diff --git a/src/lib/maintenance-records.ts b/src/lib/maintenance-records.ts
new file mode 100644
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+++ b/src/lib/maintenance-records.ts
@@ -0,0 +1,413 @@
+import { z } from "zod";
+import { Prisma } from "@prisma/client";
+import { prisma } from "./prisma";
+import type { AssetItemStatus } from "./assets";
+
+export type MaintenanceType = "repair" | "warranty" | "preventive";
+
+export interface MaintenanceRecordRecord {
+  id: string;
+  asset_item_id: string;
+  type: MaintenanceType;
+  vendor_id: string | null;
+  issue_description: string;
+  resolution_notes: string | null;
+  start_date: string;
+  end_date: string | null;
+  created_at: string;
+}
+
+// resolutionNotes/endDate are deliberately NOT accepted from the client at
+// creation time — same precedent as Assignment.returnedAt not being
+// accepted at creation (see src/lib/assignments.ts's CreateAssignmentInput
+// doc comment): a MaintenanceRecord always opens with endDate/
+// resolutionNotes null, only closeMaintenanceRecord() sets them later.
+export interface CreateMaintenanceRecordInput {
+  assetItemId: string;
+  type: MaintenanceType;
+  vendorId?: string | null;
+  issueDescription: string;
+  startDate: Date;
+}
+
+export type ValidationResult =
+  | { ok: true; value: CreateMaintenanceRecordInput }
+  | { ok: false; error: string };
+
+// Mirrors src/lib/assets.ts's nonEmptyString helper.
+function nonEmptyString(message: string) {
+  return z.string({ required_error: message, invalid_type_error: message }).refine(
+    (value) => value.trim() !== "",
+    { message }
+  );
+}
+
+// Mirrors src/lib/assignments.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));
+}
+
+const createMaintenanceRecordSchema = z.object({
+  // FK to AssetItem — only a UUID *format* check here. Unlike a plain
+  // supply-side FK (e.g. AssetItem.purchaseOrderId), existence is checked
+  // explicitly inside the transaction below (not deferred entirely to
+  // Prisma's insert-time FK constraint), because createMaintenanceRecord()
+  // needs to read the referenced row anyway to enforce the status/active-
+  // assignment/already-open business rules. Mirrors
+  // src/lib/assignments.ts's assetItemId handling.
+  assetItemId: z
+    .string({ required_error: "assetItemId is required and must be a valid UUID string" })
+    .uuid("assetItemId is required and must be a valid UUID string"),
+  // Mirrors src/lib/requests.ts's type z.enum() pattern.
+  type: z.enum(["repair", "warranty", "preventive"], {
+    errorMap: () => ({
+      message: "type is required and must be one of 'repair', 'warranty', 'preventive'",
+    }),
+  }),
+  // FK to Vendor — nullable/optional, null means an internal repair with no
+  // outside vendor involved (see schema.prisma's MaintenanceRecord comment).
+  // Only a UUID *format* check here, whether it references a real vendor is
+  // left to Prisma's own FK constraint at insert time (see
+  // createMaintenanceRecord()'s P2003 handling below). Mirrors
+  // src/lib/licenses.ts's vendorId handling (except nullable here).
+  vendorId: z
+    .string({ invalid_type_error: "vendorId must be a valid UUID string" })
+    .uuid("vendorId must be a valid UUID string")
+    .optional()
+    .nullable(),
+  issueDescription: nonEmptyString(
+    "issueDescription is required and must be a non-empty string"
+  ),
+  startDate: dateString("startDate is required and must be a valid date string"),
+});
+
+/**
+ * Validates raw (untyped) maintenance-record-creation input. assetItemId
+ * must be a valid UUID string, type must be one of the three enum values,
+ * vendorId is optional/nullable but must be a valid UUID string if present,
+ * issueDescription must be a non-empty string, startDate must be a valid
+ * date string. resolutionNotes/endDate are not accepted here — see
+ * CreateMaintenanceRecordInput's doc comment for why.
+ */
+export function validateCreateMaintenanceRecordInput(input: {
+  assetItemId?: unknown;
+  type?: unknown;
+  vendorId?: unknown;
+  issueDescription?: unknown;
+  startDate?: unknown;
+}): ValidationResult {
+  const result = createMaintenanceRecordSchema.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 };
+}
+
+// Closed set of the 4 AssetItemStatus enum values — reused verbatim (not
+// re-derived) as the z.enum() literal list backing targetStatus below.
