Fix invoice number race condition: use DB lock for atomic increment

app/Listeners/InvoiceCreatingListener.php

@@ -5,6 +5,7 @@ namespace App\Listeners;
 use App\Events\Invoice\Creating;
 use App\Models\Invoice;
 use App\Models\Setting;
+use Illuminate\Support\Facades\DB;
 
 class InvoiceCreatingListener
 {
@@ -13,15 +14,30 @@ class InvoiceCreatingListener
      */
     public function handle(Creating $event): void
     {
+        // Use database lock to prevent duplicate invoice numbers across clustered nodes
+        $number = DB::transaction(function () {
+            $setting = Setting::where('key', 'invoice_number')
+                ->whereNull('settingable_id')
+                ->lockForUpdate()
+                ->first();
+
+            $current = $setting ? (int) $setting->value : (int) config('settings.invoice_number', 0);
+            $next = $current + 1;
+
+            Setting::updateOrCreate([
+                'key' => 'invoice_number',
+                'settingable_id' => null,
+                'settingable_type' => null,
+            ], [
+                'value' => $next,
+            ]);
+
+            // Update in-memory config so subsequent calls in the same request are correct
+            config(['settings.invoice_number' => $next]);
+
+            return $next;
+        });
 
-        // Get the next invoice number
-        $number = config('settings.invoice_number', 1) + 1;
-        // Update setting
-        Setting::updateOrCreate([
-            'key' => 'invoice_number',
-        ], [
-            'value' => $number,
-        ]);
         // Pad the invoice number with leading zeros
         $paddedNumber = str_pad($number, config('settings.invoice_number_padding', 1), '0', STR_PAD_LEFT);