Fix #12: roll back mutations when saving fails

README.md

@@ -75,8 +75,6 @@ sorting, DNS refresh, movement, undo, and redo.
 ## Safety and known limitations
 
 - Reloading discards unsaved in-memory state.
-- A failed save can leave the interface changed while `/etc/hosts` remains
-  unchanged.
 - Pre-edit Backups are not listed or restored by the TUI and have no retention
   management. Manual recovery is documented in the user guide.
 - Leaving Privileged Mode clears the application's session state but does not

docs/user-guide.md

@@ -75,8 +75,9 @@ Default Entries represent protected baseline localhost or broadcasthost
 mappings. They cannot be changed, deleted, activated, deactivated, or moved.
 
 Successful mutations are saved to `/etc/hosts` immediately. Read the
-status message after every action. A message that reports a save failure means
-the interface may have changed while the system file did not.
+status message after every action. If saving fails, the application restores
+the Host Entries, visible selection, and undo/redo history from before the
+action.
 
 ## Use a DNS Entry
 
@@ -120,13 +121,9 @@ Adding, editing, deleting, moving, activating, deactivating, undoing, redoing,
 and successfully refreshing DNS Entries save immediately. `Ctrl+S` explicitly
 saves the entire current in-memory Hosts File.
 
-If saving an undo or redo result fails, the application restores the prior
-in-memory state and undo/redo history. Reload with `Ctrl+R` to verify the
-on-disk state before attempting another change.
-
-Other save failures can leave the interface changed while the file on disk is
-unchanged. Reload with `Ctrl+R` to return the interface to the on-disk state
-before attempting another change.
+If an immediate save fails, the application restores the complete pre-action
+in-memory state, visible selection, and undo/redo history. A later mutation
+therefore cannot accidentally persist the failed change.
 
 ### Locate a Pre-edit Backup
 

src/hosts/core/manager.py

@@ -8,6 +8,8 @@ and safe file modifications with backup and validation.
 import os
 import subprocess
 import tempfile
+from copy import deepcopy
+from dataclasses import dataclass
 from pathlib import Path
 from typing import Optional, Tuple
 from .models import HostEntry, HostsFile
@@ -23,6 +25,14 @@ from .commands import (
 )
 
 
+@dataclass
+class MutationState:
+    """Hosts File and history state from before a persisted mutation."""
+
+    hosts_file: HostsFile
+    undo_redo_history: UndoRedoHistory
+
+
 class PermissionManager:
     """
     Manages sudo permissions for hosts file editing.
@@ -591,6 +601,22 @@ class HostsManager:
         """Get description of the operation that would be redone."""
         return self.undo_redo_history.get_redo_description()
 
+    def capture_mutation_state(self, hosts_file: HostsFile) -> MutationState:
+        """Capture the Hosts File and history before a persisted mutation."""
+        saved_hosts_file, saved_history = deepcopy((hosts_file, self.undo_redo_history))
+        return MutationState(saved_hosts_file, saved_history)
+
+    def save_mutation(
+        self, hosts_file: HostsFile, state: MutationState
+    ) -> Tuple[bool, str, HostsFile]:
+        """Save a mutation or restore its pre-action model and history."""
+        success, message = self.save_hosts_file(hosts_file)
+        if success:
+            return True, message, hosts_file
+
+        self.undo_redo_history = state.undo_redo_history
+        return False, message, state.hosts_file
+
     def save_hosts_file(self, hosts_file: HostsFile) -> Tuple[bool, str]:
         """
         Save the hosts file to disk with sudo permissions.

src/hosts/tui/app.py

@@ -5,7 +5,7 @@ This module contains the main application class that orchestrates
 all the handlers and provides the primary user interface.
 """
 
-from collections.abc import Callable
+from dataclasses import dataclass
 
 from textual.app import App, ComposeResult, SuspendNotSupported
 from textual.containers import Horizontal, Vertical
@@ -21,10 +21,9 @@ from textual.widgets import (
 from textual.reactive import reactive
 
 from ..core.parser import HostsParser
-from ..core.models import HostsFile
-from ..core.commands import OperationResult
+from ..core.models import HostEntry, HostsFile
 from ..core.config import Config
-from ..core.manager import HostsManager
+from ..core.manager import HostsManager, MutationState
 from ..core.dns import DNSService
 from ..core.filters import EntryFilter, FilterOptions
 from .config_modal import ConfigModal
@@ -40,6 +39,14 @@ from .edit_handler import EditHandler
 from .navigation_handler import NavigationHandler
 
 
+@dataclass
+class MutationSnapshot:
+    """TUI and core state that must survive a failed persistence attempt."""
+
+    manager_state: MutationState
+    selected_entry_index: int
+
+
 class HostsManagerApp(App):
     """
     Main application class for the hosts TUI manager.
@@ -353,6 +360,44 @@ class HostsManagerApp(App):
         except Exception:
             pass
 
+    def capture_mutation_state(self) -> MutationSnapshot:
+        """Capture the model, selection, and history before a mutation."""
+        return MutationSnapshot(
+            manager_state=self.manager.capture_mutation_state(self.hosts_file),
+            selected_entry_index=self.selected_entry_index,
+        )
+
+    def save_mutation(self, snapshot: MutationSnapshot, action: str) -> bool:
+        """Persist a mutation, restoring its complete pre-action state on failure."""
+        save_success, save_message, hosts_file = self.manager.save_mutation(
+            self.hosts_file, snapshot.manager_state
+        )
+        if save_success:
+            return True
+
+        self.hosts_file = hosts_file
+        self.selected_entry_index = snapshot.selected_entry_index
+
+        self.table_handler.populate_entries_table()
+        self.table_handler.move_cursor_to_entry_index(self.selected_entry_index)
+        self.details_handler.update_entry_details()
+        self.update_status(
+            f"❌ {action} save failed; previous state restored: {save_message}"
+        )
+        return False
+
+    def get_pending_dns_entry(
+        self, entry_index: int, dns_name: str, hostnames: list[str]
+    ) -> HostEntry | None:
+        """Return the original DNS Entry if it is unchanged after an await."""
+        if not 0 <= entry_index < len(self.hosts_file.entries):
+            return None
+
+        entry = self.hosts_file.entries[entry_index]
+        if entry.dns_name != dns_name or entry.hostnames != hostnames:
+            return None
+        return entry
+
     # Event handlers
     def on_data_table_row_highlighted(self, event: DataTable.RowHighlighted) -> None:
         """Handle row highlighting (cursor movement) in the DataTable."""
@@ -624,14 +669,13 @@ class HostsManagerApp(App):
                 self.update_status("Entry creation cancelled")
                 return
 