+const assetItemStatusValues = ["in_stock", "assigned", "repair", "retired"] as const;
+
+const closeMaintenanceRecordSchema = z.object({
+  endDate: dateString("endDate is required and must be a valid date string"),
+  // Nullable/optional — a closed record doesn't strictly require notes (e.g.
+  // a warranty swap with nothing more to say than "resolved"). Mirrors the
+  // optional().nullable() shape used for other nullable-in-DB text/FK
+  // fields throughout this codebase (e.g. AssetItem.purchaseOrderId).
+  resolutionNotes: z
+    .string({ invalid_type_error: "resolutionNotes must be a string" })
+    .optional()
+    .nullable(),
+  // Required — deliberately NOT defaulted to "in_stock", per docs/
+  // asset-license-management.md's "MaintenanceRecord" section: "không tự
+  // động mặc định về in_stock, vì sửa không phải lúc nào cũng thành công."
+  // Any of the 4 AssetItemStatus values is accepted at the Zod layer (the
+  // doc's examples are in_stock/retired, but nothing in the spec restricts
+  // the set further) — see feature-implementer report's "Assumed" section.
+  targetStatus: z.enum(assetItemStatusValues, {
+    errorMap: () => ({
+      message:
+        "targetStatus is required and must be one of 'in_stock', 'assigned', 'repair', 'retired'",
+    }),
+  }),
+});
+
+export type CloseMaintenanceRecordInput = {
+  endDate: Date;
+  resolutionNotes?: string | null;
+  targetStatus: AssetItemStatus;
+};
+
+export type CloseValidationResult =
+  | { ok: true; value: CloseMaintenanceRecordInput }
+  | { ok: false; error: string };
+
+/**
+ * Validates raw (untyped) maintenance-record-close input. endDate must be a
+ * valid date string, resolutionNotes is optional/nullable but must be a
+ * string if present, targetStatus is required and must be a valid
+ * AssetItemStatus value. endDate >= startDate cannot be checked here (it
+ * needs the already-saved record's startDate from the DB) — that's enforced
+ * inside closeMaintenanceRecord() itself.
+ */
+export function validateCloseMaintenanceRecordInput(input: {
+  endDate?: unknown;
+  resolutionNotes?: unknown;
+  targetStatus?: unknown;
+}): CloseValidationResult {
+  const result = closeMaintenanceRecordSchema.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;
+  assetItemId: string;
+  type: MaintenanceType;
+  vendorId: string | null;
+  issueDescription: string;
+  resolutionNotes: string | null;
+  startDate: Date;
+  endDate: Date | null;
+  createdAt: Date;
+}): MaintenanceRecordRecord {
+  return {
+    id: row.id,
+    asset_item_id: row.assetItemId,
+    type: row.type,
+    vendor_id: row.vendorId,
+    issue_description: row.issueDescription,
+    resolution_notes: row.resolutionNotes,
+    start_date: row.startDate.toISOString(),
+    end_date: row.endDate ? row.endDate.toISOString() : null,
+    created_at: row.createdAt.toISOString(),
+  };
+}
+
+// Internal error type used to carry a clean, already-user-facing message out
+// of the `prisma.$transaction()` callback below, distinguishing
+// application-level business-rule rejections (400) from unexpected/infra
+// errors (rethrown as-is). Not exported — callers only ever see the
+// {ok,error} result shape. Mirrors src/lib/assignments.ts's
+// AssignmentBusinessError.
+class MaintenanceRecordBusinessError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = "MaintenanceRecordBusinessError";
+  }
+}
+
+class MaintenanceRecordNotFoundError extends Error {
+  constructor() {
+    super("MaintenanceRecord not found");
+    this.name = "MaintenanceRecordNotFoundError";
+  }
+}
+
+export type CreateMaintenanceRecordResult =
+  | { ok: true; value: MaintenanceRecordRecord }
+  | { ok: false; error: string };
+
+/**
+ * Opens a MaintenanceRecord for an AssetItem, enforcing every business rule
+ * from docs/asset-license-management.md's "## MaintenanceRecord (spec BA +
+ * stakeholder, chốt 2026-08-04)" section inside a single
+ * `prisma.$transaction()`:
+ *
+ * - Rejects if the AssetItem doesn't exist.
