From a61baa96157241c2e422fd85b3527bee14b41c62 Mon Sep 17 00:00:00 2001
From: Brooklyn Nicholson <brooklyn.bb.nicholson@gmail.com>
Date: Mon, 22 Jun 2026 05:04:13 -0500
Subject: [PATCH] feat(desktop): PR-style file diffs in chat

Render write_file/edit_file/patch as a reviewable diff instead of raw
result JSON, closer to a Cursor/T3 per-edit review.

- Unified diff via FileDiffPanel: strip git file-header + @@ hunk noise,
  drop the +/- gutter, color by line with a 2px gutter accent, full-bleed
  to the card, transparent context lines, compact scroll height.
- Header shows filename + language icon + +N/-N stats; full path moves to
  a hover tooltip (no Edited verb, no ms).
- Treat the three file-edit tools uniformly (isFileEditTool); read diff
  from inline_diff or patch's diff field; suppress raw-arg detail.
- Reusable FileTypeIcon primitive sharing the code-block icon mapping
  (codiconForFilename), codicon fallback.
- Per-row scaffolding fade (not the group wrapper, which trapped child
  opacity); expanded edits stay full, collapsed fade; keyboard-only focus
  lift. Hide diff-less rehydrated creates that read as dupes.
---
 .../assistant-ui/tool-fallback-model.test.ts  |  55 +++++++-
 .../assistant-ui/tool-fallback-model.ts       | 122 +++++++++++++++---
 .../components/assistant-ui/tool-fallback.tsx | 104 ++++++++++++---
 .../src/components/chat/diff-lines.tsx        | 122 +++++++++++++++++-
 .../src/components/ui/file-type-icon.tsx      |  22 ++++
 apps/desktop/src/lib/markdown-code.ts         |  50 +++++++
 apps/desktop/src/styles.css                   |  26 +++-
 7 files changed, 451 insertions(+), 50 deletions(-)
 create mode 100644 apps/desktop/src/components/ui/file-type-icon.tsx

diff --git a/apps/desktop/src/components/assistant-ui/tool-fallback-model.test.ts b/apps/desktop/src/components/assistant-ui/tool-fallback-model.test.ts
index 55b7755973e..bf4409384c0 100644
--- a/apps/desktop/src/components/assistant-ui/tool-fallback-model.test.ts
+++ b/apps/desktop/src/components/assistant-ui/tool-fallback-model.test.ts
@@ -1,6 +1,11 @@
 import { describe, expect, it } from 'vitest'
 
-import { buildToolView, type ToolPart } from './tool-fallback-model'
+import {
+  buildToolView,
+  countDiffLineStats,
+  inlineDiffFromResult,
+  type ToolPart
+} from './tool-fallback-model'
 
 const part = (overrides: Partial<ToolPart>): ToolPart => ({
   args: {},
@@ -64,3 +69,51 @@ describe('buildToolView terminal exit-code status', () => {
     )
   })
 })
+
+describe('buildToolView file edit diffs', () => {
+  const patchDiff = '--- a/src/demo.ts\n+++ b/src/demo.ts\n@@ -1 +1 @@\n-old\n+new'
+
+  it('reads inline_diff and diff fields from patch results', () => {
+    expect(inlineDiffFromResult({ inline_diff: patchDiff })).toBe(patchDiff)
+    expect(inlineDiffFromResult({ diff: patchDiff })).toBe(patchDiff)
+  })
+
+  it('suppresses raw patch args when a diff is available', () => {
+    const view = buildToolView(
+      part({
+        args: { context: 'src/demo.ts', mode: 'replace', new_string: 'new', path: 'src/demo.ts' },
+        result: { diff: patchDiff, success: true },
+        toolName: 'patch'
+      }),
+      patchDiff
+    )
+
+    expect(view.title).toBe('demo.ts')
+    expect(view.subtitle).toBe('src/demo.ts')
+    expect(view.detail).toBe('')
+    expect(view.inlineDiff).toBe(patchDiff)
+  })
+
+  it('shows path subtitle instead of patch args JSON while pending', () => {
+    const view = buildToolView(
+      part({
+        args: { context: 'src/demo.ts', mode: 'replace', new_string: 'new', path: 'src/demo.ts' },
+        result: undefined,
+        toolName: 'patch'
+      }),
+      ''
+    )
+
+    expect(view.title).toBe('demo.ts')
+    expect(view.subtitle).toBe('src/demo.ts')
+    expect(view.detail).toBe('')
+  })
+})
+
+describe('countDiffLineStats', () => {
+  it('counts added and removed lines', () => {
+    expect(
+      countDiffLineStats(`--- a/x\n+++ b/x\n@@\n-old\n+new\n context\n+another`)
+    ).toEqual({ added: 2, removed: 1 })
+  })
+})
diff --git a/apps/desktop/src/components/assistant-ui/tool-fallback-model.ts b/apps/desktop/src/components/assistant-ui/tool-fallback-model.ts
index 3618d8011fb..6e67b0b9a4b 100644
--- a/apps/desktop/src/components/assistant-ui/tool-fallback-model.ts
+++ b/apps/desktop/src/components/assistant-ui/tool-fallback-model.ts
@@ -72,6 +72,46 @@ export interface MessageRunningStateSlice {
   }
 }
 
