diff --git a/tests/maintenance-records.test.ts b/tests/maintenance-records.test.ts
new file mode 100644
index 0000000..62230bb
--- /dev/null
+++ b/tests/maintenance-records.test.ts
@@ -0,0 +1,809 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import type { Mock } from "vitest";
+import type { Session } from "next-auth";
+import {
+  closeMaintenanceRecord,
+  createMaintenanceRecord,
+  listMaintenanceRecords,
+  validateCloseMaintenanceRecordInput,
+  validateCreateMaintenanceRecordInput,
+} from "@/lib/maintenance-records";
+import { prisma } from "@/lib/prisma";
+
+// This file has two layers of coverage, mirroring tests/assignments.test.ts:
+// - lib-level tests exercise src/lib/maintenance-records.ts directly
+//   (validation, transactional business rules).
+// - route-level tests exercise src/app/api/maintenance-records/route.ts and
+//   src/app/api/maintenance-records/[id]/route.ts over HTTP, including the
+//   auth() gate — mirrors tests/assignments.test.ts's @/auth mocking pattern.
+vi.mock("@/auth", () => ({ auth: vi.fn() }));
+
+import { GET, POST } from "@/app/api/maintenance-records/route";
+import { PATCH } from "@/app/api/maintenance-records/[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/maintenance-records", {
+    method: "POST",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify(body),
+  });
+}
+
+function patchRequest(body: unknown): Request {
+  return new Request("http://localhost/api/maintenance-records/x", {
+    method: "PATCH",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify(body),
+  });
+}
+
+// MaintenanceRecord.assetItemId is a real FK to AssetItem, which itself
+// requires a full AssetModel -> AssetCategory chain. Mirrors
+// tests/assignments.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-MAINT-${serialCounter}`,
+      modelId: overrides.modelId,
+      purchaseDate: new Date("2026-01-15"),
+      status: overrides.status ?? "in_stock",
+    },
+  });
+}
+
+// MaintenanceRecord.employeeId isn't a field on the model, but Assignment is
+// used to exercise the "active assignment blocks maintenance" rule, which
+// itself needs an Employee. Mirrors tests/assignments.test.ts's
+// createTestEmployee() helper.
+function createTestEmployee(overrides: { name?: string } = {}) {
+  return prisma.employee.create({
+    data: {
+      name: overrides.name ?? "Test Employee",
+      department: "IT",
+    },
+  });
+}
+
+// MaintenanceRecord.vendorId is a real (nullable) FK to Vendor. Mirrors
+// tests/assignments.test.ts's createTestVendor() helper.
+function createTestVendor(overrides: { name?: string } = {}) {
+  return prisma.vendor.create({
+    data: {
+      name: overrides.name ?? "Test Vendor",
+      contactEmail: "sales@testvendor.example",
+      contactPhone: "0281234567",
+      address: "123 Test Street",
+    },
+  });
+}
+
+beforeEach(async () => {
+  // Clear in FK-safe order: maintenance_records + assignments first
+  // (reference asset_items/licenses/vendors/employees), then asset_items/
+  // licenses (reference purchase_orders/vendors/models), then the rest.
