diff --git a/tests/Feature/Billing/StripePriceAdoptionTest.php b/tests/Feature/Billing/StripePriceAdoptionTest.php
index 54336c1..aaf86ef 100644
--- a/tests/Feature/Billing/StripePriceAdoptionTest.php
+++ b/tests/Feature/Billing/StripePriceAdoptionTest.php
@@ -12,8 +12,11 @@ use App\Services\Billing\TaxTreatment;
 use App\Services\Stripe\FakeStripeClient;
 use App\Services\Stripe\StripeClient;
 use Illuminate\Contracts\Console\Kernel;
+use Illuminate\Database\Schema\Blueprint;
 use Illuminate\Database\UniqueConstraintViolationException;
+use Illuminate\Support\Facades\DB;
 use Illuminate\Support\Facades\Log;
+use Illuminate\Support\Facades\Schema;
 
 /**
  * A run that dies between Stripe's create and our insert leaves an orphan — and
@@ -467,3 +470,65 @@ it('lets no two module rows claim one stripe price', function () {
         'reverse_charge' => true, 'amount_cents' => 2900, 'interval' => 'month']))
         ->toThrow(UniqueConstraintViolationException::class);
 });
+
+it('deletes the newer of two rows already sharing one stripe price when the migration runs', function () {
+    // This is the one branch of 2026_07_31_210000_one_row_per_stripe_price that
+    // deletes rows from a live table, and it cannot be reached through the
+    // ordinary migrated schema: RefreshDatabase already ran this migration, so
+    // its OWN unique index would refuse the very duplicate this test needs to
+    // insert. Dropping the index first puts the table back into the shape the
+    // migration was written to find — the shape a real, never-yet-migrated
+    // production table was in — so up() can be run again and actually take its
+    // delete branch instead of finding nothing to do.
+    Schema::table('stripe_addon_prices', fn (Blueprint $table) => $table->dropUnique('stripe_addon_prices_price_unique'));
+
+    // Two rows sharing one Price, differing in `reverse_charge` so the
+    // pre-existing COMPOSITE unique index (addon_key, reverse_charge,
+    // amount_cents, currency, interval) does not itself refuse the insert —
+    // the VAT-rate-zero case Block D warned about, where only the shared
+    // stripe_price_id gives the duplicate away.
+    $kept = DB::table('stripe_addon_prices')->insertGetId([
+        'addon_key' => 'priority_support', 'reverse_charge' => false,
+        'amount_cents' => 2900, 'net_cents' => 2900, 'currency' => 'EUR', 'interval' => 'month',
+        'stripe_product_id' => 'prod_support', 'stripe_price_id' => 'price_shared',
+        'created_at' => now(), 'updated_at' => now(),
+    ]);
+
+    $duplicate = DB::table('stripe_addon_prices')->insertGetId([
+        'addon_key' => 'priority_support', 'reverse_charge' => true,
+        'amount_cents' => 2900, 'net_cents' => 2900, 'currency' => 'EUR', 'interval' => 'month',
+        'stripe_product_id' => 'prod_support', 'stripe_price_id' => 'price_shared',
+        'created_at' => now(), 'updated_at' => now(),
+    ]);
+
+    // On its own Price entirely, and must survive untouched.
+    $unrelated = DB::table('stripe_addon_prices')->insertGetId([
+        'addon_key' => 'extra_storage', 'reverse_charge' => false,
+        'amount_cents' => 1000, 'net_cents' => 1000, 'currency' => 'EUR', 'interval' => 'month',
+        'stripe_product_id' => 'prod_storage', 'stripe_price_id' => 'price_untouched',
+        'created_at' => now(), 'updated_at' => now(),
+    ]);
+
+    // require, not require_once: the file `return`s a fresh anonymous-class
+    // instance every time it is evaluated, which is what lets this run the
+    // migration's up() a second time in this same process.
+    (require database_path('migrations/2026_07_31_210000_one_row_per_stripe_price.php'))->up();
+
+    // The LOWER id survives — the row that was written first, which is the one
+    // anything already billing is likeliest to have been reading. Were that
+    // ordering silently inverted, the surviving row could be one nothing ever
+    // pointed at.
+    expect(DB::table('stripe_addon_prices')->where('id', $kept)->exists())->toBeTrue()
+        ->and(DB::table('stripe_addon_prices')->where('id', $duplicate)->exists())->toBeFalse()
+        ->and(DB::table('stripe_addon_prices')->where('id', $unrelated)->exists())->toBeTrue();
+
+    // And the index is back in force: a further row on a third, otherwise
+    // distinct tuple, but the SAME Price id, is refused by stripe_price_id
+    // alone rather than being silently accepted.
+    expect(fn () => DB::table('stripe_addon_prices')->insert([
+        'addon_key' => 'priority_support', 'reverse_charge' => false,
+        'amount_cents' => 4900, 'net_cents' => 4900, 'currency' => 'EUR', 'interval' => 'year',
+        'stripe_product_id' => 'prod_support', 'stripe_price_id' => 'price_shared',
+        'created_at' => now(), 'updated_at' => now(),
+    ]))->toThrow(UniqueConstraintViolationException::class);
+});