fix(diff): git lens 折叠行接入按需展开，修复点击无反应

- src/client/changes/DiffPane.tsx / src/client/DiffTab.tsx: 按 SidebarDiffRef 构造 fold loader——commit 侧 <hash>^ 与 <hash>；staged 侧 HEAD 与 :0；unstaged 侧 :0 与工作区 fsRead（失败/二进制降级空串）；per 文件内容 Promise 缓存，目标或刷新 tick 变化时重置 - fallback 换侧时记录 effectiveStaged，loader 依实际渲染侧取数，修正切片行号错位 - src/client/locales.ts 及 19 个 locales-*.ts: 新增 changesFoldLoading / changesFoldUnavailable 全量补译（共 20 文件 21 处） - tests/diff-fold-expand.spec.tsx: 展开/折叠/缓存去重、失败降级、无 loader 保持 inert、session 路径回归背景：git 提交/工作区 diff 折叠行承诺「点击展开」却永远不可点，与 session lens 行为不一致；接入状态机后承诺为真，session 路径与现有文案零变化。设计 docs/plans/2026-09-07-git-fold-expand-design.md §4.5-4.6。
2026-09-07 23:51:10 +08:00
parent d990c10e59
commit 900654b8fd
23 changed files with 331 additions and 5 deletions
@@ -8,12 +8,13 @@
 * very content it shows. Rendering goes through the shared {@link DiffFiles}
 * renderer — the same one the changes tab's inline preview uses.
 */
-import { useCallback, useEffect, useState } from 'react'
+import { useCallback, useEffect, useMemo, useRef, useState } from 'react'
 import { IconRefreshOutline16 } from '@deepseek-ai/dsh-client-ui-primitives'
 import type { SessionScope } from './api.ts'
 import { api } from './api.ts'
 import type { SidebarDiffRef } from './state.ts'
 import { DiffFiles } from './diff/DiffFiles.tsx'
+import { displayPath, foldRowsFromContents, type DiffFile, type DiffRow, type FoldSegment } from './diff/rows.ts'
 import { t } from './locales.ts'
 import { resolveSidebarPath } from './produced-files.ts'
 import css from './sidebar.module.css'
@@ -30,6 +31,11 @@ export function DiffTab(props: { sessionId: string; cwd: string | undefined; dif
  const [error, setError] = useState<string | null>(null)
  const [data, setData] = useState<DiffData | null>(null)
  const [tick, setTick] = useState(0)
+  // The staged flag of the side ACTUALLY rendered: when the requested side's
+  // diff came back empty the load falls back to the other side, and the fold
+  // expansion must read that side's revisions (else the sliced line numbers
+  // land on the wrong contents).
+  const [effectiveStaged, setEffectiveStaged] = useState<boolean | null>(null)

  const refresh = useCallback((): void => { setTick(value => value + 1) }, [])

@@ -39,6 +45,7 @@ export function DiffTab(props: { sessionId: string; cwd: string | undefined; dif
    setLoading(true)
    setError(null)
    setData(null)
+    setEffectiveStaged(null)
    const load = async (): Promise<void> => {
      try {
        if (diff.kind === 'commit') {
@@ -53,7 +60,10 @@ export function DiffTab(props: { sessionId: string; cwd: string | undefined; dif
          // file staged after its tab opened). Both sides empty means the
          // file genuinely has no text changes.
