fix: bound money conversion after cents scaling

src/lib/domain/money.ts

@@ -7,8 +7,9 @@
 export type IskLike = string | bigint | number;
 
 const INTEGER_TEXT = /^-?\d+$/;
-// The final lookahead makes the end assertion strict: JavaScript's `$` alone
-// would also accept a match immediately before one trailing newline.
+// The final lookahead makes the end assertion strict. This intentionally
+// tightens the old ESI regex, because JavaScript's `$` alone also accepts a
+// match immediately before one trailing newline.
 const DECIMAL_TEXT = /^-?(?:0|[1-9][0-9]*)(?:\.[0-9]+)?(?:[eE][+-]?[0-9]+)?$(?![\s\S])/;
 
 /** Resource bounds for signed decimal ingestion. These reject excess input; no truncation is performed. */
@@ -68,18 +69,20 @@ export function decimalIskToCents(value: string): string {
   }
 
   const exponent = exponentText === undefined ? 0n : parseDecimalExponent(exponentText);
-  const decimalPlaces = BigInt(fraction.length) - exponent;
-  if (decimalPlaces < -MAX_DECIMAL_SHIFT || decimalPlaces > MAX_DECIMAL_SHIFT) {
+  // Convert the decimal coefficient to cents before applying the resource
+  // bound: value * 10^(exponent - fractionDigits) * 100.
+  const centsShift = exponent + 2n - BigInt(fraction.length);
+  if (centsShift < -MAX_DECIMAL_SHIFT || centsShift > MAX_DECIMAL_SHIFT) {
     throw new RangeError('ISK decimal shift exceeds resource bounds');
   }
 
   const digits = `${whole}${fraction}`.replace(/^0+(?=\d)/, '');
   const significand = BigInt(digits);
   let magnitude: bigint;
-  if (decimalPlaces <= 2n) {
-    magnitude = significand * 10n ** (2n - decimalPlaces);
+  if (centsShift >= 0n) {
+    magnitude = significand * 10n ** centsShift;
   } else {
-    const divisor = 10n ** (decimalPlaces - 2n);
+    const divisor = 10n ** -centsShift;
     const quotient = significand / divisor;
     const remainder = significand % divisor;
     // Half-away-from-zero is half-up for this non-negative magnitude.