Challenge 3: Add HATEOAS Links — Possible Solution
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{
  "id": 55,
  "status": "shipped",
  "links": {
    "self": "/orders/55",
    "track": "/orders/55/tracking",
    "invoice": "/orders/55/invoice",
    "return": "/orders/55/return"
  }
}

WHY THESE LINKS MAKE SENSE
------------------------------
Given the order's current status is "shipped," the plausible next
actions for a client are things you'd actually want to do with a
shipped order:
  - "self" — a standard link back to the resource itself, present on
    almost every HATEOAS response regardless of state.
  - "track" — since it's shipped, tracking its delivery is an obvious
    next action.
  - "invoice" — retrieving the invoice/receipt is a common related
    action for any completed order.
  - "return" — a shipped order can plausibly be returned once
    received, so surfacing that link lets the client discover this
    capability without hard-coding it.

Note what's intentionally NOT included: a "cancel" link. Once an order
has already shipped, cancelling it outright typically isn't a valid
action anymore (a return would be the correct path instead) — a
well-designed hypermedia response reflects the resource's CURRENT
state by only including links for actions that are actually valid
right now, not a fixed list of every action that could ever apply to
an order at any status.

WHY THIS WORKS AS AN ANSWER
------------------------------
The point of HATEOAS isn't just "add some links" — it's that the set
of links included should change based on the resource's actual state,
so the response itself communicates what's possible next without the
client needing to already know (or guess) the business rules around
when each action is valid.