          const other = await api.gitDiff(scope, diff.path, !diff.staged, diff.worktree)
-          if (other.diff !== '') result = other
+          if (other.diff !== '') {
+            result = other
+            if (!cancelled) setEffectiveStaged(!diff.staged)
+          }
        }
        if (result.diff !== '') {
          if (!cancelled) setData({ diff: result.diff })
@@ -82,6 +92,63 @@ export function DiffTab(props: { sessionId: string; cwd: string | undefined; dif
    return () => { cancelled = true }
  }, [sessionId, cwd, diff, tick])

+  // ── On-demand git fold expansion: a fold's hidden rows come from both
+  //    sides' full contents (git.show / fsRead), fetched ONCE per file so
+  //    sibling folds share the request, then sliced by each fold's line
+  //    ranges. The cache dies with the ref or a refresh tick. ──────────────
+  const foldContents = useRef(new Map<string, Promise<{ old: string; new: string }>>())
+  useEffect(() => { foldContents.current = new Map() }, [diff, tick])
+  const foldLoader = useMemo(() => {
+    const sidesOf = (file: DiffFile): Promise<{ old: string; new: string }> => {
+      const fetchSides = async (): Promise<{ old: string; new: string }> => {
+        const scope: SessionScope = { sessionId, cwd, ...(diff.repoRoot !== undefined ? { repoRoot: diff.repoRoot } : {}) }
+        if (diff.kind === 'commit') {
+          // The patch's -m --first-parent shape: old side from the parent,
+          // new side from the commit (a root commit's parent read fails → '').
+          const [oldSide, newSide] = await Promise.all([
+            file.oldPath === '/dev/null'
+              ? Promise.resolve({ content: null })
+              : api.gitShow(scope, `${diff.hashFull}^`, displayPath(file.oldPath), diff.worktree),
+            file.newPath === '/dev/null'
+              ? Promise.resolve({ content: null })
+              : api.gitShow(scope, diff.hashFull, displayPath(file.newPath), diff.worktree),
+          ])
+          return { old: oldSide.content ?? '', new: newSide.content ?? '' }
+        }
+        // Worktree change: staged is HEAD vs index, unstaged is index vs
+        // worktree (the worktree side reads the live file).
+        const staged = effectiveStaged ?? diff.staged
+        if (staged) {
+          const [oldSide, newSide] = await Promise.all([
+            file.oldPath === '/dev/null'
+              ? Promise.resolve({ content: null })
+              : api.gitShow(scope, 'HEAD', displayPath(file.oldPath), diff.worktree),
+            file.newPath === '/dev/null'
+              ? Promise.resolve({ content: null })
+              : api.gitShow(scope, ':0', displayPath(file.newPath), diff.worktree),
+          ])
+          return { old: oldSide.content ?? '', new: newSide.content ?? '' }
+        }
+        const [oldSide, worktree] = await Promise.all([
+          file.oldPath === '/dev/null'
+            ? Promise.resolve({ content: null })
+            : api.gitShow(scope, ':0', displayPath(file.oldPath), diff.worktree),
+          api.fsRead(scope, resolveSidebarPath(diff.repoRoot ?? diff.worktree ?? cwd, displayPath(file.newPath))).catch(() => null),
+        ])
+        return { old: oldSide.content ?? '', new: worktree !== null && worktree.kind === 'text' ? worktree.content : '' }
+      }
+      const path = displayPath(file.newPath === '/dev/null' ? file.oldPath : file.newPath)
+      let promise = foldContents.current.get(path)
+      if (promise === undefined) {
+        promise = fetchSides()
+        foldContents.current.set(path, promise)
+      }
+      return promise
+    }
+    return (file: DiffFile, segment: FoldSegment): Promise<readonly DiffRow[]> =>
+      sidesOf(file).then(sides => foldRowsFromContents(segment, sides.old, sides.new))
+  }, [sessionId, cwd, diff, effectiveStaged])
+
  return (
    <div className={css.gitDiffTab}>
      <div className={css.gitDiffTabHeader}>
@@ -104,7 +171,7 @@ export function DiffTab(props: { sessionId: string; cwd: string | undefined; dif
        <>
          {data.untracked !== undefined
            ? <DiffFiles diff="" untrackedPath={diff.kind === 'worktree' ? diff.path : ''} untrackedContent={data.untracked} />
