             hasMoreAboveTurns,
             historyLoading,
-            canLoadEarlier: hasBufferedTurns || hasMoreAboveTurns,
+            canLoadEarlier: hasMoreAboveTurns,
         };
-    }, [historyMeta, messages.length, turnStart]);
+    }, [historyMeta, messages.length]);
 
     const historySignalsRef = React.useRef(historySignals);
 
     turnModelRef.current = turnWindowModel;
-    turnStartRef.current = turnStart;
     isPinnedRef.current = isPinned;
     isLoadingOlderRef.current = isLoadingOlder;
     pendingRevealWorkRef.current = pendingRevealWork;
@@ -232,41 +224,10 @@ export const useChatTimelineController = ({
         }
         historyInteractionRef.current = false;
         initializedSessionRef.current = sessionId;
-        setTurnStart(getInitialTurnStart(turnWindowModel.turnCount));
         setIsLoadingOlder(false);
         setPendingRevealWork(false);
         setActiveTurnId(null);
-        previousTurnCountRef.current = turnWindowModel.turnCount;
-    }, [sessionId, turnWindowModel.turnCount]);
-
-    React.useLayoutEffect(() => {
-        setTurnStart((current) => clampTurnStart(current, turnWindowModel.turnCount));
-    }, [turnWindowModel.turnCount]);
-
-    React.useLayoutEffect(() => {
-        const previousTurnCount = previousTurnCountRef.current;
-        const nextTurnCount = turnWindowModel.turnCount;
-        if (previousTurnCount === nextTurnCount) {
-            return;
-        }
-
-        setTurnStart((current) => {
-            const previousInitial = getInitialTurnStart(previousTurnCount);
-            const nextInitial = getInitialTurnStart(nextTurnCount);
-            if (
-                !historyInteractionRef.current
-                && !isLoadingOlderRef.current
-                && !pendingRevealWorkRef.current
-                && isPinnedRef.current
-                && current === previousInitial
-            ) {
-                return nextInitial;
-            }
-            return clampTurnStart(current, nextTurnCount);
-        });
-
-        previousTurnCountRef.current = nextTurnCount;
-    }, [turnWindowModel.turnCount]);
+    }, [sessionId]);
 
     const resolvePendingRenderWaiters = React.useCallback(() => {
         const resolvers = pendingRenderResolversRef.current;
@@ -277,12 +238,6 @@ export const useChatTimelineController = ({
         resolvers.forEach((resolve) => resolve());
     }, []);
 
-    const waitForNextRenderCommit = React.useCallback((): Promise<void> => {
-        return new Promise<void>((resolve) => {
-            pendingRenderResolversRef.current.push(resolve);
-        });
-    }, []);
-
     const waitForNextRenderCommitOrTimeout = React.useCallback((): Promise<void> => {
         return new Promise<void>((resolve) => {
             if (typeof window === 'undefined') {
@@ -338,7 +293,7 @@ export const useChatTimelineController = ({
             ? turnModelRef.current.turnIndexById.get(pending.id)
             : turnModelRef.current.messageToTurnIndex.get(pending.id);
 
-        if (typeof targetIndex === 'number' && targetIndex >= turnStartRef.current) {
+        if (typeof targetIndex === 'number') {
             resolvePendingScrollRequest(false);
         }
     }, [messageListRef, resolvePendingScrollRequest]);
@@ -354,14 +309,12 @@ export const useChatTimelineController = ({
         };
     }, [resolvePendingRenderWaiters, resolvePendingScrollRequest]);
 
-    const renderedMessages = React.useMemo(() => {
-        return windowMessagesByTurn(messages, turnWindowModel, turnStart);
-    }, [messages, turnStart, turnWindowModel]);
+    const renderedMessages = messages;
 
     React.useLayoutEffect(() => {
         resolvePendingRenderWaiters();
         attemptPendingScrollRequest();
-    }, [attemptPendingScrollRequest, renderedMessages, resolvePendingRenderWaiters, turnStart]);
+    }, [attemptPendingScrollRequest, renderedMessages, resolvePendingRenderWaiters]);
 
     // --- Synchronous scroll compensation for load-more / reveal ---
     // fetchOlderHistory and revealBufferedTurns store a snapshot here
@@ -401,35 +354,7 @@ export const useChatTimelineController = ({
         }
     }, [renderedMessages, scrollRef, restoreViewportAnchor]);
 
-    const revealBufferedTurns = React.useCallback(async (): Promise<boolean> => {
-        if (turnStartRef.current <= 0 || pendingRevealWorkRef.current) {
-            return false;
-        }
-
-        beginHistoryInteraction();
-        const container = scrollRef.current;
-        if (container) {
-            prePrependScrollRef.current = {
-                height: container.scrollHeight,
-                top: container.scrollTop,
-                anchor: captureViewportAnchor(),
-            };
-        }
-
-        setPendingRevealWork(true);
-        setTurnStart((current) => {
-            const next = current - TURN_WINDOW_DEFAULTS.batchTurns;
-            return next > 0 ? next : 0;
-        });
-
-        try {
-            await waitForNextRenderCommit();
-            return true;
-        } finally {
-            setPendingRevealWork(false);
-            settleHistoryInteraction();
-        }
-    }, [beginHistoryInteraction, captureViewportAnchor, scrollRef, settleHistoryInteraction, waitForNextRenderCommit]);
+    const revealBufferedTurns = React.useCallback(async (): Promise<boolean> => false, []);
 
     const fetchOlderHistory = React.useCallback(async (input: {
         preserveViewport: boolean;
@@ -518,15 +443,11 @@ export const useChatTimelineController = ({
         }
 
         try {
-            if (await revealBufferedTurns()) {
-                return;
-            }
-
             void (await fetchOlderHistory({ preserveViewport: true }));
         } finally {
             settleHistoryInteraction();
         }
-    }, [beginHistoryInteraction, fetchOlderHistory, releaseAutoFollow, revealBufferedTurns, settleHistoryInteraction]);
+    }, [beginHistoryInteraction, fetchOlderHistory, releaseAutoFollow, settleHistoryInteraction]);
 
     const handleHistoryScroll = React.useCallback(() => {
         const container = scrollRef.current;
@@ -636,10 +557,6 @@ export const useChatTimelineController = ({
                 return false;
             }
 
