Interest Accrual

Implement accruedInterest(principal, annualRate, startISO, endISO) using Actual/365 Fixed.

Requirements

1. 01accruedInterest(principal, annualRate, startISO, endISO) returns a number; equal dates return 0.
2. 02Interpret valid YYYY-MM-DD inputs as UTC calendar dates and reject an end date before the start date.
3. 03Use Actual/365 Fixed: interest = principal × annualRate × elapsed calendar days / 365.
4. 04Do not round intermediate results; return the computed number using normal floating-point precision.

Constraints

• • Submit one compact engineering spec, not implementation code.
• • The generated artifact must use the declared TypeScript adapter.
• • Scoring rewards observable behavior and prompt efficiency, not runtime.