feat(math): implement m:sSup superscript converter (SD-2372)

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

@@ -10,3 +10,4 @@ export { convertMathRun } from './math-run.js';
 export { convertFraction } from './fraction.js';
 export { convertBar } from './bar.js';
 export { convertSubscript } from './subscript.js';
+export { convertSuperscript } from './superscript.js';

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

@@ -0,0 +1,32 @@
+import type { MathObjectConverter } from '../types.js';
+
+const MATHML_NS = 'http://www.w3.org/1998/Math/MathML';
+
+/**
+ * Convert m:sSup (superscript) to MathML <msup>.
+ *
+ * OMML structure:
+ *   m:sSup → m:sSupPr (optional), m:e (base), m:sup (superscript)
+ *
+ * MathML output:
+ *   <msup> <mrow>base</mrow> <mrow>sup</mrow> </msup>
+ *
+ * @spec ECMA-376 §22.1.2.105
+ */
+export const convertSuperscript: MathObjectConverter = (node, doc, convertChildren) => {
+  const elements = node.elements ?? [];
+  const base = elements.find((e) => e.name === 'm:e');
+  const sup = elements.find((e) => e.name === 'm:sup');
+
+  const msup = doc.createElementNS(MATHML_NS, 'msup');
+
+  const baseRow = doc.createElementNS(MATHML_NS, 'mrow');
+  baseRow.appendChild(convertChildren(base?.elements ?? []));
+  msup.appendChild(baseRow);
+
+  const supRow = doc.createElementNS(MATHML_NS, 'mrow');
+  supRow.appendChild(convertChildren(sup?.elements ?? []));
+  msup.appendChild(supRow);
+
+  return msup;
+};

packages/layout-engine/painters/dom/src/features/math/omml-to-mathml.test.ts

@@ -436,3 +436,118 @@ describe('m:sSub converter', () => {
     expect(msub!.children[0]!.textContent).toBe('a');
   });
 });
+
+describe('m:sSup converter', () => {
+  it('converts m:sSup to <msup> with base and superscript', () => {
+    const omml = {
+      name: 'm:oMath',
+      elements: [
+        {
+          name: 'm:sSup',
+          elements: [
+            {
+              name: 'm:e',
+              elements: [{ name: 'm:r', elements: [{ name: 'm:t', elements: [{ type: 'text', text: 'x' }] }] }],
+            },
+            {
+              name: 'm:sup',
+              elements: [{ name: 'm:r', elements: [{ name: 'm:t', elements: [{ type: 'text', text: '2' }] }] }],
+            },
+          ],
+        },
+      ],
+    };
+    const result = convertOmmlToMathml(omml, doc);
+    expect(result).not.toBeNull();
+    const msup = result!.querySelector('msup');
+    expect(msup).not.toBeNull();
+    expect(msup!.children.length).toBe(2);
+    expect(msup!.children[0]!.textContent).toBe('x');
+    expect(msup!.children[1]!.textContent).toBe('2');
+  });
+
+  it('ignores m:sSupPr properties element', () => {
+    const omml = {
+      name: 'm:oMath',
+      elements: [
+        {
+          name: 'm:sSup',
+          elements: [
+            { name: 'm:sSupPr', elements: [{ name: 'm:ctrlPr' }] },
+            {
+              name: 'm:e',
+              elements: [{ name: 'm:r', elements: [{ name: 'm:t', elements: [{ type: 'text', text: 'a' }] }] }],
+            },
+            {
+              name: 'm:sup',
+              elements: [{ name: 'm:r', elements: [{ name: 'm:t', elements: [{ type: 'text', text: 'b' }] }] }],
+            },
+          ],
+        },
+      ],
+    };
+    const result = convertOmmlToMathml(omml, doc);
+    expect(result).not.toBeNull();
+    const msup = result!.querySelector('msup');
+    expect(msup).not.toBeNull();
+    expect(msup!.children.length).toBe(2);
+    expect(msup!.children[0]!.textContent).toBe('a');
+    expect(msup!.children[1]!.textContent).toBe('b');
+  });
+
+  it('wraps multi-part base and superscript in <mrow> for valid arity', () => {
+    // (x+1)^2 — base has 3 runs that must be grouped
+    const omml = {
+      name: 'm:oMath',
+      elements: [
+        {
+          name: 'm:sSup',
+          elements: [
+            {
+              name: 'm:e',
+              elements: [
+                { name: 'm:r', elements: [{ name: 'm:t', elements: [{ type: 'text', text: 'x' }] }] },
+                { name: 'm:r', elements: [{ name: 'm:t', elements: [{ type: 'text', text: '+' }] }] },
+                { name: 'm:r', elements: [{ name: 'm:t', elements: [{ type: 'text', text: '1' }] }] },
+              ],
+            },
+            {
+              name: 'm:sup',
+              elements: [{ name: 'm:r', elements: [{ name: 'm:t', elements: [{ type: 'text', text: '2' }] }] }],
+            },
+          ],
+        },
+      ],
+    };
+    const result = convertOmmlToMathml(omml, doc);
+    expect(result).not.toBeNull();
+    const msup = result!.querySelector('msup');
+    expect(msup).not.toBeNull();
+    // <msup> must have exactly 2 children (base + superscript), each wrapped in <mrow>
+    expect(msup!.children.length).toBe(2);
+    expect(msup!.children[0]!.textContent).toBe('x+1');
+    expect(msup!.children[1]!.textContent).toBe('2');
+  });
+
+  it('handles missing m:sup gracefully', () => {
+    const omml = {
+      name: 'm:oMath',
+      elements: [
+        {
+          name: 'm:sSup',
+          elements: [
+            {
+              name: 'm:e',
+              elements: [{ name: 'm:r', elements: [{ name: 'm:t', elements: [{ type: 'text', text: 'x' }] }] }],
+            },
+          ],
+        },
+      ],
+    };
+    const result = convertOmmlToMathml(omml, doc);
+    expect(result).not.toBeNull();
+    const msup = result!.querySelector('msup');
+    expect(msup).not.toBeNull();
+    expect(msup!.children[0]!.textContent).toBe('x');
+  });
+});

packages/layout-engine/painters/dom/src/features/math/omml-to-mathml.ts

@@ -10,7 +10,13 @@
  */
 
 import type { OmmlJsonNode, MathObjectConverter } from './types.js';
-import { convertMathRun, convertFraction, convertBar, convertSubscript } from './converters/index.js';
+import {
+  convertMathRun,
+  convertFraction,
+  convertBar,
+  convertSubscript,
+  convertSuperscript,
+} from './converters/index.js';
 
 export const MATHML_NS = 'http://www.w3.org/1998/Math/MathML';
 
@@ -33,6 +39,7 @@ const MATH_OBJECT_REGISTRY: Record<string, MathObjectConverter | null> = {
   'm:bar': convertBar, // Bar (overbar/underbar)
   'm:f': convertFraction, // Fraction (numerator/denominator)
   'm:sSub': convertSubscript, // Subscript
+  'm:sSup': convertSuperscript, // Superscript
 
   // ── Not yet implemented (community contributions welcome) ────────────────
   'm:acc': null, // Accent (diacritical mark above base)
@@ -50,7 +57,6 @@ const MATH_OBJECT_REGISTRY: Record<string, MathObjectConverter | null> = {
   'm:rad': null, // Radical (square root, nth root)
   'm:sPre': null, // Pre-sub-superscript (left of base)
   'm:sSubSup': null, // Sub-superscript (both)
-  'm:sSup': null, // Superscript
 };
 
 /** OMML argument/container elements that wrap children in <mrow>. */