feat(math): implement m:d delimiter converter (SD-2380) (#2710)

* feat(math): implement m:d delimiter converter (SD-2380)

* fix(math): address delimiter review and sync converters

* fix(math): address delimiter review feedback

* docs(math): clarify delimiter separator spec

* test(math): add behavior tests for m:d delimiter rendering

Add 5 behavior tests exercising the delimiter converter with a dedicated
test document covering all 21 ECMA-376 §22.1.2.24 compliance cases:
default parentheses, U+2502 separator, suppressed delimiters (chr without
m:val), custom Unicode delimiters (floor, ceiling, abs), and nesting.

Fix stale comment that still referred to delimiter as unimplemented.

* refactor(math): inline createExpressionGroup into single loop

Replace map + filter + forEach chain with a single for-loop that
builds expression groups directly, removing the single-use helper.

---------

Co-authored-by: Caio Pizzol <caio@harbourshare.com>

Author: andrewsrigom

packages/layout-engine/painters/dom/src/features/math/converters/delimiter.ts

@@ -0,0 +1,63 @@
+import type { MathObjectConverter, OmmlJsonNode } from '../types.js';
+
+const MATHML_NS = 'http://www.w3.org/1998/Math/MathML';
+
+const DEFAULT_BEGIN_DELIMITER = '(';
+const DEFAULT_END_DELIMITER = ')';
+const DEFAULT_SEPARATOR_DELIMITER = '\u2502'; // ECMA-376 22.1.2.95: BOX DRAWINGS LIGHT VERTICAL
+
+function getDelimiterValue(properties: OmmlJsonNode | undefined, name: string, fallback: string): string {
+  const property = properties?.elements?.find((element) => element.name === name);
+  if (!property) return fallback;
+  return property.attributes?.['m:val'] ?? '';
+}
+
+/**
+ * Convert m:d (delimiter) to MathML.
+ *
+ * OMML structure:
+ *   m:d → m:dPr (optional: begChr, endChr, sepChr) + one or more m:e expressions
+ *
+ * MathML output:
+ *   <mrow><mo>(</mo> ...content... <mo>)</mo></mrow>
+ *
+ * @spec ECMA-376 §22.1.2.24
+ */
+export const convertDelimiter: MathObjectConverter = (node, doc, convertChildren) => {
+  const elements = node.elements ?? [];
+  const delimiterProps = elements.find((element) => element.name === 'm:dPr');
+  const expressions = elements.filter((element) => element.name === 'm:e');
+
+  const beginDelimiter = getDelimiterValue(delimiterProps, 'm:begChr', DEFAULT_BEGIN_DELIMITER);
+  const endDelimiter = getDelimiterValue(delimiterProps, 'm:endChr', DEFAULT_END_DELIMITER);
+  const separatorDelimiter = getDelimiterValue(delimiterProps, 'm:sepChr', DEFAULT_SEPARATOR_DELIMITER);
+
+  const wrapper = doc.createElementNS(MATHML_NS, 'mrow');
+
+  const begin = doc.createElementNS(MATHML_NS, 'mo');
+  begin.textContent = beginDelimiter;
+  wrapper.appendChild(begin);
+
+  let renderedCount = 0;
+  for (const expression of expressions) {
+    const fragment = convertChildren(expression?.elements ?? []);
+    if (fragment.childNodes.length === 0) continue;
+
+    if (renderedCount > 0) {
+      const separator = doc.createElementNS(MATHML_NS, 'mo');
+      separator.textContent = separatorDelimiter;
+      wrapper.appendChild(separator);
+    }
+
+    const group = doc.createElementNS(MATHML_NS, 'mrow');
+    group.appendChild(fragment);
+    wrapper.appendChild(group);
+    renderedCount++;
+  }
+
+  const end = doc.createElementNS(MATHML_NS, 'mo');
+  end.textContent = endDelimiter;
+  wrapper.appendChild(end);
+
+  return wrapper;
+};

packages/layout-engine/painters/dom/src/features/math/converters/index.ts

@@ -10,6 +10,7 @@ export { convertMathRun } from './math-run.js';
 export { convertFraction } from './fraction.js';
 export { convertBar } from './bar.js';
 export { convertFunction } from './function.js';
+export { convertDelimiter } from './delimiter.js';
 export { convertSubscript } from './subscript.js';
 export { convertSuperscript } from './superscript.js';
 export { convertSubSuperscript } from './sub-superscript.js';