diff --git a/app/tests/Unit/Services/Project/SupplierSnapshotGuardTest.php b/app/tests/Unit/Services/Project/SupplierSnapshotGuardTest.php
new file mode 100644
index 00000000..bbc8f833
--- /dev/null
+++ b/app/tests/Unit/Services/Project/SupplierSnapshotGuardTest.php
@@ -0,0 +1,70 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Services\Project;
+
+use App\Services\Project\SupplierSnapshotGuard;
+use Carbon\CarbonImmutable;
+use Tests\TestCase;
+
+/**
+ * Unit-тесты для SupplierSnapshotGuard.
+ *
+ * Spec: docs/superpowers/plans/2026-05-26-supplier-snapshot-guard.md
+ */
+class SupplierSnapshotGuardTest extends TestCase
+{
+    private SupplierSnapshotGuard $guard;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->guard = new SupplierSnapshotGuard;
+    }
+
+    public function test_grace_until_for_pause_before_21_msk_is_next_day_21_msk(): void
+    {
+        $pausedAt = CarbonImmutable::parse('2026-05-25 14:00:00', 'Europe/Moscow');
+        $graceUntil = $this->guard->computeGraceUntil($pausedAt);
+
+        $this->assertSame(
+            '2026-05-26 21:00:00',
+            $graceUntil->setTimezone('Europe/Moscow')->format('Y-m-d H:i:s'),
+        );
+    }
+
+    public function test_grace_until_for_pause_after_21_msk_is_day_plus_two_21_msk(): void
+    {
+        $pausedAt = CarbonImmutable::parse('2026-05-25 22:00:00', 'Europe/Moscow');
+        $graceUntil = $this->guard->computeGraceUntil($pausedAt);
+
+        $this->assertSame(
+            '2026-05-27 21:00:00',
+            $graceUntil->setTimezone('Europe/Moscow')->format('Y-m-d H:i:s'),
+        );
+    }
+
+    public function test_grace_until_for_pause_exactly_at_21_msk_is_day_plus_two_21_msk(): void
+    {
+        $pausedAt = CarbonImmutable::parse('2026-05-25 21:00:00', 'Europe/Moscow');
+        $graceUntil = $this->guard->computeGraceUntil($pausedAt);
+
+        $this->assertSame(
+            '2026-05-27 21:00:00',
+            $graceUntil->setTimezone('Europe/Moscow')->format('Y-m-d H:i:s'),
+        );
+    }
+
+    public function test_grace_until_handles_utc_input(): void
+    {
+        // 14:00 UTC = 17:00 MSK (до 21:00) → grace = следующее 21:00 МСК +24ч
+        $pausedAt = CarbonImmutable::parse('2026-05-25 14:00:00', 'UTC');
+        $graceUntil = $this->guard->computeGraceUntil($pausedAt);
+
+        $this->assertSame(
+            '2026-05-26 21:00:00',
+            $graceUntil->setTimezone('Europe/Moscow')->format('Y-m-d H:i:s'),
+        );
+    }
+}