Guard probe_target against creating phantom local dirs when mount_root is unmounted

tests/test_coe_mirror.py

@@ -595,6 +595,51 @@ class TestPlaceIntoPloudSameFileIsNoop:
         assert test_file.stat().st_size > 0
 
 
+class TestMountRootGuard:
+    """Test probe_target() mount-root verification (phantom-dir regression guard)."""
+
+    def test_no_mount_root_configured_unchanged_behavior(self, mock_paths, setup_logging, monkeypatch):
+        """MOUNT_ROOT None + writable TARGET_DIR -> True (unchanged behavior)."""
+        monkeypatch.setattr(coe_mirror, "MOUNT_ROOT", None)
+
+        assert coe_mirror.probe_target() is True
+
+    def test_mount_root_live_target_under_it_returns_true(self, mock_paths, setup_logging, monkeypatch, tmp_path):
+        """MOUNT_ROOT set, live mount, TARGET_DIR a subdir of it -> True."""
+        mount_root = tmp_path / "pCloudDrive"
+        mount_root.mkdir()
+        target_dir = mount_root / "Hacking" / "ChurchOfMalware"
+        monkeypatch.setattr(coe_mirror, "MOUNT_ROOT", mount_root)
+        monkeypatch.setattr(coe_mirror, "TARGET_DIR", target_dir)
+        monkeypatch.setattr(coe_mirror.os.path, "ismount", lambda p: True)
+
+        assert coe_mirror.probe_target() is True
+
+    def test_mount_not_live_does_not_create_phantom_dir(self, mock_paths, setup_logging, monkeypatch, tmp_path):
+        """MOUNT_ROOT set but not mounted -> False, and TARGET_DIR is never created."""
+        mount_root = tmp_path / "pCloudDrive"
+        mount_root.mkdir()
+        target_dir = mount_root / "Hacking" / "ChurchOfMalware"
+        monkeypatch.setattr(coe_mirror, "MOUNT_ROOT", mount_root)
+        monkeypatch.setattr(coe_mirror, "TARGET_DIR", target_dir)
+        monkeypatch.setattr(coe_mirror.os.path, "ismount", lambda p: False)
+
+        assert coe_mirror.probe_target() is False
+        assert not target_dir.exists()
+
+    def test_target_dir_not_under_mount_root_returns_false(self, mock_paths, setup_logging, monkeypatch, tmp_path):
+        """MOUNT_ROOT set, live mount, but TARGET_DIR is unrelated -> False, no dir created."""
+        mount_root = tmp_path / "pCloudDrive"
+        mount_root.mkdir()
+        target_dir = tmp_path / "unrelated" / "target"
+        monkeypatch.setattr(coe_mirror, "MOUNT_ROOT", mount_root)
+        monkeypatch.setattr(coe_mirror, "TARGET_DIR", target_dir)
+        monkeypatch.setattr(coe_mirror.os.path, "ismount", lambda p: True)
+
+        assert coe_mirror.probe_target() is False
+        assert not target_dir.exists()
+
+
 # Tests for Matrix notification implementation.
 # Note: Tests requiring monkeypatched subprocess.run must use raising=False because
 # subprocess.run is not a class attribute on the coe_mirror module by default