Aggregate lifecycles

What belongs in a machine

One question: does the field have legal moves?

A status where PAID may only follow PLACED, and SHIPPED only PAID, has legal moves — the rules exist whether or not anyone wrote them down, and they are currently spread across whichever use cases happen to touch the field. A lastSeenAt has no legal moves; it is derived data, and wrapping it in a machine buys nothing.

Two more that look like lifecycles and are not:

• A boolean. isArchived toggling both ways is not worth a machine. Two states with a move each is more ceremony than copy(archived = true).
• A field the client sets freely. If any value may follow any other, there is nothing to declare. That is a validation problem — load ktor-toolkit:validation.

Before writing one, ask

Getting the graph wrong ships as a 409 on a legitimate request, and the toolkit cannot guess a lifecycle. Ask directly: