feat: v0.5.0 字符级对比模式 - 新增字符级对比开关（空白与换行结构全部不参与判等、两侧归一化为字符流 diff、跨行重组也能判等）、字符差异回映射到行（跨界行配对、单侧行回拉、锚行 zip 配对，输出仍为 DiffRow 视图/报告/导航零改动）、归一化流超 20 万字符自动降级行级对比并提示、字符级开启时三个空白选项置灰

src/renderer/src/App.tsx

@@ -95,7 +95,8 @@ export default function App(): ReactElement {
     trimWhitespace: false,
     ignoreCase: false,
     ignoreBlankLines: false,
-    ignoreAllWhitespace: false
+    ignoreAllWhitespace: false,
+    charMode: false
   })
   // 仅看差异：视图层过滤选项（不影响比较语义，也与报告导出无关，报告始终全量行）
   const [onlyDiff, setOnlyDiff] = useState(false)
@@ -212,6 +213,13 @@ export default function App(): ReactElement {
   // diff 计算已 worker 化：大输入后台计算（computing 期间 diff 为 null），小输入同步快路径
   const { diff, computing } = useDiff(paneL?.text ?? '', paneR?.text ?? '', options)
 
+  // 字符级对比因内容超限自动降级为行级时提示（依赖 diff 对象，同一结果只提示一次）
+  useEffect(() => {
+    if (diff?.charModeDowngraded) {
+      showToast('内容较大，字符级对比已自动降级为行级对比')
+    }
+  }, [diff, showToast])
+
   const rows = useMemo(() => diff?.rows ?? [], [diff])
   const changedRows = useMemo(() => rows.filter((r) => r.isChanged), [rows])
   const summary: DiffSummary = diff?.summary ?? EMPTY_SUMMARY
@@ -314,6 +322,10 @@ export default function App(): ReactElement {
     async (fmt: ReportFormat) => {
       // 计算中（diff 为 null）不导出：正常情况下导出按钮已禁用，此处兜底防御
       if (!diff) return
+      // 字符级对比降级时，报告头部按实际生效的行级语义描述（全部空白忽略 + 空行忽略）
+      const reportOptions: DiffOptions = diff.charModeDowngraded
+        ? { ...options, charMode: false, ignoreAllWhitespace: true, ignoreBlankLines: true }
+        : options
       const ctx: ReportContext = {
         leftName: paneL?.meta.name ?? '',
         rightName: paneR?.meta.name ?? '',
@@ -321,7 +333,7 @@ export default function App(): ReactElement {
         rightEncoding: paneR?.meta.encoding ?? '',
         leftPath: paneL?.path || undefined,
         rightPath: paneR?.path || undefined,
-        options
+        options: reportOptions
       }
       const content = buildReport(rows, ctx, summary, fmt)
       const defaultName = `DiffLens-report-${stamp()}.${REPORT_EXT[fmt]}`

src/renderer/src/__tests__/App.test.tsx

@@ -570,6 +570,111 @@ describe('App - F7 / Shift+F7 差异导航快捷键', () => {
   })
 })
 
+describe('App - 字符级对比', () => {
+  it('开启后跨行重组判为完全一致（行级对比的边界在此补全）', async () => {
+    window.api = mockApi({
+      openFile: async (side) =>
+        side === 'left'
+          ? { path: '/tmp/a.txt', name: 'a.txt', text: 'ab cd', encoding: 'UTF-8', binary: false }
+          : { path: '/tmp/b.txt', name: 'b.txt', text: 'ab\ncd', encoding: 'UTF-8', binary: false }
+    })
+    render(<App />)
+    fireEvent.click(screen.getByText('打开左侧'))
+    await screen.findByText('导出报告')
+    fireEvent.click(screen.getByText('打开右侧'))
+    await screen.findAllByText('b.txt')
+    // 默认行级对比：换行结构差异报“有差异”
+    expect(screen.getByText('有差异')).toBeInTheDocument()
+    // 开启字符级对比后：判为完全一致
+    fireEvent.click(screen.getByLabelText('字符级对比'))
+    expect(await screen.findByText('两文件内容完全一致')).toBeInTheDocument()
+  })
+
+  it('开启时三个空白选项被禁用', async () => {
+    window.api = mockApi()
+    render(<App />)
+    fireEvent.click(screen.getByText('打开左侧'))
+    await screen.findByText('导出报告')
+    expect(screen.getByLabelText('忽略行首尾空白')).toBeEnabled()
+    fireEvent.click(screen.getByLabelText('字符级对比'))
+    expect(screen.getByLabelText('忽略行首尾空白')).toBeDisabled()
+    expect(screen.getByLabelText('忽略空行')).toBeDisabled()
+    expect(screen.getByLabelText('忽略所有空白')).toBeDisabled()
+    expect(screen.getByLabelText('忽略大小写')).toBeEnabled()
+  })
+
+  it('内容超限时自动降级行级并给出提示', async () => {
+    // 1900 行 × 106 字符 ≈ 201,400 归一化字符（超过 20 万阈值）；
+    // 总行数 1901 未超过快路径阈值，同步计算即时降级
+    const big = Array.from({ length: 1900 }, () => 'a'.repeat(106)).join('\n')
+    window.api = mockApi({
+      openFile: async () => ({
+        path: '/tmp/big.txt',
+        name: 'big.txt',
+        text: big,
+        encoding: 'UTF-8',
+        binary: false
+      })
+    })
+    render(<App />)
+    fireEvent.click(screen.getByText('打开左侧'))
+    await screen.findByText('导出报告')
+    fireEvent.click(screen.getByLabelText('字符级对比'))
+    expect(await screen.findByText(/已自动降级为行级对比/)).toBeInTheDocument()
+  })
+
+  it('导出报告携带字符级对比说明', async () => {
+    let saved = ''
+    window.api = mockApi({
+      openFile: async () => ({
+        path: '/tmp/a.txt',
+        name: 'a.txt',
+        text: 'line1\nline2',
+        encoding: 'UTF-8',
+        binary: false
+      }),
+      saveReport: async (content: string) => {
+        saved = content
+        return { ok: true, path: 'C:/docs/r.txt' }
+      }
+    })
+    render(<App />)
+    fireEvent.click(screen.getByText('打开左侧'))
+    await screen.findByText('导出报告')
+    fireEvent.click(screen.getByLabelText('字符级对比'))
+    fireEvent.click(screen.getByText('导出报告'))
+    fireEvent.click(screen.getByText('纯文本'))
+    await screen.findByText(/报告已保存/)
+    expect(saved).toContain('比较选项：字符级对比（忽略全部空白与换行）')
+  })
+
+  it('降级后导出报告按实际生效的行级语义描述选项', async () => {
+    let saved = ''
+    const big = Array.from({ length: 1900 }, () => 'a'.repeat(106)).join('\n')
+    window.api = mockApi({
+      openFile: async (side) =>
+        side === 'left'
+          ? { path: '/tmp/big.txt', name: 'big.txt', text: big, encoding: 'UTF-8', binary: false }
+          : { path: '/tmp/b.txt', name: 'b.txt', text: 'b', encoding: 'UTF-8', binary: false },
+      saveReport: async (content: string) => {
+        saved = content
+        return { ok: true, path: 'C:/docs/r.txt' }
+      }
+    })
+    render(<App />)
+    fireEvent.click(screen.getByText('打开左侧'))
+    await screen.findByText('导出报告')
+    fireEvent.click(screen.getByText('打开右侧'))
+    await screen.findAllByText('b.txt')
+    fireEvent.click(screen.getByLabelText('字符级对比'))
+    await screen.findByText(/已自动降级为行级对比/)
+    fireEvent.click(screen.getByText('导出报告'))
+    fireEvent.click(screen.getByText('纯文本'))
+    await screen.findByText(/报告已保存/)
+    expect(saved).toContain('比较选项：忽略所有空白、忽略空行')
+  })
+})
+
 describe('App - 交换左右侧', () => {
   it('交换后左右面板文件互换', async () => {
     window.api = mockApi({

