C4 + F4 diagram example: order workflow engine

Most C4 tools stop at structure: what exists, and what talks to what. This example pairs the structure with an F4 behavioral flow — the actual sequence of steps an order goes through, laid out as swimlanes bound to the C4 elements that perform them. It is the same model either way; F4 is a second view of it, not a second diagram to keep in sync by hand.