diff --git a/services/nginx/app/modules/selfserve/classes/selfserve_wash_flow.php b/services/nginx/app/modules/selfserve/classes/selfserve_wash_flow.php
index af9f7014..cffca074 100644
--- a/services/nginx/app/modules/selfserve/classes/selfserve_wash_flow.php
+++ b/services/nginx/app/modules/selfserve/classes/selfserve_wash_flow.php
@@ -483,8 +483,8 @@ class selfserve_wash_flow implements selfserve_wash_flow_i
             if (!$session->markForceStoppedIfOpen($orderId, $eventPayload)) {
                 $summary = $this->getSessionSummary((int)$session->id);
             } else {
-            $this->logSessionEvent((int)$session->id, selfserve_wash_event_type::SESSION_FORCE_STOPPED, $eventPayload);
-            $summary = $this->getSessionSummary((int)$session->id);
+                $this->logSessionEvent((int)$session->id, selfserve_wash_event_type::SESSION_FORCE_STOPPED, $eventPayload);
+                $summary = $this->getSessionSummary((int)$session->id);
             }
         }
 
diff --git a/services/nginx/app/tests/Unit/Selfserve/SelfserveSessionRaceWiringTest.php b/services/nginx/app/tests/Unit/Selfserve/SelfserveSessionRaceWiringTest.php
new file mode 100644
index 00000000..a6e4ce9c
--- /dev/null
+++ b/services/nginx/app/tests/Unit/Selfserve/SelfserveSessionRaceWiringTest.php
@@ -0,0 +1,46 @@
+<?php
+
+it('serializes self-serve session synchronization before reading or creating open sessions', function (): void {
+    $washFlow = file_get_contents(app_path('modules/selfserve/classes/selfserve_wash_flow.php'));
+
+    expect($washFlow)->not->toBeFalse()
+        ->and($washFlow)->toContain('withSessionMutationLock')
+        ->and($washFlow)->toContain('sessionMutationLockKey')
+        ->and($washFlow)->toContain('set_if_absent_with_expiration')
+        ->and($washFlow)->toContain('GET_LOCK');
+
+    $syncOffset = strpos($washFlow, 'public function synchronizeSession');
+    expect($syncOffset)->not->toBeFalse();
+
+    $syncMethod = substr($washFlow, (int)$syncOffset, 9000);
+    $snapshotOffset = strpos($syncMethod, '$snapshot = $this->buildEligibilitySnapshot');
+    $lockOffset = strpos($syncMethod, '$mutationResult = $this->withSessionMutationLock');
+    $findOffset = strpos($syncMethod, '$session = $this->findLatestOpenSession');
+    $addOffset = strpos($syncMethod, '$session = (new selfserve_wash_sessions_o())->add');
+    $relayOffset = strpos($syncMethod, '$this->syncMachineRelayFromVisibleServices');
+
+    expect($snapshotOffset)->not->toBeFalse()
+        ->and($lockOffset)->not->toBeFalse()
+        ->and($findOffset)->not->toBeFalse()
+        ->and($addOffset)->not->toBeFalse()
+        ->and($relayOffset)->not->toBeFalse()
+        ->and($snapshotOffset)->toBeLessThan($lockOffset)
+        ->and($lockOffset)->toBeLessThan($findOffset)
+        ->and($findOffset)->toBeLessThan($addOffset)
+        ->and($addOffset)->toBeLessThan($relayOffset);
+});
+
+it('closes self-serve wash sessions with an atomic open-session guard', function (): void {
+    $sessionObject = file_get_contents(app_path('objects/selfserve_wash_sessions_o.php'));
+    $washFlow = file_get_contents(app_path('modules/selfserve/classes/selfserve_wash_flow.php'));
+
+    expect($sessionObject)->not->toBeFalse()
+        ->and($sessionObject)->toContain('markCompletedIfOpen')
+        ->and($sessionObject)->toContain('markForceStoppedIfOpen')
+        ->and($sessionObject)->toContain('AND `completed_at` IS NULL')
+        ->and($sessionObject)->toContain('AND UPPER(TRIM(`status`)) NOT IN ($terminalStatuses)');
+
+    expect($washFlow)->not->toBeFalse()
+        ->and($washFlow)->toContain('if (!$session->markCompletedIfOpen($orderId))')
+        ->and($washFlow)->toContain('if (!$session->markForceStoppedIfOpen($orderId, $eventPayload))');
+});