-            if (turnIndex < turnStartRef.current) {
-                setTurnStart(turnIndex);
-            }
-
             const result = await new Promise<boolean>((resolve) => {
                 pendingScrollRequestRef.current = {
                     sessionId: sessionIdRef.current ?? sessionId ?? '',
@@ -685,10 +602,6 @@ export const useChatTimelineController = ({
                 return false;
             }
 
-            if (turnIndex < turnStartRef.current) {
-                setTurnStart(turnIndex);
-            }
-
             const result = await new Promise<boolean>((resolve) => {
                 pendingScrollRequestRef.current = {
                     sessionId: sessionIdRef.current ?? sessionId ?? '',
@@ -712,32 +625,16 @@ export const useChatTimelineController = ({
     }, [attemptPendingScrollRequest, releaseAutoFollow, sessionId]);
 
     const resumeToBottom = React.useCallback(async () => {
-        const nextStart = getInitialTurnStart(turnModelRef.current.turnCount);
         setPendingRevealWork(false);
         setIsLoadingOlder(false);
-
-        const shouldWaitForRender = nextStart !== turnStartRef.current;
-        if (shouldWaitForRender) {
-            setTurnStart(nextStart);
-            await waitForNextRenderCommit();
-        }
-
         goToBottom('smooth');
-    }, [goToBottom, waitForNextRenderCommit]);
+    }, [goToBottom]);
 
     const resumeToBottomInstant = React.useCallback(async () => {
-        const nextStart = getInitialTurnStart(turnModelRef.current.turnCount);
         setPendingRevealWork(false);
         setIsLoadingOlder(false);
-
-        const shouldWaitForRender = nextStart !== turnStartRef.current;
-        if (shouldWaitForRender) {
-            setTurnStart(nextStart);
-            await waitForNextRenderCommit();
-        }
-
         goToBottom('instant');
-    }, [goToBottom, waitForNextRenderCommit]);
+    }, [goToBottom]);
 
     const handleActiveTurnChange = React.useCallback((turnId: string | null) => {
         setActiveTurnId(turnId);
@@ -745,7 +642,7 @@ export const useChatTimelineController = ({
 
     return {
         turnIds: turnWindowModel.turnIds,
-        turnStart,
+        turnStart: 0,
         renderedMessages,
         historySignals,
         isLoadingOlder,
diff --git a/packages/ui/src/components/chat/lib/turns/constants.ts b/packages/ui/src/components/chat/lib/turns/constants.ts
index dddc737d..8b8e5bdb 100644
--- a/packages/ui/src/components/chat/lib/turns/constants.ts
+++ b/packages/ui/src/components/chat/lib/turns/constants.ts
@@ -2,10 +2,4 @@ export const ACTIVITY_STANDALONE_TOOL_NAMES = new Set<string>(['task']);
 
 export const HIDDEN_INTERNAL_TOOL_NAMES = new Set<string>(['todowrite', 'todoread']);
 
-export const TURN_WINDOW_DEFAULTS = {
-    initialTurns: 7,
-    batchTurns: 7,
-    prefetchBuffer: 16,
-} as const;
-
 export const TURN_TEXT_THROTTLE_DEFAULT_MS = 100;
diff --git a/packages/ui/src/components/chat/lib/turns/windowTurns.ts b/packages/ui/src/components/chat/lib/turns/windowTurns.ts
index b141b4ec..ee217e6a 100644
--- a/packages/ui/src/components/chat/lib/turns/windowTurns.ts
+++ b/packages/ui/src/components/chat/lib/turns/windowTurns.ts
@@ -1,5 +1,4 @@
 import type { ChatMessageEntry } from './types';
-import { TURN_WINDOW_DEFAULTS } from './constants';
 
 const resolveMessageRole = (message: ChatMessageEntry): string => {
     const role = (message.info as { clientRole?: string | null; role?: string | null }).clientRole ?? message.info.role;
@@ -203,46 +202,3 @@ export const buildTurnWindowModel = (messages: ChatMessageEntry[]): TurnWindowMo
         turnCount: turnIds.length,
     };
 };
-
-export const getInitialTurnStart = (
-    turnCount: number,
-    initialTurns = TURN_WINDOW_DEFAULTS.initialTurns,
-): number => {
-    if (turnCount <= 0) {
-        return 0;
-    }
-    return turnCount > initialTurns ? turnCount - initialTurns : 0;
-};
-
-export const clampTurnStart = (turnStart: number, turnCount: number): number => {
-    if (turnCount <= 0) {
-        return 0;
-    }
-    if (turnStart <= 0) {
-        return 0;
-    }
-    return Math.min(turnStart, turnCount - 1);
-};
-
-export const getTurnWindowSliceStart = (
-    model: Pick<TurnWindowModel, 'turnMessageStartIndexes'>,
-    turnStart: number,
-): number => {
-    if (turnStart <= 0) {
-        return 0;
-    }
-    const from = model.turnMessageStartIndexes[turnStart];
-    return typeof from === 'number' ? from : 0;
-};
-
-export const windowMessagesByTurn = (
-    messages: ChatMessageEntry[],
-    model: Pick<TurnWindowModel, 'turnMessageStartIndexes'>,
-    turnStart: number,
-): ChatMessageEntry[] => {
-    const sliceStart = getTurnWindowSliceStart(model, turnStart);
-    if (sliceStart <= 0) {
-        return messages;
-    }
-    return messages.slice(sliceStart);
-};
diff --git a/packages/ui/src/components/chat/message/MessageBody.tsx b/packages/ui/src/components/chat/message/MessageBody.tsx
index 060e3f14..77e3aed9 100644
--- a/packages/ui/src/components/chat/message/MessageBody.tsx
+++ b/packages/ui/src/components/chat/message/MessageBody.tsx
@@ -2028,6 +2028,7 @@ const AssistantMessageBody = React.memo(({
                                             content={errorMessage ?? ''}
                                             onShowPopup={onShowPopup}
                                             className="[&_.markdown-content>*:first-child]:mt-0 [&_.markdown-content>*:last-child]:mb-0"
+                                            enableFileReferences={false}
                                         />
                                     </div>
                                 </div>
diff --git a/packages/ui/src/components/chat/message/ToolOutputDialog.tsx b/packages/ui/src/components/chat/message/ToolOutputDialog.tsx
index 6c2278f7..ec28cdfa 100644
--- a/packages/ui/src/components/chat/message/ToolOutputDialog.tsx
+++ b/packages/ui/src/components/chat/message/ToolOutputDialog.tsx
@@ -972,6 +972,7 @@ const MermaidPreviewDialog: React.FC<{
                                         allowMermaidWheelZoom
                                         className="markdown-mermaid-fullscreen h-full [&_[data-markdown='mermaid-block']_button]:hidden"
                                         mermaidControls={MERMAID_CONTROLS}
+                                        enableFileReferences={false}
                                     />
                                 </div>
                             )}
diff --git a/packages/ui/src/components/chat/message/parts/ToolPart.tsx b/packages/ui/src/components/chat/message/parts/ToolPart.tsx
index d44eefcc..5917b3f7 100644
--- a/packages/ui/src/components/chat/message/parts/ToolPart.tsx
+++ b/packages/ui/src/components/chat/message/parts/ToolPart.tsx
@@ -1,6 +1,5 @@
 
