feat(ADM-018): completed feature

work/artifacts/F-021/documenter.md

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+# Documenter — F-021 Orders module
+
+## Summary
+Orders module records purchase truth with immutable item snapshots, an explicit state machine, and ownership-scoped reads. OrderCreated is emitted on every creation; OrderPaid and OrderCancelled are emitted on those transitions.
+
+## Public API notes
+
+| Route | Access | Result |
+|---|---|---|
+| POST /orders | authenticated | Creates order with snapshots, returns PENDING |
+| POST /orders/:id/transitions | authenticated | Validates and applies state transition |
+| GET /orders/:id | authenticated | Returns order with items, scoped to user |
+
+## Errors
+- `ORDER_STATE_TRANSITION_INVALID` — HTTP 409
+- `ORDER_NOT_FOUND` — HTTP 404
+
+## State machine
+PENDING -> AWAITING_PAYMENT or CANCELLED
+AWAITING_PAYMENT -> PAID or CANCELLED
+PAID -> PROCESSING, SHIPPED, CANCELLED, REFUNDED
+PROCESSING -> SHIPPED, CANCELLED, REFUNDED
+SHIPPED -> DELIVERED, PARTIALLY_REFUNDED
+DELIVERED -> PARTIALLY_REFUNDED
+CANCELLED, REFUNDED, PARTIALLY_REFUNDED are terminal.
+
+## Evidence
+- `work/artifacts/F-021/architect.md`
+- `work/artifacts/F-021/implementer.md`
+- `work/artifacts/F-021/reviewer.json`
+- `work/artifacts/F-021/security.json`
+- `work/artifacts/F-021/qa.json`