+            snapshot = self.capture_mutation_state()
+
             # Add the entry using the command-based manager method
             result = self.manager.execute_add_command(self.hosts_file, new_entry)
             if result.success:
                 # Save the changes
-                save_success, save_message = self.manager.save_hosts_file(
-                    self.hosts_file
-                )
-                if save_success:
+                if self.save_mutation(snapshot, "Add"):
                     # Refresh the table
                     self.table_handler.populate_entries_table()
                     # Move cursor to the newly added entry (last entry)
@@ -649,8 +693,6 @@ class HostsManagerApp(App):
                         self.update_status(
                             f"✅ {result.message} - Changes saved automatically"
                         )
-                else:
-                    self.update_status(f"Entry added but save failed: {save_message}")
             else:
                 self.update_status(f"❌ {result.message}")
 
@@ -682,16 +724,15 @@ class HostsManagerApp(App):
                 self.update_status("Entry deletion cancelled")
                 return
 
+            snapshot = self.capture_mutation_state()
+
             # Delete the entry using the command-based manager method
             result = self.manager.execute_delete_command(
                 self.hosts_file, self.selected_entry_index
             )
             if result.success:
                 # Save the changes
-                save_success, save_message = self.manager.save_hosts_file(
-                    self.hosts_file
-                )
-                if save_success:
+                if self.save_mutation(snapshot, "Delete"):
                     # Adjust selected index if needed
                     if self.selected_entry_index >= len(self.hosts_file.entries):
                         self.selected_entry_index = max(
@@ -704,8 +745,6 @@ class HostsManagerApp(App):
                     self.update_status(
                         f"✅ {result.message} - Changes saved automatically"
                     )
-                else:
-                    self.update_status(f"Entry deleted but save failed: {save_message}")
             else:
                 self.update_status(f"❌ {result.message}")
 
@@ -715,25 +754,6 @@ class HostsManagerApp(App):
         """Quit the application."""
         self.navigation_handler.quit_application()
 
-    def _save_history_operation(
-        self, action: str, rollback: Callable[[HostsFile], OperationResult]
-    ) -> bool:
-        """Save a history change or restore the previous state after a failure."""
-        save_success, save_message = self.manager.save_hosts_file(self.hosts_file)
-        if save_success:
-            return True
-
-        rollback_result = rollback(self.hosts_file)
-        if rollback_result.success:
-            self.update_status(
-                f"❌ {action} save failed; previous state restored: {save_message}"
-            )
-        else:
-            self.update_status(
-                f"❌ {action} save failed and could not restore the previous state: {save_message}; {rollback_result.message}. Reload the Hosts File."
-            )
-        return False
-
     def action_undo(self) -> None:
         """Undo the last operation."""
         if not self.edit_mode:
@@ -746,13 +766,12 @@ class HostsManagerApp(App):
 
         # Get description before undoing
         description = self.manager.get_undo_description()
+        snapshot = self.capture_mutation_state()
 
         # Perform undo
         result = self.manager.undo_last_operation(self.hosts_file)
         if result.success:
-            if not self._save_history_operation(
-                "Undo", self.manager.redo_last_operation
-            ):
+            if not self.save_mutation(snapshot, "Undo"):
                 return
 
             # Refresh the table and update UI
@@ -774,13 +793,12 @@ class HostsManagerApp(App):
 
         # Get description before redoing
         description = self.manager.get_redo_description()
+        snapshot = self.capture_mutation_state()
 
         # Perform redo
         result = self.manager.redo_last_operation(self.hosts_file)
         if result.success:
-            if not self._save_history_operation(
-                "Redo", self.manager.undo_last_operation
-            ):
+            if not self.save_mutation(snapshot, "Redo"):
                 return
 
             # Refresh the table and update UI
@@ -808,13 +826,6 @@ class HostsManagerApp(App):
             self.update_status("No entries with DNS names found")
             return
 
-        # Remember the currently selected entry before DNS update
-        current_entry = None
-        if self.hosts_file.entries and self.selected_entry_index < len(
-            self.hosts_file.entries
-        ):
-            current_entry = self.hosts_file.entries[self.selected_entry_index]
-
         async def refresh_dns():
             try:
                 # Extract DNS names (not hostnames!) from entries
@@ -827,18 +838,31 @@ class HostsManagerApp(App):
                 resolved_count = 0
                 failed_count = 0
 
-                # Resolve each DNS name and apply results back to entries
-                for dns_name in dns_names:
-                    resolution = await self.dns_service.resolve_entry_async(dns_name)
+                resolutions = [
+                    (dns_name, await self.dns_service.resolve_entry_async(dns_name))
+                    for dns_name in dns_names
+                ]
+                snapshot = self.capture_mutation_state()
+                current_entry = (
+                    self.hosts_file.entries[self.selected_entry_index]
+                    if 0 <= self.selected_entry_index < len(self.hosts_file.entries)
+                    else None
+                )
+                current_dns_entries = self.hosts_file.get_dns_entries()
 
+                # Apply each DNS result back to the current entries.
+                for dns_name, resolution in resolutions:
                     # Find the corresponding entry and update it
-                    for entry in dns_entries:
+                    for entry in current_dns_entries:
                         if entry.dns_name == dns_name:
                             # Apply resolution results to entry fields
                             entry.last_resolved = resolution.resolved_at
                             entry.dns_resolution_status = resolution.status.value
 