+ * - Rejects if the AssetItem is already "retired" (thanh lý thì gửi sửa
+ *   không còn ý nghĩa).
+ * - Rejects if the AssetItem has an ACTIVE Assignment (returnedAt IS NULL)
+ *   — must be returned first, mirrors createAssignment()'s own
+ *   status precondition check.
+ * - Rejects if the AssetItem already has another OPEN MaintenanceRecord
+ *   (endDate IS NULL) — at most one open record per item at a time (a
+ *   physical item can't be in two repair places at once).
+ * - Atomically flips AssetItem.status to "repair".
+ *
+ * Race-condition note: mirrors src/lib/assignments.ts's createAssignment()
+ * pattern — the AssetItem.status flip uses a WHERE-guarded `updateMany`
+ * (`where: { id: assetItemId, status: { not: "retired" } }`) rather than a
+ * plain read-then-write. That `updateMany`'s `count` is the actual
+ * race-closing gate: two concurrent opens racing on the same AssetItem
+ * serialize on Postgres's row lock for that UPDATE, the first to commit
+ * wins, and the second's WHERE clause no longer matches (status is no
+ * longer what it read), so its `updateMany` returns `count: 0`, treated
+ * here as "lost the race". The `findUnique` above it is NOT itself the
+ * race-closing check (same TOCTOU caveat as createAssignment()'s doc
+ * comment) — it only produces a specific, friendly error message
+ * (not-found vs. retired vs. active-assignment vs. already-open) for the
+ * common (non-racing) case.
+ */
+export async function createMaintenanceRecord(
+  input: CreateMaintenanceRecordInput
+): Promise<CreateMaintenanceRecordResult> {
+  try {
+    const created = await prisma.$transaction(async (tx) => {
+      const assetItem = await tx.assetItem.findUnique({ where: { id: input.assetItemId } });
+      if (!assetItem) {
+        throw new MaintenanceRecordBusinessError(
+          "assetItemId does not reference an existing asset item"
+        );
+      }
+      if (assetItem.status === "retired") {
+        throw new MaintenanceRecordBusinessError(
+          "assetItemId refers to an AssetItem that is retired and cannot be sent for maintenance"
+        );
+      }
+
+      const activeAssignment = await tx.assignment.findFirst({
+        where: { assetItemId: input.assetItemId, returnedAt: null },
+      });
+      if (activeAssignment) {
+        throw new MaintenanceRecordBusinessError(
+          "assetItemId has an active assignment (returnedAt IS NULL) — return it before creating a maintenance record"
+        );
+      }
+
+      const openRecord = await tx.maintenanceRecord.findFirst({
+        where: { assetItemId: input.assetItemId, endDate: null },
+      });
+      if (openRecord) {
+        throw new MaintenanceRecordBusinessError(
+          "assetItemId already has an open maintenance record (endDate IS NULL)"
+        );
+      }
+
+      // Atomic race-closing gate — see this function's doc comment.
+      const statusUpdate = await tx.assetItem.updateMany({
+        where: { id: input.assetItemId, status: { not: "retired" } },
+        data: { status: "repair" },
+      });
+      if (statusUpdate.count === 0) {
+        throw new MaintenanceRecordBusinessError(
+          "assetItemId refers to an AssetItem that is retired (lost a race to a concurrent retire)"
+        );
+      }
+
+      return tx.maintenanceRecord.create({
+        data: {
+          assetItemId: input.assetItemId,
+          type: input.type,
+          vendorId: input.vendorId ?? null,
+          issueDescription: input.issueDescription,
+          startDate: input.startDate,
+          endDate: null,
+          resolutionNotes: null,
+        },
+      });
+    });
+
+    return { ok: true, value: toRecord(created) };
+  } catch (error) {
+    if (error instanceof MaintenanceRecordBusinessError) {
+      return { ok: false, error: error.message };
+    }
+    // Only vendorId can still fail with a raw FK violation here —
+    // assetItemId existence is already fully resolved above (found-or-
+    // rejected before the transaction ever reaches
+    // tx.maintenanceRecord.create()).