-            : <DiffFiles diff={data.diff} />}
+            : <DiffFiles diff={data.diff} resolveFold={foldLoader} />}
          {data.diff === '' && data.untracked === undefined && (
            <div className={css.gitEmpty}>{t('diffEmpty')}</div>
          )}
@@ -21,7 +21,7 @@ import { DiffRows, ReadRows } from '../diff/DiffRows.tsx'
 import { PdfView } from '../PdfView.tsx'
 import { DiffFiles } from '../diff/DiffFiles.tsx'
 import { langOfPath } from '../diff/highlight.ts'
-import { buildDiffSegments, diffLines, diffStats, parseUnifiedDiff, unifiedSegments, type DiffRow } from '../diff/rows.ts'
+import { buildDiffSegments, diffLines, diffStats, displayPath, foldRowsFromContents, parseUnifiedDiff, unifiedSegments, type DiffFile, type DiffRow, type FoldSegment } from '../diff/rows.ts'
 import { parseReadContent, parseReadLines, type FileOp } from './ops.ts'
 import { redactText } from '../redact.ts'
 import { rewriteLocalImageUrls } from '../markdown-images.ts'
@@ -158,7 +158,19 @@ export function DiffPane({ target, scope, height, onHeightCommit, onClose, onExp
  const [error, setError] = useState<string | null>(null)
  const [diffText, setDiffText] = useState<string | null>(null)
  const [untracked, setUntracked] = useState<string | undefined>(undefined)
+  // The staged flag of the side ACTUALLY rendered: when the requested side's
+  // diff came back empty the load falls back to the other side, and the fold
+  // expansion must read that side's revisions (else the sliced line numbers
+  // land on the wrong contents).
+  const [effectiveStaged, setEffectiveStaged] = useState<boolean | null>(null)
  const gitRef = target.kind === 'git' ? target.ref : null
+  // The scope every git call of this target shares (repoRoot folded in when
+  // the ref carries one, exactly like the load effect's paneScope).
+  const gitScope = useMemo<SessionScope>(() => ({
+    sessionId: scope.sessionId,
+    cwd: scope.cwd,
+    ...(gitRef?.repoRoot !== undefined ? { repoRoot: gitRef.repoRoot } : {}),
+  }), [scope.sessionId, scope.cwd, gitRef?.repoRoot])

  useEffect(() => {
    if (gitRef === null) return
@@ -172,6 +184,7 @@ export function DiffPane({ target, scope, height, onHeightCommit, onClose, onExp
    setError(null)
    setDiffText(null)
    setUntracked(undefined)
+    setEffectiveStaged(null)
    const load = async (): Promise<void> => {
      try {
        if (gitRef.kind === 'commit') {
@@ -184,7 +197,10 @@ export function DiffPane({ target, scope, height, onHeightCommit, onClose, onExp
          // The requested side is empty — try the OTHER side once (the change
          // may have moved sides after the preview target was minted).
          const other = await api.gitDiff(paneScope, gitRef.path, !gitRef.staged, gitRef.worktree)
-          if (other.diff !== '') result = other
+          if (other.diff !== '') {
+            result = other
+            if (!cancelled) setEffectiveStaged(!gitRef.staged)
+          }
        }
        if (result.diff !== '') {
          if (!cancelled) setDiffText(result.diff)
@@ -211,6 +227,63 @@ export function DiffPane({ target, scope, height, onHeightCommit, onClose, onExp
    return () => { cancelled = true }
  }, [gitRef, scope.sessionId, scope.cwd, tick])

+  // ── On-demand git fold expansion: a fold's hidden rows come from both
+  //    sides' full contents (git.show / fsRead), fetched ONCE per file so
+  //    sibling folds share the request, then sliced by each fold's line
+  //    ranges. The cache dies with the target or a refresh tick. ───────────
+  const foldContents = useRef(new Map<string, Promise<{ old: string; new: string }>>())
+  useEffect(() => { foldContents.current = new Map() }, [gitRef, tick])
+  const foldLoader = useMemo(() => {
+    if (gitRef === null) return undefined
+    const sidesOf = (file: DiffFile): Promise<{ old: string; new: string }> => {
+      const fetchSides = async (): Promise<{ old: string; new: string }> => {
+        if (gitRef.kind === 'commit') {
+          // The patch's -m --first-parent shape: old side from the parent,
+          // new side from the commit (a root commit's parent read fails → '').