-                            if resolution.is_success():
+                            if (
+                                resolution.is_success()
+                                and resolution.resolved_ip is not None
+                            ):
                                 # Update both resolved_ip and ip_address for the hosts file
                                 entry.ip_address = resolution.resolved_ip
                                 entry.resolved_ip = resolution.resolved_ip
@@ -849,13 +873,7 @@ class HostsManagerApp(App):
 
                 # Save hosts file with updated DNS information
                 if resolved_count > 0 or failed_count > 0:
-                    save_success, save_message = self.manager.save_hosts_file(
-                        self.hosts_file
-                    )
-                    if not save_success:
-                        self.update_status(
-                            f"❌ DNS resolution completed but save failed: {save_message}"
-                        )
+                    if not self.save_mutation(snapshot, "DNS refresh"):
                         return
 
                 # Update the UI and restore cursor position
@@ -907,33 +925,36 @@ class HostsManagerApp(App):
             self.update_status("❌ Selected entry has no DNS name to resolve")
             return
 
-        # Remember the currently selected entry before DNS update
-        current_entry = entry
+        dns_name = entry.dns_name
+        entry_hostnames = entry.hostnames.copy()
+        entry_index = self.selected_entry_index
 
         async def update_single_dns():
             try:
-                dns_name = entry.dns_name
-
                 # Resolve the DNS name
                 resolution = await self.dns_service.resolve_entry_async(dns_name)
+                current_entry = self.get_pending_dns_entry(
+                    entry_index, dns_name, entry_hostnames
+                )
+                if current_entry is None:
+                    self.update_status(
+                        f"❌ DNS entry changed before resolution completed: {dns_name}"
+                    )
+                    return
+
+                snapshot = self.capture_mutation_state()
 
                 # Apply resolution results to entry fields
-                entry.last_resolved = resolution.resolved_at
-                entry.dns_resolution_status = resolution.status.value
+                current_entry.last_resolved = resolution.resolved_at
+                current_entry.dns_resolution_status = resolution.status.value
 
-                if resolution.is_success():
+                if resolution.is_success() and resolution.resolved_ip is not None:
                     # Update both resolved_ip and ip_address for the hosts file
-                    entry.ip_address = resolution.resolved_ip
-                    entry.resolved_ip = resolution.resolved_ip
+                    current_entry.ip_address = resolution.resolved_ip
+                    current_entry.resolved_ip = resolution.resolved_ip
 
                     # Save hosts file with updated DNS information
-                    save_success, save_message = self.manager.save_hosts_file(
-                        self.hosts_file
-                    )
-                    if not save_success:
-                        self.update_status(
-                            f"❌ DNS resolution completed but save failed: {save_message}"
-                        )
+                    if not self.save_mutation(snapshot, "DNS refresh"):
                         return
 
                     # Update the UI and restore cursor position
@@ -946,14 +967,13 @@ class HostsManagerApp(App):
                     )
                 else:
                     # Resolution failed, save the status update
-                    save_success, save_message = self.manager.save_hosts_file(
-                        self.hosts_file
-                    )
-                    if save_success:
-                        # Update the UI to show failed status and restore cursor position
-                        self.table_handler.populate_entries_table()
-                        self.table_handler.restore_cursor_position(current_entry)
-                        self.details_handler.update_entry_details()
+                    if not self.save_mutation(snapshot, "DNS refresh"):
+                        return
+
+                    # Update the UI to show failed status and restore cursor position
+                    self.table_handler.populate_entries_table()
+                    self.table_handler.restore_cursor_position(current_entry)
+                    self.details_handler.update_entry_details()
 
                     error_msg = resolution.error_message or "Unknown error"
                     self.update_status(
@@ -1029,62 +1049,62 @@ class HostsManagerApp(App):
         if not hasattr(entry, "dns_name") or not entry.dns_name:
             return
 
+        dns_name = entry.dns_name
+        entry_hostnames = entry.hostnames.copy()
+        entry_index = next(
+            (
+                index
+                for index, candidate in enumerate(self.hosts_file.entries)
+                if candidate is entry
+            ),
+            -1,
+        )
+
         async def resolve_and_activate():
             try:
                 # Resolve the DNS name
-                resolution = await self.dns_service.resolve_entry_async(entry.dns_name)
+                resolution = await self.dns_service.resolve_entry_async(dns_name)
+                current_entry = self.get_pending_dns_entry(
+                    entry_index, dns_name, entry_hostnames
+                )
+                if current_entry is None:
+                    self.update_status(
+                        f"❌ DNS entry changed before resolution completed: {dns_name}"
+                    )
+                    return
 
-                if resolution.is_success():
-                    # Find the entry in the hosts file and update it
-                    for hosts_entry in self.hosts_file.entries:
-                        if (
-                            hasattr(hosts_entry, "dns_name")
-                            and hosts_entry.dns_name == entry.dns_name
-                            and hosts_entry.hostnames == entry.hostnames
-                        ):
-                            # Update the entry with resolved IP
-                            hosts_entry.ip_address = resolution.resolved_ip
-                            hosts_entry.resolved_ip = resolution.resolved_ip
-                            hosts_entry.last_resolved = resolution.resolved_at
-                            hosts_entry.dns_resolution_status = resolution.status.value
-                            hosts_entry.is_active = True  # Activate the entry
+                snapshot = self.capture_mutation_state()
 
