diff --git a/backend/src/main/java/org/raddatz/familienarchiv/repository/OcrTrainingRunRepository.java b/backend/src/main/java/org/raddatz/familienarchiv/repository/OcrTrainingRunRepository.java
index 99ff81da..b3878164 100644
--- a/backend/src/main/java/org/raddatz/familienarchiv/repository/OcrTrainingRunRepository.java
+++ b/backend/src/main/java/org/raddatz/familienarchiv/repository/OcrTrainingRunRepository.java
@@ -14,6 +14,8 @@ public interface OcrTrainingRunRepository extends JpaRepository<OcrTrainingRun,
 
     Optional<OcrTrainingRun> findFirstByStatusOrderByCreatedAtAsc(TrainingStatus status);
 
+    Optional<OcrTrainingRun> findFirstByPersonIdAndStatus(UUID personId, TrainingStatus status);
+
     boolean existsByPersonIdAndStatus(UUID personId, TrainingStatus status);
 
     List<OcrTrainingRun> findTop20ByOrderByCreatedAtDesc();
diff --git a/backend/src/main/java/org/raddatz/familienarchiv/service/SenderModelService.java b/backend/src/main/java/org/raddatz/familienarchiv/service/SenderModelService.java
index 465d6a8e..19a796db 100644
--- a/backend/src/main/java/org/raddatz/familienarchiv/service/SenderModelService.java
+++ b/backend/src/main/java/org/raddatz/familienarchiv/service/SenderModelService.java
@@ -72,9 +72,10 @@ public class SenderModelService {
     }
 
     /**
-     * Inserts a QUEUED row when training is already running (coalescing: at most one QUEUED per
-     * person_id). Runs immediately if idle. Returns true if training should start now, false if
-     * queued or skipped.
+     * Atomically checks the queue state and either creates a RUNNING row (returns true) or a
+     * QUEUED row (returns false). All three operations — idle check, duplicate-queue guard, and
+     * RUNNING row creation — happen in one transaction, eliminating the race window that would
+     * otherwise exist between the check and a separate RUNNING row creation.
      */
     @Transactional
     public boolean runOrQueueSenderTraining(UUID personId, int correctedLines) {
@@ -96,23 +97,29 @@ public class SenderModelService {
             return false;
         }
 
+        long blockCount = blockRepository.countManualKurrentBlocksByPerson(personId);
+        trainingRunRepository.save(OcrTrainingRun.builder()
+                .status(TrainingStatus.RUNNING)
+                .personId(personId)
+                .blockCount((int) blockCount)
+                .documentCount(0)
+                .modelName("sender_" + personId)
+                .build());
         return true;
     }
 
-    /** Executes sender training synchronously. Caller must run this on a background thread. */
+    /**
+     * Executes sender training synchronously. Caller must run this on a background thread.
+     * The RUNNING row is expected to already exist — created atomically by
+     * runOrQueueSenderTraining (for new runs) or by promoteNextQueuedRun (for promoted runs).
+     */
     public void triggerSenderTraining(UUID personId, int correctedLines) {
         String outputModelPath = "/app/models/sender_" + personId + ".mlmodel";
 
-        OcrTrainingRun run = Objects.requireNonNull(txTemplate.execute(status -> {
-            long blockCount = blockRepository.countManualKurrentBlocksByPerson(personId);
-            return trainingRunRepository.save(OcrTrainingRun.builder()
-                    .status(TrainingStatus.RUNNING)
-                    .personId(personId)
-                    .blockCount((int) blockCount)
-                    .documentCount(0)
-                    .modelName("sender_" + personId)
-                    .build());
-        }));
+        OcrTrainingRun run = Objects.requireNonNull(txTemplate.execute(status ->
+                trainingRunRepository.findFirstByPersonIdAndStatus(personId, TrainingStatus.RUNNING)
+                        .orElseThrow(() -> new IllegalStateException(
+                                "Expected RUNNING row for person " + personId + " but none found"))));
 
         String runId = run.getId().toString();
         MDC.put("trainingRunId", runId);
diff --git a/backend/src/test/java/org/raddatz/familienarchiv/service/SenderModelServiceTest.java b/backend/src/test/java/org/raddatz/familienarchiv/service/SenderModelServiceTest.java
index f46c5905..e08aa7b5 100644
--- a/backend/src/test/java/org/raddatz/familienarchiv/service/SenderModelServiceTest.java
+++ b/backend/src/test/java/org/raddatz/familienarchiv/service/SenderModelServiceTest.java
@@ -176,12 +176,38 @@ class SenderModelServiceTest {
         verify(trainingRunRepository, never()).save(any());
     }
 
+    @Test
+    void runOrQueueSenderTraining_createsRunningRow_atomically() {
+        // RUNNING row must be created inside the same @Transactional boundary as the idle check,
+        // eliminating the race window between the check and a separate triggerSenderTraining call.
+        when(trainingRunRepository.existsByPersonIdAndStatus(personId, TrainingStatus.QUEUED)).thenReturn(false);
+        when(trainingRunRepository.findFirstByStatus(TrainingStatus.RUNNING)).thenReturn(Optional.empty());
+        when(blockRepository.countManualKurrentBlocksByPerson(personId)).thenReturn(120L);
+        when(trainingRunRepository.save(any())).thenAnswer(inv -> {
+            OcrTrainingRun r = inv.getArgument(0);
+            if (r.getId() == null) r.setId(UUID.randomUUID());
+            return r;
+        });
+
+        boolean result = service.runOrQueueSenderTraining(personId, 120);
+
+        assertThat(result).isTrue();
+        verify(trainingRunRepository).save(argThat(r ->
+                r.getStatus() == TrainingStatus.RUNNING && personId.equals(r.getPersonId())));
+    }
+
     // ─── triggerSenderTraining — queue promotion ──────────────────────────────
 
     @Test
     void triggerSenderTraining_promotesNextQueued_afterCompletion() throws Exception {
         UUID nextPersonId = UUID.randomUUID();
 
+        OcrTrainingRun runningRun = OcrTrainingRun.builder()
+                .id(UUID.randomUUID()).status(TrainingStatus.RUNNING)
+                .personId(personId).blockCount(10).documentCount(0)
+                .modelName("sender_" + personId).build();
+        when(trainingRunRepository.findFirstByPersonIdAndStatus(personId, TrainingStatus.RUNNING))
+                .thenReturn(Optional.of(runningRun));
         when(blockRepository.countManualKurrentBlocksByPerson(personId)).thenReturn(10L);
         when(trainingRunRepository.save(any())).thenAnswer(inv -> {
             OcrTrainingRun r = inv.getArgument(0);