+const FILE_EDIT_TOOL_NAMES = new Set(['edit_file', 'patch', 'write_file'])
+
+export function isFileEditTool(toolName: string): boolean {
+  return FILE_EDIT_TOOL_NAMES.has(toolName)
+}
+
+export interface DiffLineStats {
+  added: number
+  removed: number
+}
+
+export function countDiffLineStats(diff: string): DiffLineStats {
+  let added = 0
+  let removed = 0
+
+  for (const line of diff.split('\n')) {
+    if (line.startsWith('+') && !line.startsWith('+++')) {
+      added += 1
+    } else if (line.startsWith('-') && !line.startsWith('---')) {
+      removed += 1
+    }
+  }
+
+  return { added, removed }
+}
+
+function fileEditPath(args: Record<string, unknown>, result: Record<string, unknown>): string {
+  return (
+    firstStringField(args, ['path', 'file', 'filepath']) ||
+    firstStringField(result, ['path', 'file', 'filepath', 'resolved_path']) ||
+    htmlPathFromInlineDiff(firstStringField(result, ['inline_diff', 'diff']))
+  )
+}
+
+function fileEditBasename(path: string): string {
+  const normalized = path.replace(/\\/g, '/').trim()
+
+  return normalized.split('/').filter(Boolean).pop() || normalized
+}
+
 const TOOL_META: Record<string, ToolMeta> = {
   browser_click: { done: 'Clicked page element', pending: 'Clicking page element', icon: 'globe', tone: 'browser' },
   browser_fill: { done: 'Filled form field', pending: 'Filling form field', icon: 'globe', tone: 'browser' },
@@ -95,7 +135,7 @@ const TOOL_META: Record<string, ToolMeta> = {
   execute_code: { done: 'Ran code', pending: 'Running code', icon: 'terminal', tone: 'terminal' },
   image_generate: { done: 'Generated image', pending: 'Generating image', icon: 'file-media', tone: 'image' },
   list_files: { done: 'Listed files', pending: 'Listing files', icon: 'files', tone: 'file' },
-  patch: { done: 'Patched file', pending: 'Patching file', icon: 'diff', tone: 'file' },
+  patch: { done: 'Patched file', pending: 'Patching file', icon: 'edit', tone: 'file' },
   read_file: { done: 'Read file', pending: 'Reading file', icon: 'file', tone: 'file' },
   search_files: { done: 'Searched files', pending: 'Searching files', icon: 'search', tone: 'file' },
   session_search_recall: {
@@ -797,8 +837,8 @@ function toolPreviewTarget(toolName: string, args: Record<string, unknown>, resu
     return looksLikeUrl(explicit) ? explicit : findFirstUrl(args, result)
   }
 
-  if (toolName === 'write_file' || toolName === 'edit_file') {
-    return htmlPathFromInlineDiff(firstStringField(result, ['inline_diff']))
+  if (isFileEditTool(toolName)) {
+    return htmlPathFromInlineDiff(firstStringField(result, ['inline_diff', 'diff']))
   }
 
   return ''
@@ -858,9 +898,17 @@ function stripDividerLines(value: string): string {
 }
 
 export function inlineDiffFromResult(result: unknown): string {
-  const value = parseMaybeObject(result).inline_diff
+  const record = parseMaybeObject(result)
 
-  return typeof value === 'string' ? stripInlineDiffChrome(value) : ''
+  for (const key of ['inline_diff', 'diff']) {
+    const value = record[key]
+
+    if (typeof value === 'string' && value.trim()) {
+      return stripInlineDiffChrome(value)
+    }
+  }
+
+  return ''
 }
 
 // Falls back to a string only when there's something concrete to render —
@@ -1047,15 +1095,22 @@ function toolSubtitle(
     return command ? compactPreview(command, 120) : 'Executed command'
   }
 
-  if (toolName === 'read_file' || toolName === 'write_file' || toolName === 'edit_file') {
-    const path =
-      firstStringField(argsRecord, ['path', 'file', 'filepath']) ||
-      htmlPathFromInlineDiff(firstStringField(resultRecord, ['inline_diff']))
+  if (toolName === 'read_file' || isFileEditTool(toolName)) {
+    const isEdit = isFileEditTool(toolName)
 
