fix: add atomic Assignment transfer (close old + create new in one transaction)

The only way to move an Assignment to a new employee was two separate calls
(PATCH return + POST create), which is not atomic and left a race window
where a third party could grab the now-in_stock AssetItem in between, plus
no rollback if the second call failed. Adds transferAssignment() which
closes the old Assignment and creates the new one inside a single
prisma.$transaction(), per docs/asset-license-management.md's "Assignment
(chốt 2026-08-02)" spec. Does not touch AssetItem.status or
License.seatsUsed — the resource never becomes free mid-transfer. Wired
into PATCH /api/assignments/[id]: an employeeId key in the body dispatches
to transfer, a returnedAt key to return, both together is rejected as
mutually exclusive.

CLAUDE.md

@@ -113,10 +113,15 @@ Với mỗi mục tiêu nghiệp vụ stakeholder đưa ra (vd "thêm tracking s
 - Rà lại advisory riêng của `next` (prod dependency, có vài high/moderate — vd SSRF qua WebSocket upgrade, middleware bypass) khi có dịp, tách biệt khỏi đợt retrofit Prisma/Zod này.
 - Test coverage gaps (chưa block gì, chỉ là follow-up): chưa test malformed JSON body, chưa test JSON body không phải object (array/string).
 - `Button` (shadcn) không `forwardRef`, React đang pin 18 — dormant risk, xem note ở "Trạng thái hiện tại".
-- Các entity còn lại: `PurchaseOrder`, `Receipt`, `Assignment` (`AssetItem` xong 2026-07-31, `License` xong 2026-08-02, xem "Trạng thái hiện tại"). `Assignment` là entity tiếp theo nên làm — nối `Employee`+`AssetItem`+`License`, trả lời trực tiếp câu hỏi nghiệp vụ "ai đang giữ máy/license nào" nêu ở `docs/asset-license-management.md`.
+- **`Vendor`/`PurchaseOrder`(gộp `Receipt`)/`Assignment`/`AssetCategoryAttributeDef` (2026-08-02): spec đầy đủ ở `docs/asset-license-management.md`, đã có task list phụ thuộc-đúng do `pm`-pass sequencing (2026-08-02), sẵn sàng giao `feature-implementer` theo đúng thứ tự dưới đây (3 lane độc lập, có thể xen kẽ):**
+  - **Lane A (Vendor → License.vendorId → PurchaseOrder → purchaseOrderId x3)**: (1-4) `Vendor` entity chuẩn 4 commit (model+migration/lib/API/test), không phụ thuộc gì. (5) Retrofit `License.vendor` (string) → `License.vendorId` (FK) — **1 commit gộp** (schema+migration+lib+test), theo đúng tiền lệ retrofit `Request.employeeId` (commit `49d96b7`, không tách lớp như entity mới vì tách ra sẽ để lại state nửa vời không chạy được) — tiện thể fix luôn finding cũ của `code-reviewer`: `createLicense()` chưa theo pattern `{ok,value}|{ok,error}`, giờ **bắt buộc** phải thêm vì `vendorId` là FK mới (cần bắt `P2003`). Phụ thuộc (1). (6-9) `PurchaseOrder` entity chuẩn 4 commit (`vendorId` FK, `receivedBy` FK→`Employee`, Zod `.refine()` cho ràng buộc `receivedAt`/`receivedBy` cùng null hoặc cùng có giá trị, bắt `P2003` cho cả 2 FK, theo đúng pattern `{ok,error}` ngay từ đầu) — phụ thuộc (1) `Vendor` + `Employee` (đã có). (10) `AssetItem.purchaseOrderId` — 1 commit gộp (nullable FK). (11) `License.purchaseOrderId` — 1 commit gộp **riêng** với task (5) dù cùng file, vì trigger phụ thuộc khác nhau (`Vendor` vs `PurchaseOrder`) — gộp chung sẽ vi phạm nguyên tắc 1-commit-1-thay-đổi-nghiệp-vụ. (12) `Request.purchaseOrderId` — 1 commit gộp. (10)(11)(12) đều chỉ phụ thuộc (6), độc lập lẫn nhau, thứ tự giữa 3 task này không quan trọng.
+  - **Lane B (AssetCategory → AssetCategoryAttributeDef + AssetModel → wire dynamic validation → AssetItem.modelId)**: **gap phát hiện khi sequencing** — `AssetCategory`/`AssetModel`/`ConsumableItem` đã có spec từ round BA trước (2026-08-02, xem "Phân loại tài sản" trong doc) nhưng **CHƯA build** (không có trong `prisma/schema.prisma` hiện tại, `AssetItem.model` vẫn là string tự do) — phải làm trước thì `AssetCategoryAttributeDef` mới có ý nghĩa. (13-16) `AssetCategory` entity chuẩn 4 commit (`name`, `valueGroup` enum `high_value`/`low_value`), không phụ thuộc gì. (17-20) `AssetCategoryAttributeDef` entity chuẩn 4 commit (`categoryId` FK, `key`, `label`, `dataType` enum, `required`, `sortOrder`, unique `(categoryId,key)` → bắt `P2002`) — phụ thuộc (13), độc lập với `AssetModel`. (21-24) `AssetModel` entity chuẩn 4 commit (`categoryId` FK + business rule "category phải `valueGroup=high_value`" — cần lookup DB, không phải Zod thuần; `manufacturer`, `name`, `specs` JSONB — ở task này `specs` chỉ validate lỏng là object hợp lệ, CHƯA khớp động theo `AssetCategoryAttributeDef`) — phụ thuộc (13), độc lập với (17-20). (25) Wire dynamic specs validation vào `AssetModel` create/update — **1 commit riêng**, không gộp vào (22), vì đây là logic mới/rủi ro (build Zod schema runtime từ `AssetCategoryAttributeDef`, map `dataType`→`z.string()/number()/boolean()/coerce.date()`, từ chối key lạ, bắt buộc key `required`) — phụ thuộc (18) và (22). (26) Retrofit `AssetItem.model` (string) → `AssetItem.modelId` (FK) — 1 commit gộp, phụ thuộc (21) (không cần đợi (25)).
+  - **Lane C (`Assignment`, độc lập hoàn toàn với Lane A/B — chỉ cần `Employee`+`AssetItem`+`License` đã có sẵn)**: (27) model+migration (`employeeId` FK, `assetItemId`/`licenseId` nullable FK, `assignedAt`, `returnedAt` nullable, `signedAt` nullable). (28) lib validation+CRUD — rủi ro nhất trong cả 4 entity: Zod `.refine()` XOR `assetItemId`/`licenseId`, chặn >1 `Assignment` active/`AssetItem`, transaction tăng/giảm `License.seatsUsed` kèm chặn overbook (`seatsUsed >= seatsTotal`), đồng bộ `AssetItem.status` (assigned/in_stock), helper transfer (đóng cũ+mở mới cùng 1 transaction). (29) API routes — **cần quyết định shape mới**: đây là entity đầu tiên cần thao tác "update" (return/transfer) trong khi codebase hiện tại **mọi entity đều chỉ có POST(create)+GET(list), chưa có route update nào** — đề xuất mặc định `POST /api/assignments` (assign/transfer) + `PATCH /api/assignments/[id]` (return, nhận `{returnedAt}}`), cần xác nhận lại khi giao task cho `pm`/`feature-implementer` vì không có tiền lệ. (30) tests. **(31) Bắt buộc code-reviewer pass riêng cho Assignment (diff 27-30) trước khi coi là xong** — đúng rule ở "Multi-agent dev workflow" (state-mutation-với-invariant, seat-count) — không phải 1 commit, là 1 gate.
+  - **2 câu hỏi mở đã được stakeholder trả lời (2026-08-02, xem "Assignment" trong `docs/asset-license-management.md`) — Lane C hết bị chặn**: (a) `createAssignment()` **chặn** nếu `AssetItem.status` khác `in_stock` (400). (b) Route update dùng `PATCH /api/<entity>/[id]` (áp dụng cho cả `Assignment` và `PurchaseOrder`), không dùng action-based sub-route.
+  - `ConsumableItem` (phần catalog, KHÔNG phải luồng "xin+nhận" — luồng đó vẫn BỊ CHẶN chờ 7 câu hỏi mở, xem doc): độc lập với toàn bộ 3 lane trên (chỉ cần `AssetCategory`), sẵn sàng cho `pm` chia task riêng nếu stakeholder muốn gộp vào cùng đợt — không đưa vào sequencing này vì nằm ngoài phạm vi 4 việc được giao lần này.
 - Các state tiếp theo của Request: Pending Approval → Approved → Ordered → Received → Delivered → Closed, và nhánh Rejected/Cancelled
 - UI (hiện chỉ có placeholder home page)
 - Auth/phân quyền (ai được approve request, ai được xác nhận nhận hàng/bàn giao)
 
 ---
-Cập nhật lần cuối: 2026-08-02 (deploy lên homelab ubi.toanhoang.work, License entity)
+Cập nhật lần cuối: 2026-08-02 (deploy lên homelab ubi.toanhoang.work, License entity, task sequencing cho Vendor/PurchaseOrder/Assignment/AssetCategoryAttributeDef)

docs/asset-license-management.md

@@ -23,14 +23,17 @@ Theo dõi toàn bộ vòng đời tài sản/license: **Request → Approval →
 | Entity | Ý nghĩa |
 |---|---|
 | `Employee` | id, tên, phòng ban, manager |
-| `Vendor` | nhà cung cấp |
+| `Vendor` | id, `name`, `contactEmail`, `contactPhone`, `address`, `taxCode` (nullable — mã số thuế VN), `notes` (nullable) — nhà cung cấp/reseller mua hàng qua, **khác** `AssetModel.manufacturer` (hãng sản xuất/OEM). Xem "Vendor" bên dưới |
-| `AssetItem` | hardware — serial number, model, ngày mua, bảo hành, trạng thái (in stock / assigned / repair / retired) |
+| `AssetItem` | hardware **high-value** (serial hóa bắt buộc) — serial number, model (FK → `AssetModel`, bắt buộc — không còn string tự do), ngày mua, bảo hành, trạng thái (in stock / assigned / repair / retired), `purchaseOrderId` (FK → `PurchaseOrder`, nullable — chiều cung, xem "PurchaseOrder" bên dưới). Category không còn gán trực tiếp trên `AssetItem` — suy ra qua `AssetModel.categoryId`. Xem "Phân loại tài sản" bên dưới |
-| `License` | phần mềm — tên, vendor, tổng seat, seat đã dùng, ngày hết hạn, loại (perpetual/subscription) |
+| `License` | phần mềm — tên, `vendorId` (FK → `Vendor`, retrofit từ string tự do — xem "Vendor" bên dưới), tổng seat, seat đã dùng, ngày hết hạn, loại (perpetual/subscription), `purchaseOrderId` (FK → `PurchaseOrder`, nullable — chiều cung, xem "PurchaseOrder" bên dưới) |
-| `Request` | người yêu cầu, loại (asset/license), lý do, trạng thái |
+| `Request` | người yêu cầu, loại (asset/license), lý do, trạng thái, `purchaseOrderId` (FK → `PurchaseOrder`, nullable — chiều cầu, xem "PurchaseOrder" bên dưới) — **chỉ áp dụng cho asset high-value/license**, không dùng cho consumable (xem "Phân loại tài sản" bên dưới) |
-| `PurchaseOrder` | gộp nhiều Request đã duyệt, vendor, ngày đặt, ngày dự kiến nhận |
+| `PurchaseOrder` | id, `vendorId` (FK → `Vendor`), `orderDate`, `expectedDate`, `receivedAt` (nullable — null nghĩa là chưa nhận), `receivedBy` (FK → `Employee`, nullable, set cùng lúc với `receivedAt`). **Gộp luôn `Receipt`** (không còn là entity riêng — nhận hàng là 1 phần trạng thái của chính PO), all-or-nothing theo cả PO (không nhận từng phần), không track giá/chi phí, không có `status` riêng (suy ra từ Request liên kết). Xem "PurchaseOrder" bên dưới |
-| `Receipt` | nhận hàng — đối chiếu PO, ngày nhận, người nhận |
+| `Assignment` | id, `employeeId` (FK → `Employee`), `assetItemId` (FK → `AssetItem`, nullable) / `licenseId` (FK → `License`, nullable — đúng 1 trong 2, XOR), `assignedAt`, `returnedAt` (nullable — null nghĩa đang giữ), `signedAt` (nullable — chỉ là timestamp đánh dấu đã ký, không upload file). Gán AssetItem (high-value)/License cho 1 Employee cụ thể. **Không áp dụng cho consumable** (consumable track theo tồn kho, không gắn 1 người cụ thể). Xem "Assignment" bên dưới |
-| `Assignment` | gán AssetItem/License cho Employee — ngày giao, ngày trả, biên bản ký nhận |
 | `Request.servicenow_ticket` | field text, nhập tay số ticket ServiceNow liên quan (không tích hợp API ServiceNow ngay — volume thấp, nhập tay đủ dùng; để ngỏ cho auto-sync sau nếu cần) |
+| `AssetCategory` | id, tên (vd "Laptop", "Cáp HDMI"), nhóm giá trị cố định (`high_value` \| `low_value`) — danh mục category cụ thể do IT admin tự định nghĩa, không hardcode. Xem "Phân loại tài sản" bên dưới |
+| `AssetModel` | id, category (FK → `AssetCategory`, bắt buộc, phải thuộc nhóm `high_value`), `manufacturer` (vd "Dell"), `name` (vd "Latitude 5420"), `specs` (JSONB — giá trị thật của các thuộc tính động, xem `AssetCategoryAttributeDef`) — tách riêng 2 field `manufacturer`/`name`, không gộp chung 1 string, để filter/report theo hãng. Nằm giữa `AssetCategory` và `AssetItem` (1 model có nhiều `AssetItem` serial khác nhau). Xem "Phân loại tài sản" bên dưới |
+| `AssetCategoryAttributeDef` | id, `categoryId` (FK → `AssetCategory`), `key` (slug, vd `ram_gb`), `label` (tên hiển thị, vd "RAM (GB)"), `dataType` (enum đóng: `string`/`number`/`boolean`/`date`), `required` (bool), `sortOrder` (int) — định nghĩa thuộc tính riêng theo từng category, giá trị thật nằm ở `AssetModel.specs`. Unique `(categoryId, key)`. Xem "Phân loại tài sản" bên dưới |
+| `ConsumableItem` | phụ kiện **low-value/consumable** — tên, category (bắt buộc, phải thuộc nhóm `low_value`, trỏ thẳng `AssetCategory` — **không** qua `AssetModel`, khái niệm "model" chỉ áp dụng cho asset serial hóa), số lượng tồn kho (`quantityOnHand`). **KHÔNG serial hóa, KHÔNG gắn Assignment cá nhân** — chỉ track theo số lượng. Xem "Phân loại tài sản" bên dưới |
 
 ## Luồng trạng thái Request
 
@@ -40,6 +43,79 @@ Draft → Pending Approval → Approved → Ordered → Received → Delivered
              Rejected / Cancelled
 ```
 
+## Phân loại tài sản: High-value vs Low-value/Consumable (chốt 2026-08-02)
+
+**Quyết định đã chốt với stakeholder:** tài sản được phân nhóm theo **category cố định**, KHÔNG theo ngưỡng giá tiền. Mỗi `AssetCategory` thuộc đúng 1 trong 2 nhóm giá trị (`high_value` hoặc `low_value`), category cụ thể do IT admin tự định nghĩa/mở rộng — danh sách dưới đây chỉ là **ví dụ minh hoạ, không phải danh sách đóng**:
+
+- Nhóm `high_value` → đi qua luồng `AssetItem` hiện có nguyên vẹn (serial hóa bắt buộc, track cá nhân qua `Assignment`, đi qua state machine đầy đủ của `Request`). Ví dụ category: Laptop, Màn hình, Máy in, Điện thoại công ty.
+- Nhóm `low_value` (consumable) → entity mới `ConsumableItem`, **không serial hóa**, chỉ track theo số lượng tồn kho (`quantityOnHand`), **không gắn `Assignment`** cho 1 người cụ thể. Ví dụ category: Cáp (HDMI/USB-C/LAN), Chuột, Bàn phím, Túi đựng laptop, Sạc dự phòng.
+
+**Cập nhật 2026-08-02 (2): thêm phân cấp `AssetModel` giữa `AssetCategory` và `AssetItem`.** Lý do: nhiều model khác nhau trong cùng 1 category (vd category "Laptop" có nhiều model "Dell Latitude 5420", "MacBook Pro 14"...), cần report/thống kê theo model (vd "đang có bao nhiêu Dell Latitude 5420"), tránh lỗi gõ tay khi model là string tự do như trước. Phân cấp: `AssetCategory` ("Laptop") → `AssetModel` ("Dell Latitude 5420") → từng `AssetItem` (1 serial cụ thể thuộc model đó). `AssetModel.manufacturer`/`AssetModel.name` tách riêng (không gộp 1 string) để filter/report riêng theo hãng. Khái niệm "model" chỉ có ý nghĩa cho asset serial hóa (`high_value`) — `ConsumableItem` không có model, vẫn trỏ thẳng `AssetCategory` (`low_value`) như cũ.
+
+**Cập nhật 2026-08-02 (3): thêm `AssetCategoryAttributeDef` — thuộc tính đặc thù theo từng category.** Lý do: từng category có bộ thuộc tính riêng cần track (vd RAM/CPU cho category "Laptop", độ phân giải cho "Màn hình") mà không phải asset high-value nào cũng giống nhau — cần định nghĩa động theo category, không hardcode cột cứng cho từng loại thuộc tính.
+
+- Entity mới `AssetCategoryAttributeDef`: `categoryId` (FK → `AssetCategory`), `key` (slug, vd `ram_gb`), `label` (tên hiển thị, vd "RAM (GB)"), `dataType` (enum đóng: `string`/`number`/`boolean`/`date` — đây là tập giá trị kỹ thuật cố định do dev định nghĩa, **khác** với `AssetCategory` là tập mở IT admin tự mở rộng), `required` (bool), `sortOrder` (int, thứ tự hiển thị trên form). Unique `(categoryId, key)`.
+- Mỗi `AssetCategory` có bộ attribute **riêng, độc lập** — cố tình **không** phải thư viện thuộc tính dùng chung giữa các category. Nếu 2 category cùng muốn 1 thuộc tính kiểu "khối lượng (kg)", mỗi category tự tạo 1 row `AssetCategoryAttributeDef` riêng — trùng tên `key` giữa 2 category là bình thường và được chấp nhận, đây là 2 row không liên quan tới nhau. Lý do: ở quy mô hiện tại (ít category), thiết kế thư viện thuộc tính dùng chung (tách riêng bảng `AttributeDef` + bảng join `CategoryAttribute`) cộng thêm độ phức tạp thật (thêm 1 bảng, UX phải chọn "gắn thuộc tính có sẵn hay tạo mới", sửa 1 def ảnh hưởng dây chuyền nhiều category) để đổi lấy lợi ích (sửa 1 chỗ áp dụng khắp nơi, query cross-category an toàn) mà hiện chưa cần tới — stakeholder đã từ chối rõ ràng thiết kế dùng chung để giữ đơn giản.
+- Giá trị thật nằm ở `AssetModel.specs` (cột JSONB) — **không** nằm trên `AssetItem`, vì đây là thuộc tính theo spec-sheet dùng chung cho mọi serial thuộc cùng 1 model (mọi `AssetItem` "Dell Latitude 5420" đều cùng RAM), không phải dữ liệu riêng theo từng instance. Validate động lúc ghi: app build Zod schema runtime từ các `AssetCategoryAttributeDef` thuộc category của model đó (map `dataType` → `z.string()`/`z.number()`/`z.boolean()`/`z.coerce.date()`), từ chối key lạ chưa được định nghĩa cho category, bắt buộc các key có `required = true` phải có mặt.
+- Known gap chấp nhận được, chưa chặn: nếu admin sửa/xoá 1 `AssetCategoryAttributeDef` sau khi đã có `AssetModel` mang giá trị dưới key đó trong `specs`, giá trị cũ trở thành orphaned/stale — chưa có cơ chế migration/cleanup. Ghi nhận là known gap để xử lý khi có UI quản lý attribute-def thật, không cần giải quyết ngay bây giờ.
+
+**Ràng buộc dữ liệu:**
+- `AssetModel.categoryId` bắt buộc, phải trỏ tới 1 `AssetCategory` có `valueGroup = high_value`.
+- `AssetItem.modelId` bắt buộc, phải trỏ tới 1 `AssetModel` có thật (thay cho field `model` string tự do trước đây — đã đổi, không cần chiến lược backfill vì DB chưa có `AssetItem` thật). `AssetItem` không còn giữ `categoryId` trực tiếp — category được suy ra qua `AssetItem.modelId → AssetModel.categoryId` (tránh 2 nguồn sự thật có thể lệch nhau).
+- `ConsumableItem.categoryId` bắt buộc, phải trỏ tới 1 `AssetCategory` có `valueGroup = low_value` — trỏ thẳng, không qua `AssetModel`.
+- `Request` (state machine đầy đủ) tiếp tục chỉ áp dụng cho `type: asset|license` như hiện tại — **không** mở rộng `RequestType` thêm `consumable`.
+- `AssetCategoryAttributeDef.categoryId` bắt buộc, phải trỏ tới 1 `AssetCategory` có thật. Unique `(categoryId, key)`.
+- `AssetModel.specs` (JSONB) chỉ được chứa các key đã có `AssetCategoryAttributeDef` tương ứng với category của model đó — validate ở tầng Zod (build động lúc runtime), không phải DB CHECK constraint (nhất quán với nguyên tắc "không raw SQL cho app logic" của codebase).
+
+**Luồng riêng cho consumable ("xin + nhận" đơn giản hoá):** stakeholder đã xác nhận muốn 1 luồng gọn hơn state machine đầy đủ của `Request`, nhưng **chưa chốt chi tiết state/approval/xử lý hết hàng** — xem danh sách câu hỏi mở trong spec BA (2026-08-02, lưu ở lịch sử trao đổi/PR liên quan). Không build luồng này (entity `ConsumableRequest` hoặc tương đương) tới khi có câu trả lời — chỉ mới build phần catalog (`AssetCategory`, `ConsumableItem`).
+
+## Vendor (chốt 2026-08-02)
+
+Entity mới, độc lập với `AssetModel`.
+
+- Field: `id`, `name`, `contactEmail`, `contactPhone`, `address`, `taxCode` (nullable — mã số thuế VN), `notes` (nullable).
+- **Phân biệt quan trọng:** `Vendor` (nơi mua hàng — vd nhà phân phối/reseller VN) là khái niệm **khác** `AssetModel.manufacturer` (hãng sản xuất/OEM, vd "Dell") — không phải lúc nào cũng cùng 1 công ty (vd mua laptop Dell qua reseller "FPT Trading", không mua thẳng từ Dell). Quyết định: giữ nguyên `AssetModel.manufacturer` là string tự do như hiện tại (không đổi gì); `Vendor` chỉ dùng cho quan hệ mua sắm (`PurchaseOrder`, `License`).
+- **Retrofit `License.vendor`** (hiện là string tự do) → **`License.vendorId`** (FK → `Vendor`), theo đúng tiền lệ đã có trong codebase (`Request.employeeId` string→FK khi `Employee` ra đời, `AssetItem.model` string→FK khi `AssetModel` ra đời — xem "Trạng thái hiện tại" ở `../CLAUDE.md`). Chưa có `License` thật nào trong DB production nên đây là đổi kiểu cột thuần tuý, **không cần chiến lược backfill** — giống các retrofit trước đó.
+
+**Ràng buộc dữ liệu:**
+- `License.vendorId` bắt buộc, phải trỏ tới 1 `Vendor` có thật (thay cho field `vendor` string tự do trước đây).
+
+## PurchaseOrder (gộp Receipt) (chốt 2026-08-02)
+
+**Quyết định: gộp `Receipt` vào `PurchaseOrder`, không giữ là entity riêng nữa** — nhận hàng chỉ là 1 phần trạng thái của chính PO đó (`receivedAt`/`receivedBy`), không cần 1 bảng riêng để đối chiếu. Row `Receipt` trong bảng Data model ở trên đã được xoá, gộp vào row `PurchaseOrder`.
+
+- Field: `id`, `vendorId` (FK → `Vendor`), `orderDate`, `expectedDate`, `receivedAt` (nullable DateTime — null nghĩa là chưa nhận), `receivedBy` (nullable FK → `Employee`, set cùng lúc với `receivedAt`).
+- Cố tình **không** có field giá/chi phí — stakeholder nói rõ `PurchaseOrder` không cần track tiền, chỉ cần trả lời "asset/license nào thuộc PO nào".
+- Cố tình **không** có field `PurchaseOrder.status` riêng — trạng thái suy ra từ trạng thái của các `Request` liên kết (`Request` đã có state machine `Ordered → Received → Delivered` riêng), tránh 2 nguồn sự thật.
+- **Nhận hàng là all-or-nothing theo từng PO** ("nhận 1 lần đủ cho cả PO") — không hỗ trợ nhận nhiều đợt/từng phần. Đây là đánh đổi đơn giản hoá **có chủ ý**, stakeholder đã biết rõ và chấp nhận có thể cần đổi lại sau (paraphrase: "giờ làm đơn giản vậy trước, sau này cần đổi thì tính tiếp") — ghi lại rõ đây là tradeoff/assumption đã note, không phải bỏ sót khi viết spec.
+- **Traceability** (đúng yêu cầu cốt lõi của stakeholder: "chỉ cần biết asset nằm trong PO nào"): thêm `purchaseOrderId` (nullable FK → `PurchaseOrder`) ở **CẢ BA** chỗ — `AssetItem`, `License`, và `Request`. Ba field này phục vụ mục đích khác nhau, không dư thừa:
+  - `Request.purchaseOrderId` — chiều cầu (demand-side): request nào đã duyệt được gộp vào PO này (đây vốn là mục đích ban đầu đã note trong doc cho `PurchaseOrder`: "gộp nhiều Request đã duyệt").
+  - `AssetItem.purchaseOrderId` và `License.purchaseOrderId` — chiều cung (supply-side): record tồn kho/thực tế nào tới qua PO này. Set lúc intake/tạo mới. Nullable vì không phải `AssetItem`/`License` nào cũng đi qua 1 PO chính thức (vd tồn kho lịch sử nhập trước khi có hệ thống).
+
+**Ràng buộc dữ liệu:**
+- `PurchaseOrder.vendorId` bắt buộc, trỏ tới 1 `Vendor` có thật.
+- `PurchaseOrder.receivedBy` chỉ set cùng lúc với `receivedAt` (cả hai cùng null hoặc cùng có giá trị).
+- `AssetItem.purchaseOrderId`, `License.purchaseOrderId`, `Request.purchaseOrderId` đều nullable, trỏ tới `PurchaseOrder` nếu có.
+- `PurchaseOrder` không có field `status` — suy ra qua `Request` liên kết, không lưu trùng.
+
+## Assignment (chốt 2026-08-02)
+
+- Field: `id`, `employeeId` (FK → `Employee`), `assetItemId` (FK → `AssetItem`, nullable), `licenseId` (FK → `License`, nullable), `assignedAt`, `returnedAt` (nullable — null nghĩa đang giữ), `signedAt` (nullable DateTime — null nghĩa biên bản chưa ký. Cố tình chỉ là 1 timestamp đánh dấu đã ký/chưa, **KHÔNG** phải upload file — stakeholder đã quyết định rõ không cần lưu file scan lúc này, "biên bản ký nhận" chỉ cần đánh dấu đã ký + ngày ký).
+- Đúng 1 trong 2 (`assetItemId`/`licenseId`) phải được set — không cả hai, không cả hai đều rỗng (XOR) — validate ở tầng Zod qua `.refine()`, theo đúng cách codebase đã xử lý validate cross-field (không phải DB CHECK constraint, đúng nguyên tắc "không raw SQL cho app logic" — Prisma schema cũng không diễn tả được constraint XOR này natively).
+- Không phải entity mới, nhưng có các business rule tầng application cần note lại rõ ở đây (đủ quan trọng để phát sinh bug nếu bỏ sót, nhưng là rule app phải tự enforce, không phải bản thân là 1 entity):
+  - 1 `AssetItem` chỉ có tối đa 1 `Assignment` **active** (`returnedAt IS NULL`) tại 1 thời điểm — không thể bị giữ bởi 2 người cùng lúc. Enforce trước khi tạo `Assignment` mới.
+  - Assign 1 `License` phải **tăng** `License.seatsUsed`, và phải **bị từ chối** nếu `seatsUsed >= seatsTotal` (không overbook). Trả lại (set `returnedAt`) **giảm** `seatsUsed`. Toàn bộ phải chạy trong 1 transaction — đây chính là rủi ro seat-count race condition mà `code-reviewer` đã note trước đó cho `License` (xem "Trạng thái hiện tại" ở `../CLAUDE.md`, mục `License`) — `Assignment` là chỗ thực sự implement/exercise seat counting lần đầu tiên.
+  - Chuyển tài sản giữa nhân viên (case đặc biệt đã note ở trên: "Tài sản luân chuyển giữa phòng ban / chi nhánh") = đóng `Assignment` cũ (`returnedAt = now`) + tạo `Assignment` mới, cả hai trong 1 transaction. Không cần entity "Transfer" riêng.
+  - `AssetItem.status` phải đồng bộ theo trạng thái `Assignment`: tạo `Assignment` → status `assigned`; trả lại → status `in_stock`, trừ nhánh RMA/sửa chữa đã note ở "Case đặc biệt cần xử lý" (đó là case riêng, không đi qua path trả-lại-thông-thường này).
+  - **Chốt 2026-08-02 (trả lời 2 câu hỏi mở của `pm`):** (a) `createAssignment()` phải **chặn** nếu `AssetItem.status` hiện tại khác `in_stock` (vd không cho assign 1 item đang `repair`/`retired`) — trả lỗi 400, không chỉ dựa vào điều kiện "chưa có Assignment active nào". (b) Route "update" (trả lại/chuyển giao `Assignment`, nhận hàng `PurchaseOrder`) dùng `PATCH /api/<entity>/[id]` — tiền lệ REST-shape đầu tiên cho update trong codebase, áp dụng thống nhất cho cả `Assignment` và `PurchaseOrder`, không dùng action-based sub-route.
+
+**Ràng buộc dữ liệu:**
+- `Assignment.employeeId` bắt buộc, trỏ tới 1 `Employee` có thật.
+- Đúng 1 trong `assetItemId`/`licenseId` được set (XOR) — validate Zod `.refine()`.
+- Không được có > 1 `Assignment` active cho cùng 1 `AssetItem` tại 1 thời điểm (enforce ở tầng application, không phải DB constraint).
+- Tạo `Assignment` bị chặn nếu `AssetItem.status` khác `in_stock` (400).
+- `License.seatsUsed` tăng/giảm đồng bộ trong 1 transaction khi assign/return; assign bị chặn nếu `seatsUsed >= seatsTotal`.
+
 ## Module tương lai: Rack/Slot management + IoT (chưa build, chỉ note kiến trúc)
 
 Mục tiêu xa hơn: biết chính xác asset nằm ở ô/slot nào trên tủ rack, và hướng dẫn người lấy đúng ô bằng đèn (pick-to-light).
@@ -93,7 +169,8 @@ QR gán asset vào slot (bước 1, thủ công hàng ngày) **không phải IoT
 ## Việc còn dở
 
 - Thiết kế ERD chi tiết + wireframe màn hình
-- Entity còn lại: `PurchaseOrder`, `Receipt`, `Assignment` (`Employee`, `AssetItem` đã xong 2026-07-31; `License` xong 2026-08-02, xem `../CLAUDE.md`)
+- **`Vendor`, `PurchaseOrder` (gộp `Receipt`), `Assignment`, `AssetCategoryAttributeDef` (2026-08-02): đã có spec đầy đủ (BA), sẵn sàng cho `pm` chia task** — xem các mục "Vendor", "PurchaseOrder (gộp Receipt)", "Assignment" và "Cập nhật 2026-08-02 (3)" trong "Phân loại tài sản" ở trên. Bao gồm cả retrofit `License.vendor` (string) → `License.vendorId` (FK → `Vendor`, không cần backfill vì chưa có `License` thật trong DB) và thêm `purchaseOrderId` (nullable FK) vào `AssetItem`/`License`/`Request`. Thứ tự phụ thuộc gợi ý cho `pm`: `Vendor` → retrofit `License.vendorId` → `PurchaseOrder` (+ `purchaseOrderId` trên 3 entity) → `Assignment`; `AssetCategoryAttributeDef` độc lập, có thể làm song song.
+- Consumable (2026-08-02): phần phân loại (`AssetCategory`, `ConsumableItem`) đã có spec đầy đủ (BA), sẵn sàng cho `pm` chia task. Luồng "xin + nhận" (`ConsumableRequest` hoặc tương đương) **BỊ CHẶN** — cần stakeholder trả lời các câu hỏi mở: (1) có cần approval không, ai duyệt; (2) ai được tạo request xin (tự xin cho mình hay xin hộ được); (3) có giới hạn số lượng tối đa/lần xin không; (4) hết hàng thì chặn hẳn / cho "nợ" chờ nhập thêm / fulfill một phần; (5) trừ tồn kho lúc tạo request hay lúc fulfill; (6) restock tồn kho qua luồng nào, ai được làm; (7) có cần ghi nhận người phát hàng/ký nhận không. Không tự đoán — xem chi tiết đầy đủ trong spec BA.
 - Migrate 2 request đang có (`Firefly_License_Request.docx`, `Eric Pelatan.docx`, ở workspace `ubisoft/` ngoài repo này) vào hệ thống mới sau khi có DB
 - (Xa hơn, chưa ưu tiên) Rack/Slot + IoT pick-to-light, cron email cảnh báo license hết hạn, Power BI report views
 - Setup Gitea tự host ở nhà (2026-07-31) — dự định làm remote chính sau này, giữ GitHub làm backup off-site (đây là "sản phẩm dùng cả đời" của user, không nên chỉ có 1 bản duy nhất). Tạm thời vẫn push GitHub như hiện tại, chưa làm gấp.
@@ -103,4 +180,4 @@ QR gán asset vào slot (bước 1, thủ công hàng ngày) **không phải IoT
 - Migrate entity `Request` từ SQLite sang Postgres (2026-07-30) và setup ESLint đều đã **CONFIRMED xong** qua lượt verify độc lập (test-runner riêng, không phải agent vừa code tự chấm) — 6 test pass trên Postgres thật, lint sạch, type-check sạch. Chi tiết trạng thái nằm ở `../CLAUDE.md`, không duplicate ở đây.
 
 ---
-Cập nhật lần cuối: 2026-08-02
+Cập nhật lần cuối: 2026-08-02 (spec `Vendor`, `PurchaseOrder` gộp `Receipt`, `Assignment`, `AssetCategoryAttributeDef` — sẵn sàng cho `pm` chia task)

prisma/migrations/20260802232754_add_vendor/migration.sql

@@ -0,0 +1,13 @@
+-- CreateTable
+CREATE TABLE "vendors" (
+    "id" UUID NOT NULL,
+    "name" TEXT NOT NULL,
+    "contact_email" TEXT NOT NULL,
+    "contact_phone" TEXT NOT NULL,
+    "address" TEXT NOT NULL,
+    "tax_code" TEXT,
+    "notes" TEXT,
+    "created_at" TIMESTAMPTZ(6) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "vendors_pkey" PRIMARY KEY ("id")
+);

prisma/migrations/20260802234029_retrofit_license_vendor_id/migration.sql

@@ -0,0 +1,13 @@
+/*
+  Warnings:
+
+  - You are about to drop the column `vendor` on the `licenses` table. All the data in the column will be lost.
+  - Added the required column `vendor_id` to the `licenses` table without a default value. This is not possible if the table is not empty.
+
+*/
+-- AlterTable
+ALTER TABLE "licenses" DROP COLUMN "vendor",
+ADD COLUMN     "vendor_id" UUID NOT NULL;
+
+-- AddForeignKey
+ALTER TABLE "licenses" ADD CONSTRAINT "licenses_vendor_id_fkey" FOREIGN KEY ("vendor_id") REFERENCES "vendors"("id") ON DELETE RESTRICT ON UPDATE CASCADE;

prisma/migrations/20260802235729_add_purchase_order/migration.sql

@@ -0,0 +1,18 @@
+-- CreateTable
+CREATE TABLE "purchase_orders" (
+    "id" UUID NOT NULL,
+    "vendor_id" UUID NOT NULL,
+    "order_date" TIMESTAMPTZ(6) NOT NULL,
+    "expected_date" TIMESTAMPTZ(6) NOT NULL,
+    "received_at" TIMESTAMPTZ(6),
+    "received_by" UUID,
+    "created_at" TIMESTAMPTZ(6) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "purchase_orders_pkey" PRIMARY KEY ("id")
+);
+
+-- AddForeignKey
+ALTER TABLE "purchase_orders" ADD CONSTRAINT "purchase_orders_vendor_id_fkey" FOREIGN KEY ("vendor_id") REFERENCES "vendors"("id") ON DELETE RESTRICT ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "purchase_orders" ADD CONSTRAINT "purchase_orders_received_by_fkey" FOREIGN KEY ("received_by") REFERENCES "employees"("id") ON DELETE SET NULL ON UPDATE CASCADE;

prisma/migrations/20260803000720_add_asset_item_purchase_order_id/migration.sql

@@ -0,0 +1,5 @@
+-- AlterTable
+ALTER TABLE "asset_items" ADD COLUMN     "purchase_order_id" UUID;
+
+-- AddForeignKey
+ALTER TABLE "asset_items" ADD CONSTRAINT "asset_items_purchase_order_id_fkey" FOREIGN KEY ("purchase_order_id") REFERENCES "purchase_orders"("id") ON DELETE SET NULL ON UPDATE CASCADE;

prisma/migrations/20260803001538_add_license_purchase_order_id/migration.sql

@@ -0,0 +1,5 @@
+-- AlterTable
+ALTER TABLE "licenses" ADD COLUMN     "purchase_order_id" UUID;
+
+-- AddForeignKey
+ALTER TABLE "licenses" ADD CONSTRAINT "licenses_purchase_order_id_fkey" FOREIGN KEY ("purchase_order_id") REFERENCES "purchase_orders"("id") ON DELETE SET NULL ON UPDATE CASCADE;

prisma/migrations/20260803002253_add_request_purchase_order_id/migration.sql

@@ -0,0 +1,5 @@
+-- AlterTable
+ALTER TABLE "requests" ADD COLUMN     "purchase_order_id" UUID;
+
+-- AddForeignKey
+ALTER TABLE "requests" ADD CONSTRAINT "requests_purchase_order_id_fkey" FOREIGN KEY ("purchase_order_id") REFERENCES "purchase_orders"("id") ON DELETE SET NULL ON UPDATE CASCADE;

prisma/migrations/20260803003026_add_asset_category/migration.sql

@@ -0,0 +1,12 @@
+-- CreateEnum
+CREATE TYPE "AssetCategoryValueGroup" AS ENUM ('high_value', 'low_value');
+
+-- CreateTable
+CREATE TABLE "asset_categories" (
+    "id" UUID NOT NULL,
+    "name" TEXT NOT NULL,
+    "value_group" "AssetCategoryValueGroup" NOT NULL,
+    "created_at" TIMESTAMPTZ(6) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "asset_categories_pkey" PRIMARY KEY ("id")
+);

prisma/migrations/20260803003747_add_asset_category_attribute_def/migration.sql

@@ -0,0 +1,22 @@
+-- CreateEnum
+CREATE TYPE "AssetAttributeDataType" AS ENUM ('string', 'number', 'boolean', 'date');
+
+-- CreateTable
+CREATE TABLE "asset_category_attribute_defs" (
+    "id" UUID NOT NULL,
+    "category_id" UUID NOT NULL,
+    "key" TEXT NOT NULL,
+    "label" TEXT NOT NULL,
+    "data_type" "AssetAttributeDataType" NOT NULL,
+    "required" BOOLEAN NOT NULL,
+    "sort_order" INTEGER NOT NULL,
+    "created_at" TIMESTAMPTZ(6) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "asset_category_attribute_defs_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "asset_category_attribute_defs_category_id_key_key" ON "asset_category_attribute_defs"("category_id", "key");
+
+-- AddForeignKey
+ALTER TABLE "asset_category_attribute_defs" ADD CONSTRAINT "asset_category_attribute_defs_category_id_fkey" FOREIGN KEY ("category_id") REFERENCES "asset_categories"("id") ON DELETE RESTRICT ON UPDATE CASCADE;

prisma/migrations/20260803004634_add_asset_model/migration.sql

@@ -0,0 +1,14 @@
+-- CreateTable
+CREATE TABLE "asset_models" (
+    "id" UUID NOT NULL,
+    "category_id" UUID NOT NULL,
+    "manufacturer" TEXT NOT NULL,
+    "name" TEXT NOT NULL,
+    "specs" JSONB NOT NULL DEFAULT '{}',
+    "created_at" TIMESTAMPTZ(6) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "asset_models_pkey" PRIMARY KEY ("id")
+);
+
+-- AddForeignKey
+ALTER TABLE "asset_models" ADD CONSTRAINT "asset_models_category_id_fkey" FOREIGN KEY ("category_id") REFERENCES "asset_categories"("id") ON DELETE RESTRICT ON UPDATE CASCADE;

prisma/migrations/20260803010401_retrofit_asset_item_model_id/migration.sql

@@ -0,0 +1,13 @@
+/*
+  Warnings:
+
+  - You are about to drop the column `model` on the `asset_items` table. All the data in the column will be lost.
+  - Added the required column `model_id` to the `asset_items` table without a default value. This is not possible if the table is not empty.
+
+*/
+-- AlterTable
+ALTER TABLE "asset_items" DROP COLUMN "model",
+ADD COLUMN     "model_id" UUID NOT NULL;
+
+-- AddForeignKey
+ALTER TABLE "asset_items" ADD CONSTRAINT "asset_items_model_id_fkey" FOREIGN KEY ("model_id") REFERENCES "asset_models"("id") ON DELETE RESTRICT ON UPDATE CASCADE;

prisma/migrations/20260803011331_add_assignment/migration.sql

@@ -0,0 +1,22 @@
+-- CreateTable
+CREATE TABLE "assignments" (
+    "id" UUID NOT NULL,
+    "employee_id" UUID NOT NULL,
+    "asset_item_id" UUID,
+    "license_id" UUID,
+    "assigned_at" TIMESTAMPTZ(6) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "returned_at" TIMESTAMPTZ(6),
+    "signed_at" TIMESTAMPTZ(6),
+    "created_at" TIMESTAMPTZ(6) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "assignments_pkey" PRIMARY KEY ("id")
+);
+
+-- AddForeignKey
+ALTER TABLE "assignments" ADD CONSTRAINT "assignments_employee_id_fkey" FOREIGN KEY ("employee_id") REFERENCES "employees"("id") ON DELETE RESTRICT ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "assignments" ADD CONSTRAINT "assignments_asset_item_id_fkey" FOREIGN KEY ("asset_item_id") REFERENCES "asset_items"("id") ON DELETE SET NULL ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "assignments" ADD CONSTRAINT "assignments_license_id_fkey" FOREIGN KEY ("license_id") REFERENCES "licenses"("id") ON DELETE SET NULL ON UPDATE CASCADE;

prisma/schema.prisma

@@ -40,6 +40,15 @@ model Request {
   // plain string (not an enum) until more states exist — see
   // src/lib/requests.ts's RequestStatus type.
   status          String         @default("Draft")
+  // Nullable FK to PurchaseOrder — see docs/asset-license-management.md's
+  // "## PurchaseOrder (gộp Receipt)" Traceability bullet. Semantically the
+  // DEMAND side, unlike AssetItem.purchaseOrderId/License.purchaseOrderId
+  // (supply-side intake): this records "which approved Request got grouped
+  // into this PO", not "which PO did this item come in through". Shape is
+  // identical to those two though — nullable FK, set at creation time only,
+  // no update endpoint for this field yet, same P2003-on-insert handling.
+  purchaseOrderId String?        @map("purchase_order_id") @db.Uuid
+  purchaseOrder   PurchaseOrder? @relation(fields: [purchaseOrderId], references: [id])
   createdAt       DateTime       @default(now()) @map("created_at") @db.Timestamptz(6)
 
   @@map("requests")
@@ -58,6 +67,13 @@ model Employee {
   manager                Employee?       @relation("EmployeeManager", fields: [managerId], references: [id])
   reports                Employee[]      @relation("EmployeeManager")
   requests               Request[]
+  // Back-relation for PurchaseOrder.receivedById — an Employee can be the
+  // receiver on multiple POs over time.
+  purchaseOrdersReceived PurchaseOrder[]
+  // Back-relation for Assignment.employeeId — an Employee can hold multiple
+  // Assignments (assets/licenses) over time, including several active ones
+  // at once (e.g. a laptop + a license seat simultaneously).
+  assignments            Assignment[]
   createdAt              DateTime        @default(now()) @map("created_at") @db.Timestamptz(6)
 
   @@map("employees")
@@ -75,19 +91,40 @@ enum AssetItemStatus {
 
 // Hardware inventory — see docs/asset-license-management.md's "Data model
 // (sơ bộ)" table (serial number, model, ngày mua, bảo hành, trạng thái).
-// No Vendor/Assignment relation yet — those entities don't exist yet
+// No Assignment relation yet — that entity doesn't exist yet (see "Việc còn
-// (see "Việc còn dở" in CLAUDE.md), so this is a standalone entity for now,
+// dở" in CLAUDE.md). warrantyEndDate is nullable: not every asset has known
-// same starting shape as Employee before Request grew an FK to it.
+// warranty terms at intake time (smallest sensible assumption — doesn't
-// warrantyEndDate is nullable: not every asset has known warranty terms at
+// block creation). purchaseOrderId is a nullable FK to PurchaseOrder — see
-// intake time (smallest sensible assumption — doesn't block creation).
+// docs/asset-license-management.md's "## PurchaseOrder (gộp Receipt)"
+// Traceability bullet: supply-side traceability ("which PO did this asset
+// item come in through"). Nullable because not every AssetItem goes through
+// a formal PO (e.g. historical stock predating the system). Set at
+// intake/creation time only — no update endpoint for this field yet, same
+// precedent as License.vendorId being set-at-creation with no PATCH.
