Design a declarative infrastructure orchestrator

Design a Terraform-like service. Teams publish versioned configurations that declare resources and their dependencies; they ask for a plan, review it, and apply exactly that plan. The service calls cloud provider APIs that can be slow, rate-limited or time out after succeeding, and keeps state that maps each declared resource to the real one.

Cover:

• plan and apply bound to one configuration and state version, failing if either changed since review;
• one mutating run per stack at a time;
• running in two US regions, either of which accepts commands, without ever having two coordinators for one stack during a failover;
• progress, cancellation, and detecting drift between stored state and what really exists.