-    return (
-      path ||
-      (firstStringField(resultRecord, ['inline_diff']) ? 'Changed file' : fallbackDetailText(argsRecord, resultRecord))
-    )
+    const path = isEdit
+      ? fileEditPath(argsRecord, resultRecord)
+      : firstStringField(argsRecord, ['path', 'file', 'filepath'])
+
+    if (path) {
+      return path
+    }
+
+    if (!isEdit) {
+      return fallbackDetailText(argsRecord, resultRecord)
+    }
+
+    return inlineDiffFromResult(resultRecord) ? 'Changed file' : ''
   }
 
   if (toolName === 'web_extract') {
@@ -1153,8 +1208,22 @@ function toolDetailText(
     }
   }
 
-  if (part.toolName === 'write_file' || part.toolName === 'edit_file') {
-    return inlineDiffFromResult(part.result) ? '' : fallbackDetailText(argsRecord, resultRecord)
+  if (isFileEditTool(part.toolName)) {
+    if (inlineDiffFromResult(part.result)) {
+      return ''
+    }
+
+    const summary = firstStringField(resultRecord, ['message', 'summary'])
+
+    if (summary) {
+      return summary
+    }
+
+    if (fileEditPath(argsRecord, resultRecord)) {
+      return ''
+    }
+
+    return fallbackDetailText(argsRecord, resultRecord)
   }
 
   if (part.toolName === 'web_search') {
@@ -1253,8 +1322,12 @@ export function toolCopyPayload(part: ToolPart, view: ToolView): { label: string
     }
   }
 
-  if (part.toolName === 'write_file' || part.toolName === 'edit_file') {
-    const path = firstStringField(args, ['path', 'file', 'filepath'])
+  if (isFileEditTool(part.toolName)) {
+    if (view.inlineDiff.trim()) {
+      return { label: copy.file, text: view.inlineDiff }
+    }
+
+    const path = fileEditPath(args, result)
 
     if (path) {
       return { label: copy.path, text: path }
@@ -1304,6 +1377,14 @@ function dynamicTitle(
     }
   }
 
+  if (isFileEditTool(part.toolName)) {
+    const path = fileEditPath(args, result)
+
+    if (path) {
+      return fileEditBasename(path)
+    }
+  }
+
   return fallback
 }
 
@@ -1317,7 +1398,12 @@ export function buildToolView(part: ToolPart, inlineDiff: string): ToolView {
   const title = dynamicTitle(part, argsRecord, resultRecord, baseTitle)
   const titleEnriched = title !== baseTitle
   const baseSubtitle = error || toolSubtitle(part, argsRecord, resultRecord)
-  const keepSubtitleWithTitle = part.toolName === 'terminal' || part.toolName === 'execute_code'
+
+  const keepSubtitleWithTitle =
+    part.toolName === 'terminal' ||
+    part.toolName === 'execute_code' ||
+    (isFileEditTool(part.toolName) && Boolean(baseSubtitle.trim()))
+
   const subtitle = titleEnriched && !error && !keepSubtitleWithTitle ? '' : baseSubtitle
   const detailBody = stripDividerLines(toolDetailText(part, argsRecord, resultRecord))
 