+// `modelId` was a free-text `model` String until the "Cập nhật 2026-08-02
+// (2)" retrofit (docs/asset-license-management.md's "Ràng buộc dữ liệu"
+// bullet) — same precedent as Request.employeeId/License.vendorId (string
+// -> FK once the referenced entity existed). No production `AssetItem` data
+// existed at the time of this change, so this was a plain column-type
+// migration, not a backfill. Required (not nullable) — every AssetItem must
+// belong to a real AssetModel. AssetItem deliberately does NOT carry its own
+// `categoryId` — category is derived via `modelId -> AssetModel.categoryId`
+// to avoid two sources of truth that could drift apart.
 model AssetItem {
   id              String          @id @default(uuid()) @db.Uuid
   serialNumber    String          @unique @map("serial_number")
-  model           String
+  modelId         String          @map("model_id") @db.Uuid
+  model           AssetModel      @relation(fields: [modelId], references: [id])
   purchaseDate    DateTime        @map("purchase_date") @db.Date
   warrantyEndDate DateTime?       @map("warranty_end_date") @db.Date
   status          AssetItemStatus @default(in_stock)
+  purchaseOrderId String?         @map("purchase_order_id") @db.Uuid
+  purchaseOrder   PurchaseOrder?  @relation(fields: [purchaseOrderId], references: [id])
   createdAt       DateTime        @default(now()) @map("created_at") @db.Timestamptz(6)
+  // Back-relation for Assignment.assetItemId — an AssetItem can have
+  // multiple Assignment rows over its lifetime (historical + at most one
+  // active, see Assignment model's comment), not built until this task.
+  assignments     Assignment[]
 
   @@map("asset_items")
 }
@@ -102,26 +139,267 @@ enum LicenseType {
 
 // Software license inventory — see docs/asset-license-management.md's "Data
 // model (sơ bộ)" table (tên, vendor, tổng seat, seat đã dùng, ngày hết hạn,
-// loại). `vendor` is deliberately a plain String for now, not a separate
+// loại). `vendorId` was a free-text `vendor` String until the "## Vendor
-// Vendor entity — no Vendor entity exists yet, same "plain string for now"
+// (chốt 2026-08-02)" retrofit — same precedent as Request.employeeId
-// precedent as Employee.department. `seatsUsed` is a stored counter
+// (string -> FK once Employee existed). No production `License` data
-// (defaults to 0 at creation), not a computed value — it will only ever be
+// existed at the time of this change, so this was a plain column-type
-// set to 0 here since Assignment (the thing that would consume seats)
+// migration, not a backfill. `seatsUsed` is a stored counter (defaults to 0
-// doesn't exist yet. `expiryDate` is nullable: perpetual licenses never
+// at creation), not a computed value — it will only ever be set to 0 here
-// expire, only subscription licenses usually have one.
+// since Assignment (the thing that would consume seats) doesn't exist yet.
+// `expiryDate` is nullable: perpetual licenses never expire, only
+// subscription licenses usually have one. `purchaseOrderId` is a nullable FK
+// to PurchaseOrder — see docs/asset-license-management.md's "## PurchaseOrder
+// (gộp Receipt)" Traceability bullet: supply-side traceability ("which PO
+// did this license come in through"). Nullable because not every License
+// goes through a formal PO. Mirrors AssetItem.purchaseOrderId's just-merged
+// pattern exactly — same nullable-FK shape, set at creation time only, no
+// update endpoint for this field yet.
 model License {
   id              String         @id @default(uuid()) @db.Uuid
   name            String
-  vendor      String
+  vendorId        String         @map("vendor_id") @db.Uuid
+  vendor          Vendor         @relation(fields: [vendorId], references: [id])
   seatsTotal      Int            @map("seats_total")
   seatsUsed       Int            @default(0) @map("seats_used")
   expiryDate      DateTime?      @map("expiry_date") @db.Date
   licenseType     LicenseType    @map("license_type")
+  purchaseOrderId String?        @map("purchase_order_id") @db.Uuid
+  purchaseOrder   PurchaseOrder? @relation(fields: [purchaseOrderId], references: [id])
   createdAt       DateTime       @default(now()) @map("created_at") @db.Timestamptz(6)
+  // Back-relation for Assignment.licenseId — a License can have multiple
+  // Assignment rows (one per seat handed out, plus historical returns), not
+  // built until this task.
+  assignments     Assignment[]
 
   @@map("licenses")
 }
 
+// Purchasing counterparty — see docs/asset-license-management.md's "## Vendor
+// (chốt 2026-08-02)". Deliberately independent of AssetModel.manufacturer
+// (OEM, e.g. "Dell") — Vendor is the reseller/distributor actually bought
+// from (e.g. "FPT Trading"), a different concept that isn't always the same
+// company. `licenses` is the back-relation from the License.vendor ->
+// License.vendorId retrofit (same doc section). `purchaseOrders` is the
+// back-relation from PurchaseOrder.vendorId (see "## PurchaseOrder (gộp
+// Receipt) (chốt 2026-08-02)"). taxCode/notes are nullable — not every
+// vendor record has a known VN tax code or extra notes at creation time.
+model Vendor {
+  id             String          @id @default(uuid()) @db.Uuid
+  name           String
+  contactEmail   String          @map("contact_email")
+  contactPhone   String          @map("contact_phone")
+  address        String
+  taxCode        String?         @map("tax_code")
+  notes          String?
+  createdAt      DateTime        @default(now()) @map("created_at") @db.Timestamptz(6)
+  licenses       License[]
+  purchaseOrders PurchaseOrder[]
+
+  @@map("vendors")
+}
+
+// Purchasing document — see docs/asset-license-management.md's "##
+// PurchaseOrder (gộp Receipt) (chốt 2026-08-02)". Deliberately absorbs what
+// would otherwise be a separate `Receipt` entity: receiving is just part of
+// this row's own state (`receivedAt`/`receivedBy`), not a separate table to
+// reconcile against. No `status` field — status is inferred from linked
+// `Request`s (Ordered -> Received -> Delivered), not stored here, to avoid
+// two sources of truth. No cost/price fields — stakeholder said explicitly
+// PurchaseOrder doesn't need to track money, only "which asset/license
+// belongs to which PO". Receiving is all-or-nothing per PO (no partial
+// receipt tracking) — a deliberate simplification, see doc for the
+// stakeholder-accepted tradeoff. `receivedAt`/`receivedBy` are both
+// nullable and must be co-null/co-set together (both-null = not yet
+// received) — enforced at the Zod layer (src/lib/purchase-orders.ts), not a
+// DB constraint, same approach as other cross-field invariants in this
+// codebase (e.g. Assignment's assetItemId/licenseId XOR, not built yet).
+// `assetItems` is the back-relation from the AssetItem.purchaseOrderId
+// retrofit (supply-side traceability, same doc section). `licenses` is the
+// back-relation from the License.purchaseOrderId retrofit (same doc
+// section, same rationale). `requests` is the back-relation from the
+// Request.purchaseOrderId retrofit — the DEMAND side ("which approved
+// Request got grouped into this PO"), as opposed to assetItems/licenses
+// which are the SUPPLY side (intake traceability) — see Request model's
+// comment above for the distinction.
+model PurchaseOrder {
+  id           String      @id @default(uuid()) @db.Uuid
+  vendorId     String      @map("vendor_id") @db.Uuid
+  vendor       Vendor      @relation(fields: [vendorId], references: [id])
+  orderDate    DateTime    @map("order_date") @db.Timestamptz(6)
+  expectedDate DateTime    @map("expected_date") @db.Timestamptz(6)
+  receivedAt   DateTime?   @map("received_at") @db.Timestamptz(6)
+  receivedById String?     @map("received_by") @db.Uuid
+  receivedBy   Employee?   @relation(fields: [receivedById], references: [id])
+  createdAt    DateTime    @default(now()) @map("created_at") @db.Timestamptz(6)
+  assetItems   AssetItem[]
+  licenses     License[]
+  requests     Request[]
+
+  @@map("purchase_orders")
+}
+
+// Fixed, closed set of 2 values tied to the domain (see docs/
+// asset-license-management.md's "## Phân loại tài sản: High-value vs
+// Low-value/Consumable" section) — native Postgres enum, same rationale as
+// RequestType/AssetItemStatus/LicenseType above. Determines downstream
+// rules for entities that will attach to a category later (not built in
+// this task): AssetModel.categoryId must point to a `high_value` category,
+// ConsumableItem.categoryId must point to a `low_value` category.
+enum AssetCategoryValueGroup {
+  high_value
+  low_value
+}
+
+// Asset classification catalog — see docs/asset-license-management.md's
+// "## Phân loại tài sản" section and the `AssetCategory` row in the "Data
+// model (sơ bộ)" table. Standalone entity, no FKs (same starting shape as
+// Vendor before it grew relations) — `AssetModel` and
+// `AssetCategoryAttributeDef` will attach to this via `categoryId` in
+// later tasks (not this one). IT admin defines the concrete categories
+// (e.g. "Laptop", "Cáp HDMI") freely; only `valueGroup` is a fixed 2-value
+// set.
+model AssetCategory {
+  id            String                      @id @default(uuid()) @db.Uuid
+  name          String
+  valueGroup    AssetCategoryValueGroup     @map("value_group")
+  createdAt     DateTime                    @default(now()) @map("created_at") @db.Timestamptz(6)
+  attributeDefs AssetCategoryAttributeDef[]
+  // Back-relation for AssetModel.categoryId — see "Cập nhật 2026-08-02 (2)"
+  // in docs/asset-license-management.md. Only categories with
+  // valueGroup=high_value are ever actually referenced by an AssetModel (a
+  // business rule enforced in src/lib/asset-models.ts's createAssetModel(),
+  // not expressible as a Prisma-level constraint), but the relation itself
+  // is not restricted to high_value categories at the schema level.
+  assetModels   AssetModel[]
+
+  @@map("asset_categories")
+}
+
+// Fixed, closed set of 4 values — a DEV-defined technical set (which Zod
+// validator to build dynamically for AssetModel.specs at write time: string
+// -> z.string(), number -> z.number(), boolean -> z.boolean(), date ->
+// z.coerce.date()). Deliberately a different kind of "fixed set" than
+// AssetCategoryValueGroup above: that one is a closed business classification
+// IT admins never extend; this one is a closed set of *primitive types* the
+// app's dynamic-attribute machinery knows how to handle. Still modeled as a
+// native Postgres enum per the same codebase convention (RequestType /
+// AssetItemStatus / LicenseType / AssetCategoryValueGroup), not a String +
+// hand-rolled check.
+enum AssetAttributeDataType {
+  string
+  number
+  boolean
+  date
+}
+
+// Per-category dynamic attribute definitions — see docs/
+// asset-license-management.md's "Cập nhật 2026-08-02 (3): thêm
+// AssetCategoryAttributeDef" section and the `AssetCategoryAttributeDef` row
+// in the "Data model (sơ bộ)" table. Defines the *shape* of attributes a
+// category cares about (e.g. category "Laptop" -> key `ram_gb`, label
+// "RAM (GB)", dataType number); the actual *values* live in
+// AssetModel.specs (JSONB), not built in this task. Each AssetCategory owns
+// its own independent set of attribute defs — deliberately NOT a shared
+// attribute library across categories (stakeholder explicitly rejected that
+// design to keep things simple at current scale), so the same `key` string
+// existing under two different categoryId rows is normal, not a collision —
+// only unique *within* a category, hence the composite unique below (not a
+// plain @unique on key alone). `sortOrder` is the display order on the
+// dynamic form, no uniqueness constraint of its own (ties/gaps are fine,
+// it's just a sort key).
+model AssetCategoryAttributeDef {
+  id         String                 @id @default(uuid()) @db.Uuid
+  categoryId String                 @map("category_id") @db.Uuid
+  category   AssetCategory          @relation(fields: [categoryId], references: [id])
+  key        String
+  label      String
+  dataType   AssetAttributeDataType @map("data_type")
+  required   Boolean
+  sortOrder  Int                    @map("sort_order")
+  createdAt  DateTime               @default(now()) @map("created_at") @db.Timestamptz(6)
+
+  @@unique([categoryId, key])
+  @@map("asset_category_attribute_defs")
+}
+
+// Sits between AssetCategory and AssetItem — see docs/
+// asset-license-management.md's "Cập nhật 2026-08-02 (2)" section and the
+// `AssetModel` row in the "Data model (sơ bộ)" table. 1 AssetModel has many
+// AssetItem serials (AssetItem.modelId FK, not built in this task).
+// `manufacturer`/`name` are deliberately two separate String fields (not
+// merged into one), per the doc, to allow filtering/reporting by
+// manufacturer alone (e.g. "Dell") without string-parsing a combined field.
+// `categoryId` is a required FK to AssetCategory — the DB layer doesn't
+// enforce that the referenced category is `high_value` (Prisma/Postgres FK
+// constraints can't express that), that business rule is checked in
+// src/lib/asset-models.ts's createAssetModel() via an explicit lookup
+// before the create, per the doc's "Ràng buộc dữ liệu" section. `specs` is
+// JSONB, defaulting to an empty object — the real per-category dynamic
+// attribute *values* (whose *shape* is defined by
+// AssetCategoryAttributeDef rows for this model's category). This task
+// deliberately does NOT validate specs against the category's attribute
+// defs (loose z.record(z.unknown()) validation only, see
+// src/lib/asset-models.ts) — that dynamic cross-validation is a separate
+// follow-up task per the doc's "Cập nhật 2026-08-02 (3)" section.
+model AssetModel {
+  id           String        @id @default(uuid()) @db.Uuid
+  categoryId   String        @map("category_id") @db.Uuid
+  category     AssetCategory @relation(fields: [categoryId], references: [id])
+  manufacturer String
+  name         String
+  specs        Json          @default("{}")
+  createdAt    DateTime      @default(now()) @map("created_at") @db.Timestamptz(6)
+  // Back-relation for the AssetItem.model -> AssetItem.modelId retrofit —
+  // see "Cập nhật 2026-08-02 (2)" in docs/asset-license-management.md.
+  assetItems   AssetItem[]
+
+  @@map("asset_models")
+}
+
+// Assigns an AssetItem (high-value hardware) or a License seat to a specific
+// Employee — see docs/asset-license-management.md's "## Assignment (chốt
+// 2026-08-02)" section and the `Assignment` row in the "Data model (sơ bộ)"
+// table. Exactly one of assetItemId/licenseId must be set (XOR) — enforced
+// at the Zod layer (src/lib/assignments.ts's `.refine()`), NOT a DB
+// constraint, per the same convention as PurchaseOrder's
+// receivedAt/receivedById co-nullability check: Prisma schema can't express
+// an XOR between two nullable FKs natively. Both FKs stay plain nullable
+// columns here for that reason. `assignedAt` defaults to now() but is a
+// real stored column (not derived from createdAt) because a future
+// "transfer" operation (out of scope for this task, see doc) will create a
+// new Assignment row whose assignedAt should reflect the transfer moment,
+// not necessarily row-insert time. `returnedAt` null means still held by
+// the employee — this is also what "active assignment" means throughout
+// the codebase (see the uniqueness rule below). `signedAt` is deliberately
+// just a nullable timestamp marking "handover paperwork signed" — NO file
+// upload, stakeholder explicitly decided against storing a scanned file at
+// this stage (see doc). No `@@unique` on assetItemId here for "only one
+// active assignment at a time" — a plain unique constraint would also
+// forbid a *second, already-returned* historical Assignment for the same
+// AssetItem (e.g. item reassigned after being returned), which is valid and
+// expected. The "at most one ACTIVE (returnedAt IS NULL) assignment per
+// AssetItem" invariant is instead enforced in application code
+// (src/lib/assignments.ts's createAssignment(), inside the same transaction
+// that mutates AssetItem.status/License.seatsUsed) — a partial unique index
+// (`WHERE returned_at IS NULL`) would express this at the DB level too, but
+// that's raw SQL outside a Prisma-expressible `@@unique`, so deliberately
+// not added here; see feature-implementer report for this trade-off.
+model Assignment {
+  id          String     @id @default(uuid()) @db.Uuid
+  employeeId  String     @map("employee_id") @db.Uuid
+  employee    Employee   @relation(fields: [employeeId], references: [id])
+  assetItemId String?    @map("asset_item_id") @db.Uuid
+  assetItem   AssetItem? @relation(fields: [assetItemId], references: [id])
+  licenseId   String?    @map("license_id") @db.Uuid
+  license     License?   @relation(fields: [licenseId], references: [id])
+  assignedAt  DateTime   @default(now()) @map("assigned_at") @db.Timestamptz(6)
+  returnedAt  DateTime?  @map("returned_at") @db.Timestamptz(6)
+  signedAt    DateTime?  @map("signed_at") @db.Timestamptz(6)
+  createdAt   DateTime   @default(now()) @map("created_at") @db.Timestamptz(6)
+
+  @@map("assignments")
+}
+
 // Minimal internal auth accounts — NOT company SSO (deliberately ruled out,
 // see CLAUDE.md / auth decision notes). A handful of trusted IT staff
 // accounts, created by hand via scripts/create-user.ts, no self-registration.

src/app/api/asset-categories/route.ts

@@ -0,0 +1,51 @@
+import { NextResponse } from "next/server";
+import { auth } from "@/auth";
+import {
+  createAssetCategory,
+  listAssetCategories,
+  validateCreateAssetCategoryInput,
+} from "@/lib/asset-categories";
+
+// Mirrors src/app/api/licenses/route.ts's pattern — middleware.ts excludes
+// /api from route protection, so this checks the session itself. Flat
+// permission model (CLAUDE.md): only "logged in or not", no role check.
+export async function POST(request: Request): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  let body: unknown;
+  try {
+    body = await request.json();
+  } catch {
+    return NextResponse.json({ error: "Request body must be valid JSON" }, { status: 400 });
+  }
+
+  if (typeof body !== "object" || body === null) {
+    return NextResponse.json({ error: "Request body must be a JSON object" }, { status: 400 });
+  }
+
+  const { name, valueGroup } = body as Record<string, unknown>;
+  const validation = validateCreateAssetCategoryInput({ name, valueGroup });
+
+  if (!validation.ok) {
+    return NextResponse.json({ error: validation.error }, { status: 400 });
+  }
+
+  const created = await createAssetCategory(validation.value);
+  if (!created.ok) {
+    return NextResponse.json({ error: created.error }, { status: 400 });
+  }
+  return NextResponse.json(created.value, { status: 201 });
+}
+
+export async function GET(): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  const assetCategories = await listAssetCategories();
+  return NextResponse.json(assetCategories, { status: 200 });
+}

src/app/api/asset-category-attribute-defs/route.ts

@@ -0,0 +1,59 @@
+import { NextResponse } from "next/server";
+import { auth } from "@/auth";
+import {
+  createAssetCategoryAttributeDef,
+  listAssetCategoryAttributeDefs,
+  validateCreateAssetCategoryAttributeDefInput,
+} from "@/lib/asset-category-attribute-defs";
+
+// Mirrors src/app/api/asset-categories/route.ts's pattern — middleware.ts
+// excludes /api from route protection, so this checks the session itself.
+// Flat permission model (CLAUDE.md): only "logged in or not", no role check.
+export async function POST(request: Request): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  let body: unknown;
+  try {
+    body = await request.json();
+  } catch {
+    return NextResponse.json({ error: "Request body must be valid JSON" }, { status: 400 });
+  }
+
+  if (typeof body !== "object" || body === null) {
+    return NextResponse.json({ error: "Request body must be a JSON object" }, { status: 400 });
+  }
+
+  const { categoryId, key, label, dataType, required, sortOrder } =
+    body as Record<string, unknown>;
+  const validation = validateCreateAssetCategoryAttributeDefInput({
+    categoryId,
+    key,
+    label,
+    dataType,
+    required,
+    sortOrder,
+  });
+
+  if (!validation.ok) {
+    return NextResponse.json({ error: validation.error }, { status: 400 });
+  }
+
+  const created = await createAssetCategoryAttributeDef(validation.value);
+  if (!created.ok) {
+    return NextResponse.json({ error: created.error }, { status: 400 });
+  }
+  return NextResponse.json(created.value, { status: 201 });
+}
+
+export async function GET(): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  const assetCategoryAttributeDefs = await listAssetCategoryAttributeDefs();
+  return NextResponse.json(assetCategoryAttributeDefs, { status: 200 });
+}

src/app/api/asset-models/route.ts

@@ -0,0 +1,52 @@
+import { NextResponse } from "next/server";
+import { auth } from "@/auth";
+import {
+  createAssetModel,
+  listAssetModels,
+  validateCreateAssetModelInput,
+} from "@/lib/asset-models";
+
+// Mirrors src/app/api/asset-category-attribute-defs/route.ts's pattern —
+// middleware.ts excludes /api from route protection, so this checks the
+// session itself. Flat permission model (CLAUDE.md): only "logged in or
+// not", no role check.
+export async function POST(request: Request): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  let body: unknown;
+  try {
+    body = await request.json();
+  } catch {
+    return NextResponse.json({ error: "Request body must be valid JSON" }, { status: 400 });
+  }
+
+  if (typeof body !== "object" || body === null) {
+    return NextResponse.json({ error: "Request body must be a JSON object" }, { status: 400 });
+  }
+
+  const { categoryId, manufacturer, name, specs } = body as Record<string, unknown>;
+  const validation = validateCreateAssetModelInput({ categoryId, manufacturer, name, specs });
+
+  if (!validation.ok) {
+    return NextResponse.json({ error: validation.error }, { status: 400 });
+  }
+
+  const created = await createAssetModel(validation.value);
+  if (!created.ok) {
+    return NextResponse.json({ error: created.error }, { status: 400 });
+  }
+  return NextResponse.json(created.value, { status: 201 });
+}
+
+export async function GET(): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  const assetModels = await listAssetModels();
+  return NextResponse.json(assetModels, { status: 200 });
+}

src/app/api/assets/route.ts

@@ -22,12 +22,14 @@ export async function POST(request: Request): Promise<NextResponse> {
     return NextResponse.json({ error: "Request body must be a JSON object" }, { status: 400 });
   }
 
-  const { serialNumber, model, purchaseDate, warrantyEndDate } = body as Record<string, unknown>;
+  const { serialNumber, modelId, purchaseDate, warrantyEndDate, purchaseOrderId } =
+    body as Record<string, unknown>;
   const validation = validateCreateAssetItemInput({
     serialNumber,
-    model,
+    modelId,
     purchaseDate,
     warrantyEndDate,
+    purchaseOrderId,
   });
 
   if (!validation.ok) {

src/app/api/assignments/[id]/route.ts

@@ -0,0 +1,86 @@
+import { NextResponse } from "next/server";
+import { z } from "zod";
+import { auth } from "@/auth";
+import {
+  returnAssignment,
+  transferAssignment,
+  validateReturnAssignmentInput,
+  validateTransferAssignmentInput,
+} from "@/lib/assignments";
+
+// First dynamic-segment ([id]) route in the codebase — see
+// docs/asset-license-management.md's "Assignment (chốt 2026-08-02)" section,
+// bullet (b): update routes use PATCH /api/<entity>/[id], not an
+// action-based sub-route (e.g. NOT /api/assignments/[id]/return). Next.js
+// 14 App Router route handler params are a plain synchronous object (not a
+// Promise) — that changed starting in Next.js 15, which this project does
+// not use (see package.json / CLAUDE.md).
+export async function PATCH(
+  request: Request,
+  { params }: { params: { id: string } }
+): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  // Validate the [id] path segment's format up front — an invalid UUID
+  // passed straight to Prisma's `findUnique({ where: { id } })` (a `@db.Uuid`
+  // column) throws a raw PrismaClientKnownRequestError that
+  // returnAssignment()'s try/catch doesn't specifically handle, which would
+  // otherwise leak as an uncaught 500 instead of a clean 400.
+  if (!z.string().uuid().safeParse(params.id).success) {
+    return NextResponse.json({ error: "id must be a valid UUID string" }, { status: 400 });
+  }
+
+  let body: unknown;
+  try {
+    body = await request.json();
+  } catch {
+    return NextResponse.json({ error: "Request body must be valid JSON" }, { status: 400 });
+  }
+
+  if (typeof body !== "object" || body === null) {
+    return NextResponse.json({ error: "Request body must be a JSON object" }, { status: 400 });
+  }
+
+  const { returnedAt, employeeId } = body as Record<string, unknown>;
+
+  // Dispatch on body shape — a body carrying employeeId is a transfer
+  // request, everything else is the existing return behavior. The two are
+  // mutually exclusive: don't guess intent if a caller sends both (see
+  // docs/asset-license-management.md's "Assignment (chốt 2026-08-02)"
+  // section, bullet right after the transfer rule, for why this stays a
+  // single PATCH route rather than an action-based sub-route).
+  if (employeeId !== undefined && returnedAt !== undefined) {
+    return NextResponse.json(
+      { error: "Provide either employeeId (transfer) or returnedAt (return), not both" },
+      { status: 400 }
+    );
+  }
+
+  if (employeeId !== undefined) {
+    const transferValidation = validateTransferAssignmentInput({ employeeId });
+    if (!transferValidation.ok) {
+      return NextResponse.json({ error: transferValidation.error }, { status: 400 });
+    }
+
+    const transferred = await transferAssignment(params.id, transferValidation.value);
+    if (!transferred.ok) {
+      return NextResponse.json({ error: transferred.error }, { status: transferred.status });
+    }
+    return NextResponse.json(transferred.value, { status: 200 });
+  }
+
+  const validation = validateReturnAssignmentInput({ returnedAt });
+
+  if (!validation.ok) {
+    return NextResponse.json({ error: validation.error }, { status: 400 });
+  }
+
+  const updated = await returnAssignment(params.id, validation.value);
+  if (!updated.ok) {
+    return NextResponse.json({ error: updated.error }, { status: updated.status });
+  }
+  return NextResponse.json(updated.value, { status: 200 });
+}

src/app/api/assignments/route.ts

@@ -0,0 +1,51 @@
+import { NextResponse } from "next/server";
+import { auth } from "@/auth";
+import {
+  createAssignment,
+  listAssignments,
+  validateCreateAssignmentInput,
+} from "@/lib/assignments";
+
+// Mirrors src/app/api/licenses/route.ts's pattern — middleware.ts excludes
+// /api from route protection, so this checks the session itself. Flat
+// permission model (CLAUDE.md): only "logged in or not", no role check.
+export async function POST(request: Request): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  let body: unknown;
+  try {
+    body = await request.json();
+  } catch {
+    return NextResponse.json({ error: "Request body must be valid JSON" }, { status: 400 });
+  }
+
+  if (typeof body !== "object" || body === null) {
+    return NextResponse.json({ error: "Request body must be a JSON object" }, { status: 400 });
+  }
+
+  const { employeeId, assetItemId, licenseId } = body as Record<string, unknown>;
+  const validation = validateCreateAssignmentInput({ employeeId, assetItemId, licenseId });
+
+  if (!validation.ok) {
+    return NextResponse.json({ error: validation.error }, { status: 400 });
+  }
+
+  const created = await createAssignment(validation.value);
+  if (!created.ok) {
+    return NextResponse.json({ error: created.error }, { status: 400 });
+  }
+  return NextResponse.json(created.value, { status: 201 });
+}
+
+export async function GET(): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  const assignments = await listAssignments();
+  return NextResponse.json(assignments, { status: 200 });
+}

src/app/api/licenses/route.ts

@@ -22,13 +22,15 @@ export async function POST(request: Request): Promise<NextResponse> {
     return NextResponse.json({ error: "Request body must be a JSON object" }, { status: 400 });
   }
 
-  const { name, vendor, seatsTotal, expiryDate, licenseType } = body as Record<string, unknown>;
+  const { name, vendorId, seatsTotal, expiryDate, licenseType, purchaseOrderId } =
+    body as Record<string, unknown>;
   const validation = validateCreateLicenseInput({
     name,
-    vendor,
+    vendorId,
     seatsTotal,
     expiryDate,
     licenseType,
+    purchaseOrderId,
   });
 
   if (!validation.ok) {
@@ -36,7 +38,10 @@ export async function POST(request: Request): Promise<NextResponse> {
   }
 
   const created = await createLicense(validation.value);
-  return NextResponse.json(created, { status: 201 });
+  if (!created.ok) {
+    return NextResponse.json({ error: created.error }, { status: 400 });
+  }
+  return NextResponse.json(created.value, { status: 201 });
 }
 
 export async function GET(): Promise<NextResponse> {

src/app/api/purchase-orders/route.ts

@@ -0,0 +1,58 @@
+import { NextResponse } from "next/server";
+import { auth } from "@/auth";
+import {
+  createPurchaseOrder,
+  listPurchaseOrders,
+  validateCreatePurchaseOrderInput,
+} from "@/lib/purchase-orders";
+
+// Mirrors src/app/api/licenses/route.ts's pattern — middleware.ts excludes
+// /api from route protection, so this checks the session itself. Flat
+// permission model (CLAUDE.md): only "logged in or not", no role check.
+export async function POST(request: Request): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  let body: unknown;
+  try {
+    body = await request.json();
+  } catch {
+    return NextResponse.json({ error: "Request body must be valid JSON" }, { status: 400 });
+  }
+
+  if (typeof body !== "object" || body === null) {
+    return NextResponse.json({ error: "Request body must be a JSON object" }, { status: 400 });
+  }
+
+  const { vendorId, orderDate, expectedDate, receivedAt, receivedById } =
+    body as Record<string, unknown>;
+  const validation = validateCreatePurchaseOrderInput({
+    vendorId,
+    orderDate,
+    expectedDate,
+    receivedAt,
+    receivedById,
+  });
+
+  if (!validation.ok) {
+    return NextResponse.json({ error: validation.error }, { status: 400 });
+  }
+
+  const created = await createPurchaseOrder(validation.value);
+  if (!created.ok) {
+    return NextResponse.json({ error: created.error }, { status: 400 });
+  }
+  return NextResponse.json(created.value, { status: 201 });
+}
+
+export async function GET(): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  const purchaseOrders = await listPurchaseOrders();
+  return NextResponse.json(purchaseOrders, { status: 200 });
+}

src/app/api/requests/route.ts

@@ -24,8 +24,8 @@ export async function POST(request: Request): Promise<NextResponse> {
     return NextResponse.json({ error: "Request body must be a JSON object" }, { status: 400 });
   }
 
-  const { employee_id, type, reason } = body as Record<string, unknown>;
+  const { employee_id, type, reason, purchase_order_id } = body as Record<string, unknown>;
-  const validation = validateCreateRequestInput({ employee_id, type, reason });
+  const validation = validateCreateRequestInput({ employee_id, type, reason, purchase_order_id });
 
   if (!validation.ok) {
     return NextResponse.json({ error: validation.error }, { status: 400 });

src/app/api/vendors/route.ts

@@ -0,0 +1,52 @@
+import { NextResponse } from "next/server";
+import { auth } from "@/auth";
+import { createVendor, listVendors, validateCreateVendorInput } from "@/lib/vendors";
+
+// Mirrors src/app/api/licenses/route.ts's pattern — middleware.ts excludes
+// /api from route protection, so this checks the session itself. Flat
+// permission model (CLAUDE.md): only "logged in or not", no role check.
+export async function POST(request: Request): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  let body: unknown;
+  try {
+    body = await request.json();
+  } catch {
+    return NextResponse.json({ error: "Request body must be valid JSON" }, { status: 400 });
+  }
+
+  if (typeof body !== "object" || body === null) {
+    return NextResponse.json({ error: "Request body must be a JSON object" }, { status: 400 });
+  }
+
+  const { name, contactEmail, contactPhone, address, taxCode, notes } =
+    body as Record<string, unknown>;
+  const validation = validateCreateVendorInput({
+    name,
+    contactEmail,
+    contactPhone,
+    address,
+    taxCode,
+    notes,
+  });
+
+  if (!validation.ok) {
+    return NextResponse.json({ error: validation.error }, { status: 400 });
+  }
+
+  const created = await createVendor(validation.value);
+  return NextResponse.json(created, { status: 201 });
+}
+
+export async function GET(): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  const vendors = await listVendors();
+  return NextResponse.json(vendors, { status: 200 });
+}

src/app/asset-categories/page.tsx

@@ -0,0 +1,168 @@
+"use client";
+
+import { useState, type FormEvent } from "react";
+import { useApiList } from "@/hooks/use-api-list";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import { Label } from "@/components/ui/label";
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from "@/components/ui/select";
+import {
+  Table,
+  TableBody,
+  TableCell,
+  TableHead,
+  TableHeader,
+  TableRow,
+} from "@/components/ui/table";
+
+// Shape returned by GET /api/asset-categories — snake_case per this repo's
+// API-boundary convention (see src/lib/asset-categories.ts's toRecord()).
+interface AssetCategoryRecord {
+  id: string;
+  name: string;
+  value_group: "high_value" | "low_value";
+  created_at: string;
+}
+
+const VALUE_GROUP_OPTIONS = ["high_value", "low_value"] as const;
+
+export default function AssetCategoriesPage() {
+  const {
+    data: assetCategories,
+    loading,
+    error,
+    refetch,
+  } = useApiList<AssetCategoryRecord>("/api/asset-categories");
+
+  const [name, setName] = useState("");
+  const [valueGroup, setValueGroup] = useState<(typeof VALUE_GROUP_OPTIONS)[number]>(
+    "high_value"
+  );
+  const [submitting, setSubmitting] = useState(false);
+  const [submitError, setSubmitError] = useState<string | null>(null);
+
+  async function handleSubmit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault();
+    setSubmitting(true);
+    setSubmitError(null);
+
+    try {
+      const response = await fetch("/api/asset-categories", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ name, valueGroup }),
+      });
+
+      let body: unknown;
+      try {
+        body = await response.json();
+      } catch {
+        body = null;
+      }
+
+      if (!response.ok) {
+        const message =
+          body !== null &&
+          typeof body === "object" &&
+          "error" in body &&
+          typeof (body as { error: unknown }).error === "string"
+            ? (body as { error: string }).error
+            : "Request failed";
+        setSubmitError(message);
+        return;
+      }
+
+      setName("");
+      setValueGroup("high_value");
+      refetch();
+    } catch {
+      setSubmitError("Request failed");
+    } finally {
+      setSubmitting(false);
+    }
+  }
+
+  return (
+    <div className="flex flex-col gap-8 p-6">
+      <h1 className="text-xl font-semibold">Asset Categories</h1>
+
+      <section className="flex flex-col gap-3">
+        {loading ? (
+          <p className="text-sm text-muted-foreground">Loading...</p>
+        ) : error ? (
+          <p className="text-sm text-destructive">{error}</p>
+        ) : (
+          <Table>
+            <TableHeader>
+              <TableRow>
+                <TableHead>ID</TableHead>
+                <TableHead>Name</TableHead>
+                <TableHead>Value Group</TableHead>
+                <TableHead>Created At</TableHead>
+              </TableRow>
+            </TableHeader>
+            <TableBody>
+              {assetCategories.map((assetCategory) => (
+                <TableRow key={assetCategory.id}>
+                  <TableCell>{assetCategory.id}</TableCell>
+                  <TableCell>{assetCategory.name}</TableCell>
+                  <TableCell>{assetCategory.value_group}</TableCell>
+                  <TableCell>{assetCategory.created_at}</TableCell>
+                </TableRow>
+              ))}
+            </TableBody>
+          </Table>
+        )}
+      </section>
+
+      <section className="flex max-w-sm flex-col gap-4">
+        <h2 className="text-lg font-semibold">New Asset Category</h2>
+
+        <form className="flex flex-col gap-4" onSubmit={handleSubmit}>
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="name">Name</Label>
+            <Input
+              id="name"
+              value={name}
+              onChange={(event) => setName(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="valueGroup">Value Group</Label>
+            <Select
+              value={valueGroup}
+              onValueChange={(value) =>
+                setValueGroup(value as (typeof VALUE_GROUP_OPTIONS)[number])
+              }
+            >
+              <SelectTrigger id="valueGroup" className="w-full">
+                <SelectValue />
+              </SelectTrigger>
+              <SelectContent>
+                {VALUE_GROUP_OPTIONS.map((option) => (
+                  <SelectItem key={option} value={option}>
+                    {option}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+
+          {submitError ? <p className="text-sm text-destructive">{submitError}</p> : null}
+
+          <Button type="submit" disabled={submitting}>
+            {submitting ? "Creating..." : "Create Asset Category"}
+          </Button>
+        </form>
+      </section>
+    </div>
+  );
+}

src/app/asset-category-attribute-defs/page.tsx

@@ -0,0 +1,256 @@
+"use client";
+
+import { useState, type FormEvent } from "react";
+import { useApiList } from "@/hooks/use-api-list";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import { Label } from "@/components/ui/label";
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from "@/components/ui/select";
+import {
+  Table,
+  TableBody,
+  TableCell,
+  TableHead,
+  TableHeader,
+  TableRow,
+} from "@/components/ui/table";
+
+// Shape returned by GET /api/asset-category-attribute-defs — snake_case per
+// this repo's API-boundary convention (see
+// src/lib/asset-category-attribute-defs.ts's toRecord()).
+interface AssetCategoryAttributeDefRecord {
+  id: string;
+  category_id: string;
+  key: string;
+  label: string;
+  data_type: "string" | "number" | "boolean" | "date";
+  required: boolean;
+  sort_order: number;
+  created_at: string;
+}
+
+// Shape returned by GET /api/asset-categories — snake_case per
+// src/lib/asset-categories.ts's toRecord(). Only used here to populate the
+// categoryId <Select> options.
+interface AssetCategoryRecord {
+  id: string;
+  name: string;
+  value_group: "high_value" | "low_value";
+  created_at: string;
+}
+
+// Fixed 4-value set — mirrors src/lib/asset-category-attribute-defs.ts's
+// dataType z.enum() literal values exactly.
+const DATA_TYPE_OPTIONS = ["string", "number", "boolean", "date"] as const;
+
+export default function AssetCategoryAttributeDefsPage() {
+  const {
+    data: attributeDefs,
+    loading,
+    error,
+    refetch,
+  } = useApiList<AssetCategoryAttributeDefRecord>("/api/asset-category-attribute-defs");
+
+  const { data: assetCategories } = useApiList<AssetCategoryRecord>("/api/asset-categories");
+
+  const [categoryId, setCategoryId] = useState("");
+  const [key, setKey] = useState("");
+  const [label, setLabel] = useState("");
+  const [dataType, setDataType] = useState<(typeof DATA_TYPE_OPTIONS)[number]>("string");
+  const [required, setRequired] = useState(false);
+  const [sortOrder, setSortOrder] = useState("0");
+  const [submitting, setSubmitting] = useState(false);
+  const [submitError, setSubmitError] = useState<string | null>(null);
+
+  async function handleSubmit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault();
+    setSubmitting(true);
+    setSubmitError(null);
+
+    try {
+      const response = await fetch("/api/asset-category-attribute-defs", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({
+          categoryId,
+          key,
+          label,
+          dataType,
+          required,
+          sortOrder: Number(sortOrder),
+        }),
+      });
+
+      let body: unknown;
+      try {
+        body = await response.json();
+      } catch {
+        body = null;
+      }
+
+      if (!response.ok) {
+        const message =
+          body !== null &&
+          typeof body === "object" &&
+          "error" in body &&
+          typeof (body as { error: unknown }).error === "string"
+            ? (body as { error: string }).error
+            : "Request failed";
+        setSubmitError(message);
+        return;
+      }
+
+      setCategoryId("");
+      setKey("");
+      setLabel("");
+      setDataType("string");
+      setRequired(false);
+      setSortOrder("0");
+      refetch();
+    } catch {
+      setSubmitError("Request failed");
+    } finally {
+      setSubmitting(false);
+    }
+  }
+
+  return (
+    <div className="flex flex-col gap-8 p-6">
+      <h1 className="text-xl font-semibold">Asset Category Attribute Defs</h1>
+
+      <section className="flex flex-col gap-3">
+        {loading ? (
+          <p className="text-sm text-muted-foreground">Loading...</p>
+        ) : error ? (
+          <p className="text-sm text-destructive">{error}</p>
+        ) : (
+          <Table>
+            <TableHeader>
+              <TableRow>
+                <TableHead>ID</TableHead>
+                <TableHead>Category ID</TableHead>
+                <TableHead>Key</TableHead>
+                <TableHead>Label</TableHead>
+                <TableHead>Data Type</TableHead>
+                <TableHead>Required</TableHead>
+                <TableHead>Sort Order</TableHead>
+                <TableHead>Created At</TableHead>
+              </TableRow>
+            </TableHeader>
+            <TableBody>
+              {attributeDefs.map((attributeDef) => (
+                <TableRow key={attributeDef.id}>
+                  <TableCell>{attributeDef.id}</TableCell>
+                  <TableCell>{attributeDef.category_id}</TableCell>
+                  <TableCell>{attributeDef.key}</TableCell>
+                  <TableCell>{attributeDef.label}</TableCell>
+                  <TableCell>{attributeDef.data_type}</TableCell>
+                  <TableCell>{attributeDef.required ? "Yes" : "No"}</TableCell>
+                  <TableCell>{attributeDef.sort_order}</TableCell>
+                  <TableCell>{attributeDef.created_at}</TableCell>
+                </TableRow>
+              ))}
+            </TableBody>
+          </Table>
+        )}
+      </section>
+
+      <section className="flex max-w-sm flex-col gap-4">
+        <h2 className="text-lg font-semibold">New Asset Category Attribute Def</h2>
+
+        <form className="flex flex-col gap-4" onSubmit={handleSubmit}>
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="categoryId">Category</Label>
+            <Select value={categoryId} onValueChange={setCategoryId}>
+              <SelectTrigger id="categoryId" className="w-full">
+                <SelectValue placeholder="Select a category" />
+              </SelectTrigger>
+              <SelectContent>
+                {assetCategories.map((assetCategory) => (
+                  <SelectItem key={assetCategory.id} value={assetCategory.id}>
+                    {assetCategory.name}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="key">Key</Label>
+            <Input
+              id="key"
+              value={key}
+              onChange={(event) => setKey(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="label">Label</Label>
+            <Input
+              id="label"
+              value={label}
+              onChange={(event) => setLabel(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="dataType">Data Type</Label>
+            <Select
+              value={dataType}
+              onValueChange={(value) =>
+                setDataType(value as (typeof DATA_TYPE_OPTIONS)[number])
+              }
+            >
+              <SelectTrigger id="dataType" className="w-full">
+                <SelectValue />
+              </SelectTrigger>
+              <SelectContent>
+                {DATA_TYPE_OPTIONS.map((option) => (
+                  <SelectItem key={option} value={option}>
+                    {option}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+
+          <div className="flex items-center gap-2">
+            <input
+              id="required"
+              type="checkbox"
+              checked={required}
+              onChange={(event) => setRequired(event.target.checked)}
+              className="h-4 w-4"
+            />
+            <Label htmlFor="required">Required</Label>
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="sortOrder">Sort Order</Label>
+            <Input
+              id="sortOrder"
+              type="number"
+              value={sortOrder}
+              onChange={(event) => setSortOrder(event.target.value)}
+              required
+            />
+          </div>
+
+          {submitError ? <p className="text-sm text-destructive">{submitError}</p> : null}
+
+          <Button type="submit" disabled={submitting}>
+            {submitting ? "Creating..." : "Create Attribute Def"}
+          </Button>
+        </form>
+      </section>
+    </div>
+  );
+}

src/app/asset-models/page.tsx

@@ -0,0 +1,222 @@
+"use client";
+
+import { useState, type FormEvent } from "react";
+import { useApiList } from "@/hooks/use-api-list";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import { Label } from "@/components/ui/label";
+import { Textarea } from "@/components/ui/textarea";
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from "@/components/ui/select";
+import {
+  Table,
+  TableBody,
+  TableCell,
+  TableHead,
+  TableHeader,
+  TableRow,
+} from "@/components/ui/table";
+
+// Shape returned by GET /api/asset-models — snake_case per this repo's
+// API-boundary convention (see src/lib/asset-models.ts's toRecord()).
+interface AssetModelRecord {
+  id: string;
+  category_id: string;
+  manufacturer: string;
+  name: string;
+  specs: Record<string, unknown>;
+  created_at: string;
+}
+
+// Shape returned by GET /api/asset-categories — used only to populate the
+// categoryId <Select> here, not rendered as its own table. Deliberately NOT
+// filtered to valueGroup=high_value client-side: the server
+// (createAssetModel() in src/lib/asset-models.ts) enforces that rule and
+// returns a clear {error} message if violated, which this page surfaces
+// verbatim via submitError instead of duplicating the rule client-side.
+interface AssetCategoryRecord {
+  id: string;
+  name: string;
+  value_group: "high_value" | "low_value";
+  created_at: string;
+}
+
+const DEFAULT_SPECS_TEXT = "{}";
+
+export default function AssetModelsPage() {
+  const {
+    data: assetModels,
+    loading,
+    error,
+    refetch,
+  } = useApiList<AssetModelRecord>("/api/asset-models");
+
+  const { data: assetCategories } = useApiList<AssetCategoryRecord>(
+    "/api/asset-categories"
+  );
+
+  const [categoryId, setCategoryId] = useState("");
+  const [manufacturer, setManufacturer] = useState("");
+  const [name, setName] = useState("");
+  const [specsText, setSpecsText] = useState(DEFAULT_SPECS_TEXT);
+  const [submitting, setSubmitting] = useState(false);
+  const [submitError, setSubmitError] = useState<string | null>(null);
+
+  async function handleSubmit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault();
+    setSubmitting(true);
+    setSubmitError(null);
+
+    // specs is parsed client-side first — if it's not valid JSON, fail
+    // locally without calling the API at all (per task scope).
+    let specs: unknown;
+    try {
+      specs = JSON.parse(specsText);
+    } catch {
+      setSubmitError("Invalid JSON");
+      setSubmitting(false);
+      return;
+    }
+
+    try {
+      const response = await fetch("/api/asset-models", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ categoryId, manufacturer, name, specs }),
+      });
+
+      let body: unknown;
+      try {
+        body = await response.json();
+      } catch {
+        body = null;
+      }
+
+      if (!response.ok) {
+        const message =
+          body !== null &&
+          typeof body === "object" &&
+          "error" in body &&
+          typeof (body as { error: unknown }).error === "string"
+            ? (body as { error: string }).error
+            : "Request failed";
+        setSubmitError(message);
+        return;
+      }
+
+      setCategoryId("");
+      setManufacturer("");
+      setName("");
+      setSpecsText(DEFAULT_SPECS_TEXT);
+      refetch();
+    } catch {
+      setSubmitError("Request failed");
+    } finally {
+      setSubmitting(false);
+    }
+  }
+
+  return (
+    <div className="flex flex-col gap-8 p-6">
+      <h1 className="text-xl font-semibold">Asset Models</h1>
+
+      <section className="flex flex-col gap-3">
+        {loading ? (
+          <p className="text-sm text-muted-foreground">Loading...</p>
+        ) : error ? (
+          <p className="text-sm text-destructive">{error}</p>
+        ) : (
+          <Table>
+            <TableHeader>
+              <TableRow>
+                <TableHead>ID</TableHead>
+                <TableHead>Category ID</TableHead>
+                <TableHead>Manufacturer</TableHead>
+                <TableHead>Name</TableHead>
+                <TableHead>Specs</TableHead>
+                <TableHead>Created At</TableHead>
+              </TableRow>
+            </TableHeader>
+            <TableBody>
+              {assetModels.map((assetModel) => (
+                <TableRow key={assetModel.id}>
+                  <TableCell>{assetModel.id}</TableCell>
+                  <TableCell>{assetModel.category_id}</TableCell>
+                  <TableCell>{assetModel.manufacturer}</TableCell>
+                  <TableCell>{assetModel.name}</TableCell>
+                  <TableCell>{JSON.stringify(assetModel.specs)}</TableCell>
+                  <TableCell>{assetModel.created_at}</TableCell>
+                </TableRow>
+              ))}
+            </TableBody>
+          </Table>
+        )}
+      </section>
+
+      <section className="flex max-w-sm flex-col gap-4">
+        <h2 className="text-lg font-semibold">New Asset Model</h2>
+
+        <form className="flex flex-col gap-4" onSubmit={handleSubmit}>
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="categoryId">Category</Label>
+            <Select value={categoryId} onValueChange={setCategoryId}>
+              <SelectTrigger id="categoryId" className="w-full">
+                <SelectValue placeholder="Select a category" />
+              </SelectTrigger>
+              <SelectContent>
+                {assetCategories.map((assetCategory) => (
+                  <SelectItem key={assetCategory.id} value={assetCategory.id}>
+                    {assetCategory.name}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="manufacturer">Manufacturer</Label>
+            <Input
+              id="manufacturer"
+              value={manufacturer}
+              onChange={(event) => setManufacturer(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="name">Name</Label>
+            <Input
+              id="name"
+              value={name}
+              onChange={(event) => setName(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="specs">Specs (JSON)</Label>
+            <Textarea
+              id="specs"
+              value={specsText}
+              onChange={(event) => setSpecsText(event.target.value)}
+              rows={6}
+            />
+          </div>
+
+          {submitError ? (
+            <p className="text-sm text-destructive">{submitError}</p>
+          ) : null}
+
+          <Button type="submit" disabled={submitting}>
+            {submitting ? "Creating..." : "Create Asset Model"}
+          </Button>
+        </form>
+      </section>
+    </div>
+  );
+}

src/app/assets/page.tsx

@@ -0,0 +1,254 @@
+"use client";
+
+import { useState, type FormEvent } from "react";
+import { useApiList } from "@/hooks/use-api-list";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import { Label } from "@/components/ui/label";
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from "@/components/ui/select";
+import {
+  Table,
+  TableBody,
+  TableCell,
+  TableHead,
+  TableHeader,
+  TableRow,
+} from "@/components/ui/table";
+
+// Shape returned by GET /api/assets — snake_case per this repo's
+// API-boundary convention (see src/lib/assets.ts's toRecord()).