src/renderer/src/components/Toolbar.test.tsx

@@ -5,7 +5,7 @@ import { DiffSummary } from '../diff/diffEngine'
 
 const summary: DiffSummary = { changedLines: 3, inserted: 1, deleted: 1, modified: 1 }
 
-function setup(extra?: { computing?: boolean }) {
+function setup(extra?: { computing?: boolean; charMode?: boolean }) {
   const onOptionsChange = vi.fn()
   const onNav = vi.fn()
   const onExport = vi.fn()
@@ -13,7 +13,7 @@ function setup(extra?: { computing?: boolean }) {
   const onSwap = vi.fn()
   const utils = render(
     <Toolbar
-      options={{ trimWhitespace: false, ignoreCase: false, ignoreBlankLines: false, ignoreAllWhitespace: false }}
+      options={{ trimWhitespace: false, ignoreCase: false, ignoreBlankLines: false, ignoreAllWhitespace: false, charMode: extra?.charMode ?? false }}
       onOptionsChange={onOptionsChange}
       summary={summary}
       navIndex={0}
@@ -40,25 +40,51 @@ describe('Toolbar', () => {
   it('切换忽略大小写触发 onOptionsChange', () => {
     const { onOptionsChange } = setup()
     fireEvent.click(screen.getByLabelText('忽略大小写'))
-    expect(onOptionsChange).toHaveBeenCalledWith({ trimWhitespace: false, ignoreCase: true, ignoreBlankLines: false, ignoreAllWhitespace: false })
+    expect(onOptionsChange).toHaveBeenCalledWith({ trimWhitespace: false, ignoreCase: true, ignoreBlankLines: false, ignoreAllWhitespace: false, charMode: false })
   })
 
   it('切换忽略行首尾空白触发 onOptionsChange', () => {
     const { onOptionsChange } = setup()
     fireEvent.click(screen.getByLabelText('忽略行首尾空白'))
-    expect(onOptionsChange).toHaveBeenCalledWith({ trimWhitespace: true, ignoreCase: false, ignoreBlankLines: false, ignoreAllWhitespace: false })
+    expect(onOptionsChange).toHaveBeenCalledWith({ trimWhitespace: true, ignoreCase: false, ignoreBlankLines: false, ignoreAllWhitespace: false, charMode: false })
   })
 
   it('切换忽略空行触发 onOptionsChange', () => {
     const { onOptionsChange } = setup()
     fireEvent.click(screen.getByLabelText('忽略空行'))
-    expect(onOptionsChange).toHaveBeenCalledWith({ trimWhitespace: false, ignoreCase: false, ignoreBlankLines: true, ignoreAllWhitespace: false })
+    expect(onOptionsChange).toHaveBeenCalledWith({ trimWhitespace: false, ignoreCase: false, ignoreBlankLines: true, ignoreAllWhitespace: false, charMode: false })
   })
 
