diff --git a/database/seeders/RealisticDemoSeeder.php b/database/seeders/RealisticDemoSeeder.php
index 7b5faab9..e51837d7 100644
--- a/database/seeders/RealisticDemoSeeder.php
+++ b/database/seeders/RealisticDemoSeeder.php
@@ -2,6 +2,7 @@
 
 namespace Database\Seeders;
 
+use App\Facades\Hashids;
 use App\Models\Address;
 use App\Models\AiConversation;
 use App\Models\CompanySetting;
@@ -452,6 +453,10 @@ class RealisticDemoSeeder extends Seeder
 
         // Touch timestamps to match the invoice_date so tool queries like
         // `latest('invoice_date')` match `latest('created_at')` plausibly.
+        // The PDF routes bind on unique_hash. Creating through the model rather
+        // than InvoiceService skips the one place that normally assigns it, so
+        // set it here or every seeded document 404s on preview and download.
+        $invoice->unique_hash = Hashids::connection(Invoice::class)->encode($invoice->id);
         $invoice->created_at = $invoiceDate;
         $invoice->updated_at = $invoiceDate;
         $invoice->save();
@@ -515,6 +520,8 @@ class RealisticDemoSeeder extends Seeder
             'notes' => null,
         ]);
 
+        // See seedInvoice(): the PDF routes bind on unique_hash.
+        $payment->unique_hash = Hashids::connection(Payment::class)->encode($payment->id);
         $payment->created_at = $paymentDate;
         $payment->updated_at = $paymentDate;
         $payment->save();
@@ -585,6 +592,8 @@ class RealisticDemoSeeder extends Seeder
             'notes' => null,
         ]);
 
+        // See seedInvoice(): the PDF routes bind on unique_hash.
+        $estimate->unique_hash = Hashids::connection(Estimate::class)->encode($estimate->id);
         $estimate->created_at = $estimateDate;
         $estimate->updated_at = $estimateDate;
         $estimate->save();
diff --git a/tests/Feature/Admin/RealisticDemoSeederTest.php b/tests/Feature/Admin/RealisticDemoSeederTest.php
new file mode 100644
index 00000000..583145ad
--- /dev/null
+++ b/tests/Feature/Admin/RealisticDemoSeederTest.php
@@ -0,0 +1,31 @@
+<?php
+
+use App\Models\Estimate;
+use App\Models\Invoice;
+use App\Models\Payment;
+use Illuminate\Support\Facades\Artisan;
+
+beforeEach(function () {
+    Artisan::call('db:seed', ['--class' => 'DatabaseSeeder', '--force' => true]);
+    Artisan::call('db:seed', ['--class' => 'RealisticDemoSeeder', '--force' => true]);
+});
+
+/**
+ * The PDF routes bind on unique_hash (`/invoices/pdf/{invoice:unique_hash}`), and
+ * the seeder builds its documents with Model::create() rather than through the
+ * service layer that normally assigns it. When that was missed, every seeded
+ * document produced a `/invoices/pdf/` URL with an empty segment — a 404, surfaced
+ * in the UI only as "Unable to load document preview", with nothing in the log.
+ *
+ * Anything the seeder creates that the app then serves by hash has to carry one.
+ */
+test('every seeded document has the unique hash its pdf route binds on', function (string $model) {
+    expect($model::count())->toBeGreaterThan(0);
+
+    expect($model::whereNull('unique_hash')->orWhere('unique_hash', '')->count())
+        ->toBe(0);
+})->with([
+    Invoice::class,
+    Estimate::class,
+    Payment::class,
+]);