fix(mailu): extend backup/restore seed to cover /mail Maildir volume (ADV-mailu-01)

tests/mailu/test_backup.py

@@ -1,8 +1,9 @@
-"""mailu — BACKUP overlay: assert the seeded mailbox is present at backup time.
+"""mailu — BACKUP overlay: assert both the seeded mailbox (sqlite /data) and the injected
+mail message (imap /mail) are present at backup time.
 
-ops.pre_backup created citest@<domain> via the admin container; this overlay verifies the admin
-sqlite DB contains that user at the moment the backup is taken. The backup→restore divergence
-is in ops.pre_restore (which deletes the user before restore runs)."""
+ops.pre_backup created citest@<domain> AND injected a message with subject ccci-backup-probe;
+this overlay asserts both are present at the moment the backup snapshot is taken.
+The backup→restore divergence is in ops.pre_restore (deletes user + wipes maildir)."""
 
 from __future__ import annotations
 
@@ -12,7 +13,11 @@ import sys
 sys.path.insert(0, os.path.join(os.path.dirname(__file__), "functional"))
 import _mailu  # noqa: E402
 
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "runner"))
+from harness import lifecycle  # noqa: E402
+
 _CI_LOCALPART = "citest"
+_CI_MAIL_SUBJECT = "ccci-backup-probe"
 
 
 def test_backup_captures_mailbox(live_app):
@@ -23,3 +28,16 @@ def test_backup_captures_mailbox(live_app):
         f"seeded mailbox {email!r} not found in config-export at backup time; "
         f"users present: {emails}"
     )
+
+
+def test_backup_captures_mail_message(live_app):
+    email = f"{_CI_LOCALPART}@{live_app}"
+    out = lifecycle.exec_in_app(
+        live_app,
+        ["sh", "-c", f"doveadm search -u '{email}' mailbox INBOX header subject '{_CI_MAIL_SUBJECT}'"],
+        service="imap",
+    )
+    assert out.strip(), (
+        f"test message {_CI_MAIL_SUBJECT!r} not found in INBOX for {email!r} at backup time; "
+        f"the /mail Maildir was not seeded as expected"
+    )