   it('切换忽略所有空白触发 onOptionsChange', () => {
     const { onOptionsChange } = setup()
     fireEvent.click(screen.getByLabelText('忽略所有空白'))
-    expect(onOptionsChange).toHaveBeenCalledWith({ trimWhitespace: false, ignoreCase: false, ignoreBlankLines: false, ignoreAllWhitespace: true })
+    expect(onOptionsChange).toHaveBeenCalledWith({ trimWhitespace: false, ignoreCase: false, ignoreBlankLines: false, ignoreAllWhitespace: true, charMode: false })
+  })
+
+  it('切换字符级对比触发 onOptionsChange', () => {
+    const { onOptionsChange } = setup()
+    fireEvent.click(screen.getByLabelText('字符级对比'))
+    expect(onOptionsChange).toHaveBeenCalledWith({ trimWhitespace: false, ignoreCase: false, ignoreBlankLines: false, ignoreAllWhitespace: false, charMode: true })
+  })
+
+  it('字符级对比开启时三个空白选项被禁用（语义已被包含）', () => {
+    setup({ charMode: true })
+    expect(screen.getByLabelText('忽略行首尾空白')).toBeDisabled()
+    expect(screen.getByLabelText('忽略空行')).toBeDisabled()
+    expect(screen.getByLabelText('忽略所有空白')).toBeDisabled()
+  })
+
+  it('字符级对比开启时忽略大小写仍可用', () => {
+    setup({ charMode: true })
+    expect(screen.getByLabelText('忽略大小写')).toBeEnabled()
+    expect(screen.getByLabelText('字符级对比')).toBeEnabled()
+  })
+
+  it('字符级对比关闭时空白选项恢复可用', () => {
+    setup()
+    expect(screen.getByLabelText('忽略行首尾空白')).toBeEnabled()
+    expect(screen.getByLabelText('忽略空行')).toBeEnabled()
+    expect(screen.getByLabelText('忽略所有空白')).toBeEnabled()
   })
 
   it('切换仅看差异触发 onOnlyDiffChange(true)', () => {

src/renderer/src/components/Toolbar.tsx

@@ -52,10 +52,18 @@ export default function Toolbar({
     <div className="toolbar">
       <div className="tool-group">
         <span className="tool-label">比较选项</span>
-        <label className="switch">
+        <label
+          className="switch"
+          title={
+            options.charMode
+              ? '已被“字符级对比”包含（字符级忽略全部空白与换行）'
+              : '忽略行首尾空白差异'
+          }
+        >
           <input
             type="checkbox"
             checked={options.trimWhitespace}
+            disabled={options.charMode}
             onChange={(e) => set({ trimWhitespace: e.target.checked })}
           />
           忽略行首尾空白
@@ -68,25 +76,49 @@ export default function Toolbar({
           />
           忽略大小写
         </label>
-        <label className="switch">
+        <label
+          className="switch"
+          title={
+            options.charMode
+              ? '已被“字符级对比”包含（字符级忽略全部空白与换行）'
+              : '忽略空行差异（两侧空白行互相判等）'
+          }
+        >
           <input
             type="checkbox"
             checked={options.ignoreBlankLines ?? false}
+            disabled={options.charMode}
             onChange={(e) => set({ ignoreBlankLines: e.target.checked })}
           />
           忽略空行
         </label>
         <label
           className="switch"
-          title="忽略行内全部空白（空格/制表符/全角空格），仅比较实际文字；换行结构仍参与对比"
+          title={
+            options.charMode
+              ? '已被“字符级对比”包含（字符级忽略全部空白与换行）'
+              : '忽略行内全部空白（空格/制表符/全角空格），仅比较实际文字；换行结构仍参与对比'
+          }
         >
           <input
             type="checkbox"
             checked={options.ignoreAllWhitespace ?? false}
+            disabled={options.charMode}
             onChange={(e) => set({ ignoreAllWhitespace: e.target.checked })}
           />
           忽略所有空白
         </label>
+        <label
+          className="switch"
+          title="空白与换行结构全部不参与判等，差异以字符粒度定位（跨行重组也能判等；超大内容自动降级行级对比）"
+        >
+          <input
+            type="checkbox"
+            checked={options.charMode ?? false}
+            onChange={(e) => set({ charMode: e.target.checked })}
+          />
+          字符级对比
+        </label>
       </div>
 
       <div className="tool-group">

src/renderer/src/diff/diffEngine.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest'
-import { computeDiff } from './diffEngine'
+import { computeDiff, CHAR_DIFF_MAX_CHARS } from './diffEngine'
 