 import React from 'react';
-import type { AnimationPlaybackControls } from 'motion';
 import { RuntimeAPIContext } from '@/contexts/runtimeAPIContext';
 import { PatchDiff } from '@pierre/diffs/react';
 import { cn } from '@/lib/utils';
@@ -201,29 +200,59 @@ const LiveDuration: React.FC<{ start: number; end?: number; active: boolean }> =
     return <>{formatDuration(start, end, now)}</>;
 };
 
-const EXPANDED_CONTENT_TRANSITION_MS = 0;
+const deferredToolBodyMounts: Array<{ active: boolean; fn: () => void }> = [];
+let deferredToolBodyFrame: number | undefined;
 
-const useAnimatedExpandedContent = (isExpanded: boolean) => {
-    const [shouldRender, setShouldRender] = React.useState(isExpanded);
+const flushDeferredToolBodyMounts = () => {
+    while (deferredToolBodyMounts.length > 0) {
+        const item = deferredToolBodyMounts.pop();
+        if (!item) {
+            break;
+        }
+        if (item.active) {
+            item.fn();
+            deferredToolBodyFrame = deferredToolBodyMounts.length > 0
+                ? window.requestAnimationFrame(flushDeferredToolBodyMounts)
+                : undefined;
+            return;
+        }
+    }
+
+    deferredToolBodyFrame = undefined;
+};
+
+const scheduleDeferredToolBodyMount = (fn: () => void) => {
+    if (typeof window === 'undefined') {
+        fn();
+        return () => undefined;
+    }
+
+    const item = { active: true, fn };
+    deferredToolBodyMounts.push(item);
+
+    if (deferredToolBodyFrame === undefined) {
+        deferredToolBodyFrame = window.requestAnimationFrame(() => {
+            deferredToolBodyFrame = window.requestAnimationFrame(flushDeferredToolBodyMounts);
+        });
+    }
+
+    return () => {
+        item.active = false;
+    };
+};
+
+const useDeferredExpandedContent = (isExpanded: boolean) => {
+    const [shouldRender, setShouldRender] = React.useState(false);
 
     React.useEffect(() => {
-        if (typeof window === 'undefined') {
-            setShouldRender(isExpanded);
-            return;
-        }
-
-        if (isExpanded) {
-            setShouldRender(true);
-            return;
-        }
-
-        const timer = window.setTimeout(() => {
+        if (!isExpanded) {
             setShouldRender(false);
-        }, EXPANDED_CONTENT_TRANSITION_MS);
+            return;
+        }
 
-        return () => {
-            window.clearTimeout(timer);
-        };
+        return scheduleDeferredToolBodyMount(() => {
+            setShouldRender(true);
+        });
     }, [isExpanded]);
 
     return shouldRender;
@@ -1573,6 +1602,7 @@ interface ToolExpandedContentProps {
     state: ToolStateUnion;
     syntaxTheme: { [key: string]: React.CSSProperties };
     currentDirectory: string;
+    isExpanded: boolean;
     onShowPopup?: (content: ToolPopupContent) => void;
 }
 
@@ -1581,6 +1611,7 @@ const ToolExpandedContent: React.FC<ToolExpandedContentProps> = React.memo(({
     state,
     syntaxTheme,
     currentDirectory,
+    isExpanded,
     onShowPopup,
 }) => {
     const { t } = useI18n();
@@ -1873,7 +1904,7 @@ const ToolExpandedContent: React.FC<ToolExpandedContentProps> = React.memo(({
                                     </blockquote>
                                 ),
                                 {
-                                    maxHeightClass: 'max-h-60',
+                                    maxHeightClass: isWriteLikeTool && writeLikeInputPatch && isExpanded ? 'max-h-[50vh]' : 'max-h-60',
                                     className: part.tool === 'bash' ? 'tool-input-surface p-0 rounded-none' : 'tool-input-surface',
                                 }
                             )}
@@ -1979,8 +2010,6 @@ const ToolPartContent: React.FC<ToolPartProps> = ({
     const onContentChangeRef = React.useRef(onContentChange);
     onContentChangeRef.current = onContentChange;
     const expandedContentRef = React.useRef<HTMLDivElement>(null);
-    const expandedContentAnimationRef = React.useRef<AnimationPlaybackControls | null>(null);
-    const expandedContentMountedRef = React.useRef(false);
 
     React.useLayoutEffect(() => {
         if (isTaskTool) {
@@ -1992,9 +2021,6 @@ const ToolPartContent: React.FC<ToolPartProps> = ({
             return;
         }
 
-        expandedContentMountedRef.current = true;
-        expandedContentAnimationRef.current?.stop();
-        expandedContentAnimationRef.current = null;
         element.style.height = isExpanded ? 'auto' : '0px';
         element.style.overflow = isExpanded ? 'visible' : 'hidden';
 
@@ -2003,13 +2029,6 @@ const ToolPartContent: React.FC<ToolPartProps> = ({
         }
     }, [isExpanded, isTaskTool, shouldNotifyStructuralChange]);
 