+          const [oldSide, newSide] = await Promise.all([
+            file.oldPath === '/dev/null'
+              ? Promise.resolve({ content: null })
+              : api.gitShow(gitScope, `${gitRef.hashFull}^`, displayPath(file.oldPath), gitRef.worktree),
+            file.newPath === '/dev/null'
+              ? Promise.resolve({ content: null })
+              : api.gitShow(gitScope, gitRef.hashFull, displayPath(file.newPath), gitRef.worktree),
+          ])
+          return { old: oldSide.content ?? '', new: newSide.content ?? '' }
+        }
+        // Worktree change: staged is HEAD vs index, unstaged is index vs
+        // worktree (the worktree side reads the live file).
+        const staged = effectiveStaged ?? gitRef.staged
+        if (staged) {
+          const [oldSide, newSide] = await Promise.all([
+            file.oldPath === '/dev/null'
+              ? Promise.resolve({ content: null })
+              : api.gitShow(gitScope, 'HEAD', displayPath(file.oldPath), gitRef.worktree),
+            file.newPath === '/dev/null'
+              ? Promise.resolve({ content: null })
+              : api.gitShow(gitScope, ':0', displayPath(file.newPath), gitRef.worktree),
+          ])
+          return { old: oldSide.content ?? '', new: newSide.content ?? '' }
+        }
+        const [oldSide, worktree] = await Promise.all([
+          file.oldPath === '/dev/null'
+            ? Promise.resolve({ content: null })
+            : api.gitShow(gitScope, ':0', displayPath(file.oldPath), gitRef.worktree),
+          api.fsRead(gitScope, resolveSidebarPath(gitRef.repoRoot ?? gitRef.worktree ?? scope.cwd, displayPath(file.newPath))).catch(() => null),
+        ])
+        return { old: oldSide.content ?? '', new: worktree !== null && worktree.kind === 'text' ? worktree.content : '' }
+      }
+      const path = displayPath(file.newPath === '/dev/null' ? file.oldPath : file.newPath)
+      let promise = foldContents.current.get(path)
+      if (promise === undefined) {
+        promise = fetchSides()
+        foldContents.current.set(path, promise)
+      }
+      return promise
+    }
+    return (file: DiffFile, segment: FoldSegment): Promise<readonly DiffRow[]> =>
+      sidesOf(file).then(sides => foldRowsFromContents(segment, sides.old, sides.new))
+  }, [gitRef, gitScope, effectiveStaged, scope])
+
  // ── Op target material (pure snapshots; the prior content came with the
  //    target so a running op shows what is already known). ────────────────
  const opRaw = target.kind === 'op' ? target.op : null
@@ -508,6 +581,7 @@ export function DiffPane({ target, scope, height, onHeightCommit, onClose, onExp
                    {diffText !== null && diffText !== '' && (
                      <DiffFiles
                        diff={diffText}
+                        resolveFold={foldLoader}
                        untrackedPath={untracked !== undefined && target.ref.kind === 'worktree' ? target.ref.path : undefined}
                        untrackedContent={untracked}
                      />
@@ -31,6 +31,8 @@ export const ar: Record<string, string> = {
  changesRunning: 'قيد التنفيذ',
  changesError: 'خطأ',
  changesFold: '{count} أسطر… انقر للتوسيع',
+  changesFoldLoading: 'جارٍ التوسيع…',
+  changesFoldUnavailable: 'السياق غير متوفر',
  changesContext: 'سياق',
  changesPriorUnknown: 'المحتوى السابق خارج النافذة؛ يُعرض كما لو أُضيف بالكامل',