 describe('computeDiff - 空文本', () => {
   it('空 vs 空 不产生任何行', () => {
@@ -249,4 +249,222 @@ describe('computeDiff - 行切分细节', () => {
     expect(rows[0].rowKind).toBe('unchanged')
     expect(summary.changedLines).toBe(0)
   })
+})
+
+describe('computeDiff - 字符级对比（判等）', () => {
+  it('跨行重组一致：换行位置不同判为一致（行级对比的边界在此补全）', () => {
+    const { summary } = computeDiff('ab cd', 'ab\ncd', { charMode: true })
+    expect(summary.changedLines).toBe(0)
+  })
+
+  it('空行数量差异不构成差异', () => {
+    const { summary } = computeDiff('a\n\nb', 'ab', { charMode: true })
+    expect(summary.changedLines).toBe(0)
+  })
+
+  it('行内空白差异不构成差异（隐含忽略所有空白）', () => {
+    const { summary } = computeDiff('a b\tc', 'abc', { charMode: true })
+    expect(summary.changedLines).toBe(0)
+  })
+
+  it('全角空格与中文内容正常判等', () => {
+    const { summary } = computeDiff('你好 世界', '你好世界', { charMode: true })
+    expect(summary.changedLines).toBe(0)
+  })
+
+  it('与忽略大小写组合生效', () => {
+    const { summary } = computeDiff('AB CD', 'ab\ncd', { charMode: true, ignoreCase: true })
+    expect(summary.changedLines).toBe(0)
+  })
+
+  it('实际字符差异仍被识别', () => {
+    const { summary } = computeDiff('abc', 'abd', { charMode: true })
+    expect(summary.changedLines).toBe(1)
+  })
+
+  it('完全一致且行结构相同：常规 unchanged 配对', () => {
+    const { rows, summary } = computeDiff('a\nb', 'a\nb', { charMode: true })
+    expect(summary.changedLines).toBe(0)
+    expect(rows).toHaveLength(2)
+    expect(rows[0]).toMatchObject({ rowKind: 'unchanged' })
+    expect(rows[0].left.lineNo).toBe(1)
+    expect(rows[0].right.lineNo).toBe(1)
+    expect(rows[1].left.lineNo).toBe(2)
+    expect(rows[1].right.lineNo).toBe(2)
+  })
+
+  it('一致但行数不等：短侧空槽仍为 unchanged，行数取较大侧', () => {
+    const { rows, summary } = computeDiff('a\n\nb', 'ab', { charMode: true })
+    expect(summary.changedLines).toBe(0)
+    expect(rows).toHaveLength(3)
+    expect(rows[1].left.lineNo).toBe(2)
+    expect(rows[1].right.lineNo).toBeNull()
+    expect(rows.every((r) => r.rowKind === 'unchanged')).toBe(true)
+  })
+
+  it('展示文本始终为原始行（不因归一化改写）', () => {
+    const { rows } = computeDiff('  a  b ', 'a b', { charMode: true })
+    expect(rows[0].left.text).toBe('  a  b ')
+    expect(rows[0].right.text).toBe('a b')
+  })
+})
+
+describe('computeDiff - 字符级对比（差异定位与回映射）', () => {
+  it('行内替换配对 modified，segs 含 common/删除/新增段', () => {
+    const { rows, summary } = computeDiff('cat', 'cap', { charMode: true })
+    expect(summary.modified).toBe(1)
+    const m = rows.find((r) => r.rowKind === 'modified')!
+    expect(m.left.segs).not.toBeNull()
+    expect(m.right.segs).not.toBeNull()
+    expect(m.left.segs!.some((s) => s.kind === 'common' && s.text === 'ca')).toBe(true)
+    expect(m.left.segs!.some((s) => s.kind === 'delete' && s.text.includes('t'))).toBe(true)
+    expect(m.right.segs!.some((s) => s.kind === 'insert' && s.text.includes('p'))).toBe(true)
+  })
+
+  it('行内删除显示为 modified（对侧行回拉），删除字符精确高亮', () => {
+    const { rows, summary } = computeDiff('abcXYZdef', 'abcdef', { charMode: true })
+    expect(summary.modified).toBe(1)
+    expect(summary.deleted).toBe(0)
+    const m = rows.find((r) => r.rowKind === 'modified')!
+    expect(m.left.lineNo).toBe(1)
+    expect(m.right.lineNo).toBe(1)
+    expect(m.left.segs!.some((s) => s.kind === 'delete' && s.text.includes('XYZ'))).toBe(true)
+    // 右侧无新增字符：整行 common
+    expect(m.right.segs!.every((s) => s.kind === 'common')).toBe(true)
+  })
+
+  it('行内新增显示为 modified，新增字符精确高亮', () => {
+    const { rows, summary } = computeDiff('abcdef', 'abcXYZdef', { charMode: true })
+    expect(summary.modified).toBe(1)
+    expect(summary.inserted).toBe(0)
+    const m = rows.find((r) => r.rowKind === 'modified')!
+    expect(m.right.segs!.some((s) => s.kind === 'insert' && s.text.includes('XYZ'))).toBe(true)
+    expect(m.left.segs!.every((s) => s.kind === 'common')).toBe(true)
+  })
+
+  it('行尾追加（流尾跨界）同样回拉配对 modified', () => {
+    const { rows, summary } = computeDiff('abc', 'abcXYZ', { charMode: true })
+    expect(summary.modified).toBe(1)
+    const m = rows.find((r) => r.rowKind === 'modified')!
+    expect(m.right.segs!.some((s) => s.kind === 'insert' && s.text.includes('XYZ'))).toBe(true)
+  })
+
+  it('行首插入（流首跨界）同样回拉配对 modified', () => {
+    const { summary } = computeDiff('abc', 'XYZabc', { charMode: true })
+    expect(summary.modified).toBe(1)
+  })
+
+  it('整行删除（跨行不跨界）保持 removed 语义，不误配对', () => {
+    const { rows, summary } = computeDiff('aa\nbb\ncc', 'aa\ncc', { charMode: true })
+    expect(summary.changedLines).toBe(1)
+    expect(summary.deleted).toBe(1)
+    const rem = rows.find((r) => r.rowKind === 'removed')!
+    expect(rem.left.lineNo).toBe(2)
+    expect(rem.left.text).toBe('bb')
+    // 其余行锚定配对
+    const anchor = rows.filter((r) => r.rowKind === 'unchanged')
+    expect(anchor.map((r) => [r.left.lineNo, r.right.lineNo])).toEqual([
+      [1, 1],
+      [3, 2]
+    ])
+  })
+
+  it('整行新增保持 added 语义', () => {
+    const { rows, summary } = computeDiff('aa\ncc', 'aa\nbb\ncc', { charMode: true })
+    expect(summary.inserted).toBe(1)
+    const add = rows.find((r) => r.rowKind === 'added')!
+    expect(add.right.lineNo).toBe(2)
+    expect(add.right.text).toBe('bb')
+  })
+
+  it('多个独立修改块各自配对 modified，锚行穿插', () => {
+    const { rows, summary } = computeDiff('a\nX\nb\nY\nc', 'a\nZ\nb\nW\nc', { charMode: true })
+    expect(summary.modified).toBe(2)
+    expect(summary.changedLines).toBe(2)
+    const mods = rows.filter((r) => r.rowKind === 'modified')
+    expect(mods[0].left.text).toBe('X')
+    expect(mods[0].right.text).toBe('Z')
+    expect(mods[1].left.text).toBe('Y')
+    expect(mods[1].right.text).toBe('W')
+    expect(rows.filter((r) => r.rowKind === 'unchanged')).toHaveLength(3)
+  })
+
+  it('删除文本中间的空白归入删除段（空白继承规则）', () => {
+    const { rows, summary } = computeDiff('hello big world', 'hello world', { charMode: true })
+    expect(summary.modified).toBe(1)
+    const m = rows.find((r) => r.rowKind === 'modified')!
+    const del = m.left.segs!.find((s) => s.kind === 'delete')!
+    // 'big' 与其后空白一并划入删除段
+    expect(del.text).toContain('big')
+  })
+
+  it('跨行变更配对：共享字符行锚定，变更行配 modified', () => {
+    const { rows, summary } = computeDiff('ab', 'a\nx', { charMode: true })
+    expect(summary.changedLines).toBe(1)
+    expect(summary.modified).toBe(1)
+    const m = rows.find((r) => r.rowKind === 'modified')!
+    expect(m.left.text).toBe('ab')
+    expect(m.right.text).toBe('x')
+    expect(m.left.segs!.some((s) => s.kind === 'delete' && s.text.includes('b'))).toBe(true)
+    // 双侧行号序列各自单调不减（空槽跳过）
+    const lNos = rows.map((r) => r.left.lineNo).filter((n): n is number => n !== null)
+    const rNos = rows.map((r) => r.right.lineNo).filter((n): n is number => n !== null)
+    expect([...lNos].sort((a, b) => a - b)).toEqual(lNos)
+    expect([...rNos].sort((a, b) => a - b)).toEqual(rNos)
+  })
+
+  it('空 vs 非空全部为新增行', () => {
+    const { rows, summary } = computeDiff('', 'a\nb', { charMode: true })
+    expect(summary.inserted).toBe(2)
+    expect(rows.every((r) => r.rowKind === 'added')).toBe(true)
+  })
+
+  it('空 vs 空 不产生任何行', () => {
+    const { rows, summary } = computeDiff('', '', { charMode: true })
+    expect(rows).toHaveLength(0)
+    expect(summary.changedLines).toBe(0)
+  })
+
+  it('忽略大小写只影响判等，diff 定位按原字符', () => {
+    const { summary } = computeDiff('Cat', 'car', { charMode: true, ignoreCase: true })
+    // 'ca' 一致，t 与 r 为一处修改
+    expect(summary.modified).toBe(1)
+  })
+})
+
+describe('computeDiff - 字符级对比（超限降级）', () => {
+  it('归一化流超限自动降级行级并携带降级标志', () => {
+    const left = 'a'.repeat(100001)
+    const right = 'a'.repeat(100001)
+    const result = computeDiff(left, right, { charMode: true })
+    expect(result.charModeDowngraded).toBe(true)
+    // 降级行级采用“忽略所有空白 + 忽略空行”语义：全 a 单行仍判一致
+    expect(result.summary.changedLines).toBe(0)
+  })
+
+  it('降级结果与等效行级选项直接计算一致', () => {
+    const left = 'a'.repeat(100001) + '\nb'
+    const right = 'a'.repeat(100001) + '\nc'
+    const result = computeDiff(left, right, { charMode: true })
+    expect(result.charModeDowngraded).toBe(true)
+    const direct = computeDiff(left, right, {
+      ignoreAllWhitespace: true,
+      ignoreBlankLines: true
+    })
+    expect(result.summary).toEqual(direct.summary)
+  })
+
+  it('恰好阈值不降级', () => {
+    const half = CHAR_DIFF_MAX_CHARS / 2
+    const { summary, charModeDowngraded } = computeDiff('a'.repeat(half), 'a'.repeat(half), {
+      charMode: true
+    })
+    expect(charModeDowngraded).toBeUndefined()
+    expect(summary.changedLines).toBe(0)
+  })
+
+  it('未开启 charMode 时不携带降级标志', () => {
+    const { charModeDowngraded } = computeDiff('a', 'b', {})
+    expect(charModeDowngraded).toBeUndefined()
+  })
 })

