diff --git a/app/tests/Feature/RedisCacheStoreIsolationTest.php b/app/tests/Feature/RedisCacheStoreIsolationTest.php
new file mode 100644
index 00000000..c80e8e17
--- /dev/null
+++ b/app/tests/Feature/RedisCacheStoreIsolationTest.php
@@ -0,0 +1,24 @@
+<?php
+
+declare(strict_types=1);
+
+use Illuminate\Cache\ArrayStore;
+use Illuminate\Support\Facades\Cache;
+
+/**
+ * Quirk 72 regression guard — see tests/TestCase.php::setUp().
+ *
+ * Supplier code (SupplierPortalClient::loadSession, RefreshSupplierSessionJob,
+ * CsvReconcileJob, RouteSupplierLeadJob) hardcodes Cache::store('redis'),
+ * bypassing phpunit.xml's CACHE_STORE=array. The Redis store is a shared
+ * external service: under `pest --parallel` every worker collides on the
+ * global `supplier:session` key, so one worker's afterEach forget()/flush()
+ * races another worker's mid-test loadSession().
+ *
+ * TestCase::setUp() repoints the `redis` cache store at the in-process
+ * `array` driver, making it hermetic and worker-local. This test fails
+ * (RedisStore) if that override is ever removed.
+ */
+test('redis cache store resolves to the in-process array driver under tests', function (): void {
+    expect(Cache::store('redis')->getStore())->toBeInstanceOf(ArrayStore::class);
+});
diff --git a/app/tests/TestCase.php b/app/tests/TestCase.php
index fe1ffc2f..e5f98cf4 100644
--- a/app/tests/TestCase.php
+++ b/app/tests/TestCase.php
@@ -6,5 +6,20 @@ use Illuminate\Foundation\Testing\TestCase as BaseTestCase;
 
 abstract class TestCase extends BaseTestCase
 {
-    //
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        // Quirk 72: supplier code (SupplierPortalClient::loadSession,
+        // RefreshSupplierSessionJob, CsvReconcileJob, RouteSupplierLeadJob)
+        // hardcodes Cache::store('redis'), bypassing phpunit.xml's
+        // CACHE_STORE=array. The Redis store is a shared external service —
+        // under `pest --parallel` every worker collides on the global
+        // `supplier:session` key, so one worker's afterEach forget()/flush()
+        // races another worker's mid-test loadSession(). Repoint the `redis`
+        // cache store at the in-process `array` driver: each worker then gets
+        // a hermetic, worker-local cache. Production keeps the real `redis`
+        // driver — this override only ever runs under APP_ENV=testing.
+        config(['cache.stores.redis.driver' => 'array']);
+    }
 }