  explorer: 'المستكشف',
@@ -16,6 +16,8 @@ export const de: Record<string, string> = {
  changesRunning: 'läuft',
  changesError: 'Fehler',
  changesFold: '{count} Zeilen… zum Aufklappen klicken',
+  changesFoldLoading: 'Wird aufgeklappt…',
+  changesFoldUnavailable: 'Kontext nicht verfügbar',
  changesContext: 'Kontext',
  changesPriorUnknown: 'Inhalt vor der Änderung liegt außerhalb des Fensters; als vollständig neu angezeigt',
  explorer: 'Explorer',
@@ -23,6 +23,8 @@ export const fr: Record<string, string> = {
  changesRunning: 'en cours',
  changesError: 'erreur',
  changesFold: '{count} lignes… cliquer pour déplier',
+  changesFoldLoading: 'Dépliage…',
+  changesFoldUnavailable: 'Contexte indisponible',
  changesContext: 'contexte',
  changesPriorUnknown: 'Le contenu antérieur est hors de la fenêtre ; affiché comme entièrement ajouté',
  explorer: 'Explorateur',
@@ -30,6 +30,8 @@ export const hi: Record<string, string> = {
  changesRunning: 'चल रहा है',
  changesError: 'त्रुटि',
  changesFold: '{count} पंक्तियाँ… विस्तार के लिए क्लिक करें',
+  changesFoldLoading: 'विस्तार हो रहा है…',
+  changesFoldUnavailable: 'संदर्भ अनुपलब्ध',
  changesContext: 'संदर्भ',
  changesPriorUnknown: 'बदलाव से पहले की सामग्री विंडो में नहीं है; पूरी नई जोड़ी गई दिखाई जाती है',
  explorer: 'एक्सप्लोरर',
@@ -28,6 +28,8 @@ export const id: Record<string, string> = {
  changesRunning: 'berjalan',
  changesError: 'error',
  changesFold: '{count} baris… klik untuk meluaskan',
+  changesFoldLoading: 'Meluaskan…',
+  changesFoldUnavailable: 'Konteks tidak tersedia',
  changesContext: 'konteks',
  changesPriorUnknown: 'Konten sebelum perubahan berada di luar jendela; ditampilkan sebagai sepenuhnya baru',
  explorer: 'Explorer',
@@ -21,6 +21,8 @@ export const it: Record<string, string> = {
  changesRunning: 'in esecuzione',
  changesError: 'errore',
  changesFold: '{count} righe… clicca per espandere',
+  changesFoldLoading: 'Espansione…',
+  changesFoldUnavailable: 'Contesto non disponibile',
  changesContext: 'contesto',
  changesPriorUnknown: 'Il contenuto precedente è fuori dalla finestra; mostrato come interamente aggiunto',
  explorer: 'Esplora risorse',
@@ -30,6 +30,8 @@ export const ja: Record<string, string> = {
  changesRunning: '実行中',
  changesError: 'エラー',
  changesFold: '{count} 行…クリックで展開',
+  changesFoldLoading: '展開中…',
+  changesFoldUnavailable: 'コンテキスト未読み込み',
  changesContext: 'コンテキスト',
  changesPriorUnknown: '変更前の内容がウィンドウ内になく、すべて新規追加として表示されます',
  explorer: 'エクスプローラー',
@@ -22,6 +22,8 @@ export const ko: Record<string, string> = {
  changesRunning: '실행 중',
  changesError: '오류',
  changesFold: '{count}줄… 클릭하여 펼치기',
+  changesFoldLoading: '펼치는 중…',
+  changesFoldUnavailable: '컨텍스트를 불러올 수 없음',
  changesContext: '컨텍스트',
  changesPriorUnknown: '변경 전 내용이 창에 없어 모두 새로 추가된 것으로 표시됩니다',
  explorer: '탐색기',
@@ -28,6 +28,8 @@ export const nl: Record<string, string> = {
  changesRunning: 'actief',
  changesError: 'fout',
  changesFold: '{count} regels… klik om uit te klappen',
+  changesFoldLoading: 'Uitklappen…',
+  changesFoldUnavailable: 'Context niet beschikbaar',
  changesContext: 'context',
  changesPriorUnknown: 'Eerdere inhoud valt buiten het venster; getoond als volledig nieuw',
  explorer: 'Verkenner',
@@ -32,6 +32,8 @@ export const pl: Record<string, string> = {
  changesRunning: 'w toku',
  changesError: 'błąd',
  changesFold: '{count} wierszy… kliknij, aby rozwinąć',