src/renderer/src/diff/diffEngine.ts

@@ -1,4 +1,4 @@
-import { diffArrays, diffWordsWithSpace } from 'diff'
+import { diffArrays, diffChars, diffWordsWithSpace } from 'diff'
 
 /** 词级分段类型 */
 export type SegKind = 'common' | 'insert' | 'delete'
@@ -43,11 +43,19 @@ export interface DiffOptions {
   ignoreBlankLines?: boolean
   /** 忽略全部行内空白（空格/制表符/全角空格等），仅比较实际文字内容；换行结构仍参与对比 */
   ignoreAllWhitespace?: boolean
+  /**
+   * 字符级对比：全部空白与换行结构都不参与判等，两侧全文归一化为字符流做 diff，
+   * 差异以字符粒度回映射到行（跨行重组也能判等）。隐含 ignoreAllWhitespace 的全部语义；
+   * 归一化流超限（CHAR_DIFF_MAX_CHARS）时自动降级为行级对比并置 charModeDowngraded。
+   */
+  charMode?: boolean
 }
 
 export interface DiffResult {
   rows: DiffRow[]
   summary: DiffSummary
+  /** 字符级对比因内容超限自动降级为行级对比时为 true（供界面与报告提示） */
+  charModeDowngraded?: boolean
 }
 
 function emptyLine(): SideCell {
@@ -93,13 +101,39 @@ export function splitLines(text: string): string[] {
 }
 