-    React.useEffect(() => {
-        return () => {
-            expandedContentAnimationRef.current?.stop();
-            expandedContentAnimationRef.current = null;
-        };
-    }, []);
-
     const stateWithData = state as ToolStateWithMetadata;
     const metadata = stateWithData.metadata;
     const partMetadata = (part as unknown as { metadata?: unknown }).metadata;
@@ -2662,7 +2681,8 @@ const ToolPartContent: React.FC<ToolPartProps> = ({
 
     const iconStyle = !isTaskTool && isError ? TOOL_ERROR_ICON_STYLE : TOOL_NORMAL_ICON_STYLE;
     const titleStyle = !isTaskTool && isError ? TOOL_ERROR_TITLE_STYLE : TOOL_NORMAL_TITLE_STYLE;
-    const shouldRenderExpandedContent = useAnimatedExpandedContent(isExpanded);
+    const shouldRenderTaskSummary = useDeferredExpandedContent(isTaskTool && (taskSummaryEntries.length > 0 || isActive || shouldTreatAsFinalized || !!taskSessionId));
+    const shouldRenderExpandedContent = useDeferredExpandedContent(!isTaskTool && isExpanded);
 
     if (!shouldTreatAsFinalized && !isActive && !isTaskTool) {
         return null;
@@ -2795,7 +2815,7 @@ const ToolPartContent: React.FC<ToolPartProps> = ({
             </div>
 
             {}
-            {isTaskTool && (taskSummaryEntries.length > 0 || isActive || shouldTreatAsFinalized || taskSessionId) ? (
+            {shouldRenderTaskSummary ? (
                 <TaskToolSummary
                     entries={taskSummaryEntries}
                     isExpanded={isExpanded}
@@ -2822,10 +2842,6 @@ const ToolPartContent: React.FC<ToolPartProps> = ({
                     {shouldRenderExpandedContent ? (
                         <div
                             className="relative ml-2 pl-3"
-                            style={{
-                                opacity: isExpanded ? 1 : 0,
-                                transform: isExpanded ? 'translateY(0)' : 'translateY(-4px)',
-                            }}
                         >
                             <span
                                 aria-hidden="true"
@@ -2837,6 +2853,7 @@ const ToolPartContent: React.FC<ToolPartProps> = ({
                                 state={state}
                                 syntaxTheme={syntaxTheme}
                                 currentDirectory={currentDirectory}
+                                isExpanded={isExpanded}
                                 onShowPopup={onShowPopup}
                             />
                         </div>
diff --git a/packages/ui/src/components/chat/message/parts/UserTextPart.tsx b/packages/ui/src/components/chat/message/parts/UserTextPart.tsx
index a43de232..41024580 100644
--- a/packages/ui/src/components/chat/message/parts/UserTextPart.tsx
+++ b/packages/ui/src/components/chat/message/parts/UserTextPart.tsx
@@ -272,7 +272,8 @@ const UserTextPart: React.FC<UserTextPartProps> = ({ part, messageId, agentMenti
                                 "[&_[data-component='markdown-code']_code]:inline",
                             ]
                         )}
-                        disableLinkSafety 
+                        disableLinkSafety
+                        enableFileReferences={false}
                     />
                 ) : (
                     plainTextContent
diff --git a/packages/ui/src/components/chat/message/parts/VirtualizedCodeBlock.tsx b/packages/ui/src/components/chat/message/parts/VirtualizedCodeBlock.tsx
index 179c366f..b43b2284 100644
--- a/packages/ui/src/components/chat/message/parts/VirtualizedCodeBlock.tsx
+++ b/packages/ui/src/components/chat/message/parts/VirtualizedCodeBlock.tsx
@@ -3,14 +3,14 @@
  *
  * Replaces per-line <SyntaxHighlighter> with:
  *   1. ONE Prism.highlight() call to tokenize all code at once
- *   2. @tanstack/react-virtual to only render visible rows
+ *   2. virtua to only render visible rows
  *
  * This drops mount cost from O(N * Prism) to O(1 * Prism) + O(visible_rows).
  * For a 2000-line file, ~2000 SyntaxHighlighter instances → ~30 plain <div>s.
  */
 
 import React from 'react';
-import { useVirtualizer } from '@tanstack/react-virtual';
+import { Virtualizer } from 'virtua';
 import Prism from 'prismjs';
 
 // Ensure common languages are loaded (react-syntax-highlighter lazy-loads them,
@@ -244,52 +244,31 @@ const VirtualizedRows: React.FC<VirtualizedRowsProps> = React.memo(({
   lineStyles,
 }) => {
   const parentRef = React.useRef<HTMLDivElement>(null);
-
-  const virtualizer = useVirtualizer({
-    count: lines.length,
-    getScrollElement: () => parentRef.current,
-    estimateSize: () => ROW_HEIGHT,
-    overscan: 20, // render 20 extra rows above/below viewport
-  });
+  const viewportHeight = `min(${lines.length * ROW_HEIGHT}px, ${maxHeight})`;
 
   return (
     <div
       ref={parentRef}
       className="typography-code font-mono w-full min-w-0 oc-virtualized-prism"
-      style={{ maxHeight, overflow: 'auto' }}
+      style={{ height: viewportHeight, maxHeight, overflow: 'auto' }}
     >
       {prismThemeCss ? <style>{prismThemeCss}</style> : null}
-      <div
-        style={{
-          height: `${virtualizer.getTotalSize()}px`,
-          width: '100%',
-          position: 'relative',
-        }}
+      <Virtualizer
+        data={lines}
+        itemSize={ROW_HEIGHT}
+        bufferSize={ROW_HEIGHT * 20}
+        scrollRef={parentRef}
       >
-        {virtualizer.getVirtualItems().map((vItem) => {
-          const line = lines[vItem.index];
-          return (
-            <div
-              key={vItem.index}
-              style={{
-                position: 'absolute',
-                top: 0,
-                left: 0,
-                width: '100%',
-                height: `${vItem.size}px`,
-                transform: `translateY(${vItem.start}px)`,
-              }}
-            >
-              <Row
-                line={line}
-                language={language}
-                showLineNumbers={showLineNumbers}
-                style={lineStyles?.(line)}
-              />
-            </div>
-          );
-        })}
-      </div>
+        {(line, index) => (
+          <Row
+            key={index}
+            line={line}
+            language={language}
+            showLineNumbers={showLineNumbers}
+            style={lineStyles?.(line)}
+          />
+        )}
+      </Virtualizer>
     </div>
   );
 });
diff --git a/packages/ui/src/components/sections/skills/SkillsPage.tsx b/packages/ui/src/components/sections/skills/SkillsPage.tsx
index 1b6d65f6..4b65785d 100644
--- a/packages/ui/src/components/sections/skills/SkillsPage.tsx
+++ b/packages/ui/src/components/sections/skills/SkillsPage.tsx
@@ -608,6 +608,7 @@ const SkillsInstalledPage: React.FC = () => {
                       content={skillMarkdown}
                       className="typography-markdown-body"
                       stripFrontmatter
+                      enableFileReferences={false}
                     />
                   </div>
                 </ScrollableOverlay>
diff --git a/packages/ui/src/components/session/sidebar/SessionGroupSection.tsx b/packages/ui/src/components/session/sidebar/SessionGroupSection.tsx
index f3c94e8c..f66157f9 100644
--- a/packages/ui/src/components/session/sidebar/SessionGroupSection.tsx
+++ b/packages/ui/src/components/session/sidebar/SessionGroupSection.tsx
@@ -1,12 +1,12 @@
 import React from 'react';
-import { useVirtualizer } from '@tanstack/react-virtual';
+import { Virtualizer } from 'virtua';
 import type { Session } from '@opencode-ai/sdk/v2';
 