-                            # Save the updated hosts file
-                            save_success, save_message = self.manager.save_hosts_file(
-                                self.hosts_file
-                            )
-                            if save_success:
-                                # Update UI - use direct calls since we're in the same async context
-                                self.table_handler.populate_entries_table()
-                                self.details_handler.update_entry_details()
-                                self.update_status(
-                                    f"✅ DNS resolved: {entry.dns_name} → {resolution.resolved_ip} (entry activated)"
-                                )
-                            else:
-                                self.update_status(
-                                    f"❌ DNS resolved but save failed: {save_message}"
-                                )
-                            break
+                if resolution.is_success() and resolution.resolved_ip is not None:
+                    # Update the entry with resolved IP
+                    current_entry.ip_address = resolution.resolved_ip
+                    current_entry.resolved_ip = resolution.resolved_ip
+                    current_entry.last_resolved = resolution.resolved_at
+                    current_entry.dns_resolution_status = resolution.status.value
+                    current_entry.is_active = True  # Activate the entry
+
+                    # Save the updated hosts file
+                    if self.save_mutation(snapshot, "DNS activation"):
+                        # Update UI - use direct calls since we're in the same async context
+                        self.table_handler.populate_entries_table()
+                        self.details_handler.update_entry_details()
+                        self.update_status(
+                            f"✅ DNS resolved: {dns_name} → {resolution.resolved_ip} (entry activated)"
+                        )
                 else:
                     # Resolution failed, update status but keep entry inactive
-                    for hosts_entry in self.hosts_file.entries:
-                        if (
-                            hasattr(hosts_entry, "dns_name")
-                            and hosts_entry.dns_name == entry.dns_name
-                            and hosts_entry.hostnames == entry.hostnames
-                        ):
-                            hosts_entry.dns_resolution_status = resolution.status.value
-                            hosts_entry.last_resolved = resolution.resolved_at
-                            break
+                    current_entry.dns_resolution_status = resolution.status.value
+                    current_entry.last_resolved = resolution.resolved_at
+
+                    if not self.save_mutation(snapshot, "DNS refresh"):
+                        return
 
                     self.update_status(
-                        f"❌ DNS resolution failed for {entry.dns_name}: {resolution.error_message or 'Unknown error'}"
+                        f"❌ DNS resolution failed for {dns_name}: {resolution.error_message or 'Unknown error'}"
                     )
 
             except Exception as e:
-                self.update_status(
-                    f"❌ DNS resolution error for {entry.dns_name}: {str(e)}"
-                )
+                self.update_status(f"❌ DNS resolution error for {dns_name}: {str(e)}")
 
         # Start the resolution in background
         self.run_worker(resolve_and_activate(), exclusive=False)

src/hosts/tui/edit_handler.py

@@ -355,6 +355,7 @@ class EditHandler:
         hostnames = [h.strip() for h in hostname_input.value.split(",") if h.strip()]
         comment = comment_input.value.strip() or None
         is_active = active_checkbox.value
+        snapshot = self.app.capture_mutation_state()
 
         # Update entry based on type
         if entry_type == "ip":
@@ -390,8 +391,7 @@ class EditHandler:
         entry.is_active = is_active
 
         # Save to file
-        success, message = self.app.manager.save_hosts_file(self.app.hosts_file)
-        if success:
+        if self.app.save_mutation(snapshot, "Edit"):
             # Update the table display
             self.app.table_handler.populate_entries_table()
             # Restore cursor position
@@ -410,9 +410,7 @@ class EditHandler:
             else:
                 self.app.update_status("Entry saved successfully")
             return True
-        else:
-            self.app.update_status(f"❌ Error saving entry: {message}")
-            return False
+        return False
 
     def navigate_to_next_field(self) -> None:
         """Move to the next field in edit mode."""

src/hosts/tui/navigation_handler.py

@@ -29,6 +29,7 @@ class NavigationHandler:
 
         # Remember current entry for cursor position restoration
         current_entry = self.app.hosts_file.entries[self.app.selected_entry_index]
+        snapshot = self.app.capture_mutation_state()
 
         # Use command-based method for undo/redo support
         result = self.app.manager.execute_toggle_command(
@@ -36,10 +37,7 @@ class NavigationHandler:
         )
         if result.success:
             # Auto-save the changes immediately
-            save_success, save_message = self.app.manager.save_hosts_file(
-                self.app.hosts_file
-            )
-            if save_success:
+            if self.app.save_mutation(snapshot, "Toggle"):
                 self.app.table_handler.populate_entries_table()
                 # Restore cursor position to the same entry
                 self.app.set_timer(
@@ -52,8 +50,6 @@ class NavigationHandler:
                 self.app.update_status(
                     f"{result.message} - Changes saved automatically"
                 )
-            else:
-                self.app.update_status(f"Entry toggled but save failed: {save_message}")
         else:
             self.app.update_status(f"Error toggling entry: {result.message}")
 
@@ -69,16 +65,15 @@ class NavigationHandler:
             self.app.update_status("No entries to move")
             return
 
+        snapshot = self.app.capture_mutation_state()
+
         # Use command-based method for undo/redo support
         result = self.app.manager.execute_move_command(
             self.app.hosts_file, self.app.selected_entry_index, "up"
         )
         if result.success:
             # Auto-save the changes immediately
-            save_success, save_message = self.app.manager.save_hosts_file(
-                self.app.hosts_file
-            )
-            if save_success:
+            if self.app.save_mutation(snapshot, "Move"):
                 # Update the selection index to follow the moved entry
                 if self.app.selected_entry_index > 0:
                     self.app.selected_entry_index -= 1
@@ -94,8 +89,6 @@ class NavigationHandler:
                 self.app.update_status(
                     f"{result.message} - Changes saved automatically"
                 )
-            else:
-                self.app.update_status(f"Entry moved but save failed: {save_message}")
         else:
             self.app.update_status(f"Error moving entry: {result.message}")
 
@@ -111,16 +104,15 @@ class NavigationHandler:
             self.app.update_status("No entries to move")
             return
 
