fix(web): cover deep document headings

tools/web-ux/browser-tests/memory_document_fixture_server.ts

@@ -25,7 +25,7 @@ const paragraphs = Array.from(
 const bodyMd =
   `# Workspace Memory\n\nThis document is read-only.\n\n| Very wide heading | Another heading | Decision |\n| --- | --- | --- |\n| ${
     "wide-value-".repeat(16)
-  } | stable | keep scrolling local |\n\n\`\`\`rust\nfn example() { println!("${
+  } | stable | keep scrolling local |\n\n##### Deep document heading\n\n###### Deepest document heading\n\n\`\`\`rust\nfn example() { println!("${
     "wide-code-".repeat(18)
   }"); }\n\`\`\`\n\n[Safe link](https://example.com) [Unsafe link](javascript:alert(1))\n\n<img src=x onerror=alert(1)>\n\n${paragraphs}\n\n## T-661 UNIQUE END MARKER`;
 

tools/web-ux/browser-tests/memory_document_shell_test.ts

@@ -165,6 +165,21 @@ Deno.test("production Memory shell renders safe Markdown and scrolls to its end
           );
           assertEquals(await page.locator("blockquote").count() > 0, true);
           assertEquals(await page.locator("ul li").count() > 0, true);
+          for (
+            const heading of [
+              { selector: "h5", text: "Deep document heading" },
+              { selector: "h6", text: "Deepest document heading" },
+            ]
+          ) {
+            const element = page.locator(heading.selector, { hasText: heading.text });
+            assertEquals(await element.count(), 1);
+            assert(
+              await element.evaluate((node) =>
+                Number.parseFloat((globalThis as any).getComputedStyle(node).fontSize) >= 12
+              ),
+              `${heading.selector} fell below the design language minimum text size`,
+            );
+          }
           assertEquals(await page.locator('a[href="https://example.com"]').count(), 1);
           assertEquals(await page.locator('a[href^="javascript:"]').count(), 0);
           assertEquals(await page.locator("article img, article script").count(), 0);