diff --git a/apps/desktop/src/components/assistant-ui/tool-fallback.tsx b/apps/desktop/src/components/assistant-ui/tool-fallback.tsx
index e93eabe1557..900d4767f7b 100644
--- a/apps/desktop/src/components/assistant-ui/tool-fallback.tsx
+++ b/apps/desktop/src/components/assistant-ui/tool-fallback.tsx
@@ -8,7 +8,7 @@ import { AnsiText } from '@/components/assistant-ui/ansi-text'
 import { useElapsedSeconds } from '@/components/chat/activity-timer'
 import { ActivityTimerText } from '@/components/chat/activity-timer-text'
 import { CompactMarkdown } from '@/components/chat/compact-markdown'
-import { DiffLines } from '@/components/chat/diff-lines'
+import { FileDiffPanel } from '@/components/chat/diff-lines'
 import { DisclosureRow } from '@/components/chat/disclosure-row'
 import { PreviewAttachment } from '@/components/chat/preview-attachment'
 import { ZoomableImage } from '@/components/chat/zoomable-image'
@@ -16,6 +16,7 @@ import { Button } from '@/components/ui/button'
 import { Codicon } from '@/components/ui/codicon'
 import { CopyButton } from '@/components/ui/copy-button'
 import { FadeText } from '@/components/ui/fade-text'
+import { FileTypeIcon } from '@/components/ui/file-type-icon'
 import { GlyphSpinner } from '@/components/ui/glyph-spinner'
 import { ToolIcon } from '@/components/ui/tool-icon'
 import { Tip } from '@/components/ui/tooltip'
@@ -32,7 +33,9 @@ import { PendingToolApproval } from './tool-approval'
 import {
   buildToolView,
   cleanVisibleText,
+  countDiffLineStats,
   inlineDiffFromResult,
+  isFileEditTool,
   isPreviewableTarget,
   looksRedundant,
   type SearchResultRow,
@@ -133,9 +136,21 @@ function statusGlyph(status: ToolStatus, copy: ToolStatusCopy): ReactNode {
 // Leading glyph for any tool-row header. Status (running/error/warning)
 // takes precedence; otherwise falls back to the tool's codicon. Returns
 // null when neither applies so callers can render unconditionally.
-function ToolGlyph({ copy, icon, status }: { copy: ToolStatusCopy; icon?: string; status?: ToolStatus }) {
+function ToolGlyph({
+  copy,
+  filePath,
+  icon,
+  status
+}: {
+  copy: ToolStatusCopy
+  filePath?: string
+  icon?: string
+  status?: ToolStatus
+}) {
   const node = status ? (
     statusGlyph(status, copy)
+  ) : filePath ? (
+    <FileTypeIcon className="text-(--ui-text-tertiary)" path={filePath} size="0.875rem" />
   ) : icon ? (
     <ToolIcon className="text-(--ui-text-tertiary)" name={icon} size="0.875rem" />
   ) : null
@@ -204,8 +219,13 @@ function ToolEntry({ part }: ToolEntryProps) {
   const toolViewMode = useStore($toolViewMode)
   const disclosureId = `tool-entry:${messageId}:${toolPartDisclosureId(part)}`
   const dismissed = useStore($toolRowDismissed(disclosureId))
-  const open = useDisclosureOpen(disclosureId)
   const isPending = messageRunning && part.result === undefined
+  const liveDiffs = useStore($toolInlineDiffs)
+  const sideDiff = part.toolCallId ? liveDiffs[part.toolCallId] || '' : ''
+  const inlineDiff = stripInlineDiffChrome(sideDiff) || inlineDiffFromResult(part.result)
+  const isFileEdit = isFileEditTool(part.toolName)
+  const defaultOpen = Boolean(inlineDiff)
+  const open = useDisclosureOpen(disclosureId, defaultOpen)
   const canDismiss = !isPending && !embedded
   // Only animate entries that mount while their message is actively
   // streaming — historical sessions mount with `messageRunning === false`,
@@ -213,9 +233,6 @@ function ToolEntry({ part }: ToolEntryProps) {
   // handles its own enter animation, so embedded children skip it.
   const enterRef = useEnterAnimation(messageRunning && !embedded, `tool-entry:${disclosureId}`)
   const elapsed = useElapsedSeconds(isPending, `tool:${disclosureId}`)
-  const liveDiffs = useStore($toolInlineDiffs)
-  const sideDiff = part.toolCallId ? liveDiffs[part.toolCallId] || '' : ''
-  const inlineDiff = stripInlineDiffChrome(sideDiff) || inlineDiffFromResult(part.result)
 
   // Stale parts (no result, but message stopped running) get a synthetic
   // empty result so buildToolView treats them as completed-no-output.
@@ -253,11 +270,12 @@ function ToolEntry({ part }: ToolEntryProps) {
   const detailMatchesSubtitle = looksRedundant(view.subtitle, view.detail)
 
   const showDetail =
-    (view.status === 'error' && Boolean(detailSections.summary || detailSections.body)) ||
-    (view.status !== 'error' &&
-      Boolean(view.detail) &&
-      !looksRedundant(view.title, view.detail) &&
-      !detailMatchesSubtitle)
+    !view.inlineDiff &&
+    ((view.status === 'error' && Boolean(detailSections.summary || detailSections.body)) ||
+      (view.status !== 'error' &&
+        Boolean(view.detail) &&
+        !looksRedundant(view.title, view.detail) &&
+        !detailMatchesSubtitle))
 
   const renderDetailAsCode =
     view.status !== 'error' &&
@@ -283,6 +301,13 @@ function ToolEntry({ part }: ToolEntryProps) {
 
   const copyAction = useMemo(() => toolCopyPayload(part, view), [part, view])
 
