This is a phenomenal architectural write-up! Moving from tightly coupled orchestration to event-driven choreography is the exact inflection point where an e-commerce platform transitions from an MVP to a resilient, enterprise-grade system.

Your breakdown of the event taxonomy—specifically the distinction between an immutable fact (order.placed) and an orchestration command masquerading as an event—is a crucial lesson that many backend engineers learn the hard way. Validating the envelope contract via Pydantic before it ever touches the message broker is a beautiful pattern that keeps the pipeline loud and reliable.

If I can offer one supportive critique for the upcoming Day 2 topic: when you dive into Google Cloud Pub/Sub subscriptions, it would be awesome to see how you handle idempotency on the consumer side, especially since Pub/Sub guarantees at-least-once delivery.

Looking forward to the deep dive into dead-letter topics! Outstanding work!