+        snapshot = self.app.capture_mutation_state()
+
         # Use command-based method for undo/redo support
         result = self.app.manager.execute_move_command(
             self.app.hosts_file, self.app.selected_entry_index, "down"
         )
         if result.success:
             # Auto-save the changes immediately
-            save_success, save_message = self.app.manager.save_hosts_file(
-                self.app.hosts_file
-            )
-            if save_success:
+            if self.app.save_mutation(snapshot, "Move"):
                 # Update the selection index to follow the moved entry
                 if self.app.selected_entry_index < len(self.app.hosts_file.entries) - 1:
                     self.app.selected_entry_index += 1
@@ -136,8 +128,6 @@ class NavigationHandler:
                 self.app.update_status(
                     f"{result.message} - Changes saved automatically"
                 )
-            else:
-                self.app.update_status(f"Entry moved but save failed: {save_message}")
         else:
             self.app.update_status(f"Error moving entry: {result.message}")
 

src/hosts/tui/table_handler.py

@@ -123,7 +123,7 @@ class TableHandler:
 
     def actual_index_to_display_index(self, actual_index: int) -> int:
         """Convert an actual hosts file entry index to a display table index."""
-        if actual_index >= len(self.app.hosts_file.entries):
+        if actual_index < 0 or actual_index >= len(self.app.hosts_file.entries):
             return 0
 
         target_entry = self.app.hosts_file.entries[actual_index]
@@ -136,6 +136,14 @@ class TableHandler:
 
         return 0
 
+    def move_cursor_to_entry_index(self, actual_index: int) -> None:
+        """Move the table cursor to an exact Hosts File entry index."""
+        table = self.app.query_one("#entries-table", DataTable)
+        display_index = self.actual_index_to_display_index(actual_index)
+        if table.row_count > 0 and display_index < table.row_count:
+            table.move_cursor(row=display_index)
+            table.focus()
+
     def populate_entries_table(self) -> None:
         """Populate the left pane with hosts entries using DataTable."""
         table = self.app.query_one("#entries-table", DataTable)

tests/test_main.py

@@ -5,19 +5,31 @@ This module contains unit tests for the HostsManagerApp class,
 validating application behavior, navigation, and user interactions.
 """
 
-from unittest.mock import Mock, patch
+from datetime import datetime
+from unittest.mock import AsyncMock, Mock, patch
+
+import pytest
 
 
 from hosts.tui.app import HostsManagerApp
 from hosts.core.models import HostEntry, HostsFile
 from hosts.core.parser import HostsParser
 from hosts.core.config import Config
-from hosts.core.manager import HostsManager
+from hosts.core.dns import DNSResolution, DNSResolutionStatus
 
 
 class TestHostsManagerApp:
     """Test cases for the HostsManagerApp class."""
 
+    @staticmethod
+    def fail_saves(app: HostsManagerApp) -> None:
+        """Configure a TUI app with an isolated failed-persistence boundary."""
+        app.manager.save_hosts_file = Mock(return_value=(False, "Permission denied"))
+        app.table_handler.populate_entries_table = Mock()
+        app.table_handler.move_cursor_to_entry_index = Mock()
+        app.details_handler.update_entry_details = Mock()
+        app.update_status = Mock()
+
     def test_app_initialization(self):
         """Test application initialization."""
         with patch("hosts.tui.app.HostsParser"), patch("hosts.tui.app.Config"):
@@ -537,8 +549,7 @@ class TestHostsManagerApp:
             app.update_status = Mock()
 
             serialized_files = []
-            app.manager = Mock(spec=HostsManager)
-            app.manager.enter_edit_mode.return_value = (True, "Edit mode enabled")
+            app.manager.enter_edit_mode = Mock(return_value=(True, "Edit mode enabled"))
 
             def toggle_entry(hosts_file, index):
                 hosts_file.toggle_entry(index)
@@ -548,8 +559,8 @@ class TestHostsManagerApp:
                 serialized_files.append(HostsParser().serialize(hosts_file))
                 return True, "Hosts file saved successfully"
 
-            app.manager.execute_toggle_command.side_effect = toggle_entry
-            app.manager.save_hosts_file.side_effect = save_hosts_file
+            app.manager.execute_toggle_command = Mock(side_effect=toggle_entry)
+            app.manager.save_hosts_file = Mock(side_effect=save_hosts_file)
 
             app.action_sort_by_ip()
             assert app.edit_mode is False
@@ -1138,20 +1149,16 @@ class TestHostsManagerApp:
             entry = HostEntry(ip_address="192.168.1.1", hostnames=["test.local"])
             app.hosts_file.add_entry(entry)
             app.manager.execute_toggle_command(app.hosts_file, 0)
-            app.manager.save_hosts_file = Mock(
-                return_value=(False, "Permission denied")
-            )
-            app.table_handler.populate_entries_table = Mock()
-            app.details_handler.update_entry_details = Mock()
-            app.update_status = Mock()
+            self.fail_saves(app)
 
             app.action_undo()
 
