Order Management API

Build an order management API with FastAPI and Python for a small e-commerce backend.

Endpoints

• POST /api/orders -- create an order with customer_email: str, items: list where each item has product_name: str, quantity: int (> 0), unit_price: float (> 0)
• GET /api/orders/{order_id} -- get order details including computed total
• GET /api/orders -- list orders, with optional status: str filter and customer_email: str filter
• PATCH /api/orders/{order_id}/status -- update order status with status: str (allowed transitions: "pending" -> "confirmed" -> "shipped" -> "delivered"; any state -> "cancelled" except "delivered")
• POST /api/orders/{order_id}/notes -- add a note to an order with text: str, author: str
• GET /api/orders/{order_id}/notes -- list notes for an order

Business rules:

• An order must have at least one item
• Status transitions must follow the allowed state machine
• Cannot add notes to a cancelled order
• Order total is computed from items (quantity * unit_price)

Output

Produce Python files:

• app/main.py -- FastAPI app with routes
• app/models.py -- Pydantic schemas for requests and responses
• app/store.py -- in-memory data store (no real database)

Do not include test files or deployment configuration.