Stage two: packages, enums, interfaces and ordinary objects
JDK 25 or newer. From THIS structured directory:

mkdir out
javac --release 25 -d out @sources.txt
java -cp out com.homannsoftware.shop.app.Shop
java -cp out com.homannsoftware.shop.StructuredTest

In PowerShell, quote the argument-file token: "@sources.txt".
Expected demo:
STANDARD: 3290 cents
EXPRESS: 3790 cents
COLLECTION: 2800 cents
Expected test summary: 23 structured checks passed

The original root-level example is stage one; do not mix the classpaths.
Standard shipping keeps the stage-one rule. Express is always 990 cents;
collection is free. Null policy/delivery/line values are rejected with NPE.
No payment, tax, stock, persistence or actual delivery booking.
