feat(ui): 权限确认对话框支持 Diff 预览

- 添加 Diff 按钮，点击可展开/折叠文件变更预览
- Server 端生成 diff 信息并传递到前端
- 默认折叠，用户可按需查看

packages/server/src/permission/handler.ts

@@ -9,6 +9,8 @@ import type {
   PermissionRequestPayload,
   PermissionDisplayContext,
   ServerMessage,
+  DiffInfo,
+  DiffHunkInfo,
 } from '../types.js';
 import { inferPermissionType } from '@ai-assistant/core';
 import type { PermissionDecision, PermissionContext, PermissionType } from '@ai-assistant/core';
@@ -79,6 +81,73 @@ function isAutoApproved(sessionId: string, ctx: PermissionContext): boolean {
   return false;
 }
 
+/**
+ * 生成简单的行级别 diff 信息
+ * 用于在权限确认对话框中显示文件变更预览
+ */
+function generateDiffInfo(oldContent: string | undefined, newContent: string | undefined): DiffInfo | undefined {
+  // 如果没有内容，无法生成 diff
+  if (newContent === undefined) {
+    return undefined;
+  }
+
+  const isNew = !oldContent;
+  const oldLines = oldContent ? oldContent.split('\n') : [];
+  const newLines = newContent.split('\n');
+
+  // 简单的行级别 diff
+  const lines: DiffHunkInfo['lines'] = [];
+  let additions = 0;
+  let deletions = 0;
+
+  if (isNew) {
+    // 新文件：所有行都是添加
+    newLines.forEach((line, index) => {
+      lines.push({
+        type: 'add',
+        lineNumber: index + 1,
+        content: line,
+      });
+      additions++;
+    });
+  } else {
+    // 编辑：显示删除和添加
+    // 对于 edit_file（search-replace），oldContent 是被替换的部分，newContent 是替换后的部分
+    oldLines.forEach((line, index) => {
+      lines.push({
+        type: 'remove',
+        lineNumber: index + 1,
+        content: line,
+      });
+      deletions++;
+    });
+    newLines.forEach((line, index) => {
+      lines.push({
+        type: 'add',
+        lineNumber: index + 1,
+        content: line,
+      });
+      additions++;
+    });
+  }
+
+  // 构建单个 hunk
+  const hunk: DiffHunkInfo = {
+    oldStart: 1,
+    oldCount: oldLines.length,
+    newStart: 1,
+    newCount: newLines.length,
+    lines,
+  };
+
+  return {
+    isNew,
+    additions,
+    deletions,
+    hunks: [hunk],
+  };
+}
+
 /**
  * 构建权限请求显示上下文
  * 将 Core 的完整 PermissionContext 转换为用于前端显示的精简格式
@@ -135,11 +204,18 @@ export function createServerPermissionCallback(sessionId: string) {
     const permissionType = inferPermissionType(permCtx);
     const context = buildDisplayContext(permCtx);
 
+    // 为文件操作生成 diff
+    let diff: DiffInfo | undefined;
+    if (permissionType === 'file' && (permCtx.fileOperation === 'write' || permCtx.fileOperation === 'edit')) {
+      diff = generateDiffInfo(permCtx.oldContent, permCtx.newContent);
+    }
+
     // 构建请求 payload
     const payload: PermissionRequestPayload = {
       requestId,
       permissionType,
       context,
+      diff,
     };
 
     // 发送权限请求到客户端