chore: strengthen backend eslint profile

src/common/decimal.ts

@@ -1,8 +1,10 @@
-export type Decimal = { value: bigint; scale: number };
+export type Decimal = { scale: number; value: bigint };
 
 export function decimalFromString(value: string): Decimal {
-  if (!/^-?(?:0|[1-9]\d*)(?:\.\d+)?$/.test(value))
+  // eslint-disable-next-line security/detect-unsafe-regex -- Anchored decimal grammar: the literal decimal point separates disjoint digit runs; backtracking is linear.
+  if (!/^-?(?:0|[1-9]\d*)(?:\.\d+)?$/.test(value)) {
     throw new Error('Invalid decimal string');
+  }
   const negative = value.startsWith('-');
   const [whole, fraction = ''] = (negative ? value.slice(1) : value).split('.');
   return {
@@ -46,8 +48,12 @@ export function formatDecimal({ value, scale }: Decimal): string {
     .toString()
     .padStart(scale + 1, '0');
   const whole = digits.slice(0, -scale) || '0';
-  const fraction = digits.slice(-scale).replace(/0+$/, '');
-  return `${sign}${whole}${fraction ? `.${fraction}` : ''}`;
+  const rawFraction = digits.slice(-scale);
+  let fractionEnd = rawFraction.length;
+  while (rawFraction.charAt(fractionEnd - 1) === '0') fractionEnd -= 1;
+  const fraction = rawFraction.slice(0, fractionEnd);
+  const fractionalPart = fraction ? '.' + fraction : '';
+  return `${sign}${whole}${fractionalPart}`;
 }
 
 // Round half away from zero; callers choose presentation precision explicitly.
@@ -55,7 +61,7 @@ export function divide(left: Decimal, right: Decimal, scale: number): Decimal {
   if (right.value === 0n) throw new Error('Division by zero');
   const numerator = left.value * 10n ** BigInt(right.scale + scale);
   const denominator = right.value * 10n ** BigInt(left.scale);
-  const sign = numerator < 0n !== denominator < 0n ? -1n : 1n;
+  const sign = (numerator < 0n) !== (denominator < 0n) ? -1n : 1n;
   const n = numerator < 0n ? -numerator : numerator;
   const d = denominator < 0n ? -denominator : denominator;
   return { value: sign * ((n + d / 2n) / d), scale };