Auto-fill AssetItem.warrantyEndDate from AssetModel.warrantyMonths

AssetModel gains an optional warrantyMonths (standard vendor warranty
length). createAssetItem() now defaults warrantyEndDate to purchaseDate +
warrantyMonths (month-end clamped, e.g. Dec 31 + 2mo -> Feb 28, not Mar 3)
whenever the caller omits warrantyEndDate -- still overridable per item
for batches with extended/different warranty terms. /asset-models UI gets
an input for the new field; /assets needs no change since it already
omits warrantyEndDate from the payload when left blank.

Hand-written migration + manual smoke test (tsx script, not Vitest),
same deviation as the other 2026-08-2x work in this branch -- see
CLAUDE.md. tsc/lint clean.

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

@@ -27,8 +27,14 @@ export async function POST(request: Request): Promise<NextResponse> {
     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 });
+  const { categoryId, manufacturer, name, specs, warrantyMonths } = body as Record<string, unknown>;
+  const validation = validateCreateAssetModelInput({
+    categoryId,
+    manufacturer,
+    name,
+    specs,
+    warrantyMonths,
+  });
 
   if (!validation.ok) {
     return NextResponse.json({ error: validation.error }, { status: 400 });

src/app/asset-models/page.tsx

@@ -30,6 +30,7 @@ interface AssetModelRecord {
   manufacturer: string;
   name: string;
   specs: Record<string, unknown>;
+  warranty_months: number | null;
   created_at: string;
 }
 
@@ -64,6 +65,7 @@ export default function AssetModelsPage() {
   const [manufacturer, setManufacturer] = useState("");
   const [name, setName] = useState("");
   const [specsText, setSpecsText] = useState(DEFAULT_SPECS_TEXT);
+  const [warrantyMonths, setWarrantyMonths] = useState("");
   const [submitting, setSubmitting] = useState(false);
   const [submitError, setSubmitError] = useState<string | null>(null);
 
@@ -83,11 +85,24 @@ export default function AssetModelsPage() {
       return;
     }
 
+    const trimmedWarranty = warrantyMonths.trim();
+    if (trimmedWarranty !== "" && Number.isNaN(Number(trimmedWarranty))) {
+      setSubmitError("Warranty (months) must be a number");
+      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 }),
+        body: JSON.stringify({
+          categoryId,
+          manufacturer,
+          name,
+          specs,
+          ...(trimmedWarranty !== "" ? { warrantyMonths: Number(trimmedWarranty) } : {}),
+        }),
       });
 
       let body: unknown;
@@ -113,6 +128,7 @@ export default function AssetModelsPage() {
       setManufacturer("");
       setName("");
       setSpecsText(DEFAULT_SPECS_TEXT);
+      setWarrantyMonths("");
       refetch();
     } catch {
       setSubmitError("Request failed");
@@ -139,6 +155,7 @@ export default function AssetModelsPage() {
                 <TableHead>Manufacturer</TableHead>
                 <TableHead>Name</TableHead>
                 <TableHead>Specs</TableHead>
+                <TableHead>Warranty (months)</TableHead>
                 <TableHead>Created At</TableHead>
               </TableRow>
             </TableHeader>
@@ -150,6 +167,7 @@ export default function AssetModelsPage() {
                   <TableCell>{assetModel.manufacturer}</TableCell>
                   <TableCell>{assetModel.name}</TableCell>
                   <TableCell>{JSON.stringify(assetModel.specs)}</TableCell>
+                  <TableCell>{assetModel.warranty_months ?? "-"}</TableCell>
                   <TableCell>{assetModel.created_at}</TableCell>
                 </TableRow>
               ))}
@@ -208,6 +226,23 @@ export default function AssetModelsPage() {
             />
           </div>
 
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="warrantyMonths">Standard Warranty (months, optional)</Label>
+            <Input
+              id="warrantyMonths"
+              type="number"
+              min={1}
+              step={1}
+              value={warrantyMonths}
+              onChange={(event) => setWarrantyMonths(event.target.value)}
+              placeholder="e.g. 36"
+            />
+            <p className="text-xs text-muted-foreground">
+              Used as a default when creating an Asset Item with this model -- warranty end date
+              is auto-filled from purchase date if left blank there, still editable per item.
+            </p>
+          </div>
+
           {submitError ? (
             <p className="text-sm text-destructive">{submitError}</p>
           ) : null}

src/lib/asset-models.ts

@@ -9,6 +9,7 @@ export interface AssetModelRecord {
   manufacturer: string;
   name: string;
   specs: Record<string, unknown>;
+  warranty_months: number | null;
   created_at: string;
 }
 