+interface AssetItemRecord {
+  id: string;
+  serial_number: string;
+  model_id: string;
+  purchase_date: string;
+  warranty_end_date: string | null;
+  status: "in_stock" | "assigned" | "repair" | "retired";
+  purchase_order_id: string | null;
+  created_at: string;
+}
+
+// Shape returned by GET /api/asset-models — only the fields used to populate
+// the modelId <Select> here (see src/app/asset-models/page.tsx's
+// AssetModelRecord for the full shape).
+interface AssetModelRecord {
+  id: string;
+  manufacturer: string;
+  name: string;
+}
+
+// Shape returned by GET /api/purchase-orders — only the id, used to populate
+// the purchaseOrderId <Select> here. PurchaseOrder has no obviously
+// human-readable name field (see src/app/purchase-orders/page.tsx's
+// PurchaseOrderRecord for the full shape), so the id itself is shown as the
+// label.
+interface PurchaseOrderRecord {
+  id: string;
+}
+
+// Radix <Select.Item> can't take an empty-string value, so "no purchase
+// order" is represented by this sentinel in the form state and translated to
+// "omit the key" on submit — same pattern as purchase-orders page's
+// NOT_RECEIVED_VALUE / employees page's NO_MANAGER_VALUE.
+const NO_PURCHASE_ORDER_VALUE = "none";
+
+export default function AssetsPage() {
+  const {
+    data: assetItems,
+    loading,
+    error,
+    refetch,
+  } = useApiList<AssetItemRecord>("/api/assets");
+
+  const { data: assetModels } = useApiList<AssetModelRecord>("/api/asset-models");
+  const { data: purchaseOrders } = useApiList<PurchaseOrderRecord>("/api/purchase-orders");
+
+  const [serialNumber, setSerialNumber] = useState("");
+  const [modelId, setModelId] = useState("");
+  const [purchaseDate, setPurchaseDate] = useState("");
+  const [warrantyEndDate, setWarrantyEndDate] = useState("");
+  const [purchaseOrderId, setPurchaseOrderId] = useState(NO_PURCHASE_ORDER_VALUE);
+  const [submitting, setSubmitting] = useState(false);
+  const [submitError, setSubmitError] = useState<string | null>(null);
+
+  async function handleSubmit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault();
+    setSubmitting(true);
+    setSubmitError(null);
+
+    const hasWarrantyEndDate = warrantyEndDate.trim() !== "";
+    const hasPurchaseOrderId = purchaseOrderId !== NO_PURCHASE_ORDER_VALUE;
+
+    try {
+      const response = await fetch("/api/assets", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({
+          serialNumber,
+          modelId,
+          purchaseDate,
+          // Omit optional keys entirely when left blank, rather than
+          // sending null — matches the create-form pattern used on other
+          // pages (e.g. purchase-orders page's receivedAt/receivedById).
+          ...(hasWarrantyEndDate ? { warrantyEndDate } : {}),
+          ...(hasPurchaseOrderId ? { purchaseOrderId } : {}),
+        }),
+      });
+
+      let body: unknown;
+      try {
+        body = await response.json();
+      } catch {
+        body = null;
+      }
+
+      if (!response.ok) {
+        const message =
+          body !== null &&
+          typeof body === "object" &&
+          "error" in body &&
+          typeof (body as { error: unknown }).error === "string"
+            ? (body as { error: string }).error
+            : "Request failed";
+        setSubmitError(message);
+        return;
+      }
+
+      setSerialNumber("");
+      setModelId("");
+      setPurchaseDate("");
+      setWarrantyEndDate("");
+      setPurchaseOrderId(NO_PURCHASE_ORDER_VALUE);
+      refetch();
+    } catch {
+      setSubmitError("Request failed");
+    } finally {
+      setSubmitting(false);
+    }
+  }
+
+  return (
+    <div className="flex flex-col gap-8 p-6">
+      <h1 className="text-xl font-semibold">Assets</h1>
+
+      <section className="flex flex-col gap-3">
+        {loading ? (
+          <p className="text-sm text-muted-foreground">Loading...</p>
+        ) : error ? (
+          <p className="text-sm text-destructive">{error}</p>
+        ) : (
+          <Table>
+            <TableHeader>
+              <TableRow>
+                <TableHead>ID</TableHead>
+                <TableHead>Serial Number</TableHead>
+                <TableHead>Model ID</TableHead>
+                <TableHead>Purchase Date</TableHead>
+                <TableHead>Warranty End Date</TableHead>
+                <TableHead>Status</TableHead>
+                <TableHead>Purchase Order ID</TableHead>
+                <TableHead>Created At</TableHead>
+              </TableRow>
+            </TableHeader>
+            <TableBody>
+              {assetItems.map((assetItem) => (
+                <TableRow key={assetItem.id}>
+                  <TableCell>{assetItem.id}</TableCell>
+                  <TableCell>{assetItem.serial_number}</TableCell>
+                  <TableCell>{assetItem.model_id}</TableCell>
+                  <TableCell>{assetItem.purchase_date}</TableCell>
+                  <TableCell>{assetItem.warranty_end_date ?? "-"}</TableCell>
+                  <TableCell>{assetItem.status}</TableCell>
+                  <TableCell>{assetItem.purchase_order_id ?? "-"}</TableCell>
+                  <TableCell>{assetItem.created_at}</TableCell>
+                </TableRow>
+              ))}
+            </TableBody>
+          </Table>
+        )}
+      </section>
+
+      <section className="flex max-w-sm flex-col gap-4">
+        <h2 className="text-lg font-semibold">New Asset</h2>
+
+        <form className="flex flex-col gap-4" onSubmit={handleSubmit}>
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="serialNumber">Serial Number</Label>
+            <Input
+              id="serialNumber"
+              value={serialNumber}
+              onChange={(event) => setSerialNumber(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="modelId">Model</Label>
+            <Select value={modelId} onValueChange={setModelId} required>
+              <SelectTrigger id="modelId" className="w-full">
+                <SelectValue placeholder="Select a model" />
+              </SelectTrigger>
+              <SelectContent>
+                {assetModels.map((assetModel) => (
+                  <SelectItem key={assetModel.id} value={assetModel.id}>
+                    {assetModel.manufacturer} {assetModel.name}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="purchaseDate">Purchase Date</Label>
+            <Input
+              id="purchaseDate"
+              type="date"
+              value={purchaseDate}
+              onChange={(event) => setPurchaseDate(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="warrantyEndDate">Warranty End Date (optional)</Label>
+            <Input
+              id="warrantyEndDate"
+              type="date"
+              value={warrantyEndDate}
+              onChange={(event) => setWarrantyEndDate(event.target.value)}
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="purchaseOrderId">Purchase Order (optional)</Label>
+            <Select value={purchaseOrderId} onValueChange={setPurchaseOrderId}>
+              <SelectTrigger id="purchaseOrderId" className="w-full">
+                <SelectValue />
+              </SelectTrigger>
+              <SelectContent>
+                <SelectItem value={NO_PURCHASE_ORDER_VALUE}>None</SelectItem>
+                {purchaseOrders.map((purchaseOrder) => (
+                  <SelectItem key={purchaseOrder.id} value={purchaseOrder.id}>
+                    {purchaseOrder.id}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+
+          {submitError ? <p className="text-sm text-destructive">{submitError}</p> : null}
+
+          <Button type="submit" disabled={submitting}>
+            {submitting ? "Creating..." : "Create Asset"}
+          </Button>
+        </form>
+      </section>
+    </div>
+  );
+}

src/app/assignments/page.tsx

@@ -0,0 +1,329 @@
+"use client";
+
+import { useState, type FormEvent } from "react";
+import { useApiList } from "@/hooks/use-api-list";
+import { Button } from "@/components/ui/button";
+import { Label } from "@/components/ui/label";
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from "@/components/ui/select";
+import {
+  Table,
+  TableBody,
+  TableCell,
+  TableHead,
+  TableHeader,
+  TableRow,
+} from "@/components/ui/table";
+
+// Shape returned by GET /api/assignments — snake_case per this repo's
+// API-boundary convention (see src/lib/assignments.ts's toRecord()).
+interface AssignmentRecord {
+  id: string;
+  employee_id: string;
+  asset_item_id: string | null;
+  license_id: string | null;
+  assigned_at: string;
+  returned_at: string | null;
+  signed_at: string | null;
+  created_at: string;
+}
+
+// Shape returned by GET /api/employees — only the field used to populate the
+// employeeId <Select> here (see src/app/employees/page.tsx's EmployeeRecord
+// for the full shape).
+interface EmployeeRecord {
+  id: string;
+  name: string;
+}
+
+// Shape returned by GET /api/assets — only the field used to populate the
+// assetItemId <Select> here (see src/app/assets/page.tsx's AssetItemRecord
+// for the full shape).
+interface AssetItemRecord {
+  id: string;
+  serial_number: string;
+}
+
+// Shape returned by GET /api/licenses — only the field used to populate the
+// licenseId <Select> here (see src/app/licenses/page.tsx's LicenseRecord for
+// the full shape).
+interface LicenseRecord {
+  id: string;
+  name: string;
+}
+
+// The create form's XOR toggle — mirrors the server's own XOR rule in
+// src/lib/assignments.ts's createAssignmentSchema .refine() (exactly one of
+// assetItemId/licenseId must be set). This is purely a UI convenience to
+// decide which single <Select> to show/submit — the actual business rule is
+// still enforced server-side, this doesn't reimplement it.
+type TargetKind = "asset_item" | "license";
+
+export default function AssignmentsPage() {
+  const {
+    data: assignments,
+    loading,
+    error,
+    refetch,
+  } = useApiList<AssignmentRecord>("/api/assignments");
+
+  const { data: employees } = useApiList<EmployeeRecord>("/api/employees");
+  const { data: assetItems } = useApiList<AssetItemRecord>("/api/assets");
+  const { data: licenses } = useApiList<LicenseRecord>("/api/licenses");
+
+  const [employeeId, setEmployeeId] = useState("");
+  const [targetKind, setTargetKind] = useState<TargetKind>("asset_item");
+  const [assetItemId, setAssetItemId] = useState("");
+  const [licenseId, setLicenseId] = useState("");
+  const [submitting, setSubmitting] = useState(false);
+  const [submitError, setSubmitError] = useState<string | null>(null);
+
+  // Per-row error surfaced next to the "Return" button that was clicked, keyed
+  // by assignment id — kept simple (no modal) per task scope.
+  const [returnErrors, setReturnErrors] = useState<Record<string, string>>({});
+  const [returningId, setReturningId] = useState<string | null>(null);
+
+  async function handleSubmit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault();
+    setSubmitError(null);
+    setSubmitting(true);
+
+    try {
+      const response = await fetch("/api/assignments", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({
+          employeeId,
+          // Only the one FK relevant to the selected toggle is sent — mirrors
+          // the server's XOR rule (see createAssignmentSchema's .refine()).
+          ...(targetKind === "asset_item" ? { assetItemId } : { licenseId }),
+        }),
+      });
+
+      let body: unknown;
+      try {
+        body = await response.json();
+      } catch {
+        body = null;
+      }
+
+      if (!response.ok) {
+        const message =
+          body !== null &&
+          typeof body === "object" &&
+          "error" in body &&
+          typeof (body as { error: unknown }).error === "string"
+            ? (body as { error: string }).error
+            : "Request failed";
+        setSubmitError(message);
+        return;
+      }
+
+      setEmployeeId("");
+      setTargetKind("asset_item");
+      setAssetItemId("");
+      setLicenseId("");
+      refetch();
+    } catch {
+      setSubmitError("Request failed");
+    } finally {
+      setSubmitting(false);
+    }
+  }
+
+  async function handleReturn(id: string) {
+    setReturningId(id);
+    setReturnErrors((previous) => {
+      const next = { ...previous };
+      delete next[id];
+      return next;
+    });
+
+    try {
+      // PATCH /api/assignments/[id]'s body is `{returnedAt?: string}` — see
+      // src/lib/assignments.ts's validateReturnAssignmentInput(). returnedAt
+      // is optional and defaults to "now" server-side (returnAssignment()),
+      // so an empty body is sent here rather than guessing a timestamp
+      // client-side.
+      const response = await fetch(`/api/assignments/${id}`, {
+        method: "PATCH",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({}),
+      });
+
+      let body: unknown;
+      try {
+        body = await response.json();
+      } catch {
+        body = null;
+      }
+
+      if (!response.ok) {
+        const message =
+          body !== null &&
+          typeof body === "object" &&
+          "error" in body &&
+          typeof (body as { error: unknown }).error === "string"
+            ? (body as { error: string }).error
+            : "Request failed";
+        setReturnErrors((previous) => ({ ...previous, [id]: message }));
+        return;
+      }
+
+      refetch();
+    } catch {
+      setReturnErrors((previous) => ({ ...previous, [id]: "Request failed" }));
+    } finally {
+      setReturningId(null);
+    }
+  }
+
+  return (
+    <div className="flex flex-col gap-8 p-6">
+      <h1 className="text-xl font-semibold">Assignments</h1>
+
+      <section className="flex flex-col gap-3">
+        {loading ? (
+          <p className="text-sm text-muted-foreground">Loading...</p>
+        ) : error ? (
+          <p className="text-sm text-destructive">{error}</p>
+        ) : (
+          <Table>
+            <TableHeader>
+              <TableRow>
+                <TableHead>ID</TableHead>
+                <TableHead>Employee ID</TableHead>
+                <TableHead>Asset Item ID</TableHead>
+                <TableHead>License ID</TableHead>
+                <TableHead>Assigned At</TableHead>
+                <TableHead>Returned At</TableHead>
+                <TableHead>Signed At</TableHead>
+                <TableHead>Created At</TableHead>
+                <TableHead>Actions</TableHead>
+              </TableRow>
+            </TableHeader>
+            <TableBody>
+              {assignments.map((assignment) => (
+                <TableRow key={assignment.id}>
+                  <TableCell>{assignment.id}</TableCell>
+                  <TableCell>{assignment.employee_id}</TableCell>
+                  <TableCell>{assignment.asset_item_id ?? "-"}</TableCell>
+                  <TableCell>{assignment.license_id ?? "-"}</TableCell>
+                  <TableCell>{assignment.assigned_at}</TableCell>
+                  <TableCell>{assignment.returned_at ?? "-"}</TableCell>
+                  <TableCell>{assignment.signed_at ?? "-"}</TableCell>
+                  <TableCell>{assignment.created_at}</TableCell>
+                  <TableCell>
+                    {assignment.returned_at === null ? (
+                      <div className="flex flex-col gap-1">
+                        <Button
+                          type="button"
+                          size="sm"
+                          variant="outline"
+                          disabled={returningId === assignment.id}
+                          onClick={() => handleReturn(assignment.id)}
+                        >
+                          {returningId === assignment.id ? "Returning..." : "Return"}
+                        </Button>
+                        {returnErrors[assignment.id] ? (
+                          <p className="text-xs text-destructive">
+                            {returnErrors[assignment.id]}
+                          </p>
+                        ) : null}
+                      </div>
+                    ) : (
+                      "-"
+                    )}
+                  </TableCell>
+                </TableRow>
+              ))}
+            </TableBody>
+          </Table>
+        )}
+      </section>
+
+      <section className="flex max-w-sm flex-col gap-4">
+        <h2 className="text-lg font-semibold">New Assignment</h2>
+
+        <form className="flex flex-col gap-4" onSubmit={handleSubmit}>
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="employeeId">Employee</Label>
+            <Select value={employeeId} onValueChange={setEmployeeId} required>
+              <SelectTrigger id="employeeId" className="w-full">
+                <SelectValue placeholder="Select an employee" />
+              </SelectTrigger>
+              <SelectContent>
+                {employees.map((employee) => (
+                  <SelectItem key={employee.id} value={employee.id}>
+                    {employee.name}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="targetKind">Assign</Label>
+            <Select
+              value={targetKind}
+              onValueChange={(value) => setTargetKind(value as TargetKind)}
+            >
+              <SelectTrigger id="targetKind" className="w-full">
+                <SelectValue />
+              </SelectTrigger>
+              <SelectContent>
+                <SelectItem value="asset_item">Asset Item</SelectItem>
+                <SelectItem value="license">License</SelectItem>
+              </SelectContent>
+            </Select>
+          </div>
+
+          {targetKind === "asset_item" ? (
+            <div className="flex flex-col gap-2">
+              <Label htmlFor="assetItemId">Asset Item</Label>
+              <Select value={assetItemId} onValueChange={setAssetItemId} required>
+                <SelectTrigger id="assetItemId" className="w-full">
+                  <SelectValue placeholder="Select an asset item" />
+                </SelectTrigger>
+                <SelectContent>
+                  {assetItems.map((assetItem) => (
+                    <SelectItem key={assetItem.id} value={assetItem.id}>
+                      {assetItem.serial_number}
+                    </SelectItem>
+                  ))}
+                </SelectContent>
+              </Select>
+            </div>
+          ) : (
+            <div className="flex flex-col gap-2">
+              <Label htmlFor="licenseId">License</Label>
+              <Select value={licenseId} onValueChange={setLicenseId} required>
+                <SelectTrigger id="licenseId" className="w-full">
+                  <SelectValue placeholder="Select a license" />
+                </SelectTrigger>
+                <SelectContent>
+                  {licenses.map((license) => (
+                    <SelectItem key={license.id} value={license.id}>
+                      {license.name}
+                    </SelectItem>
+                  ))}
+                </SelectContent>
+              </Select>
+            </div>
+          )}
+
+          {submitError ? <p className="text-sm text-destructive">{submitError}</p> : null}
+
+          <Button type="submit" disabled={submitting}>
+            {submitting ? "Creating..." : "Create Assignment"}
+          </Button>
+        </form>
+      </section>
+    </div>
+  );
+}

src/app/employees/page.tsx

@@ -0,0 +1,183 @@
+"use client";
+
+import { useState, type FormEvent } from "react";
+import { useApiList } from "@/hooks/use-api-list";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import { Label } from "@/components/ui/label";
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from "@/components/ui/select";
+import {
+  Table,
+  TableBody,
+  TableCell,
+  TableHead,
+  TableHeader,
+  TableRow,
+} from "@/components/ui/table";
+
+// Shape returned by GET /api/employees — snake_case per this repo's
+// API-boundary convention (see src/lib/employees.ts's toRecord()).
+interface EmployeeRecord {
+  id: string;
+  name: string;
+  department: string;
+  manager_id: string | null;
+  created_at: string;
+}
+
+// Radix <Select.Item> can't take an empty-string value, so "no manager" is
+// represented by this sentinel in the form state and translated to
+// `undefined` (omitted from the request body) on submit.
+const NO_MANAGER_VALUE = "none";
+
+export default function EmployeesPage() {
+  const { data: employees, loading, error, refetch } = useApiList<EmployeeRecord>(
+    "/api/employees"
+  );
+
+  const [name, setName] = useState("");
+  const [department, setDepartment] = useState("");
+  const [managerId, setManagerId] = useState(NO_MANAGER_VALUE);
+  const [submitting, setSubmitting] = useState(false);
+  const [submitError, setSubmitError] = useState<string | null>(null);
+
+  async function handleSubmit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault();
+    setSubmitting(true);
+    setSubmitError(null);
+
+    try {
+      const response = await fetch("/api/employees", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({
+          name,
+          department,
+          ...(managerId !== NO_MANAGER_VALUE ? { managerId } : {}),
+        }),
+      });
+
+      let body: unknown;
+      try {
+        body = await response.json();
+      } catch {
+        body = null;
+      }
+
+      if (!response.ok) {
+        const message =
+          body !== null &&
+          typeof body === "object" &&
+          "error" in body &&
+          typeof (body as { error: unknown }).error === "string"
+            ? (body as { error: string }).error
+            : "Request failed";
+        setSubmitError(message);
+        return;
+      }
+
+      setName("");
+      setDepartment("");
+      setManagerId(NO_MANAGER_VALUE);
+      refetch();
+    } catch {
+      setSubmitError("Request failed");
+    } finally {
+      setSubmitting(false);
+    }
+  }
+
+  return (
+    <div className="flex flex-col gap-8 p-6">
+      <h1 className="text-xl font-semibold">Employees</h1>
+
+      <section className="flex flex-col gap-3">
+        {loading ? (
+          <p className="text-sm text-muted-foreground">Loading...</p>
+        ) : error ? (
+          <p className="text-sm text-destructive">{error}</p>
+        ) : (
+          <Table>
+            <TableHeader>
+              <TableRow>
+                <TableHead>ID</TableHead>
+                <TableHead>Name</TableHead>
+                <TableHead>Department</TableHead>
+                <TableHead>Manager ID</TableHead>
+                <TableHead>Created At</TableHead>
+              </TableRow>
+            </TableHeader>
+            <TableBody>
+              {employees.map((employee) => (
+                <TableRow key={employee.id}>
+                  <TableCell>{employee.id}</TableCell>
+                  <TableCell>{employee.name}</TableCell>
+                  <TableCell>{employee.department}</TableCell>
+                  <TableCell>{employee.manager_id ?? "-"}</TableCell>
+                  <TableCell>{employee.created_at}</TableCell>
+                </TableRow>
+              ))}
+            </TableBody>
+          </Table>
+        )}
+      </section>
+
+      <section className="flex max-w-sm flex-col gap-4">
+        <h2 className="text-lg font-semibold">New Employee</h2>
+
+        <form className="flex flex-col gap-4" onSubmit={handleSubmit}>
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="name">Name</Label>
+            <Input
+              id="name"
+              value={name}
+              onChange={(event) => setName(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="department">Department</Label>
+            <Input
+              id="department"
+              value={department}
+              onChange={(event) => setDepartment(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="managerId">Manager</Label>
+            <Select value={managerId} onValueChange={setManagerId}>
+              <SelectTrigger id="managerId" className="w-full">
+                <SelectValue />
+              </SelectTrigger>
+              <SelectContent>
+                <SelectItem value={NO_MANAGER_VALUE}>None</SelectItem>
+                {employees.map((employee) => (
+                  <SelectItem key={employee.id} value={employee.id}>
+                    {employee.name}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+
+          {submitError ? (
+            <p className="text-sm text-destructive">{submitError}</p>
+          ) : null}
+
+          <Button type="submit" disabled={submitting}>
+            {submitting ? "Creating..." : "Create Employee"}
+          </Button>
+        </form>
+      </section>
+    </div>
+  );
+}

src/app/layout.tsx

@@ -1,15 +1,27 @@
 import type { ReactNode } from "react";
 import "./globals.css";
+import { auth } from "@/auth";
+import { Nav } from "@/components/nav";
 
 export const metadata = {
   title: "Asset & License Management",
   description: "Internal IT asset & license management — Ubisoft VN local IT",
 };
 
-export default function RootLayout({ children }: { children: ReactNode }) {
+// Root layout wraps every route, including /login (middleware.ts can't
+// exclude it — it's the one page unauthenticated users must be able to
+// reach). Gate <Nav/> on session presence here rather than rendering it
+// unconditionally, so it only shows on authenticated pages as intended,
+// without needing a client-side pathname check.
+export default async function RootLayout({ children }: { children: ReactNode }) {
+  const session = await auth();
+
   return (
     <html lang="en">
-      <body>{children}</body>
+      <body>
+        {session ? <Nav /> : null}
+        {children}
+      </body>
     </html>
   );
 }

src/app/licenses/page.tsx

@@ -0,0 +1,270 @@
+"use client";
+
+import { useState, type FormEvent } from "react";
+import { useApiList } from "@/hooks/use-api-list";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import { Label } from "@/components/ui/label";
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from "@/components/ui/select";
+import {
+  Table,
+  TableBody,
+  TableCell,
+  TableHead,
+  TableHeader,
+  TableRow,
+} from "@/components/ui/table";
+
+// Shape returned by GET /api/licenses — snake_case per this repo's
+// API-boundary convention (see src/lib/licenses.ts's toRecord()).
+interface LicenseRecord {
+  id: string;
+  name: string;
+  vendor_id: string;
+  seats_total: number;
+  seats_used: number;
+  expiry_date: string | null;
+  license_type: "perpetual" | "subscription";
+  purchase_order_id: string | null;
+  created_at: string;
+}
+
+// Shape returned by GET /api/vendors — only the fields used to populate the
+// vendorId <Select> (see src/app/vendors/page.tsx's VendorRecord for the
+// full shape).
+interface VendorRecord {
+  id: string;
+  name: string;
+}
+
+// Shape returned by GET /api/purchase-orders — only the field used to
+// populate the purchaseOrderId <Select> (id as label — a PurchaseOrder has
+// no human-friendly name field, see src/app/purchase-orders/page.tsx).
+interface PurchaseOrderRecord {
+  id: string;
+}
+
+// Radix <Select.Item> can't take an empty-string value, so "no purchase
+// order" is represented by this sentinel in the form state and translated
+// to "omit the key" on submit — same pattern as purchase-orders page's
+// NOT_RECEIVED_VALUE / employees page's NO_MANAGER_VALUE.
+const NO_PURCHASE_ORDER_VALUE = "none";
+
+export default function LicensesPage() {
+  const {
+    data: licenses,
+    loading,
+    error,
+    refetch,
+  } = useApiList<LicenseRecord>("/api/licenses");
+  const { data: vendors } = useApiList<VendorRecord>("/api/vendors");
+  const { data: purchaseOrders } = useApiList<PurchaseOrderRecord>(
+    "/api/purchase-orders"
+  );
+
+  const [name, setName] = useState("");
+  const [vendorId, setVendorId] = useState("");
+  const [seatsTotal, setSeatsTotal] = useState("");
+  const [expiryDate, setExpiryDate] = useState("");
+  const [licenseType, setLicenseType] = useState("");
+  const [purchaseOrderId, setPurchaseOrderId] = useState(NO_PURCHASE_ORDER_VALUE);
+  const [submitting, setSubmitting] = useState(false);
+  const [submitError, setSubmitError] = useState<string | null>(null);
+
+  async function handleSubmit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault();
+    setSubmitError(null);
+    setSubmitting(true);
+
+    try {
+      const response = await fetch("/api/licenses", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({
+          name,
+          vendorId,
+          seatsTotal: Number(seatsTotal),
+          licenseType,
+          // Omit optional keys entirely when left blank, rather than
+          // sending null — matches the create-form pattern used on other
+          // pages (e.g. purchase-orders page's receivedAt/receivedById).
+          ...(expiryDate.trim() !== "" ? { expiryDate } : {}),
+          ...(purchaseOrderId !== NO_PURCHASE_ORDER_VALUE ? { purchaseOrderId } : {}),
+        }),
+      });
+
+      let body: unknown;
+      try {
+        body = await response.json();
+      } catch {
+        body = null;
+      }
+
+      if (!response.ok) {
+        const message =
+          body !== null &&
+          typeof body === "object" &&
+          "error" in body &&
+          typeof (body as { error: unknown }).error === "string"
+            ? (body as { error: string }).error
+            : "Request failed";
+        setSubmitError(message);
+        return;
+      }
+
+      setName("");
+      setVendorId("");
+      setSeatsTotal("");
+      setExpiryDate("");
+      setLicenseType("");
+      setPurchaseOrderId(NO_PURCHASE_ORDER_VALUE);
+      refetch();
+    } catch {
+      setSubmitError("Request failed");
+    } finally {
+      setSubmitting(false);
+    }
+  }
+
+  return (
+    <div className="flex flex-col gap-8 p-6">
+      <h1 className="text-xl font-semibold">Licenses</h1>
+
+      <section className="flex flex-col gap-3">
+        {loading ? (
+          <p className="text-sm text-muted-foreground">Loading...</p>
+        ) : error ? (
+          <p className="text-sm text-destructive">{error}</p>
+        ) : (
+          <Table>
+            <TableHeader>
+              <TableRow>
+                <TableHead>ID</TableHead>
+                <TableHead>Name</TableHead>
+                <TableHead>Vendor ID</TableHead>
+                <TableHead>Seats Total</TableHead>
+                <TableHead>Seats Used</TableHead>
+                <TableHead>Expiry Date</TableHead>
+                <TableHead>License Type</TableHead>
+                <TableHead>Purchase Order ID</TableHead>
+                <TableHead>Created At</TableHead>
+              </TableRow>
+            </TableHeader>
+            <TableBody>
+              {licenses.map((license) => (
+                <TableRow key={license.id}>
+                  <TableCell>{license.id}</TableCell>
+                  <TableCell>{license.name}</TableCell>
+                  <TableCell>{license.vendor_id}</TableCell>
+                  <TableCell>{license.seats_total}</TableCell>
+                  <TableCell>{license.seats_used}</TableCell>
+                  <TableCell>{license.expiry_date ?? "-"}</TableCell>
+                  <TableCell>{license.license_type}</TableCell>
+                  <TableCell>{license.purchase_order_id ?? "-"}</TableCell>
+                  <TableCell>{license.created_at}</TableCell>
+                </TableRow>
+              ))}
+            </TableBody>
+          </Table>
+        )}
+      </section>
+
+      <section className="flex max-w-sm flex-col gap-4">
+        <h2 className="text-lg font-semibold">New License</h2>
+
+        <form className="flex flex-col gap-4" onSubmit={handleSubmit}>
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="name">Name</Label>
+            <Input
+              id="name"
+              value={name}
+              onChange={(event) => setName(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="vendorId">Vendor</Label>
+            <Select value={vendorId} onValueChange={setVendorId} required>
+              <SelectTrigger id="vendorId" className="w-full">
+                <SelectValue placeholder="Select a vendor" />
+              </SelectTrigger>
+              <SelectContent>
+                {vendors.map((vendor) => (
+                  <SelectItem key={vendor.id} value={vendor.id}>
+                    {vendor.name}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="seatsTotal">Seats Total</Label>
+            <Input
+              id="seatsTotal"
+              type="number"
+              min={1}
+              step={1}
+              value={seatsTotal}
+              onChange={(event) => setSeatsTotal(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="expiryDate">Expiry Date (optional)</Label>
+            <Input
+              id="expiryDate"
+              type="date"
+              value={expiryDate}
+              onChange={(event) => setExpiryDate(event.target.value)}
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="licenseType">License Type</Label>
+            <Select value={licenseType} onValueChange={setLicenseType} required>
+              <SelectTrigger id="licenseType" className="w-full">
+                <SelectValue placeholder="Select a license type" />
+              </SelectTrigger>
+              <SelectContent>
+                <SelectItem value="perpetual">perpetual</SelectItem>
+                <SelectItem value="subscription">subscription</SelectItem>
+              </SelectContent>
+            </Select>
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="purchaseOrderId">Purchase Order (optional)</Label>
+            <Select value={purchaseOrderId} onValueChange={setPurchaseOrderId}>
+              <SelectTrigger id="purchaseOrderId" className="w-full">
+                <SelectValue />
+              </SelectTrigger>
+              <SelectContent>
+                <SelectItem value={NO_PURCHASE_ORDER_VALUE}>None</SelectItem>
+                {purchaseOrders.map((purchaseOrder) => (
+                  <SelectItem key={purchaseOrder.id} value={purchaseOrder.id}>
+                    {purchaseOrder.id}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+
+          {submitError ? <p className="text-sm text-destructive">{submitError}</p> : null}
+
+          <Button type="submit" disabled={submitting}>
+            {submitting ? "Creating..." : "Create License"}
+          </Button>
+        </form>
+      </section>
+    </div>
+  );
+}

src/app/purchase-orders/page.tsx

@@ -0,0 +1,258 @@
+"use client";
+
+import { useState, type FormEvent } from "react";
+import { useApiList } from "@/hooks/use-api-list";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import { Label } from "@/components/ui/label";
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from "@/components/ui/select";
+import {
+  Table,
+  TableBody,
+  TableCell,
+  TableHead,
+  TableHeader,
+  TableRow,
+} from "@/components/ui/table";
+
+// Shape returned by GET /api/purchase-orders — snake_case per this repo's
+// API-boundary convention (see src/lib/purchase-orders.ts's toRecord()).
+interface PurchaseOrderRecord {
+  id: string;
+  vendor_id: string;
+  order_date: string;
+  expected_date: string;
+  received_at: string | null;
+  received_by: string | null;
+  created_at: string;
+}
+
+// Shape returned by GET /api/vendors — only the fields used to populate the
+// vendorId <Select> (see src/app/vendors/page.tsx's VendorRecord for the
+// full shape).
+interface VendorRecord {
+  id: string;
+  name: string;
+}
+
+// Shape returned by GET /api/employees — only the fields used to populate
+// the receivedById <Select> (see src/app/employees/page.tsx's
+// EmployeeRecord for the full shape).
+interface EmployeeRecord {
+  id: string;
+  name: string;
+}
+
+// Radix <Select.Item> can't take an empty-string value, so "not received
+// yet" is represented by this sentinel in the form state and translated to
+// "omit the key" on submit — same pattern as employees page's
+// NO_MANAGER_VALUE.
+const NOT_RECEIVED_VALUE = "none";
+
+export default function PurchaseOrdersPage() {
+  const {
+    data: purchaseOrders,
+    loading,
+    error,
+    refetch,
+  } = useApiList<PurchaseOrderRecord>("/api/purchase-orders");
+  const { data: vendors } = useApiList<VendorRecord>("/api/vendors");
+  const { data: employees } = useApiList<EmployeeRecord>("/api/employees");
+
+  const [vendorId, setVendorId] = useState("");
+  const [orderDate, setOrderDate] = useState("");
+  const [expectedDate, setExpectedDate] = useState("");
+  const [receivedAt, setReceivedAt] = useState("");
+  const [receivedById, setReceivedById] = useState(NOT_RECEIVED_VALUE);
+  const [submitting, setSubmitting] = useState(false);
+  const [submitError, setSubmitError] = useState<string | null>(null);
+
+  async function handleSubmit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault();
+    setSubmitError(null);
+
+    // Mirror the server's .refine(): receivedAt/receivedById must both be
+    // empty or both be filled (src/lib/purchase-orders.ts's
+    // createPurchaseOrderSchema). Server is still the source of truth if
+    // this check somehow disagrees with it.
+    const hasReceivedAt = receivedAt.trim() !== "";
+    const hasReceivedById = receivedById !== NOT_RECEIVED_VALUE;
+    if (hasReceivedAt !== hasReceivedById) {
+      setSubmitError("receivedAt and receivedById must both be set or both be unset");
+      return;
+    }
+
+    setSubmitting(true);
+
+    try {
+      const response = await fetch("/api/purchase-orders", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({
+          vendorId,
+          orderDate,
+          expectedDate,
+          // Omit both keys entirely when left empty, rather than sending
+          // null — matches the create-form pattern used on other pages
+          // (e.g. employees page's managerId).
+          ...(hasReceivedAt ? { receivedAt } : {}),
+          ...(hasReceivedById ? { receivedById } : {}),
+        }),
+      });
+
+      let body: unknown;
+      try {
+        body = await response.json();
+      } catch {
+        body = null;
+      }
+
+      if (!response.ok) {
+        const message =
+          body !== null &&
+          typeof body === "object" &&
+          "error" in body &&
+          typeof (body as { error: unknown }).error === "string"
+            ? (body as { error: string }).error
+            : "Request failed";
+        setSubmitError(message);
+        return;
+      }
+
+      setVendorId("");
+      setOrderDate("");
+      setExpectedDate("");
+      setReceivedAt("");
+      setReceivedById(NOT_RECEIVED_VALUE);
+      refetch();
+    } catch {
+      setSubmitError("Request failed");
+    } finally {
+      setSubmitting(false);
+    }
+  }
+
+  return (
+    <div className="flex flex-col gap-8 p-6">
+      <h1 className="text-xl font-semibold">Purchase Orders</h1>
+
+      <section className="flex flex-col gap-3">
+        {loading ? (
+          <p className="text-sm text-muted-foreground">Loading...</p>
+        ) : error ? (
+          <p className="text-sm text-destructive">{error}</p>
+        ) : (
+          <Table>
+            <TableHeader>
+              <TableRow>
+                <TableHead>ID</TableHead>
+                <TableHead>Vendor ID</TableHead>
+                <TableHead>Order Date</TableHead>
+                <TableHead>Expected Date</TableHead>
+                <TableHead>Received At</TableHead>
+                <TableHead>Received By</TableHead>
+                <TableHead>Created At</TableHead>
+              </TableRow>
+            </TableHeader>
+            <TableBody>
+              {purchaseOrders.map((purchaseOrder) => (
+                <TableRow key={purchaseOrder.id}>
+                  <TableCell>{purchaseOrder.id}</TableCell>
+                  <TableCell>{purchaseOrder.vendor_id}</TableCell>
+                  <TableCell>{purchaseOrder.order_date}</TableCell>
+                  <TableCell>{purchaseOrder.expected_date}</TableCell>
+                  <TableCell>{purchaseOrder.received_at ?? "-"}</TableCell>
+                  <TableCell>{purchaseOrder.received_by ?? "-"}</TableCell>
+                  <TableCell>{purchaseOrder.created_at}</TableCell>
+                </TableRow>
+              ))}
+            </TableBody>
+          </Table>
+        )}
+      </section>
+
+      <section className="flex max-w-sm flex-col gap-4">
+        <h2 className="text-lg font-semibold">New Purchase Order</h2>
+
+        <form className="flex flex-col gap-4" onSubmit={handleSubmit}>
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="vendorId">Vendor</Label>
+            <Select value={vendorId} onValueChange={setVendorId} required>
+              <SelectTrigger id="vendorId" className="w-full">
+                <SelectValue placeholder="Select a vendor" />
+              </SelectTrigger>
+              <SelectContent>
+                {vendors.map((vendor) => (
+                  <SelectItem key={vendor.id} value={vendor.id}>
+                    {vendor.name}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="orderDate">Order Date</Label>
+            <Input
+              id="orderDate"
+              type="date"
+              value={orderDate}
+              onChange={(event) => setOrderDate(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="expectedDate">Expected Date</Label>
+            <Input
+              id="expectedDate"
+              type="date"
+              value={expectedDate}
+              onChange={(event) => setExpectedDate(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="receivedAt">Received At (optional)</Label>
+            <Input
+              id="receivedAt"
+              type="date"
+              value={receivedAt}
+              onChange={(event) => setReceivedAt(event.target.value)}
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="receivedById">Received By (optional)</Label>
+            <Select value={receivedById} onValueChange={setReceivedById}>
+              <SelectTrigger id="receivedById" className="w-full">
+                <SelectValue />
+              </SelectTrigger>
+              <SelectContent>
+                <SelectItem value={NOT_RECEIVED_VALUE}>Not received</SelectItem>
+                {employees.map((employee) => (
+                  <SelectItem key={employee.id} value={employee.id}>
+                    {employee.name}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+
+          {submitError ? <p className="text-sm text-destructive">{submitError}</p> : null}
+
+          <Button type="submit" disabled={submitting}>
+            {submitting ? "Creating..." : "Create Purchase Order"}
+          </Button>
+        </form>
+      </section>
+    </div>
+  );
+}

src/app/requests/page.tsx

@@ -0,0 +1,251 @@
+"use client";
+
+import { useState, type FormEvent } from "react";
+import { useApiList } from "@/hooks/use-api-list";
+import { Button } from "@/components/ui/button";
+import { Label } from "@/components/ui/label";
+import { Textarea } from "@/components/ui/textarea";
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from "@/components/ui/select";
+import {
+  Table,
+  TableBody,
+  TableCell,
+  TableHead,
+  TableHeader,
+  TableRow,
+} from "@/components/ui/table";
+
+// Shape returned by GET /api/requests — snake_case per this repo's
+// API-boundary convention (see src/lib/requests.ts's toRecord()). `status`
+// is always "Draft" right now (no state-machine transitions built yet), see
+// src/lib/requests.ts's RequestStatus comment.
+interface RequestRecord {
+  id: string;
+  employee_id: string;
+  type: "asset" | "license";
+  reason: string;
+  status: string;
+  purchase_order_id: string | null;
+  created_at: string;
+}
+
+// Shape returned by GET /api/employees — only the fields used to populate
+// the employeeId <Select> (see src/app/employees/page.tsx's EmployeeRecord
+// for the full shape).
+interface EmployeeRecord {
+  id: string;
+  name: string;
+}
+
+// Shape returned by GET /api/purchase-orders — only the id, shown as the
+// <Select> label since PurchaseOrder has no human-friendly name field (see
+// src/app/purchase-orders/page.tsx's PurchaseOrderRecord for the full
+// shape).
+interface PurchaseOrderRecord {
+  id: string;
+}
+
+// The exact enum literal values from RequestType (src/lib/requests.ts) —
+// don't invent labels not accepted by the Zod schema.
+const REQUEST_TYPES = ["asset", "license"] as const;
+
+// Radix <Select.Item> can't take an empty-string value, so "no purchase
+// order" is represented by this sentinel in the form state and translated
+// to "omit the key" on submit — same pattern as employees page's
+// NO_MANAGER_VALUE / purchase-orders page's NOT_RECEIVED_VALUE.
+const NO_PURCHASE_ORDER_VALUE = "none";
+
+export default function RequestsPage() {
+  const {
+    data: requests,
+    loading,
+    error,
+    refetch,
+  } = useApiList<RequestRecord>("/api/requests");
+  const { data: employees } = useApiList<EmployeeRecord>("/api/employees");
+  const { data: purchaseOrders } = useApiList<PurchaseOrderRecord>(
+    "/api/purchase-orders"
+  );
+
+  const [employeeId, setEmployeeId] = useState("");
+  const [type, setType] = useState<(typeof REQUEST_TYPES)[number] | "">("");
+  const [reason, setReason] = useState("");
+  const [purchaseOrderId, setPurchaseOrderId] = useState(NO_PURCHASE_ORDER_VALUE);
+  const [submitting, setSubmitting] = useState(false);
+  const [submitError, setSubmitError] = useState<string | null>(null);
+
+  async function handleSubmit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault();
+    setSubmitting(true);
+    setSubmitError(null);
+
+    const hasPurchaseOrderId = purchaseOrderId !== NO_PURCHASE_ORDER_VALUE;
+
+    try {
+      const response = await fetch("/api/requests", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({
+          employeeId,
+          type,
+          reason,
+          // Omit the key entirely when left unset, rather than sending
+          // null — matches the create-form pattern used on other pages
+          // (e.g. employees page's managerId).
+          ...(hasPurchaseOrderId ? { purchaseOrderId } : {}),
+        }),
+      });
+
+      let body: unknown;
+      try {
+        body = await response.json();
+      } catch {
+        body = null;
+      }
+
+      if (!response.ok) {
+        const message =
+          body !== null &&
+          typeof body === "object" &&
+          "error" in body &&
+          typeof (body as { error: unknown }).error === "string"
+            ? (body as { error: string }).error
+            : "Request failed";
+        setSubmitError(message);
+        return;
+      }
+
+      setEmployeeId("");
+      setType("");
+      setReason("");
+      setPurchaseOrderId(NO_PURCHASE_ORDER_VALUE);
+      refetch();
+    } catch {
+      setSubmitError("Request failed");
+    } finally {
+      setSubmitting(false);
+    }
+  }
+
+  return (
+    <div className="flex flex-col gap-8 p-6">
+      <h1 className="text-xl font-semibold">Requests</h1>
+
+      <section className="flex flex-col gap-3">
+        {loading ? (
+          <p className="text-sm text-muted-foreground">Loading...</p>
+        ) : error ? (
+          <p className="text-sm text-destructive">{error}</p>
+        ) : (
+          <Table>
+            <TableHeader>
+              <TableRow>
+                <TableHead>ID</TableHead>
+                <TableHead>Employee ID</TableHead>
+                <TableHead>Type</TableHead>
+                <TableHead>Reason</TableHead>
+                <TableHead>Status</TableHead>
+                <TableHead>Purchase Order ID</TableHead>
+                <TableHead>Created At</TableHead>
+              </TableRow>
+            </TableHeader>
+            <TableBody>
+              {requests.map((request) => (
+                <TableRow key={request.id}>
+                  <TableCell>{request.id}</TableCell>
+                  <TableCell>{request.employee_id}</TableCell>
+                  <TableCell>{request.type}</TableCell>
+                  <TableCell>{request.reason}</TableCell>
+                  <TableCell>{request.status}</TableCell>
+                  <TableCell>{request.purchase_order_id ?? "-"}</TableCell>
+                  <TableCell>{request.created_at}</TableCell>
+                </TableRow>
+              ))}
+            </TableBody>
+          </Table>
+        )}
+      </section>
+
+      <section className="flex max-w-sm flex-col gap-4">
+        <h2 className="text-lg font-semibold">New Request</h2>
+
+        <form className="flex flex-col gap-4" onSubmit={handleSubmit}>
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="employeeId">Employee</Label>
+            <Select value={employeeId} onValueChange={setEmployeeId} required>
+              <SelectTrigger id="employeeId" className="w-full">
+                <SelectValue placeholder="Select an employee" />
+              </SelectTrigger>
+              <SelectContent>
+                {employees.map((employee) => (
+                  <SelectItem key={employee.id} value={employee.id}>
+                    {employee.name}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="type">Type</Label>
+            <Select
+              value={type}
+              onValueChange={(value) => setType(value as (typeof REQUEST_TYPES)[number])}
+              required
+            >
+              <SelectTrigger id="type" className="w-full">
+                <SelectValue placeholder="Select a type" />
+              </SelectTrigger>
+              <SelectContent>
+                {REQUEST_TYPES.map((requestType) => (
+                  <SelectItem key={requestType} value={requestType}>
+                    {requestType}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="reason">Reason</Label>
+            <Textarea
+              id="reason"
+              value={reason}
+              onChange={(event) => setReason(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="purchaseOrderId">Purchase Order (optional)</Label>
+            <Select value={purchaseOrderId} onValueChange={setPurchaseOrderId}>
+              <SelectTrigger id="purchaseOrderId" className="w-full">
+                <SelectValue />
+              </SelectTrigger>
+              <SelectContent>
+                <SelectItem value={NO_PURCHASE_ORDER_VALUE}>None</SelectItem>
+                {purchaseOrders.map((purchaseOrder) => (
+                  <SelectItem key={purchaseOrder.id} value={purchaseOrder.id}>
+                    {purchaseOrder.id}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+
+          {submitError ? <p className="text-sm text-destructive">{submitError}</p> : null}
+
+          <Button type="submit" disabled={submitting}>
+            {submitting ? "Creating..." : "Create Request"}
+          </Button>
+        </form>
+      </section>
+    </div>
+  );
+}

src/app/vendors/page.tsx

@@ -0,0 +1,216 @@
+"use client";
+
+import { useState, type FormEvent } from "react";
+import { useApiList } from "@/hooks/use-api-list";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import { Label } from "@/components/ui/label";
+import { Textarea } from "@/components/ui/textarea";
+import {
+  Table,
+  TableBody,
+  TableCell,
+  TableHead,
+  TableHeader,
+  TableRow,
+} from "@/components/ui/table";
+
+// Shape returned by GET /api/vendors — snake_case per this repo's
+// API-boundary convention (see src/lib/vendors.ts's toRecord()).
