Hosts page UX, draft/UI split, and managed hosts save summary

- Split effective-config session into Draft + Ui (IEffectiveConfigDraft, IEffectiveConfigUiState)
- Hosts: managed overlay, edit mode from table, validation deferred to blur/Escape/Enter
- Managed hosts save modal: line-level diff (add/remove/modify/order)
- Hosts group headers: editable/read-only badges, empty-group row, Effective names help
- hosts-ui.js for touch vs hover help; table inline bind oninput for live preview
- HostsEntryEditValidator and ManagedHostsPendingChangeDiff with tests

src/DnsmasqWebUI.Tests/Models/EffectiveConfig/ManagedHostsPendingChangeDiffTests.cs

@@ -0,0 +1,90 @@
+using DnsmasqWebUI.Models.Dnsmasq.EffectiveConfig;
+using DnsmasqWebUI.Models.Hosts;
+
+namespace DnsmasqWebUI.Tests.Models.EffectiveConfig;
+
+public class ManagedHostsPendingChangeDiffTests
+{
+    [Fact]
+    public void Build_same_entries_returns_empty()
+    {
+        var e = new HostEntry { Id = "a", LineNumber = 1, Address = "10.0.0.1", Names = new List<string> { "h" } };
+        var oldL = new List<HostEntry> { e };
+        var newL = new List<HostEntry>
+        {
+            new()
+            {
+                Id = e.Id,
+                LineNumber = e.LineNumber,
+                Address = e.Address,
+                Names = new List<string>(e.Names)
+            }
+        };
+        Assert.Empty(ManagedHostsPendingChangeDiff.Build(oldL, newL));
+    }
+
+    [Fact]
+    public void Build_added_entry()
+    {
+        var oldL = new List<HostEntry>();
+        var newL = new List<HostEntry>
+        {
+            new() { Id = "new:x", LineNumber = 1, Address = "192.168.0.1", Names = new List<string> { "router" } }
+        };
+        var d = ManagedHostsPendingChangeDiff.Build(oldL, newL);
+        var a = Assert.Single(d);
+        Assert.Equal(ManagedHostsLineDiffKind.Added, a.Kind);
+        Assert.Contains("192.168.0.1", a.AfterLine, StringComparison.Ordinal);
+        Assert.Contains("router", a.AfterLine, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Build_removed_entry()
+    {
+        var oldL = new List<HostEntry>
+        {
+            new() { Id = "1", LineNumber = 1, Address = "10.0.0.2", Names = new List<string> { "x" } }
+        };
+        var newL = new List<HostEntry>();
+        var d = ManagedHostsPendingChangeDiff.Build(oldL, newL);
+        var r = Assert.Single(d);
+        Assert.Equal(ManagedHostsLineDiffKind.Removed, r.Kind);
+        Assert.Contains("10.0.0.2", r.BeforeLine, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Build_modified_address()
+    {
+        var oldL = new List<HostEntry>
+        {
+            new() { Id = "k", LineNumber = 1, Address = "10.0.0.1", Names = new List<string> { "h" } }
+        };
+        var newL = new List<HostEntry>
+        {
+            new() { Id = "k", LineNumber = 1, Address = "10.0.0.9", Names = new List<string> { "h" } }
+        };
+        var d = ManagedHostsPendingChangeDiff.Build(oldL, newL);
+        var m = Assert.Single(d);
+        Assert.Equal(ManagedHostsLineDiffKind.Modified, m.Kind);
+        Assert.Contains("10.0.0.1", m.BeforeLine, StringComparison.Ordinal);
+        Assert.Contains("10.0.0.9", m.AfterLine, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Build_order_only()
+    {
+        var oldL = new List<HostEntry>
+        {
+            new() { Id = "a", LineNumber = 1, Address = "10.0.0.1", Names = new List<string> { "a" } },
+            new() { Id = "b", LineNumber = 2, Address = "10.0.0.2", Names = new List<string> { "b" } }
+        };
+        var newL = new List<HostEntry>
+        {
+            new() { Id = "b", LineNumber = 1, Address = "10.0.0.2", Names = new List<string> { "b" } },
+            new() { Id = "a", LineNumber = 2, Address = "10.0.0.1", Names = new List<string> { "a" } }
+        };
+        var d = ManagedHostsPendingChangeDiff.Build(oldL, newL);
+        var o = Assert.Single(d);
+        Assert.Equal(ManagedHostsLineDiffKind.OrderOnly, o.Kind);
+    }
+}

src/DnsmasqWebUI.Tests/Models/Hosts/HostsEntryEditValidatorTests.cs

@@ -0,0 +1,34 @@
+using DnsmasqWebUI.Models.Hosts;
+
+namespace DnsmasqWebUI.Tests.Models.Hosts;
+
+public class HostsEntryEditValidatorTests
+{
+    [Fact]
+    public void Empty_is_invalid()
+    {
+        var e = HostsEntryEditValidator.GetErrors("", Array.Empty<string>());
+        Assert.NotEmpty(e);
+    }
+
+    [Fact]
+    public void Valid_ipv4_and_name_ok()
+    {
+        Assert.True(HostsEntryEditValidator.IsValid("192.168.1.1", new[] { "router" }));
+    }
+
+    [Fact]
+    public void Missing_names_invalid()
+    {
+        var e = HostsEntryEditValidator.GetErrors("10.0.0.1", Array.Empty<string>());
+        Assert.Contains(e, x => x.Contains("hostname", StringComparison.OrdinalIgnoreCase));
+    }
+
+    [Fact]
+    public void Field_errors_split_address_and_names()
+    {
+        Assert.NotEmpty(HostsEntryEditValidator.GetAddressFieldErrors(""));
+        Assert.Empty(HostsEntryEditValidator.GetHostnameFieldErrors(new[] { "h" }));
+        Assert.NotEmpty(HostsEntryEditValidator.GetHostnameFieldErrors(Array.Empty<string>()));
+    }
+}

src/DnsmasqWebUI.Tests/Services/EffectiveConfig/EffectiveConfigEditSessionChangedEventTests.cs

@@ -14,10 +14,10 @@ public class EffectiveConfigEditSessionChangedEventTests
     {
         var saveService = new StubSaveService();
         var session = new EffectiveConfigEditSession(saveService);
-        session.EnterEditMode();
+        session.Ui.EnterEditMode();
         var raised = false;
         session.Changed += () => raised = true;
-        session.TrackCommit(new EffectiveConfigEditCommittedArgs("resolver", "port", null, 5353, null));
+        session.Draft.TrackCommit(new EffectiveConfigEditCommittedArgs("resolver", "port", null, 5353, null));
         Assert.True(raised);
     }
 
@@ -28,7 +28,7 @@ public class EffectiveConfigEditSessionChangedEventTests
         var session = new EffectiveConfigEditSession(saveService);
         var raised = false;
         session.Changed += () => raised = true;
-        session.EnterEditMode();
+        session.Ui.EnterEditMode();
         Assert.True(raised);
     }
 