 // Archived buckets routinely grow into the hundreds/thousands; virtualize
 // when we cross this row count so the DOM stays bounded.
 const ARCHIVED_VIRTUALIZE_THRESHOLD = 50;
 // Compact rows in the archived bucket without nested subagents render
-// around 24-32px; tanstack-virtual will measure precisely via the row ref.
+// around 24-32px; virtua measures mounted rows and uses this as the initial hint.
 const ARCHIVED_ROW_ESTIMATE_PX = 28;
 import { Tooltip, TooltipContent, TooltipTrigger } from '@/components/ui/tooltip';
 import { Icon } from "@/components/icon/Icon";
@@ -274,9 +274,10 @@ export function SessionGroupSection(props: Props): React.ReactNode {
     && visibleSessions.length >= ARCHIVED_VIRTUALIZE_THRESHOLD;
 
   const archivedVirtualContainerRef = React.useRef<HTMLDivElement | null>(null);
+  const archivedScrollRef = React.useRef<HTMLElement | null>(null);
   const [archivedScrollEl, setArchivedScrollEl] = React.useState<HTMLElement | null>(null);
   // Offset of the virtual container from the scroll element's content origin.
-  // tanstack-virtual reads scrollMargin from useVirtualizer options and uses it
+  // virtua reads startMargin from Virtualizer options and uses it
   // to translate scrollTop into container-relative coordinates. Without this,
   // when the scroll element is an ancestor (the sidebar's ScrollableOverlay),
   // the virtualizer assumes the container starts at the top of the scroll
@@ -287,15 +288,6 @@ export function SessionGroupSection(props: Props): React.ReactNode {
   // routes its scroll through `ScrollableOverlay` higher up the tree;
   // threading a ref through every intermediate component would be invasive
   // for this single use case.
-  const archivedVirtualizer = useVirtualizer({
-    count: visibleSessions.length,
-    getScrollElement: () => archivedScrollEl,
-    estimateSize: () => ARCHIVED_ROW_ESTIMATE_PX,
-    overscan: 8,
-    enabled: shouldVirtualizeArchived && archivedScrollEl !== null,
-    scrollMargin: archivedScrollMargin,
-  });
-
   // Resolve the scrolling ancestor and measure the virtual container's offset
   // from its content origin, both on every render. The container ref is null
   // while the archived bucket is collapsed (the body isn't mounted), so a
@@ -309,6 +301,7 @@ export function SessionGroupSection(props: Props): React.ReactNode {
   React.useLayoutEffect(() => {
     if (!shouldVirtualizeArchived) {
       if (archivedScrollEl !== null) setArchivedScrollEl(null);
+      archivedScrollRef.current = null;
       if (archivedScrollMargin !== 0) setArchivedScrollMargin(0);
       return;
     }
@@ -332,6 +325,7 @@ export function SessionGroupSection(props: Props): React.ReactNode {
         el = el.parentElement;
       }
       if (scrollEl !== archivedScrollEl) {
+        archivedScrollRef.current = scrollEl;
         setArchivedScrollEl(scrollEl);
         // setState triggers a re-render; bail out and let the next pass
         // measure the margin against the fresh element.
@@ -345,29 +339,6 @@ export function SessionGroupSection(props: Props): React.ReactNode {
     setArchivedScrollMargin((prev) => (Math.abs(prev - offset) < 1 ? prev : offset));
   });
 
-  // Re-measure when the sidebar's scroll container resizes (e.g. window
-  // resize, sidebar width change). Mirrors the pattern in ChangesSection.
-  React.useEffect(() => {
-    if (!shouldVirtualizeArchived || !archivedScrollEl) return;
-    const observer = new ResizeObserver(() => {
-      archivedVirtualizer.measure();
-    });
-    observer.observe(archivedScrollEl);
-    return () => observer.disconnect();
-  }, [shouldVirtualizeArchived, archivedScrollEl, archivedVirtualizer]);
-
-  const archivedTotalSize = archivedVirtualizer.getTotalSize();
-  // Read virtual rows directly in render rather than via useMemo. The
-  // virtualizer instance is a stable reference across renders, and on a
-  // pure scroll event neither it nor `archivedTotalSize` change — only the
-  // virtualizer's internal scroll offset does. Memoizing here would return
-  // stale rows after every scroll. tanstack-virtual v3 expects callers to
-  // read getVirtualItems() inline; it's cheap and returns [] when the
-  // virtualizer is disabled.
-  const archivedVirtualRows = shouldVirtualizeArchived && archivedScrollEl !== null
-    ? archivedVirtualizer.getVirtualItems()
-    : [];
-
   if (hasSessionSearchQuery && !groupMatchesSearch && rootFolders.length === 0 && ungroupedSessions.length === 0) {
     return null;
   }
@@ -576,41 +547,16 @@ export function SessionGroupSection(props: Props): React.ReactNode {
     >
       {renderFolderItems()}
       {shouldVirtualizeArchived ? (
-        <div
-          ref={archivedVirtualContainerRef}
-          style={{
-            position: 'relative',
-            // Reserve scroll height for all archived rows so the parent
-            // scroll thumb reflects the full list. Individual rows are
-            // absolutely positioned by translateY.
-            height: archivedTotalSize > 0 ? archivedTotalSize : undefined,
-            width: '100%',
-          }}
-        >
-          {archivedVirtualRows.map((virtualRow) => {
-            const node = visibleSessions[virtualRow.index];
-            if (!node) return null;
-            return (
-              <div
-                key={virtualRow.key}
-                data-index={virtualRow.index}
-                ref={archivedVirtualizer.measureElement}
-                style={{
-                  position: 'absolute',
-                  top: 0,
-                  left: 0,
-                  width: '100%',
-                  // virtualRow.start is in scroll-element coordinates (offset by
-                  // scrollMargin). Subtract scrollMargin to position within the
-                  // container, which itself starts at scrollMargin in the scroll
-                  // element.
-                  transform: `translateY(${virtualRow.start - archivedScrollMargin}px)`,
-                }}
-              >
-                {renderSessionNode(node, 0, group.directory, projectId, true)}
-              </div>
-            );
-          })}
+        <div ref={archivedVirtualContainerRef}>
+          <Virtualizer
+            data={visibleSessions}
+            itemSize={ARCHIVED_ROW_ESTIMATE_PX}
+            bufferSize={ARCHIVED_ROW_ESTIMATE_PX * 8}
+            scrollRef={archivedScrollRef}
+            startMargin={archivedScrollMargin}
+          >
+            {(node) => renderSessionNode(node, 0, group.directory, projectId, true) as React.ReactElement}
+          </Virtualizer>
         </div>
       ) : (
         visibleSessions.map((node) => renderSessionNode(node, 0, group.directory, projectId, group.isArchivedBucket === true))
diff --git a/packages/ui/src/components/ui/JsonTreeViewer.tsx b/packages/ui/src/components/ui/JsonTreeViewer.tsx
index 6e094a9d..d5b7b0e1 100644
--- a/packages/ui/src/components/ui/JsonTreeViewer.tsx
+++ b/packages/ui/src/components/ui/JsonTreeViewer.tsx
@@ -1,5 +1,5 @@
 import React from 'react';
-import { useVirtualizer } from '@tanstack/react-virtual';
+import { Virtualizer } from 'virtua';
 
