chore: import upstream snapshot with attribution

apps/sim/lib/billing/utils/decimal.ts

@@ -0,0 +1,36 @@
+import Decimal from 'decimal.js'
+
+/**
+ * Configure Decimal.js for billing precision.
+ * 20 significant digits is more than enough for currency calculations.
+ */
+Decimal.set({ precision: 20, rounding: Decimal.ROUND_HALF_UP })
+
+/**
+ * Parse a value to Decimal for precise billing calculations.
+ * Handles null, undefined, empty strings, and number/string inputs.
+ */
+export function toDecimal(value: string | number | null | undefined): Decimal {
+  if (value === null || value === undefined || value === '') {
+    return new Decimal(0)
+  }
+  return new Decimal(value)
+}
+
+/**
+ * Convert Decimal back to number for storage/API responses.
+ * Use this at the final step when returning values.
+ */
+export function toNumber(value: Decimal): number {
+  return value.toNumber()
+}
+
+/**
+ * Format a Decimal to a fixed string for database storage.
+ * Uses 6 decimal places which matches current DB precision.
+ */
+export function toFixedString(value: Decimal, decimalPlaces = 6): string {
+  return value.toFixed(decimalPlaces)
+}
+
+export { Decimal }