Ловушка у ящика (TRAP): что ящик отправляет — в его же INBOX, наружу ничего

Для staging@: staging-стенд шлёт через настоящий mail.jambocheck.com,
но тестовые письма не доходят до живых людей.
- V5: users.is_trap
- MailRouter: отправитель-ловушка → все получатели LOCAL, одна копия в INBOX отправителя
- PUT /api/admin/mailboxes/{id}/trap, MailboxView.trap
- MAILBOXES: кнопка outbox/move_to_inbox, метка TRAP
- тесты: router + admin (77 тестов)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/src/main/java/com/mailserver/smtp/MailRouter.java

@@ -17,6 +17,8 @@ import java.util.Locale;
  * an existing mailbox of our domain → that mailbox; catch-all set → everything else into the catch-all mailbox
  * (nothing goes outside, existing mailboxes still get their own mail); otherwise our domain without such a mailbox →
  * "no such user", someone else's domain → the delivery queue, only for a logged-in sender (never an open relay).
+ * A logged-in TRAP mailbox (staging@) sends nowhere: every recipient is accepted and ONE copy is stored in the
+ * sender's own INBOX — a staging stand uses the real server, but its test mail never reaches people.
  */
 @Service
 public class MailRouter implements SmtpBackend {
@@ -48,6 +50,9 @@ public class MailRouter implements SmtpBackend {
 
     @Override
     public Route route(String recipient, String authenticatedUser) {
+        if (isTrap(authenticatedUser)) {
+            return Route.LOCAL;
+        }
         if (domains.isLocal(recipient) && mailboxExists(recipient)) {
             return Route.LOCAL;
         }
@@ -66,6 +71,11 @@ public class MailRouter implements SmtpBackend {
     @Override
     public void accept(Envelope envelope, byte[] message) throws Exception {
         boolean trusted = envelope.authenticatedUser() != null;
+        if (isTrap(envelope.authenticatedUser())) {
+            localDelivery.deliver(message, envelope.authenticatedUser().toLowerCase(Locale.ROOT), envelope.remoteIp(),
+                    envelope.mailFrom(), true);
+            return;
+        }
         byte[] signed = null;
         for (Recipient recipient : envelope.recipients()) {
             switch (recipient.route()) {
@@ -92,6 +102,15 @@ public class MailRouter implements SmtpBackend {
         return domains.catchAll();
     }
 
+    /** The logged-in sender is an active trap mailbox. */
+    boolean isTrap(String authenticatedUser) {
+        if (authenticatedUser == null) {
+            return false;
+        }
+        User user = users.findByEmail(authenticatedUser.toLowerCase(Locale.ROOT)).block();
+        return user != null && user.isTrap();
+    }
+
     private boolean mailboxExists(String address) {
         return Boolean.TRUE.equals(users.existsByEmail(address.toLowerCase(Locale.ROOT)).block());
     }