diff --git a/src/lib/invoice-generation.ts b/src/lib/invoice-generation.ts
index b7c9eac..6038a97 100644
--- a/src/lib/invoice-generation.ts
+++ b/src/lib/invoice-generation.ts
@@ -145,6 +145,47 @@ export async function generateInvoiceForClient(args: GenerateInvoiceArgs): Promi
   return { invoiceId: inv.id, invoiceNumber: inv.invoice_number };
 }
 
+// Find or create a per-client placeholder invoice used to mark items
+// as "already invoiced" outside of normal invoice generation (e.g. manual
+// flagging or imports). Items linked to this invoice are treated as billed
+// and won't appear on unbilled lists.
+export async function ensureMarkedInvoicedPlaceholder(
+  clientId: string,
+  caseId: string | null,
+  createdBy: string,
+): Promise<string> {
+  // Look for an existing placeholder for this client (any case).
+  const { data: existing } = await supabase
+    .from("invoices")
+    .select("id")
+    .eq("client_id", clientId)
+    .like("invoice_number", "MARKED-INVOICED-%")
+    .order("created_at", { ascending: false })
+    .limit(1)
+    .maybeSingle();
+  if (existing?.id) return existing.id;
+
+  const invNumber = `MARKED-INVOICED-${Date.now()}-${Math.floor(Math.random() * 10000)}`;
+  const { data, error } = await supabase
+    .from("invoices")
+    .insert({
+      client_id: clientId,
+      case_id: caseId,
+      invoice_number: invNumber,
+      status: "void",
+      issue_date: new Date().toISOString().slice(0, 10),
+      subtotal: 0,
+      tax: 0,
+      total: 0,
+      notes: "Placeholder invoice for items manually marked as already invoiced.",
+      created_by: createdBy,
+    } as any)
+    .select("id")
+    .single();
+  if (error || !data) throw error ?? new Error("Could not create placeholder invoice");
+  return data.id;
+}
+
 export async function recalcInvoiceTotals(invoiceId: string, taxRate?: number) {
   const { data: items } = await supabase
     .from("invoice_line_items")