 /**
- * 计算文本差异。
- * diffArrays 以“归一化行”做行级 LCS，得到增/删/同；
+ * 计算文本差异（统一入口）。
+ * charMode 开启时走字符级对比（超限自动降级行级并携带降级标志）；否则走行级对比。
+ */
+export function computeDiff(
+  leftText: string,
+  rightText: string,
+  options: DiffOptions = {}
+): DiffResult {
+  if (options.charMode) {
+    const charResult = computeCharDiff(leftText, rightText, options)
+    if (charResult) return charResult
+    // 归一化流超限：降级为行级对比，选项取字符级语义的最接近子集
+    // （全部空白忽略 + 空行忽略；换行结构差异是行级架构无法消除的边界）
+    const result = computeLineDiff(leftText, rightText, {
+      ...options,
+      charMode: false,
+      ignoreAllWhitespace: true,
+      ignoreBlankLines: true,
+      trimWhitespace: false
+    })
+    result.charModeDowngraded = true
+    return result
+  }
+  return computeLineDiff(leftText, rightText, options)
+}
+
+/**
+ * 行级对比：diffArrays 以“归一化行”做行级 LCS，得到增/删/同；
  * 删除段与新增段配对为“修改”行并做词级内联高亮。
  * trimWhitespace / ignoreCase / ignoreAllWhitespace 只影响“是否判等”，展示文本始终取原始行；
  * ignoreBlankLines 则把空白行从比较与视图中整体剔除（行号保留原值）。
  */
-export function computeDiff(
+function computeLineDiff(
   leftText: string,
   rightText: string,
   options: DiffOptions = {}
@@ -246,5 +280,363 @@ export function computeDiff(
     modified: rows.filter((r) => r.rowKind === 'modified').length
   }
 