+  const diffStats = useMemo(
+    () => (isFileEdit && view.inlineDiff ? countDiffLineStats(view.inlineDiff) : null),
+    [isFileEdit, view.inlineDiff]
+  )
+
+  const showDiffStats = !isPending && Boolean(diffStats && (diffStats.added > 0 || diffStats.removed > 0))
+
   // The header trailing slot only carries the live duration timer while the
   // tool is running. The copy control used to live here too, but an
   // `opacity-0` (yet still clickable) button straddling the caret/duration made
@@ -299,7 +324,12 @@ function ToolEntry({ part }: ToolEntryProps) {
     <Tip label={statusCopy.dismiss}>
       <Button
         aria-label={statusCopy.dismiss}
-        className="size-5 rounded-md text-(--ui-text-tertiary) opacity-0 transition-opacity hover:text-(--ui-text-primary) hover:opacity-100 group-hover/disclosure-row:opacity-80 group-focus-within/disclosure-row:opacity-80"
+        className={cn(
+          'size-5 rounded-md text-(--ui-text-tertiary) transition-opacity hover:text-(--ui-text-primary) hover:opacity-100',
+          open
+            ? 'opacity-80'
+            : 'opacity-0 group-hover/disclosure-row:opacity-80 group-focus-within/disclosure-row:opacity-80'
+        )}
         onClick={event => {
           event.stopPropagation()
           dismissToolRow(disclosureId)
@@ -317,13 +347,24 @@ function ToolEntry({ part }: ToolEntryProps) {
     return null
   }
 
+  // A completed file edit with no diff to review is a bare, unexpandable row.
+  // This is almost always a `write_file` create after a reload: only `patch`
+  // persists its diff in the tool result, so creates rehydrate diff-less and
+  // read like dead duplicates of the real diff row. Hide them — but keep
+  // in-flight writes (activity) and failures (errors) visible.
+  if (isFileEdit && !isPending && view.status !== 'error' && !view.inlineDiff) {
+    return null
+  }
+
   return (
     <div
       className={cn(
         'min-w-0 max-w-full overflow-hidden text-[length:var(--conversation-tool-font-size)] text-(--ui-text-tertiary)',
         open && 'rounded-[0.625rem] border border-(--ui-stroke-tertiary)'
       )}
+      data-file-edit={isFileEdit && open ? '' : undefined}
       data-slot="tool-block"
+      data-tool-row=""
       ref={enterRef}
     >
       <div className={cn(open && 'border-b border-(--ui-stroke-tertiary) px-2 py-1.5')}>
@@ -333,8 +374,16 @@ function ToolEntry({ part }: ToolEntryProps) {
           open={open}
           trailing={trailing}
         >
-          <span className="flex min-w-0 items-center gap-1.5">
-            <ToolGlyph copy={copy} icon={view.icon} status={leadingStatus(isPending, view.status)} />
+          <span
+            className="flex min-w-0 items-center gap-1.5"
+            title={isFileEdit && view.subtitle ? view.subtitle : undefined}
+          >
+            <ToolGlyph
+              copy={copy}
+              filePath={isFileEdit ? view.subtitle : undefined}
+              icon={view.icon}
+              status={leadingStatus(isPending, view.status)}
+            />
             <FadeText
               className={cn(
                 TOOL_HEADER_TITLE_CLASS,
@@ -346,7 +395,17 @@ function ToolEntry({ part }: ToolEntryProps) {
               {view.title}
             </FadeText>
             {!isPending && view.countLabel && <span className={TOOL_HEADER_DURATION_CLASS}>{view.countLabel}</span>}
-            {!isPending && view.durationLabel && (
+            {showDiffStats && diffStats && (
+              <span className="flex shrink-0 items-center gap-1 font-mono text-[0.625rem] tabular-nums">
+                {diffStats.added > 0 && (
+                  <span className="text-emerald-600 dark:text-emerald-400">+{diffStats.added}</span>
+                )}
+                {diffStats.removed > 0 && (
+                  <span className="text-rose-600 dark:text-rose-400">−{diffStats.removed}</span>
+                )}
+              </span>
+            )}
+            {!isFileEdit && !isPending && view.durationLabel && (
               <span className={TOOL_HEADER_DURATION_CLASS}>{view.durationLabel}</span>
             )}
           </span>
@@ -358,7 +417,7 @@ function ToolEntry({ part }: ToolEntryProps) {
           {copyAction.text && (
             <CopyButton
               appearance="inline"
-              className="absolute right-1.5 top-1.5 z-10 h-5 gap-0 rounded-md border border-(--ui-stroke-tertiary) bg-background/80 px-1 opacity-60 backdrop-blur-sm transition-opacity hover:opacity-100 focus-visible:opacity-100"
+              className="absolute right-1.5 top-1.5 z-10 h-5 gap-0 rounded-md border border-(--ui-stroke-tertiary) bg-background/80 px-1 opacity-100 backdrop-blur-sm transition-opacity hover:opacity-100 focus-visible:opacity-100"
               iconClassName="size-3"
               label={copyAction.label}
               showLabel={false}
@@ -380,6 +439,7 @@ function ToolEntry({ part }: ToolEntryProps) {
               <SearchResultsList hits={view.searchHits} />
             </div>
           )}
+          {view.inlineDiff && <FileDiffPanel diff={view.inlineDiff} />}
           {showDetail &&
             toolViewMode !== 'technical' &&
             (view.status === 'error' ? (
@@ -448,14 +508,21 @@ function ToolEntry({ part }: ToolEntryProps) {
               </pre>
             </details>
           )}
-          {toolViewMode === 'technical' && (
+          {toolViewMode === 'technical' && !(isFileEdit && view.inlineDiff) && (
             <pre className={cn(TOOL_SECTION_PRE_CLASS, 'whitespace-pre-wrap wrap-anywhere')}>
               {rawTechnicalTrace(part.args, part.result)}
             </pre>
           )}
+          {toolViewMode === 'technical' && isFileEdit && view.inlineDiff && (
+            <details className="max-w-full">
+              <summary className={cn(TOOL_SECTION_LABEL_CLASS, 'mb-0 cursor-pointer')}>Tool payload</summary>
+              <pre className={cn(TOOL_SECTION_PRE_CLASS, 'mt-1 whitespace-pre-wrap wrap-anywhere')}>
+                {rawTechnicalTrace(part.args, part.result)}
+              </pre>
+            </details>
+          )}
         </div>
       )}
-      {open && view.inlineDiff && <DiffLines text={view.inlineDiff} />}
     </div>
   )
 }
@@ -488,6 +555,7 @@ export const ToolGroupSlot: FC<PropsWithChildren<{ endIndex: number; startIndex:
       <div
         className="grid min-w-0 max-w-full gap-(--tool-row-gap) overflow-hidden"
         data-slot="tool-block"
+        data-tool-group=""
         ref={enterRef}
       >
         {children}
diff --git a/apps/desktop/src/components/chat/diff-lines.tsx b/apps/desktop/src/components/chat/diff-lines.tsx
index a6e025ae2ac..a8a1bfc314b 100644
--- a/apps/desktop/src/components/chat/diff-lines.tsx
+++ b/apps/desktop/src/components/chat/diff-lines.tsx
@@ -15,11 +15,17 @@ interface DiffLineKind {
 
