fix(page-number): fall back for unknown formats

Author: luccas-harbour

packages/layout-engine/contracts/src/page-number-formatting.test.ts

@@ -18,6 +18,10 @@ describe('page number formatting', () => {
     expect(formatPageNumber(Number.NaN, 'decimal')).toBe('1');
   });
 
+  it('falls back to decimal for unsupported runtime formats', () => {
+    expect(formatPageNumber(5, 'chicago' as never)).toBe('5');
+  });
+
   it('falls back to decimal for roman numerals beyond 3999', () => {
     expect(formatPageNumber(4000, 'upperRoman')).toBe('4000');
   });

packages/layout-engine/layout-engine/src/pageNumbering.test.ts

@@ -31,6 +31,10 @@ describe('formatPageNumber', () => {
     it('should truncate fractional numbers before formatting', () => {
       expect(formatPageNumber(4.9, 'decimal')).toBe('4');
     });
+
+    it('should fall back to decimal for unsupported runtime formats', () => {
+      expect(formatPageNumber(5, 'chicago' as never)).toBe('5');
+    });
   });
 
   describe('numberInDash format', () => {