+interface VendorRecord {
+  id: string;
+  name: string;
+  contact_email: string;
+  contact_phone: string;
+  address: string;
+  tax_code: string | null;
+  notes: string | null;
+  created_at: string;
+}
+
+export default function VendorsPage() {
+  const { data: vendors, loading, error, refetch } = useApiList<VendorRecord>(
+    "/api/vendors"
+  );
+
+  const [name, setName] = useState("");
+  const [contactEmail, setContactEmail] = useState("");
+  const [contactPhone, setContactPhone] = useState("");
+  const [address, setAddress] = useState("");
+  const [taxCode, setTaxCode] = useState("");
+  const [notes, setNotes] = useState("");
+  const [submitting, setSubmitting] = useState(false);
+  const [submitError, setSubmitError] = useState<string | null>(null);
+
+  async function handleSubmit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault();
+    setSubmitting(true);
+    setSubmitError(null);
+
+    try {
+      const response = await fetch("/api/vendors", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({
+          name,
+          contactEmail,
+          contactPhone,
+          address,
+          // taxCode/notes are optional+nullable and must be non-empty
+          // strings if present (src/lib/vendors.ts's createVendorSchema) —
+          // omit the key entirely when the field is left blank, same
+          // pattern as employees page's managerId.
+          ...(taxCode.trim() !== "" ? { taxCode } : {}),
+          ...(notes.trim() !== "" ? { notes } : {}),
+        }),
+      });
+
+      let body: unknown;
+      try {
+        body = await response.json();
+      } catch {
+        body = null;
+      }
+
+      if (!response.ok) {
+        const message =
+          body !== null &&
+          typeof body === "object" &&
+          "error" in body &&
+          typeof (body as { error: unknown }).error === "string"
+            ? (body as { error: string }).error
+            : "Request failed";
+        setSubmitError(message);
+        return;
+      }
+
+      setName("");
+      setContactEmail("");
+      setContactPhone("");
+      setAddress("");
+      setTaxCode("");
+      setNotes("");
+      refetch();
+    } catch {
+      setSubmitError("Request failed");
+    } finally {
+      setSubmitting(false);
+    }
+  }
+
+  return (
+    <div className="flex flex-col gap-8 p-6">
+      <h1 className="text-xl font-semibold">Vendors</h1>
+
+      <section className="flex flex-col gap-3">
+        {loading ? (
+          <p className="text-sm text-muted-foreground">Loading...</p>
+        ) : error ? (
+          <p className="text-sm text-destructive">{error}</p>
+        ) : (
+          <Table>
+            <TableHeader>
+              <TableRow>
+                <TableHead>ID</TableHead>
+                <TableHead>Name</TableHead>
+                <TableHead>Contact Email</TableHead>
+                <TableHead>Contact Phone</TableHead>
+                <TableHead>Address</TableHead>
+                <TableHead>Tax Code</TableHead>
+                <TableHead>Notes</TableHead>
+                <TableHead>Created At</TableHead>
+              </TableRow>
+            </TableHeader>
+            <TableBody>
+              {vendors.map((vendor) => (
+                <TableRow key={vendor.id}>
+                  <TableCell>{vendor.id}</TableCell>
+                  <TableCell>{vendor.name}</TableCell>
+                  <TableCell>{vendor.contact_email}</TableCell>
+                  <TableCell>{vendor.contact_phone}</TableCell>
+                  <TableCell>{vendor.address}</TableCell>
+                  <TableCell>{vendor.tax_code ?? "-"}</TableCell>
+                  <TableCell>{vendor.notes ?? "-"}</TableCell>
+                  <TableCell>{vendor.created_at}</TableCell>
+                </TableRow>
+              ))}
+            </TableBody>
+          </Table>
+        )}
+      </section>
+
+      <section className="flex max-w-sm flex-col gap-4">
+        <h2 className="text-lg font-semibold">New Vendor</h2>
+
+        <form className="flex flex-col gap-4" onSubmit={handleSubmit}>
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="name">Name</Label>
+            <Input
+              id="name"
+              value={name}
+              onChange={(event) => setName(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="contactEmail">Contact Email</Label>
+            <Input
+              id="contactEmail"
+              type="email"
+              value={contactEmail}
+              onChange={(event) => setContactEmail(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="contactPhone">Contact Phone</Label>
+            <Input
+              id="contactPhone"
+              value={contactPhone}
+              onChange={(event) => setContactPhone(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="address">Address</Label>
+            <Input
+              id="address"
+              value={address}
+              onChange={(event) => setAddress(event.target.value)}
+              required
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="taxCode">Tax Code</Label>
+            <Input
+              id="taxCode"
+              value={taxCode}
+              onChange={(event) => setTaxCode(event.target.value)}
+            />
+          </div>
+
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="notes">Notes</Label>
+            <Textarea
+              id="notes"
+              value={notes}
+              onChange={(event) => setNotes(event.target.value)}
+            />
+          </div>
+
+          {submitError ? (
+            <p className="text-sm text-destructive">{submitError}</p>
+          ) : null}
+
+          <Button type="submit" disabled={submitting}>
+            {submitting ? "Creating..." : "Create Vendor"}
+          </Button>
+        </form>
+      </section>
+    </div>
+  );
+}

src/components/nav.tsx

@@ -0,0 +1,55 @@
+"use client";
+
+import Link from "next/link";
+import { signOut } from "next-auth/react";
+import { Button } from "@/components/ui/button";
+
+// Shared top nav for every authenticated page. Links point at the entity
+// routes each later task in this "basic functional UI" batch will build
+// (Employee, Vendor, AssetCategory, AssetCategoryAttributeDef, AssetModel,
+// PurchaseOrder, AssetItem, License, Request, Assignment) — most of these
+// routes don't exist yet and will 404 until their own task lands, which is
+// expected (see task scope: no conditional hiding needed).
+const ENTITY_LINKS = [
+  { href: "/employees", label: "Employees" },
+  { href: "/vendors", label: "Vendors" },
+  { href: "/asset-categories", label: "Asset Categories" },
+  { href: "/asset-category-attribute-defs", label: "Attribute Defs" },
+  { href: "/asset-models", label: "Asset Models" },
+  { href: "/assets", label: "Assets" },
+  { href: "/licenses", label: "Licenses" },
+  { href: "/purchase-orders", label: "Purchase Orders" },
+  { href: "/requests", label: "Requests" },
+  { href: "/assignments", label: "Assignments" },
+] as const;
+
+export function Nav() {
+  return (
+    <nav className="flex flex-wrap items-center gap-4 border-b border-border px-4 py-3">
+      <Link href="/" className="font-semibold whitespace-nowrap">
+        Asset & License Mgmt
+      </Link>
+
+      <div className="flex flex-1 flex-wrap gap-3 text-sm">
+        {ENTITY_LINKS.map((link) => (
+          <Link
+            key={link.href}
+            href={link.href}
+            className="text-muted-foreground hover:text-foreground"
+          >
+            {link.label}
+          </Link>
+        ))}
+      </div>
+
+      <Button
+        type="button"
+        variant="outline"
+        size="sm"
+        onClick={() => signOut({ callbackUrl: "/login" })}
+      >
+        Sign out
+      </Button>
+    </nav>
+  );
+}

src/components/ui/label.tsx

@@ -0,0 +1,24 @@
+"use client"
+
+import * as React from "react"
+import { Label as LabelPrimitive } from "radix-ui"
+
+import { cn } from "@/lib/utils"
+
+function Label({
+  className,
+  ...props
+}: React.ComponentProps<typeof LabelPrimitive.Root>) {
+  return (
+    <LabelPrimitive.Root
+      data-slot="label"
+      className={cn(
+        "flex items-center gap-2 text-sm leading-none font-medium select-none group-data-[disabled=true]:pointer-events-none group-data-[disabled=true]:opacity-50 peer-disabled:cursor-not-allowed peer-disabled:opacity-50",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+export { Label }

src/components/ui/select.tsx

@@ -0,0 +1,190 @@
+"use client"
+
+import * as React from "react"
+import { CheckIcon, ChevronDownIcon, ChevronUpIcon } from "lucide-react"
+import { Select as SelectPrimitive } from "radix-ui"
+
+import { cn } from "@/lib/utils"
+
+function Select({
+  ...props
+}: React.ComponentProps<typeof SelectPrimitive.Root>) {
+  return <SelectPrimitive.Root data-slot="select" {...props} />
+}
+
+function SelectGroup({
+  ...props
+}: React.ComponentProps<typeof SelectPrimitive.Group>) {
+  return <SelectPrimitive.Group data-slot="select-group" {...props} />
+}
+
+function SelectValue({
+  ...props
+}: React.ComponentProps<typeof SelectPrimitive.Value>) {
+  return <SelectPrimitive.Value data-slot="select-value" {...props} />
+}
+
+function SelectTrigger({
+  className,
+  size = "default",
+  children,
+  ...props
+}: React.ComponentProps<typeof SelectPrimitive.Trigger> & {
+  size?: "sm" | "default"
+}) {
+  return (
+    <SelectPrimitive.Trigger
+      data-slot="select-trigger"
+      data-size={size}
+      className={cn(
+        "flex w-fit items-center justify-between gap-2 rounded-md border border-input bg-transparent px-3 py-2 text-sm whitespace-nowrap shadow-xs transition-[color,box-shadow] outline-none focus-visible:border-ring focus-visible:ring-[3px] focus-visible:ring-ring/50 disabled:cursor-not-allowed disabled:opacity-50 aria-invalid:border-destructive aria-invalid:ring-destructive/20 data-[placeholder]:text-muted-foreground data-[size=default]:h-9 data-[size=sm]:h-8 *:data-[slot=select-value]:line-clamp-1 *:data-[slot=select-value]:flex *:data-[slot=select-value]:items-center *:data-[slot=select-value]:gap-2 dark:bg-input/30 dark:hover:bg-input/50 dark:aria-invalid:ring-destructive/40 [&_svg]:pointer-events-none [&_svg]:shrink-0 [&_svg:not([class*='size-'])]:size-4 [&_svg:not([class*='text-'])]:text-muted-foreground",
+        className
+      )}
+      {...props}
+    >
+      {children}
+      <SelectPrimitive.Icon asChild>
+        <ChevronDownIcon className="size-4 opacity-50" />
+      </SelectPrimitive.Icon>
+    </SelectPrimitive.Trigger>
+  )
+}
+
+function SelectContent({
+  className,
+  children,
+  position = "item-aligned",
+  align = "center",
+  ...props
+}: React.ComponentProps<typeof SelectPrimitive.Content>) {
+  return (
+    <SelectPrimitive.Portal>
+      <SelectPrimitive.Content
+        data-slot="select-content"
+        className={cn(
+          "relative z-50 max-h-(--radix-select-content-available-height) min-w-[8rem] origin-(--radix-select-content-transform-origin) overflow-x-hidden overflow-y-auto rounded-md border bg-popover text-popover-foreground shadow-md data-[side=bottom]:slide-in-from-top-2 data-[side=left]:slide-in-from-right-2 data-[side=right]:slide-in-from-left-2 data-[side=top]:slide-in-from-bottom-2 data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=closed]:zoom-out-95 data-[state=open]:animate-in data-[state=open]:fade-in-0 data-[state=open]:zoom-in-95",
+          position === "popper" &&
+            "data-[side=bottom]:translate-y-1 data-[side=left]:-translate-x-1 data-[side=right]:translate-x-1 data-[side=top]:-translate-y-1",
+          className
+        )}
+        position={position}
+        align={align}
+        {...props}
+      >
+        <SelectScrollUpButton />
+        <SelectPrimitive.Viewport
+          className={cn(
+            "p-1",
+            position === "popper" &&
+              "h-[var(--radix-select-trigger-height)] w-full min-w-[var(--radix-select-trigger-width)] scroll-my-1"
+          )}
+        >
+          {children}
+        </SelectPrimitive.Viewport>
+        <SelectScrollDownButton />
+      </SelectPrimitive.Content>
+    </SelectPrimitive.Portal>
+  )
+}
+
+function SelectLabel({
+  className,
+  ...props
+}: React.ComponentProps<typeof SelectPrimitive.Label>) {
+  return (
+    <SelectPrimitive.Label
+      data-slot="select-label"
+      className={cn("px-2 py-1.5 text-xs text-muted-foreground", className)}
+      {...props}
+    />
+  )
+}
+
+function SelectItem({
+  className,
+  children,
+  ...props
+}: React.ComponentProps<typeof SelectPrimitive.Item>) {
+  return (
+    <SelectPrimitive.Item
+      data-slot="select-item"
+      className={cn(
+        "relative flex w-full cursor-default items-center gap-2 rounded-sm py-1.5 pr-8 pl-2 text-sm outline-hidden select-none focus:bg-accent focus:text-accent-foreground data-[disabled]:pointer-events-none data-[disabled]:opacity-50 [&_svg]:pointer-events-none [&_svg]:shrink-0 [&_svg:not([class*='size-'])]:size-4 [&_svg:not([class*='text-'])]:text-muted-foreground *:[span]:last:flex *:[span]:last:items-center *:[span]:last:gap-2",
+        className
+      )}
+      {...props}
+    >
+      <span
+        data-slot="select-item-indicator"
+        className="absolute right-2 flex size-3.5 items-center justify-center"
+      >
+        <SelectPrimitive.ItemIndicator>
+          <CheckIcon className="size-4" />
+        </SelectPrimitive.ItemIndicator>
+      </span>
+      <SelectPrimitive.ItemText>{children}</SelectPrimitive.ItemText>
+    </SelectPrimitive.Item>
+  )
+}
+
+function SelectSeparator({
+  className,
+  ...props
+}: React.ComponentProps<typeof SelectPrimitive.Separator>) {
+  return (
+    <SelectPrimitive.Separator
+      data-slot="select-separator"
+      className={cn("pointer-events-none -mx-1 my-1 h-px bg-border", className)}
+      {...props}
+    />
+  )
+}
+
+function SelectScrollUpButton({
+  className,
+  ...props
+}: React.ComponentProps<typeof SelectPrimitive.ScrollUpButton>) {
+  return (
+    <SelectPrimitive.ScrollUpButton
+      data-slot="select-scroll-up-button"
+      className={cn(
+        "flex cursor-default items-center justify-center py-1",
+        className
+      )}
+      {...props}
+    >
+      <ChevronUpIcon className="size-4" />
+    </SelectPrimitive.ScrollUpButton>
+  )
+}
+
+function SelectScrollDownButton({
+  className,
+  ...props
+}: React.ComponentProps<typeof SelectPrimitive.ScrollDownButton>) {
+  return (
+    <SelectPrimitive.ScrollDownButton
+      data-slot="select-scroll-down-button"
+      className={cn(
+        "flex cursor-default items-center justify-center py-1",
+        className
+      )}
+      {...props}
+    >
+      <ChevronDownIcon className="size-4" />
+    </SelectPrimitive.ScrollDownButton>
+  )
+}
+
+export {
+  Select,
+  SelectContent,
+  SelectGroup,
+  SelectItem,
+  SelectLabel,
+  SelectScrollDownButton,
+  SelectScrollUpButton,
+  SelectSeparator,
+  SelectTrigger,
+  SelectValue,
+}

src/components/ui/table.tsx

@@ -0,0 +1,116 @@
+"use client"
+
+import * as React from "react"
+
+import { cn } from "@/lib/utils"
+
+function Table({ className, ...props }: React.ComponentProps<"table">) {
+  return (
+    <div
+      data-slot="table-container"
+      className="relative w-full overflow-x-auto"
+    >
+      <table
+        data-slot="table"
+        className={cn("w-full caption-bottom text-sm", className)}
+        {...props}
+      />
+    </div>
+  )
+}
+
+function TableHeader({ className, ...props }: React.ComponentProps<"thead">) {
+  return (
+    <thead
+      data-slot="table-header"
+      className={cn("[&_tr]:border-b", className)}
+      {...props}
+    />
+  )
+}
+
+function TableBody({ className, ...props }: React.ComponentProps<"tbody">) {
+  return (
+    <tbody
+      data-slot="table-body"
+      className={cn("[&_tr:last-child]:border-0", className)}
+      {...props}
+    />
+  )
+}
+
+function TableFooter({ className, ...props }: React.ComponentProps<"tfoot">) {
+  return (
+    <tfoot
+      data-slot="table-footer"
+      className={cn(
+        "border-t bg-muted/50 font-medium [&>tr]:last:border-b-0",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+function TableRow({ className, ...props }: React.ComponentProps<"tr">) {
+  return (
+    <tr
+      data-slot="table-row"
+      className={cn(
+        "border-b transition-colors hover:bg-muted/50 has-aria-expanded:bg-muted/50 data-[state=selected]:bg-muted",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+function TableHead({ className, ...props }: React.ComponentProps<"th">) {
+  return (
+    <th
+      data-slot="table-head"
+      className={cn(
+        "h-10 px-2 text-left align-middle font-medium whitespace-nowrap text-foreground [&:has([role=checkbox])]:pr-0 [&>[role=checkbox]]:translate-y-[2px]",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+function TableCell({ className, ...props }: React.ComponentProps<"td">) {
+  return (
+    <td
+      data-slot="table-cell"
+      className={cn(
+        "p-2 align-middle whitespace-nowrap [&:has([role=checkbox])]:pr-0 [&>[role=checkbox]]:translate-y-[2px]",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+function TableCaption({
+  className,
+  ...props
+}: React.ComponentProps<"caption">) {
+  return (
+    <caption
+      data-slot="table-caption"
+      className={cn("mt-4 text-sm text-muted-foreground", className)}
+      {...props}
+    />
+  )
+}
+
+export {
+  Table,
+  TableHeader,
+  TableBody,
+  TableFooter,
+  TableHead,
+  TableRow,
+  TableCell,
+  TableCaption,
+}

src/components/ui/textarea.tsx

@@ -0,0 +1,18 @@
+import * as React from "react"
+
+import { cn } from "@/lib/utils"
+
+function Textarea({ className, ...props }: React.ComponentProps<"textarea">) {
+  return (
+    <textarea
+      data-slot="textarea"
+      className={cn(
+        "flex field-sizing-content min-h-16 w-full rounded-md border border-input bg-transparent px-3 py-2 text-base shadow-xs transition-[color,box-shadow] outline-none placeholder:text-muted-foreground focus-visible:border-ring focus-visible:ring-[3px] focus-visible:ring-ring/50 disabled:cursor-not-allowed disabled:opacity-50 aria-invalid:border-destructive aria-invalid:ring-destructive/20 md:text-sm dark:bg-input/30 dark:aria-invalid:ring-destructive/40",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+export { Textarea }

src/hooks/use-api-list.ts

@@ -0,0 +1,91 @@
+"use client";
+
+import { useCallback, useEffect, useState } from "react";
+
+// Small shared data-fetching hook used by every entity page — both for its
+// own list table (GET /api/<entity>) and for populating FK <Select>
+// dropdowns from other entities' GET endpoints (e.g. an AssetItem page
+// fetching /api/employees to build an "assigned to" picker). Deliberately
+// minimal: no caching/dedupe/revalidation library, just fetch + state,
+// matching the "no polish, just clickable manual testing" scope of this
+// task (see CLAUDE.md's "basic functional UI" batch note).
+//
+// Every API route in this app returns a JSON array on success (200) or
+// `{error: string}` on failure (see e.g. src/app/api/employees/route.ts's
+// GET/POST) — this hook follows that same shape convention.
+type UseApiListResult<T> = {
+  data: T[];
+  loading: boolean;
+  error: string | null;
+  refetch: () => void;
+};
+
+const GENERIC_ERROR_MESSAGE = "Request failed";
+
+export function useApiList<T>(endpoint: string): UseApiListResult<T> {
+  const [data, setData] = useState<T[]>([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+  const [refetchCount, setRefetchCount] = useState(0);
+
+  const refetch = useCallback(() => {
+    setRefetchCount((count) => count + 1);
+  }, []);
+
+  useEffect(() => {
+    let cancelled = false;
+
+    async function load(): Promise<void> {
+      setLoading(true);
+      setError(null);
+
+      try {
+        const response = await fetch(endpoint);
+        let body: unknown;
+
+        try {
+          body = await response.json();
+        } catch {
+          body = null;
+        }
+
+        if (!response.ok) {
+          const message =
+            body !== null &&
+            typeof body === "object" &&
+            "error" in body &&
+            typeof (body as { error: unknown }).error === "string"
+              ? (body as { error: string }).error
+              : GENERIC_ERROR_MESSAGE;
+
+          if (!cancelled) {
+            setData([]);
+            setError(message);
+          }
+          return;
+        }
+
+        if (!cancelled) {
+          setData(Array.isArray(body) ? (body as T[]) : []);
+        }
+      } catch {
+        if (!cancelled) {
+          setData([]);
+          setError(GENERIC_ERROR_MESSAGE);
+        }
+      } finally {
+        if (!cancelled) {
+          setLoading(false);
+        }
+      }
+    }
+
+    void load();
+
+    return () => {
+      cancelled = true;
+    };
+  }, [endpoint, refetchCount]);
+
+  return { data, loading, error, refetch };
+}

src/lib/asset-categories.ts

@@ -0,0 +1,107 @@
+import { z } from "zod";
+import { prisma } from "./prisma";
+
+export type AssetCategoryValueGroup = "high_value" | "low_value";
+
+export interface AssetCategoryRecord {
+  id: string;
+  name: string;
+  value_group: AssetCategoryValueGroup;
+  created_at: string;
+}
+
+export interface CreateAssetCategoryInput {
+  name: string;
+  valueGroup: AssetCategoryValueGroup;
+}
+
+export type ValidationResult =
+  | { ok: true; value: CreateAssetCategoryInput }
+  | { ok: false; error: string };
+
+// Mirrors src/lib/vendors.ts's nonEmptyString helper.
+function nonEmptyString(message: string) {
+  return z.string({ required_error: message, invalid_type_error: message }).refine(
+    (value) => value.trim() !== "",
+    { message }
+  );
+}
+
+const createAssetCategorySchema = z.object({
+  name: nonEmptyString("name is required and must be a non-empty string"),
+  // Fixed 2-value set (see docs/asset-license-management.md's "## Phân
+  // loại tài sản" section) — mirrors src/lib/licenses.ts's licenseType
+  // z.enum() pattern.
+  valueGroup: z.enum(["high_value", "low_value"], {
+    errorMap: () => ({
+      message: "valueGroup is required and must be either 'high_value' or 'low_value'",
+    }),
+  }),
+});
+
+/**
+ * Validates raw (untyped) asset-category-creation input. name must be a
+ * non-empty string, valueGroup must be one of the two fixed enum values
+ * (per the "## Phân loại tài sản" spec in docs/asset-license-management.md).
+ */
+export function validateCreateAssetCategoryInput(input: {
+  name?: unknown;
+  valueGroup?: unknown;
+}): ValidationResult {
+  const result = createAssetCategorySchema.safeParse(input);
+  if (!result.success) {
+    const message = result.error.issues[0]?.message ?? "Invalid input";
+    return { ok: false, error: message };
+  }
+  return { ok: true, value: result.data };
+}
+
+function toRecord(row: {
+  id: string;
+  name: string;
+  valueGroup: AssetCategoryValueGroup;
+  createdAt: Date;
+}): AssetCategoryRecord {
+  return {
+    id: row.id,
+    name: row.name,
+    value_group: row.valueGroup,
+    created_at: row.createdAt.toISOString(),
+  };
+}
+
+export type CreateAssetCategoryResult =
+  | { ok: true; value: AssetCategoryRecord }
+  | { ok: false; error: string };
+
+/**
+ * Creates an AssetCategory. No unique constraint on any field, no FKs
+ * either (see docs/asset-license-management.md's "## Phân loại tài sản"
+ * spec — standalone entity, same starting shape as Vendor before it grew
+ * relations) — so there's no known Prisma error code to catch/translate
+ * here today. Still returns the `{ok,value}|{ok,error}` shape (rather than
+ * a bare Promise<AssetCategoryRecord> like createVendor()) to match the
+ * convention used across the newer entities (AssetItem/License) — see the
+ * code-reviewer finding on createLicense() in CLAUDE.md's "Trạng thái hiện
+ * tại": adding this shape up front avoids a silent 500 if a unique
+ * constraint is added later (e.g. on `name`) without remembering to also
+ * add P2002 handling here.
+ */
+export async function createAssetCategory(
+  input: CreateAssetCategoryInput
+): Promise<CreateAssetCategoryResult> {
+  const created = await prisma.assetCategory.create({
+    data: {
+      name: input.name,
+      valueGroup: input.valueGroup,
+    },
+  });
+  return { ok: true, value: toRecord(created) };
+}
+
+export async function listAssetCategories(): Promise<AssetCategoryRecord[]> {
+  const rows = await prisma.assetCategory.findMany({
+    orderBy: [{ createdAt: "desc" }, { id: "desc" }],
+  });
+  return rows.map(toRecord);
+}

src/lib/asset-category-attribute-defs.ts

@@ -0,0 +1,169 @@
+import { z } from "zod";
+import { Prisma } from "@prisma/client";
+import { prisma } from "./prisma";
+
+export type AssetAttributeDataType = "string" | "number" | "boolean" | "date";
+
+export interface AssetCategoryAttributeDefRecord {
+  id: string;
+  category_id: string;
+  key: string;
+  label: string;
+  data_type: AssetAttributeDataType;
+  required: boolean;
+  sort_order: number;
+  created_at: string;
+}
+
+export interface CreateAssetCategoryAttributeDefInput {
+  categoryId: string;
+  key: string;
+  label: string;
+  dataType: AssetAttributeDataType;
+  required: boolean;
+  sortOrder: number;
+}
+
+export type ValidationResult =
+  | { ok: true; value: CreateAssetCategoryAttributeDefInput }
+  | { ok: false; error: string };
+
+// Mirrors src/lib/asset-categories.ts's nonEmptyString helper.
+function nonEmptyString(message: string) {
+  return z.string({ required_error: message, invalid_type_error: message }).refine(
+    (value) => value.trim() !== "",
+    { message }
+  );
+}
+
+const createAssetCategoryAttributeDefSchema = z.object({
+  // FK to AssetCategory — only a UUID *format* check here, whether it
+  // references a real category is left to Prisma's own FK constraint at
+  // insert time (see createAssetCategoryAttributeDef()'s P2003 handling
+  // below). Mirrors src/lib/purchase-orders.ts's vendorId handling.
+  categoryId: z
+    .string({ required_error: "categoryId is required and must be a valid UUID string" })
+    .uuid("categoryId is required and must be a valid UUID string"),
+  // Slug-style, e.g. "ram_gb" — only unique *within* a category (composite
+  // unique (categoryId, key) at the DB layer), not globally. Just requires
+  // non-empty here; the DB-level uniqueness is enforced by
+  // createAssetCategoryAttributeDef()'s P2002 handling below.
+  key: nonEmptyString("key is required and must be a non-empty string"),
+  label: nonEmptyString("label is required and must be a non-empty string"),
+  // Fixed 4-value set (see docs/asset-license-management.md's "Cập nhật
+  // 2026-08-02 (3)" section) — a DEV-defined closed technical set, mirrors
+  // src/lib/asset-categories.ts's valueGroup z.enum() pattern.
+  dataType: z.enum(["string", "number", "boolean", "date"], {
+    errorMap: () => ({
+      message: "dataType is required and must be one of 'string', 'number', 'boolean', 'date'",
+    }),
+  }),
+  required: z.boolean({
+    required_error: "required is required and must be a boolean",
+    invalid_type_error: "required is required and must be a boolean",
+  }),
+  sortOrder: z.number({
+    required_error: "sortOrder is required and must be an integer",
+    invalid_type_error: "sortOrder is required and must be an integer",
+  })
+    .int("sortOrder is required and must be an integer"),
+});
+
+/**
+ * Validates raw (untyped) asset-category-attribute-def-creation input.
+ * categoryId must be a valid UUID string, key/label must be non-empty
+ * strings, dataType must be one of the four fixed enum values, required
+ * must be a boolean, sortOrder must be an integer. Whether categoryId
+ * references a real AssetCategory, and whether (categoryId, key) is
+ * actually unique, are both left to Prisma's constraints at insert time
+ * (see createAssetCategoryAttributeDef() below).
+ */
+export function validateCreateAssetCategoryAttributeDefInput(input: {
+  categoryId?: unknown;
+  key?: unknown;
+  label?: unknown;
+  dataType?: unknown;
+  required?: unknown;
+  sortOrder?: unknown;
+}): ValidationResult {
+  const result = createAssetCategoryAttributeDefSchema.safeParse(input);
+  if (!result.success) {
+    const message = result.error.issues[0]?.message ?? "Invalid input";
+    return { ok: false, error: message };
+  }
+  return { ok: true, value: result.data };
+}
+
+function toRecord(row: {
+  id: string;
+  categoryId: string;
+  key: string;
+  label: string;
+  dataType: AssetAttributeDataType;
+  required: boolean;
+  sortOrder: number;
+  createdAt: Date;
+}): AssetCategoryAttributeDefRecord {
+  return {
+    id: row.id,
+    category_id: row.categoryId,
+    key: row.key,
+    label: row.label,
+    data_type: row.dataType,
+    required: row.required,
+    sort_order: row.sortOrder,
+    created_at: row.createdAt.toISOString(),
+  };
+}
+
+export type CreateAssetCategoryAttributeDefResult =
+  | { ok: true; value: AssetCategoryAttributeDefRecord }
+  | { ok: false; error: string };
+
+/**
+ * Creates an AssetCategoryAttributeDef. If (categoryId, key) collides with
+ * an existing row, Prisma raises P2002 (composite unique constraint
+ * violation) — caught here and translated into a clean {ok:false,error},
+ * same pattern as createAssetItem()'s serialNumber P2002 handling in
+ * src/lib/assets.ts. Note this is a *composite* uniqueness (unique within a
+ * category, not globally) — the same `key` under a *different* categoryId
+ * is expected to succeed, per docs/asset-license-management.md's "Cập nhật
+ * 2026-08-02 (3)" section. If categoryId doesn't reference an existing
+ * AssetCategory, Prisma raises P2003 (FK constraint violation) — caught the
+ * same way, mirrors src/lib/purchase-orders.ts's createPurchaseOrder() P2003
+ * handling.
+ */
+export async function createAssetCategoryAttributeDef(
+  input: CreateAssetCategoryAttributeDefInput
+): Promise<CreateAssetCategoryAttributeDefResult> {
+  try {
+    const created = await prisma.assetCategoryAttributeDef.create({
+      data: {
+        categoryId: input.categoryId,
+        key: input.key,
+        label: input.label,
+        dataType: input.dataType,
+        required: input.required,
+        sortOrder: input.sortOrder,
+      },
+    });
+    return { ok: true, value: toRecord(created) };
+  } catch (error) {
+    if (error instanceof Prisma.PrismaClientKnownRequestError && error.code === "P2002") {
+      return { ok: false, error: "key already exists for this category" };
+    }
+    if (error instanceof Prisma.PrismaClientKnownRequestError && error.code === "P2003") {
+      return { ok: false, error: "categoryId does not reference an existing asset category" };
+    }
+    throw error;
+  }
+}
+
+export async function listAssetCategoryAttributeDefs(): Promise<
+  AssetCategoryAttributeDefRecord[]
+> {
+  const rows = await prisma.assetCategoryAttributeDef.findMany({
+    orderBy: [{ createdAt: "desc" }, { id: "desc" }],
+  });
+  return rows.map(toRecord);
+}

src/lib/asset-models.ts

@@ -0,0 +1,214 @@
+import { z } from "zod";
+import { Prisma } from "@prisma/client";
+import type { AssetAttributeDataType } from "./asset-category-attribute-defs";
+import { prisma } from "./prisma";
+
+export interface AssetModelRecord {
+  id: string;
+  category_id: string;
+  manufacturer: string;
+  name: string;
+  specs: Record<string, unknown>;
+  created_at: string;
+}
+
+export interface CreateAssetModelInput {
+  categoryId: string;
+  manufacturer: string;
+  name: string;
+  specs: Record<string, unknown>;
+}
+
+export type ValidationResult =
+  | { ok: true; value: CreateAssetModelInput }
+  | { ok: false; error: string };
+
+// Mirrors src/lib/asset-category-attribute-defs.ts's nonEmptyString helper.
+function nonEmptyString(message: string) {
+  return z.string({ required_error: message, invalid_type_error: message }).refine(
+    (value) => value.trim() !== "",
+    { message }
+  );
+}
+
+const createAssetModelSchema = z.object({
+  // FK to AssetCategory — only a UUID *format* check here, whether it
+  // references a real category (and whether that category is
+  // valueGroup=high_value) is left to createAssetModel()'s explicit lookup
+  // below — that's a business rule, not something pure Zod schema
+  // validation on this input alone can express. Mirrors
+  // src/lib/asset-category-attribute-defs.ts's categoryId handling.
+  categoryId: z
+    .string({ required_error: "categoryId is required and must be a valid UUID string" })
+    .uuid("categoryId is required and must be a valid UUID string"),
+  manufacturer: nonEmptyString("manufacturer is required and must be a non-empty string"),
+  name: nonEmptyString("name is required and must be a non-empty string"),
+  // Deliberately LOOSE at this stage — just "a plain JSON object" (no
+  // arrays, no primitives at the top level). The category-specific dynamic
+  // shape (which keys are allowed, which are required, and their types) is
+  // validated separately in createAssetModel() below, via a runtime Zod
+  // schema built from that category's AssetCategoryAttributeDef rows — it
+  // can't be done here because that requires a DB lookup keyed on
+  // categoryId, which this pure-input-shape schema doesn't have access to.
+  // Defaults to {} when omitted, matching the DB column default.
+  specs: z
+    .record(z.unknown(), {
+      invalid_type_error: "specs must be a JSON object",
+    })
+    .optional()
+    .default({}),
+});
+
+/**
+ * Validates raw (untyped) asset-model-creation input. categoryId must be a
+ * valid UUID string, manufacturer/name must be non-empty strings, specs
+ * must be a plain JSON object (or omitted, defaulting to {}). Whether
+ * categoryId references a real, high_value AssetCategory is checked in
+ * createAssetModel() below, not here — that requires a DB lookup.
+ */
+export function validateCreateAssetModelInput(input: {
+  categoryId?: unknown;
+  manufacturer?: unknown;
+  name?: unknown;
+  specs?: unknown;
+}): ValidationResult {
+  const result = createAssetModelSchema.safeParse(input);
+  if (!result.success) {
+    const message = result.error.issues[0]?.message ?? "Invalid input";
+    return { ok: false, error: message };
+  }
+  return { ok: true, value: result.data };
+}
+
+function toRecord(row: {
+  id: string;
+  categoryId: string;
+  manufacturer: string;
+  name: string;
+  specs: Prisma.JsonValue;
+  createdAt: Date;
+}): AssetModelRecord {
+  return {
+    id: row.id,
+    category_id: row.categoryId,
+    manufacturer: row.manufacturer,
+    name: row.name,
+    specs: (row.specs as Record<string, unknown>) ?? {},
+    created_at: row.createdAt.toISOString(),
+  };
+}
+
+// Maps an AssetCategoryAttributeDef.dataType to the corresponding Zod leaf
+// type, per docs/asset-license-management.md's "Cập nhật 2026-08-02 (3)"
+// section: string -> z.string(), number -> z.number(), boolean ->
+// z.boolean(), date -> z.coerce.date() (coerce so a JSON-transported date
+// *string*, e.g. "2027-01-01", is accepted — JSON has no native Date type).
+function zodTypeForDataType(dataType: AssetAttributeDataType): z.ZodTypeAny {
+  switch (dataType) {
+    case "string":
+      return z.string();
+    case "number":
+      return z.number();
+    case "boolean":
+      return z.boolean();
+    case "date":
+      return z.coerce.date();
+  }
+}
+
+/**
+ * Builds a Zod object schema AT RUNTIME from a category's
+ * AssetCategoryAttributeDef rows: one shape entry per attribute def (typed
+ * per zodTypeForDataType() above), optional when `required` is false via
+ * `.optional()`, and `.strict()` on the overall object so any `specs` key
+ * not defined for this category is rejected (no unknown keys allowed), per
+ * the doc section referenced above.
+ */
+function buildSpecsSchema(
+  attributeDefs: { key: string; dataType: AssetAttributeDataType; required: boolean }[]
+): z.ZodTypeAny {
+  const shape: Record<string, z.ZodTypeAny> = {};
+  for (const def of attributeDefs) {
+    const leaf = zodTypeForDataType(def.dataType);
+    shape[def.key] = def.required ? leaf : leaf.optional();
+  }
+  return z.object(shape).strict();
+}
+
+export type CreateAssetModelResult =
+  | { ok: true; value: AssetModelRecord }
+  | { ok: false; error: string };
+
+/**
+ * Creates an AssetModel. categoryId must reference a real AssetCategory
+ * (checked here via an explicit prisma.assetCategory.findUnique() lookup —
+ * not left to Prisma's P2003 FK-violation catch like other entities'
+ * simple FK checks, e.g. src/lib/asset-category-attribute-defs.ts's
+ * categoryId handling), because there's an additional business rule to
+ * enforce beyond "does this row exist": the referenced category's
+ * valueGroup must be `high_value` (per docs/asset-license-management.md's
+ * "Ràng buộc dữ liệu" section under "Cập nhật 2026-08-02 (2)") — a rule
+ * that can't be expressed as a Postgres FK constraint, so it can't be
+ * caught via a Prisma error code the way a plain missing-FK case can. If
+ * the category doesn't exist at all, or exists but is `low_value`, this
+ * returns a distinct {ok:false,error} for each case rather than a raw
+ * P2003/500.
+ */
+export async function createAssetModel(
+  input: CreateAssetModelInput
+): Promise<CreateAssetModelResult> {
+  const category = await prisma.assetCategory.findUnique({
+    where: { id: input.categoryId },
+  });
+
+  if (!category) {
+    return { ok: false, error: "categoryId does not reference an existing asset category" };
+  }
+
+  if (category.valueGroup !== "high_value") {
+    return { ok: false, error: "categoryId must reference a category with valueGroup=high_value" };
+  }
+
+  // Dynamic specs validation, per docs/asset-license-management.md's
+  // "Cập nhật 2026-08-02 (3)" section: build a Zod schema at runtime from
+  // this category's AssetCategoryAttributeDef rows, and validate the
+  // incoming specs object against it. Deliberately done here (after the
+  // category existence/high_value checks above), not inside
+  // validateCreateAssetModelInput()'s static schema, because it needs a DB
+  // lookup keyed on categoryId.
+  const attributeDefs = await prisma.assetCategoryAttributeDef.findMany({
+    where: { categoryId: input.categoryId },
+  });
+  const specsSchema = buildSpecsSchema(attributeDefs);
+  const specsResult = specsSchema.safeParse(input.specs);
+  if (!specsResult.success) {
+    const message = specsResult.error.issues[0]?.message ?? "Invalid specs";
+    const path = specsResult.error.issues[0]?.path.join(".");
+    return {
+      ok: false,
+      error: path ? `specs.${path}: ${message}` : `specs: ${message}`,
+    };
+  }
+
+  const created = await prisma.assetModel.create({
+    data: {
+      categoryId: input.categoryId,
+      manufacturer: input.manufacturer,
+      name: input.name,
+      // input.specs is validated by Zod to be a plain JSON object
+      // (Record<string, unknown>), but Prisma's generated InputJsonValue
+      // type doesn't structurally accept an index-signature Record — cast
+      // is safe here since the Zod schema already guarantees JSON-shaped
+      // values.
+      specs: input.specs as Prisma.InputJsonValue,
+    },
+  });
+  return { ok: true, value: toRecord(created) };
+}
+
+export async function listAssetModels(): Promise<AssetModelRecord[]> {
+  const rows = await prisma.assetModel.findMany({
+    orderBy: [{ createdAt: "desc" }, { id: "desc" }],
+  });
+  return rows.map(toRecord);
+}

src/lib/assets.ts

@@ -7,18 +7,20 @@ export type AssetItemStatus = "in_stock" | "assigned" | "repair" | "retired";
 export interface AssetItemRecord {
   id: string;
   serial_number: string;
-  model: string;
+  model_id: string;
   purchase_date: string;
   warranty_end_date: string | null;
   status: AssetItemStatus;
+  purchase_order_id: string | null;
   created_at: string;
 }
 
 export interface CreateAssetItemInput {
   serialNumber: string;
-  model: string;
+  modelId: string;
   purchaseDate: Date;
   warrantyEndDate?: Date;
+  purchaseOrderId?: string | null;
 }
 
 export type ValidationResult =
@@ -45,24 +47,45 @@ function dateString(message: string) {
 
 const createAssetItemSchema = z.object({
   serialNumber: nonEmptyString("serialNumber is required and must be a non-empty string"),
-  model: nonEmptyString("model is required and must be a non-empty string"),
+  // Required FK to AssetModel — replaced the free-text `model` String (see
+  // schema.prisma / docs/asset-license-management.md's "Cập nhật 2026-08-02
+  // (2)" section). Only a UUID *format* check here, whether it references a
+  // real AssetModel is left to Prisma's own FK constraint at insert time
+  // (see createAssetItem()'s P2003 handling below). Mirrors
+  // src/lib/licenses.ts's vendorId handling.
+  modelId: z
+    .string({ required_error: "modelId is required and must be a valid UUID string" })
+    .uuid("modelId is required and must be a valid UUID string"),
   purchaseDate: dateString("purchaseDate is required and must be a valid date string"),
   warrantyEndDate: dateString("warrantyEndDate must be a valid date string").optional(),
+  // FK to PurchaseOrder — nullable/optional, supply-side traceability (not
+  // every AssetItem goes through a formal PO). Only a UUID *format* check
+  // here, whether it references a real PurchaseOrder is left to Prisma's
+  // own FK constraint at insert time (see createAssetItem()'s P2003
+  // handling below). Mirrors src/lib/purchase-orders.ts's receivedById
+  // optional().nullable() pattern.
+  purchaseOrderId: z
+    .string({ invalid_type_error: "purchaseOrderId must be a valid UUID string" })
+    .uuid("purchaseOrderId must be a valid UUID string")
+    .optional()
+    .nullable(),
 });
 
 /**
- * Validates raw (untyped) asset-item-creation input. serialNumber/model
+ * Validates raw (untyped) asset-item-creation input. serialNumber must be a
- * must be non-empty strings, purchaseDate must be a valid date string,
+ * non-empty string, modelId must be a valid UUID string, purchaseDate must
- * warrantyEndDate is optional but must be a valid date string if present.
+ * be a valid date string, warrantyEndDate is optional but must be a valid
- * status is not accepted here — new assets always start "in_stock" (same
+ * date string if present. purchaseOrderId is optional/nullable but must be
- * pattern as Request always starting "Draft"), later states are set via
+ * a valid UUID if present. status is not accepted here — new assets always
- * other operations, not at creation.
+ * start "in_stock" (same pattern as Request always starting "Draft"), later
+ * states are set via other operations, not at creation.
  */
 export function validateCreateAssetItemInput(input: {
   serialNumber?: unknown;
-  model?: unknown;
+  modelId?: unknown;
   purchaseDate?: unknown;
   warrantyEndDate?: unknown;
+  purchaseOrderId?: unknown;
 }): ValidationResult {
   const result = createAssetItemSchema.safeParse(input);
   if (!result.success) {
@@ -75,19 +98,21 @@ export function validateCreateAssetItemInput(input: {
 function toRecord(row: {
   id: string;
   serialNumber: string;
-  model: string;
+  modelId: string;
   purchaseDate: Date;
   warrantyEndDate: Date | null;
   status: AssetItemStatus;
+  purchaseOrderId: string | null;
   createdAt: Date;
 }): AssetItemRecord {
   return {
     id: row.id,
     serial_number: row.serialNumber,
-    model: row.model,
+    model_id: row.modelId,
     purchase_date: row.purchaseDate.toISOString(),
     warranty_end_date: row.warrantyEndDate ? row.warrantyEndDate.toISOString() : null,
     status: row.status,
+    purchase_order_id: row.purchaseOrderId,
     created_at: row.createdAt.toISOString(),
   };
 }
@@ -102,7 +127,14 @@ export type CreateAssetItemResult =
  * caught here and translated into the same `{ok:false,error}` shape as
  * input validation failures, rather than letting a raw Prisma error leak
  * to the API layer. Mirrors createEmployee()/createRequest()'s P2003
- * handling for FK violations.
+ * handling for FK violations. Two separate FKs can fail here (modelId ->
+ * AssetModel, purchaseOrderId -> PurchaseOrder) — Prisma raises the same
+ * error code (P2003) for either, so the FK constraint name in
+ * `error.meta.field_name` is used to tell them apart and return a targeted
+ * message, rather than a raw Prisma error leaking to the API layer. Mirrors
+ * src/lib/licenses.ts's createLicense() / src/lib/purchase-orders.ts's
+ * createPurchaseOrder() pattern for disambiguating between two FKs on the
+ * same model.