@@ -37,27 +37,39 @@ public class EffectiveConfigEditSessionChangedEventTests
     {
         var saveService = new StubSaveService();
         var session = new EffectiveConfigEditSession(saveService);
-        session.EnterEditMode();
-        session.TrackCommit(new EffectiveConfigEditCommittedArgs("resolver", "port", null, 5353, null));
+        session.Ui.EnterEditMode();
+        session.Draft.TrackCommit(new EffectiveConfigEditCommittedArgs("resolver", "port", null, 5353, null));
         var raised = false;
         session.Changed += () => raised = true;
-        session.RevertChange("resolver", "port");
+        session.Draft.RevertChange("resolver", "port");
         Assert.True(raised);
     }
 
     [Fact]
-    public void TrackManagedHostsChange_StoresChange_AndRevertManagedHostsChange_RemovesIt()
+    public void Ui_EnterEditMode_DoesNotClearDraft()
     {
         var saveService = new StubSaveService();
         var session = new EffectiveConfigEditSession(saveService);
-        session.EnterEditMode();
+        var oldEntries = new List<HostEntry> { new() { Address = "1.2.3.4", Names = new List<string> { "a" } } };
+        var newEntries = new List<HostEntry> { new() { Address = "1.2.3.4", Names = new List<string> { "b" } } };
+        session.Draft.SetManagedHostsDraft(oldEntries, newEntries, "/tmp/managed.hosts");
+        Assert.Single(session.Draft.PendingChanges);
+        session.Ui.EnterEditMode();
+        Assert.Single(session.Draft.PendingChanges.OfType<PendingManagedHostsChange>());
+    }
+
+    [Fact]
+    public void SetManagedHostsDraft_StoresChange_AndRevertManagedHostsDraft_RemovesIt()
+    {
+        var saveService = new StubSaveService();
+        var session = new EffectiveConfigEditSession(saveService);
+        session.Ui.EnterEditMode();
         var oldEntries = new List<HostEntry> { new() { Address = "1.2.3.4", Names = new List<string> { "a" } } };
         var newEntries = new List<HostEntry> { new() { Address = "1.2.3.4", Names = new List<string> { "a", "b" } } };
-        var change = new PendingManagedHostsChange(oldEntries, newEntries, "/etc/hosts");
-        session.TrackManagedHostsChange(change);
-        Assert.Single(session.PendingChanges.OfType<PendingManagedHostsChange>());
-        session.RevertManagedHostsChange();
-        Assert.Empty(session.PendingChanges.OfType<PendingManagedHostsChange>());
+        session.Draft.SetManagedHostsDraft(oldEntries, newEntries, "/etc/hosts");
+        Assert.Single(session.Draft.PendingChanges.OfType<PendingManagedHostsChange>());
+        session.Draft.RevertManagedHostsDraft();
+        Assert.Empty(session.Draft.PendingChanges.OfType<PendingManagedHostsChange>());
     }
 
     private sealed class StubSaveService : IEffectiveConfigSaveService

src/DnsmasqWebUI/Components/EffectiveConfig/Common/EffectiveConfigValueDisplayBase.cs

@@ -31,7 +31,7 @@ public abstract class EffectiveConfigValueDisplayBase : ComponentBase
     /// <summary>Returns the value to display: pending change NewValue if this field has one, else descriptor value (not yet written to disk).</summary>
     protected object? GetEffectiveDisplayValue()
     {
-        var pending = Session?.PendingChanges.OfType<PendingOptionChange>().FirstOrDefault(c =>
+        var pending = Session?.Draft.PendingChanges.OfType<PendingOptionChange>().FirstOrDefault(c =>
             string.Equals(c.SectionId, Descriptor.SectionId, StringComparison.OrdinalIgnoreCase) &&
             string.Equals(c.OptionName, Descriptor.OptionName, StringComparison.OrdinalIgnoreCase));
         return pending != null ? pending.NewValue : Descriptor.GetValue();

src/DnsmasqWebUI/Components/EffectiveConfig/Composition/EffectiveConfigSection.razor

@@ -18,17 +18,17 @@
         var _allSectionsExpanded = _sectionViews.Count > 0 && _sectionViews.All(v => _openPanels.Contains(v.SectionId));
     }
     <EffectiveConfigToolbar ShowSearchBox="@ShowSearchBox" SearchTerm="@_searchTerm" SearchTermChanged="@OnSearchTermChanged"
-        IsEditMode="@Session.IsEditMode" PendingChangesCount="@Session.PendingChanges.Count"
-        ValidationSummary="@Session.GetValidationSummary()"
+        IsEditMode="@Session.Ui.IsEditMode" PendingChangesCount="@Session.Draft.PendingChanges.Count"
+        ValidationSummary="@Session.Draft.GetValidationSummary()"
         AllSectionsExpanded="@_allSectionsExpanded"
         OnExpandAll="ExpandAll" OnCollapseAll="CollapseAll" OnEnterEditMode="EnterEditMode" OnExitEditModeWithConfirm="ExitEditModeWithConfirmAsync" OnOpenSaveModal="OpenSaveModal" />
     <CascadingValue Value="@Session">
     <CascadingValue Value="@_uiContext">
         <EffectiveConfigPanels Status="@Status" Context="@Context" SearchTerm="@_searchTerm" OpenSectionIds="@_openPanels"
-            OnSectionToggle="OnSectionToggle" IsEditMode="@Session.IsEditMode" ActiveFieldKey="@Session.ActiveFieldKey" />
+            OnSectionToggle="OnSectionToggle" IsEditMode="@Session.Ui.IsEditMode" ActiveFieldKey="@Session.Ui.ActiveFieldKey" />
     </CascadingValue>
     </CascadingValue>
-    <EffectiveConfigSaveFlow ShowModal="@_showSaveModal" PendingChanges="@Session.PendingChanges" Status="@Status" Session="@Session"
+    <EffectiveConfigSaveFlow ShowModal="@_showSaveModal" PendingChanges="@Session.Draft.PendingChanges" Status="@Status" Session="@Session"
         OnClose="CloseSaveModal" OnRevertedNotify="OnRevertedFromSaveModal" OnSaveCompleted="OnSaveCompleted" OnContinueEditingAfterSavedFailure="ContinueEditingAfterSavedFailureAsync" OnCloseAndEndEdit="CloseSaveModalAndEndEdit" />
 </div>
 }
@@ -71,9 +71,9 @@
                 return Task.CompletedTask;
             },
             ActivateFieldAsync = fieldKey => { ActivateField(fieldKey); return Task.CompletedTask; },
-            DeactivateFieldAsync = () => { Session.DeactivateField(); return InvokeAsync(StateHasChanged); },
+            DeactivateFieldAsync = () => { Session.Ui.DeactivateField(); return InvokeAsync(StateHasChanged); },
             CommitFieldAsync = args => { HandleFieldEditCommitted(args); return Task.CompletedTask; },
-            RevertFieldAsync = (sectionId, optionName) => { Session.RevertChange(sectionId, optionName); RunCrossOptionEvaluator(); return InvokeAsync(StateHasChanged); }
+            RevertFieldAsync = (sectionId, optionName) => { Session.Draft.RevertChange(sectionId, optionName); RunCrossOptionEvaluator(); return InvokeAsync(StateHasChanged); }
         };
     }
 