 const DIFF_LINE_KINDS: DiffLineKind[] = [
   {
-    className: 'text-emerald-700 dark:text-emerald-300',
+    className: 'border-emerald-500 bg-emerald-500/12 text-emerald-800 dark:text-emerald-200',
     match: line => line.startsWith('+') && !line.startsWith('+++')
   },
-  { className: 'text-rose-700 dark:text-rose-300', match: line => line.startsWith('-') && !line.startsWith('---') },
-  { className: 'text-sky-700 dark:text-sky-300', match: line => line.startsWith('@@') },
+  {
+    className: 'border-rose-500 bg-rose-500/12 text-rose-800 dark:text-rose-200',
+    match: line => line.startsWith('-') && !line.startsWith('---')
+  },
+  {
+    className: 'text-sky-700 dark:text-sky-300',
+    match: line => line.startsWith('@@')
+  },
   {
     className: 'text-muted-foreground/70',
     match: line => line.startsWith('---') || line.startsWith('+++') || / → /.test(line.slice(0, 60))
@@ -30,25 +36,127 @@ function classifyLine(line: string): string | undefined {
   return DIFF_LINE_KINDS.find(kind => kind.match(line))?.className
 }
 
+// Drop the leading +/-/space gutter character so changes read by color alone
+// (like Cursor), keeping the rest of the indentation intact. Hunk headers
+// (`@@`) and any stray file headers are left untouched.
+function stripDiffMarker(line: string): string {
+  if (line.startsWith('@@')) {
+    return line
+  }
+
+  if ((line.startsWith('+') && !line.startsWith('+++')) || (line.startsWith('-') && !line.startsWith('---'))) {
+    return line.slice(1)
+  }
+
+  if (line.startsWith(' ')) {
+    return line.slice(1)
+  }
+
+  return line
+}
+
+interface DisplayLine {
+  className?: string
+  text: string
+}
+
+// Build the rendered line list: drop `@@ … @@` hunk headers (git noise in a
+// GUI) and the +/- gutter, but keep a blank separator between hunks so
+// multi-hunk diffs don't visually merge.
+function toDisplayLines(text: string): DisplayLine[] {
+  const out: DisplayLine[] = []
+  let emitted = false
+
+  for (const line of text.split('\n')) {
+    if (line.startsWith('@@')) {
+      if (emitted) {
+        out.push({ text: '' })
+      }
+
+      continue
+    }
+
+    out.push({ className: classifyLine(line), text: stripDiffMarker(line) })
+    emitted = true
+  }
+
+  return out
+}
+
 interface DiffLinesProps extends Omit<React.ComponentProps<'pre'>, 'children'> {
   text: string
 }
 
