Design an extensible expense rule evaluator

## Scenario You are building a corporate employee expense card product. Admins define policies (“rules”) to prevent misuse and to flag policy violations. You need to design a rules evaluation component that takes: - a list of **rules** - a list of **expenses** (each expense is a hash map / dictionary) and returns a result that clearly marks: - which **individual expenses** violate which rules - which **trips** (a trip is a group of expenses sharing the same `trip_id`) violate which rules All keys and values in the input expense objects are **strings**. ### Example rules (initial set) Assume money is in USD. 1. Any restaurant expense must not exceed `X` dollars. (`merchant_type == "restaurant"`) 2. No airfare purchases allowed. (`category == "airfare"`) 3. No entertainment purchases allowed. (`category == "entertainment"`) 4. Any single transaction must not exceed `Y` dollars. 5. Total spend per trip must not exceed `Z` dollars. 6. Total restaurant spend per trip must not exceed `R` dollars. ### Example expense object Each expense is a dictionary like: - `expense_id`: "001" - `trip_id`: "001" - `amount`: "23.312" (string) - `purpose`: "client hosting" - `merchant_type`: "restaurant" - `merchant_name`: "Outback Roadhouse" ### Task Design the function: `evaluate_rules(rules: List[...], expenses: List[Dict[str, str]]) -> ???` 1. Propose a **return type** (structure/schema) that supports: - per-expense violations - per-trip violations - clear human-readable reasons - machine-readable rule identifiers 2. Explain how you would design the rules representation so that **new rule types** can be added later, and rules can eventually be created via an API (i.e., emphasize extensibility and maintainability). You do **not** need to write code; focus on interface and design.