+  await prisma.maintenanceRecord.deleteMany();
+  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("validateCreateMaintenanceRecordInput", () => {
+  it("accepts valid input without vendorId", () => {
+    const result = validateCreateMaintenanceRecordInput({
+      assetItemId: "11111111-1111-1111-1111-111111111111",
+      type: "repair",
+      issueDescription: "Screen flickers",
+      startDate: "2026-08-01",
+    });
+    expect(result.ok).toBe(true);
+  });
+
+  it("accepts valid input with vendorId set", () => {
+    const result = validateCreateMaintenanceRecordInput({
+      assetItemId: "11111111-1111-1111-1111-111111111111",
+      type: "warranty",
+      vendorId: "22222222-2222-2222-2222-222222222222",
+      issueDescription: "Battery swollen",
+      startDate: "2026-08-01",
+    });
+    expect(result.ok).toBe(true);
+  });
+
+  it("rejects a missing assetItemId", () => {
+    const result = validateCreateMaintenanceRecordInput({
+      type: "repair",
+      issueDescription: "Screen flickers",
+      startDate: "2026-08-01",
+    });
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/assetItemId/i);
+    }
+  });
+
+  it("rejects an invalid type", () => {
+    const result = validateCreateMaintenanceRecordInput({
+      assetItemId: "11111111-1111-1111-1111-111111111111",
+      type: "not-a-type",
+      issueDescription: "Screen flickers",
+      startDate: "2026-08-01",
+    });
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/type/i);
+    }
+  });
+});
+
+describe("createMaintenanceRecord", () => {
+  it("opens a maintenance record, flips AssetItem.status to repair", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+
+    const created = await createMaintenanceRecord({
+      assetItemId: assetItem.id,
+      type: "repair",
+      issueDescription: "Screen flickers",
+      startDate: new Date("2026-08-01"),
+    });
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    expect(created.value.asset_item_id).toBe(assetItem.id);
+    expect(created.value.vendor_id).toBeNull();
+    expect(created.value.end_date).toBeNull();
+
+    const updatedItem = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
+    expect(updatedItem.status).toBe("repair");
+  });
+
+  it("creates successfully without a vendorId", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+
+    const created = await createMaintenanceRecord({
+      assetItemId: assetItem.id,
+      type: "preventive",
+      issueDescription: "Routine cleaning",
+      startDate: new Date("2026-08-01"),
+    });
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    expect(created.value.vendor_id).toBeNull();
+  });
+
+  it("creates successfully with a vendorId", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+    const vendor = await createTestVendor();
+
+    const created = await createMaintenanceRecord({
+      assetItemId: assetItem.id,
+      type: "warranty",
+      vendorId: vendor.id,
+      issueDescription: "Battery swollen",
+      startDate: new Date("2026-08-01"),
+    });
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+    expect(created.value.vendor_id).toBe(vendor.id);
+  });
+
+  it("rejects opening a record for an AssetItem that has an active assignment", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId, status: "assigned" });
+    const employee = await createTestEmployee();
+    await prisma.assignment.create({
+      data: { employeeId: employee.id, assetItemId: assetItem.id, assignedAt: new Date() },
+    });
+
+    const created = await createMaintenanceRecord({
+      assetItemId: assetItem.id,
+      type: "repair",
+      issueDescription: "Screen flickers",
+      startDate: new Date("2026-08-01"),
+    });
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/active assignment/i);
+
+    const remaining = await prisma.maintenanceRecord.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("rejects opening a record for an AssetItem that is already retired", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId, status: "retired" });
+
+    const created = await createMaintenanceRecord({
+      assetItemId: assetItem.id,
+      type: "repair",
+      issueDescription: "Screen flickers",
+      startDate: new Date("2026-08-01"),
+    });
+    expect(created.ok).toBe(false);
+    if (created.ok) return;
+    expect(created.error).toMatch(/retired/i);
+
+    const remaining = await prisma.maintenanceRecord.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+
+  it("rejects opening a second record while one is already open for the same AssetItem", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+
+    const first = await createMaintenanceRecord({
+      assetItemId: assetItem.id,
+      type: "repair",
+      issueDescription: "Screen flickers",
+      startDate: new Date("2026-08-01"),
