A real account of building an Async Job Queue with Backpressure & Priority Scheduling using Python, FastAPI, and Redis Streams — covering the Reaper service, 47 tests, 85% coverage, and every bug along the way. No Celery. No shortcuts. No pretending the first approach worked. I decided to build a production-grade project from scratch to bypass the abstraction layer of tools like Celery and truly master backend internals—the kind of work you can defend in any technical interview. Instead of reaching for a framework that abstracts the hard parts, I built an async job queue from scratch — backpressure, priority scheduling, crash recovery, zombie detection, the full picture. This is the honest account of what I built, in what order, what broke, what I fixed, and what the final numbers looked like. Stack: Python 3.12, FastAPI, Redis Streams, PostgreSQL, SQLAlchemy, Alembic, Prometheus, Grafana, Locust, Docker Final state: 47 tests passing, 85% coverage, services layer at ~92% Why a Job Queue?…