This Commit has code related to fixing/handling of the SaveEvent dup…

snd/src/org/labkey/snd/SNDManager.java

@@ -2207,6 +2207,24 @@ public boolean eventExists(Container c, User u, int eventId)
         return selector.exists();
     }
 
+    /**
+     * Returns the EventId for an existing event that was saved with the given ObjectId, or null if not found.
+     * Used by saveEvent for idempotent retries: when a client-generated ObjectId is provided and already
+     * exists in the DB, the event was already committed and should not be inserted again.
+     */
+    public Integer getEventIdByObjectId(Container c, User u, String objectId)
+    {
+        UserSchema schema = getSndUserSchema(c, u);
+
+        SQLFragment sql = new SQLFragment("SELECT EventId FROM ");
+        sql.append(schema.getTable(SNDSchema.EVENTS_TABLE_NAME), "ev");
+        sql.append(" WHERE ObjectId = ?");
+        sql.add(objectId);
+        SqlSelector selector = new SqlSelector(schema.getDbSchema(), sql);
+
+        return selector.getObject(Integer.class);
+    }
+
     /**
      * Get a project ObjectId given a projectId and revision in the format projectId|rev (ex. 61|1).
      */

snd/src/org/labkey/snd/SNDServiceImpl.java

@@ -349,6 +349,24 @@ public Event saveEvent(Container c, User u, Event event, boolean validateOnly)
     {
         try (DbScope.Transaction tx = SNDSchema.getInstance().getSchema().getScope().ensureTransaction(lock))
         {
+            // Idempotency check: if a client-generated objectId is present, look up whether
+            // this event was already committed (e.g. device lost the response after the server
+            // wrote the row). If found, override the auto-generated eventId with the existing one
+            // so the request falls through to the update path instead of creating a duplicate.
+            // Note: the Event constructor always auto-assigns an eventId via SNDSequencer even
+            // when the caller passes null, so checking event.getEventId() == null would never
+            // be true here and the idempotency check would never run. We guard only on objectId.
+            // For update requests the client omits objectId, so the controller supplies a random
+            // GUID that will never match an existing row — making this lookup a safe no-op.
+            if (event.getObjectId() != null)
+            {
+                Integer existingEventId = SNDManager.get().getEventIdByObjectId(c, u, event.getObjectId());
+                if (existingEventId != null)
+                {
+                    event.setEventId(existingEventId);
+                }
+            }
+
             if (event.getEventId() != null && SNDManager.get().eventExists(c, u, event.getEventId()))
             {
                 if ((event.getEventData() == null || event.getEventData().isEmpty()) &&