 import {
   parseJsonToTree,
@@ -204,14 +204,6 @@ const JsonTreeViewer = React.forwardRef<{ expandAll: () => void; collapseAll: ()
     const shouldVirtualize = flatNodes.length > VIRTUALIZE_THRESHOLD;
     const parentRef = React.useRef<HTMLDivElement>(null);
 
-    const virtualizer = useVirtualizer({
-      count: flatNodes.length,
-      getScrollElement: () => parentRef.current,
-      estimateSize: () => ROW_HEIGHT,
-      overscan: 20,
-      enabled: shouldVirtualize,
-    });
-
     const handleToggle = React.useCallback((id: string) => {
       setCollapsedPaths((prev) => {
         const next = new Set(prev);
@@ -246,37 +238,21 @@ const JsonTreeViewer = React.forwardRef<{ expandAll: () => void; collapseAll: ()
           className={className}
           style={{ maxHeight, overflow: 'auto' }}
         >
-          <div
-            style={{
-              height: `${virtualizer.getTotalSize()}px`,
-              width: '100%',
-              position: 'relative',
-            }}
+          <Virtualizer
+            data={flatNodes}
+            itemSize={ROW_HEIGHT}
+            bufferSize={ROW_HEIGHT * 20}
+            scrollRef={parentRef}
           >
-            {virtualizer.getVirtualItems().map((virtualRow) => {
-              const flatNode = flatNodes[virtualRow.index];
-              if (!flatNode) return null;
-              return (
-                <div
-                  key={flatNode.node.id}
-                  style={{
-                    position: 'absolute',
-                    top: 0,
-                    left: 0,
-                    width: '100%',
-                    height: `${virtualRow.size}px`,
-                    transform: `translateY(${virtualRow.start}px)`,
-                  }}
-                >
-                  <JsonRow
-                    flatNode={flatNode}
-                    onToggle={handleToggle}
-                    onCopyPath={onCopyPath}
-                  />
-                </div>
-              );
-            })}
-          </div>
+            {(flatNode) => (
+              <JsonRow
+                key={flatNode.node.id}
+                flatNode={flatNode}
+                onToggle={handleToggle}
+                onCopyPath={onCopyPath}
+              />
+            )}
+          </Virtualizer>
         </div>
       );
     }
diff --git a/packages/ui/src/components/ui/UpdateDialog.tsx b/packages/ui/src/components/ui/UpdateDialog.tsx
index 757d0128..b50add83 100644
--- a/packages/ui/src/components/ui/UpdateDialog.tsx
+++ b/packages/ui/src/components/ui/UpdateDialog.tsx
@@ -369,7 +369,7 @@ export const UpdateDialog: React.FC<UpdateDialogProps> = ({
                       }
                     }}
                   >
-                    <SimpleMarkdownRenderer content={changelog.content} disableLinkSafety={true} />
+                    <SimpleMarkdownRenderer content={changelog.content} disableLinkSafety={true} enableFileReferences={false} />
                   </div>
                 ) : (
                   <div className="divide-y divide-[var(--surface-subtle)]">
@@ -395,7 +395,7 @@ export const UpdateDialog: React.FC<UpdateDialogProps> = ({
                             }
                           }}
                         >
-                          <SimpleMarkdownRenderer content={section.content} disableLinkSafety={true} />
+                          <SimpleMarkdownRenderer content={section.content} disableLinkSafety={true} enableFileReferences={false} />
                         </div>
                       </div>
                     ))}
diff --git a/packages/ui/src/components/views/FilesView.tsx b/packages/ui/src/components/views/FilesView.tsx
index 18dff29d..25d4bdcf 100644
--- a/packages/ui/src/components/views/FilesView.tsx
+++ b/packages/ui/src/components/views/FilesView.tsx
@@ -3789,11 +3789,12 @@ export const FilesView: React.FC<FilesViewProps> = ({ mode = 'full' }) => {
                   </div>
                 }
               >
-                <SimpleMarkdownRenderer
-                  content={fileContent}
-                  className="typography-markdown-body"
-                  stripFrontmatter
-                />
+                <SimpleMarkdownRenderer
+                  content={fileContent}
+                  className="typography-markdown-body"
+                  stripFrontmatter
+                  enableFileReferences={false}
+                />
               </ErrorBoundary>
             </div>
           ) : selectedFile && isHtml && htmlViewMode === 'preview' ? (
@@ -4129,11 +4130,12 @@ export const FilesView: React.FC<FilesViewProps> = ({ mode = 'full' }) => {
                   </div>
                 }
               >
-                <SimpleMarkdownRenderer
-                  content={fileContent}
-                  className="typography-markdown-body"
-                  stripFrontmatter
-                />
+                <SimpleMarkdownRenderer
+                  content={fileContent}
+                  className="typography-markdown-body"
+                  stripFrontmatter
+                  enableFileReferences={false}
+                />
               </ErrorBoundary>
             </div>
           ) : canUseShikiFileView && textViewMode === 'view' ? (
diff --git a/packages/ui/src/components/views/PlanView.tsx b/packages/ui/src/components/views/PlanView.tsx
index 189cfd01..7066e6d5 100644
--- a/packages/ui/src/components/views/PlanView.tsx
+++ b/packages/ui/src/components/views/PlanView.tsx
@@ -787,7 +787,7 @@ export const PlanView: React.FC<PlanViewProps> = ({ targetPath = null }) => {
                         </div>
                       }
                     >
-                      <SimpleMarkdownRenderer content={content} className="typography-markdown-body" />
+                      <SimpleMarkdownRenderer content={content} className="typography-markdown-body" enableFileReferences={false} />
                     </ErrorBoundary>
                   </div>
                 ) : (
diff --git a/packages/ui/src/components/views/git/ChangesPanel.tsx b/packages/ui/src/components/views/git/ChangesPanel.tsx
index 409d0a01..51a549d3 100644
--- a/packages/ui/src/components/views/git/ChangesPanel.tsx
+++ b/packages/ui/src/components/views/git/ChangesPanel.tsx
@@ -1,5 +1,5 @@
 import React from 'react';
-import { useVirtualizer } from '@tanstack/react-virtual';
+import { Virtualizer, type VirtualizerHandle } from 'virtua';
 import { Button } from '@/components/ui/button';
 import {
   Dialog,
@@ -195,30 +195,16 @@ export const ChangesPanel: React.FC<ChangesPanelProps> = ({
 