+  changesFoldLoading: 'Rozwijanie…',
+  changesFoldUnavailable: 'Kontekst niedostępny',
  changesContext: 'kontekst',
  changesPriorUnknown: 'Zawartość sprzed zmiany jest poza oknem; pokazana jako w całości nowa',
  explorer: 'Eksplorator',
@@ -13,6 +13,8 @@ export const pt: Record<string, string> = {
  changesRunning: 'em execução',
  changesError: 'erro',
  changesFold: '{count} linhas… clique para expandir',
+  changesFoldLoading: 'Expandindo…',
+  changesFoldUnavailable: 'Contexto indisponível',
  changesContext: 'contexto',
  changesPriorUnknown: 'O conteúdo anterior está fora da janela; mostrado como totalmente adicionado',
  explorer: 'Explorador',
@@ -26,6 +26,8 @@ export const ru: Record<string, string> = {
  changesRunning: 'выполняется',
  changesError: 'ошибка',
  changesFold: '{count} строк… нажмите, чтобы развернуть',
+  changesFoldLoading: 'Разворачивание…',
+  changesFoldUnavailable: 'Контекст недоступен',
  changesContext: 'контекст',
  changesPriorUnknown: 'Содержимое до изменения вне окна; показано как полностью добавленное',
  explorer: 'Проводник',
@@ -13,6 +13,8 @@ export const sv: Record<string, string> = {
  changesRunning: 'körs',
  changesError: 'fel',
  changesFold: '{count} rader… klicka för att expandera',
+  changesFoldLoading: 'Expanderar…',
+  changesFoldUnavailable: 'Kontext ej tillgänglig',
  changesContext: 'kontext',
  changesPriorUnknown: 'Innehållet före ändringen ligger utanför fönstret; visas som helt nytt',
  explorer: 'Utforskare',
@@ -30,6 +30,8 @@ export const th: Record<string, string> = {
  changesRunning: 'กำลังทำงาน',
  changesError: 'ข้อผิดพลาด',
  changesFold: '{count} บรรทัด… คลิกเพื่อขยาย',
+  changesFoldLoading: 'กำลังขยาย…',
+  changesFoldUnavailable: 'ไม่สามารถโหลดบริบทได้',
  changesContext: 'บริบท',
  changesPriorUnknown: 'เนื้อหาก่อนแก้ไขอยู่นอกหน้าต่าง แสดงเป็นเพิ่มใหม่ทั้งหมด',
  explorer: 'ตัวสำรวจ',
@@ -30,6 +30,8 @@ export const tr: Record<string, string> = {
  changesRunning: 'çalışıyor',
  changesError: 'hata',
  changesFold: '{count} satır… genişletmek için tıklayın',
+  changesFoldLoading: 'Genişletiliyor…',
+  changesFoldUnavailable: 'Bağlam yüklenemedi',
  changesContext: 'bağlam',
  changesPriorUnknown: 'Değişiklik öncesi içerik pencere dışında; tamamen yeni eklenmiş olarak gösteriliyor',
  explorer: 'Gezgin',
@@ -30,6 +30,8 @@ export const vi: Record<string, string> = {
  changesRunning: 'đang chạy',
  changesError: 'lỗi',
  changesFold: '{count} dòng… bấm để mở rộng',
+  changesFoldLoading: 'Đang mở rộng…',
+  changesFoldUnavailable: 'Không tải được ngữ cảnh',
  changesContext: 'ngữ cảnh',
  changesPriorUnknown: 'Nội dung trước thay đổi nằm ngoài cửa sổ; hiển thị như toàn bộ mới thêm',
  explorer: 'Trình khám phá',
@@ -45,6 +45,8 @@ export const zhHK: Record<string, string> = {
  changesRunning: '執行中',
  changesError: '出錯',
  changesFold: '{count} 行…點擊展開',
+  changesFoldLoading: '展開中…',
+  changesFoldUnavailable: '上下文未載入',
  changesContext: '上下文',
  changesPriorUnknown: '變更前的內容不在視窗內，顯示為全部新增',
  explorer: '檔案總管',
@@ -45,6 +45,8 @@ export const zhMO: Record<string, string> = {
  changesRunning: '執行中',
  changesError: '出錯',
  changesFold: '{count} 行…點擊展開',
+  changesFoldLoading: '展開中…',
+  changesFoldUnavailable: '上下文未載入',
  changesContext: '上下文',
  changesPriorUnknown: '變更前的內容不在視窗內，顯示為全部新增',
  explorer: '檔案總管',
@@ -45,6 +45,8 @@ export const zhTW: Record<string, string> = {