  */
 export async function createAssetItem(
   input: CreateAssetItemInput
@@ -111,9 +143,10 @@ export async function createAssetItem(
     const created = await prisma.assetItem.create({
       data: {
         serialNumber: input.serialNumber,
-        model: input.model,
+        modelId: input.modelId,
         purchaseDate: input.purchaseDate,
         warrantyEndDate: input.warrantyEndDate ?? null,
+        purchaseOrderId: input.purchaseOrderId ?? null,
       },
     });
     return { ok: true, value: toRecord(created) };
@@ -121,6 +154,13 @@ export async function createAssetItem(
     if (error instanceof Prisma.PrismaClientKnownRequestError && error.code === "P2002") {
       return { ok: false, error: "serialNumber already exists" };
     }
+    if (error instanceof Prisma.PrismaClientKnownRequestError && error.code === "P2003") {
+      const fieldName = typeof error.meta?.field_name === "string" ? error.meta.field_name : "";
+      if (fieldName.includes("purchase_order")) {
+        return { ok: false, error: "purchaseOrderId does not reference an existing purchase order" };
+      }
+      return { ok: false, error: "modelId does not reference an existing asset model" };
+    }
     throw error;
   }
 }

src/lib/assignments.ts

@@ -0,0 +1,533 @@
+import { z } from "zod";
+import { Prisma } from "@prisma/client";
+import { prisma } from "./prisma";
+
+export interface AssignmentRecord {
+  id: string;
+  employee_id: string;
+  asset_item_id: string | null;
+  license_id: string | null;
+  assigned_at: string;
+  returned_at: string | null;
+  signed_at: string | null;
+  created_at: string;
+}
+
+// assignedAt/returnedAt/signedAt are all deliberately NOT accepted from the
+// client at creation time — same precedent as AssetItem.status always
+// starting "in_stock" and License.seatsUsed always starting 0:
+// assignedAt is a system-set "moment of assignment" timestamp
+// (Prisma's @default(now()) on Assignment.assignedAt), returnedAt must be
+// null on creation (an Assignment cannot be created already-returned — that
+// would make no sense given the seat/status side-effects below), and
+// signedAt (marking handover paperwork as signed) is not wired to any
+// endpoint in this task at all — see feature-implementer report's "Out of
+// scope" section. It stays null until a future "mark as signed" operation
+// is built.
+export interface CreateAssignmentInput {
+  employeeId: string;
+  assetItemId?: string | null;
+  licenseId?: string | null;
+}
+
+export type ValidationResult =
+  | { ok: true; value: CreateAssignmentInput }
+  | { ok: false; error: string };
+
+// Mirrors src/lib/purchase-orders.ts's dateString helper — accepts any
+// string Date.parse() can handle and transforms it into a Date for Prisma.
+function dateString(message: string) {
+  return z
+    .string({ required_error: message, invalid_type_error: message })
+    .refine((value) => !Number.isNaN(Date.parse(value)), { message })
+    .transform((value) => new Date(value));
+}
+
+// Shared between createAssignmentSchema's employeeId field and
+// transferAssignmentSchema below — kept as a standalone Zod schema (rather
+// than inlined in both places) so the two stay byte-for-byte in sync on the
+// exact error message, instead of two copies drifting apart over time.
+const employeeIdSchema = z
+  .string({ required_error: "employeeId is required and must be a valid UUID string" })
+  .uuid("employeeId is required and must be a valid UUID string");
+
+const createAssignmentSchema = z
+  .object({
+    // FK to Employee — only a UUID *format* check here, whether it
+    // references a real employee is left to Prisma's own FK constraint at
+    // insert time (see createAssignment()'s P2003 handling below). Mirrors
+    // src/lib/requests.ts's employee_id handling.
+    employeeId: employeeIdSchema,
+    // Exactly one of assetItemId/licenseId must be set — see the .refine()
+    // below for the XOR check. Unlike other nullable FKs in this codebase
+    // (e.g. AssetItem.purchaseOrderId), whether these reference a real row
+    // is NOT deferred entirely to Prisma's insert-time FK constraint —
+    // createAssignment() needs to read the referenced row anyway (to check
+    // AssetItem.status / License.seatsUsed business rules), so existence is
+    // checked explicitly inside the transaction instead. Only format
+    // validation happens here at the Zod layer.
+    assetItemId: z
+      .string({ invalid_type_error: "assetItemId must be a valid UUID string" })
+      .uuid("assetItemId must be a valid UUID string")
+      .optional()
+      .nullable(),
+    licenseId: z
+      .string({ invalid_type_error: "licenseId must be a valid UUID string" })
+      .uuid("licenseId must be a valid UUID string")
+      .optional()
+      .nullable(),
+  })
+  .refine(
+    (value) => {
+      const hasAssetItem = value.assetItemId !== undefined && value.assetItemId !== null;
+      const hasLicense = value.licenseId !== undefined && value.licenseId !== null;
+      // XOR: exactly one of the two must be set.
+      return hasAssetItem !== hasLicense;
+    },
+    {
+      message: "Exactly one of assetItemId or licenseId must be set (not both, not neither)",
+      // Attach the error to both fields so it surfaces regardless of which
+      // one the caller looks at first — mirrors
+      // src/lib/purchase-orders.ts's receivedAt/receivedById co-nullability
+      // refine, which attaches to a single path for the same reason.
+      path: ["assetItemId"],
+    }
+  );
+
+/**
+ * Validates raw (untyped) assignment-creation input. employeeId must be a
+ * valid UUID string. Exactly one of assetItemId/licenseId must be a valid
+ * UUID string (XOR — both set or both unset is rejected). assignedAt,
+ * returnedAt, and signedAt are not accepted here — see CreateAssignmentInput's
+ * doc comment for why.
+ */
+export function validateCreateAssignmentInput(input: {
+  employeeId?: unknown;
+  assetItemId?: unknown;
+  licenseId?: unknown;
+}): ValidationResult {
+  const result = createAssignmentSchema.safeParse(input);
+  if (!result.success) {
+    const message = result.error.issues[0]?.message ?? "Invalid input";
+    return { ok: false, error: message };
+  }
+  return { ok: true, value: result.data };
+}
+
+const returnAssignmentSchema = z.object({
+  // Optional — defaults to "now" at the time returnAssignment() runs if not
+  // provided (mirrors Assignment.assignedAt's own default-now behavior at
+  // creation). Accepting an explicit value lets a caller backdate a return
+  // (e.g. recording a return that was physically handled yesterday but only
+  // entered into the system today) — same spirit as PurchaseOrder accepting
+  // an explicit receivedAt rather than always stamping "now".
+  returnedAt: dateString("returnedAt must be a valid date string").optional(),
+});
+
+export type ReturnValidationResult =
+  | { ok: true; value: { returnedAt?: Date } }
+  | { ok: false; error: string };
+
+/**
+ * Validates raw (untyped) assignment-return input. returnedAt is optional
+ * but must be a valid date string if present.
+ */
+export function validateReturnAssignmentInput(input: {
+  returnedAt?: unknown;
+}): ReturnValidationResult {
+  const result = returnAssignmentSchema.safeParse(input);
+  if (!result.success) {
+    const message = result.error.issues[0]?.message ?? "Invalid input";
+    return { ok: false, error: message };
+  }
+  return { ok: true, value: result.data };
+}
+
+const transferAssignmentSchema = z.object({
+  // Reuses employeeIdSchema (see its doc comment above) — the new employee
+  // to hand the same AssetItem/License over to. assetItemId/licenseId are
+  // deliberately NOT accepted here: transferAssignment() reuses whichever
+  // one the original Assignment already had (see that function's doc
+  // comment), the caller doesn't get to change it via a transfer.
+  employeeId: employeeIdSchema,
+});
+
+export type TransferValidationResult =
+  | { ok: true; value: { employeeId: string } }
+  | { ok: false; error: string };
+
+/**
+ * Validates raw (untyped) assignment-transfer input. employeeId must be a
+ * valid UUID string (same format check as validateCreateAssignmentInput's
+ * employeeId field).
+ */
+export function validateTransferAssignmentInput(input: {
+  employeeId?: unknown;
+}): TransferValidationResult {
+  const result = transferAssignmentSchema.safeParse(input);
+  if (!result.success) {
+    const message = result.error.issues[0]?.message ?? "Invalid input";
+    return { ok: false, error: message };
+  }
+  return { ok: true, value: result.data };
+}
+
+function toRecord(row: {
+  id: string;
+  employeeId: string;
+  assetItemId: string | null;
+  licenseId: string | null;
+  assignedAt: Date;
+  returnedAt: Date | null;
+  signedAt: Date | null;
+  createdAt: Date;
+}): AssignmentRecord {
+  return {
+    id: row.id,
+    employee_id: row.employeeId,
+    asset_item_id: row.assetItemId,
+    license_id: row.licenseId,
+    assigned_at: row.assignedAt.toISOString(),
+    returned_at: row.returnedAt ? row.returnedAt.toISOString() : null,
+    signed_at: row.signedAt ? row.signedAt.toISOString() : null,
+    created_at: row.createdAt.toISOString(),
+  };
+}
+
+// Internal error type used to carry a clean, already-user-facing message out
+// of the `prisma.$transaction()` callback below, distinguishing
+// application-level business-rule rejections (400) from unexpected/infra
+// errors (rethrown as-is). Not exported — callers only ever see the
+// {ok,error} result shape.
+class AssignmentBusinessError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = "AssignmentBusinessError";
+  }
+}
+
+class AssignmentNotFoundError extends Error {
+  constructor() {
+    super("Assignment not found");
+    this.name = "AssignmentNotFoundError";
+  }
+}
+
+export type CreateAssignmentResult =
+  | { ok: true; value: AssignmentRecord }
+  | { ok: false; error: string };
+
+/**
+ * Creates an Assignment (assigns an AssetItem or a License seat to an
+ * Employee), enforcing every business rule from docs/
+ * asset-license-management.md's "## Assignment (chốt 2026-08-02)" section
+ * inside a single `prisma.$transaction()`:
+ *
+ * - AssetItem branch: rejects if the AssetItem doesn't exist, rejects if its
+ *   current status isn't "in_stock" (stakeholder-confirmed precondition —
+ *   see the doc's "chốt 2026-08-02 (2)" note), rejects if there's already an
+ *   ACTIVE Assignment (returnedAt IS NULL) for it (explicit
+ *   belt-and-suspenders invariant per the doc, on top of the status check),
+ *   then atomically flips AssetItem.status to "assigned".
+ * - License branch: rejects if the License doesn't exist, rejects if
+ *   seatsUsed >= seatsTotal (no overbooking), then atomically increments
+ *   seatsUsed by 1.
+ *
+ * Race-condition note (read this before touching the transaction body):
+ * both branches use a two-step "read for validation, then conditional
+ * `updateMany` with a WHERE guard" pattern instead of a plain read-then-write
+ * (`findUnique` then `update`). The WHERE-guarded `updateMany` — e.g.
+ * `updateMany({ where: { id, status: "in_stock" }, data: { status:
+ * "assigned" } })` — is the actual race-closing mechanism: Postgres
+ * evaluates and applies that as a single atomic UPDATE statement, taking a
+ * row lock for its duration. Two concurrent transactions racing on the same
+ * AssetItem/License row serialize on that lock — the first to commit wins,
+ * and the second's WHERE clause is re-evaluated against the now-committed
+ * row and no longer matches, so its `updateMany` returns `count: 0`, which
+ * this function treats as a "lost the race" rejection. This is why the
+ * `findUnique` calls right before each `updateMany` are NOT the
+ * race-closing check by themselves (there's a real TOCTOU gap between a
+ * `findUnique` and a later `update` in isolation) — they only exist to
+ * produce a specific, friendly error message (not-found vs. wrong-status vs.
+ * no-seats) for the *common* (non-racing) case; the `updateMany`'s `count`
+ * is always re-checked afterwards and is what actually gets trusted.
+ * seatsTotal itself is read once via that same `findUnique` and reused in
+ * the `updateMany`'s WHERE clause (`seatsUsed: { lt: seatsTotal }`) — this
+ * is safe because nothing in this codebase ever mutates seatsTotal after
+ * creation (no update endpoint exists for it), so it can't go stale between
+ * the read and the write within the same transaction.
+ *
+ * The explicit "no existing active Assignment for this AssetItem" check
+ * (`tx.assignment.findFirst({ where: { assetItemId, returnedAt: null } })`)
+ * is intentionally layered BEFORE the atomic status update, as defense in
+ * depth against AssetItem.status/Assignment-row drift (e.g. manual DB
+ * intervention) — under normal operation this codebase always keeps
+ * `status === "assigned"` in exact sync with "has an active Assignment", so
+ * the atomic status-guarded `updateMany` above is what actually closes the
+ * concurrency race for the AssetItem branch; this check does not need its
+ * own atomic guard on top because the transaction's row lock (from the
+ * subsequent `updateMany`) is what makes the overall operation safe, not
+ * this read on its own.
+ */
+export async function createAssignment(
+  input: CreateAssignmentInput
+): Promise<CreateAssignmentResult> {
+  try {
+    const created = await prisma.$transaction(async (tx) => {
+      if (input.assetItemId) {
+        const assetItem = await tx.assetItem.findUnique({ where: { id: input.assetItemId } });
+        if (!assetItem) {
+          throw new AssignmentBusinessError(
+            "assetItemId does not reference an existing asset item"
+          );
+        }
+        if (assetItem.status !== "in_stock") {
+          throw new AssignmentBusinessError(
+            `assetItemId refers to an AssetItem that is not in_stock (current status: ${assetItem.status})`
+          );
+        }
+        const existingActive = await tx.assignment.findFirst({
+          where: { assetItemId: input.assetItemId, returnedAt: null },
+        });
+        if (existingActive) {
+          throw new AssignmentBusinessError(
+            "assetItemId already has an active assignment (returnedAt IS NULL)"
+          );
+        }
+
+        // Atomic race-closing gate — see this function's doc comment.
+        const statusUpdate = await tx.assetItem.updateMany({
+          where: { id: input.assetItemId, status: "in_stock" },
+          data: { status: "assigned" },
+        });
+        if (statusUpdate.count === 0) {
+          throw new AssignmentBusinessError(
+            "assetItemId refers to an AssetItem that is not in_stock (lost a race to another concurrent assignment)"
+          );
+        }
+      }
+
+      if (input.licenseId) {
+        const license = await tx.license.findUnique({ where: { id: input.licenseId } });
+        if (!license) {
+          throw new AssignmentBusinessError("licenseId does not reference an existing license");
+        }
+        if (license.seatsUsed >= license.seatsTotal) {
+          throw new AssignmentBusinessError(
+            "licenseId has no seats remaining (seatsUsed >= seatsTotal)"
+          );
+        }
+
+        // Atomic race-closing gate — see this function's doc comment.
+        const seatUpdate = await tx.license.updateMany({
+          where: { id: input.licenseId, seatsUsed: { lt: license.seatsTotal } },
+          data: { seatsUsed: { increment: 1 } },
+        });
+        if (seatUpdate.count === 0) {
+          throw new AssignmentBusinessError(
+            "licenseId has no seats remaining (lost a race to another concurrent assignment)"
+          );
+        }
+      }
+
+      return tx.assignment.create({
+        data: {
+          employeeId: input.employeeId,
+          assetItemId: input.assetItemId ?? null,
+          licenseId: input.licenseId ?? null,
+        },
+      });
+    });
+
+    return { ok: true, value: toRecord(created) };
+  } catch (error) {
+    if (error instanceof AssignmentBusinessError) {
+      return { ok: false, error: error.message };
+    }
+    // Only employeeId can still fail with a raw FK violation here —
+    // assetItemId/licenseId existence is already fully resolved above
+    // (found-or-rejected before the transaction ever reaches
+    // tx.assignment.create()).
+    if (error instanceof Prisma.PrismaClientKnownRequestError && error.code === "P2003") {
+      return { ok: false, error: "employeeId does not reference an existing employee" };
+    }
+    throw error;
+  }
+}
+
+export async function listAssignments(): Promise<AssignmentRecord[]> {
+  const rows = await prisma.assignment.findMany({
+    orderBy: [{ createdAt: "desc" }, { id: "desc" }],
+  });
+  return rows.map(toRecord);
+}
+
+export type ReturnAssignmentResult =
+  | { ok: true; value: AssignmentRecord }
+  | { ok: false; status: 404 | 400; error: string };
+
+/**
+ * Marks an Assignment as returned (sets returnedAt), and reverses its
+ * side-effects from createAssignment() inside the same transaction:
+ * - If assetItemId is set: flips AssetItem.status back to "in_stock" —
+ *   always, regardless of any RMA/repair path (there isn't one built yet,
+ *   per the task's instructions; see feature-implementer report).
+ * - If licenseId is set: atomically decrements License.seatsUsed by 1.
+ *
+ * Race-condition note: double-return is closed the same way as
+ * createAssignment()'s races — an atomic, WHERE-guarded `updateMany`
+ * (`where: { id, returnedAt: null }`) is the actual gate. Two concurrent
+ * PATCH-return calls against the same Assignment race on that row's UPDATE
+ * lock; only the first to commit gets `count: 1`, the second gets `count: 0`
+ * and is rejected as "already returned". The initial `findUnique` (used to
+ * read assetItemId/licenseId for the AssetItem/License side-effects, and to
+ * distinguish "not found" from "already returned" in the common case) is
+ * NOT itself the race-closing check, same caveat as createAssignment()'s
+ * doc comment. Decrementing seatsUsed does not need its own conditional
+ * `updateMany` guard the way incrementing did on the assign side — a bare
+ * `{ decrement: 1 }` is a single atomic UPDATE with no upper bound to
+ * enforce (unlike assign's seatsUsed < seatsTotal check), so a plain
+ * `update()` is race-safe on its own here.
+ */
+export async function returnAssignment(
+  id: string,
+  input: { returnedAt?: Date }
+): Promise<ReturnAssignmentResult> {
+  try {
+    const updated = await prisma.$transaction(async (tx) => {
+      const assignment = await tx.assignment.findUnique({ where: { id } });
+      if (!assignment) {
+        throw new AssignmentNotFoundError();
+      }
+
+      const returnedAt = input.returnedAt ?? new Date();
+
+      // Atomic race-closing gate — see this function's doc comment. Also
+      // doubles as the "already returned" rejection in the non-racing case,
+      // since `assignment.returnedAt !== null` implies this WHERE clause
+      // won't match either.
+      const claim = await tx.assignment.updateMany({
+        where: { id, returnedAt: null },
+        data: { returnedAt },
+      });
+      if (claim.count === 0) {
+        throw new AssignmentBusinessError("Assignment has already been returned");
+      }
+
+      if (assignment.assetItemId) {
+        await tx.assetItem.update({
+          where: { id: assignment.assetItemId },
+          data: { status: "in_stock" },
+        });
+      }
+
+      if (assignment.licenseId) {
+        await tx.license.update({
+          where: { id: assignment.licenseId },
+          data: { seatsUsed: { decrement: 1 } },
+        });
+      }
+
+      return tx.assignment.findUniqueOrThrow({ where: { id } });
+    });
+
+    return { ok: true, value: toRecord(updated) };
+  } catch (error) {
+    if (error instanceof AssignmentNotFoundError) {
+      return { ok: false, status: 404, error: "Assignment not found" };
+    }
+    if (error instanceof AssignmentBusinessError) {
+      return { ok: false, status: 400, error: error.message };
+    }
+    throw error;
+  }
+}
+
+export type TransferAssignmentResult =
+  | { ok: true; value: AssignmentRecord }
+  | { ok: false; status: 404 | 400; error: string };
+
+/**
+ * Transfers an Assignment's underlying AssetItem/License to a new employee —
+ * docs/asset-license-management.md's "## Assignment (chốt 2026-08-02)":
+ * "Chuyển tài sản giữa nhân viên ... = đóng Assignment cũ (returnedAt = now)
+ * + tạo Assignment mới, cả hai trong 1 transaction." Closes the existing
+ * Assignment row (returnedAt = now) and creates a brand-new one for the new
+ * employee, reusing the SAME assetItemId/licenseId as the original, all
+ * inside a single `prisma.$transaction()`.
+ *
+ * Deliberately does NOT touch AssetItem.status or License.seatsUsed — unlike
+ * createAssignment()/returnAssignment(), a transfer is a same-resource
+ * handover, not a release-then-reacquire: the AssetItem never becomes
+ * "in_stock" and the License seat is never freed at any point during a
+ * transfer (no race window for a third party to grab either one mid-transfer
+ * — that's the whole point of doing this in one transaction instead of a
+ * separate PATCH-return followed by a POST-create, which is exactly the gap
+ * this function closes). AssetItem.status stays "assigned" throughout;
+ * seatsUsed is net zero (same seat, new holder).
+ *
+ * Race-condition note: mirrors returnAssignment()'s exact race-closing
+ * pattern — double-transfer (or transfer-racing-return) is closed by the
+ * same atomic, WHERE-guarded `updateMany` (`where: { id, returnedAt: null }`)
+ * on the OLD Assignment row. Only the first caller to commit gets
+ * `count: 1`; a second, concurrent call against the same id gets `count: 0`
+ * and is rejected as "already returned" — same semantics as
+ * returnAssignment(), since from the old Assignment row's point of view a
+ * transfer's first half *is* a return. The `findUnique` right before the
+ * `updateMany` is NOT the race-closing check by itself (same caveat as
+ * createAssignment()/returnAssignment()'s doc comments) — it only exists to
+ * read assetItemId/licenseId for the new row and to distinguish "not found"
+ * from "already returned" in the common (non-racing) case.
+ */
+export async function transferAssignment(
+  id: string,
+  input: { employeeId: string }
+): Promise<TransferAssignmentResult> {
+  try {
+    const created = await prisma.$transaction(async (tx) => {
+      const assignment = await tx.assignment.findUnique({ where: { id } });
+      if (!assignment) {
+        throw new AssignmentNotFoundError();
+      }
+
+      // Atomic race-closing gate — see this function's doc comment. Also
+      // doubles as the "already returned" rejection in the non-racing case.
+      const claim = await tx.assignment.updateMany({
+        where: { id, returnedAt: null },
+        data: { returnedAt: new Date() },
+      });
+      if (claim.count === 0) {
+        throw new AssignmentBusinessError("Assignment has already been returned");
+      }
+
+      return tx.assignment.create({
+        data: {
+          employeeId: input.employeeId,
+          assetItemId: assignment.assetItemId,
+          licenseId: assignment.licenseId,
+        },
+      });
+    });
+
+    return { ok: true, value: toRecord(created) };
+  } catch (error) {
+    if (error instanceof AssignmentNotFoundError) {
+      return { ok: false, status: 404, error: "Assignment not found" };
+    }
+    if (error instanceof AssignmentBusinessError) {
+      return { ok: false, status: 400, error: error.message };
+    }
+    // Only employeeId can fail with a raw FK violation here — assetItemId/
+    // licenseId are reused verbatim from an already-valid Assignment row,
+    // so they're guaranteed to still reference existing rows (nothing in
+    // this codebase deletes AssetItem/License rows that have Assignments).
+    if (error instanceof Prisma.PrismaClientKnownRequestError && error.code === "P2003") {
+      return {
+        ok: false,
+        status: 400,
+        error: "employeeId does not reference an existing employee",
+      };
+    }
+    throw error;
+  }
+}

src/lib/licenses.ts

@@ -1,4 +1,5 @@
 import { z } from "zod";
+import { Prisma } from "@prisma/client";
 import { prisma } from "./prisma";
 
 export type LicenseType = "perpetual" | "subscription";
@@ -6,20 +7,22 @@ export type LicenseType = "perpetual" | "subscription";
 export interface LicenseRecord {
   id: string;
   name: string;
-  vendor: string;
+  vendor_id: string;
   seats_total: number;
   seats_used: number;
   expiry_date: string | null;
   license_type: LicenseType;
+  purchase_order_id: string | null;
   created_at: string;
 }
 
 export interface CreateLicenseInput {
   name: string;
-  vendor: string;
+  vendorId: string;
   seatsTotal: number;
   expiryDate?: Date | null;
   licenseType: LicenseType;
+  purchaseOrderId?: string | null;
 }
 
 export type ValidationResult =
@@ -46,7 +49,14 @@ function dateString(message: string) {
 
 const createLicenseSchema = z.object({
   name: nonEmptyString("name is required and must be a non-empty string"),
-  vendor: nonEmptyString("vendor is required and must be a non-empty string"),
+  // Now a real FK to Vendor (see schema.prisma) — only a UUID *format*
+  // check here — whether it references a real vendor is left to Prisma's
+  // own FK constraint at insert time (see createLicense()'s P2003 handling
+  // below), rather than an extra pre-check query. Mirrors the same pattern
+  // used for Request.employeeId in src/lib/requests.ts.
+  vendorId: z
+    .string({ required_error: "vendorId is required and must be a valid UUID string" })
+    .uuid("vendorId is required and must be a valid UUID string"),
   seatsTotal: z
     .number({ required_error: "seatsTotal is required and must be a positive integer", invalid_type_error: "seatsTotal is required and must be a positive integer" })
     .int({ message: "seatsTotal is required and must be a positive integer" })
@@ -57,23 +67,36 @@ const createLicenseSchema = z.object({
       message: "licenseType is required and must be either 'perpetual' or 'subscription'",
     }),
   }),
+  // FK to PurchaseOrder — nullable/optional, supply-side traceability (not
+  // every License goes through a formal PO). Only a UUID *format* check
+  // here, whether it references a real PurchaseOrder is left to Prisma's
+  // own FK constraint at insert time (see createLicense()'s P2003 handling
+  // below). Mirrors src/lib/assets.ts's purchaseOrderId
+  // optional().nullable() pattern exactly.
+  purchaseOrderId: z
+    .string({ invalid_type_error: "purchaseOrderId must be a valid UUID string" })
+    .uuid("purchaseOrderId must be a valid UUID string")
+    .optional()
+    .nullable(),
 });
 
 /**
- * Validates raw (untyped) license-creation input. name/vendor must be
+ * Validates raw (untyped) license-creation input. name must be a non-empty
- * non-empty strings, seatsTotal must be a positive integer, expiryDate is
+ * string, vendorId must be a valid UUID string, seatsTotal must be a
- * optional/nullable but must be a valid date string if present, licenseType
+ * positive integer, expiryDate is optional/nullable but must be a valid
- * must be one of the two enum values. seatsUsed is not accepted here — new
+ * date string if present, licenseType must be one of the two enum values.
- * licenses always start at 0 (same pattern as AssetItem always starting
+ * seatsUsed is not accepted here — new licenses always start at 0 (same
- * "in_stock"), seats are only ever consumed via other operations (once
+ * pattern as AssetItem always starting "in_stock"), seats are only ever
- * Assignment exists), not at creation.
+ * consumed via other operations (once Assignment exists), not at creation.
+ * purchaseOrderId is optional/nullable but must be a valid UUID if present.
  */
 export function validateCreateLicenseInput(input: {
   name?: unknown;
-  vendor?: unknown;
+  vendorId?: unknown;
   seatsTotal?: unknown;
   expiryDate?: unknown;
   licenseType?: unknown;
+  purchaseOrderId?: unknown;
 }): ValidationResult {
   const result = createLicenseSchema.safeParse(input);
   if (!result.success) {
@@ -86,41 +109,63 @@ export function validateCreateLicenseInput(input: {
 function toRecord(row: {
   id: string;
   name: string;
-  vendor: string;
+  vendorId: string;
   seatsTotal: number;
   seatsUsed: number;
   expiryDate: Date | null;
   licenseType: LicenseType;
+  purchaseOrderId: string | null;
   createdAt: Date;
 }): LicenseRecord {
   return {
     id: row.id,
     name: row.name,
-    vendor: row.vendor,
+    vendor_id: row.vendorId,
     seats_total: row.seatsTotal,
     seats_used: row.seatsUsed,
     expiry_date: row.expiryDate ? row.expiryDate.toISOString() : null,
     license_type: row.licenseType,
+    purchase_order_id: row.purchaseOrderId,
     created_at: row.createdAt.toISOString(),
   };
 }
 
+export type CreateLicenseResult =
+  | { ok: true; value: LicenseRecord }
+  | { ok: false; error: string };
+
 /**
- * Creates a License. No unique constraint exists on `name` (unlike
+ * Creates a License. Two separate FKs can fail here (vendorId -> Vendor,
- * AssetItem.serialNumber), so unlike createAssetItem() there's no known
+ * purchaseOrderId -> PurchaseOrder) — Prisma raises the same error code
- * Prisma error code to catch/translate here.
+ * (P2003) for either, so the FK constraint name in `error.meta.field_name`
+ * is used to tell them apart and return a targeted message, rather than a
+ * raw Prisma error leaking to the API layer. Mirrors
+ * src/lib/purchase-orders.ts's createPurchaseOrder() pattern for
+ * disambiguating between two FKs on the same model.
  */
-export async function createLicense(input: CreateLicenseInput): Promise<LicenseRecord> {
+export async function createLicense(input: CreateLicenseInput): Promise<CreateLicenseResult> {
+  try {
     const created = await prisma.license.create({
       data: {
         name: input.name,
-      vendor: input.vendor,
+        vendorId: input.vendorId,
         seatsTotal: input.seatsTotal,
         expiryDate: input.expiryDate ?? null,
         licenseType: input.licenseType,
+        purchaseOrderId: input.purchaseOrderId ?? null,
       },
     });
-  return toRecord(created);
+    return { ok: true, value: toRecord(created) };
+  } catch (error) {
+    if (error instanceof Prisma.PrismaClientKnownRequestError && error.code === "P2003") {
+      const fieldName = typeof error.meta?.field_name === "string" ? error.meta.field_name : "";
+      if (fieldName.includes("purchase_order")) {
+        return { ok: false, error: "purchaseOrderId does not reference an existing purchase order" };
+      }
+      return { ok: false, error: "vendorId does not reference an existing vendor" };
+    }
+    throw error;
+  }
 }
 
 export async function listLicenses(): Promise<LicenseRecord[]> {

src/lib/purchase-orders.ts

@@ -0,0 +1,161 @@
+import { z } from "zod";
+import { Prisma } from "@prisma/client";
+import { prisma } from "./prisma";
+
+export interface PurchaseOrderRecord {
+  id: string;
+  vendor_id: string;
+  order_date: string;
+  expected_date: string;
+  received_at: string | null;
+  received_by: string | null;
+  created_at: string;
+}
+
+export interface CreatePurchaseOrderInput {
+  vendorId: string;
+  orderDate: Date;
+  expectedDate: Date;
+  receivedAt?: Date | null;
+  receivedById?: string | null;
+}
+
+export type ValidationResult =
+  | { ok: true; value: CreatePurchaseOrderInput }
+  | { ok: false; error: string };
+
+// Mirrors src/lib/licenses.ts's dateString helper — accepts any string
+// Date.parse() can handle and transforms it into a Date for Prisma. Used
+// here for orderDate/expectedDate/receivedAt, which are all Timestamptz
+// (not just Date) columns, so datetime strings (not just "2026-07-31") are
+// also accepted.
+function dateString(message: string) {
+  return z
+    .string({ required_error: message, invalid_type_error: message })
+    .refine((value) => !Number.isNaN(Date.parse(value)), { message })
+    .transform((value) => new Date(value));
+}
+
+const createPurchaseOrderSchema = z
+  .object({
+    // FK to Vendor — only a UUID *format* check here, whether it references
+    // a real vendor is left to Prisma's own FK constraint at insert time
+    // (see createPurchaseOrder()'s P2003 handling below). Mirrors
+    // src/lib/licenses.ts's vendorId handling.
+    vendorId: z
+      .string({ required_error: "vendorId is required and must be a valid UUID string" })
+      .uuid("vendorId is required and must be a valid UUID string"),
+    orderDate: dateString("orderDate is required and must be a valid date string"),
+    expectedDate: dateString("expectedDate is required and must be a valid date string"),
+    // Both nullable — null means "not yet received". Co-nullability with
+    // receivedById is enforced by the .refine() below, not here.
+    receivedAt: dateString("receivedAt must be a valid date string").optional().nullable(),
+    receivedById: z
+      .string({ invalid_type_error: "receivedById must be a valid UUID string" })
+      .uuid("receivedById must be a valid UUID string")
+      .optional()
+      .nullable(),
+  })
+  .refine(
+    (value) => {
+      const hasReceivedAt = value.receivedAt !== undefined && value.receivedAt !== null;
+      const hasReceivedById = value.receivedById !== undefined && value.receivedById !== null;
+      return hasReceivedAt === hasReceivedById;
+    },
+    {
+      message: "receivedAt and receivedById must both be set or both be unset",
+      // Attach the error to both fields so it surfaces regardless of which
+      // one the caller looks at first.
+      path: ["receivedAt"],
+    }
+  );
+
+/**
+ * Validates raw (untyped) purchase-order-creation input. vendorId must be a
+ * valid UUID string, orderDate/expectedDate must be valid date strings,
+ * receivedAt/receivedById are optional/nullable but must both be set or
+ * both be unset (co-nullability invariant — receiving a PO always records
+ * both "when" and "who" together). No status field is accepted — PurchaseOrder
+ * deliberately has no stored status (see schema.prisma comment), it's
+ * inferred from linked Requests.
+ */
+export function validateCreatePurchaseOrderInput(input: {
+  vendorId?: unknown;
+  orderDate?: unknown;
+  expectedDate?: unknown;
+  receivedAt?: unknown;
+  receivedById?: unknown;
+}): ValidationResult {
+  const result = createPurchaseOrderSchema.safeParse(input);
+  if (!result.success) {
+    const message = result.error.issues[0]?.message ?? "Invalid input";
+    return { ok: false, error: message };
+  }
+  return { ok: true, value: result.data };
+}
+
+function toRecord(row: {
+  id: string;
+  vendorId: string;
+  orderDate: Date;
+  expectedDate: Date;
+  receivedAt: Date | null;
+  receivedById: string | null;
+  createdAt: Date;
+}): PurchaseOrderRecord {
+  return {
+    id: row.id,
+    vendor_id: row.vendorId,
+    order_date: row.orderDate.toISOString(),
+    expected_date: row.expectedDate.toISOString(),
+    received_at: row.receivedAt ? row.receivedAt.toISOString() : null,
+    received_by: row.receivedById,
+    created_at: row.createdAt.toISOString(),
+  };
+}
+
+export type CreatePurchaseOrderResult =
+  | { ok: true; value: PurchaseOrderRecord }
+  | { ok: false; error: string };
+
+/**
+ * Creates a PurchaseOrder. Two separate FKs can fail here (vendorId ->
+ * Vendor, receivedById -> Employee) — Prisma raises the same error code
+ * (P2003) for either, so the FK constraint name in `error.meta.field_name`
+ * is used to tell them apart and return a targeted message, rather than a
+ * raw Prisma error leaking to the API layer. Mirrors
+ * src/lib/licenses.ts's createLicense() pattern, extended for the
+ * two-FK case.
+ */
+export async function createPurchaseOrder(
+  input: CreatePurchaseOrderInput
+): Promise<CreatePurchaseOrderResult> {
+  try {
+    const created = await prisma.purchaseOrder.create({
+      data: {
+        vendorId: input.vendorId,
+        orderDate: input.orderDate,
+        expectedDate: input.expectedDate,
+        receivedAt: input.receivedAt ?? null,
+        receivedById: input.receivedById ?? null,
+      },
+    });
+    return { ok: true, value: toRecord(created) };
+  } catch (error) {
+    if (error instanceof Prisma.PrismaClientKnownRequestError && error.code === "P2003") {
+      const fieldName = typeof error.meta?.field_name === "string" ? error.meta.field_name : "";
+      if (fieldName.includes("received_by")) {
+        return { ok: false, error: "receivedById does not reference an existing employee" };
+      }
+      return { ok: false, error: "vendorId does not reference an existing vendor" };
+    }
+    throw error;
+  }
+}
+
+export async function listPurchaseOrders(): Promise<PurchaseOrderRecord[]> {
+  const rows = await prisma.purchaseOrder.findMany({
+    orderBy: [{ createdAt: "desc" }, { id: "desc" }],
+  });
+  return rows.map(toRecord);
+}

src/lib/requests.ts

@@ -16,6 +16,7 @@ export interface RequestRecord {
   type: RequestType;
   reason: string;
   status: RequestStatus;
+  purchase_order_id: string | null;
   created_at: string;
 }
 
@@ -23,6 +24,7 @@ export interface CreateRequestInput {
   employee_id: string;
   type: RequestType;
   reason: string;
+  purchase_order_id?: string | null;
 }
 
 export type ValidationResult =
@@ -55,6 +57,18 @@ const createRequestSchema = z.object({
       message: "type is required and must be exactly 'asset' or 'license'",
     }),
   }),
+  // Nullable/optional FK to PurchaseOrder — see schema.prisma's comment on
+  // Request.purchaseOrderId for the demand-vs-supply-side distinction from
+  // AssetItem/License's purchaseOrderId. Only a UUID *format* check here,
+  // whether it references a real PurchaseOrder is left to Prisma's own FK
+  // constraint at insert time (see createRequest()'s P2003 handling below).
+  // Mirrors src/lib/assets.ts's purchaseOrderId optional().nullable()
+  // pattern exactly.
+  purchase_order_id: z
+    .string({ invalid_type_error: "purchase_order_id must be a valid UUID string" })
+    .uuid("purchase_order_id must be a valid UUID string")
+    .optional()
+    .nullable(),
 });
 
 /**
@@ -66,6 +80,7 @@ export function validateCreateRequestInput(input: {
   employee_id?: unknown;
   type?: unknown;
   reason?: unknown;
+  purchase_order_id?: unknown;
 }): ValidationResult {
   const result = createRequestSchema.safeParse(input);
   if (!result.success) {
@@ -81,6 +96,7 @@ function toRecord(row: {
   type: RequestType;
   reason: string;
   status: string;
+  purchaseOrderId: string | null;
   createdAt: Date;
 }): RequestRecord {
   return {
@@ -89,6 +105,7 @@ function toRecord(row: {
     type: row.type,
     reason: row.reason,
     status: row.status as RequestStatus,
+    purchase_order_id: row.purchaseOrderId,
     created_at: row.createdAt.toISOString(),
   };
 }
@@ -98,11 +115,13 @@ export type CreateRequestResult =
   | { ok: false; error: string };
 
 /**
- * Creates a Request. If employee_id doesn't reference an existing Employee,
+ * Creates a Request. Two separate FKs can fail here (employee_id ->
- * Prisma raises a known error (code P2003, FK violation) — caught here and
+ * Employee, purchase_order_id -> PurchaseOrder) — Prisma raises the same
- * translated into the same `{ok:false,error}` shape as input validation
+ * error code (P2003) for either, so the FK constraint name in
- * failures, rather than letting a raw Prisma error leak to the API layer.
+ * `error.meta.field_name` is used to tell them apart and return a targeted
- * Mirrors src/lib/employees.ts's createEmployee() pattern for managerId.
+ * message, rather than a raw Prisma error leaking to the API layer. Mirrors
+ * src/lib/licenses.ts's createLicense() pattern for disambiguating between
+ * two FKs on the same model.
  */
 export async function createRequest(input: CreateRequestInput): Promise<CreateRequestResult> {
   try {
@@ -111,11 +130,16 @@ export async function createRequest(input: CreateRequestInput): Promise<CreateRe
         employeeId: input.employee_id,
         type: input.type,
         reason: input.reason,
+        purchaseOrderId: input.purchase_order_id ?? null,
       },
     });
     return { ok: true, value: toRecord(created) };
   } catch (error) {
     if (error instanceof Prisma.PrismaClientKnownRequestError && error.code === "P2003") {
+      const fieldName = typeof error.meta?.field_name === "string" ? error.meta.field_name : "";
+      if (fieldName.includes("purchase_order")) {
+        return { ok: false, error: "purchase_order_id does not reference an existing purchase order" };
+      }
       return { ok: false, error: "employee_id does not reference an existing employee" };
     }
     throw error;

src/lib/vendors.ts

@@ -0,0 +1,123 @@
+import { z } from "zod";
+import { prisma } from "./prisma";
+
+export interface VendorRecord {
+  id: string;
+  name: string;
+  contact_email: string;
+  contact_phone: string;
+  address: string;
+  tax_code: string | null;
+  notes: string | null;
+  created_at: string;
+}
+
+export interface CreateVendorInput {
+  name: string;
+  contactEmail: string;
+  contactPhone: string;
+  address: string;
+  taxCode?: string | null;
+  notes?: string | null;
+}
+
+export type ValidationResult =
+  | { ok: true; value: CreateVendorInput }
+  | { ok: false; error: string };
+
+// Mirrors src/lib/licenses.ts's nonEmptyString helper.
+function nonEmptyString(message: string) {
+  return z.string({ required_error: message, invalid_type_error: message }).refine(
+    (value) => value.trim() !== "",
+    { message }
+  );
+}
+
+const createVendorSchema = z.object({
+  name: nonEmptyString("name is required and must be a non-empty string"),
+  contactEmail: z
+    .string({
+      required_error: "contactEmail is required and must be a valid email",
+      invalid_type_error: "contactEmail is required and must be a valid email",
+    })
+    .email("contactEmail is required and must be a valid email"),
+  contactPhone: nonEmptyString("contactPhone is required and must be a non-empty string"),
+  address: nonEmptyString("address is required and must be a non-empty string"),
+  // Nullable, per docs/asset-license-management.md's "## Vendor" spec — not
+  // every vendor record has a known VN tax code at creation time.
+  taxCode: nonEmptyString("taxCode must be a non-empty string").optional().nullable(),
+  notes: nonEmptyString("notes must be a non-empty string").optional().nullable(),
+});
+
+/**
+ * Validates raw (untyped) vendor-creation input. name/contactPhone/address
+ * must be non-empty strings, contactEmail must be a valid email string,
+ * taxCode/notes are optional/nullable (per the "## Vendor" spec in
+ * docs/asset-license-management.md) but must be non-empty strings if
+ * present.
+ */
+export function validateCreateVendorInput(input: {
+  name?: unknown;
+  contactEmail?: unknown;
+  contactPhone?: unknown;
+  address?: unknown;
+  taxCode?: unknown;
+  notes?: unknown;
+}): ValidationResult {
+  const result = createVendorSchema.safeParse(input);
+  if (!result.success) {
+    const message = result.error.issues[0]?.message ?? "Invalid input";
+    return { ok: false, error: message };
+  }
+  return { ok: true, value: result.data };
+}
+
+function toRecord(row: {
+  id: string;
+  name: string;
+  contactEmail: string;
+  contactPhone: string;
+  address: string;
+  taxCode: string | null;
+  notes: string | null;
+  createdAt: Date;
+}): VendorRecord {
+  return {
+    id: row.id,
+    name: row.name,
+    contact_email: row.contactEmail,
+    contact_phone: row.contactPhone,
+    address: row.address,
+    tax_code: row.taxCode,
+    notes: row.notes,
+    created_at: row.createdAt.toISOString(),
+  };
+}
+
+/**
+ * Creates a Vendor. No unique constraint exists on any field, no FKs
+ * either (see docs/asset-license-management.md's "## Vendor" spec — this
+ * is a standalone entity, same starting shape as Employee/License before
+ * they grew relations) — so unlike createAssetItem()/createEmployee()
+ * there's no known Prisma error code to catch/translate here.
+ */
+export async function createVendor(input: CreateVendorInput): Promise<VendorRecord> {
+  const created = await prisma.vendor.create({
+    data: {
+      name: input.name,
+      contactEmail: input.contactEmail,
+      contactPhone: input.contactPhone,
+      address: input.address,
+      taxCode: input.taxCode ?? null,
+      notes: input.notes ?? null,
+    },
+  });
+  return toRecord(created);
+}
+
+export async function listVendors(): Promise<VendorRecord[]> {
+  const rows = await prisma.vendor.findMany({
+    orderBy: [{ createdAt: "desc" }, { id: "desc" }],
+  });
+  return rows.map(toRecord);
+}

tests/asset-categories.test.ts

@@ -0,0 +1,306 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import type { Mock } from "vitest";
+import type { Session } from "next-auth";
+import {
+  createAssetCategory,
+  listAssetCategories,
+  validateCreateAssetCategoryInput,
+} from "@/lib/asset-categories";
+import { prisma } from "@/lib/prisma";
+
+// Note: this file has two layers of coverage, mirroring tests/vendors.test.ts:
+// - lib-level tests below exercise src/lib/asset-categories.ts directly
+//   (validation, valueGroup enum, list ordering).
+// - route-level tests (further down) exercise
+//   src/app/api/asset-categories/route.ts over HTTP, including the auth()
+//   gate — mirrors tests/vendors.test.ts's @/auth mocking pattern.
+vi.mock("@/auth", () => ({ auth: vi.fn() }));
+
+import { GET, POST } from "@/app/api/asset-categories/route";
+import { auth } from "@/auth";
+
+const mockedAuth = auth as unknown as Mock<() => Promise<Session | null>>;
+
+const testSession: Session = {
+  user: { id: "test-user-id" },
+  expires: new Date(Date.now() + 60 * 60 * 1000).toISOString(),
+};
+
+function postRequest(body: unknown): Request {
+  return new Request("http://localhost/api/asset-categories", {
+    method: "POST",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify(body),
+  });
+}
+
+beforeEach(async () => {
+  // Each test starts from an empty table so listing/order assertions are
+  // deterministic.
+  await prisma.assetCategory.deleteMany();
+  // Default to a logged-in session — the lib-level tests below don't go
+  // through the route at all (so this is a no-op for them), and the
+  // route-level tests exercise business logic, not auth gating (that's
+  // covered by the "auth gating" describe block further down).
+  mockedAuth.mockResolvedValue(testSession);
+});
+
+describe("validateCreateAssetCategoryInput", () => {
+  it("accepts a valid high_value category", () => {
+    const result = validateCreateAssetCategoryInput({
+      name: "Laptop",
+      valueGroup: "high_value",
+    });
+
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value).toMatchObject({ name: "Laptop", valueGroup: "high_value" });
+    }
+  });
+
+  it("accepts a valid low_value category", () => {
+    const result = validateCreateAssetCategoryInput({
+      name: "Cáp HDMI",
+      valueGroup: "low_value",
+    });
+
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value).toMatchObject({ name: "Cáp HDMI", valueGroup: "low_value" });
+    }
+  });
+
+  it("rejects an empty name", () => {
+    const result = validateCreateAssetCategoryInput({
+      name: "",
+      valueGroup: "high_value",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/name/i);
+    }
+  });
+
+  it("rejects a missing name", () => {
+    const result = validateCreateAssetCategoryInput({
+      valueGroup: "high_value",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/name/i);
+    }
+  });
+
+  it("rejects an invalid valueGroup", () => {
+    const result = validateCreateAssetCategoryInput({
+      name: "Laptop",
+      valueGroup: "medium_value",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/valueGroup/i);
+    }
+  });
+
+  it("rejects a missing valueGroup", () => {
+    const result = validateCreateAssetCategoryInput({
+      name: "Laptop",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/valueGroup/i);
+    }
+  });
+});
+
+describe("createAssetCategory", () => {
+  it("creates a high_value category", async () => {
+    const result = validateCreateAssetCategoryInput({
+      name: "Laptop",
+      valueGroup: "high_value",
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createAssetCategory(result.value);
+
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    expect(created.value).toMatchObject({ name: "Laptop", value_group: "high_value" });
+    expect(typeof created.value.id).toBe("string");
+    expect(created.value.id.length).toBeGreaterThan(0);
+    expect(Number.isNaN(Date.parse(created.value.created_at))).toBe(false);
+  });
+
+  it("creates a low_value category", async () => {
+    const result = validateCreateAssetCategoryInput({
+      name: "Cáp HDMI",
+      valueGroup: "low_value",
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createAssetCategory(result.value);
+
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    expect(created.value).toMatchObject({ name: "Cáp HDMI", value_group: "low_value" });
+  });
+});
+
+describe("listAssetCategories", () => {
+  it("lists created categories, newest first", async () => {
+    const first = validateCreateAssetCategoryInput({ name: "Cáp HDMI", valueGroup: "low_value" });
+    expect(first.ok).toBe(true);
+    if (first.ok) await createAssetCategory(first.value);
+
+    // Ensure a distinct created_at ordering even on fast filesystems/clocks.
