fix(po): pre-fill vendor from cart when all items share the same vendor

App/pelagia-portal/app/(portal)/po/new/new-po-form.tsx

@@ -20,13 +20,15 @@ interface Props {
   accounts: Account[];
   vendors: Vendor[];
   initialLineItems?: LineItemInput[];
+  initialVendorId?: string;
 }
 
-export function NewPoForm({ vessels, accounts, vendors, initialLineItems }: Props) {
+export function NewPoForm({ vessels, accounts, vendors, initialLineItems, initialVendorId }: Props) {
   const router = useRouter();
   const [lineItems, setLineItems] = useState<LineItemInput[]>(
     initialLineItems && initialLineItems.length > 0 ? initialLineItems : [EMPTY_LINE]
   );
+  const [vendorId, setVendorId] = useState(initialVendorId ?? "");
   const [files, setFiles] = useState<File[]>([]);
   const [submitting, setSubmitting] = useState<"draft" | "submit" | null>(null);
   const [error, setError] = useState("");
@@ -189,7 +191,12 @@ export function NewPoForm({ vessels, accounts, vendors, initialLineItems }: Prop
           <label className="block text-sm font-medium text-neutral-700 mb-1.5">
             Vendor (optional — can be added later)
           </label>
-          <select name="vendorId" className={INPUT_CLS}>
+          <select
+            name="vendorId"
+            value={vendorId}
+            onChange={(e) => setVendorId(e.target.value)}
+            className={INPUT_CLS}
+          >
             <option value="">No vendor selected</option>
             {vendors.map((v) => (
               <option key={v.id} value={v.id}>

App/pelagia-portal/app/(portal)/po/new/page.tsx

@@ -24,6 +24,7 @@ export default async function NewPoPage({ searchParams }: Props) {
   const { cart } = await searchParams;
 
   let initialLineItems: LineItemInput[] | undefined;
+  let initialVendorId: string | undefined;
   if (cart) {
     try {
       const cartItems: CartItem[] = JSON.parse(decodeURIComponent(cart));
@@ -38,6 +39,9 @@ export default async function NewPoPage({ searchParams }: Props) {
           gstRate: 0.18,
           productId: item.productId,
         }));
+        // Pre-fill vendor only when all items share the same vendor
+        const vendorIds = [...new Set(cartItems.map((i) => i.vendorId).filter(Boolean))];
+        if (vendorIds.length === 1) initialVendorId = vendorIds[0];
       }
     } catch {
       // malformed cart param — ignore and start empty
@@ -58,7 +62,7 @@ export default async function NewPoPage({ searchParams }: Props) {
           Fill in the details below. You can save as draft or submit directly for approval.
         </p>
       </div>
-      <NewPoForm vessels={vessels} accounts={accounts} vendors={vendors} initialLineItems={initialLineItems} />
+      <NewPoForm vessels={vessels} accounts={accounts} vendors={vendors} initialLineItems={initialLineItems} initialVendorId={initialVendorId} />
     </div>
   );
 }