feat(ai): diff弹窗文档对比高亮 + 二次修改未弹窗修复

- 引入diff库，实现字符级差异比对
- diffModal左右两侧增加diff高亮：左侧删除内容标红，右侧新增内容标绿
- systemPrompt增加绝对强制条款：无论指令多小都必须返回updatedHtml
- 前端校验兜底：修改模式下未返回updatedHtml时在聊天面板给出提示
- confirmAiInjection注入前清理diff高亮span，避免污染编辑器

src/pages/ReportEditor.tsx

@@ -12,6 +12,7 @@ import { User, Report, Template, CapturedFrame, SystemSettings, FormField, DEFAU
 import { defaultReportContent } from '../utils/defaultContent';
 import { printDocument } from '../utils/print';
 import { storage } from '../utils/storage';
+import { diffChars } from 'diff';
 
 export default function ReportEditor() {
   const navigate = useNavigate();
@@ -823,6 +824,28 @@ export default function ReportEditor() {
     }).filter(r => r.id);
   };
 
+  const stripHtml = (html: string): string => {
+    const tmp = document.createElement('div');
+    tmp.innerHTML = html.replace(/<\/p>/gi, '</p>\n').replace(/<br\s*\/?>/gi, '\n');
+    return (tmp.innerText || tmp.textContent || '').trim();
+  };
+
+  const computeDiffHtml = (oldText: string, newText: string, side: 'left' | 'right'): string => {
+    const diffs = diffChars(oldText, newText);
+    let html = '';
+    for (const part of diffs) {
+      let value = part.value.replace(/</g, '&lt;').replace(/>/g, '&gt;').replace(/\n/g, '<br>');
+      if (side === 'left' && part.removed) {
+        html += `<span class="diff-removed" style="background-color:#fee2e2;color:#dc2626;text-decoration:line-through;">${value}</span>`;
+      } else if (side === 'right' && part.added) {
+        html += `<span class="diff-added" style="background-color:#dcfce7;color:#16a34a;font-weight:500;">${value}</span>`;
+      } else if (!part.added && !part.removed) {
+        html += value;
+      }
+    }
+    return html;
+  };
+
   const toggleListening = () => {
     if (isListening) {
       setIsListening(false);
@@ -952,6 +975,9 @@ export default function ReportEditor() {
       if (responseJson.reply) {
         setChatMessages(prev => [...prev, { id: Date.now().toString(), role: 'model', content: responseJson.reply }]);
       }
+      if (aiModifyEnabled && !responseJson.updatedHtml) {
+        setChatMessages(prev => [...prev, { id: Date.now().toString(), role: 'model', content: '【系统提示】AI 未能生成修改内容，请尝试重新描述您的需求。' }]);
+      }
       if (responseJson.updatedHtml && aiModifyEnabled) {
         let cleanHtml = responseJson.updatedHtml;
         cleanHtml = cleanHtml.replace(/<br\s*\/?>/gi, '');
@@ -981,6 +1007,7 @@ export default function ReportEditor() {
 