 export function DiffLines({ className, text, ...props }: DiffLinesProps) {
+  const lines = React.useMemo(() => toDisplayLines(text), [text])
+
   return (
     <pre
       className={cn(
-        'mt-1 mb-1.5 max-h-96 max-w-full min-w-0 overflow-auto rounded-md border border-border/60 bg-muted/35 px-2.5 py-1.5 font-mono text-[0.7rem] leading-relaxed text-muted-foreground',
+        'max-h-[12rem] max-w-full min-w-0 overflow-auto overscroll-contain px-0 py-1 font-mono text-[0.7rem] leading-relaxed text-(--ui-text-secondary)',
         className
       )}
       data-slot="diff-lines"
       {...props}
     >
-      {text.split('\n').map((line, index) => (
-        <span className={cn('block min-w-max whitespace-pre', classifyLine(line))} key={`${index}-${line}`}>
-          {line || ' '}
+      {lines.map((line, index) => (
+        <span
+          className={cn('block min-w-max border-l-2 border-transparent whitespace-pre px-2.5 py-px', line.className)}
+          key={`${index}-${line.text}`}
+        >
+          {line.text || ' '}
         </span>
       ))}
     </pre>
   )
 }
+
+// Git-style unified diffs arrive with a file-header preamble — `diff --git`,
+// `index …`, `--- a/path`, `+++ b/path`, and Hermes' own `a/path → b/path`
+// arrow line. That preamble just repeats the path (which the tool row already
+// shows) and reads especially badly for absolute paths (`a//Users/…`). Strip
+// the leading header zone up to the first hunk so the panel shows only hunks +
+// changes, the way Cursor does.
+const DIFF_HEADER_PREFIXES = ['diff --git', 'index ', '--- ', '+++ ', 'similarity ', 'rename ', 'new file', 'deleted file']
+
+function isArrowHeaderLine(line: string): boolean {
+  const trimmed = line.trim()
+
+  return trimmed.includes('→') && /^\S.*→\s*\S+$/.test(trimmed) && !/^[+\-@]/.test(trimmed)
+}
+
+/** Exported for tests. */
+export function stripDiffFileHeaders(diff: string): string {
+  const lines = diff.split('\n')
+  let start = 0
+
+  for (; start < lines.length; start += 1) {
+    const line = lines[start]
+
+    if (line.startsWith('@@')) {
+      break
+    }
+
+    if (line.trim() === '' || isArrowHeaderLine(line) || DIFF_HEADER_PREFIXES.some(prefix => line.startsWith(prefix))) {
+      continue
+    }
+
+    break
+  }
+
+  return lines.slice(start).join('\n')
+}
+
+interface FileDiffPanelProps {
+  diff: string
+}
+
+export function FileDiffPanel({ diff }: FileDiffPanelProps) {
+  const display = React.useMemo(() => stripDiffFileHeaders(diff), [diff])
+
+  // Bleed out of the tool-card body's `p-1.5` so changed-line tints/borders run
+  // flush to the card edges (rounded corners clip via the card's overflow).
+  // `max-w-none` lifts the base `max-w-full` cap that would otherwise stop the
+  // negative margins from widening the block.
+  return <DiffLines className="-mx-1.5 -mb-1.5 max-w-none" data-slot="file-diff-panel" text={display} />
+}
diff --git a/apps/desktop/src/components/ui/file-type-icon.tsx b/apps/desktop/src/components/ui/file-type-icon.tsx
new file mode 100644
index 00000000000..fe40c4f2437
--- /dev/null
+++ b/apps/desktop/src/components/ui/file-type-icon.tsx
@@ -0,0 +1,22 @@
+import { ToolIcon, type ToolIconProps } from '@/components/ui/tool-icon'
+import { codiconForFilename, codiconForLanguage } from '@/lib/markdown-code'
+
+export interface FileTypeIconProps extends Omit<ToolIconProps, 'name'> {
+  /** A code-fence language tag (e.g. `ts`, `json`). Used when no `path`. */
+  language?: string
+  /** A file path or bare name; its extension selects the icon. Wins over `language`. */
+  path?: string
+}
+
+/**
+ * Icon for a file or code language, resolved through the one mapping shared
+ * with code blocks (`codiconForFilename` / `codiconForLanguage`). Renders via
+ * `ToolIcon`, so it uses a filled glyph when one exists and falls back to the
+ * outline codicon font otherwise. Pass a `path` for file rows or a `language`
+ * for fenced code.
+ */
+export function FileTypeIcon({ language, path, ...props }: FileTypeIconProps) {
+  const name = path ? codiconForFilename(path) : codiconForLanguage(language)
+
+  return <ToolIcon name={name} {...props} />
+}
diff --git a/apps/desktop/src/lib/markdown-code.ts b/apps/desktop/src/lib/markdown-code.ts
index 0b105727490..6c34b1fcac3 100644
--- a/apps/desktop/src/lib/markdown-code.ts
+++ b/apps/desktop/src/lib/markdown-code.ts
@@ -108,6 +108,56 @@ export function codiconForLanguage(language: string | undefined): string {
   return CODICON_BY_LANGUAGE[sanitizeLanguageTag(language || '')] || 'code'
 }
 
