fix(ui): preserve standalone safe line breaks

ui/src/components/markdown-parser.ts

@@ -73,8 +73,8 @@ function renderRawMarkdownHtml(
   if (progressBars) {
     return PROGRESS_HTML_RE.test(content.trim()) ? content : "";
   }
-  if (!block && /^<br\s*\/?>$/iu.test(content)) {
-    return "<br>";
+  if (/^<br\s*\/?>$/iu.test(content.trim())) {
+    return block ? "<br>\n" : "<br>";
   }
   return escapeMarkdownHtml(content) + (block ? "\n" : "");
 }

ui/src/components/markdown.test.ts

@@ -145,6 +145,12 @@ describe("toSanitizedMarkdownHtml", () => {
       expect(cell?.textContent).toBe("一二");
     });
 
+    it("renders an attribute-free line break between Markdown blocks", () => {
+      const html = toSanitizedMarkdownHtml("before\n\n<br>\n\nafter");
+
+      expect(html).toBe("<p>before</p>\n<br>\n<p>after</p>\n");
+    });
+
     it.each([
       '<br onclick="alert(1)">',
       '<br onmouseover="alert(1)" />',