   const confirmAiInjection = (newHtml: string, regionId: string) => {
     if (!editorRef.current) return;
+    const cleanHtml = newHtml.replace(/<span class="diff-(added|removed)"[^>]*>(.*?)<\/span>/gi, '$2');
     const targetContent = editorRef.current.querySelector(`.ai-region[data-ai-id="${regionId}"] .ai-content`) as HTMLElement;
     if (targetContent) {
       targetContent.focus();
@@ -2623,27 +2650,35 @@ export default function ReportEditor() {
               </div>
               <button onClick={() => setDiffModal(null)} className="text-slate-400 hover:text-slate-600"><X size={20}/></button>
             </div>
-            <div className="flex-1 overflow-hidden flex gap-4 p-6 bg-slate-100">
-              <div className="flex-1 flex flex-col bg-white border border-red-200 rounded-xl overflow-hidden shadow-sm">
-                <div className="bg-red-50 px-3 py-2 text-xs font-bold text-red-600 border-b border-red-100 uppercase tracking-wider">原始版本</div>
-                <div className="p-4 flex-1 overflow-y-auto opacity-70 cursor-not-allowed custom-scrollbar"
-                  dangerouslySetInnerHTML={{ __html: diffModal.originalHtml }}></div>
-              </div>
-              <div className="flex-1 flex flex-col bg-white border border-green-400 rounded-xl overflow-hidden shadow-md relative">
-                <div className="bg-green-50 px-3 py-2 text-xs font-bold text-green-700 border-b border-green-200 uppercase tracking-wider flex justify-between">
-                  <span>AI 提议版本 (可直接编辑)</span>
-                  <span className="text-[10px] bg-green-200 px-1.5 py-0.5 rounded text-green-800">编辑态</span>
+            {(() => {
+              const oldText = stripHtml(diffModal.originalHtml);
+              const newText = stripHtml(diffModal.newHtml);
+              const leftDiffHtml = computeDiffHtml(oldText, newText, 'left');
+              const rightDiffHtml = computeDiffHtml(oldText, newText, 'right');
+              return (
+                <div className="flex-1 overflow-hidden flex gap-4 p-6 bg-slate-100">
+                  <div className="flex-1 flex flex-col bg-white border border-red-200 rounded-xl overflow-hidden shadow-sm">
+                    <div className="bg-red-50 px-3 py-2 text-xs font-bold text-red-600 border-b border-red-100 uppercase tracking-wider">原始版本</div>
+                    <div className="p-4 flex-1 overflow-y-auto opacity-70 cursor-not-allowed custom-scrollbar"
+                      dangerouslySetInnerHTML={{ __html: leftDiffHtml }}></div>
+                  </div>
+                  <div className="flex-1 flex flex-col bg-white border border-green-400 rounded-xl overflow-hidden shadow-md relative">
+                    <div className="bg-green-50 px-3 py-2 text-xs font-bold text-green-700 border-b border-green-200 uppercase tracking-wider flex justify-between">
+                      <span>AI 提议版本 (可直接编辑)</span>
+                      <span className="text-[10px] bg-green-200 px-1.5 py-0.5 rounded text-green-800">编辑态</span>
+                    </div>
+                    <div
+                      className="p-4 flex-1 overflow-y-auto outline-none custom-scrollbar"
+                      contentEditable
+                      suppressContentEditableWarning
+                      onBlur={(e) => setDiffModal(prev => prev ? { ...prev, newHtml: e.target.innerHTML } : null)}
+                      dangerouslySetInnerHTML={{ __html: rightDiffHtml }}
+                      style={{ fontFamily: 'SimSun, "Microsoft YaHei", serif', fontSize: '12pt', lineHeight: '1.5' }}
+                    ></div>
+                  </div>
                 </div>
-                <div
-                  className="p-4 flex-1 overflow-y-auto outline-none custom-scrollbar"
-                  contentEditable
-                  suppressContentEditableWarning
-                  onBlur={(e) => setDiffModal(prev => prev ? { ...prev, newHtml: e.target.innerHTML } : null)}
-                  dangerouslySetInnerHTML={{ __html: diffModal.newHtml }}
-                  style={{ fontFamily: 'SimSun, "Microsoft YaHei", serif', fontSize: '12pt', lineHeight: '1.5' }}
-                ></div>
-              </div>
-            </div>
+              );
+            })()}
             <div className="px-6 py-4 border-t border-slate-100 flex justify-end gap-3 bg-white">
               <button onClick={() => setDiffModal(null)} className="px-6 py-2 rounded-lg text-slate-600 font-medium hover:bg-slate-100">放弃修改</button>
               <button onClick={() => confirmAiInjection(diffModal.newHtml, diffModal.targetId)} className="px-6 py-2 rounded-lg bg-blue-600 text-white font-medium hover:bg-blue-700 shadow-sm flex items-center gap-2">