@@ -154,14 +154,14 @@
 
     private void EnterEditMode()
     {
-        Session.EnterEditMode();
+        Session.Ui.EnterEditMode();
         RefreshCrossOptionAfterEnteringEditMode();
         StateHasChanged();
     }
 
     private async Task ExitEditModeWithConfirmAsync()
     {
-        if (Session.PendingChanges.Count > 0)
+        if (Session.Draft.PendingChanges.Count > 0)
         {
             var module = await JSRuntime.InvokeAsync<IJSObjectReference>("import", "./js/dialog.js");
             try
@@ -174,41 +174,43 @@
                 await module.DisposeAsync();
             }
         }
-        Session.ExitEditModeDiscard();
+        Session.Draft.DiscardAllDraft();
+        Session.Ui.ExitEditMode();
         StateHasChanged();
     }
 
     private void DeactivateActiveFieldIfClicked()
     {
-        if (Session.IsEditMode && Session.ActiveFieldKey != null)
+        if (Session.Ui.IsEditMode && Session.Ui.ActiveFieldKey != null)
         {
-            Session.DeactivateField();
+            Session.Ui.DeactivateField();
             StateHasChanged();
         }
     }
 
     private void ActivateField(string fieldKey)
     {
-        Session.ActivateField(fieldKey);
+        Session.Ui.ActivateField(fieldKey);
         StateHasChanged();
     }
 
     private void HandleFieldEditCommitted(EffectiveConfigEditCommittedArgs args)
     {
-        Session.TrackCommit(args);
+        Session.Draft.TrackCommit(args);
+        Session.Ui.DeactivateField();
         RunCrossOptionEvaluator();
         StateHasChanged();
     }
 
     private void RunCrossOptionEvaluator()
     {
-        var optionChanges = Session.PendingChanges.OfType<PendingOptionChange>().ToList();
+        var optionChanges = Session.Draft.PendingChanges.OfType<PendingOptionChange>().ToList();
         var issues = CrossOptionValidation.Validate(Status, optionChanges);
-        Session.SetCrossOptionIssues(issues);
+        Session.Draft.SetCrossOptionIssues(issues);
     }
 
     /// <summary>
-    /// <see cref="IEffectiveConfigEditSession.EnterEditMode"/> clears cross-option issues; repopulate from disk + pending.
+    /// After entering edit mode, repopulate cross-option issues from disk + pending.
     /// </summary>
     private void RefreshCrossOptionAfterEnteringEditMode()
     {
@@ -224,8 +226,8 @@
 
     private void OpenSaveModal()
     {
-        var hasPending = Session.PendingChanges.Count > 0;
-        var hasValidation = Session.GetValidationSummary().Count > 0;
+        var hasPending = Session.Draft.PendingChanges.Count > 0;
+        var hasValidation = Session.Draft.GetValidationSummary().Count > 0;
         if (!hasPending && !hasValidation)
             return;
         _showSaveModal = true;
@@ -241,9 +243,10 @@
     private async Task ContinueEditingAfterSavedFailureAsync()
     {
         _showSaveModal = false;
-        Session.ExitEditModeDiscard();
+        Session.Draft.DiscardAllDraft();
+        Session.Ui.ExitEditMode();
         await OnSaveCompleted.InvokeAsync();
-        Session.EnterEditMode();
+        Session.Ui.EnterEditMode();
         RefreshCrossOptionAfterEnteringEditMode();
         StateHasChanged();
     }
@@ -251,7 +254,8 @@
     private void CloseSaveModalAndEndEdit()
     {
         _showSaveModal = false;
-        Session.ExitEditModeDiscard();
+        Session.Draft.DiscardAllDraft();
+        Session.Ui.ExitEditMode();
         StateHasChanged();
     }
 }

src/DnsmasqWebUI/Components/EffectiveConfig/Composition/EffectiveConfigSection.razor.css

@@ -262,6 +262,18 @@
     margin-bottom: 0;
 }
 
+/* Multivalue display mode: editable entry row (no list number; align with list content) */
+::deep .ec-field-value-list li.ec-multi-list-entry-point {
+    list-style: none;
+    margin-left: -1.25rem;
+    margin-top: 0.15rem;
+}
+
+::deep .ec-field-value-list li.ec-multi-list-empty-hint {
+    list-style: none;
+    margin-left: -1.25rem;
+}
+
 /* Long paths/URLs wrap; allow break anywhere so nothing is clipped */
 ::deep .ec-field-value-item {
     display: inline;

src/DnsmasqWebUI/Components/EffectiveConfig/CustomDisplays/Do0x20EncodeDisplay.razor

@@ -52,7 +52,7 @@ else
             return;
         }
 
-        var pending = Session?.PendingChanges.OfType<PendingOptionChange>().FirstOrDefault(c =>
+        var pending = Session?.Draft.PendingChanges.OfType<PendingOptionChange>().FirstOrDefault(c =>
             string.Equals(c.SectionId, Descriptor.SectionId, StringComparison.OrdinalIgnoreCase) &&
             string.Equals(c.OptionName, Descriptor.OptionName, StringComparison.OrdinalIgnoreCase));
         if (pending?.OldValue is ExplicitToggleState previousState)

src/DnsmasqWebUI/Components/EffectiveConfig/Fields/EffectiveConfigFieldDisplay.razor