+// File extension → language tag, so a filename can resolve to the same icon a
+// fenced code block of that language would get. Only extensions that map to a
+// non-generic codicon need an entry; everything else falls through to `code`.
+const LANGUAGE_BY_EXTENSION: Record<string, string> = {
+  bash: 'bash',
+  cfg: 'ini',
+  conf: 'ini',
+  css: 'css',
+  dockerfile: 'dockerfile',
+  env: 'env',
+  gql: 'graphql',
+  graphql: 'graphql',
+  ini: 'ini',
+  json: 'json',
+  json5: 'json',
+  less: 'less',
+  markdown: 'markdown',
+  md: 'markdown',
+  mdx: 'markdown',
+  mmd: 'mermaid',
+  ps1: 'powershell',
+  psql: 'sql',
+  sass: 'sass',
+  scss: 'scss',
+  sh: 'bash',
+  sql: 'sql',
+  svg: 'svg',
+  toml: 'toml',
+  yaml: 'yaml',
+  yml: 'yml',
+  zsh: 'zsh'
+}
+
+// Pick an icon for a file path by its extension (or bare name like
+// `Dockerfile`), reusing the language→codicon map so file-edit rows and code
+// blocks share one visual vocabulary. Unknown / generic code files get `code`.
+export function codiconForFilename(path: string | undefined): string {
+  const base = (path || '').replace(/\\/g, '/').split('/').pop()?.trim().toLowerCase() || ''
+
+  if (!base) {
+    return 'code'
+  }
+
+  const dot = base.lastIndexOf('.')
+  const token = dot > 0 ? base.slice(dot + 1) : base
+  const language = LANGUAGE_BY_EXTENSION[token] || token
+
+  return codiconForLanguage(language)
+}
+
 function proseLineCount(body: string): number {
   return body.split('\n').filter(line => {
     const trimmed = line.trim()
diff --git a/apps/desktop/src/styles.css b/apps/desktop/src/styles.css
index 36ef859ce12..f3fe3da0d28 100644
--- a/apps/desktop/src/styles.css
+++ b/apps/desktop/src/styles.css
@@ -1214,19 +1214,33 @@ canvas {
   background: transparent !important;
 }
 
-[data-slot='aui_assistant-message-content'] > :is([data-slot='tool-block'], [data-slot='aui_thinking-disclosure']) {
+/* Fade scaffolding so the prose reading column stays primary. Two targets:
+   a thinking disclosure fades as one block, and each *individual* tool row
+   (`[data-tool-row]`) fades on its own. We deliberately do NOT fade the tool
+   group wrapper (`[data-tool-group]`): opacity on a parent opens a stacking
+   context, so a child row can never be more opaque than the group — that made
+   it impossible to keep one row lit (an open diff) while its siblings faded.
+   With the fade per-row, each row hovers/focuses independently. */
+[data-slot='aui_assistant-message-content'] > [data-slot='aui_thinking-disclosure'],
+[data-slot='aui_assistant-message-content'] [data-slot='tool-block'][data-tool-row] {
   opacity: 0.67;
   transition: opacity 120ms ease-out;
 }
 
-[data-slot='aui_assistant-message-content']
-  > :is([data-slot='tool-block'], [data-slot='aui_thinking-disclosure']):is(:hover, :focus-within) {
+/* Lift on hover or *keyboard* focus only. `:focus-within` also matches the
+   focus a mouse click leaves on the disclosure toggle, which kept a row lit
+   after you clicked to collapse it; `:has(:focus-visible)` excludes that. */
+[data-slot='aui_assistant-message-content'] > [data-slot='aui_thinking-disclosure']:is(:hover, :has(:focus-visible)),
+[data-slot='aui_assistant-message-content'] [data-slot='tool-block'][data-tool-row]:is(:hover, :has(:focus-visible)) {
   opacity: 1;
 }
 
-/* A generated image is the deliverable, not scaffolding — keep it at full
-   strength instead of dimming it until hover. */
-[data-slot='aui_assistant-message-content'] > [data-slot='tool-block']:has([data-slot='aui_generated-image']) {
+/* File edits (write_file / edit_file / patch) are the deliverable, not
+   scaffolding — the diff is what the user reviews, like a PR. An *expanded*
+   edit stays at full strength; collapsed it fades like any other row. The
+   `data-file-edit` marker sits on the same row element and is only present
+   while the row is open. */
+[data-slot='aui_assistant-message-content'] [data-slot='tool-block'][data-tool-row][data-file-edit] {
   opacity: 1;
 }