   const rowCount = rows.length;
   const shouldVirtualize = rowCount >= CHANGE_LIST_VIRTUALIZE_THRESHOLD;
-  const rowVirtualizer = useVirtualizer({
-    count: rowCount,
-    getScrollElement: () => scrollRef.current,
-    estimateSize: () => CHANGE_ROW_ESTIMATE_PX,
-    overscan: 12,
-    enabled: shouldVirtualize,
-  });
+  const rowVirtualizerRef = React.useRef<VirtualizerHandle | null>(null);
+  const [visibleStartIndex, setVisibleStartIndex] = React.useState(0);
 
-  // Remeasure when the container transitions from display:none (hidden tab) back
-  // to visible layout, otherwise stale zero-height measurements render no rows.
-  React.useEffect(() => {
-    if (!shouldVirtualize) return;
-    const el = scrollRef.current;
-    if (!el) return;
-    const observer = new ResizeObserver(() => rowVirtualizer.measure());
-    observer.observe(el);
-    return () => observer.disconnect();
-  }, [shouldVirtualize, rowVirtualizer]);
-
-  const totalSize = rowVirtualizer.getTotalSize();
-  const virtualRows = React.useMemo(
-    () => (shouldVirtualize && totalSize >= 0 ? rowVirtualizer.getVirtualItems() : []),
-    [shouldVirtualize, rowVirtualizer, totalSize]
-  );
+  const updateVisibleStartIndex = React.useCallback((offset: number) => {
+    const virtualizer = rowVirtualizerRef.current;
+    const next = virtualizer
+      ? virtualizer.findItemIndex(offset)
+      : Math.floor(offset / CHANGE_ROW_ESTIMATE_PX);
+    setVisibleStartIndex((previous) => (previous === next ? previous : next));
+  }, []);
 
   React.useEffect(() => {
     if (!onVisiblePathsChange) {
@@ -246,11 +232,16 @@ export const ChangesPanel: React.FC<ChangesPanelProps> = ({
     }
 
     onVisiblePathsChange(
-      virtualRows
-        .map((item) => collectFromRow(rows[item.index]))
+      rows
+        .slice(
+          visibleStartIndex,
+          visibleStartIndex + Math.ceil((scrollRef.current?.clientHeight ?? 0) / CHANGE_ROW_ESTIMATE_PX) + VISIBLE_PREFETCH_LIMIT
+        )
+        .map((row) => collectFromRow(row))
         .filter((value): value is string => Boolean(value))
+        .slice(0, VISIBLE_PREFETCH_LIMIT)
     );
-  }, [onVisiblePathsChange, rowCount, rows, shouldVirtualize, virtualRows]);
+  }, [onVisiblePathsChange, rowCount, rows, shouldVirtualize, visibleStartIndex]);
 
