fix: stop normalizeMoneyAmount from silently truncating sub-cent Stellar amounts (Closes #439)

tests/money-amount.test.ts

@@ -47,6 +47,62 @@ describe('MoneyAmount decimal normalization', () => {
     expect(result.amount).toBe('1.2345678');
   });
 
+  it('supports explicit scale and round options via options object', () => {
+    const input: MoneyAmount = { assetCode: 'USDC', amount: '1.234567' };
+    const truncated = normalizeMoneyAmount(input, { scale: 2 });
+    expect(truncated.amount).toBe('1.23');
+
+    const rounded = normalizeMoneyAmount(input, { scale: 2, round: true });
+    expect(rounded.amount).toBe('1.23');
+  });
+
+  it('rounds half-up when rounding is explicitly requested', () => {
+    const input: MoneyAmount = { assetCode: 'USDC', amount: '1.235' };
+    const result = normalizeMoneyAmount(input, 2, { round: true });
+    expect(result.amount).toBe('1.24');
+  });
+
+  it('rounds sub-cent amounts to target scale when requested', () => {
+    const input: MoneyAmount = { assetCode: 'XLM', amount: '0.0000009' };
+    const result = normalizeMoneyAmount(input, 6, { round: true });
+    expect(result.amount).toBe('0.000001');
+  });
+
+  it('rounds amounts exceeding 7 decimal places to Stellar maximum precision', () => {
+    const roundUp: MoneyAmount = { assetCode: 'XLM', amount: '0.00000019' };
+    expect(normalizeMoneyAmount(roundUp).amount).toBe('0.0000002');
+
+    const roundDown: MoneyAmount = { assetCode: 'XLM', amount: '0.00000012' };
+    expect(normalizeMoneyAmount(roundDown).amount).toBe('0.0000001');
+  });
+
+  it('throws RangeError for invalid scale values', () => {
+    const input: MoneyAmount = { assetCode: 'USDC', amount: '10.50' };
+    expect(() => normalizeMoneyAmount(input, -1)).toThrow(RangeError);
+    expect(() => normalizeMoneyAmount(input, 8)).toThrow(RangeError);
+    expect(() => normalizeMoneyAmount(input, 2.5)).toThrow(RangeError);
+  });
+
+  it('produces output accepted by validateMoneyAmount', () => {
+    const standard: MoneyAmount = { assetCode: 'USDC', amount: '0075.5' };
+    expect(() => {
+      validateMoneyAmount(normalizeMoneyAmount(standard), 'test');
+    }).not.toThrow();
+
+    const subCent: MoneyAmount = { assetCode: 'XLM', amount: '0.0000001' };
+    expect(() => {
+      validateMoneyAmount(normalizeMoneyAmount(subCent), 'test');
+    }).not.toThrow();
+
+    const rounded: MoneyAmount = { assetCode: 'XLM', amount: '0.0000009' };
+    expect(() => {
+      validateMoneyAmount(
+        normalizeMoneyAmount(rounded, 6, { round: true }),
+        'test',
+      );
+    }).not.toThrow();
+  });
+
   it('handles amounts with leading zeros', () => {
     const input: MoneyAmount = {
       assetCode: 'USDC',