test(controllers): match relaxed validation message in testValidationRejectsExistingDestDir

Commit e6caf85 ("feat(controller): allow OpenNotebookController clone
into non-existing or empty dest") relaxed validateCloneInput's dest
predicate from "must NOT exist" to "non-existing OR existing empty
directory", and changed the rejection message accordingly. The test
testValidationRejectsExistingDestDir still asserted the OLD message
substring ("already exists") and was failing with

  validation message must mention 'already exists'
  (got: Local root folder must be empty (contains 1 item(s)).)

The test's setup already creates a non-empty dest dir (with a sentinel
file), so the test's intent is still valid: NON-EMPTY existing dirs
must be rejected. Only the assertion substring needed updating to
"must be empty". The renamed local var (already_exists -> non_empty_exists)
and the expanded comment now correctly reflect the post-e6caf855
behavior contract.

Author: tamlok

tests/controllers/test_open_notebook_controller_clone.cpp

@@ -321,8 +321,14 @@ void TestOpenNotebookControllerClone::testValidationRejectsExistingDestDir() {
   TempDirFixture localTemp;
   QVERIFY(localTemp.isValid());
 
-  // Pre-create the user-chosen destination -- validateCloneInput must reject.
-  const QString existingDestDir = localTemp.filePath(QStringLiteral("already_exists"));
+  // Pre-create the user-chosen destination as a NON-EMPTY dir --
+  // validateCloneInput must reject. Per commit e6caf855 ("allow
+  // OpenNotebookController clone into non-existing or empty dest"), EMPTY
+  // existing dirs are now accepted (the worker rmdirs them before the
+  // staging->final rename); only NON-EMPTY existing dirs are rejected. The
+  // sentinel file below both verifies post-rollback safety AND makes the dir
+  // non-empty, which is what triggers the validation failure tested here.
+  const QString existingDestDir = localTemp.filePath(QStringLiteral("non_empty_exists"));
   QVERIFY(QDir().mkpath(existingDestDir));
   // Add a sentinel file so we can confirm we don't touch it on rollback.
   QFile sentinel(existingDestDir + QStringLiteral("/sentinel.txt"));
@@ -338,9 +344,9 @@ void TestOpenNotebookControllerClone::testValidationRejectsExistingDestDir() {
   OpenNotebookController controller(m_services);
   // Pre-flight validate: synchronous answer, no worker dispatch.
   const auto validation = controller.validateCloneInput(input);
-  QVERIFY2(!validation.valid, "existing dest dir must be rejected by validation");
-  QVERIFY2(validation.message.contains(QStringLiteral("already exists")),
-           qPrintable(QStringLiteral("validation message must mention 'already exists' (got: %1)")
+  QVERIFY2(!validation.valid, "non-empty existing dest dir must be rejected by validation");
+  QVERIFY2(validation.message.contains(QStringLiteral("must be empty")),
+           qPrintable(QStringLiteral("validation message must mention 'must be empty' (got: %1)")
                           .arg(validation.message)));
 
   // cloneAndOpen with the same input must short-circuit through