-            assert entry.is_active is False
+            assert app.hosts_file.entries[0].is_active is False
             assert app.manager.can_undo()
             assert not app.manager.can_redo()
-            app.table_handler.populate_entries_table.assert_not_called()
-            app.details_handler.update_entry_details.assert_not_called()
+            app.table_handler.populate_entries_table.assert_called_once()
+            app.table_handler.move_cursor_to_entry_index.assert_called_once_with(0)
+            app.details_handler.update_entry_details.assert_called_once()
             app.update_status.assert_called_once_with(
                 "❌ Undo save failed; previous state restored: Permission denied"
             )
@@ -1190,22 +1197,449 @@ class TestHostsManagerApp:
             app.hosts_file.add_entry(entry)
             app.manager.execute_toggle_command(app.hosts_file, 0)
             app.manager.undo_last_operation(app.hosts_file)
+            self.fail_saves(app)
+
+            app.action_redo()
+
+            assert app.hosts_file.entries[0].is_active is True
+            assert not app.manager.can_undo()
+            assert app.manager.can_redo()
+            app.table_handler.populate_entries_table.assert_called_once()
+            app.table_handler.move_cursor_to_entry_index.assert_called_once_with(0)
+            app.details_handler.update_entry_details.assert_called_once()
+            app.update_status.assert_called_once_with(
+                "❌ Redo save failed; previous state restored: Permission denied"
+            )
+
+    def test_toggle_save_failure_restores_model_selection_and_history(self):
+        """A failed toggle restores all user-visible and undoable state."""
+        with patch("hosts.tui.app.HostsParser"), patch("hosts.tui.app.Config"):
+            app = HostsManagerApp()
+            app.edit_mode = True
+            app.manager.edit_mode = True
+            app.hosts_file = HostsFile(
+                entries=[
+                    HostEntry(ip_address="192.0.2.1", hostnames=["one.test"]),
+                    HostEntry(ip_address="192.0.2.2", hostnames=["two.test"]),
+                ]
+            )
+            app.selected_entry_index = 0
+            app.manager.execute_toggle_command(app.hosts_file, 1)
+            app.manager.undo_last_operation(app.hosts_file)
+            self.fail_saves(app)
+
+            app.action_toggle_entry()
+
+            assert app.hosts_file.entries[0].is_active is True
+            assert app.selected_entry_index == 0
+            assert not app.manager.can_undo()
+            assert app.manager.can_redo()
+            app.update_status.assert_called_once_with(
+                "❌ Toggle save failed; previous state restored: Permission denied"
+            )
+
+    def test_move_save_failure_restores_entry_order_and_selection(self):
+        """A failed move leaves the selected Host Entry in its original position."""
+        with patch("hosts.tui.app.HostsParser"), patch("hosts.tui.app.Config"):
+            app = HostsManagerApp()
+            app.edit_mode = True
+            app.manager.edit_mode = True
+            app.hosts_file = HostsFile(
+                entries=[
+                    HostEntry(ip_address="192.0.2.1", hostnames=["one.test"]),
+                    HostEntry(ip_address="192.0.2.2", hostnames=["two.test"]),
+                ]
+            )
+            app.selected_entry_index = 1
+            self.fail_saves(app)
+
+            app.action_move_entry_up()
+
+            assert [entry.hostnames[0] for entry in app.hosts_file.entries] == [
+                "one.test",
+                "two.test",
+            ]
+            assert app.selected_entry_index == 1
+            assert not app.manager.can_undo()
+            app.update_status.assert_called_once_with(
+                "❌ Move save failed; previous state restored: Permission denied"
+            )
+
+    def test_add_save_failure_removes_entry_and_restores_history(self):
+        """A failed add restores the prior entries and history."""
+        with patch("hosts.tui.app.HostsParser"), patch("hosts.tui.app.Config"):
+            app = HostsManagerApp()
+            app.edit_mode = True
+            app.manager.edit_mode = True
+            existing = HostEntry(ip_address="192.0.2.1", hostnames=["one.test"])
+            added = HostEntry(ip_address="192.0.2.2", hostnames=["two.test"])
+            app.hosts_file = HostsFile(entries=[existing])
+            app.selected_entry_index = 0
+            self.fail_saves(app)
+            app.push_screen = Mock(
+                side_effect=lambda _screen, callback: callback(added)
+            )
+
+            app.action_add_entry()
+
+            assert [entry.hostnames[0] for entry in app.hosts_file.entries] == [
+                "one.test"
+            ]
+            assert app.selected_entry_index == 0
+            assert not app.manager.can_undo()
+            app.update_status.assert_called_once_with(
+                "❌ Add save failed; previous state restored: Permission denied"
+            )
+
+    def test_later_mutation_does_not_persist_failed_add(self):
+        """A later successful save excludes a previously failed addition."""
+        with patch("hosts.tui.app.HostsParser"), patch("hosts.tui.app.Config"):
+            app = HostsManagerApp()
+            app.edit_mode = True
+            app.manager.edit_mode = True
+            existing = HostEntry(ip_address="192.0.2.1", hostnames=["one.test"])
+            added = HostEntry(ip_address="192.0.2.2", hostnames=["two.test"])
+            app.hosts_file = HostsFile(entries=[existing])
             app.manager.save_hosts_file = Mock(
                 return_value=(False, "Permission denied")
             )
             app.table_handler.populate_entries_table = Mock()
+            app.table_handler.move_cursor_to_entry_index = Mock()
+            app.table_handler.restore_cursor_position = Mock()
+            app.details_handler.update_entry_details = Mock()
+            app.update_status = Mock()
+            app.set_timer = Mock()
+            app.push_screen = Mock(
+                side_effect=lambda _screen, callback: callback(added)
+            )
+            app.action_add_entry()
+
+            persisted = []
+
+            def save_hosts_file(hosts_file):
+                persisted.append(HostsParser().serialize(hosts_file))
+                return True, "Hosts file saved"
+
+            app.manager.save_hosts_file = Mock(side_effect=save_hosts_file)
+            app.action_toggle_entry()
+
+            assert len(persisted) == 1
+            assert "one.test" in persisted[0]
+            assert "two.test" not in persisted[0]
+
+    def test_save_failure_restores_exact_duplicate_selection(self):
+        """Rollback keeps the second of two identical Host Entries selected."""
+        with patch("hosts.tui.app.HostsParser"), patch("hosts.tui.app.Config"):
+            app = HostsManagerApp()
+            app.edit_mode = True
+            app.manager.edit_mode = True
+            app.hosts_file = HostsFile(
+                entries=[
+                    HostEntry(ip_address="192.0.2.1", hostnames=["same.test"]),
+                    HostEntry(ip_address="192.0.2.1", hostnames=["same.test"]),
+                ]
+            )
+            app.selected_entry_index = 1
+            app.manager.save_hosts_file = Mock(
+                return_value=(False, "Permission denied")
+            )
+            table = Mock(row_count=2)
+            app.query_one = Mock(return_value=table)
+            app.table_handler.populate_entries_table = Mock()
             app.details_handler.update_entry_details = Mock()
             app.update_status = Mock()
 
-            app.action_redo()
+            app.action_toggle_entry()
 