+    });
+    expect(first.ok).toBe(true);
+
+    const second = await createMaintenanceRecord({
+      assetItemId: assetItem.id,
+      type: "preventive",
+      issueDescription: "Another issue",
+      startDate: new Date("2026-08-02"),
+    });
+    expect(second.ok).toBe(false);
+    if (second.ok) return;
+    expect(second.error).toMatch(/already has an open maintenance record/i);
+
+    const records = await prisma.maintenanceRecord.findMany({ where: { assetItemId: assetItem.id } });
+    expect(records).toHaveLength(1);
+  });
+});
+
+describe("closeMaintenanceRecord", () => {
+  it.each(["in_stock", "retired"] as const)(
+    "closes a record and applies targetStatus %s to the AssetItem",
+    async (targetStatus) => {
+      const modelId = await createTestModelId();
+      const assetItem = await createTestAssetItem({ modelId });
+      const created = await createMaintenanceRecord({
+        assetItemId: assetItem.id,
+        type: "repair",
+        issueDescription: "Screen flickers",
+        startDate: new Date("2026-08-01"),
+      });
+      expect(created.ok).toBe(true);
+      if (!created.ok) return;
+
+      const closed = await closeMaintenanceRecord(created.value.id, {
+        endDate: new Date("2026-08-05"),
+        targetStatus,
+      });
+      expect(closed.ok).toBe(true);
+      if (!closed.ok) return;
+      expect(closed.value.end_date).not.toBeNull();
+
+      const item = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
+      expect(item.status).toBe(targetStatus);
+    }
+  );
+
+  it("rejects double-closing a record", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+    const created = await createMaintenanceRecord({
+      assetItemId: assetItem.id,
+      type: "repair",
+      issueDescription: "Screen flickers",
+      startDate: new Date("2026-08-01"),
+    });
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+
+    const firstClose = await closeMaintenanceRecord(created.value.id, {
+      endDate: new Date("2026-08-05"),
+      targetStatus: "in_stock",
+    });
+    expect(firstClose.ok).toBe(true);
+
+    const secondClose = await closeMaintenanceRecord(created.value.id, {
+      endDate: new Date("2026-08-06"),
+      targetStatus: "in_stock",
+    });
+    expect(secondClose.ok).toBe(false);
+    if (secondClose.ok) return;
+    expect(secondClose.status).toBe(400);
+    expect(secondClose.error).toMatch(/already been closed/i);
+  });
+
+  it("rejects an endDate before the record's startDate", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+    const created = await createMaintenanceRecord({
+      assetItemId: assetItem.id,
+      type: "repair",
+      issueDescription: "Screen flickers",
+      startDate: new Date("2026-08-05"),
+    });
+    expect(created.ok).toBe(true);
+    if (!created.ok) return;
+
+    const closed = await closeMaintenanceRecord(created.value.id, {
+      endDate: new Date("2026-08-01"),
+      targetStatus: "in_stock",
+    });
+    expect(closed.ok).toBe(false);
+    if (closed.ok) return;
+    expect(closed.status).toBe(400);
+    expect(closed.error).toMatch(/endDate must be on or after startDate/i);
+  });
+
+  it("returns 404 for a nonexistent record id", async () => {
+    const result = await closeMaintenanceRecord("00000000-0000-0000-0000-000000000000", {
+      endDate: new Date("2026-08-05"),
+      targetStatus: "in_stock",
+    });
+    expect(result.ok).toBe(false);
+    if (result.ok) return;
+    expect(result.status).toBe(404);
+    expect(result.error).toMatch(/not found/i);
+  });
+});
+
+describe("validateCloseMaintenanceRecordInput", () => {
+  it("accepts valid input", () => {
+    const result = validateCloseMaintenanceRecordInput({
+      endDate: "2026-08-05",
+      targetStatus: "in_stock",
+    });
+    expect(result.ok).toBe(true);
+  });
+
+  it("rejects a missing targetStatus", () => {
+    const result = validateCloseMaintenanceRecordInput({ endDate: "2026-08-05" });
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/targetStatus/i);
+    }
+  });
+
+  it("rejects a missing endDate", () => {
+    const result = validateCloseMaintenanceRecordInput({ targetStatus: "in_stock" });
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error).toMatch(/endDate/i);
+    }
+  });
+});
+
+describe("listMaintenanceRecords", () => {
+  it("lists created records, newest first", async () => {
+    const modelId = await createTestModelId();
+    const item1 = await createTestAssetItem({ modelId });
+    const item2 = await createTestAssetItem({ modelId });
+
+    const first = await createMaintenanceRecord({
+      assetItemId: item1.id,
+      type: "repair",
+      issueDescription: "Issue 1",
+      startDate: new Date("2026-08-01"),
+    });
+    expect(first.ok).toBe(true);
+    await new Promise((resolve) => setTimeout(resolve, 5));