@@ -58,7 +58,7 @@ else if (Descriptor.IsMultiValue)
                 </CascadingValue>
             </span>
             <OptionStateBadge AnchorId="@_readonlyBadgeAnchorId" Source="@_multiValueRowSource" OptionName="@Descriptor.OptionName" Value="@_multiValueItems"
-                IsInteractive="@(IsEditMode && !Descriptor.IsCapabilityDisabled)" ShowEditableBadge="@(IsEditMode && !Descriptor.IsCapabilityDisabled)" HasPendingChange="@_multiValueHasPendingOrDraft" EditableAsButton="true" FieldKey="@FieldKey" IsActiveEditor="@(IsEditMode && IsActive && !Descriptor.IsCapabilityDisabled)"
+                IsInteractive="@(IsEditMode && !Descriptor.IsCapabilityDisabled)" ShowEditableBadge="@(!Descriptor.IsCapabilityDisabled)" HasPendingChange="@_multiValueHasPendingOrDraft" EditableAsButton="true" FieldKey="@FieldKey" IsActiveEditor="@(IsEditMode && IsActive && !Descriptor.IsCapabilityDisabled)"
                 IsCapabilityDisabled="@Descriptor.IsCapabilityDisabled" CapabilityDisabledReason="@Descriptor.CapabilityDisabledReason"
                 OnConfirmRequested="@HandleConfirmEdit" OnCancelRequested="@HandleCancelEdit" OnRevertRequested="@HandleRevertEdit" />
         </li>
@@ -68,7 +68,7 @@ else if (Descriptor.IsMultiValue)
         @* Multi-value state is computed in OnParametersSet and in HandleMultiValueChanged; we only read cached fields here. *@
         <EffectiveConfigMultiValueRow Descriptor="@Descriptor" Label="@Descriptor.OptionName" Items="@_multiValueItems" LabelTooltip="@_labelTooltip" OptionHelpKey="@_optionHelpKey" OptionHelpAnchorId="@_anchorId"
             IsActiveEditor="@(IsEditMode && IsActive && !Descriptor.IsCapabilityDisabled)" IsEditMode="@IsEditMode" ReadonlyBadgeAnchorIdBase="@_readonlyBadgeAnchorId"
-            Source="@_multiValueRowSource" ShowEditableBadge="@(IsEditMode && !Descriptor.IsCapabilityDisabled)" HasPendingChange="@_multiValueHasPendingOrDraft" FieldKey="@FieldKey"
+            Source="@_multiValueRowSource" ShowEditableBadge="@(!Descriptor.IsCapabilityDisabled)" HasPendingChange="@_multiValueHasPendingOrDraft" FieldKey="@FieldKey"
             ItemsChanged="@HandleMultiValueChanged" OnConfirmRequested="@HandleConfirmEdit" OnCancelRequested="@HandleCancelEdit" OnRevertRequested="@HandleRevertEdit" />
     }
 }
@@ -137,7 +137,7 @@ else
         _fragmentWithCallback = RenderFragmentRegistry.BuildFieldComponentFragment(Descriptor.SectionId, Descriptor.OptionName, EventCallback.Factory.Create<object?>(this, HandleValueChanged));
         _labelTooltip = DnsmasqOptionTooltips.Get(Descriptor.OptionName);
         _optionHelpKey = Descriptor.OptionName;
-        var pending = Session?.PendingChanges.OfType<PendingOptionChange>().FirstOrDefault(c =>
+        var pending = Session?.Draft.PendingChanges.OfType<PendingOptionChange>().FirstOrDefault(c =>
             string.Equals(c.SectionId, Descriptor.SectionId, StringComparison.OrdinalIgnoreCase) &&
             string.Equals(c.OptionName, Descriptor.OptionName, StringComparison.OrdinalIgnoreCase));
         var descriptorValue = Descriptor.IsMultiValue
@@ -305,7 +305,7 @@ else
     {
         _draftValue = null;
         _hasDraftValue = false;
-        Session?.RevertChange(Descriptor.SectionId, Descriptor.OptionName);
+        Session?.Draft.RevertChange(Descriptor.SectionId, Descriptor.OptionName);
         _exitAction = ExitAction.Revert;
         if (Ui != null)
             await Ui.DeactivateFieldAsync();

src/DnsmasqWebUI/Components/EffectiveConfig/Fields/EffectiveConfigMultiValueItem.razor

@@ -2,12 +2,17 @@
 @using DnsmasqWebUI.Models.Dnsmasq
 @using DnsmasqWebUI.Models.Dnsmasq.EffectiveConfig
 
-<span class="ec-field-value-item" title="@(ReadonlyClickActivatesField ? ReadonlyTitleOverride : Source?.GetReadOnlyTooltip())">
+<span class="ec-field-value-item" title="@Source?.GetReadOnlyTooltip()">
     @Value
-    <OptionStateBadge AnchorId="@(ReadonlyBadgeAnchorId ?? "")" Source="@Source" OptionName="@OptionName" Value="@Value"
-                     IsInteractive="@(IsEditMode && !ReadonlyClickActivatesField && !string.IsNullOrEmpty(ReadonlyBadgeAnchorId))"
-                     ShowEditableBadge="@(Source?.IsReadOnly != true)" EditableAsButton="true"
-                     FieldKey="@FieldKey" ReadonlyClickActivatesField="@ReadonlyClickActivatesField" ReadonlyTitleOverride="@ReadonlyTitleOverride" />
+    <OptionStateBadge
+        AnchorId="@(ReadonlyBadgeAnchorId ?? "")"
+        Source="@Source"
+        OptionName="@OptionName"
+        Value="@Value"
+        IsInteractive="@(IsEditMode && !string.IsNullOrEmpty(ReadonlyBadgeAnchorId))"
+        ShowEditableBadge="@(Source?.IsReadOnly != true)"
+        EditableAsButton="true"
+        FieldKey="@FieldKey" />
 </span>
 
 @code {
@@ -17,6 +22,4 @@
     [Parameter] public bool IsEditMode { get; set; }
     [Parameter] public string? ReadonlyBadgeAnchorId { get; set; }
     [Parameter] public string? FieldKey { get; set; }
-    [Parameter] public bool ReadonlyClickActivatesField { get; set; }
-    [Parameter] public string? ReadonlyTitleOverride { get; set; }
 }

src/DnsmasqWebUI/Components/EffectiveConfig/Fields/EffectiveConfigMultiValueRow.razor