  changesRunning: '執行中',
  changesError: '出錯',
  changesFold: '{count} 行…點擊展開',
+  changesFoldLoading: '展開中…',
+  changesFoldUnavailable: '上下文未載入',
  changesContext: '上下文',
  changesPriorUnknown: '變更前的內容不在視窗內，顯示為全部新增',
  explorer: '檔案總管',
@@ -42,6 +42,8 @@ export const zh = {
  changesRedactOffLabel: '脱敏关',
  changesRedactBanner: '已脱敏',
  changesFold: '{count} 行…点击展开',
+  changesFoldLoading: '展开中…',
+  changesFoldUnavailable: '上下文未加载',
  changesContext: '上下文',
  changesPriorUnknown: '变更前的内容不在窗口内，显示为全新增',
  explorer: '资源管理器',
@@ -489,6 +491,8 @@ export const en: Record<keyof typeof zh, string> = {
  changesRedactOffLabel: 'Redaction off',
  changesRedactBanner: 'Redacted',
  changesFold: '{count} lines…click to expand',
+  changesFoldLoading: 'Expanding…',
+  changesFoldUnavailable: 'Context unavailable',
  changesContext: 'context',
  changesPriorUnknown: 'Prior content is outside the loaded window; shown as all-added',
  explorer: 'Explorer',
@@ -0,0 +1,143 @@
+// @vitest-environment jsdom
+/**
+ * The git fold expansion path: DiffFiles forwards a resolveFold loader to
+ * DiffRows, whose first click on a rows-less git gap fold fetches the hidden
+ * rows (loading/failed markers in between) and later clicks toggle; folds
+ * that carry rows (the session-op path) expand directly, and gaps without a
+ * loader stay inert markers — the pre-fix behavior for op diffs.
+ */
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { createElement } from 'react'
+import { createRoot, type Root } from 'react-dom/client'
+import { act } from 'react-dom/test-utils'
+import { DiffFiles } from '../src/client/diff/DiffFiles.tsx'
+import { DiffRows } from '../src/client/diff/DiffRows.tsx'
+import { buildDiffSegments, diffLines, type DiffFile, type FoldSegment } from '../src/client/diff/rows.ts'
+
+import { setupReactAct } from './test-utils.ts'
+setupReactAct()
+
+// A git-shaped two-hunk patch: the gap between the hunks (old/new lines
+// 2..11) is a fold WITHOUT rows — expandable only through a resolveFold.
+const gapDiff = [
+  'diff --git a/src/a.ts b/src/a.ts',
+  '--- a/src/a.ts',
+  '+++ b/src/a.ts',
+  '@@ -1 +1 @@',
+  '-old',
+  '+new',
+  '@@ -12 +12 @@',
+  '-tail',
+  '+tail2',
+].join('\n')
+
+// The hidden context rows a loader slices out of both sides' contents.
+const hiddenRows = Array.from({ length: 10 }, (_, i) => ({
+  kind: 'context' as const,
+  oldLine: i + 2,
+  newLine: i + 2,
+  text: `ctx-${String(i + 2)}`,
+}))
+
+afterEach(() => { document.body.innerHTML = '' })
+
+describe('DiffFiles on-demand fold expansion', () => {
+  it('expands a git gap fold through resolveFold, then collapses back', async () => {
+    const resolveFold = vi.fn((_file: DiffFile, _segment: FoldSegment) => Promise.resolve(hiddenRows))
+    const container = document.createElement('div')
+    document.body.append(container)
+    const root: Root = createRoot(container)
+    try {
+      act(() => { root.render(createElement(DiffFiles, { diff: gapDiff, resolveFold })) })
+      const fold = container.querySelector<HTMLElement>('[data-expandable="true"]')
+      expect(fold).not.toBeNull()
+      expect(container.textContent).not.toContain('ctx-5')
+
+      await act(async () => { fold!.click() })
+      expect(resolveFold).toHaveBeenCalledOnce()
+      expect(container.textContent).toContain('ctx-5')
+      // The loader received the gap fold itself (line ranges on board).