+    await new Promise((resolve) => setTimeout(resolve, 5));
+
+    const second = validateCreateAssetCategoryInput({ name: "Laptop", valueGroup: "high_value" });
+    expect(second.ok).toBe(true);
+    if (second.ok) await createAssetCategory(second.value);
+
+    const records = await listAssetCategories();
+
+    expect(records).toHaveLength(2);
+    // newest first
+    expect(records[0]).toMatchObject({ name: "Laptop" });
+    expect(records[1]).toMatchObject({ name: "Cáp HDMI" });
+  });
+
+  it("returns an empty list when there are no categories", async () => {
+    const records = await listAssetCategories();
+    expect(records).toEqual([]);
+  });
+});
+
+describe("POST /api/asset-categories", () => {
+  it("creates a high_value category on valid input", async () => {
+    const res = await POST(postRequest({ name: "Laptop", valueGroup: "high_value" }));
+
+    expect(res.status).toBe(201);
+    const body = await res.json();
+
+    expect(body).toMatchObject({ name: "Laptop", value_group: "high_value" });
+    expect(typeof body.id).toBe("string");
+    expect(body.id.length).toBeGreaterThan(0);
+    expect(Number.isNaN(Date.parse(body.created_at))).toBe(false);
+  });
+
+  it("creates a low_value category on valid input", async () => {
+    const res = await POST(postRequest({ name: "Cáp HDMI", valueGroup: "low_value" }));
+
+    expect(res.status).toBe(201);
+    const body = await res.json();
+    expect(body).toMatchObject({ name: "Cáp HDMI", value_group: "low_value" });
+  });
+
+  it("rejects an empty name", async () => {
+    const res = await POST(postRequest({ name: "", valueGroup: "high_value" }));
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/name/i);
+  });
+
+  it("rejects an invalid valueGroup", async () => {
+    const res = await POST(postRequest({ name: "Laptop", valueGroup: "medium_value" }));
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/valueGroup/i);
+  });
+
+  it("rejects a missing valueGroup", async () => {
+    const res = await POST(postRequest({ name: "Laptop" }));
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/valueGroup/i);
+  });
+
+  it("rejects an invalid JSON body", async () => {
+    const req = new Request("http://localhost/api/asset-categories", {
+      method: "POST",
+      headers: { "content-type": "application/json" },
+      body: "not json",
+    });
+
+    const res = await POST(req);
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/JSON/i);
+  });
+
+  it("rejects a non-object JSON body", async () => {
+    // Note: arrays are `typeof "object"` in JS, so they pass the route's
+    // object check (same behavior as /api/vendors) — use a JSON string
+    // primitive here to actually exercise the "not an object" branch.
+    const res = await POST(postRequest("not an object"));
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/JSON object/i);
+  });
+});
+
+describe("GET /api/asset-categories", () => {
+  it("lists created categories, newest first", async () => {
+    await POST(postRequest({ name: "Cáp HDMI", valueGroup: "low_value" }));
+    // Ensure a distinct created_at ordering even on fast filesystems/clocks.
+    await new Promise((resolve) => setTimeout(resolve, 5));
+    await POST(postRequest({ name: "Laptop", valueGroup: "high_value" }));
+
+    const res = await GET();
+    expect(res.status).toBe(200);
+
+    const body = await res.json();
+    expect(Array.isArray(body)).toBe(true);
+    expect(body).toHaveLength(2);
+
+    // newest first
+    expect(body[0]).toMatchObject({ name: "Laptop" });
+    expect(body[1]).toMatchObject({ name: "Cáp HDMI" });
+  });
+
+  it("returns an empty list when there are no categories", async () => {
+    const res = await GET();
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body).toEqual([]);
+  });
+});
+
+describe("auth gating on /api/asset-categories", () => {
+  // Mirrors tests/vendors.test.ts's "auth gating" block — only checks
+  // session presence, per the flat permission model (no role/permission
+  // logic).
+  it("POST /api/asset-categories returns 401 without a session", async () => {
+    mockedAuth.mockResolvedValue(null);
+
+    const res = await POST(postRequest({ name: "Laptop", valueGroup: "high_value" }));
+
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body).toEqual({ error: "Unauthorized" });
+
+    // And it must not have created anything.
+    const remaining = await prisma.assetCategory.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("GET /api/asset-categories returns 401 without a session", async () => {
+    mockedAuth.mockResolvedValue(null);
+
+    const res = await GET();
+
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body).toEqual({ error: "Unauthorized" });
+  });
+});

tests/asset-category-attribute-defs.test.ts

@@ -0,0 +1,660 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import type { Mock } from "vitest";
+import type { Session } from "next-auth";
+import {
+  createAssetCategoryAttributeDef,
+  listAssetCategoryAttributeDefs,
+  validateCreateAssetCategoryAttributeDefInput,
+} from "@/lib/asset-category-attribute-defs";
+import { prisma } from "@/lib/prisma";
+
+// Note: this file has two layers of coverage, mirroring
+// tests/purchase-orders.test.ts:
+// - lib-level tests below exercise src/lib/asset-category-attribute-defs.ts
+//   directly (validation, FK/unique error handling, list ordering).
+// - route-level tests (further down) exercise
+//   src/app/api/asset-category-attribute-defs/route.ts over HTTP, including
+//   the auth() gate.
+vi.mock("@/auth", () => ({ auth: vi.fn() }));
+
+import { GET, POST } from "@/app/api/asset-category-attribute-defs/route";
+import { auth } from "@/auth";
+
+const mockedAuth = auth as unknown as Mock<() => Promise<Session | null>>;
+
+const testSession: Session = {
+  user: { id: "test-user-id" },
+  expires: new Date(Date.now() + 60 * 60 * 1000).toISOString(),
+};
+
+function postRequest(body: unknown): Request {
+  return new Request("http://localhost/api/asset-category-attribute-defs", {
+    method: "POST",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify(body),
+  });
+}
+
+// AssetCategoryAttributeDef.categoryId is a real FK to AssetCategory (see
+// schema.prisma / src/lib/asset-category-attribute-defs.ts) — tests that
+// need valid ids create real rows first and use their ids. Mirrors
+// tests/purchase-orders.test.ts's createTestVendor()/createTestEmployee()
+// helpers.
+function createTestAssetCategory(overrides: { name?: string } = {}) {
+  return prisma.assetCategory.create({
+    data: {
+      name: overrides.name ?? "Laptop",
+      valueGroup: "high_value",
+    },
+  });
+}
+
+beforeEach(async () => {
+  // Each test starts from empty tables so listing/order/uniqueness
+  // assertions are deterministic. asset_category_attribute_defs must be
+  // cleared before asset_categories since it has an FK (ON DELETE RESTRICT)
+  // to it.
+  await prisma.assetCategoryAttributeDef.deleteMany();
+  await prisma.assetCategory.deleteMany();
+  // Default to a logged-in session — the lib-level tests below don't go
+  // through the route at all (so this is a no-op for them), and the
+  // route-level tests exercise business logic, not auth gating (that's
+  // covered by the "auth gating" describe block further down).
+  mockedAuth.mockResolvedValue(testSession);
+});
+
+describe("validateCreateAssetCategoryAttributeDefInput", () => {
+  it("accepts valid input", () => {
+    const result = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: "11111111-1111-1111-1111-111111111111",
+      key: "ram_gb",
+      label: "RAM (GB)",
+      dataType: "number",
+      required: true,
+      sortOrder: 1,
+    });
+
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value).toMatchObject({
+        categoryId: "11111111-1111-1111-1111-111111111111",
+        key: "ram_gb",
+        label: "RAM (GB)",
+        dataType: "number",
+        required: true,
+        sortOrder: 1,
+      });
+    }
+  });
+
+  it("accepts each of the four fixed dataType values", () => {
+    for (const dataType of ["string", "number", "boolean", "date"] as const) {
+      const result = validateCreateAssetCategoryAttributeDefInput({
+        categoryId: "11111111-1111-1111-1111-111111111111",
+        key: `key_${dataType}`,
+        label: "Label",
+        dataType,
+        required: false,
+        sortOrder: 0,
+      });
+      expect(result.ok).toBe(true);
+    }
+  });
+
+  it("rejects a missing categoryId", () => {
+    const result = validateCreateAssetCategoryAttributeDefInput({
+      key: "ram_gb",
+      label: "RAM (GB)",
+      dataType: "number",
+      required: true,
+      sortOrder: 1,
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/categoryId/i);
+    }
+  });
+
+  it("rejects a categoryId that is not a valid UUID", () => {
+    const result = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: "not-a-uuid",
+      key: "ram_gb",
+      label: "RAM (GB)",
+      dataType: "number",
+      required: true,
+      sortOrder: 1,
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/categoryId/i);
+    }
+  });
+
+  it("rejects an empty key", () => {
+    const result = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: "11111111-1111-1111-1111-111111111111",
+      key: "",
+      label: "RAM (GB)",
+      dataType: "number",
+      required: true,
+      sortOrder: 1,
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/key/i);
+    }
+  });
+
+  it("rejects an empty label", () => {
+    const result = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: "11111111-1111-1111-1111-111111111111",
+      key: "ram_gb",
+      label: "",
+      dataType: "number",
+      required: true,
+      sortOrder: 1,
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/label/i);
+    }
+  });
+
+  it("rejects an invalid dataType", () => {
+    const result = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: "11111111-1111-1111-1111-111111111111",
+      key: "ram_gb",
+      label: "RAM (GB)",
+      dataType: "float",
+      required: true,
+      sortOrder: 1,
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/dataType/i);
+    }
+  });
+
+  it("rejects a missing dataType", () => {
+    const result = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: "11111111-1111-1111-1111-111111111111",
+      key: "ram_gb",
+      label: "RAM (GB)",
+      required: true,
+      sortOrder: 1,
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/dataType/i);
+    }
+  });
+
+  it("rejects a non-boolean required", () => {
+    const result = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: "11111111-1111-1111-1111-111111111111",
+      key: "ram_gb",
+      label: "RAM (GB)",
+      dataType: "number",
+      required: "yes",
+      sortOrder: 1,
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/required/i);
+    }
+  });
+
+  it("rejects a non-integer sortOrder", () => {
+    const result = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: "11111111-1111-1111-1111-111111111111",
+      key: "ram_gb",
+      label: "RAM (GB)",
+      dataType: "number",
+      required: true,
+      sortOrder: 1.5,
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/sortOrder/i);
+    }
+  });
+
+  it("rejects a missing sortOrder", () => {
+    const result = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: "11111111-1111-1111-1111-111111111111",
+      key: "ram_gb",
+      label: "RAM (GB)",
+      dataType: "number",
+      required: true,
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/sortOrder/i);
+    }
+  });
+});
+
+describe("createAssetCategoryAttributeDef", () => {
+  it("creates an attribute def for a real category", async () => {
+    const category = await createTestAssetCategory();
+    const result = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: category.id,
+      key: "ram_gb",
+      label: "RAM (GB)",
+      dataType: "number",
+      required: true,
+      sortOrder: 1,
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createAssetCategoryAttributeDef(result.value);
+
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    expect(created.value).toMatchObject({
+      category_id: category.id,
+      key: "ram_gb",
+      label: "RAM (GB)",
+      data_type: "number",
+      required: true,
+      sort_order: 1,
+    });
+    expect(typeof created.value.id).toBe("string");
+    expect(created.value.id.length).toBeGreaterThan(0);
+    expect(Number.isNaN(Date.parse(created.value.created_at))).toBe(false);
+  });
+
+  it("returns a clean error when categoryId doesn't reference an existing category", async () => {
+    const result = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: "00000000-0000-0000-0000-000000000000",
+      key: "ram_gb",
+      label: "RAM (GB)",
+      dataType: "number",
+      required: true,
+      sortOrder: 1,
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createAssetCategoryAttributeDef(result.value);
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/categoryId/i);
+    expect(created.error).toMatch(/does not reference an existing asset category/i);
+
+    const remaining = await prisma.assetCategoryAttributeDef.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("rejects a duplicate key within the same category with a clean 400-style error", async () => {
+    const category = await createTestAssetCategory();
+    const first = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: category.id,
+      key: "ram_gb",
+      label: "RAM (GB)",
+      dataType: "number",
+      required: true,
+      sortOrder: 1,
+    });
+    expect(first.ok).toBe(true);
+    if (first.ok) {
+      const firstCreated = await createAssetCategoryAttributeDef(first.value);
+      expect(firstCreated.ok).toBe(true);
+    }
+
+    const second = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: category.id,
+      key: "ram_gb",
+      label: "RAM (GB) duplicate",
+      dataType: "number",
+      required: false,
+      sortOrder: 2,
+    });
+    expect(second.ok).toBe(true);
+    if (!second.ok) return;
+
+    const created = await createAssetCategoryAttributeDef(second.value);
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/key/i);
+
+    const remaining = await prisma.assetCategoryAttributeDef.findMany();
+    expect(remaining).toHaveLength(1);
+  });
+
+  it("allows the same key across two different categories", async () => {
+    const laptop = await createTestAssetCategory({ name: "Laptop" });
+    const monitor = await createTestAssetCategory({ name: "Màn hình" });
+
+    const first = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: laptop.id,
+      key: "weight_kg",
+      label: "Khối lượng (kg)",
+      dataType: "number",
+      required: false,
+      sortOrder: 1,
+    });
+    expect(first.ok).toBe(true);
+    if (first.ok) {
+      const firstCreated = await createAssetCategoryAttributeDef(first.value);
+      expect(firstCreated.ok).toBe(true);
+    }
+
+    const second = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: monitor.id,
+      key: "weight_kg",
+      label: "Khối lượng (kg)",
+      dataType: "number",
+      required: false,
+      sortOrder: 1,
+    });
+    expect(second.ok).toBe(true);
+    if (!second.ok) return;
+
+    const created = await createAssetCategoryAttributeDef(second.value);
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    expect(created.value.category_id).toBe(monitor.id);
+    expect(created.value.key).toBe("weight_kg");
+
+    const remaining = await prisma.assetCategoryAttributeDef.findMany();
+    expect(remaining).toHaveLength(2);
+  });
+});
+
+describe("listAssetCategoryAttributeDefs", () => {
+  it("lists created attribute defs, newest first", async () => {
+    const category = await createTestAssetCategory();
+
+    const first = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: category.id,
+      key: "ram_gb",
+      label: "RAM (GB)",
+      dataType: "number",
+      required: true,
+      sortOrder: 1,
+    });
+    expect(first.ok).toBe(true);
+    if (first.ok) await createAssetCategoryAttributeDef(first.value);
+
+    // Ensure a distinct created_at ordering even on fast filesystems/clocks.
+    await new Promise((resolve) => setTimeout(resolve, 5));
+
+    const second = validateCreateAssetCategoryAttributeDefInput({
+      categoryId: category.id,
+      key: "cpu",
+      label: "CPU",
+      dataType: "string",
+      required: false,
+      sortOrder: 2,
+    });
+    expect(second.ok).toBe(true);
+    if (second.ok) await createAssetCategoryAttributeDef(second.value);
+
+    const records = await listAssetCategoryAttributeDefs();
+
+    expect(records).toHaveLength(2);
+    // newest first
+    expect(records[0]).toMatchObject({ key: "cpu" });
+    expect(records[1]).toMatchObject({ key: "ram_gb" });
+  });
+
+  it("returns an empty list when there are no attribute defs", async () => {
+    const records = await listAssetCategoryAttributeDefs();
+    expect(records).toEqual([]);
+  });
+});
+
+describe("POST /api/asset-category-attribute-defs", () => {
+  it("creates an attribute def on valid input", async () => {
+    const category = await createTestAssetCategory();
+    const res = await POST(
+      postRequest({
+        categoryId: category.id,
+        key: "ram_gb",
+        label: "RAM (GB)",
+        dataType: "number",
+        required: true,
+        sortOrder: 1,
+      })
+    );
+
+    expect(res.status).toBe(201);
+    const body = await res.json();
+
+    expect(body).toMatchObject({
+      category_id: category.id,
+      key: "ram_gb",
+      label: "RAM (GB)",
+      data_type: "number",
+      required: true,
+      sort_order: 1,
+    });
+    expect(typeof body.id).toBe("string");
+    expect(body.id.length).toBeGreaterThan(0);
+    expect(Number.isNaN(Date.parse(body.created_at))).toBe(false);
+  });
+
+  it("rejects an invalid dataType", async () => {
+    const category = await createTestAssetCategory();
+    const res = await POST(
+      postRequest({
+        categoryId: category.id,
+        key: "ram_gb",
+        label: "RAM (GB)",
+        dataType: "float",
+        required: true,
+        sortOrder: 1,
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/dataType/i);
+  });
+
+  it("rejects a categoryId that is a well-formed UUID but doesn't reference an existing category", async () => {
+    const res = await POST(
+      postRequest({
+        categoryId: "00000000-0000-0000-0000-000000000000",
+        key: "ram_gb",
+        label: "RAM (GB)",
+        dataType: "number",
+        required: true,
+        sortOrder: 1,
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/categoryId/i);
+    expect(body.error).toMatch(/does not reference an existing asset category/i);
+
+    const remaining = await prisma.assetCategoryAttributeDef.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("rejects a duplicate (categoryId, key) with a clean 400, not a raw 500", async () => {
+    const category = await createTestAssetCategory();
+    const first = await POST(
+      postRequest({
+        categoryId: category.id,
+        key: "ram_gb",
+        label: "RAM (GB)",
+        dataType: "number",
+        required: true,
+        sortOrder: 1,
+      })
+    );
+    expect(first.status).toBe(201);
+
+    const second = await POST(
+      postRequest({
+        categoryId: category.id,
+        key: "ram_gb",
+        label: "RAM (GB) duplicate",
+        dataType: "number",
+        required: false,
+        sortOrder: 2,
+      })
+    );
+
+    expect(second.status).toBe(400);
+    const body = await second.json();
+    expect(body.error).toMatch(/key/i);
+
+    const remaining = await prisma.assetCategoryAttributeDef.findMany();
+    expect(remaining).toHaveLength(1);
+  });
+
+  it("allows the same key across two different categories via the route", async () => {
+    const laptop = await createTestAssetCategory({ name: "Laptop" });
+    const monitor = await createTestAssetCategory({ name: "Màn hình" });
+
+    const first = await POST(
+      postRequest({
+        categoryId: laptop.id,
+        key: "weight_kg",
+        label: "Khối lượng (kg)",
+        dataType: "number",
+        required: false,
+        sortOrder: 1,
+      })
+    );
+    expect(first.status).toBe(201);
+
+    const second = await POST(
+      postRequest({
+        categoryId: monitor.id,
+        key: "weight_kg",
+        label: "Khối lượng (kg)",
+        dataType: "number",
+        required: false,
+        sortOrder: 1,
+      })
+    );
+    expect(second.status).toBe(201);
+
+    const remaining = await prisma.assetCategoryAttributeDef.findMany();
+    expect(remaining).toHaveLength(2);
+  });
+
+  it("rejects an invalid JSON body", async () => {
+    const req = new Request("http://localhost/api/asset-category-attribute-defs", {
+      method: "POST",
+      headers: { "content-type": "application/json" },
+      body: "not json",
+    });
+
+    const res = await POST(req);
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/JSON/i);
+  });
+
+  it("rejects a non-object JSON body", async () => {
+    // Note: arrays are `typeof "object"` in JS, so they pass the route's
+    // object check (same behavior as /api/asset-categories) — use a JSON
+    // string primitive here to actually exercise the "not an object" branch.
+    const res = await POST(postRequest("not an object"));
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/JSON object/i);
+  });
+});
+
+describe("GET /api/asset-category-attribute-defs", () => {
+  it("lists created attribute defs, newest first", async () => {
+    const category = await createTestAssetCategory();
+    await POST(
+      postRequest({
+        categoryId: category.id,
+        key: "ram_gb",
+        label: "RAM (GB)",
+        dataType: "number",
+        required: true,
+        sortOrder: 1,
+      })
+    );
+    // Ensure a distinct created_at ordering even on fast filesystems/clocks.
+    await new Promise((resolve) => setTimeout(resolve, 5));
+    await POST(
+      postRequest({
+        categoryId: category.id,
+        key: "cpu",
+        label: "CPU",
+        dataType: "string",
+        required: false,
+        sortOrder: 2,
+      })
+    );
+
+    const res = await GET();
+    expect(res.status).toBe(200);
+
+    const body = await res.json();
+    expect(Array.isArray(body)).toBe(true);
+    expect(body).toHaveLength(2);
+
+    // newest first
+    expect(body[0]).toMatchObject({ key: "cpu" });
+    expect(body[1]).toMatchObject({ key: "ram_gb" });
+  });
+
+  it("returns an empty list when there are no attribute defs", async () => {
+    const res = await GET();
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body).toEqual([]);
+  });
+});
+
+describe("auth gating on /api/asset-category-attribute-defs", () => {
+  // Mirrors tests/asset-categories.test.ts's "auth gating" block — only
+  // checks session presence, per the flat permission model (no
+  // role/permission logic).
+  it("POST /api/asset-category-attribute-defs returns 401 without a session", async () => {
+    const category = await createTestAssetCategory();
+    mockedAuth.mockResolvedValue(null);
+
+    const res = await POST(
+      postRequest({
+        categoryId: category.id,
+        key: "ram_gb",
+        label: "RAM (GB)",
+        dataType: "number",
+        required: true,
+        sortOrder: 1,
+      })
+    );
+
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body).toEqual({ error: "Unauthorized" });
+
+    // And it must not have created anything.
+    const remaining = await prisma.assetCategoryAttributeDef.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("GET /api/asset-category-attribute-defs returns 401 without a session", async () => {
+    mockedAuth.mockResolvedValue(null);
+
+    const res = await GET();
+
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body).toEqual({ error: "Unauthorized" });
+  });
+});

tests/asset-models.test.ts

@@ -0,0 +1,731 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import type { Mock } from "vitest";
+import type { Session } from "next-auth";
+import {
+  createAssetModel,
+  listAssetModels,
+  validateCreateAssetModelInput,
+} from "@/lib/asset-models";
+import { prisma } from "@/lib/prisma";
+
+// Note: this file has two layers of coverage, mirroring
+// tests/asset-category-attribute-defs.test.ts:
+// - lib-level tests below exercise src/lib/asset-models.ts directly
+//   (validation, FK/business-rule error handling, list ordering).
+// - route-level tests (further down) exercise
+//   src/app/api/asset-models/route.ts over HTTP, including the auth() gate,
+//   malformed JSON, and non-object bodies.
+vi.mock("@/auth", () => ({ auth: vi.fn() }));
+
+import { GET, POST } from "@/app/api/asset-models/route";
+import { auth } from "@/auth";
+
+const mockedAuth = auth as unknown as Mock<() => Promise<Session | null>>;
+
+const testSession: Session = {
+  user: { id: "test-user-id" },
+  expires: new Date(Date.now() + 60 * 60 * 1000).toISOString(),
+};
+
+function postRequest(body: unknown): Request {
+  return new Request("http://localhost/api/asset-models", {
+    method: "POST",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify(body),
+  });
+}
+
+// AssetModel.categoryId is a real FK to AssetCategory, and the referenced
+// category must be valueGroup=high_value (see docs/
+// asset-license-management.md's "Cập nhật 2026-08-02 (2)" section). Tests
+// that need valid ids create real rows first and use their ids. Mirrors
+// tests/asset-category-attribute-defs.test.ts's createTestAssetCategory()
+// helper.
+function createTestAssetCategory(
+  overrides: { name?: string; valueGroup?: "high_value" | "low_value" } = {}
+) {
+  return prisma.assetCategory.create({
+    data: {
+      name: overrides.name ?? "Laptop",
+      valueGroup: overrides.valueGroup ?? "high_value",
+    },
+  });
+}
+
+// Helper for the dynamic-specs-validation tests below: creates an
+// AssetCategoryAttributeDef row directly via Prisma (no need to go through
+// src/lib/asset-category-attribute-defs.ts's validation for test setup).
+// Mirrors tests/asset-category-attribute-defs.test.ts's
+// createTestAssetCategory() helper pattern.
+function createTestAttributeDef(overrides: {
+  categoryId: string;
+  key: string;
+  label?: string;
+  dataType: "string" | "number" | "boolean" | "date";
+  required: boolean;
+  sortOrder?: number;
+}) {
+  return prisma.assetCategoryAttributeDef.create({
+    data: {
+      categoryId: overrides.categoryId,
+      key: overrides.key,
+      label: overrides.label ?? overrides.key,
+      dataType: overrides.dataType,
+      required: overrides.required,
+      sortOrder: overrides.sortOrder ?? 0,
+    },
+  });
+}
+
+beforeEach(async () => {
+  // Each test starts from empty tables so listing/order assertions are
+  // deterministic. asset_models must be cleared before asset_categories
+  // since it has an FK (ON DELETE RESTRICT) to it. asset_category_attribute_defs
+  // also has an FK (ON DELETE RESTRICT) to asset_categories, so it must be
+  // cleared before asset_categories too — mirrors tests/
+  // asset-category-attribute-defs.test.ts's cleanup order.
+  await prisma.assetModel.deleteMany();
+  await prisma.assetCategoryAttributeDef.deleteMany();
+  await prisma.assetCategory.deleteMany();
+  // Default to a logged-in session — the lib-level tests below don't go
+  // through the route at all (so this is a no-op for them), and the
+  // route-level tests exercise business logic, not auth gating (that's
+  // covered by the "auth gating" describe block further down).
+  mockedAuth.mockResolvedValue(testSession);
+});
+
+describe("validateCreateAssetModelInput", () => {
+  it("accepts valid input with a non-trivial specs object", () => {
+    const result = validateCreateAssetModelInput({
+      categoryId: "11111111-1111-1111-1111-111111111111",
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+      specs: { ram_gb: 16, cpu: "i7-1165G7" },
+    });
+
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value).toMatchObject({
+        categoryId: "11111111-1111-1111-1111-111111111111",
+        manufacturer: "Dell",
+        name: "Latitude 5420",
+        specs: { ram_gb: 16, cpu: "i7-1165G7" },
+      });
+    }
+  });
+
+  it("defaults specs to {} when omitted", () => {
+    const result = validateCreateAssetModelInput({
+      categoryId: "11111111-1111-1111-1111-111111111111",
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+    });
+
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value.specs).toEqual({});
+    }
+  });
+
+  it("rejects a missing categoryId", () => {
+    const result = validateCreateAssetModelInput({
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/categoryId/i);
+    }
+  });
+
+  it("rejects a categoryId that is not a valid UUID", () => {
+    const result = validateCreateAssetModelInput({
+      categoryId: "not-a-uuid",
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/categoryId/i);
+    }
+  });
+
+  it("rejects an empty manufacturer", () => {
+    const result = validateCreateAssetModelInput({
+      categoryId: "11111111-1111-1111-1111-111111111111",
+      manufacturer: "",
+      name: "Latitude 5420",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/manufacturer/i);
+    }
+  });
+
+  it("rejects an empty name", () => {
+    const result = validateCreateAssetModelInput({
+      categoryId: "11111111-1111-1111-1111-111111111111",
+      manufacturer: "Dell",
+      name: "",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/name/i);
+    }
+  });
+
+  it("rejects a specs value that is not a plain object", () => {
+    const result = validateCreateAssetModelInput({
+      categoryId: "11111111-1111-1111-1111-111111111111",
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+      specs: "not an object",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/specs/i);
+    }
+  });
+
+  it("rejects a specs value that is an array", () => {
+    const result = validateCreateAssetModelInput({
+      categoryId: "11111111-1111-1111-1111-111111111111",
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+      specs: ["not", "an", "object"],
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/specs/i);
+    }
+  });
+});
+
+describe("createAssetModel", () => {
+  it("creates a model for a real high_value category, with a non-trivial specs object", async () => {
+    const category = await createTestAssetCategory({ valueGroup: "high_value" });
+    await createTestAttributeDef({
+      categoryId: category.id,
+      key: "ram_gb",
+      dataType: "number",
+      required: true,
+    });
+    await createTestAttributeDef({
+      categoryId: category.id,
+      key: "cpu",
+      dataType: "string",
+      required: true,
+    });
+    const result = validateCreateAssetModelInput({
+      categoryId: category.id,
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+      specs: { ram_gb: 16, cpu: "i7-1165G7" },
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createAssetModel(result.value);
+
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    expect(created.value).toMatchObject({
+      category_id: category.id,
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+      specs: { ram_gb: 16, cpu: "i7-1165G7" },
+    });
+    expect(typeof created.value.id).toBe("string");
+    expect(created.value.id.length).toBeGreaterThan(0);
+    expect(Number.isNaN(Date.parse(created.value.created_at))).toBe(false);
+  });
+
+  it("defaults specs to {} in the created record when omitted", async () => {
+    const category = await createTestAssetCategory({ valueGroup: "high_value" });
+    const result = validateCreateAssetModelInput({
+      categoryId: category.id,
+      manufacturer: "Apple",
+      name: "MacBook Pro 14",
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createAssetModel(result.value);
+
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    expect(created.value.specs).toEqual({});
+  });
+
+  it("returns a clean error when categoryId doesn't reference an existing category", async () => {
+    const result = validateCreateAssetModelInput({
+      categoryId: "00000000-0000-0000-0000-000000000000",
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createAssetModel(result.value);
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/categoryId/i);
+    expect(created.error).toMatch(/does not reference an existing asset category/i);
+
+    const remaining = await prisma.assetModel.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("returns a distinct clean error when categoryId references an existing but low_value category", async () => {
+    const category = await createTestAssetCategory({
+      name: "Cáp HDMI",
+      valueGroup: "low_value",
+    });
+    const result = validateCreateAssetModelInput({
+      categoryId: category.id,
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createAssetModel(result.value);
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/high_value/i);
+    // Distinct message from the "doesn't exist at all" case.
+    expect(created.error).not.toMatch(/does not reference an existing asset category/i);
+
+    const remaining = await prisma.assetModel.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+});
+
+// Dynamic specs validation, per docs/asset-license-management.md's "Cập
+// nhật 2026-08-02 (3)" section: createAssetModel() builds a Zod schema at
+// runtime from the category's AssetCategoryAttributeDef rows and validates
+// `specs` against it — unknown keys rejected, required keys enforced, and
+// each key's value type-checked per its dataType.
+describe("createAssetModel: dynamic specs validation", () => {
+  it("accepts specs that supply all required keys with correct types", async () => {
+    const category = await createTestAssetCategory({ valueGroup: "high_value" });
+    await createTestAttributeDef({
+      categoryId: category.id,
+      key: "ram_gb",
+      dataType: "number",
+      required: true,
+    });
+    await createTestAttributeDef({
+      categoryId: category.id,
+      key: "cpu",
+      dataType: "string",
+      required: true,
+    });
+    await createTestAttributeDef({
+      categoryId: category.id,
+      key: "has_touchscreen",
+      dataType: "boolean",
+      required: true,
+    });
+
+    const result = validateCreateAssetModelInput({
+      categoryId: category.id,
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+      specs: { ram_gb: 16, cpu: "i7-1165G7", has_touchscreen: false },
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createAssetModel(result.value);
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    expect(created.value.specs).toEqual({ ram_gb: 16, cpu: "i7-1165G7", has_touchscreen: false });
+  });
+
+  it("rejects specs missing a required key with a clean 400-style error", async () => {
+    const category = await createTestAssetCategory({ valueGroup: "high_value" });
+    await createTestAttributeDef({
+      categoryId: category.id,
+      key: "ram_gb",
+      dataType: "number",
+      required: true,
+    });
+
+    const result = validateCreateAssetModelInput({
+      categoryId: category.id,
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+      specs: {},
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createAssetModel(result.value);
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/ram_gb/i);
+
+    const remaining = await prisma.assetModel.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("rejects a specs value of the wrong type for its dataType (string where number is expected)", async () => {
+    const category = await createTestAssetCategory({ valueGroup: "high_value" });
+    await createTestAttributeDef({
+      categoryId: category.id,
+      key: "ram_gb",
+      dataType: "number",
+      required: true,
+    });
+
+    const result = validateCreateAssetModelInput({
+      categoryId: category.id,
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+      specs: { ram_gb: "16" },
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createAssetModel(result.value);
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/ram_gb/i);
+
+    const remaining = await prisma.assetModel.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("rejects a specs key not defined as an AssetCategoryAttributeDef for that category", async () => {
+    const category = await createTestAssetCategory({ valueGroup: "high_value" });
+    await createTestAttributeDef({
+      categoryId: category.id,
+      key: "ram_gb",
+      dataType: "number",
+      required: true,
+    });
+
+    const result = validateCreateAssetModelInput({
+      categoryId: category.id,
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+      specs: { ram_gb: 16, unknown_key: "surprise" },
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createAssetModel(result.value);
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/specs/i);
+
+    const remaining = await prisma.assetModel.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("accepts specs that omit an optional (required=false) attribute def key", async () => {
+    const category = await createTestAssetCategory({ valueGroup: "high_value" });
+    await createTestAttributeDef({
+      categoryId: category.id,
+      key: "ram_gb",
+      dataType: "number",
+      required: true,
+    });
+    await createTestAttributeDef({
+      categoryId: category.id,
+      key: "weight_kg",
+      dataType: "number",
+      required: false,
+    });
+
+    const result = validateCreateAssetModelInput({
+      categoryId: category.id,
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+      specs: { ram_gb: 16 },
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createAssetModel(result.value);
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    expect(created.value.specs).toEqual({ ram_gb: 16 });
+  });
+
+  it("accepts a valid date string for a date-typed attribute def", async () => {
+    const category = await createTestAssetCategory({ valueGroup: "high_value" });
+    await createTestAttributeDef({
+      categoryId: category.id,
+      key: "warranty_end",
+      dataType: "date",
+      required: true,
+    });
+
+    const result = validateCreateAssetModelInput({
+      categoryId: category.id,
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+      specs: { warranty_end: "2027-01-01" },
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createAssetModel(result.value);
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    expect(created.value.specs).toEqual({ warranty_end: "2027-01-01" });
+  });
+});
+
+describe("listAssetModels", () => {
+  it("lists created models, newest first", async () => {
+    const category = await createTestAssetCategory({ valueGroup: "high_value" });
+
+    const first = validateCreateAssetModelInput({
+      categoryId: category.id,
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+    });
+    expect(first.ok).toBe(true);
+    if (first.ok) await createAssetModel(first.value);
+
+    // Ensure a distinct created_at ordering even on fast filesystems/clocks.
+    await new Promise((resolve) => setTimeout(resolve, 5));
+
+    const second = validateCreateAssetModelInput({
+      categoryId: category.id,
+      manufacturer: "Apple",
+      name: "MacBook Pro 14",
+    });
+    expect(second.ok).toBe(true);
+    if (second.ok) await createAssetModel(second.value);
+
+    const records = await listAssetModels();
+
+    expect(records).toHaveLength(2);
+    // newest first
+    expect(records[0]).toMatchObject({ name: "MacBook Pro 14" });
+    expect(records[1]).toMatchObject({ name: "Latitude 5420" });
+  });
+
+  it("returns an empty list when there are no models", async () => {
+    const records = await listAssetModels();
+    expect(records).toEqual([]);
+  });
+});
+
+describe("POST /api/asset-models", () => {
+  it("creates a model on valid input", async () => {
+    const category = await createTestAssetCategory({ valueGroup: "high_value" });
+    await createTestAttributeDef({
+      categoryId: category.id,
+      key: "ram_gb",
+      dataType: "number",
+      required: true,
+    });
+    await createTestAttributeDef({
+      categoryId: category.id,
+      key: "cpu",
+      dataType: "string",
+      required: true,
+    });
+    const res = await POST(
+      postRequest({
+        categoryId: category.id,
+        manufacturer: "Dell",
+        name: "Latitude 5420",
+        specs: { ram_gb: 16, cpu: "i7-1165G7" },
+      })
+    );
+
+    expect(res.status).toBe(201);
+    const body = await res.json();
+
+    expect(body).toMatchObject({
+      category_id: category.id,
+      manufacturer: "Dell",
+      name: "Latitude 5420",
+      specs: { ram_gb: 16, cpu: "i7-1165G7" },
+    });
+    expect(typeof body.id).toBe("string");
+    expect(body.id.length).toBeGreaterThan(0);
+    expect(Number.isNaN(Date.parse(body.created_at))).toBe(false);
+  });
+
+  it("defaults specs to {} when omitted from the request body", async () => {
+    const category = await createTestAssetCategory({ valueGroup: "high_value" });
+    const res = await POST(
+      postRequest({
+        categoryId: category.id,
+        manufacturer: "Dell",
+        name: "Latitude 5420",
+      })
+    );
+
+    expect(res.status).toBe(201);
+    const body = await res.json();
+    expect(body.specs).toEqual({});
+  });
+
+  it("rejects a missing manufacturer", async () => {
+    const category = await createTestAssetCategory({ valueGroup: "high_value" });
+    const res = await POST(
+      postRequest({
+        categoryId: category.id,
+        name: "Latitude 5420",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/manufacturer/i);
+  });
+
+  it("rejects a categoryId that is a well-formed UUID but doesn't reference an existing category", async () => {
+    const res = await POST(
+      postRequest({
+        categoryId: "00000000-0000-0000-0000-000000000000",
+        manufacturer: "Dell",
+        name: "Latitude 5420",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/categoryId/i);
+    expect(body.error).toMatch(/does not reference an existing asset category/i);
+
+    const remaining = await prisma.assetModel.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("rejects a categoryId referencing an existing but low_value category, with a distinct 400", async () => {
+    const category = await createTestAssetCategory({
+      name: "Cáp HDMI",
+      valueGroup: "low_value",
+    });
+    const res = await POST(
+      postRequest({
+        categoryId: category.id,
+        manufacturer: "Dell",
+        name: "Latitude 5420",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/high_value/i);
+
+    const remaining = await prisma.assetModel.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("rejects an invalid JSON body", async () => {
+    const req = new Request("http://localhost/api/asset-models", {
+      method: "POST",
+      headers: { "content-type": "application/json" },
+      body: "not json",
+    });
+
+    const res = await POST(req);
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/JSON/i);
+  });
+
+  it("rejects a non-object JSON body", async () => {
+    // Note: arrays are `typeof "object"` in JS, so they pass the route's
+    // object check (same behavior as /api/asset-category-attribute-defs) —
+    // use a JSON string primitive here to actually exercise the "not an
+    // object" branch.
+    const res = await POST(postRequest("not an object"));
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/JSON object/i);
+  });
+});
+
+describe("GET /api/asset-models", () => {
+  it("lists created models, newest first", async () => {
+    const category = await createTestAssetCategory({ valueGroup: "high_value" });
+    await POST(
+      postRequest({
+        categoryId: category.id,
+        manufacturer: "Dell",
+        name: "Latitude 5420",
+      })
+    );
+    // Ensure a distinct created_at ordering even on fast filesystems/clocks.
+    await new Promise((resolve) => setTimeout(resolve, 5));
+    await POST(
+      postRequest({
+        categoryId: category.id,
+        manufacturer: "Apple",
+        name: "MacBook Pro 14",
+      })
+    );
+
+    const res = await GET();
+    expect(res.status).toBe(200);
+
+    const body = await res.json();
+    expect(Array.isArray(body)).toBe(true);
+    expect(body).toHaveLength(2);
+
+    // newest first
+    expect(body[0]).toMatchObject({ name: "MacBook Pro 14" });
+    expect(body[1]).toMatchObject({ name: "Latitude 5420" });
+  });
+
+  it("returns an empty list when there are no models", async () => {
+    const res = await GET();
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body).toEqual([]);
+  });
+});
+
+describe("auth gating on /api/asset-models", () => {
+  // Mirrors tests/asset-category-attribute-defs.test.ts's "auth gating"
+  // block — only checks session presence, per the flat permission model (no
+  // role/permission logic).
+  it("POST /api/asset-models returns 401 without a session", async () => {
+    const category = await createTestAssetCategory({ valueGroup: "high_value" });
+    mockedAuth.mockResolvedValue(null);
+
+    const res = await POST(
+      postRequest({
+        categoryId: category.id,
+        manufacturer: "Dell",
+        name: "Latitude 5420",
+      })
+    );
+
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body).toEqual({ error: "Unauthorized" });
+
+    // And it must not have created anything.
+    const remaining = await prisma.assetModel.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("GET /api/asset-models returns 401 without a session", async () => {
+    mockedAuth.mockResolvedValue(null);
+
+    const res = await GET();
+
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body).toEqual({ error: "Unauthorized" });
+  });
+});

tests/assets.test.ts

@@ -24,10 +24,78 @@ function postRequest(body: unknown): Request {
   });
 }
 
+// AssetItem.purchaseOrderId is a real FK to PurchaseOrder (see
+// schema.prisma / src/lib/assets.ts), and PurchaseOrder.vendorId is a real
+// FK to Vendor — tests that need a valid purchaseOrderId create real rows
+// first and use their ids. Mirrors tests/purchase-orders.test.ts's
+// createTestVendor() helper.
+function createTestVendor(overrides: { name?: string } = {}) {
+  return prisma.vendor.create({
+    data: {
+      name: overrides.name ?? "Test Vendor",
+      contactEmail: "[email protected]",
+      contactPhone: "0281234567",
+      address: "123 Test Street",
+    },
+  });
+}
+
+function createTestPurchaseOrder(overrides: { vendorId?: string } = {}) {
+  return prisma.purchaseOrder.create({
+    data: {
+      vendorId: overrides.vendorId as string,
+      orderDate: new Date("2026-08-01"),
+      expectedDate: new Date("2026-08-10"),
+    },
+  });
+}
+
+// AssetItem.modelId is a real FK to AssetModel (see schema.prisma /
+// src/lib/assets.ts), and AssetModel.categoryId is a real FK to
+// AssetCategory — tests that need a valid modelId create the full chain
+// first and use the model's id. Mirrors tests/asset-models.test.ts's
+// createTestAssetCategory() helper. Category is always high_value here —
+// AssetModel only ever references high_value categories per
+// src/lib/asset-models.ts's business rule.
+function createTestAssetCategory(overrides: { name?: string } = {}) {
+  return prisma.assetCategory.create({
+    data: {
+      name: overrides.name ?? "Laptop",
+      valueGroup: "high_value",
+    },
+  });
+}
+
+function createTestAssetModel(overrides: { categoryId?: string } = {}) {
+  return prisma.assetModel.create({
+    data: {
+      categoryId: overrides.categoryId as string,
+      manufacturer: "Dell",
+      name: "Latitude 5440",
+    },
+  });
+}
+
+async function createTestModelId(): Promise<string> {
+  const category = await createTestAssetCategory();
+  const model = await createTestAssetModel({ categoryId: category.id });
+  return model.id;
+}
+
 beforeEach(async () => {
-  // Each test starts from an empty table so listing/order assertions are
+  // Each test starts from empty tables so listing/order assertions are
-  // deterministic.
+  // deterministic. asset_items must be cleared before purchase_orders/
+  // vendors/asset_models/asset_categories since asset_items has FKs to all
+  // of them — deleteMany order avoids relying on cascade behavior in tests.
+  // purchase_orders must be cleared before vendors (ON DELETE RESTRICT to
+  // vendors, mirrors tests/purchase-orders.test.ts). asset_models must be
+  // cleared before asset_categories (ON DELETE RESTRICT, mirrors
+  // tests/asset-models.test.ts's cleanup order).
   await prisma.assetItem.deleteMany();
+  await prisma.purchaseOrder.deleteMany();
+  await prisma.vendor.deleteMany();
+  await prisma.assetModel.deleteMany();
+  await prisma.assetCategory.deleteMany();
   // Default to a logged-in session — the tests below exercise business
   // logic, not auth gating (that's covered by the "auth gating" describe
   // block further down).
@@ -36,8 +104,9 @@ beforeEach(async () => {
 
 describe("POST /api/assets", () => {
   it("creates an asset item in in_stock status on valid input, with no warrantyEndDate", async () => {
+    const modelId = await createTestModelId();
     const res = await POST(
-      postRequest({ serialNumber: "SN-001", model: "Dell Latitude 5440", purchaseDate: "2026-01-15" })
+      postRequest({ serialNumber: "SN-001", modelId, purchaseDate: "2026-01-15" })
     );
 
     expect(res.status).toBe(201);
@@ -45,7 +114,7 @@ describe("POST /api/assets", () => {
 
     expect(body).toMatchObject({
       serial_number: "SN-001",
-      model: "Dell Latitude 5440",
+      model_id: modelId,
       status: "in_stock",
       warranty_end_date: null,
     });
@@ -56,10 +125,11 @@ describe("POST /api/assets", () => {
   });
 
   it("creates an asset item with a warrantyEndDate", async () => {
+    const modelId = await createTestModelId();
     const res = await POST(
       postRequest({
         serialNumber: "SN-002",
-        model: "Dell Latitude 5440",
+        modelId,
         purchaseDate: "2026-01-15",
         warrantyEndDate: "2029-01-15",
       })
@@ -71,24 +141,26 @@ describe("POST /api/assets", () => {
   });
 
   it("rejects an empty serialNumber", async () => {
-    const res = await POST(postRequest({ serialNumber: "", model: "Dell", purchaseDate: "2026-01-15" }));
+    const modelId = await createTestModelId();
+    const res = await POST(postRequest({ serialNumber: "", modelId, purchaseDate: "2026-01-15" }));
 
     expect(res.status).toBe(400);
     const body = await res.json();
     expect(body.error).toMatch(/serialNumber/i);
   });
 
-  it("rejects an empty model", async () => {
+  it("rejects a missing modelId", async () => {
-    const res = await POST(postRequest({ serialNumber: "SN-003", model: "", purchaseDate: "2026-01-15" }));
+    const res = await POST(postRequest({ serialNumber: "SN-003", purchaseDate: "2026-01-15" }));
 
     expect(res.status).toBe(400);
     const body = await res.json();
-    expect(body.error).toMatch(/model/i);
+    expect(body.error).toMatch(/modelId/i);
   });
 
   it("rejects an invalid purchaseDate", async () => {
+    const modelId = await createTestModelId();
     const res = await POST(
-      postRequest({ serialNumber: "SN-004", model: "Dell", purchaseDate: "not-a-date" })
+      postRequest({ serialNumber: "SN-004", modelId, purchaseDate: "not-a-date" })
     );
 
     expect(res.status).toBe(400);
@@ -97,10 +169,11 @@ describe("POST /api/assets", () => {
   });
 
   it("rejects an invalid warrantyEndDate", async () => {
+    const modelId = await createTestModelId();
     const res = await POST(
       postRequest({
         serialNumber: "SN-005",
-        model: "Dell",
+        modelId,
         purchaseDate: "2026-01-15",
         warrantyEndDate: "not-a-date",
       })
@@ -111,9 +184,77 @@ describe("POST /api/assets", () => {
     expect(body.error).toMatch(/warrantyEndDate/i);
   });
 
+  it("creates an asset item with a purchaseOrderId that references a real purchase order", async () => {
+    const modelId = await createTestModelId();
+    const vendor = await createTestVendor();
+    const purchaseOrder = await createTestPurchaseOrder({ vendorId: vendor.id });
+
+    const res = await POST(
+      postRequest({
+        serialNumber: "SN-007",
+        modelId,
+        purchaseDate: "2026-01-15",
+        purchaseOrderId: purchaseOrder.id,
+      })
+    );
+
+    expect(res.status).toBe(201);
+    const body = await res.json();
+    expect(body.purchase_order_id).toBe(purchaseOrder.id);
+  });
+
+  it("creates an asset item with no purchaseOrderId (stays null)", async () => {
+    const modelId = await createTestModelId();
+    const res = await POST(
+      postRequest({ serialNumber: "SN-008", modelId, purchaseDate: "2026-01-15" })
+    );
+
+    expect(res.status).toBe(201);
+    const body = await res.json();
+    expect(body.purchase_order_id).toBeNull();
+  });
+
+  it("rejects a purchaseOrderId that is a well-formed UUID but doesn't reference an existing purchase order", async () => {
+    const modelId = await createTestModelId();
+    const res = await POST(
+      postRequest({
+        serialNumber: "SN-009",
+        modelId,
+        purchaseDate: "2026-01-15",
+        purchaseOrderId: "00000000-0000-0000-0000-000000000000",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/purchaseOrderId/i);
+    expect(body.error).toMatch(/does not reference an existing purchase order/i);
+
+    // And it must not have created anything.