@@ -25,22 +25,64 @@
     else
     {
         <div class="ec-field-value ec-field-value-multi">
+            <ol class="ec-field-value-list">
                 @if (Items?.Count > 0)
                 {
-                <ol class="ec-field-value-list">
                     @foreach (var (item, index) in Items!.Select((item, index) => (item, index)))
                     {
-                        var anchorId = ReadonlyBadgeAnchorIdBase != null ? ReadonlyBadgeAnchorIdBase + "-" + index : "";
-                        <li><EffectiveConfigMultiValueItem Value="@item.Value" Source="@item.Source" OptionName="@Label" IsEditMode="@IsEditMode" ReadonlyBadgeAnchorId="@anchorId" FieldKey="@FieldKey" ReadonlyClickActivatesField="true" ReadonlyTitleOverride="New values can still be added. Click to edit." /></li>
+                        var anchorId = ReadonlyBadgeAnchorIdBase != null
+                            ? $"{ReadonlyBadgeAnchorIdBase}-{index}"
+                            : "";
+                        <li>
+                            <EffectiveConfigMultiValueItem
+                                Value="@item.Value"
+                                Source="@item.Source"
+                                OptionName="@Label"
+                                IsEditMode="@IsEditMode"
+                                ReadonlyBadgeAnchorId="@anchorId"
+                                FieldKey="@FieldKey" />
+                        </li>
                     }
-                </ol>
+                }
+                @if (ShowEditableBadge && (Items?.Count ?? 0) > 0)
+                {
+                    <li class="ec-multi-list-entry-point">
+                        <OptionStateBadge
+                            OptionName="@Label"
+                            ShowEditableBadge="true"
+                            EditableAsButton="true"
+                            FieldKey="@FieldKey"
+                            IsActiveEditor="false"
+                            IsInteractive="true"
+                            HasPendingChange="@HasPendingChange"
+                            IsCapabilityDisabled="@(Descriptor?.IsCapabilityDisabled == true)"
+                            CapabilityDisabledReason="@Descriptor?.CapabilityDisabledReason" />
+                    </li>
+                }
+                else if ((Items?.Count ?? 0) == 0)
+                {
+                    <li class="ec-multi-list-empty-hint">
+                        @if (ShowEditableBadge)
+                        {
+                            <span class="text-muted">(none)</span>
+                            <OptionStateBadge
+                                OptionName="@Label"
+                                ShowEditableBadge="true"
+                                EditableAsButton="true"
+                                FieldKey="@FieldKey"
+                                IsActiveEditor="false"
+                                IsInteractive="true"
+                                HasPendingChange="@HasPendingChange"
+                                IsCapabilityDisabled="@(Descriptor?.IsCapabilityDisabled == true)"
+                                CapabilityDisabledReason="@Descriptor?.CapabilityDisabledReason" />
                         }
                         else
                         {
                             <span class="text-muted">(none)</span>
-                <OptionStateBadge OptionName="@Label" ShowEditableBadge="@(!(Descriptor?.IsCapabilityDisabled == true))" EditableAsButton="true"
-                    FieldKey="@FieldKey" IsActiveEditor="false" IsInteractive="true" IsCapabilityDisabled="@(Descriptor?.IsCapabilityDisabled == true)" CapabilityDisabledReason="@Descriptor?.CapabilityDisabledReason" />
                         }
+                    </li>
+                }
+            </ol>
         </div>
     }
 </li>

src/DnsmasqWebUI/Components/EffectiveConfig/Modals/EffectiveConfigSaveFlow.razor

@@ -69,8 +69,8 @@
 
     private async Task HandleSave()
     {
-        if (Session.PendingChanges.Count == 0) return;
-        if (Session.HasBlockingValidationErrors())
+        if (Session.Draft.PendingChanges.Count == 0) return;
+        if (Session.Draft.HasBlockingValidationErrors())
         {
             NotificationService.ShowError("Fix validation errors before saving.");
             return;
@@ -81,14 +81,16 @@
         _restoreResult = null;
         await InvokeAsync(StateHasChanged);
 
-        var result = await Session.ApplyAsync();
+        var result = await Session.Draft.ApplyAsync();
 
         _saveResult = result;
         if (result.Saved)
         {
-            // Changes were written to disk, so clear them from session state.
-            // Whether to stay in edit mode depends on whether restart succeeded.
-            Session.AcceptAppliedChanges(stayInEditMode: result.IsValidateFailed || !result.Restarted);
+            Session.Draft.AcceptAppliedChanges();
+            if (!result.IsValidateFailed && result.Restarted)
+                Session.Ui.ExitEditMode();
+            else
+                Session.Ui.EnterEditMode();
         }
 
         if (result.Saved && result.Restarted)
@@ -127,8 +129,8 @@
         _restoreResult = result;
         if (result.Restored)
         {
-            // Restore wrote to disk, so clear any pending changes from session.
-            Session.AcceptAppliedChanges(stayInEditMode: false);
+            Session.Draft.AcceptAppliedChanges();
+            Session.Ui.ExitEditMode();
         }
 
         if (result.Restored && result.Restarted)

src/DnsmasqWebUI/Components/EffectiveConfig/Modals/EffectiveConfigSaveModal.razor

@@ -228,13 +228,39 @@
                                 }
                                 else if (c is PendingManagedHostsChange hostChange)
                                 {
+                                    var hostLineDiffs = ManagedHostsPendingChangeDiff.Build(hostChange);
                                     <div class="list-group-item ec-save-modal-item d-flex align-items-start gap-3 py-3 px-0 border-0 border-bottom">
                                         <div class="ec-save-modal-item-body flex-grow-1 min-width-0">
-                                            <div class="d-flex align-items-center gap-2">
+                                            <div class="d-flex align-items-center flex-wrap gap-2">
                                                 <StatusBadge Kind="StatusBadgeKind.NeutralPill" Text="Managed hosts" Class="ec-save-modal-option me-2" />
-                                                <span class="ec-save-modal-diff text-body">@hostChange.OldEntries.Count entries → @hostChange.NewEntries.Count entries</span>
+                                                <span class="ec-save-modal-diff text-muted">@hostChange.OldEntries.Count → @hostChange.NewEntries.Count entries</span>
                                             </div>
                                             <div class="small text-muted mt-1">@System.IO.Path.GetFileName(hostChange.ManagedHostsFilePath)</div>
+                                            @if (hostLineDiffs.Count > 0)
+                                            {
+                                                <div class="ec-save-modal-managed-hosts-diff small mt-2 ps-2 border-start border-secondary border-opacity-25">
+                                                    @foreach (var d in hostLineDiffs)
+                                                    {
+                                                        @if (d.Kind == ManagedHostsLineDiffKind.Added)
+                                                        {
+                                                            <div class="text-success font-monospace text-break">+ @d.AfterLine</div>
+                                                        }
+                                                        else if (d.Kind == ManagedHostsLineDiffKind.Removed)
+                                                        {
+                                                            <div class="text-muted text-decoration-line-through font-monospace text-break">− @d.BeforeLine</div>
+                                                        }
+                                                        else if (d.Kind == ManagedHostsLineDiffKind.Modified)
+                                                        {
+                                                            <div class="text-muted text-decoration-line-through font-monospace text-break">~ @d.BeforeLine</div>
+                                                            <div class="text-success font-monospace text-break ms-1">→ @d.AfterLine</div>
+                                                        }
+                                                        else if (d.Kind == ManagedHostsLineDiffKind.OrderOnly)
+                                                        {
+                                                            <div class="text-muted fst-italic">Line order changed (same entries).</div>
+                                                        }
+                                                    }
+                                                </div>
+                                            }
                                         </div>
                                         <button type="button" class="btn btn-sm btn-outline-danger flex-shrink-0" @onclick="RevertManagedHosts" title="Revert managed hosts change" aria-label="Revert managed hosts">
                                             <i class="bi bi-arrow-counterclockwise me-1" aria-hidden="true"></i>Revert
@@ -304,9 +330,9 @@
         return list;
     }
 