+      const segment = resolveFold.mock.calls[0]![1]
+      expect(segment.kind).toBe('fold')
+      expect(segment.oldStart).toBe(2)
+
+      // Collapse: the marker is back; the fetch never repeats.
+      const expanded = container.querySelector<HTMLElement>('[data-expandable="true"]')
+      await act(async () => { expanded!.click() })
+      expect(container.textContent).not.toContain('ctx-5')
+      expect(resolveFold).toHaveBeenCalledOnce()
+
+      // Re-expanding resolves from the per-fold cache (no second fetch).
+      const collapsed = container.querySelector<HTMLElement>('[data-expandable="true"]')
+      await act(async () => { collapsed!.click() })
+      expect(container.textContent).toContain('ctx-5')
+      expect(resolveFold).toHaveBeenCalledOnce()
+    } finally {
+      act(() => { root.unmount() })
+      container.remove()
+    }
+  })
+
+  it('degrades to the unavailable marker when the loader rejects', async () => {
+    const resolveFold = vi.fn(() => Promise.reject(new Error('boom')))
+    const container = document.createElement('div')
+    document.body.append(container)
+    const root: Root = createRoot(container)
+    try {
+      act(() => { root.render(createElement(DiffFiles, { diff: gapDiff, resolveFold })) })
+      const fold = container.querySelector<HTMLElement>('[data-expandable="true"]')
+      await act(async () => { fold!.click() })
+      // The degraded fold promises no interaction.
+      expect(container.querySelector('[data-expandable]')).toBeNull()
+      expect(container.textContent).not.toContain('ctx-5')
+      // jsdom's navigator.language is en-US → the en copy.
+      expect(container.textContent).toContain('Context unavailable')
+    } finally {
+      act(() => { root.unmount() })
+      container.remove()
+    }
+  })
+
+  it('keeps git gap folds inert without a resolver (session surfaces unchanged)', () => {
+    const container = document.createElement('div')
+    document.body.append(container)
+    const root: Root = createRoot(container)
+    try {
+      act(() => { root.render(createElement(DiffFiles, { diff: gapDiff })) })
+      expect(container.querySelector('[data-expandable]')).toBeNull()
+      // The quiet marker still shows the hidden line count.
+      expect(container.textContent).toContain('10 lines')
+    } finally {
+      act(() => { root.unmount() })
+      container.remove()
+    }
+  })
+
+  it('expands session folds (rows carried) directly, without any loader', async () => {
+    // buildDiffSegments output — the session-op path: folds carry their rows,
+    // so they toggle on click exactly as before the git expansion existed.
+    const rows = diffLines(
+      'a\nb\nc\nd\ne\nX\nf\ng\nh\ni\nj\nk\nl\n',
+      'a\nb\nc\nd\ne\nY\nf\ng\nh\ni\nj\nk\nl\n',
+    )
+    const segments = buildDiffSegments(rows)
+    const container = document.createElement('div')
+    document.body.append(container)
+    const root: Root = createRoot(container)
+    try {
+      act(() => { root.render(createElement(DiffRows, { segments })) })
+      const fold = container.querySelector<HTMLElement>('[data-expandable="true"]')
+      expect(fold).not.toBeNull()
+      // 'j' is hidden in the tail fold (the marker copy carries no 'j').
+      expect(container.textContent).not.toContain('j')
+      await act(async () => { fold!.click() })
+      expect(container.textContent).toContain('j')
+      const expanded = container.querySelector<HTMLElement>('[data-expandable="true"]')
+      await act(async () => { expanded!.click() })
+      expect(container.textContent).not.toContain('j')
+    } finally {
+      act(() => { root.unmount() })
+      container.remove()
+    }
+  })
+})