Fix #13: Expose Pre-edit Backup restoration

Preserve full diff opcodes before grouping, route modal navigation to a two-axis viewport-sized scroller, and calculate side-by-side layout using terminal cell widths so tabbed Hosts File lines keep a stable divider.

tests/test_manager.py

@@ -13,6 +13,7 @@ from unittest.mock import Mock, patch
 from src.hosts.core.manager import PermissionManager, HostsManager
 from src.hosts.core.models import HostEntry, HostsFile
 from src.hosts.core.commands import ToggleEntryCommand
+from src.hosts.core.restore_preview import fingerprint_file
 
 
 class TestPermissionManager:
@@ -592,15 +593,69 @@ class TestHostsManager:
                 manager._backup_path = Path(backup_file.name)
 
             try:
+                manager.undo_redo_history.clear_history = Mock()
                 success, message = manager.restore_backup()
 
                 assert success
                 assert "restored successfully" in message
-                mock_run.assert_called_once()
+                assert mock_run.call_count == 2
+                assert mock_run.call_args_list[0].args[0][:2] == ["sudo", "cp"]
+                assert mock_run.call_args_list[0].args[0][-1] != temp_file.name
+                assert mock_run.call_args_list[1].args[0][:2] == ["sudo", "mv"]
+                assert mock_run.call_args_list[1].args[0][-1] == temp_file.name
+                manager.undo_redo_history.clear_history.assert_called_once_with()
             finally:
                 # Clean up
                 manager._backup_path.unlink()
 
+    @patch("subprocess.run")
+    def test_restore_backup_copy_failure_leaves_hosts_file_target_untouched(
+        self, mock_run
+    ):
+        """A failed staged copy never opens the Hosts File target for writing."""
+        mock_run.return_value = Mock(returncode=1, stderr="Disk full")
+
+        with tempfile.NamedTemporaryFile() as temp_file:
+            manager = HostsManager(temp_file.name)
+            manager.edit_mode = True
+            with tempfile.NamedTemporaryFile(delete=False) as backup_file:
+                manager._backup_path = Path(backup_file.name)
+
+            try:
+                success, message = manager.restore_backup()
+
+                assert not success
+                assert "Disk full" in message
+                mock_run.assert_called_once()
+                assert mock_run.call_args.args[0][-1] != temp_file.name
+            finally:
+                manager._backup_path.unlink()
+
+    @patch("subprocess.run")
+    def test_restore_backup_refuses_files_that_changed_since_preview(self, mock_run):
+        """The privileged write uses the exact source and target the user reviewed."""
+        with tempfile.NamedTemporaryFile() as temp_file:
+            manager = HostsManager(temp_file.name)
+            manager.edit_mode = True
+            with tempfile.NamedTemporaryFile(delete=False) as backup_file:
+                backup_file.write(b"127.0.0.1 restored.test\n")
+                manager._backup_path = Path(backup_file.name)
+
+            try:
+                backup_digest = fingerprint_file(
+                    manager._backup_path, "Pre-edit Backup"
+                )
+                hosts_digest = fingerprint_file(manager.parser.file_path, "Hosts File")
+                Path(temp_file.name).write_text("192.0.2.2 changed.test\n")
+
+                success, message = manager.restore_backup(backup_digest, hosts_digest)
+
+                assert not success
+                assert "changed since review" in message
+                mock_run.assert_not_called()
+            finally:
+                manager._backup_path.unlink()
+
     def test_restore_backup_not_in_edit_mode(self):
         """Test restoring backup when not in edit mode."""
         with tempfile.NamedTemporaryFile() as temp_file: