Stabilize mobile auth session handling

app/(app)/invoices/send/[id].tsx

@@ -51,10 +51,10 @@ export default function InvoiceSendScreen() {
     onError: (err) => Alert.alert("Could not send invoice", err.message),
   });
 
-  const invoice = invoiceQuery.data;
   const previewInput = useMemo(
-    () => (invoice ? buildPreviewPdfInputFromInvoice(invoice) : null),
-    [invoice],
+    () =>
+      invoiceQuery.data ? buildPreviewPdfInputFromInvoice(invoiceQuery.data) : null,
+    [invoiceQuery.data],
   );
 
   if (!id) {
@@ -65,10 +65,11 @@ export default function InvoiceSendScreen() {
     return <LoadingScreen message="Loading invoice…" />;
   }
 
-  if (!invoice) {
+  if (!invoiceQuery.data) {
     return <LoadingScreen message="Invoice not found" />;
   }
 
+  const invoice = invoiceQuery.data;
   const status = getInvoiceStatus(invoice);
   const clientEmail = invoice.client?.email?.trim() ?? "";
   const businessName = invoice.business?.name ?? "Your business";
@@ -91,7 +92,7 @@ export default function InvoiceSendScreen() {
     }
 
     sendInvoice.mutate({
-      invoiceId: invoice!.id,
+      invoiceId: invoice.id,
       customMessage: customMessage.trim() || undefined,
     });
   }