-            assert entry.is_active is True
+            assert app.selected_entry_index == 1
+            table.move_cursor.assert_called_once_with(row=1)
+
+    def test_delete_save_failure_restores_entry_and_selection(self):
+        """A failed delete restores the removed Host Entry and selection."""
+        with patch("hosts.tui.app.HostsParser"), patch("hosts.tui.app.Config"):
+            app = HostsManagerApp()
+            app.edit_mode = True
+            app.manager.edit_mode = True
+            app.hosts_file = HostsFile(
+                entries=[
+                    HostEntry(ip_address="192.0.2.1", hostnames=["one.test"]),
+                    HostEntry(ip_address="192.0.2.2", hostnames=["two.test"]),
+                ]
+            )
+            app.selected_entry_index = 1
+            self.fail_saves(app)
+            app.push_screen = Mock(side_effect=lambda _screen, callback: callback(True))
+
+            app.action_delete_entry()
+
+            assert [entry.hostnames[0] for entry in app.hosts_file.entries] == [
+                "one.test",
+                "two.test",
+            ]
+            assert app.selected_entry_index == 1
             assert not app.manager.can_undo()
-            assert app.manager.can_redo()
-            app.table_handler.populate_entries_table.assert_not_called()
-            app.details_handler.update_entry_details.assert_not_called()
             app.update_status.assert_called_once_with(
-                "❌ Redo save failed; previous state restored: Permission denied"
+                "❌ Delete save failed; previous state restored: Permission denied"
+            )
+
+    def test_entry_editor_save_failure_restores_all_entry_fields(self):
+        """A failed editor save restores ordinary fields and DNS metadata."""
+        with patch("hosts.tui.app.HostsParser"), patch("hosts.tui.app.Config"):
+            app = HostsManagerApp()
+            app.edit_mode = True
+            app.manager.edit_mode = True
+            resolved_at = datetime(2026, 9, 4, 10, 30)
+            app.hosts_file = HostsFile(
+                entries=[
+                    HostEntry(
+                        ip_address="192.0.2.1",
+                        hostnames=["one.test", "alias.test"],
+                        comment="original",
+                        is_active=False,
+                        dns_name="source.test",
+                        resolved_ip="192.0.2.1",
+                        last_resolved=resolved_at,
+                        dns_resolution_status="resolved",
+                    )
+                ]
+            )
+            app.selected_entry_index = 0
+            app.entry_edit_mode = True
+            app.manager.save_hosts_file = Mock(
+                return_value=(False, "Permission denied")
+            )
+            app.table_handler.populate_entries_table = Mock()
+            app.table_handler.move_cursor_to_entry_index = Mock()
+            app.update_status = Mock()
+
+            ip_input = Mock(value="198.51.100.8")
+            hostname_input = Mock(value="changed.test")
+            comment_input = Mock(value="changed")
+            active_checkbox = Mock(value=True)
+            dns_input = Mock(value="")
+            ip_radio = Mock(id="edit-ip-entry-radio", value=True)
+            dns_radio = Mock(id="edit-dns-entry-radio", value=False)
+            radio_set = Mock(pressed_button=ip_radio)
+            widgets = {
+                "#entry-details-display": Mock(),
+                "#entry-edit-form": Mock(),
+                "#ip-input": ip_input,
+                "#hostname-input": hostname_input,
+                "#comment-input": comment_input,
+                "#active-checkbox": active_checkbox,
+                "#dns-name-input": dns_input,
+                "#edit-entry-type-radio": radio_set,
+                "#edit-ip-entry-radio": ip_radio,
+                "#edit-dns-entry-radio": dns_radio,
+                "#edit-ip-section": Mock(),
+                "#edit-dns-section": Mock(),
+            }
+            app.query_one = Mock(side_effect=lambda selector, *_args: widgets[selector])
+            app.set_timer = Mock(side_effect=lambda _delay, callback: callback())
+
+            saved = app.edit_handler.validate_and_save_entry_changes()
+
+            entry = app.hosts_file.entries[0]
+            assert saved is False
+            assert entry.ip_address == "192.0.2.1"
+            assert entry.hostnames == ["one.test", "alias.test"]
+            assert entry.comment == "original"
+            assert entry.is_active is False
+            assert entry.dns_name == "source.test"
+            assert entry.resolved_ip == "192.0.2.1"
+            assert entry.last_resolved == resolved_at
+            assert entry.dns_resolution_status == "resolved"
+            assert ip_input.value == "192.0.2.1"
+            assert hostname_input.value == "one.test, alias.test"
+            assert comment_input.value == "original"
+            assert active_checkbox.value is False
+            assert dns_input.value == "source.test"
+            app.update_status.assert_called_once_with(
+                "❌ Edit save failed; previous state restored: Permission denied"
+            )
+
+    @pytest.mark.asyncio
+    async def test_batch_dns_save_failure_restores_mapping_and_metadata(self):
+        """A failed batch DNS refresh restores every changed DNS field."""
+        with patch("hosts.tui.app.HostsParser"), patch("hosts.tui.app.Config"):
+            app = HostsManagerApp()
+            app.edit_mode = True
+            app.manager.edit_mode = True
+            original_time = datetime(2026, 9, 3, 8, 0)
+            resolved_time = datetime(2026, 9, 4, 11, 0)
+            app.hosts_file = HostsFile(
+                entries=[
+                    HostEntry(
+                        ip_address="192.0.2.1",
+                        hostnames=["one.test"],
+                        dns_name="source.test",
+                        resolved_ip="192.0.2.1",
+                        last_resolved=original_time,
+                        dns_resolution_status="match",
+                    )
+                ]
+            )
+            app.selected_entry_index = 0
+            app.dns_service.resolve_entry_async = AsyncMock(
+                return_value=DNSResolution(
+                    hostname="source.test",
+                    resolved_ip="198.51.100.9",
+                    status=DNSResolutionStatus.RESOLVED,
+                    resolved_at=resolved_time,
+                )
+            )
+            self.fail_saves(app)
+            workers = []
+            app.run_worker = Mock(
+                side_effect=lambda worker, **_kwargs: workers.append(worker)
+            )
+
+            app.action_refresh_dns()
+            await workers[0]
+
+            entry = app.hosts_file.entries[0]
+            assert entry.ip_address == "192.0.2.1"
+            assert entry.resolved_ip == "192.0.2.1"
+            assert entry.last_resolved == original_time
+            assert entry.dns_resolution_status == "match"
+            assert app.selected_entry_index == 0