-    private IReadOnlyList<FieldIssue> ValidationErrors => Session.GetValidationSummary().Where(i => i.Severity == FieldIssueSeverity.Error).ToList();
-    private IReadOnlyList<FieldIssue> ValidationWarnings => Session.GetValidationSummary().Where(i => i.Severity == FieldIssueSeverity.Warning).ToList();
-    private bool HasBlockingValidationErrors => Session.HasBlockingValidationErrors();
+    private IReadOnlyList<FieldIssue> ValidationErrors => Session.Draft.GetValidationSummary().Where(i => i.Severity == FieldIssueSeverity.Error).ToList();
+    private IReadOnlyList<FieldIssue> ValidationWarnings => Session.Draft.GetValidationSummary().Where(i => i.Severity == FieldIssueSeverity.Warning).ToList();
+    private bool HasBlockingValidationErrors => Session.Draft.HasBlockingValidationErrors();
 
     private static string GetValidationFailedOutput(EffectiveConfigSaveResult result)
     {
@@ -371,13 +397,13 @@
 
     private async Task RevertOption(PendingOptionChange change)
     {
-        Session.RevertChange(change.SectionId, change.OptionName);
+        Session.Draft.RevertChange(change.SectionId, change.OptionName);
         await OnReverted.InvokeAsync();
     }
 
     private async Task RevertManagedHosts()
     {
-        Session.RevertManagedHostsChange();
+        Session.Draft.RevertManagedHostsDraft();
         await OnReverted.InvokeAsync();
     }
 

src/DnsmasqWebUI/Components/EffectiveConfig/Modals/EffectiveConfigSaveModal.razor.css

@@ -39,6 +39,15 @@
     font-size: 0.9375rem;
 }
 
+.ec-save-modal-managed-hosts-diff {
+    font-size: 0.8125rem;
+    line-height: 1.45;
+}
+
+.ec-save-modal-managed-hosts-diff > div + div {
+    margin-top: 0.2rem;
+}
+
 .ec-save-modal-override {
     font-size: 0.8125rem;
 }

src/DnsmasqWebUI/Components/EffectiveConfig/Popovers/OptionStateBadge.razor

@@ -11,15 +11,8 @@
 }
 else if (Source?.IsReadOnly == true)
 {
-    var readonlyTitle = !string.IsNullOrEmpty(ReadonlyTitleOverride) ? ReadonlyTitleOverride : Source?.GetReadOnlyTooltip();
-    if (ReadonlyClickActivatesField && Ui != null && !string.IsNullOrEmpty(FieldKey))
-    {
-        <StatusBadge Kind="StatusBadgeKind.ReadOnly" Text="readonly" Clickable="true"
-                     Id="@AnchorId" Title="@readonlyTitle"
-                     OnClick="OnEditableClick"
-                     Class="status-badge-inline" />
-    }
-    else if (IsInteractive && Ui != null)
+    var readonlyTitle = Source?.GetReadOnlyTooltip();
+    if (IsInteractive && Ui != null)
     {
         <StatusBadge Kind="StatusBadgeKind.ReadOnly" Text="readonly" Clickable="true"
                      Id="@AnchorId" Title="@readonlyTitle"
@@ -88,10 +81,6 @@ else if (ShowEditableBadge)
     [Parameter] public string? FieldKey { get; set; }
     /// <summary>Optional: when set, editable-badge click invokes this instead of activating the field by key (e.g. list editor per-item edit).</summary>
     [Parameter] public EventCallback OnEditableClickRequested { get; set; }
-    /// <summary>When true, readonly badge click activates the field for editing instead of showing the readonly popover (e.g. for multi-value where new items can still be added).</summary>
-    [Parameter] public bool ReadonlyClickActivatesField { get; set; }
-    /// <summary>Optional tooltip for readonly badge when <see cref="ReadonlyClickActivatesField"/> is true (e.g. "New values can still be added. Click to edit.").</summary>
-    [Parameter] public string? ReadonlyTitleOverride { get; set; }
     /// <summary>When true, option is disabled because dnsmasq build does not support it (e.g. no DNSSEC).</summary>
     [Parameter] public bool IsCapabilityDisabled { get; set; }
     /// <summary>Tooltip shown when <see cref="IsCapabilityDisabled"/> is true (e.g. "This dnsmasq build does not support DNSSEC; option not written.").</summary>

src/DnsmasqWebUI/Components/Pages/Hosts.razor

@@ -8,6 +8,7 @@
 @using DnsmasqWebUI.Infrastructure.Services.EffectiveConfig.Abstractions
 @using DnsmasqWebUI.Infrastructure.Services.Dnsmasq.Hosts.Abstractions
 @using DnsmasqWebUI.Components.EffectiveConfig
+@using DnsmasqWebUI.Infrastructure.Services.UI.Notifications.Abstractions
 @using Microsoft.AspNetCore.Components.Web
 @using Microsoft.JSInterop
 @implements IDisposable
@@ -16,6 +17,7 @@
 @inject IEffectiveConfigEditSession Session
 @inject IHostsPageProjectionService HostsProjection
 @inject IJSRuntime JSRuntime
+@inject INotificationService NotificationService
 @inject IOptions<ApplicationOptions> AppOptions
 <PageTitle>Hosts | @AppTitle</PageTitle>
 