+  return { rows, summary }
+}
+
+/** ============ 字符级对比 ============ */
+
+/**
+ * 字符级对比的字符总量上限（两侧归一化流合计）：
+ * diffChars 为 O(ND)，超限后计算可能耗时失控，自动降级为行级对比。
+ */
+export const CHAR_DIFF_MAX_CHARS = 200000
+
+/** 空白字符判定：与 ignoreAllWhitespace 的 \s 语义一致（含换行、制表符、全角空格） */
+function isWsChar(ch: string): boolean {
+  return /\s/.test(ch)
+}
+
+/** 归一化字符流：剔除全部空白后的连续字符，并记录每个字符的原始行号与码点列号 */
+interface CharStream {
+  /** 归一化字符连成的字符串（供 diffChars 直接消费） */
+  text: string
+  /** 与 text 逐字符对应的原始行号（1 基） */
+  lineNos: number[]
+  /** 与 text 逐字符对应的原始码点列号（0 基） */
+  cols: number[]
+}
+
+function buildCharStream(lines: string[], norm: (ch: string) => string): CharStream {
+  const chars: string[] = []
+  const lineNos: number[] = []
+  const cols: number[] = []
+  lines.forEach((text, i) => {
+    let col = 0
+    for (const ch of text) {
+      if (!isWsChar(ch)) {
+        chars.push(norm(ch))
+        lineNos.push(i + 1)
+        cols.push(col)
+      }
+      col++
+    }
+  })
+  return { text: chars.join(''), lineNos, cols }
+}
+
+/**
+ * 按行内字符状态重建高亮分段（modified 行的 segs）：
+ * 非空白字符查状态表（缺省 common）；空白字符继承前一个非空白字符的状态（行首空白按 common），
+ * 保证被删除文本中间的空白归入删除段、新增文本中间的空白归入新增段。
+ */
+function charSegs(text: string, stat: Map<number, number> | undefined): Seg[] {
+  const segs: Seg[] = []
+  let cur: SegKind | null = null
+  let buf = ''
+  let lastStat = 0
+  let col = 0
+  for (const ch of text) {
+    let st: number
+    if (isWsChar(ch)) {
+      st = lastStat
+    } else {
+      st = stat?.get(col) ?? 0
+      lastStat = st
+    }
+    const kind: SegKind = st === 1 ? 'delete' : st === 2 ? 'insert' : 'common'
+    if (kind !== cur) {
+      if (cur !== null) segs.push({ text: buf, kind: cur })
+      cur = kind
+      buf = ch
+    } else {
+      buf += ch
+    }
+    col++
+  }
+  if (cur !== null) segs.push({ text: buf, kind: cur })
+  return segs
+}
+
+/**
+ * 字符级对比：两侧全文归一化为字符流 → diffChars 对齐 → 字符差异回映射为 DiffRow。
+ *
+ * 回映射规则（输出仍为 DiffRow，视图/报告/导航零改动）：
+ * - 含变更（删除/新增）字符的行为“变更行”（跨界行——既有 common 又有变更字符——也划归变更行，
+ *   其 common 部分在 modified 行的 segs 中以 common 段呈现，信息不丢失）；
+ * - 连续变更行组配对：等长配 modified（segs 按整行重建），多余侧降级 removed / added（与行级 commitModified 同构）；
+ * - 变更组之间的行（含纯空白行）为“锚行”，左右按序 zip 配对输出 unchanged，短侧空槽仍标 unchanged
+ *   （字符级语义下纯空白行不构成差异）。
+ *
+ * 内容超限（CHAR_DIFF_MAX_CHARS）返回 null，由调用方降级行级。
+ */
+function computeCharDiff(
+  leftText: string,
+  rightText: string,
+  options: DiffOptions
+): DiffResult | null {
+  const leftOrig = splitLines(leftText)
+  const rightOrig = splitLines(rightText)
+  // 大小写归一化在构造流时完成：toLowerCase 展开为多字符的字符（如 İ→i̇）退回原样，
+  // 避免归一化后字符数变化破坏流索引
+  const normCh = (ch: string): string => {
+    if (!options.ignoreCase) return ch
+    const lo = ch.toLowerCase()
+    return lo.length === 1 ? lo : ch
+  }
+  const left = buildCharStream(leftOrig, normCh)
+  const right = buildCharStream(rightOrig, normCh)
+  if (left.text.length + right.text.length > CHAR_DIFF_MAX_CHARS) return null
+
+  const parts = diffChars(left.text, right.text)
+
+  // 流区间块序列：common 为 eq 块，连续 removed/added 合并为 ne 块（与行级 parts 循环同构）
+  interface Block {
+    eq: boolean
+    l0: number
+    l1: number
+    r0: number
+    r1: number
+    /** removed-only 时回拉的对侧配对行（见下方预处理说明） */
+    pullR?: number
+    /** added-only 时回拉的对侧配对行 */
+    pullL?: number
+  }
+  const blocks: Block[] = []
+  let li = 0
+  let ri = 0
+  for (const part of parts) {
+    const len = part.value.length
+    const isEq = !part.added && !part.removed
+    const last = blocks[blocks.length - 1]
+    if (!last || last.eq !== isEq) {
+      blocks.push({ eq: isEq, l0: li, l1: li, r0: ri, r1: ri })
+    }
+    const b = blocks[blocks.length - 1]
+    if (isEq) {
+      b.l1 += len
+      b.r1 += len
+      li += len
+      ri += len
+    } else if (part.removed) {
+      b.l1 += len
+      li += len
+    } else {
+      b.r1 += len
+      ri += len
+    }
+  }
+
+  // ne 块字符状态与涉及行集合（跨界行划归变更组）
+  const changedL = new Set<number>()
+  const changedR = new Set<number>()
+  for (const b of blocks) {
+    if (b.eq) continue
+    for (let i = b.l0; i < b.l1; i++) changedL.add(left.lineNos[i])
+    for (let i = b.r0; i < b.r1; i++) changedR.add(right.lineNos[i])
+  }
+
+  // 已划归变更组的行（含跨界行与回拉行），锚段输出时排除
+  const pairedL = new Set(changedL)
+  const pairedR = new Set(changedR)
+
+  // 单侧变更块（removed-only / added-only）的对侧行回拉：
+  // 变更行与相邻 eq 块同行（跨界延续，如行内删除 abcXYZdef → abcdef）时，
+  // 把对侧对齐行拉入变更组配对，使行内增删显示为 modified（字符高亮）而非整行 removed/added；
+  // 跨行整行增删（变更行与相邻 eq 块不同行）不回拉，维持 removed/added 语义。
+  for (let bi = 0; bi < blocks.length; bi++) {
+    const b = blocks[bi]
+    if (b.eq) continue
+    const pe = bi > 0 && blocks[bi - 1].eq ? blocks[bi - 1] : undefined
+    const nx = bi + 1 < blocks.length && blocks[bi + 1].eq ? blocks[bi + 1] : undefined
+    if (b.l0 < b.l1 && b.r0 === b.r1) {
+      // removed-only：左侧变更行跨界时回拉右侧对齐行
+      const firstL = left.lineNos[b.l0]
+      const lastL = left.lineNos[b.l1 - 1]
+      const crossL =
+        (pe !== undefined && firstL === left.lineNos[pe.l1 - 1]) ||
+        (nx !== undefined && lastL === left.lineNos[nx.l0])
+      if (!crossL) continue
+      const rn =
+        b.r0 < right.lineNos.length
+          ? right.lineNos[b.r0]
+          : right.lineNos.length > 0
+            ? right.lineNos[right.lineNos.length - 1]
+            : 0
+      if (rn < 1) continue
+      const crossR =
+        (pe !== undefined && rn === right.lineNos[pe.r1 - 1]) ||
+        (nx !== undefined && rn === right.lineNos[nx.r0])
+      if (crossR) {
+        b.pullR = rn
+        pairedR.add(rn)
+      }
+    } else if (b.r0 < b.r1 && b.l0 === b.l1) {
+      // added-only：右侧变更行跨界时回拉左侧对齐行
+      const firstR = right.lineNos[b.r0]
+      const lastR = right.lineNos[b.r1 - 1]
+      const crossR =
+        (pe !== undefined && firstR === right.lineNos[pe.r1 - 1]) ||
+        (nx !== undefined && lastR === right.lineNos[nx.r0])
+      if (!crossR) continue
+      const ln =
+        b.l0 < left.lineNos.length
+          ? left.lineNos[b.l0]
+          : left.lineNos.length > 0
+            ? left.lineNos[left.lineNos.length - 1]
+            : 0
+      if (ln < 1) continue
+      const crossL =
+        (pe !== undefined && ln === left.lineNos[pe.l1 - 1]) ||
+        (nx !== undefined && ln === left.lineNos[nx.l0])
+      if (crossL) {
+        b.pullL = ln
+        pairedL.add(ln)
+      }
+    }
+  }
+
+  // 行内变更字符的列位状态（行号 → 列号 → 1 删除 / 2 新增），供 segs 重建
+  const statByLineL = new Map<number, Map<number, number>>()
+  const statByLineR = new Map<number, Map<number, number>>()
+  for (const b of blocks) {
+    if (b.eq) continue
+    for (let i = b.l0; i < b.l1; i++) {
+      const ln = left.lineNos[i]
+      let m = statByLineL.get(ln)
+      if (!m) {
+        m = new Map()
+        statByLineL.set(ln, m)
+      }
+      m.set(left.cols[i], 1)
+    }
+    for (let i = b.r0; i < b.r1; i++) {
+      const rn = right.lineNos[i]
+      let m = statByLineR.get(rn)
+      if (!m) {
+        m = new Map()
+        statByLineR.set(rn, m)
+      }
+      m.set(right.cols[i], 2)
+    }
+  }
+
+  let rowSeq = 0
+  const rows: DiffRow[] = []
+  let pendingL: number[] = []
+  let pendingR: number[] = []
+
+  /** 变更行组配对输出（与行级 commitModified 同构：等长 modified / 多余降级 removed·added） */
+  const flushChange = (): void => {
+    const n = Math.max(pendingL.length, pendingR.length)
+    for (let i = 0; i < n; i++) {
+      const ln = pendingL[i]
+      const rn = pendingR[i]
+      if (ln !== undefined && rn !== undefined) {
+        rows.push({
+          id: `r${rowSeq++}`,
+          rowKind: 'modified',
+          isChanged: true,
+          left: {
+            lineNo: ln,
+            text: leftOrig[ln - 1],
+            segs: charSegs(leftOrig[ln - 1], statByLineL.get(ln))
+          },
+          right: {
+            lineNo: rn,
+            text: rightOrig[rn - 1],
+            segs: charSegs(rightOrig[rn - 1], statByLineR.get(rn))
+          }
+        })
+      } else if (ln !== undefined) {
+        rows.push({
+          id: `r${rowSeq++}`,
+          rowKind: 'removed',
+          isChanged: true,
+          left: { lineNo: ln, text: leftOrig[ln - 1], segs: null },
+          right: emptyLine()
+        })
+      } else if (rn !== undefined) {
+        rows.push({
+          id: `r${rowSeq++}`,
+          rowKind: 'added',
+          isChanged: true,
+          left: emptyLine(),
+          right: { lineNo: rn, text: rightOrig[rn - 1], segs: null }
+        })
+      }
+    }
+    pendingL = []
+    pendingR = []
+  }
+
+  /** 锚行组按序 zip 配对输出 unchanged（短侧空槽，纯空白行不构成差异） */
+  const emitAnchors = (la: number[], ra: number[]): void => {
+    const n = Math.max(la.length, ra.length)
+    for (let i = 0; i < n; i++) {
+      const ln = la[i] ?? null
+      const rn = ra[i] ?? null
+      rows.push({
+        id: `r${rowSeq++}`,
+        rowKind: 'unchanged',
+        isChanged: false,
+        left: ln === null ? emptyLine() : { lineNo: ln, text: leftOrig[ln - 1], segs: null },
+        right: rn === null ? emptyLine() : { lineNo: rn, text: rightOrig[rn - 1], segs: null }
+      })
+    }
+  }
+
+  // 行游标推进：锚段右边界 = 下一 ne 块首字符行 - 1（流尽则为文件末行）
+  let lCursor = 1
+  let rCursor = 1
+  for (const b of blocks) {
+    if (b.eq) {
+      flushChange()
+      const lEnd = b.l1 < left.lineNos.length ? left.lineNos[b.l1] - 1 : leftOrig.length
+      const rEnd = b.r1 < right.lineNos.length ? right.lineNos[b.r1] - 1 : rightOrig.length
+      const la: number[] = []
+      for (let ln = lCursor; ln <= lEnd; ln++) {
+        if (!pairedL.has(ln)) la.push(ln)
+      }
+      const ra: number[] = []
+      for (let rn = rCursor; rn <= rEnd; rn++) {
+        if (!pairedR.has(rn)) ra.push(rn)
+      }
+      emitAnchors(la, ra)
+      lCursor = lEnd + 1
+      rCursor = rEnd + 1
+    } else {
+      // 变更行收集（ne 块内行号单调不减，尾去重即可）；单侧变更块带上回拉的对侧配对行
+      for (let i = b.l0; i < b.l1; i++) {
+        const ln = left.lineNos[i]
+        if (pendingL[pendingL.length - 1] !== ln) pendingL.push(ln)
+      }
+      for (let i = b.r0; i < b.r1; i++) {
+        const rn = right.lineNos[i]
+        if (pendingR[pendingR.length - 1] !== rn) pendingR.push(rn)
+      }
+      if (b.pullR !== undefined && pendingR.length === 0) pendingR.push(b.pullR)
+      if (b.pullL !== undefined && pendingL.length === 0) pendingL.push(b.pullL)
+    }
+  }
+  flushChange()
+
+  // 尾部剩余行（最后一块之后的空白行/未覆盖行）按锚行输出
+  const tailLa: number[] = []
+  for (let ln = lCursor; ln <= leftOrig.length; ln++) {
+    if (!pairedL.has(ln)) tailLa.push(ln)
+  }
+  const tailRa: number[] = []
+  for (let rn = rCursor; rn <= rightOrig.length; rn++) {
+    if (!pairedR.has(rn)) tailRa.push(rn)
+  }
+  emitAnchors(tailLa, tailRa)
+
+  const summary: DiffSummary = {
+    changedLines: rows.filter((r) => r.isChanged).length,
+    inserted: rows.filter((r) => r.rowKind === 'added').length,
+    deleted: rows.filter((r) => r.rowKind === 'removed').length,
+    modified: rows.filter((r) => r.rowKind === 'modified').length
+  }
+
   return { rows, summary }
 }

