引入正文安全子集并收紧呈现创作口径，避免本局任意脚本美化。

创作只选壳与分区，渲染与提示共用同一份白名单语法。

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

tests/markdown-render.test.ts

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+import { describe, expect, it } from "vitest";
+import { renderMarkdownToHtml } from "../web/markdown.js";
+
+describe("markdown safe subset render", () => {
+  it("renders GFM tables", () => {
+    const html = renderMarkdownToHtml(
+      ["| 甲 | 乙 |", "| --- | --- |", "| 1 | **粗** |"].join("\n"),
+    );
+    expect(html).toContain('<table class="md-table">');
+    expect(html).toContain("<th>");
+    expect(html).toContain("<td>");
+    expect(html).toContain("<strong>粗</strong>");
+    expect(html).not.toContain("| 甲 |");
+  });
+
+  it("renders details folds", () => {
+    const html = renderMarkdownToHtml(
+      [":::details 规则说明", "里面有 *斜体*", ":::"].join("\n"),
+    );
+    expect(html).toContain('<details class="md-details">');
+    expect(html).toContain('<summary class="md-summary">');
+    expect(html).toContain("规则说明");
+    expect(html).toContain("<em>斜体</em>");
+  });
+
+  it("supports open details", () => {
+    const html = renderMarkdownToHtml(
+      [":::details open 已展开", "内容", ":::"].join("\n"),
+    );
+    expect(html).toContain("<details class=\"md-details\" open>");
+  });
+
+  it("escapes raw html tags", () => {
+    const html = renderMarkdownToHtml("<script>alert(1)</script>");
+    expect(html).not.toContain("<script>");
+    expect(html).toContain("&lt;script&gt;");
+  });
+});