+    const remaining = await prisma.assetItem.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("rejects a purchaseOrderId that is not a valid UUID", async () => {
+    const modelId = await createTestModelId();
+    const res = await POST(
+      postRequest({
+        serialNumber: "SN-012",
+        modelId,
+        purchaseDate: "2026-01-15",
+        purchaseOrderId: "not-a-uuid",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/purchaseOrderId/i);
+  });
+
   it("rejects a duplicate serialNumber", async () => {
-    await POST(postRequest({ serialNumber: "SN-006", model: "Dell", purchaseDate: "2026-01-15" }));
+    const modelId = await createTestModelId();
-    const res = await POST(postRequest({ serialNumber: "SN-006", model: "HP", purchaseDate: "2026-02-01" }));
+    await POST(postRequest({ serialNumber: "SN-006", modelId, purchaseDate: "2026-01-15" }));
+    const res = await POST(postRequest({ serialNumber: "SN-006", modelId, purchaseDate: "2026-02-01" }));
 
     expect(res.status).toBe(400);
     const body = await res.json();
@@ -123,14 +264,48 @@ describe("POST /api/assets", () => {
     const remaining = await prisma.assetItem.findMany();
     expect(remaining).toHaveLength(1);
   });
+
+  it("rejects a modelId that is not a valid UUID", async () => {
+    const res = await POST(
+      postRequest({ serialNumber: "SN-013", modelId: "not-a-uuid", purchaseDate: "2026-01-15" })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/modelId/i);
+
+    // And it must not have created anything.
+    const remaining = await prisma.assetItem.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("rejects a modelId that is a well-formed UUID but doesn't reference an existing asset model", async () => {
+    const res = await POST(
+      postRequest({
+        serialNumber: "SN-014",
+        modelId: "00000000-0000-0000-0000-000000000000",
+        purchaseDate: "2026-01-15",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/modelId/i);
+    expect(body.error).toMatch(/does not reference an existing asset model/i);
+
+    // And it must not have created anything.
+    const remaining = await prisma.assetItem.findMany();
+    expect(remaining).toHaveLength(0);
+  });
 });
 
 describe("GET /api/assets", () => {
   it("lists created asset items, newest first", async () => {
-    await POST(postRequest({ serialNumber: "SN-010", model: "Dell", purchaseDate: "2026-01-15" }));
+    const modelId = await createTestModelId();
+    await POST(postRequest({ serialNumber: "SN-010", modelId, purchaseDate: "2026-01-15" }));
     // Ensure a distinct created_at ordering even on fast filesystems/clocks.
     await new Promise((resolve) => setTimeout(resolve, 5));
-    await POST(postRequest({ serialNumber: "SN-011", model: "HP", purchaseDate: "2026-02-01" }));
+    await POST(postRequest({ serialNumber: "SN-011", modelId, purchaseDate: "2026-02-01" }));
 
     const res = await GET();
     expect(res.status).toBe(200);
@@ -140,8 +315,8 @@ describe("GET /api/assets", () => {
     expect(body).toHaveLength(2);
 
     // newest first
-    expect(body[0]).toMatchObject({ serial_number: "SN-011", model: "HP" });
+    expect(body[0]).toMatchObject({ serial_number: "SN-011", model_id: modelId });
-    expect(body[1]).toMatchObject({ serial_number: "SN-010", model: "Dell" });
+    expect(body[1]).toMatchObject({ serial_number: "SN-010", model_id: modelId });
   });
 
   it("returns an empty list when there are no asset items", async () => {
@@ -157,10 +332,11 @@ describe("auth gating on /api/assets", () => {
   // session presence, per the flat permission model (no role/permission
   // logic).
   it("POST /api/assets returns 401 without a session", async () => {
+    const modelId = await createTestModelId();
     mockedAuth.mockResolvedValue(null);
 
     const res = await POST(
-      postRequest({ serialNumber: "SN-020", model: "Dell", purchaseDate: "2026-01-15" })
+      postRequest({ serialNumber: "SN-020", modelId, purchaseDate: "2026-01-15" })
     );
 
     expect(res.status).toBe(401);

tests/assignments.test.ts

@@ -0,0 +1,956 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import type { Mock } from "vitest";
+import type { Session } from "next-auth";
+import {
+  createAssignment,
+  listAssignments,
+  returnAssignment,
+  transferAssignment,
+  validateCreateAssignmentInput,
+  validateReturnAssignmentInput,
+  validateTransferAssignmentInput,
+} from "@/lib/assignments";
+import { prisma } from "@/lib/prisma";
+
+// This file has two layers of coverage, mirroring tests/licenses.test.ts:
+// - lib-level tests exercise src/lib/assignments.ts directly (validation,
+//   transactional business rules, race conditions).
+// - route-level tests exercise src/app/api/assignments/route.ts and
+//   src/app/api/assignments/[id]/route.ts over HTTP, including the auth()
+//   gate — mirrors tests/licenses.test.ts's @/auth mocking pattern.
+vi.mock("@/auth", () => ({ auth: vi.fn() }));
+
+import { GET, POST } from "@/app/api/assignments/route";
+import { PATCH } from "@/app/api/assignments/[id]/route";
+import { auth } from "@/auth";
+
+const mockedAuth = auth as unknown as Mock<() => Promise<Session | null>>;
+
+const testSession: Session = {
+  user: { id: "test-user-id" },
+  expires: new Date(Date.now() + 60 * 60 * 1000).toISOString(),
+};
+
+function postRequest(body: unknown): Request {
+  return new Request("http://localhost/api/assignments", {
+    method: "POST",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify(body),
+  });
+}
+
+function patchRequest(body: unknown): Request {
+  return new Request("http://localhost/api/assignments/x", {
+    method: "PATCH",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify(body),
+  });
+}
+
+// Assignment.employeeId is a real FK to Employee — mirrors
+// tests/requests.test.ts's createTestEmployee() helper.
+function createTestEmployee(overrides: { name?: string } = {}) {
+  return prisma.employee.create({
+    data: {
+      name: overrides.name ?? "Test Employee",
+      department: "IT",
+    },
+  });
+}
+
+// Assignment.assetItemId is a real FK to AssetItem, which itself requires a
+// full AssetModel -> AssetCategory chain. Mirrors tests/assets.test.ts's
+// createTestModelId() helper.
+async function createTestModelId(): Promise<string> {
+  const category = await prisma.assetCategory.create({
+    data: { name: "Laptop", valueGroup: "high_value" },
+  });
+  const model = await prisma.assetModel.create({
+    data: { categoryId: category.id, manufacturer: "Dell", name: "Latitude 5440" },
+  });
+  return model.id;
+}
+
+let serialCounter = 0;
+function createTestAssetItem(overrides: { modelId: string; status?: "in_stock" | "assigned" | "repair" | "retired" }) {
+  serialCounter += 1;
+  return prisma.assetItem.create({
+    data: {
+      serialNumber: `SN-ASSIGN-${serialCounter}`,
+      modelId: overrides.modelId,
+      purchaseDate: new Date("2026-01-15"),
+      status: overrides.status ?? "in_stock",
+    },
+  });
+}
+
+// Assignment.licenseId is a real FK to License, which itself requires a
+// Vendor. Mirrors tests/licenses.test.ts's createTestVendor() helper.
+function createTestVendor(overrides: { name?: string } = {}) {
+  return prisma.vendor.create({
+    data: {
+      name: overrides.name ?? "Test Vendor",
+      contactEmail: "[email protected]",
+      contactPhone: "0281234567",
+      address: "123 Test Street",
+    },
+  });
+}
+
+function createTestLicense(overrides: {
+  vendorId: string;
+  seatsTotal?: number;
+  seatsUsed?: number;
+}) {
+  return prisma.license.create({
+    data: {
+      name: "Adobe Creative Cloud",
+      vendorId: overrides.vendorId,
+      seatsTotal: overrides.seatsTotal ?? 5,
+      seatsUsed: overrides.seatsUsed ?? 0,
+      licenseType: "subscription",
+    },
+  });
+}
+
+async function createTestLicenseId(overrides: { seatsTotal?: number; seatsUsed?: number } = {}): Promise<string> {
+  const vendor = await createTestVendor();
+  const license = await createTestLicense({ vendorId: vendor.id, ...overrides });
+  return license.id;
+}
+
+beforeEach(async () => {
+  // Clear in FK-safe order: assignments first (references everything else),
+  // then asset_items/licenses (reference purchase_orders/vendors/models),
+  // then the rest.
+  await prisma.assignment.deleteMany();
+  await prisma.assetItem.deleteMany();
+  await prisma.license.deleteMany();
+  await prisma.assetModel.deleteMany();
+  await prisma.assetCategory.deleteMany();
+  await prisma.purchaseOrder.deleteMany();
+  await prisma.vendor.deleteMany();
+  await prisma.employee.deleteMany();
+  serialCounter = 0;
+  // Default to a logged-in session — the lib-level tests don't go through
+  // the route at all (no-op for them), and the route-level tests exercise
+  // business logic, not auth gating (covered by the "auth gating" block).
+  mockedAuth.mockResolvedValue(testSession);
+});
+
+describe("validateCreateAssignmentInput", () => {
+  it("accepts input with only assetItemId set", () => {
+    const result = validateCreateAssignmentInput({
+      employeeId: "11111111-1111-1111-1111-111111111111",
+      assetItemId: "22222222-2222-2222-2222-222222222222",
+    });
+    expect(result.ok).toBe(true);
+  });
+
+  it("accepts input with only licenseId set", () => {
+    const result = validateCreateAssignmentInput({
+      employeeId: "11111111-1111-1111-1111-111111111111",
+      licenseId: "33333333-3333-3333-3333-333333333333",
+    });
+    expect(result.ok).toBe(true);
+  });
+
+  it("rejects input with neither assetItemId nor licenseId set", () => {
+    const result = validateCreateAssignmentInput({
+      employeeId: "11111111-1111-1111-1111-111111111111",
+    });
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/exactly one/i);
+    }
+  });
+
+  it("rejects input with both assetItemId and licenseId set", () => {
+    const result = validateCreateAssignmentInput({
+      employeeId: "11111111-1111-1111-1111-111111111111",
+      assetItemId: "22222222-2222-2222-2222-222222222222",
+      licenseId: "33333333-3333-3333-3333-333333333333",
+    });
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/exactly one/i);
+    }
+  });
+
+  it("rejects a missing employeeId", () => {
+    const result = validateCreateAssignmentInput({
+      assetItemId: "22222222-2222-2222-2222-222222222222",
+    });
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/employeeId/i);
+    }
+  });
+
+  it("rejects a non-UUID assetItemId", () => {
+    const result = validateCreateAssignmentInput({
+      employeeId: "11111111-1111-1111-1111-111111111111",
+      assetItemId: "not-a-uuid",
+    });
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/assetItemId/i);
+    }
+  });
+});
+
+describe("validateReturnAssignmentInput", () => {
+  it("accepts an empty body (returnedAt defaults to now later)", () => {
+    const result = validateReturnAssignmentInput({});
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value.returnedAt).toBeUndefined();
+    }
+  });
+
+  it("accepts an explicit returnedAt", () => {
+    const result = validateReturnAssignmentInput({ returnedAt: "2026-08-05" });
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value.returnedAt).toBeInstanceOf(Date);
+    }
+  });
+
+  it("rejects an invalid returnedAt", () => {
+    const result = validateReturnAssignmentInput({ returnedAt: "not-a-date" });
+    expect(result.ok).toBe(false);
+  });
+});
+
+describe("createAssignment", () => {
+  it("assigns an in_stock AssetItem, flips its status to assigned", async () => {
+    const employee = await createTestEmployee();
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+
+    const created = await createAssignment({ employeeId: employee.id, assetItemId: assetItem.id });
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    expect(created.value.asset_item_id).toBe(assetItem.id);
+    expect(created.value.license_id).toBeNull();
+    expect(created.value.returned_at).toBeNull();
+
+    const updatedItem = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
+    expect(updatedItem.status).toBe("assigned");
+  });
+
+  it.each(["repair", "retired", "assigned"] as const)(
+    "rejects assigning an AssetItem whose status is %s",
+    async (status) => {
+      const employee = await createTestEmployee();
+      const modelId = await createTestModelId();
+      const assetItem = await createTestAssetItem({ modelId, status });
+
+      const created = await createAssignment({ employeeId: employee.id, assetItemId: assetItem.id });
+      expect(created.ok).toBe(false);
+      if (created.ok) return;
+      expect(created.error).toMatch(/not in_stock/i);
+
+      const remaining = await prisma.assignment.findMany();
+      expect(remaining).toHaveLength(0);
+    }
+  );
+
+  it("rejects assigning an AssetItem that already has an active assignment (belt-and-suspenders check)", async () => {
+    const employee = await createTestEmployee();
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+
+    const first = await createAssignment({ employeeId: employee.id, assetItemId: assetItem.id });
+    expect(first.ok).toBe(true);
+
+    // Manually force status back to in_stock without closing the active
+    // Assignment row, to exercise the explicit "active assignment already
+    // exists" invariant independently of the status check (data-drift
+    // scenario per src/lib/assignments.ts's doc comment).
+    await prisma.assetItem.update({ where: { id: assetItem.id }, data: { status: "in_stock" } });
+
+    const second = await createAssignment({ employeeId: employee.id, assetItemId: assetItem.id });
+    expect(second.ok).toBe(false);
+    if (second.ok) return;
+    expect(second.error).toMatch(/already has an active assignment/i);
+  });
+
+  it("rejects assigning an AssetItem for a second employee while the first assignment is still active", async () => {
+    const employee1 = await createTestEmployee({ name: "Employee 1" });
+    const employee2 = await createTestEmployee({ name: "Employee 2" });
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+
+    const first = await createAssignment({ employeeId: employee1.id, assetItemId: assetItem.id });
+    expect(first.ok).toBe(true);
+
+    const second = await createAssignment({ employeeId: employee2.id, assetItemId: assetItem.id });
+    expect(second.ok).toBe(false);
+    if (second.ok) return;
+    expect(second.error).toMatch(/not in_stock/i);
+
+    const activeAssignments = await prisma.assignment.findMany({ where: { assetItemId: assetItem.id, returnedAt: null } });
+    expect(activeAssignments).toHaveLength(1);
+  });
+
+  it("allows re-assigning an AssetItem to a new employee after it has been returned", async () => {
+    const employee1 = await createTestEmployee({ name: "Employee 1" });
+    const employee2 = await createTestEmployee({ name: "Employee 2" });
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+
+    const first = await createAssignment({ employeeId: employee1.id, assetItemId: assetItem.id });
+    expect(first.ok).toBe(true);
+    if (!first.ok) return;
+    const returned = await returnAssignment(first.value.id, {});
+    expect(returned.ok).toBe(true);
+
+    const second = await createAssignment({ employeeId: employee2.id, assetItemId: assetItem.id });
+    expect(second.ok).toBe(true);
+    if (!second.ok) return;
+    expect(second.value.employee_id).toBe(employee2.id);
+
+    const updatedItem = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
+    expect(updatedItem.status).toBe("assigned");
+  });
+
+  it("returns a clean error when assetItemId doesn't reference an existing asset item", async () => {
+    const employee = await createTestEmployee();
+    const created = await createAssignment({
+      employeeId: employee.id,
+      assetItemId: "00000000-0000-0000-0000-000000000000",
+    });
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/assetItemId/i);
+    expect(created.error).toMatch(/does not reference an existing asset item/i);
+  });
+
+  it("returns a clean error when employeeId doesn't reference an existing employee", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+
+    const created = await createAssignment({
+      employeeId: "00000000-0000-0000-0000-000000000000",
+      assetItemId: assetItem.id,
+    });
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/employeeId/i);
+    expect(created.error).toMatch(/does not reference an existing employee/i);
+
+    // And the AssetItem's status must NOT have been mutated — the
+    // transaction must have rolled back entirely.
+    const item = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
+    expect(item.status).toBe("in_stock");
+  });
+
+  it("assigns a license seat, increments seatsUsed", async () => {
+    const employee = await createTestEmployee();
+    const licenseId = await createTestLicenseId({ seatsTotal: 5, seatsUsed: 2 });
+
+    const created = await createAssignment({ employeeId: employee.id, licenseId });
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    expect(created.value.license_id).toBe(licenseId);
+
+    const license = await prisma.license.findUniqueOrThrow({ where: { id: licenseId } });
+    expect(license.seatsUsed).toBe(3);
+  });
+
+  it("rejects assigning a license with no seats remaining (seatsUsed >= seatsTotal)", async () => {
+    const employee = await createTestEmployee();
+    const licenseId = await createTestLicenseId({ seatsTotal: 3, seatsUsed: 3 });
+
+    const created = await createAssignment({ employeeId: employee.id, licenseId });
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/no seats remaining/i);
+
+    const license = await prisma.license.findUniqueOrThrow({ where: { id: licenseId } });
+    expect(license.seatsUsed).toBe(3);
+    const remaining = await prisma.assignment.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("returns a clean error when licenseId doesn't reference an existing license", async () => {
+    const employee = await createTestEmployee();
+    const created = await createAssignment({
+      employeeId: employee.id,
+      licenseId: "00000000-0000-0000-0000-000000000000",
+    });
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/licenseId/i);
+    expect(created.error).toMatch(/does not reference an existing license/i);
+  });
+
+  it("closes the race: two concurrent createAssignment calls against a license with exactly 1 remaining seat — at least one must fail, seatsUsed never exceeds seatsTotal", async () => {
+    const employee1 = await createTestEmployee({ name: "Racer 1" });
+    const employee2 = await createTestEmployee({ name: "Racer 2" });
+    // seatsTotal=3, seatsUsed=2 -> exactly 1 seat remaining.
+    const licenseId = await createTestLicenseId({ seatsTotal: 3, seatsUsed: 2 });
+
+    const [resultA, resultB] = await Promise.all([
+      createAssignment({ employeeId: employee1.id, licenseId }),
+      createAssignment({ employeeId: employee2.id, licenseId }),
+    ]);
+
+    const outcomes = [resultA, resultB];
+    const succeeded = outcomes.filter((r) => r.ok);
+    const failed = outcomes.filter((r) => !r.ok);
+
+    expect(succeeded).toHaveLength(1);
+    expect(failed).toHaveLength(1);
+    if (!failed[0].ok) {
+      expect(failed[0].error).toMatch(/no seats remaining/i);
+    }
+
+    const license = await prisma.license.findUniqueOrThrow({ where: { id: licenseId } });
+    expect(license.seatsUsed).toBe(3);
+    expect(license.seatsUsed).toBeLessThanOrEqual(license.seatsTotal);
+
+    const assignments = await prisma.assignment.findMany({ where: { licenseId } });
+    expect(assignments).toHaveLength(1);
+  });
+
+  it("closes the race: two concurrent createAssignment calls against the same in_stock AssetItem — at least one must fail", async () => {
+    const employee1 = await createTestEmployee({ name: "Racer 1" });
+    const employee2 = await createTestEmployee({ name: "Racer 2" });
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+
+    const [resultA, resultB] = await Promise.all([
+      createAssignment({ employeeId: employee1.id, assetItemId: assetItem.id }),
+      createAssignment({ employeeId: employee2.id, assetItemId: assetItem.id }),
+    ]);
+
+    const outcomes = [resultA, resultB];
+    const succeeded = outcomes.filter((r) => r.ok);
+    const failed = outcomes.filter((r) => !r.ok);
+
+    expect(succeeded).toHaveLength(1);
+    expect(failed).toHaveLength(1);
+
+    const item = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
+    expect(item.status).toBe("assigned");
+
+    const activeAssignments = await prisma.assignment.findMany({
+      where: { assetItemId: assetItem.id, returnedAt: null },
+    });
+    expect(activeAssignments).toHaveLength(1);
+  });
+});
+
+describe("returnAssignment", () => {
+  it("returns an AssetItem assignment: sets returnedAt, flips status back to in_stock", async () => {
+    const employee = await createTestEmployee();
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+
+    const created = await createAssignment({ employeeId: employee.id, assetItemId: assetItem.id });
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+
+    const returned = await returnAssignment(created.value.id, {});
+    expect(returned.ok).toBe(true);
+    if (!returned.ok) return;
+    expect(returned.value.returned_at).not.toBeNull();
+
+    const item = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
+    expect(item.status).toBe("in_stock");
+  });
+
+  it("accepts an explicit returnedAt", async () => {
+    const employee = await createTestEmployee();
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+    const created = await createAssignment({ employeeId: employee.id, assetItemId: assetItem.id });
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+
+    const explicitDate = new Date("2026-08-01T00:00:00.000Z");
+    const returned = await returnAssignment(created.value.id, { returnedAt: explicitDate });
+    expect(returned.ok).toBe(true);
+    if (!returned.ok) return;
+    expect(returned.value.returned_at).toBe(explicitDate.toISOString());
+  });
+
+  it("returns a license assignment: sets returnedAt, decrements seatsUsed", async () => {
+    const employee = await createTestEmployee();
+    const licenseId = await createTestLicenseId({ seatsTotal: 5, seatsUsed: 2 });
+
+    const created = await createAssignment({ employeeId: employee.id, licenseId });
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+
+    let license = await prisma.license.findUniqueOrThrow({ where: { id: licenseId } });
+    expect(license.seatsUsed).toBe(3);
+
+    const returned = await returnAssignment(created.value.id, {});
+    expect(returned.ok).toBe(true);
+
+    license = await prisma.license.findUniqueOrThrow({ where: { id: licenseId } });
+    expect(license.seatsUsed).toBe(2);
+  });
+
+  it("rejects returning an already-returned assignment (double return)", async () => {
+    const employee = await createTestEmployee();
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+    const created = await createAssignment({ employeeId: employee.id, assetItemId: assetItem.id });
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+
+    const firstReturn = await returnAssignment(created.value.id, {});
+    expect(firstReturn.ok).toBe(true);
+
+    const secondReturn = await returnAssignment(created.value.id, {});
+    expect(secondReturn.ok).toBe(false);
+    if (secondReturn.ok) return;
+    expect(secondReturn.status).toBe(400);
+    expect(secondReturn.error).toMatch(/already been returned/i);
+  });
+
+  it("returns 404 when returning a nonexistent assignment", async () => {
+    const result = await returnAssignment("00000000-0000-0000-0000-000000000000", {});
+    expect(result.ok).toBe(false);
+    if (result.ok) return;
+    expect(result.status).toBe(404);
+    expect(result.error).toMatch(/not found/i);
+  });
+
+  it("closes the race: two concurrent returnAssignment calls against the same assignment — only one succeeds", async () => {
+    const employee = await createTestEmployee();
+    const licenseId = await createTestLicenseId({ seatsTotal: 5, seatsUsed: 0 });
+    const created = await createAssignment({ employeeId: employee.id, licenseId });
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+
+    const [resultA, resultB] = await Promise.all([
+      returnAssignment(created.value.id, {}),
+      returnAssignment(created.value.id, {}),
+    ]);
+
+    const outcomes = [resultA, resultB];
+    const succeeded = outcomes.filter((r) => r.ok);
+    const failed = outcomes.filter((r) => !r.ok);
+    expect(succeeded).toHaveLength(1);
+    expect(failed).toHaveLength(1);
+
+    const license = await prisma.license.findUniqueOrThrow({ where: { id: licenseId } });
+    expect(license.seatsUsed).toBe(0);
+  });
+});
+
+describe("transferAssignment", () => {
+  it("transfers an AssetItem assignment to a new employee, keeping status assigned throughout", async () => {
+    const employee1 = await createTestEmployee({ name: "Employee 1" });
+    const employee2 = await createTestEmployee({ name: "Employee 2" });
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+
+    const created = await createAssignment({ employeeId: employee1.id, assetItemId: assetItem.id });
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+
+    const transferred = await transferAssignment(created.value.id, { employeeId: employee2.id });
+    expect(transferred.ok).toBe(true);
+    if (!transferred.ok) return;
+    expect(transferred.value.employee_id).toBe(employee2.id);
+    expect(transferred.value.asset_item_id).toBe(assetItem.id);
+    expect(transferred.value.returned_at).toBeNull();
+
+    // The AssetItem must remain "assigned" throughout the transfer — never
+    // flipped to in_stock mid-way (that's the whole point of doing this in
+    // one transaction rather than a separate return + create).
+    const item = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
+    expect(item.status).toBe("assigned");
+
+    const original = await prisma.assignment.findUniqueOrThrow({ where: { id: created.value.id } });
+    expect(original.returnedAt).not.toBeNull();
+
+    const rows = await prisma.assignment.findMany({ where: { assetItemId: assetItem.id } });
+    expect(rows).toHaveLength(2);
+    const newRow = rows.find((row) => row.id !== created.value.id);
+    expect(newRow).toBeDefined();
+    expect(newRow?.employeeId).toBe(employee2.id);
+    expect(newRow?.returnedAt).toBeNull();
+  });
+
+  it("transfers a License assignment to a new employee without changing seatsUsed", async () => {
+    const employee1 = await createTestEmployee({ name: "Employee 1" });
+    const employee2 = await createTestEmployee({ name: "Employee 2" });
+    const licenseId = await createTestLicenseId({ seatsTotal: 5, seatsUsed: 2 });
+
+    const created = await createAssignment({ employeeId: employee1.id, licenseId });
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+
+    let license = await prisma.license.findUniqueOrThrow({ where: { id: licenseId } });
+    expect(license.seatsUsed).toBe(3);
+
+    const transferred = await transferAssignment(created.value.id, { employeeId: employee2.id });
+    expect(transferred.ok).toBe(true);
+    if (!transferred.ok) return;
+    expect(transferred.value.employee_id).toBe(employee2.id);
+    expect(transferred.value.license_id).toBe(licenseId);
+
+    license = await prisma.license.findUniqueOrThrow({ where: { id: licenseId } });
+    expect(license.seatsUsed).toBe(3);
+
+    const original = await prisma.assignment.findUniqueOrThrow({ where: { id: created.value.id } });
+    expect(original.returnedAt).not.toBeNull();
+  });
+
+  it("rejects transferring an already-returned assignment", async () => {
+    const employee1 = await createTestEmployee({ name: "Employee 1" });
+    const employee2 = await createTestEmployee({ name: "Employee 2" });
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+
+    const created = await createAssignment({ employeeId: employee1.id, assetItemId: assetItem.id });
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+
+    const returned = await returnAssignment(created.value.id, {});
+    expect(returned.ok).toBe(true);
+
+    const transferred = await transferAssignment(created.value.id, { employeeId: employee2.id });
+    expect(transferred.ok).toBe(false);
+    if (transferred.ok) return;
+    expect(transferred.status).toBe(400);
+    expect(transferred.error).toMatch(/already been returned/i);
+  });
+
+  it("returns 404 when transferring a nonexistent assignment", async () => {
+    const employee = await createTestEmployee();
+    const result = await transferAssignment("00000000-0000-0000-0000-000000000000", {
+      employeeId: employee.id,
+    });
+    expect(result.ok).toBe(false);
+    if (result.ok) return;
+    expect(result.status).toBe(404);
+    expect(result.error).toMatch(/not found/i);
+  });
+
+  it("returns a clean 400 when transferring to a nonexistent employeeId", async () => {
+    const employee1 = await createTestEmployee({ name: "Employee 1" });
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+
+    const created = await createAssignment({ employeeId: employee1.id, assetItemId: assetItem.id });
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+
+    const transferred = await transferAssignment(created.value.id, {
+      employeeId: "00000000-0000-0000-0000-000000000000",
+    });
+    expect(transferred.ok).toBe(false);
+    if (transferred.ok) return;
+    expect(transferred.status).toBe(400);
+    expect(transferred.error).toMatch(/employeeId/i);
+    expect(transferred.error).toMatch(/does not reference an existing employee/i);
+
+    // Original assignment must not have been closed — the whole transfer
+    // must have rolled back.
+    const original = await prisma.assignment.findUniqueOrThrow({ where: { id: created.value.id } });
+    expect(original.returnedAt).toBeNull();
+    const item = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
+    expect(item.status).toBe("assigned");
+  });
+});
+
+describe("validateTransferAssignmentInput", () => {
+  it("accepts a valid employeeId", () => {
+    const result = validateTransferAssignmentInput({
+      employeeId: "11111111-1111-1111-1111-111111111111",
+    });
+    expect(result.ok).toBe(true);
+  });
+
+  it("rejects a missing employeeId", () => {
+    const result = validateTransferAssignmentInput({});
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/employeeId/i);
+    }
+  });
+
+  it("rejects a non-UUID employeeId", () => {
+    const result = validateTransferAssignmentInput({ employeeId: "not-a-uuid" });
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/employeeId/i);
+    }
+  });
+});
+
+describe("listAssignments", () => {
+  it("lists created assignments, newest first", async () => {
+    const employee = await createTestEmployee();
+    const modelId = await createTestModelId();
+    const item1 = await createTestAssetItem({ modelId });
+    const item2 = await createTestAssetItem({ modelId });
+
+    const first = await createAssignment({ employeeId: employee.id, assetItemId: item1.id });
+    expect(first.ok).toBe(true);
+    await new Promise((resolve) => setTimeout(resolve, 5));
+    const second = await createAssignment({ employeeId: employee.id, assetItemId: item2.id });
+    expect(second.ok).toBe(true);
+
+    const records = await listAssignments();
+    expect(records).toHaveLength(2);
+    expect(records[0].asset_item_id).toBe(item2.id);
+    expect(records[1].asset_item_id).toBe(item1.id);
+  });
+
+  it("returns an empty list when there are no assignments", async () => {
+    const records = await listAssignments();
+    expect(records).toEqual([]);
+  });
+});
+
+describe("POST /api/assignments", () => {
+  it("creates an assignment on valid input", async () => {
+    const employee = await createTestEmployee();
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+
+    const res = await POST(postRequest({ employeeId: employee.id, assetItemId: assetItem.id }));
+    expect(res.status).toBe(201);
+    const body = await res.json();
+    expect(body).toMatchObject({ employee_id: employee.id, asset_item_id: assetItem.id, license_id: null });
+  });
+
+  it("rejects both assetItemId and licenseId set", async () => {
+    const employee = await createTestEmployee();
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+    const licenseId = await createTestLicenseId();
+
+    const res = await POST(
+      postRequest({ employeeId: employee.id, assetItemId: assetItem.id, licenseId })
+    );
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/exactly one/i);
+  });
+
+  it("rejects neither assetItemId nor licenseId set", async () => {
+    const employee = await createTestEmployee();
+    const res = await POST(postRequest({ employeeId: employee.id }));
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/exactly one/i);
+  });
+
+  it("rejects assigning an AssetItem that isn't in_stock", async () => {
+    const employee = await createTestEmployee();
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId, status: "repair" });
+
+    const res = await POST(postRequest({ employeeId: employee.id, assetItemId: assetItem.id }));
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/not in_stock/i);
+  });
+
+  it("rejects an invalid JSON body", async () => {
+    const req = new Request("http://localhost/api/assignments", {
+      method: "POST",
+      headers: { "content-type": "application/json" },
+      body: "not json",
+    });
+    const res = await POST(req);
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/JSON/i);
+  });
+
+  it("rejects a non-object JSON body", async () => {
+    const res = await POST(postRequest("not an object"));
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/JSON object/i);
+  });
+});
+
+describe("GET /api/assignments", () => {
+  it("lists created assignments, newest first", async () => {
+    const employee = await createTestEmployee();
+    const modelId = await createTestModelId();
+    const item1 = await createTestAssetItem({ modelId });
+    const item2 = await createTestAssetItem({ modelId });
+
+    await POST(postRequest({ employeeId: employee.id, assetItemId: item1.id }));
+    await new Promise((resolve) => setTimeout(resolve, 5));
+    await POST(postRequest({ employeeId: employee.id, assetItemId: item2.id }));
+
+    const res = await GET();
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body).toHaveLength(2);
+    expect(body[0].asset_item_id).toBe(item2.id);
+    expect(body[1].asset_item_id).toBe(item1.id);
+  });
+
+  it("returns an empty list when there are no assignments", async () => {
+    const res = await GET();
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body).toEqual([]);
+  });
+});
+
+describe("PATCH /api/assignments/[id]", () => {
+  it("returns an assignment on valid input", async () => {
+    const employee = await createTestEmployee();
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+    const createRes = await POST(postRequest({ employeeId: employee.id, assetItemId: assetItem.id }));
+    const created = await createRes.json();
+
+    const res = await PATCH(patchRequest({}), { params: { id: created.id } });
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body.returned_at).not.toBeNull();
+
+    const item = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
+    expect(item.status).toBe("in_stock");
+  });
+
+  it("returns 404 for a nonexistent assignment id", async () => {
+    const res = await PATCH(patchRequest({}), {
+      params: { id: "00000000-0000-0000-0000-000000000000" },
+    });
+    expect(res.status).toBe(404);
+    const body = await res.json();
+    expect(body.error).toMatch(/not found/i);
+  });
+
+  it("returns 400 for a malformed id (not a UUID)", async () => {
+    const res = await PATCH(patchRequest({}), { params: { id: "not-a-uuid" } });
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/UUID/i);
+  });
+
+  it("rejects double-return with 400", async () => {
+    const employee = await createTestEmployee();
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+    const createRes = await POST(postRequest({ employeeId: employee.id, assetItemId: assetItem.id }));
+    const created = await createRes.json();
+
+    await PATCH(patchRequest({}), { params: { id: created.id } });
+    const res = await PATCH(patchRequest({}), { params: { id: created.id } });
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/already been returned/i);
+  });
+
+  it("rejects an invalid JSON body", async () => {
+    const req = new Request("http://localhost/api/assignments/x", {
+      method: "PATCH",
+      headers: { "content-type": "application/json" },
+      body: "not json",
+    });
+    const res = await PATCH(req, { params: { id: "00000000-0000-0000-0000-000000000000" } });
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/JSON/i);
+  });
+
+  it("rejects a non-object JSON body", async () => {
+    const res = await PATCH(patchRequest("not an object"), {
+      params: { id: "00000000-0000-0000-0000-000000000000" },
+    });
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/JSON object/i);
+  });
+
+  it("returns 401 without a session", async () => {
+    mockedAuth.mockResolvedValue(null);
+    const res = await PATCH(patchRequest({}), {
+      params: { id: "00000000-0000-0000-0000-000000000000" },
+    });
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body).toEqual({ error: "Unauthorized" });
+  });
+
+  it("transfers an assignment to a new employee on valid employeeId input", async () => {
+    const employee1 = await createTestEmployee({ name: "Employee 1" });
+    const employee2 = await createTestEmployee({ name: "Employee 2" });
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+    const createRes = await POST(postRequest({ employeeId: employee1.id, assetItemId: assetItem.id }));
+    const created = await createRes.json();
+
+    const res = await PATCH(patchRequest({ employeeId: employee2.id }), { params: { id: created.id } });
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body.employee_id).toBe(employee2.id);
+    expect(body.asset_item_id).toBe(assetItem.id);
+    expect(body.returned_at).toBeNull();
+
+    const item = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
+    expect(item.status).toBe("assigned");
+  });
+
+  it("rejects a body with both employeeId and returnedAt with a mutual-exclusivity 400", async () => {
+    const employee1 = await createTestEmployee({ name: "Employee 1" });
+    const employee2 = await createTestEmployee({ name: "Employee 2" });
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+    const createRes = await POST(postRequest({ employeeId: employee1.id, assetItemId: assetItem.id }));
+    const created = await createRes.json();
+
+    const res = await PATCH(
+      patchRequest({ employeeId: employee2.id, returnedAt: "2026-08-01" }),
+      { params: { id: created.id } }
+    );
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/either employeeId.*or returnedAt/i);
+  });
+
+  it("returns 401 for a transfer request without a session", async () => {
+    const employee = await createTestEmployee();
+    mockedAuth.mockResolvedValue(null);
+    const res = await PATCH(patchRequest({ employeeId: employee.id }), {
+      params: { id: "00000000-0000-0000-0000-000000000000" },
+    });
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body).toEqual({ error: "Unauthorized" });
+  });
+});
+
+describe("auth gating on /api/assignments", () => {
+  it("POST /api/assignments returns 401 without a session", async () => {
+    const employee = await createTestEmployee();
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+    mockedAuth.mockResolvedValue(null);
+
+    const res = await POST(postRequest({ employeeId: employee.id, assetItemId: assetItem.id }));
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body).toEqual({ error: "Unauthorized" });
+
+    const remaining = await prisma.assignment.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("GET /api/assignments returns 401 without a session", async () => {
+    mockedAuth.mockResolvedValue(null);
+    const res = await GET();
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body).toEqual({ error: "Unauthorized" });
+  });
+});

tests/licenses.test.ts

@@ -34,10 +34,45 @@ function postRequest(body: unknown): Request {
   });
 }
 
+// License.vendorId is a real FK to Vendor (see schema.prisma /
+// src/lib/licenses.ts) — tests that need a valid vendorId create a real
+// Vendor row first and use its id, rather than an arbitrary string. Mirrors
+// tests/requests.test.ts's createTestEmployee() helper.
+function createTestVendor(overrides: { name?: string } = {}) {
+  return prisma.vendor.create({
+    data: {
+      name: overrides.name ?? "Test Vendor",
+      contactEmail: "[email protected]",
+      contactPhone: "0281234567",
+      address: "123 Test Street",
+    },
+  });
+}
+
+// License.purchaseOrderId is a real FK to PurchaseOrder (see schema.prisma /
+// src/lib/licenses.ts) — tests that need a valid purchaseOrderId create a
+// real PurchaseOrder row first and use its id. Mirrors
+// tests/assets.test.ts's createTestPurchaseOrder() helper.
+function createTestPurchaseOrder(overrides: { vendorId?: string } = {}) {
+  return prisma.purchaseOrder.create({
+    data: {
+      vendorId: overrides.vendorId as string,
+      orderDate: new Date("2026-08-01"),
+      expectedDate: new Date("2026-08-10"),
+    },
+  });
+}
+
 beforeEach(async () => {
-  // Each test starts from an empty table so listing/order assertions are
+  // Each test starts from empty tables so listing/order assertions are
-  // deterministic.
+  // deterministic. licenses must be cleared before purchase_orders/vendors
+  // since licenses has FKs (ON DELETE RESTRICT to vendors, ON DELETE SET
+  // NULL to purchase_orders) to both. purchase_orders must be cleared
+  // before vendors (ON DELETE RESTRICT to vendors, mirrors
+  // tests/assets.test.ts).
   await prisma.license.deleteMany();
+  await prisma.purchaseOrder.deleteMany();
+  await prisma.vendor.deleteMany();
   // Default to a logged-in session — the lib-level tests below don't go
   // through the route at all (so this is a no-op for them), and the
   // route-level tests exercise business logic, not auth gating (that's
@@ -49,7 +84,7 @@ describe("validateCreateLicenseInput", () => {
   it("accepts valid input with an expiryDate", () => {
     const result = validateCreateLicenseInput({
       name: "Adobe Creative Cloud",
-      vendor: "Adobe",
+      vendorId: "11111111-1111-1111-1111-111111111111",
       seatsTotal: 10,
       expiryDate: "2027-01-15",
       licenseType: "subscription",
@@ -59,7 +94,7 @@ describe("validateCreateLicenseInput", () => {
     if (result.ok) {
       expect(result.value).toMatchObject({
         name: "Adobe Creative Cloud",
-        vendor: "Adobe",
+        vendorId: "11111111-1111-1111-1111-111111111111",
         seatsTotal: 10,
         licenseType: "subscription",
       });
@@ -70,7 +105,7 @@ describe("validateCreateLicenseInput", () => {
   it("accepts valid input with no expiryDate (perpetual license)", () => {
     const result = validateCreateLicenseInput({
       name: "Windows Server 2022",
-      vendor: "Microsoft",
+      vendorId: "11111111-1111-1111-1111-111111111111",
       seatsTotal: 5,
       licenseType: "perpetual",
     });
@@ -84,7 +119,7 @@ describe("validateCreateLicenseInput", () => {
   it("rejects an empty name", () => {
     const result = validateCreateLicenseInput({
       name: "",
-      vendor: "Adobe",
+      vendorId: "11111111-1111-1111-1111-111111111111",
       seatsTotal: 10,
       licenseType: "subscription",
     });
@@ -95,24 +130,37 @@ describe("validateCreateLicenseInput", () => {
     }
   });
 
-  it("rejects an empty vendor", () => {
+  it("rejects a vendorId that is not a valid UUID", () => {
     const result = validateCreateLicenseInput({
       name: "Adobe Creative Cloud",
-      vendor: "",
+      vendorId: "not-a-uuid",
       seatsTotal: 10,
       licenseType: "subscription",
     });
 
     expect(result.ok).toBe(false);
     if (!result.ok) {
-      expect(result.error).toMatch(/vendor/i);
+      expect(result.error).toMatch(/vendorId/i);
+    }
+  });
+
+  it("rejects a missing vendorId", () => {
+    const result = validateCreateLicenseInput({
+      name: "Adobe Creative Cloud",
+      seatsTotal: 10,
+      licenseType: "subscription",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/vendorId/i);
     }
   });
 
   it("rejects a zero seatsTotal", () => {
     const result = validateCreateLicenseInput({
       name: "Adobe Creative Cloud",
-      vendor: "Adobe",
+      vendorId: "11111111-1111-1111-1111-111111111111",
       seatsTotal: 0,
       licenseType: "subscription",
     });
@@ -126,7 +174,7 @@ describe("validateCreateLicenseInput", () => {
   it("rejects a negative seatsTotal", () => {
     const result = validateCreateLicenseInput({
       name: "Adobe Creative Cloud",
-      vendor: "Adobe",
+      vendorId: "11111111-1111-1111-1111-111111111111",
       seatsTotal: -5,
       licenseType: "subscription",
     });
@@ -140,7 +188,7 @@ describe("validateCreateLicenseInput", () => {
   it("rejects a non-integer seatsTotal", () => {
     const result = validateCreateLicenseInput({
       name: "Adobe Creative Cloud",
-      vendor: "Adobe",
+      vendorId: "11111111-1111-1111-1111-111111111111",
       seatsTotal: 3.5,
       licenseType: "subscription",
     });
@@ -154,7 +202,7 @@ describe("validateCreateLicenseInput", () => {
   it("rejects an invalid expiryDate", () => {
     const result = validateCreateLicenseInput({
       name: "Adobe Creative Cloud",
-      vendor: "Adobe",
+      vendorId: "11111111-1111-1111-1111-111111111111",
       seatsTotal: 10,
       expiryDate: "not-a-date",
       licenseType: "subscription",
@@ -169,7 +217,7 @@ describe("validateCreateLicenseInput", () => {
   it("rejects an invalid licenseType", () => {
     const result = validateCreateLicenseInput({
       name: "Adobe Creative Cloud",
-      vendor: "Adobe",
+      vendorId: "11111111-1111-1111-1111-111111111111",
       seatsTotal: 10,
       licenseType: "trial",
     });
@@ -183,7 +231,7 @@ describe("validateCreateLicenseInput", () => {
   it("rejects a missing licenseType", () => {
     const result = validateCreateLicenseInput({
       name: "Adobe Creative Cloud",
-      vendor: "Adobe",
+      vendorId: "11111111-1111-1111-1111-111111111111",
       seatsTotal: 10,
     });
 
@@ -192,13 +240,29 @@ describe("validateCreateLicenseInput", () => {
       expect(result.error).toMatch(/licenseType/i);
     }
   });
+
+  it("rejects a purchaseOrderId that is not a valid UUID", () => {
+    const result = validateCreateLicenseInput({
+      name: "Adobe Creative Cloud",
+      vendorId: "11111111-1111-1111-1111-111111111111",
+      seatsTotal: 10,
+      licenseType: "subscription",
+      purchaseOrderId: "not-a-uuid",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/purchaseOrderId/i);
+    }
+  });
 });
 
 describe("createLicense", () => {
   it("creates a license with seatsUsed always 0, regardless of client input", async () => {
+    const vendor = await createTestVendor();
     const result = validateCreateLicenseInput({
       name: "Adobe Creative Cloud",
-      vendor: "Adobe",
+      vendorId: vendor.id,
       seatsTotal: 10,
       // @ts-expect-error -- seatsUsed is intentionally not part of
       // CreateLicenseInput; this simulates a client trying to sneak it in.