@@ -72,16 +74,16 @@ else
                 </div>
             </div>
 
-            @if (_unifiedRows == null || _unifiedRows.Count == 0)
+            @if (VisibleGroups.Count == 0)
             {
                 <p class="text-muted">No hosts entries found.</p>
             }
-            else if (VisibleGroups.Count == 0)
+            else
+            {
+                @if (TotalVisibleDataRows == 0 && !string.IsNullOrWhiteSpace(_search))
                 {
                     <p class="text-muted">No rows match the current search.</p>
                 }
-            else
-            {
                 <div class="app-table-scroll-shell" data-table-scroll-cue>
                     <div class="app-table-scroll-region" data-table-scroll-region role="region" aria-label="Hosts entries table" tabindex="0">
                         <table class="table table-bordered table-hover app-data-table hosts-table mb-0">
@@ -90,7 +92,17 @@ else
                                 <tr>
                                     <th scope="col">Address</th>
                                     <th scope="col">Names</th>
-                                    <th scope="col">Effective names</th>
+                                    <th scope="col" class="hosts-effective-names-th">
+                                        <span class="align-middle">Effective names</span>
+                                        <button type="button"
+                                                class="btn btn-link btn-sm text-muted hosts-effective-names-help p-0 ms-1 align-middle border-0"
+                                                title="@EffectiveNamesHelpText"
+                                                aria-label="@EffectiveNamesHelpText"
+                                                @onclick="OnEffectiveNamesHelpClickAsync"
+                                                @onclick:stopPropagation="true">
+                                            <i class="bi bi-question-circle" aria-hidden="true"></i>
+                                        </button>
+                                    </th>
                                 </tr>
                             </thead>
                             @foreach (var group in VisibleGroups)
@@ -101,22 +113,53 @@ else
                                             <div class="hosts-group-header__content">
                                                 <div class="hosts-group-header__title">
                                                     <span>@group.Title</span>
-                                                    @if (group.GroupContainsEditableRows)
-                                                    {
-                                                        <span class="badge bg-primary">Editable</span>
-                                                    }
                                                     @if (!group.IsActive)
                                                     {
                                                         <span class="badge bg-warning text-dark">Inactive</span>
                                                     }
+                                                </div>
+                                                <div class="hosts-group-header__path">
                                                     @if (!string.IsNullOrWhiteSpace(group.Subtitle))
                                                     {
                                                         <span class="hosts-group-header__subtitle text-muted small">@group.Subtitle</span>
                                                     }
+                                                    @if (group.SourceKind == HostsRowSourceKind.Managed && group.IsSourceEditable)
+                                                    {
+                                                        <StatusBadge Kind="StatusBadgeKind.Editable"
+                                                                     Text="editable"
+                                                                     Class="hosts-group-header__badge"
+                                                                     Clickable="true"
+                                                                     Disabled="@IsInlineEditing"
+                                                                     Title="@(IsInlineEditing ? "Finish editing the current row before adding another." : "Add a host entry")"
+                                                                     AriaLabel="@(IsInlineEditing ? "Finish the current row edit first" : "Add a host entry")"
+                                                                     OnClick="AddManagedHostFromBadge" />
+                                                    }
+                                                    else if (group.IsSourceEditable)
+                                                    {
+                                                        <StatusBadge Kind="StatusBadgeKind.Editable"
+                                                                     Text="editable"
+                                                                     Class="hosts-group-header__badge" />
+                                                    }
+                                                    else
+                                                    {
+                                                        <StatusBadge Kind="StatusBadgeKind.ReadOnly"
+                                                                     Text="read-only"
+                                                                     Class="hosts-group-header__badge" />
+                                                    }
                                                 </div>
                                             </div>
                                         </th>
                                     </tr>
+                                    @if (group.Rows.Count == 0)
+                                    {
+                                        <tr class="hosts-row hosts-row--empty" @key="@("empty:" + group.Key)">
+                                            <td colspan="3" class="text-muted small text-center hosts-empty-group-message py-3">
+                                                @EmptyGroupMessage
+                                            </td>
+                                        </tr>
+                                    }
+                                    else
+                                    {
                                         @foreach (var row in group.Rows)
                                         {
                                             @if (IsEditingRow(row))
@@ -126,10 +169,23 @@ else
                                                     @ref="_editingRowRef"
                                                     @onfocusout="OnEditingRowFocusOut">
                                                     <td>
-                                                    <input class="form-control form-control-sm" @bind="_editAddress" autofocus />
+                                                        <input @ref="_editAddressInputRef"
+                                                               class="form-control form-control-sm @(_showHostFieldValidation && CurrentAddressFieldErrors.Count > 0 ? "is-invalid" : "")"
+                                                               title="@HostEditAddressTooltip"
+                                                               aria-invalid="@(_showHostFieldValidation && CurrentAddressFieldErrors.Count > 0 ? "true" : null)"
+                                                               @bind="_editAddress"
+                                                               @bind:event="oninput"
+                                                               @onkeydown="OnEditFieldKeyDown"
+                                                               autofocus />
                                                     </td>
                                                     <td>
-                                                    <input class="form-control form-control-sm" placeholder="Comma-separated names" @bind="_editNames" />
+                                                        <input class="form-control form-control-sm @(_showHostFieldValidation && CurrentHostnameFieldErrors.Count > 0 ? "is-invalid" : "")"
+                                                               placeholder="Comma-separated names"
+                                                               title="@HostEditNamesTooltip"
+                                                               aria-invalid="@(_showHostFieldValidation && CurrentHostnameFieldErrors.Count > 0 ? "true" : null)"
+                                                               @bind="_editNames"
+                                                               @bind:event="oninput"
+                                                               @onkeydown="OnEditFieldKeyDown" />
                                                     </td>
                                                     <td class="text-muted small">@string.Join(", ", HostsEffectiveNames.Expand(ParseNamesList(_editNames), pageState.ExpandHostsEnabled, pageState.ExpansionDomain))</td>
                                                 </tr>
@@ -138,8 +194,8 @@ else
                                             {
                                                 <tr class="@RowClass(row)"
                                                     @key="@row.Id"
-                                                title="@(row.IsEditable ? "Double-click to edit" : string.Empty)"
-                                                @ondblclick="@(() => OnRowDoubleClick(row))">
+                                                    title="@RowTitle(row)"
+                                                    @ondblclick="@(async () => await OnRowDoubleClickAsync(row))">
                                                     <td><code>@row.Address</code></td>
                                                     <td>@string.Join(", ", row.Names)</td>
                                                     <td>
@@ -155,6 +211,7 @@ else
                                                 </tr>
                                             }
                                         }
+                                    }
                                 </tbody>
                             }
                         </table>
@@ -165,6 +222,36 @@ else
         </section>
     }
 
+    @if (_showInvalidHostEditModal)
+    {
+        <div class="modal fade show" style="display: block;" tabindex="-1" role="dialog" aria-labelledby="hosts-invalid-edit-title" aria-modal="true">
+            <div class="modal-dialog" role="document">
+                <div class="modal-content">
+                    <div class="modal-header">
+                        <h5 class="modal-title" id="hosts-invalid-edit-title">Host entry incomplete</h5>
+                    </div>
+                    <div class="modal-body">
+                        <p class="mb-2">This row is not valid yet. You can keep editing, or discard @(_editingRowIsNew ? "the new row" : "your changes on this row").</p>
+                        @if (CurrentEditValidationErrors.Count > 0)
+                        {
+                            <ul class="small text-danger mb-0 ps-3">
+                                @foreach (var err in CurrentEditValidationErrors)
+                                {
+                                    <li>@err</li>
+                                }
+                            </ul>
+                        }
+                    </div>
+                    <div class="modal-footer">
+                        <button type="button" class="btn btn-primary" @onclick="OnInvalidEditContinue">Keep editing</button>
+                        <button type="button" class="btn btn-outline-secondary" @onclick="OnInvalidEditDiscardAsync">Discard</button>
+                    </div>
+                </div>
+            </div>
+        </div>
+        <div class="modal-backdrop fade show"></div>
+    }
+
     <div class="hosts-page-notes mt-3 d-flex flex-column gap-2">
         @if (!pageState.SystemHostsActive && !string.IsNullOrEmpty(pageState.SystemHostsInactiveReason))
         {
@@ -185,11 +272,14 @@ else
 </div>
 