   const toggleGroupCollapsed = React.useCallback((groupId: string) => {
     setCollapsedGroups((previous) => {
@@ -490,27 +481,27 @@ export const ChangesPanel: React.FC<ChangesPanelProps> = ({
           className="overlay-scrollbar-target overlay-scrollbar-container min-h-0 w-full flex-1 overflow-x-hidden overflow-y-auto"
         >
           {shouldVirtualize ? (
-            <div className="relative w-full" style={{ height: `${rowVirtualizer.getTotalSize()}px` }}>
-              {virtualRows.map((item) => {
-                const row = rows[item.index];
-                if (!row) return null;
-                return (
-                  <div
-                    key={row.key}
-                    ref={rowVirtualizer.measureElement}
-                    data-index={item.index}
-                    className={cn(
-                      'absolute left-0 top-0 w-full',
-                      showDivider(item.index) &&
-                        'before:pointer-events-none before:absolute before:left-0 before:right-2 before:top-0 before:border-t before:border-border/60'
-                    )}
-                    style={{ transform: `translateY(${item.start}px)` }}
-                  >
-                    {renderRow(row, item.index === 0)}
-                  </div>
-                );
-              })}
-            </div>
+            <Virtualizer
+              ref={rowVirtualizerRef}
+              data={rows}
+              itemSize={CHANGE_ROW_ESTIMATE_PX}
+              bufferSize={CHANGE_ROW_ESTIMATE_PX * 12}
+              scrollRef={scrollRef}
+              onScroll={updateVisibleStartIndex}
+            >
+              {(row, index) => (
+                <div
+                  key={row.key}
+                  className={cn(
+                    'relative',
+                    showDivider(index) &&
+                      'before:pointer-events-none before:absolute before:left-0 before:right-2 before:top-0 before:border-t before:border-border/60'
+                  )}
+                >
+                  {renderRow(row, index === 0)}
+                </div>
+              )}
+            </Virtualizer>
           ) : (
             <div role="list" aria-label={t('gitView.changes.changedFilesAria')}>
               {rows.map((row, index) => (
diff --git a/packages/ui/src/components/views/git/PullRequestSection.tsx b/packages/ui/src/components/views/git/PullRequestSection.tsx
index 4ac6d5e6..560f02fe 100644
--- a/packages/ui/src/components/views/git/PullRequestSection.tsx
+++ b/packages/ui/src/components/views/git/PullRequestSection.tsx
@@ -1527,6 +1527,7 @@ export const PullRequestSection: React.FC<{
                           <SimpleMarkdownRenderer
                             content={pr.body}
                             className="typography-markdown-body text-muted-foreground break-words mt-1"
+                            enableFileReferences={false}
                           />
                         ) : (
                           <div className="typography-micro text-muted-foreground whitespace-pre-wrap break-words mt-1">
@@ -2031,6 +2032,7 @@ export const PullRequestSection: React.FC<{
                                   'typography-markdown-body text-foreground break-words [&_a]:no-underline [&_a:hover]:no-underline',
                                   selfMentionHighlightClass,
                                 ].filter(Boolean).join(' ')}
+                                enableFileReferences={false}
                               />
                             </div>
                           </div>
diff --git a/packages/vscode/src/bridge-localfs-proxy-runtime.test.js b/packages/vscode/src/bridge-localfs-proxy-runtime.test.js
new file mode 100644
index 00000000..54eb8bad
--- /dev/null
+++ b/packages/vscode/src/bridge-localfs-proxy-runtime.test.js
@@ -0,0 +1,59 @@
+import { describe, expect, it, mock } from 'bun:test';
+
+mock.module('fs', () => ({
+  promises: {
+    realpath: mock(async () => {
+      const error = new Error('missing');
+      error.code = 'ENOENT';
+      throw error;
+    }),
+    stat: mock(async () => {
+      const error = new Error('missing');
+      error.code = 'ENOENT';
+      throw error;
+    }),
+  },
+  default: {
+    promises: {
+      realpath: mock(async () => {
+        const error = new Error('missing');
+        error.code = 'ENOENT';
+        throw error;
+      }),
+      stat: mock(async () => {
+        const error = new Error('missing');
+        error.code = 'ENOENT';
+        throw error;
+      }),
+    },
+  },
+}));
+
+mock.module('vscode', () => ({
+  Uri: {
+    file: (fsPath) => ({ fsPath }),
+  },
+  workspace: {
+    workspaceFolders: [{ uri: { fsPath: '/workspace' } }],
+  },
+}));
+
+const { tryHandleLocalFsProxy } = await import('./bridge-localfs-proxy-runtime');
+
+describe('bridge local fs proxy', () => {
+  it('returns a quiet optional stat miss for missing files', async () => {
+    const response = await tryHandleLocalFsProxy('GET', '/api/fs/stat?path=%2Fmissing.ts&optional=true');
+
+    expect(response?.status).toBe(200);
+    expect(JSON.parse(Buffer.from(response?.bodyBase64 ?? '', 'base64').toString('utf8'))).toEqual({
+      path: '/missing.ts',
+      exists: false,
+    });
+  });
+
+  it('keeps regular stat miss behavior without optional flag', async () => {
+    const response = await tryHandleLocalFsProxy('GET', '/api/fs/stat?path=%2Fmissing.ts');
+
+    expect(response?.status).toBe(404);
+  });
+});
diff --git a/packages/vscode/src/bridge-localfs-proxy-runtime.ts b/packages/vscode/src/bridge-localfs-proxy-runtime.ts
index b7946444..a372181c 100644
--- a/packages/vscode/src/bridge-localfs-proxy-runtime.ts
+++ b/packages/vscode/src/bridge-localfs-proxy-runtime.ts
@@ -65,8 +65,19 @@ export const tryHandleLocalFsProxy = async (method: string, requestPath: string)
   }
 
   const targetPath = parsed.searchParams.get('path') || '';
+  const optional = parsed.searchParams.get('optional') === 'true';
   const resolution: FsReadPathResolution = await resolveFileReadPath(targetPath);
   if (!resolution.ok) {
+    if (fsProxyPath === '/api/fs/stat' && optional && resolution.status === 404) {
+      return {
+        status: 200,
+        headers: {
+          'content-type': 'application/json',
+          'cache-control': 'no-store',
+        },
+        bodyBase64: base64EncodeUtf8(JSON.stringify({ path: targetPath, exists: false })),
+      };
+    }
     return buildProxyJsonError(resolution.status, resolution.error);
   }
 
@@ -116,6 +127,16 @@ export const tryHandleLocalFsProxy = async (method: string, requestPath: string)
   } catch (error) {
     const err = error as NodeJS.ErrnoException;
     if (err?.code === 'ENOENT') {
+      if (fsProxyPath === '/api/fs/stat' && optional) {
+        return {
+          status: 200,
+          headers: {
+            'content-type': 'application/json',
+            'cache-control': 'no-store',
+          },
+          bodyBase64: base64EncodeUtf8(JSON.stringify({ path: targetPath, exists: false })),
+        };
+      }
       return buildProxyJsonError(404, 'File not found');
     }
     if (fsProxyPath === '/api/fs/stat') {
diff --git a/packages/web/server/lib/fs/routes.js b/packages/web/server/lib/fs/routes.js
index 20fb5844..b9cbc783 100644
--- a/packages/web/server/lib/fs/routes.js
+++ b/packages/web/server/lib/fs/routes.js
@@ -699,6 +699,7 @@ export const registerFsRoutes = (app, dependencies) => {
 
   app.get('/api/fs/stat', async (req, res) => {
     const filePath = typeof req.query.path === 'string' ? req.query.path.trim() : '';
+    const optional = req.query.optional === 'true';
     if (!filePath) {
       return res.status(400).json({ error: 'Path is required' });
     }
@@ -740,6 +741,9 @@ export const registerFsRoutes = (app, dependencies) => {
     } catch (error) {
       const err = error;
       if (err && typeof err === 'object' && err.code === 'ENOENT') {
+        if (optional) {
+          return res.json({ path: filePath, exists: false });
+        }
         return res.status(404).json({ error: 'File not found' });
       }
       if (err && typeof err === 'object' && err.code === 'EACCES') {