Defines coding conventions, error handling patterns, async practices, logging standards, API response formats, and testing workflows for the Order Service — a FastAPI/Python microservice. Covers typed exception classes with FastAPI exception handler registration, structlog structured logging, Pydantic request/response models, and pytest-asyncio endpoint tests. Use when writing or modifying order endpoints, implementing order processing logic, adding error handling, or working with any file matching app/**/*.py or tests/**/*.py in the Order Service.