+    const second = await createMaintenanceRecord({
+      assetItemId: item2.id,
+      type: "repair",
+      issueDescription: "Issue 2",
+      startDate: new Date("2026-08-01"),
+    });
+    expect(second.ok).toBe(true);
+
+    const records = await listMaintenanceRecords();
+    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 records", async () => {
+    const records = await listMaintenanceRecords();
+    expect(records).toEqual([]);
+  });
+});
+
+describe("POST /api/maintenance-records", () => {
+  it("creates a record on valid input", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+
+    const res = await POST(
+      postRequest({
+        assetItemId: assetItem.id,
+        type: "repair",
+        issueDescription: "Screen flickers",
+        startDate: "2026-08-01",
+      })
+    );
+    expect(res.status).toBe(201);
+    const body = await res.json();
+    expect(body).toMatchObject({
+      asset_item_id: assetItem.id,
+      type: "repair",
+      vendor_id: null,
+      end_date: null,
+    });
+
+    const item = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
+    expect(item.status).toBe("repair");
+  });
+
+  it("returns the full expected snake_case shape", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+    const vendor = await createTestVendor();
+
+    const res = await POST(
+      postRequest({
+        assetItemId: assetItem.id,
+        type: "warranty",
+        vendorId: vendor.id,
+        issueDescription: "Battery swollen",
+        startDate: "2026-08-01",
+      })
+    );
+    expect(res.status).toBe(201);
+    const body = await res.json();
+    expect(body).toMatchObject({
+      id: expect.any(String),
+      asset_item_id: assetItem.id,
+      type: "warranty",
+      vendor_id: vendor.id,
+      issue_description: "Battery swollen",
+      resolution_notes: null,
+      start_date: expect.any(String),
+      end_date: null,
+      created_at: expect.any(String),
+    });
+  });
+
+  it("rejects creating a record for an AssetItem with an active assignment", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId, status: "assigned" });
+    const employee = await createTestEmployee();
+    await prisma.assignment.create({
+      data: { employeeId: employee.id, assetItemId: assetItem.id, assignedAt: new Date() },
+    });
+
+    const res = await POST(
+      postRequest({
+        assetItemId: assetItem.id,
+        type: "repair",
+        issueDescription: "Screen flickers",
+        startDate: "2026-08-01",
+      })
+    );
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/active assignment/i);
+  });
+
+  it("rejects creating a record for a retired AssetItem", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId, status: "retired" });
+
+    const res = await POST(
+      postRequest({
+        assetItemId: assetItem.id,
+        type: "repair",
+        issueDescription: "Screen flickers",
+        startDate: "2026-08-01",
+      })
+    );
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/retired/i);
+  });
+
+  it("rejects creating a second open record for the same AssetItem", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+
+    await POST(
+      postRequest({
+        assetItemId: assetItem.id,
+        type: "repair",
+        issueDescription: "Screen flickers",
+        startDate: "2026-08-01",
+      })
+    );
+    const res = await POST(
+      postRequest({
+        assetItemId: assetItem.id,
+        type: "preventive",
+        issueDescription: "Another issue",
+        startDate: "2026-08-02",
+      })
+    );
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/already has an open maintenance record/i);
+  });
+
+  it("rejects an invalid JSON body", async () => {
+    const req = new Request("http://localhost/api/maintenance-records", {
+      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 (string)", 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);
+  });
+
+  it("rejects a non-object JSON body (number)", async () => {
+    const res = await POST(postRequest(123));
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/JSON object/i);
+  });
+});
+
+describe("GET /api/maintenance-records", () => {
+  it("lists created records, newest first", async () => {
+    const modelId = await createTestModelId();
+    const item1 = await createTestAssetItem({ modelId });
+    const item2 = await createTestAssetItem({ modelId });
+
+    await POST(
+      postRequest({
+        assetItemId: item1.id,
+        type: "repair",
+        issueDescription: "Issue 1",
+        startDate: "2026-08-01",
+      })
+    );
+    await new Promise((resolve) => setTimeout(resolve, 5));
+    await POST(
+      postRequest({
+        assetItemId: item2.id,
+        type: "repair",
+        issueDescription: "Issue 2",
