Facade

Facade: one simple entry point over a messy subsystem

Problem: doing one useful thing requires orchestrating several objects in the right order, and every caller repeats that dance.

PawWalk scenario: booking a walk means pricing, then payment, then notification. BookingService.book! hides all three behind one call.

A facade doesn't add new logic — it just provides a friendly front door so callers don't wire the subsystem themselves.