+    if (error instanceof Prisma.PrismaClientKnownRequestError && error.code === "P2003") {
+      return { ok: false, error: "vendorId does not reference an existing vendor" };
+    }
+    throw error;
+  }
+}
+
+export async function listMaintenanceRecords(): Promise<MaintenanceRecordRecord[]> {
+  const rows = await prisma.maintenanceRecord.findMany({
+    orderBy: [{ createdAt: "desc" }, { id: "desc" }],
+  });
+  return rows.map(toRecord);
+}
+
+export type CloseMaintenanceRecordResult =
+  | { ok: true; value: MaintenanceRecordRecord }
+  | { ok: false; status: 404 | 400; error: string };
+
+/**
+ * Closes a MaintenanceRecord (sets endDate + resolutionNotes) and applies
+ * the caller-chosen `targetStatus` to its AssetItem, inside a single
+ * `prisma.$transaction()` — docs/asset-license-management.md's
+ * "MaintenanceRecord" section, "Đóng MaintenanceRecord" bullet.
+ * targetStatus is never defaulted (e.g. to "in_stock") — repair doesn't
+ * always succeed, the caller must say explicitly what state the item ends
+ * up in (e.g. "in_stock" if fixed, "retired" if the repair failed).
+ *
+ * Race-condition note: mirrors src/lib/assignments.ts's
+ * returnAssignment()/transferAssignment() pattern exactly — double-close is
+ * closed by a single atomic, WHERE-guarded `updateMany`
+ * (`where: { id, endDate: null }`) that both checks AND writes endDate/
+ * resolutionNotes in one statement, rather than a separate guard check
+ * followed by a plain `update()`. Two concurrent close calls against the
+ * same MaintenanceRecord 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 closed". The initial `findUnique` (used to read startDate for
+ * the endDate>=startDate check, and to distinguish "not found" from
+ * "already closed" in the common case) is NOT itself the race-closing check
+ * — same caveat as the Assignment lib's doc comments. The endDate>=startDate
+ * business-rule check is deliberately done BEFORE the atomic updateMany
+ * (using the record read by the preceding findUnique) since it only needs
+ * the record's already-immutable startDate, not anything the race could
+ * change. The subsequent AssetItem.status write does not need its own
+ * atomic guard — same rationale as returnAssignment()'s plain
+ * `tx.assetItem.update()` for its own status flip: targetStatus is applied
+ * unconditionally, there's no upper/lower bound to race on the way there
+ * was for License.seatsUsed at create time.
+ */
+export async function closeMaintenanceRecord(
+  id: string,
+  input: CloseMaintenanceRecordInput
+): Promise<CloseMaintenanceRecordResult> {
+  try {
+    const updated = await prisma.$transaction(async (tx) => {
+      const record = await tx.maintenanceRecord.findUnique({ where: { id } });
+      if (!record) {
+        throw new MaintenanceRecordNotFoundError();
+      }
+
+      if (input.endDate.getTime() < record.startDate.getTime()) {
+        throw new MaintenanceRecordBusinessError("endDate must be on or after startDate");
+      }
+
+      // Atomic race-closing gate — see this function's doc comment. Also
+      // doubles as the "already closed" rejection in the non-racing case,
+      // since `record.endDate !== null` implies this WHERE clause won't
+      // match either.
+      const claim = await tx.maintenanceRecord.updateMany({
+        where: { id, endDate: null },
+        data: {
+          endDate: input.endDate,
+          resolutionNotes: input.resolutionNotes ?? null,
+        },
+      });
+      if (claim.count === 0) {
+        throw new MaintenanceRecordBusinessError("MaintenanceRecord has already been closed");
+      }
+
+      await tx.assetItem.update({
+        where: { id: record.assetItemId },
+        data: { status: input.targetStatus },
+      });
+
+      return tx.maintenanceRecord.findUniqueOrThrow({ where: { id } });
+    });
+
+    return { ok: true, value: toRecord(updated) };
+  } catch (error) {
+    if (error instanceof MaintenanceRecordNotFoundError) {
+      return { ok: false, status: 404, error: "MaintenanceRecord not found" };
+    }
+    if (error instanceof MaintenanceRecordBusinessError) {
+      return { ok: false, status: 400, error: error.message };
+    }
+    throw error;
+  }
+}