Strangler Fig Data Migration: Orders Service Extraction

The core problem: two systems (monolith DB + new Orders microservice DB) need to represent the same truth during the transition, with zero downtime and zero data loss, until you can cut over completely.

Here's the depth version, phase by phase.

Phase 1: Dual Writes (Synchronization begins)

Before the new service takes any real traffic, you need both databases populated and kept in sync.