+        startDate: "2026-08-01",
+      })
+    );
+
+    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 records", async () => {
+    const res = await GET();
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body).toEqual([]);
+  });
+
+  it("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" });
+  });
+});
+
+describe("PATCH /api/maintenance-records/[id]", () => {
+  it.each(["in_stock", "retired"] as const)(
+    "closes a record with targetStatus %s",
+    async (targetStatus) => {
+      const modelId = await createTestModelId();
+      const assetItem = await createTestAssetItem({ modelId });
+      const createRes = await POST(
+        postRequest({
+          assetItemId: assetItem.id,
+          type: "repair",
+          issueDescription: "Screen flickers",
+          startDate: "2026-08-01",
+        })
+      );
+      const created = await createRes.json();
+
+      const res = await PATCH(
+        patchRequest({ endDate: "2026-08-05", targetStatus }),
+        { params: { id: created.id } }
+      );
+      expect(res.status).toBe(200);
+      const body = await res.json();
+      expect(body.end_date).not.toBeNull();
+
+      const item = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
+      expect(item.status).toBe(targetStatus);
+    }
+  );
+
+  it("returns 400 when targetStatus is missing", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+    const createRes = await POST(
+      postRequest({
+        assetItemId: assetItem.id,
+        type: "repair",
+        issueDescription: "Screen flickers",
+        startDate: "2026-08-01",
+      })
+    );
+    const created = await createRes.json();
+
+    const res = await PATCH(patchRequest({ endDate: "2026-08-05" }), {
+      params: { id: created.id },
+    });
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/targetStatus/i);
+  });
+
+  it("rejects double-closing a record with 400", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+    const createRes = await POST(
+      postRequest({
+        assetItemId: assetItem.id,
+        type: "repair",
+        issueDescription: "Screen flickers",
+        startDate: "2026-08-01",
+      })
+    );
+    const created = await createRes.json();
+
+    await PATCH(patchRequest({ endDate: "2026-08-05", targetStatus: "in_stock" }), {
+      params: { id: created.id },
+    });
+    const res = await PATCH(patchRequest({ endDate: "2026-08-06", targetStatus: "in_stock" }), {
+      params: { id: created.id },
+    });
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/already been closed/i);
+  });
+
+  it("rejects an endDate before startDate with 400", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+    const createRes = await POST(
+      postRequest({
+        assetItemId: assetItem.id,
+        type: "repair",
+        issueDescription: "Screen flickers",
+        startDate: "2026-08-05",
+      })
+    );
+    const created = await createRes.json();
+
+    const res = await PATCH(patchRequest({ endDate: "2026-08-01", targetStatus: "in_stock" }), {
+      params: { id: created.id },
+    });
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/endDate must be on or after startDate/i);
+  });
+
+  it("returns 404 for a nonexistent record id", async () => {
+    const res = await PATCH(patchRequest({ endDate: "2026-08-05", targetStatus: "in_stock" }), {
+      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({ endDate: "2026-08-05", targetStatus: "in_stock" }), {
+      params: { id: "not-a-uuid" },
+    });
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toMatch(/UUID/i);
+  });
+
+  it("rejects an invalid JSON body", async () => {
+    const req = new Request("http://localhost/api/maintenance-records/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 (string)", 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("rejects a non-object JSON body (number)", async () => {
+    const res = await PATCH(patchRequest(123), {
+      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({ endDate: "2026-08-05", targetStatus: "in_stock" }), {
+      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/maintenance-records", () => {
+  it("POST /api/maintenance-records returns 401 without a session", async () => {
+    const modelId = await createTestModelId();
+    const assetItem = await createTestAssetItem({ modelId });
+    mockedAuth.mockResolvedValue(null);
+
+    const res = await POST(
+      postRequest({
+        assetItemId: assetItem.id,
+        type: "repair",
+        issueDescription: "Screen flickers",
+        startDate: "2026-08-01",
+      })
+    );
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body).toEqual({ error: "Unauthorized" });
+
+    const remaining = await prisma.maintenanceRecord.findMany();
+    expect(remaining).toHaveLength(0);
+  });
+});