+            app.update_status.assert_any_call(
+                "❌ DNS refresh save failed; previous state restored: Permission denied"
+            )
+
+    @pytest.mark.asyncio
+    async def test_single_dns_save_failure_restores_mapping_and_metadata(self):
+        """A failed selected-entry DNS refresh restores every changed field."""
+        with patch("hosts.tui.app.HostsParser"), patch("hosts.tui.app.Config"):
+            app = HostsManagerApp()
+            app.edit_mode = True
+            app.manager.edit_mode = True
+            original_time = datetime(2026, 9, 3, 8, 0)
+            app.hosts_file = HostsFile(
+                entries=[
+                    HostEntry(
+                        ip_address="192.0.2.1",
+                        hostnames=["one.test"],
+                        dns_name="source.test",
+                        resolved_ip="192.0.2.1",
+                        last_resolved=original_time,
+                        dns_resolution_status="match",
+                    )
+                ]
+            )
+            app.dns_service.resolve_entry_async = AsyncMock(
+                return_value=DNSResolution(
+                    hostname="source.test",
+                    resolved_ip="198.51.100.9",
+                    status=DNSResolutionStatus.RESOLVED,
+                    resolved_at=datetime(2026, 9, 4, 11, 0),
+                )
+            )
+            self.fail_saves(app)
+            workers = []
+            app.run_worker = Mock(
+                side_effect=lambda worker, **_kwargs: workers.append(worker)
+            )
+
+            app.action_update_single_dns()
+            await workers[0]
+
+            entry = app.hosts_file.entries[0]
+            assert entry.ip_address == "192.0.2.1"
+            assert entry.resolved_ip == "192.0.2.1"
+            assert entry.last_resolved == original_time
+            assert entry.dns_resolution_status == "match"
+            app.update_status.assert_any_call(
+                "❌ DNS refresh save failed; previous state restored: Permission denied"
+            )
+
+    @pytest.mark.asyncio
+    async def test_single_dns_refresh_updates_selected_duplicate(self):
+        """DNS refresh retains the selected entry identity across its await."""
+        with patch("hosts.tui.app.HostsParser"), patch("hosts.tui.app.Config"):
+            app = HostsManagerApp()
+            app.edit_mode = True
+            app.manager.edit_mode = True
+            app.hosts_file = HostsFile(
+                entries=[
+                    HostEntry(
+                        ip_address="192.0.2.1",
+                        hostnames=["same.test"],
+                        dns_name="source.test",
+                    ),
+                    HostEntry(
+                        ip_address="192.0.2.2",
+                        hostnames=["same.test"],
+                        dns_name="source.test",
+                    ),
+                ]
+            )
+            app.selected_entry_index = 1
+            app.dns_service.resolve_entry_async = AsyncMock(
+                return_value=DNSResolution(
+                    hostname="source.test",
+                    resolved_ip="198.51.100.9",
+                    status=DNSResolutionStatus.RESOLVED,
+                    resolved_at=datetime(2026, 9, 4, 11, 0),
+                )
+            )
+            app.manager.save_hosts_file = Mock(return_value=(True, "Saved"))
+            app.table_handler.populate_entries_table = Mock()
+            app.table_handler.restore_cursor_position = Mock()
+            app.details_handler.update_entry_details = Mock()
+            app.update_status = Mock()
+            workers = []
+            app.run_worker = Mock(
+                side_effect=lambda worker, **_kwargs: workers.append(worker)
+            )
+
+            app.action_update_single_dns()
+            await workers[0]
+
+            assert app.hosts_file.entries[0].ip_address == "192.0.2.1"
+            assert app.hosts_file.entries[1].ip_address == "198.51.100.9"
+
+    @pytest.mark.asyncio
+    async def test_new_entry_dns_save_failure_keeps_saved_placeholder(self):
+        """Failed post-add DNS persistence keeps the already-saved DNS placeholder."""
+        with patch("hosts.tui.app.HostsParser"), patch("hosts.tui.app.Config"):
+            app = HostsManagerApp()
+            app.edit_mode = True
+            app.manager.edit_mode = True
+            app.hosts_file = HostsFile()
+            entry = HostEntry(
+                ip_address="0.0.0.0",
+                hostnames=["one.test"],
+                is_active=False,
+                dns_name="source.test",
+            )
+            app.manager.execute_add_command(app.hosts_file, entry)
+            app.dns_service.resolve_entry_async = AsyncMock(
+                return_value=DNSResolution(
+                    hostname="source.test",
+                    resolved_ip="198.51.100.9",
+                    status=DNSResolutionStatus.RESOLVED,
+                    resolved_at=datetime(2026, 9, 4, 11, 0),
+                )
+            )
+            self.fail_saves(app)
+            workers = []
+            app.run_worker = Mock(
+                side_effect=lambda worker, **_kwargs: workers.append(worker)
+            )
+
+            app._resolve_new_dns_entry(entry)
+            await workers[0]
+
+            restored = app.hosts_file.entries[0]
+            assert restored.ip_address == "0.0.0.0"
+            assert restored.resolved_ip is None
+            assert restored.last_resolved is None
+            assert restored.dns_resolution_status is None
+            assert restored.is_active is False
+            assert app.manager.can_undo()
+            app.update_status.assert_any_call(
+                "❌ DNS activation save failed; previous state restored: Permission denied"
             )
 
     def test_main_function(self):

tests/test_manager.py

@@ -556,6 +556,28 @@ class TestHostsManager:
             assert not success
             assert "No sudo permissions" in message
 
+    def test_save_mutation_failure_restores_hosts_file_and_history(self):
+        """The manager owns rollback of model and undo/redo state."""
+        manager = HostsManager()
+        manager.edit_mode = True
+        hosts_file = HostsFile(
+            entries=[HostEntry("192.0.2.1", ["one.test"], is_active=True)]
+        )
+        manager.execute_toggle_command(hosts_file, 0)
+        manager.undo_last_operation(hosts_file)
+        state = manager.capture_mutation_state(hosts_file)
+
+        manager.execute_toggle_command(hosts_file, 0)
+        manager.save_hosts_file = Mock(return_value=(False, "Permission denied"))
+
+        success, message, restored_hosts_file = manager.save_mutation(hosts_file, state)
+
+        assert success is False
+        assert message == "Permission denied"
+        assert restored_hosts_file.entries[0].is_active is True
+        assert not manager.can_undo()
+        assert manager.can_redo()
+
     @patch("subprocess.run")
     def test_restore_backup_success(self, mock_run):
         """Test restoring backup successfully."""