src/renderer/src/diff/report.test.ts

@@ -183,6 +183,18 @@ describe('plainOptions - 比较选项描述', () => {
   it('忽略所有空白遮蔽行首尾空白（超集不重复列出）', () => {
     expect(plainOptions({ ignoreAllWhitespace: true, trimWhitespace: true })).toBe('忽略所有空白')
   })
+
+  it('字符级对比单独描述并遮蔽全部空白类选项', () => {
+    expect(
+      plainOptions({ charMode: true, trimWhitespace: true, ignoreAllWhitespace: true, ignoreBlankLines: true })
+    ).toBe('字符级对比（忽略全部空白与换行）')
+  })
+
+  it('字符级对比与忽略大小写组合列出', () => {
+    expect(plainOptions({ charMode: true, ignoreCase: true })).toBe(
+      '字符级对比（忽略全部空白与换行）、忽略大小写'
+    )
+  })
 })
 
 describe('报告头部比较选项说明', () => {

src/renderer/src/diff/report.ts

@@ -120,6 +120,12 @@ export function plainSummary(summary: DiffSummary): string {
 
 /** 已生效比较选项的人话描述（报告头部展示；无选项生效时说明为严格对比） */
 export function plainOptions(options?: DiffOptions): string {
+  // 字符级对比为最强空白语义（全部空白与换行都不参与判等），单独描述并遮蔽空白类子选项
+  if (options?.charMode) {
+    const on = ['字符级对比（忽略全部空白与换行）']
+    if (options.ignoreCase) on.push('忽略大小写')
+    return on.join('、')
+  }
   const on: string[] = []
   // 忽略所有空白为行首尾空白的超集，同时开启时只列前者，避免误导
   if (options?.ignoreAllWhitespace) on.push('忽略所有空白')