Bill transfer storage monthly with a 15-day grace period before deletion.

Files stay available while wallet renewals succeed each month. Failed renewals
keep files for TRANSFER_GRACE_PERIOD_DAYS (default 15) before automatic cleanup.

Co-authored-by: Cursor <cursoragent@cursor.com>

database/migrations/2026_06_09_120000_add_transfer_billing_period_columns.php

@@ -0,0 +1,35 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::table('transfers', function (Blueprint $table) {
+            $table->timestamp('paid_until')->nullable()->after('expires_at');
+            $table->timestamp('grace_ends_at')->nullable()->after('paid_until');
+            $table->timestamp('last_billed_at')->nullable()->after('grace_ends_at');
+
+            $table->index(['status', 'paid_until']);
+            $table->index(['status', 'grace_ends_at']);
+        });
+
+        DB::table('transfers')
+            ->whereNull('paid_until')
+            ->whereNotNull('expires_at')
+            ->update(['paid_until' => DB::raw('expires_at')]);
+    }
+
+    public function down(): void
+    {
+        Schema::table('transfers', function (Blueprint $table) {
+            $table->dropIndex(['status', 'paid_until']);
+            $table->dropIndex(['status', 'grace_ends_at']);
+            $table->dropColumn(['paid_until', 'grace_ends_at', 'last_billed_at']);
+        });
+    }
+};