fix: 改进流式 write_file 沙箱预览与 Mermaid 旧浏览器兼容

同轮次非末尾 write_file 也能自动打开沙箱并跳过 JSON 大文件预览；Mermaid 改用 SVG 标签；agentfx 强制先写 md 再写 json。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend-web/scripts/check-chrome109-css.mjs

@@ -31,6 +31,11 @@ const requiredLegacyFallbacks = [
     pattern: /<InputGroup className="h-auto min-h-16">/,
     description: "Prompt textarea must not rely on :has() for its parent height",
   },
+  {
+    file: "src/core/utils/mermaid.ts",
+    pattern: /htmlLabels:\s*false[\s\S]*secure:\s*\[[\s\S]*"htmlLabels"/,
+    description: "Sandbox flowcharts must use native SVG labels in legacy browsers",
+  },
 ];
 
 for (const file of cssFiles) {