@@ -17,6 +18,7 @@ export interface CreateAssetModelInput {
   manufacturer: string;
   name: string;
   specs: Record<string, unknown>;
+  warrantyMonths?: number | null;
 }
 
 export type ValidationResult =
@@ -57,6 +59,14 @@ const createAssetModelSchema = z.object({
     })
     .optional()
     .default({}),
+  // Optional standard warranty length -- see schema.prisma's
+  // AssetModel.warrantyMonths comment for what this drives.
+  warrantyMonths: z
+    .number({ invalid_type_error: "warrantyMonths must be a positive integer" })
+    .int("warrantyMonths must be a positive integer")
+    .positive("warrantyMonths must be a positive integer")
+    .optional()
+    .nullable(),
 });
 
 /**
@@ -71,6 +81,7 @@ export function validateCreateAssetModelInput(input: {
   manufacturer?: unknown;
   name?: unknown;
   specs?: unknown;
+  warrantyMonths?: unknown;
 }): ValidationResult {
   const result = createAssetModelSchema.safeParse(input);
   if (!result.success) {
@@ -86,6 +97,7 @@ function toRecord(row: {
   manufacturer: string;
   name: string;
   specs: Prisma.JsonValue;
+  warrantyMonths: number | null;
   createdAt: Date;
 }): AssetModelRecord {
   return {
@@ -94,6 +106,7 @@ function toRecord(row: {
     manufacturer: row.manufacturer,
     name: row.name,
     specs: (row.specs as Record<string, unknown>) ?? {},
+    warranty_months: row.warrantyMonths,
     created_at: row.createdAt.toISOString(),
   };
 }
@@ -201,6 +214,7 @@ export async function createAssetModel(
       // is safe here since the Zod schema already guarantees JSON-shaped
       // values.
       specs: input.specs as Prisma.InputJsonValue,
+      warrantyMonths: input.warrantyMonths ?? null,
     },
   });
   return { ok: true, value: toRecord(created) };

src/lib/assets.ts

@@ -136,16 +136,53 @@ export type CreateAssetItemResult =
  * createPurchaseOrder() pattern for disambiguating between two FKs on the
  * same model.
  */
+// Adds `months` calendar months to `date`, clamping to the last day of the
+// target month rather than letting JS's native Date rollover push into the
+// month after (e.g. Jan 31 + 1 month must land on Feb 28/29, not Mar
+// 2/3 -- `date.setMonth()` alone does the latter). UTC throughout: Prisma
+// @db.Date fields round-trip as UTC-midnight Dates (see dateString()
+// above), and doing this in UTC avoids the host server's local timezone
+// shifting the day near midnight.
+function addMonthsClamped(date: Date, months: number): Date {
+  const targetMonthIndex = date.getUTCMonth() + months;
+  const daysInTargetMonth = new Date(
+    Date.UTC(date.getUTCFullYear(), targetMonthIndex + 1, 0)
+  ).getUTCDate();
+  return new Date(
+    Date.UTC(
+      date.getUTCFullYear(),
+      targetMonthIndex,
+      Math.min(date.getUTCDate(), daysInTargetMonth)
+    )
+  );
+}
+
 export async function createAssetItem(
   input: CreateAssetItemInput
 ): Promise<CreateAssetItemResult> {
   try {
+    // warrantyEndDate defaults from the model's standard warranty term
+    // (AssetModel.warrantyMonths) when the caller doesn't supply one
+    // explicitly -- see schema.prisma's AssetModel.warrantyMonths comment
+    // for why this stays a suggestion (still overridable per item) rather
+    // than a hard-computed column. A modelId that doesn't exist is left for
+    // the insert below's own P2003 handling, same as before this lookup was
+    // added -- this just also opportunistically uses the model row if it's
+    // there.
+    let warrantyEndDate = input.warrantyEndDate ?? null;
+    if (!warrantyEndDate) {
+      const model = await prisma.assetModel.findUnique({ where: { id: input.modelId } });
+      if (model?.warrantyMonths) {
+        warrantyEndDate = addMonthsClamped(input.purchaseDate, model.warrantyMonths);
+      }
+    }
+
     const created = await prisma.assetItem.create({
       data: {
         serialNumber: input.serialNumber,
         modelId: input.modelId,
         purchaseDate: input.purchaseDate,
-        warrantyEndDate: input.warrantyEndDate ?? null,
+        warrantyEndDate,
         purchaseOrderId: input.purchaseOrderId ?? null,
       },
     });