@@ -209,12 +273,15 @@ describe("createLicense", () => {
     expect(result.ok).toBe(true);
     if (!result.ok) return;
 
-    const record = await createLicense(result.value);
+    const created = await createLicense(result.value);
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    const record = created.value;
 
     expect(record.seats_used).toBe(0);
     expect(record).toMatchObject({
       name: "Adobe Creative Cloud",
-      vendor: "Adobe",
+      vendor_id: vendor.id,
       seats_total: 10,
       license_type: "subscription",
     });
@@ -225,28 +292,113 @@ describe("createLicense", () => {
   });
 
   it("creates a perpetual license with no expiryDate", async () => {
+    const vendor = await createTestVendor();
     const result = validateCreateLicenseInput({
       name: "Windows Server 2022",
-      vendor: "Microsoft",
+      vendorId: vendor.id,
       seatsTotal: 5,
       licenseType: "perpetual",
     });
     expect(result.ok).toBe(true);
     if (!result.ok) return;
 
-    const record = await createLicense(result.value);
+    const created = await createLicense(result.value);
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    const record = created.value;
 
     expect(record.expiry_date).toBeNull();
     expect(record.seats_used).toBe(0);
     expect(record.license_type).toBe("perpetual");
   });
+
+  it("returns a clean error when vendorId doesn't reference an existing vendor", async () => {
+    const result = validateCreateLicenseInput({
+      name: "Adobe Creative Cloud",
+      vendorId: "00000000-0000-0000-0000-000000000000",
+      seatsTotal: 10,
+      licenseType: "subscription",
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createLicense(result.value);
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/vendorId/i);
+    expect(created.error).toMatch(/does not reference an existing vendor/i);
+
+    const remaining = await prisma.license.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("creates a license with a purchaseOrderId that references a real purchase order", async () => {
+    const vendor = await createTestVendor();
+    const purchaseOrder = await createTestPurchaseOrder({ vendorId: vendor.id });
+    const result = validateCreateLicenseInput({
+      name: "Adobe Creative Cloud",
+      vendorId: vendor.id,
+      seatsTotal: 10,
+      licenseType: "subscription",
+      purchaseOrderId: purchaseOrder.id,
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createLicense(result.value);
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    expect(created.value.purchase_order_id).toBe(purchaseOrder.id);
+  });
+
+  it("creates a license with no purchaseOrderId (stays null)", async () => {
+    const vendor = await createTestVendor();
+    const result = validateCreateLicenseInput({
+      name: "Adobe Creative Cloud",
+      vendorId: vendor.id,
+      seatsTotal: 10,
+      licenseType: "subscription",
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createLicense(result.value);
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    expect(created.value.purchase_order_id).toBeNull();
+  });
+
+  it("returns a clean error when purchaseOrderId doesn't reference an existing purchase order", async () => {
+    const vendor = await createTestVendor();
+    const result = validateCreateLicenseInput({
+      name: "Adobe Creative Cloud",
+      vendorId: vendor.id,
+      seatsTotal: 10,
+      licenseType: "subscription",
+      purchaseOrderId: "00000000-0000-0000-0000-000000000000",
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createLicense(result.value);
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/purchaseOrderId/i);
+    expect(created.error).toMatch(/does not reference an existing purchase order/i);
+
+    const remaining = await prisma.license.findMany();
+    expect(remaining).toHaveLength(0);
+  });
 });
 
 describe("listLicenses", () => {
   it("lists created licenses, newest first", async () => {
+    const vendor1 = await createTestVendor({ name: "Microsoft VN" });
+    const vendor2 = await createTestVendor({ name: "Adobe VN" });
+
     const first = validateCreateLicenseInput({
       name: "Windows Server 2022",
-      vendor: "Microsoft",
+      vendorId: vendor1.id,
       seatsTotal: 5,
       licenseType: "perpetual",
     });
@@ -258,7 +410,7 @@ describe("listLicenses", () => {
 
     const second = validateCreateLicenseInput({
       name: "Adobe Creative Cloud",
-      vendor: "Adobe",
+      vendorId: vendor2.id,
       seatsTotal: 10,
       licenseType: "subscription",
     });
@@ -269,8 +421,8 @@ describe("listLicenses", () => {
 
     expect(records).toHaveLength(2);
     // newest first
-    expect(records[0]).toMatchObject({ name: "Adobe Creative Cloud", vendor: "Adobe" });
+    expect(records[0]).toMatchObject({ name: "Adobe Creative Cloud", vendor_id: vendor2.id });
-    expect(records[1]).toMatchObject({ name: "Windows Server 2022", vendor: "Microsoft" });
+    expect(records[1]).toMatchObject({ name: "Windows Server 2022", vendor_id: vendor1.id });
   });
 
   it("returns an empty list when there are no licenses", async () => {
@@ -281,10 +433,11 @@ describe("listLicenses", () => {
 
 describe("POST /api/licenses", () => {
   it("creates a license with seatsUsed always 0 on valid input", async () => {
+    const vendor = await createTestVendor();
     const res = await POST(
       postRequest({
         name: "Adobe Creative Cloud",
-        vendor: "Adobe",
+        vendorId: vendor.id,
         seatsTotal: 10,
         expiryDate: "2027-01-15",
         licenseType: "subscription",
@@ -296,7 +449,7 @@ describe("POST /api/licenses", () => {
 
     expect(body).toMatchObject({
       name: "Adobe Creative Cloud",
-      vendor: "Adobe",
+      vendor_id: vendor.id,
       seats_total: 10,
       seats_used: 0,
       license_type: "subscription",
@@ -308,10 +461,11 @@ describe("POST /api/licenses", () => {
   });
 
   it("creates a perpetual license with no expiryDate", async () => {
+    const vendor = await createTestVendor();
     const res = await POST(
       postRequest({
         name: "Windows Server 2022",
-        vendor: "Microsoft",
+        vendorId: vendor.id,
         seatsTotal: 5,
         licenseType: "perpetual",
       })
@@ -324,8 +478,9 @@ describe("POST /api/licenses", () => {
   });
 
   it("rejects an empty name", async () => {
+    const vendor = await createTestVendor();
     const res = await POST(
-      postRequest({ name: "", vendor: "Adobe", seatsTotal: 10, licenseType: "subscription" })
+      postRequest({ name: "", vendorId: vendor.id, seatsTotal: 10, licenseType: "subscription" })
     );
 
     expect(res.status).toBe(400);
@@ -333,19 +488,45 @@ describe("POST /api/licenses", () => {
     expect(body.error).toMatch(/name/i);
   });
 
-  it("rejects an empty vendor", async () => {
+  it("rejects a vendorId that is not a valid UUID", async () => {
     const res = await POST(
-      postRequest({ name: "Adobe Creative Cloud", vendor: "", seatsTotal: 10, licenseType: "subscription" })
+      postRequest({
+        name: "Adobe Creative Cloud",
+        vendorId: "not-a-uuid",
+        seatsTotal: 10,
+        licenseType: "subscription",
+      })
     );
 
     expect(res.status).toBe(400);
     const body = await res.json();
-    expect(body.error).toMatch(/vendor/i);
+    expect(body.error).toMatch(/vendorId/i);
+  });
+
+  it("rejects a vendorId that is a well-formed UUID but doesn't reference an existing vendor", async () => {
+    const res = await POST(
+      postRequest({
+        name: "Adobe Creative Cloud",
+        vendorId: "00000000-0000-0000-0000-000000000000",
+        seatsTotal: 10,
+        licenseType: "subscription",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/vendorId/i);
+    expect(body.error).toMatch(/does not reference an existing vendor/i);
+
+    // And it must not have created anything.
+    const remaining = await prisma.license.findMany();
+    expect(remaining).toHaveLength(0);
   });
 
   it("rejects a zero seatsTotal", async () => {
+    const vendor = await createTestVendor();
     const res = await POST(
-      postRequest({ name: "Adobe Creative Cloud", vendor: "Adobe", seatsTotal: 0, licenseType: "subscription" })
+      postRequest({ name: "Adobe Creative Cloud", vendorId: vendor.id, seatsTotal: 0, licenseType: "subscription" })
     );
 
     expect(res.status).toBe(400);
@@ -354,10 +535,11 @@ describe("POST /api/licenses", () => {
   });
 
   it("rejects an invalid expiryDate", async () => {
+    const vendor = await createTestVendor();
     const res = await POST(
       postRequest({
         name: "Adobe Creative Cloud",
-        vendor: "Adobe",
+        vendorId: vendor.id,
         seatsTotal: 10,
         expiryDate: "not-a-date",
         licenseType: "subscription",
@@ -370,8 +552,9 @@ describe("POST /api/licenses", () => {
   });
 
   it("rejects an invalid licenseType", async () => {
+    const vendor = await createTestVendor();
     const res = await POST(
-      postRequest({ name: "Adobe Creative Cloud", vendor: "Adobe", seatsTotal: 10, licenseType: "trial" })
+      postRequest({ name: "Adobe Creative Cloud", vendorId: vendor.id, seatsTotal: 10, licenseType: "trial" })
     );
 
     expect(res.status).toBe(400);
@@ -379,6 +562,74 @@ describe("POST /api/licenses", () => {
     expect(body.error).toMatch(/licenseType/i);
   });
 
+  it("creates a license with a purchaseOrderId that references a real purchase order", async () => {
+    const vendor = await createTestVendor();
+    const purchaseOrder = await createTestPurchaseOrder({ vendorId: vendor.id });
+    const res = await POST(
+      postRequest({
+        name: "Adobe Creative Cloud",
+        vendorId: vendor.id,
+        seatsTotal: 10,
+        licenseType: "subscription",
+        purchaseOrderId: purchaseOrder.id,
+      })
+    );
+
+    expect(res.status).toBe(201);
+    const body = await res.json();
+    expect(body.purchase_order_id).toBe(purchaseOrder.id);
+  });
+
+  it("creates a license with no purchaseOrderId (stays null)", async () => {
+    const vendor = await createTestVendor();
+    const res = await POST(
+      postRequest({ name: "Adobe Creative Cloud", vendorId: vendor.id, seatsTotal: 10, licenseType: "subscription" })
+    );
+
+    expect(res.status).toBe(201);
+    const body = await res.json();
+    expect(body.purchase_order_id).toBeNull();
+  });
+
+  it("rejects a purchaseOrderId that is a well-formed UUID but doesn't reference an existing purchase order", async () => {
+    const vendor = await createTestVendor();
+    const res = await POST(
+      postRequest({
+        name: "Adobe Creative Cloud",
+        vendorId: vendor.id,
+        seatsTotal: 10,
+        licenseType: "subscription",
+        purchaseOrderId: "00000000-0000-0000-0000-000000000000",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/purchaseOrderId/i);
+    expect(body.error).toMatch(/does not reference an existing purchase order/i);
+
+    // And it must not have created anything.
+    const remaining = await prisma.license.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("rejects a purchaseOrderId that is not a valid UUID", async () => {
+    const vendor = await createTestVendor();
+    const res = await POST(
+      postRequest({
+        name: "Adobe Creative Cloud",
+        vendorId: vendor.id,
+        seatsTotal: 10,
+        licenseType: "subscription",
+        purchaseOrderId: "not-a-uuid",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/purchaseOrderId/i);
+  });
+
   it("rejects an invalid JSON body", async () => {
     const req = new Request("http://localhost/api/licenses", {
       method: "POST",
@@ -406,13 +657,16 @@ describe("POST /api/licenses", () => {
 
 describe("GET /api/licenses", () => {
   it("lists created licenses, newest first", async () => {
+    const vendor1 = await createTestVendor({ name: "Microsoft VN" });
+    const vendor2 = await createTestVendor({ name: "Adobe VN" });
+
     await POST(
-      postRequest({ name: "Windows Server 2022", vendor: "Microsoft", seatsTotal: 5, licenseType: "perpetual" })
+      postRequest({ name: "Windows Server 2022", vendorId: vendor1.id, seatsTotal: 5, licenseType: "perpetual" })
     );
     // Ensure a distinct created_at ordering even on fast filesystems/clocks.
     await new Promise((resolve) => setTimeout(resolve, 5));
     await POST(
-      postRequest({ name: "Adobe Creative Cloud", vendor: "Adobe", seatsTotal: 10, licenseType: "subscription" })
+      postRequest({ name: "Adobe Creative Cloud", vendorId: vendor2.id, seatsTotal: 10, licenseType: "subscription" })
     );
 
     const res = await GET();
@@ -423,8 +677,8 @@ describe("GET /api/licenses", () => {
     expect(body).toHaveLength(2);
 
     // newest first
-    expect(body[0]).toMatchObject({ name: "Adobe Creative Cloud", vendor: "Adobe" });
+    expect(body[0]).toMatchObject({ name: "Adobe Creative Cloud", vendor_id: vendor2.id });
-    expect(body[1]).toMatchObject({ name: "Windows Server 2022", vendor: "Microsoft" });
+    expect(body[1]).toMatchObject({ name: "Windows Server 2022", vendor_id: vendor1.id });
   });
 
   it("returns an empty list when there are no licenses", async () => {
@@ -440,10 +694,11 @@ describe("auth gating on /api/licenses", () => {
   // session presence, per the flat permission model (no role/permission
   // logic).
   it("POST /api/licenses returns 401 without a session", async () => {
+    const vendor = await createTestVendor();
     mockedAuth.mockResolvedValue(null);
 
     const res = await POST(
-      postRequest({ name: "Adobe Creative Cloud", vendor: "Adobe", seatsTotal: 10, licenseType: "subscription" })
+      postRequest({ name: "Adobe Creative Cloud", vendorId: vendor.id, seatsTotal: 10, licenseType: "subscription" })
     );
 
     expect(res.status).toBe(401);

tests/purchase-orders.test.ts

@@ -0,0 +1,577 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import type { Mock } from "vitest";
+import type { Session } from "next-auth";
+import {
+  createPurchaseOrder,
+  listPurchaseOrders,
+  validateCreatePurchaseOrderInput,
+} from "@/lib/purchase-orders";
+import { prisma } from "@/lib/prisma";
+
+// Note: this file has two layers of coverage, mirroring tests/licenses.test.ts:
+// - lib-level tests below exercise src/lib/purchase-orders.ts directly
+//   (validation, co-nullability refine, FK error handling, list ordering).
+// - route-level tests (further down) exercise
+//   src/app/api/purchase-orders/route.ts over HTTP, including the auth() gate.
+vi.mock("@/auth", () => ({ auth: vi.fn() }));
+
+import { GET, POST } from "@/app/api/purchase-orders/route";
+import { auth } from "@/auth";
+
+const mockedAuth = auth as unknown as Mock<() => Promise<Session | null>>;
+
+const testSession: Session = {
+  user: { id: "test-user-id" },
+  expires: new Date(Date.now() + 60 * 60 * 1000).toISOString(),
+};
+
+function postRequest(body: unknown): Request {
+  return new Request("http://localhost/api/purchase-orders", {
+    method: "POST",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify(body),
+  });
+}
+
+// PurchaseOrder.vendorId/receivedById are real FKs to Vendor/Employee (see
+// schema.prisma / src/lib/purchase-orders.ts) — tests that need valid ids
+// create real rows first and use their ids. Mirrors
+// tests/licenses.test.ts's createTestVendor() and tests/requests.test.ts's
+// createTestEmployee() helpers.
+function createTestVendor(overrides: { name?: string } = {}) {
+  return prisma.vendor.create({
+    data: {
+      name: overrides.name ?? "Test Vendor",
+      contactEmail: "[email protected]",
+      contactPhone: "0281234567",
+      address: "123 Test Street",
+    },
+  });
+}
+
+function createTestEmployee(overrides: { name?: string; department?: string } = {}) {
+  return prisma.employee.create({
+    data: {
+      name: overrides.name ?? "Test Employee",
+      department: overrides.department ?? "IT",
+    },
+  });
+}
+
+beforeEach(async () => {
+  // Each test starts from empty tables so listing/order assertions are
+  // deterministic. purchase_orders must be cleared before vendors/employees
+  // since purchase_orders has FKs (ON DELETE RESTRICT to vendors, ON DELETE
+  // SET NULL to employees) to both.
+  await prisma.purchaseOrder.deleteMany();
+  await prisma.vendor.deleteMany();
+  await prisma.employee.deleteMany();
+  // Default to a logged-in session — the lib-level tests below don't go
+  // through the route at all (so this is a no-op for them), and the
+  // route-level tests exercise business logic, not auth gating (that's
+  // covered by the "auth gating" describe block further down).
+  mockedAuth.mockResolvedValue(testSession);
+});
+
+describe("validateCreatePurchaseOrderInput", () => {
+  it("accepts valid input with no receivedAt/receivedById (not yet received)", () => {
+    const result = validateCreatePurchaseOrderInput({
+      vendorId: "11111111-1111-1111-1111-111111111111",
+      orderDate: "2026-08-01",
+      expectedDate: "2026-08-10",
+    });
+
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value.vendorId).toBe("11111111-1111-1111-1111-111111111111");
+      expect(result.value.orderDate).toBeInstanceOf(Date);
+      expect(result.value.expectedDate).toBeInstanceOf(Date);
+      expect(result.value.receivedAt).toBeUndefined();
+      expect(result.value.receivedById).toBeUndefined();
+    }
+  });
+
+  it("accepts valid input with both receivedAt and receivedById explicitly null (not yet received)", () => {
+    const result = validateCreatePurchaseOrderInput({
+      vendorId: "11111111-1111-1111-1111-111111111111",
+      orderDate: "2026-08-01",
+      expectedDate: "2026-08-10",
+      receivedAt: null,
+      receivedById: null,
+    });
+
+    expect(result.ok).toBe(true);
+  });
+
+  it("accepts valid input with both receivedAt and receivedById set (received)", () => {
+    const result = validateCreatePurchaseOrderInput({
+      vendorId: "11111111-1111-1111-1111-111111111111",
+      orderDate: "2026-08-01",
+      expectedDate: "2026-08-10",
+      receivedAt: "2026-08-12",
+      receivedById: "22222222-2222-2222-2222-222222222222",
+    });
+
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value.receivedAt).toBeInstanceOf(Date);
+      expect(result.value.receivedById).toBe("22222222-2222-2222-2222-222222222222");
+    }
+  });
+
+  it("rejects receivedAt set without receivedById", () => {
+    const result = validateCreatePurchaseOrderInput({
+      vendorId: "11111111-1111-1111-1111-111111111111",
+      orderDate: "2026-08-01",
+      expectedDate: "2026-08-10",
+      receivedAt: "2026-08-12",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/receivedAt/i);
+      expect(result.error).toMatch(/receivedById/i);
+    }
+  });
+
+  it("rejects receivedById set without receivedAt", () => {
+    const result = validateCreatePurchaseOrderInput({
+      vendorId: "11111111-1111-1111-1111-111111111111",
+      orderDate: "2026-08-01",
+      expectedDate: "2026-08-10",
+      receivedById: "22222222-2222-2222-2222-222222222222",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/receivedAt/i);
+      expect(result.error).toMatch(/receivedById/i);
+    }
+  });
+
+  it("rejects a missing vendorId", () => {
+    const result = validateCreatePurchaseOrderInput({
+      orderDate: "2026-08-01",
+      expectedDate: "2026-08-10",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/vendorId/i);
+    }
+  });
+
+  it("rejects a vendorId that is not a valid UUID", () => {
+    const result = validateCreatePurchaseOrderInput({
+      vendorId: "not-a-uuid",
+      orderDate: "2026-08-01",
+      expectedDate: "2026-08-10",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/vendorId/i);
+    }
+  });
+
+  it("rejects a missing orderDate", () => {
+    const result = validateCreatePurchaseOrderInput({
+      vendorId: "11111111-1111-1111-1111-111111111111",
+      expectedDate: "2026-08-10",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/orderDate/i);
+    }
+  });
+
+  it("rejects an invalid expectedDate", () => {
+    const result = validateCreatePurchaseOrderInput({
+      vendorId: "11111111-1111-1111-1111-111111111111",
+      orderDate: "2026-08-01",
+      expectedDate: "not-a-date",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/expectedDate/i);
+    }
+  });
+
+  it("rejects a receivedById that is not a valid UUID", () => {
+    const result = validateCreatePurchaseOrderInput({
+      vendorId: "11111111-1111-1111-1111-111111111111",
+      orderDate: "2026-08-01",
+      expectedDate: "2026-08-10",
+      receivedAt: "2026-08-12",
+      receivedById: "not-a-uuid",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/receivedById/i);
+    }
+  });
+});
+
+describe("createPurchaseOrder", () => {
+  it("creates a purchase order that is not yet received", async () => {
+    const vendor = await createTestVendor();
+    const result = validateCreatePurchaseOrderInput({
+      vendorId: vendor.id,
+      orderDate: "2026-08-01",
+      expectedDate: "2026-08-10",
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createPurchaseOrder(result.value);
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    const record = created.value;
+
+    expect(record.vendor_id).toBe(vendor.id);
+    expect(record.received_at).toBeNull();
+    expect(record.received_by).toBeNull();
+    expect(typeof record.id).toBe("string");
+    expect(record.id.length).toBeGreaterThan(0);
+    expect(Number.isNaN(Date.parse(record.order_date))).toBe(false);
+    expect(Number.isNaN(Date.parse(record.expected_date))).toBe(false);
+    expect(Number.isNaN(Date.parse(record.created_at))).toBe(false);
+  });
+
+  it("creates a purchase order that has already been received", async () => {
+    const vendor = await createTestVendor();
+    const employee = await createTestEmployee();
+    const result = validateCreatePurchaseOrderInput({
+      vendorId: vendor.id,
+      orderDate: "2026-08-01",
+      expectedDate: "2026-08-10",
+      receivedAt: "2026-08-12",
+      receivedById: employee.id,
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createPurchaseOrder(result.value);
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    const record = created.value;
+
+    expect(record.received_by).toBe(employee.id);
+    expect(Number.isNaN(Date.parse(record.received_at as string))).toBe(false);
+  });
+
+  it("returns a clean error when vendorId doesn't reference an existing vendor", async () => {
+    const result = validateCreatePurchaseOrderInput({
+      vendorId: "00000000-0000-0000-0000-000000000000",
+      orderDate: "2026-08-01",
+      expectedDate: "2026-08-10",
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createPurchaseOrder(result.value);
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/vendorId/i);
+    expect(created.error).toMatch(/does not reference an existing vendor/i);
+
+    const remaining = await prisma.purchaseOrder.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("returns a clean error when receivedById doesn't reference an existing employee", async () => {
+    const vendor = await createTestVendor();
+    const result = validateCreatePurchaseOrderInput({
+      vendorId: vendor.id,
+      orderDate: "2026-08-01",
+      expectedDate: "2026-08-10",
+      receivedAt: "2026-08-12",
+      receivedById: "00000000-0000-0000-0000-000000000000",
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const created = await createPurchaseOrder(result.value);
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/receivedById/i);
+    expect(created.error).toMatch(/does not reference an existing employee/i);
+
+    const remaining = await prisma.purchaseOrder.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+});
+
+describe("listPurchaseOrders", () => {
+  it("lists created purchase orders, newest first", async () => {
+    const vendor1 = await createTestVendor({ name: "Microsoft VN" });
+    const vendor2 = await createTestVendor({ name: "Adobe VN" });
+
+    const first = validateCreatePurchaseOrderInput({
+      vendorId: vendor1.id,
+      orderDate: "2026-08-01",
+      expectedDate: "2026-08-10",
+    });
+    expect(first.ok).toBe(true);
+    if (first.ok) await createPurchaseOrder(first.value);
+
+    // Ensure a distinct created_at ordering even on fast filesystems/clocks.
+    await new Promise((resolve) => setTimeout(resolve, 5));
+
+    const second = validateCreatePurchaseOrderInput({
+      vendorId: vendor2.id,
+      orderDate: "2026-08-02",
+      expectedDate: "2026-08-11",
+    });
+    expect(second.ok).toBe(true);
+    if (second.ok) await createPurchaseOrder(second.value);
+
+    const records = await listPurchaseOrders();
+
+    expect(records).toHaveLength(2);
+    // newest first
+    expect(records[0]).toMatchObject({ vendor_id: vendor2.id });
+    expect(records[1]).toMatchObject({ vendor_id: vendor1.id });
+  });
+
+  it("returns an empty list when there are no purchase orders", async () => {
+    const records = await listPurchaseOrders();
+    expect(records).toEqual([]);
+  });
+});
+
+describe("POST /api/purchase-orders", () => {
+  it("creates a purchase order that is not yet received on valid input", async () => {
+    const vendor = await createTestVendor();
+    const res = await POST(
+      postRequest({
+        vendorId: vendor.id,
+        orderDate: "2026-08-01",
+        expectedDate: "2026-08-10",
+      })
+    );
+
+    expect(res.status).toBe(201);
+    const body = await res.json();
+
+    expect(body).toMatchObject({ vendor_id: vendor.id, received_at: null, received_by: null });
+    expect(typeof body.id).toBe("string");
+    expect(body.id.length).toBeGreaterThan(0);
+    expect(Number.isNaN(Date.parse(body.order_date))).toBe(false);
+    expect(Number.isNaN(Date.parse(body.expected_date))).toBe(false);
+    expect(Number.isNaN(Date.parse(body.created_at))).toBe(false);
+  });
+
+  it("creates a purchase order that has already been received", async () => {
+    const vendor = await createTestVendor();
+    const employee = await createTestEmployee();
+    const res = await POST(
+      postRequest({
+        vendorId: vendor.id,
+        orderDate: "2026-08-01",
+        expectedDate: "2026-08-10",
+        receivedAt: "2026-08-12",
+        receivedById: employee.id,
+      })
+    );
+
+    expect(res.status).toBe(201);
+    const body = await res.json();
+    expect(body.received_by).toBe(employee.id);
+    expect(Number.isNaN(Date.parse(body.received_at))).toBe(false);
+  });
+
+  it("rejects a missing vendorId", async () => {
+    const res = await POST(
+      postRequest({ orderDate: "2026-08-01", expectedDate: "2026-08-10" })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/vendorId/i);
+  });
+
+  it("rejects a vendorId that is a well-formed UUID but doesn't reference an existing vendor", async () => {
+    const res = await POST(
+      postRequest({
+        vendorId: "00000000-0000-0000-0000-000000000000",
+        orderDate: "2026-08-01",
+        expectedDate: "2026-08-10",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/vendorId/i);
+    expect(body.error).toMatch(/does not reference an existing vendor/i);
+
+    // And it must not have created anything.
+    const remaining = await prisma.purchaseOrder.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("rejects a receivedById that is a well-formed UUID but doesn't reference an existing employee", async () => {
+    const vendor = await createTestVendor();
+    const res = await POST(
+      postRequest({
+        vendorId: vendor.id,
+        orderDate: "2026-08-01",
+        expectedDate: "2026-08-10",
+        receivedAt: "2026-08-12",
+        receivedById: "00000000-0000-0000-0000-000000000000",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/receivedById/i);
+    expect(body.error).toMatch(/does not reference an existing employee/i);
+
+    // And it must not have created anything.
+    const remaining = await prisma.purchaseOrder.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("rejects receivedAt set without receivedById", async () => {
+    const vendor = await createTestVendor();
+    const res = await POST(
+      postRequest({
+        vendorId: vendor.id,
+        orderDate: "2026-08-01",
+        expectedDate: "2026-08-10",
+        receivedAt: "2026-08-12",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/receivedAt/i);
+    expect(body.error).toMatch(/receivedById/i);
+  });
+
+  it("rejects receivedById set without receivedAt", async () => {
+    const vendor = await createTestVendor();
+    const employee = await createTestEmployee();
+    const res = await POST(
+      postRequest({
+        vendorId: vendor.id,
+        orderDate: "2026-08-01",
+        expectedDate: "2026-08-10",
+        receivedById: employee.id,
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/receivedAt/i);
+    expect(body.error).toMatch(/receivedById/i);
+  });
+
+  it("rejects an invalid expectedDate", async () => {
+    const vendor = await createTestVendor();
+    const res = await POST(
+      postRequest({
+        vendorId: vendor.id,
+        orderDate: "2026-08-01",
+        expectedDate: "not-a-date",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/expectedDate/i);
+  });
+
+  it("rejects an invalid JSON body", async () => {
+    const req = new Request("http://localhost/api/purchase-orders", {
+      method: "POST",
+      headers: { "content-type": "application/json" },
+      body: "not json",
+    });
+
+    const res = await POST(req);
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/JSON/i);
+  });
+
+  it("rejects a non-object JSON body", async () => {
+    // Note: arrays are `typeof "object"` in JS, so they pass the route's
+    // object check (same behavior as /api/licenses) — use a JSON string
+    // primitive here to actually exercise the "not an object" branch.
+    const res = await POST(postRequest("not an object"));
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/JSON object/i);
+  });
+});
+
+describe("GET /api/purchase-orders", () => {
+  it("lists created purchase orders, newest first", async () => {
+    const vendor1 = await createTestVendor({ name: "Microsoft VN" });
+    const vendor2 = await createTestVendor({ name: "Adobe VN" });
+
+    await POST(
+      postRequest({ vendorId: vendor1.id, orderDate: "2026-08-01", expectedDate: "2026-08-10" })
+    );
+    // Ensure a distinct created_at ordering even on fast filesystems/clocks.
+    await new Promise((resolve) => setTimeout(resolve, 5));
+    await POST(
+      postRequest({ vendorId: vendor2.id, orderDate: "2026-08-02", expectedDate: "2026-08-11" })
+    );
+
+    const res = await GET();
+    expect(res.status).toBe(200);
+
+    const body = await res.json();
+    expect(Array.isArray(body)).toBe(true);
+    expect(body).toHaveLength(2);
+
+    // newest first
+    expect(body[0]).toMatchObject({ vendor_id: vendor2.id });
+    expect(body[1]).toMatchObject({ vendor_id: vendor1.id });
+  });
+
+  it("returns an empty list when there are no purchase orders", async () => {
+    const res = await GET();
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body).toEqual([]);
+  });
+});
+
+describe("auth gating on /api/purchase-orders", () => {
+  // Mirrors tests/licenses.test.ts's "auth gating" block — only checks
+  // session presence, per the flat permission model (no role/permission
+  // logic).
+  it("POST /api/purchase-orders returns 401 without a session", async () => {
+    const vendor = await createTestVendor();
+    mockedAuth.mockResolvedValue(null);
+
+    const res = await POST(
+      postRequest({ vendorId: vendor.id, orderDate: "2026-08-01", expectedDate: "2026-08-10" })
+    );
+
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body).toEqual({ error: "Unauthorized" });
+
+    // And it must not have created anything.
+    const remaining = await prisma.purchaseOrder.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("GET /api/purchase-orders returns 401 without a session", async () => {
+    mockedAuth.mockResolvedValue(null);
+
+    const res = await GET();
+
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body).toEqual({ error: "Unauthorized" });
+  });
+});

tests/requests.test.ts

@@ -50,12 +50,44 @@ function createTestEmployee(overrides: { name?: string; department?: string } =
   });
 }
 
+// Request.purchaseOrderId is a real FK to PurchaseOrder (see schema.prisma /
+// src/lib/requests.ts) — tests that need a valid purchase_order_id create a
+// real PurchaseOrder row (and the Vendor it requires) first and use its id.
+// Mirrors tests/licenses.test.ts's createTestVendor()/createTestPurchaseOrder()
+// helpers.
+function createTestVendor(overrides: { name?: string } = {}) {
+  return prisma.vendor.create({
+    data: {
+      name: overrides.name ?? "Test Vendor",
+      contactEmail: "[email protected]",
+      contactPhone: "0281234567",
+      address: "123 Test Street",
+    },
+  });
+}
+
+function createTestPurchaseOrder(overrides: { vendorId?: string } = {}) {
+  return prisma.purchaseOrder.create({
+    data: {
+      vendorId: overrides.vendorId as string,
+      orderDate: new Date("2026-08-01"),
+      expectedDate: new Date("2026-08-10"),
+    },
+  });
+}
+
 beforeEach(async () => {
   // Each test starts from empty tables so listing/order assertions are
-  // deterministic. requests must be cleared before employees since
+  // deterministic. requests must be cleared before employees/purchase_orders
-  // requests.employee_id has an FK (ON DELETE RESTRICT) to employees.
+  // since requests.employee_id has an FK (ON DELETE RESTRICT) to employees
+  // and requests.purchase_order_id has an FK (ON DELETE SET NULL) to
+  // purchase_orders. purchase_orders must be cleared before employees/vendors
+  // (ON DELETE RESTRICT to vendors, mirrors tests/licenses.test.ts) — order:
+  // requests -> purchase_orders -> employees -> vendors.
   await prisma.request.deleteMany();
+  await prisma.purchaseOrder.deleteMany();
   await prisma.employee.deleteMany();
+  await prisma.vendor.deleteMany();
   // Default to a logged-in session — the tests below exercise request
   // business logic, not auth gating (that's covered by the "auth gating"
   // describe block further down).
@@ -141,6 +173,72 @@ describe("POST /api/requests", () => {
     const remaining = await prisma.request.findMany();
     expect(remaining).toHaveLength(0);
   });
+
+  it("creates a request with a purchase_order_id that references a real purchase order", async () => {
+    const employee = await createTestEmployee();
+    const vendor = await createTestVendor();
+    const purchaseOrder = await createTestPurchaseOrder({ vendorId: vendor.id });
+    const res = await POST(
+      postRequest({
+        employee_id: employee.id,
+        type: "asset",
+        reason: "New laptop for onboarding",
+        purchase_order_id: purchaseOrder.id,
+      })
+    );
+
+    expect(res.status).toBe(201);
+    const body = await res.json();
+    expect(body.purchase_order_id).toBe(purchaseOrder.id);
+  });
+
+  it("creates a request with no purchase_order_id (stays null)", async () => {
+    const employee = await createTestEmployee();
+    const res = await POST(
+      postRequest({ employee_id: employee.id, type: "asset", reason: "New laptop for onboarding" })
+    );
+
+    expect(res.status).toBe(201);
+    const body = await res.json();
+    expect(body.purchase_order_id).toBeNull();
+  });
+
+  it("rejects a purchase_order_id that is a well-formed UUID but doesn't reference an existing purchase order", async () => {
+    const employee = await createTestEmployee();
+    const res = await POST(
+      postRequest({
+        employee_id: employee.id,
+        type: "asset",
+        reason: "New laptop for onboarding",
+        purchase_order_id: "00000000-0000-0000-0000-000000000000",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/purchase_order_id/i);
+    expect(body.error).toMatch(/does not reference an existing purchase order/i);
+
+    // And it must not have created anything.
+    const remaining = await prisma.request.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("rejects a purchase_order_id that is not a valid UUID", async () => {
+    const employee = await createTestEmployee();
+    const res = await POST(
+      postRequest({
+        employee_id: employee.id,
+        type: "asset",
+        reason: "New laptop for onboarding",
+        purchase_order_id: "not-a-uuid",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/purchase_order_id/i);
+  });
 });
 
 describe("GET /api/requests", () => {

tests/vendors.test.ts

@@ -0,0 +1,476 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import type { Mock } from "vitest";
+import type { Session } from "next-auth";
+import {
+  createVendor,
+  listVendors,
+  validateCreateVendorInput,
+} from "@/lib/vendors";
+import { prisma } from "@/lib/prisma";
+
+// Note: this file has two layers of coverage, mirroring tests/licenses.test.ts:
+// - lib-level tests below exercise src/lib/vendors.ts directly (validation,
+//   nullable taxCode/notes, list ordering).
+// - route-level tests (further down) exercise src/app/api/vendors/route.ts
+//   over HTTP, including the auth() gate — mirrors tests/licenses.test.ts's
+//   @/auth mocking pattern.
+vi.mock("@/auth", () => ({ auth: vi.fn() }));
+
+import { GET, POST } from "@/app/api/vendors/route";
+import { auth } from "@/auth";
+
+const mockedAuth = auth as unknown as Mock<() => Promise<Session | null>>;
+
+const testSession: Session = {
+  user: { id: "test-user-id" },
+  expires: new Date(Date.now() + 60 * 60 * 1000).toISOString(),
+};
+
+function postRequest(body: unknown): Request {
+  return new Request("http://localhost/api/vendors", {
+    method: "POST",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify(body),
+  });
+}
+
+beforeEach(async () => {
+  // Each test starts from an empty table so listing/order assertions are
+  // deterministic.
+  await prisma.vendor.deleteMany();
+  // Default to a logged-in session — the lib-level tests below don't go
+  // through the route at all (so this is a no-op for them), and the
+  // route-level tests exercise business logic, not auth gating (that's
+  // covered by the "auth gating" describe block further down).
+  mockedAuth.mockResolvedValue(testSession);
+});
+
+describe("validateCreateVendorInput", () => {
+  it("accepts valid input with taxCode and notes", () => {
+    const result = validateCreateVendorInput({
+      name: "FPT Trading",
+      contactEmail: "[email protected]",
+      contactPhone: "0281234567",
+      address: "123 Nguyen Van Linh, Q7, HCMC",
+      taxCode: "0301234567",
+      notes: "Preferred reseller for Dell laptops",
+    });
+
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value).toMatchObject({
+        name: "FPT Trading",
+        contactEmail: "[email protected]",
+        contactPhone: "0281234567",
+        address: "123 Nguyen Van Linh, Q7, HCMC",
+        taxCode: "0301234567",
+        notes: "Preferred reseller for Dell laptops",
+      });
+    }
+  });
+
+  it("accepts valid input with no taxCode/notes", () => {
+    const result = validateCreateVendorInput({
+      name: "Synnex FPT",
+      contactEmail: "[email protected]",
+      contactPhone: "0287654321",
+      address: "456 Le Van Viet, Q9, HCMC",
+    });
+
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value.taxCode).toBeUndefined();
+      expect(result.value.notes).toBeUndefined();
+    }
+  });
+
+  it("rejects an empty name", () => {
+    const result = validateCreateVendorInput({
+      name: "",
+      contactEmail: "[email protected]",
+      contactPhone: "0281234567",
+      address: "123 Nguyen Van Linh, Q7, HCMC",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/name/i);
+    }
+  });
+
+  it("rejects an invalid contactEmail", () => {
+    const result = validateCreateVendorInput({
+      name: "FPT Trading",
+      contactEmail: "not-an-email",
+      contactPhone: "0281234567",
+      address: "123 Nguyen Van Linh, Q7, HCMC",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/contactEmail/i);
+    }
+  });
+
+  it("rejects a missing contactEmail", () => {
+    const result = validateCreateVendorInput({
+      name: "FPT Trading",
+      contactPhone: "0281234567",
+      address: "123 Nguyen Van Linh, Q7, HCMC",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/contactEmail/i);
+    }
+  });
+
+  it("rejects an empty contactPhone", () => {
+    const result = validateCreateVendorInput({
+      name: "FPT Trading",
+      contactEmail: "[email protected]",
+      contactPhone: "",
+      address: "123 Nguyen Van Linh, Q7, HCMC",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/contactPhone/i);
+    }
+  });
+
+  it("rejects an empty address", () => {
+    const result = validateCreateVendorInput({
+      name: "FPT Trading",
+      contactEmail: "[email protected]",
+      contactPhone: "0281234567",
+      address: "",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/address/i);
+    }
+  });
+
+  it("rejects an empty taxCode when provided", () => {
+    const result = validateCreateVendorInput({
+      name: "FPT Trading",
+      contactEmail: "[email protected]",
+      contactPhone: "0281234567",
+      address: "123 Nguyen Van Linh, Q7, HCMC",
+      taxCode: "",
+    });
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/taxCode/i);
+    }
+  });
+
+  it("accepts a null taxCode/notes explicitly", () => {
+    const result = validateCreateVendorInput({
+      name: "FPT Trading",
+      contactEmail: "[email protected]",
+      contactPhone: "0281234567",
+      address: "123 Nguyen Van Linh, Q7, HCMC",
+      taxCode: null,
+      notes: null,
+    });
+
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value.taxCode).toBeNull();
+      expect(result.value.notes).toBeNull();
+    }
+  });
+});
+
+describe("createVendor", () => {
+  it("creates a vendor with taxCode and notes", async () => {
+    const result = validateCreateVendorInput({
+      name: "FPT Trading",
+      contactEmail: "[email protected]",
+      contactPhone: "0281234567",
+      address: "123 Nguyen Van Linh, Q7, HCMC",
+      taxCode: "0301234567",
+      notes: "Preferred reseller for Dell laptops",
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const record = await createVendor(result.value);
+
+    expect(record).toMatchObject({
+      name: "FPT Trading",
+      contact_email: "[email protected]",
+      contact_phone: "0281234567",
+      address: "123 Nguyen Van Linh, Q7, HCMC",
+      tax_code: "0301234567",
+      notes: "Preferred reseller for Dell laptops",
+    });
+    expect(typeof record.id).toBe("string");
+    expect(record.id.length).toBeGreaterThan(0);
+    expect(Number.isNaN(Date.parse(record.created_at))).toBe(false);
+  });
+
+  it("creates a vendor with no taxCode/notes (both null)", async () => {
+    const result = validateCreateVendorInput({
+      name: "Synnex FPT",
+      contactEmail: "[email protected]",
+      contactPhone: "0287654321",
+      address: "456 Le Van Viet, Q9, HCMC",
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+
+    const record = await createVendor(result.value);
+
+    expect(record.tax_code).toBeNull();
+    expect(record.notes).toBeNull();
+  });
+});
+
+describe("listVendors", () => {
+  it("lists created vendors, newest first", async () => {
+    const first = validateCreateVendorInput({
+      name: "Synnex FPT",
+      contactEmail: "[email protected]",
+      contactPhone: "0287654321",
+      address: "456 Le Van Viet, Q9, HCMC",
+    });
+    expect(first.ok).toBe(true);
+    if (first.ok) await createVendor(first.value);
+
+    // Ensure a distinct created_at ordering even on fast filesystems/clocks.
+    await new Promise((resolve) => setTimeout(resolve, 5));
+
+    const second = validateCreateVendorInput({
+      name: "FPT Trading",
+      contactEmail: "[email protected]",
+      contactPhone: "0281234567",
+      address: "123 Nguyen Van Linh, Q7, HCMC",
+    });
+    expect(second.ok).toBe(true);
+    if (second.ok) await createVendor(second.value);
+
+    const records = await listVendors();
+
+    expect(records).toHaveLength(2);
+    // newest first
+    expect(records[0]).toMatchObject({ name: "FPT Trading" });
+    expect(records[1]).toMatchObject({ name: "Synnex FPT" });
+  });
+
+  it("returns an empty list when there are no vendors", async () => {
+    const records = await listVendors();
+    expect(records).toEqual([]);
+  });
+});
+
+describe("POST /api/vendors", () => {
+  it("creates a vendor on valid input", async () => {
+    const res = await POST(
+      postRequest({
+        name: "FPT Trading",
+        contactEmail: "[email protected]",
+        contactPhone: "0281234567",
+        address: "123 Nguyen Van Linh, Q7, HCMC",
+        taxCode: "0301234567",
+        notes: "Preferred reseller for Dell laptops",
+      })
+    );
+
+    expect(res.status).toBe(201);
+    const body = await res.json();
+
+    expect(body).toMatchObject({
+      name: "FPT Trading",
+      contact_email: "[email protected]",
+      contact_phone: "0281234567",
+      address: "123 Nguyen Van Linh, Q7, HCMC",
+      tax_code: "0301234567",
+      notes: "Preferred reseller for Dell laptops",
+    });
+    expect(typeof body.id).toBe("string");
+    expect(body.id.length).toBeGreaterThan(0);
+    expect(Number.isNaN(Date.parse(body.created_at))).toBe(false);
+  });
+
+  it("creates a vendor with no taxCode/notes", async () => {
+    const res = await POST(
+      postRequest({
+        name: "Synnex FPT",
+        contactEmail: "[email protected]",
+        contactPhone: "0287654321",
+        address: "456 Le Van Viet, Q9, HCMC",
+      })
+    );
+
+    expect(res.status).toBe(201);
+    const body = await res.json();
+    expect(body.tax_code).toBeNull();
+    expect(body.notes).toBeNull();
+  });
+
+  it("rejects an empty name", async () => {
+    const res = await POST(
+      postRequest({
+        name: "",
+        contactEmail: "[email protected]",
+        contactPhone: "0281234567",
+        address: "123 Nguyen Van Linh, Q7, HCMC",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/name/i);
+  });
+
+  it("rejects an invalid contactEmail", async () => {
+    const res = await POST(
+      postRequest({
+        name: "FPT Trading",
+        contactEmail: "not-an-email",
+        contactPhone: "0281234567",
+        address: "123 Nguyen Van Linh, Q7, HCMC",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/contactEmail/i);
+  });
+
+  it("rejects an empty contactPhone", async () => {
+    const res = await POST(
+      postRequest({
+        name: "FPT Trading",
+        contactEmail: "[email protected]",
+        contactPhone: "",
+        address: "123 Nguyen Van Linh, Q7, HCMC",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/contactPhone/i);
+  });
+
+  it("rejects an empty address", async () => {
+    const res = await POST(
+      postRequest({
+        name: "FPT Trading",
+        contactEmail: "[email protected]",
+        contactPhone: "0281234567",
+        address: "",
+      })
+    );
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/address/i);
+  });
+
+  it("rejects an invalid JSON body", async () => {
+    const req = new Request("http://localhost/api/vendors", {
+      method: "POST",
+      headers: { "content-type": "application/json" },
+      body: "not json",
+    });
+
+    const res = await POST(req);
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/JSON/i);
+  });
+
+  it("rejects a non-object JSON body", async () => {
+    // Note: arrays are `typeof "object"` in JS, so they pass the route's
+    // object check (same behavior as /api/licenses) — use a JSON string
+    // primitive here to actually exercise the "not an object" branch.
+    const res = await POST(postRequest("not an object"));
+
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/JSON object/i);
+  });
+});
+
+describe("GET /api/vendors", () => {
+  it("lists created vendors, newest first", async () => {
+    await POST(
+      postRequest({
+        name: "Synnex FPT",
+        contactEmail: "[email protected]",
+        contactPhone: "0287654321",
+        address: "456 Le Van Viet, Q9, HCMC",
+      })
+    );
+    // Ensure a distinct created_at ordering even on fast filesystems/clocks.
+    await new Promise((resolve) => setTimeout(resolve, 5));
+    await POST(
+      postRequest({
+        name: "FPT Trading",
+        contactEmail: "[email protected]",
+        contactPhone: "0281234567",
+        address: "123 Nguyen Van Linh, Q7, HCMC",
+      })
+    );
+
+    const res = await GET();
+    expect(res.status).toBe(200);
+
+    const body = await res.json();
+    expect(Array.isArray(body)).toBe(true);
+    expect(body).toHaveLength(2);
+
+    // newest first
+    expect(body[0]).toMatchObject({ name: "FPT Trading" });
+    expect(body[1]).toMatchObject({ name: "Synnex FPT" });
+  });
+
+  it("returns an empty list when there are no vendors", async () => {
+    const res = await GET();
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body).toEqual([]);
+  });
+});
+
+describe("auth gating on /api/vendors", () => {
+  // Mirrors tests/licenses.test.ts's "auth gating" block — only checks
+  // session presence, per the flat permission model (no role/permission
+  // logic).
+  it("POST /api/vendors returns 401 without a session", async () => {
+    mockedAuth.mockResolvedValue(null);
+
+    const res = await POST(
+      postRequest({
+        name: "FPT Trading",
+        contactEmail: "[email protected]",
+        contactPhone: "0281234567",
+        address: "123 Nguyen Van Linh, Q7, HCMC",
+      })
+    );
+
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body).toEqual({ error: "Unauthorized" });
+
+    // And it must not have created anything.
+    const remaining = await prisma.vendor.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("GET /api/vendors returns 401 without a session", async () => {
+    mockedAuth.mockResolvedValue(null);
+
+    const res = await GET();
+
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body).toEqual({ error: "Unauthorized" });
+  });
+});