 @code {
+    private const string EffectiveNamesHelpText =
+        "Effective names show how dnsmasq resolves this row from your Address and Names columns. If expand-hosts and a domain are enabled, short hostnames get that suffix. This preview updates as you type.";
+
     private string AppTitle => AppOptions!.Value!.EffectiveTitle;
     private DnsmasqServiceStatus? _status;
     private IReadOnlyList<HostsPageRow> _unifiedRows = Array.Empty<HostsPageRow>();
-    private List<HostEntry> _managedEntries = new();
-    private List<HostEntry> _originalManagedEntries = new();
+    private List<HostsPageRow> _restUnifiedRows = new();
+    private List<HostEntry> _baselineManagedEntries = new();
     private string? _error;
 
     private string _search = "";
@@ -198,31 +288,100 @@ else
     private string _editAddress = "";
     private string _editNames = "";
     private ElementReference _editingRowRef;
+    private ElementReference _editAddressInputRef;
     private IJSObjectReference? _hostsTableScrollCueModule;
+    private IJSObjectReference? _hostsUiModule;
+    private bool _showInvalidHostEditModal;
+    private bool _refocusEditAfterRender;
+    /// <summary>When false, invalid state is hidden until the first blur, Escape, or Enter.</summary>
+    private bool _showHostFieldValidation;
+
+    private IReadOnlyList<HostEntry> CurrentManagedEntries =>
+        Session.Draft.ManagedHostsDraft?.NewEntries ?? _baselineManagedEntries;
 
-    // Memoize: markup reads VisibleGroups.Count then foreach — avoid building twice per render.
     private IReadOnlyList<HostsPageGroup>? _visibleGroupsCache;
     private object? _visibleGroupsCacheRowsRef;
     private string _visibleGroupsCacheSearch = "\0";
+    private string _visibleGroupsCacheManagedPath = "\0";
 
     private IReadOnlyList<HostsPageGroup> VisibleGroups
     {
         get
         {
+            var managedPath = _status?.ManagedHostsFilePath ?? "";
             if (_visibleGroupsCache != null
                 && ReferenceEquals(_visibleGroupsCacheRowsRef, _unifiedRows)
-                && _visibleGroupsCacheSearch == _search)
+                && _visibleGroupsCacheSearch == _search
+                && _visibleGroupsCacheManagedPath == managedPath)
             {
                 return _visibleGroupsCache;
             }
 
-            _visibleGroupsCache = HostsProjection.BuildGroups(_unifiedRows, BuildQuery());
+            var built = HostsProjection.BuildGroups(_unifiedRows, BuildQuery());
+            _visibleGroupsCache = EnsureManagedHostsHeaderGroup(built);
             _visibleGroupsCacheRowsRef = _unifiedRows;
             _visibleGroupsCacheSearch = _search;
+            _visibleGroupsCacheManagedPath = managedPath;
             return _visibleGroupsCache;
         }
     }
 
+    private int TotalVisibleDataRows => VisibleGroups.Sum(g => g.Rows.Count);
+
+    private bool IsInlineEditing => !string.IsNullOrEmpty(_editingRowId);
+
+    private bool _editingRowIsNew =>
+        !string.IsNullOrEmpty(_editingRowId) && _editingRowId.StartsWith("new:", StringComparison.Ordinal);
+
+    private IReadOnlyList<string> CurrentEditValidationErrors =>
+        string.IsNullOrEmpty(_editingRowId)
+            ? Array.Empty<string>()
+            : HostsEntryEditValidator.GetErrors(_editAddress.Trim(), ParseNamesList(_editNames));
+
+    private bool IsCurrentEditValid => CurrentEditValidationErrors.Count == 0;
+
+    private IReadOnlyList<string> CurrentAddressFieldErrors =>
+        string.IsNullOrEmpty(_editingRowId)
+            ? Array.Empty<string>()
+            : HostsEntryEditValidator.GetAddressFieldErrors(_editAddress.Trim());
+
+    private IReadOnlyList<string> CurrentHostnameFieldErrors =>
+        string.IsNullOrEmpty(_editingRowId)
+            ? Array.Empty<string>()
+            : HostsEntryEditValidator.GetHostnameFieldErrors(ParseNamesList(_editNames));
+
+    private string? HostEditAddressTooltip =>
+        !_showHostFieldValidation ? null : JoinHostFieldTooltip(CurrentAddressFieldErrors);
+
+    private string? HostEditNamesTooltip =>
+        !_showHostFieldValidation ? null : JoinHostFieldTooltip(CurrentHostnameFieldErrors);
+
+    private static string? JoinHostFieldTooltip(IReadOnlyList<string> errors) =>
+        errors.Count == 0 ? null : string.Join(" · ", errors);
+
+    private IReadOnlyList<HostsPageGroup> EnsureManagedHostsHeaderGroup(IReadOnlyList<HostsPageGroup> groups)
+    {
+        if (_status == null || string.IsNullOrWhiteSpace(_status.ManagedHostsFilePath))
+            return groups;
+        var path = _status.ManagedHostsFilePath;
+        if (groups.Any(g => g.SourceKind == HostsRowSourceKind.Managed))
+            return groups;
+
+        var placeholder = new HostsPageGroup(
+            Key: $"{HostsRowSourceKind.Managed}:{path}",
+            Title: "Managed hosts",
+            Subtitle: path,
+            SourceKind: HostsRowSourceKind.Managed,
+            GroupContainsEditableRows: true,
+            IsActive: true,
+            InactiveReason: null,
+            VisibleRowCount: 0,
+            Rows: Array.Empty<HostsPageRow>(),
+            IsSourceEditable: true);
+
+        return new[] { placeholder }.Concat(groups).ToList();
+    }
+
     private HostsPageQueryState BuildQuery()
     {
         return new HostsPageQueryState(
@@ -235,6 +394,24 @@ else
             ActiveFilter: null);
     }
 
+    private void InvalidateVisibleGroupsCache()
+    {
+        _visibleGroupsCache = null;
+    }
+
+    private async Task OnEffectiveNamesHelpClickAsync()
+    {
+        try
+        {
+            _hostsUiModule ??= await JSRuntime.InvokeAsync<IJSObjectReference>("import", "/js/modules/hosts-ui.js");
+            if (await _hostsUiModule.InvokeAsync<bool>("preferEffectiveNamesHelpToast"))
+                NotificationService.ShowInfo(EffectiveNamesHelpText);
+        }
+        catch (JSDisconnectedException)
+        {
+        }
+    }
+
     private static string RowClass(HostsPageRow row)
     {
         var parts = new List<string> { "hosts-row" };
@@ -245,21 +422,87 @@ else
         return string.Join(" ", parts);
     }
 
-    private void OnRowDoubleClick(HostsPageRow row) => BeginEdit(row);
+    private string RowTitle(HostsPageRow row) =>
+        row.IsEditable ? "Double-click to edit" : string.Empty;
+
+    private string EmptyGroupMessage =>
+        string.IsNullOrWhiteSpace(_search) ? "No entries." : "No matching entries.";
 
     private bool IsEditingRow(HostsPageRow row) =>
         !string.IsNullOrEmpty(_editingRowId) && string.Equals(_editingRowId, row.Id, StringComparison.Ordinal);
 
-    private void BeginEdit(HostsPageRow row)
+    private async Task OnRowDoubleClickAsync(HostsPageRow row)
     {
         if (!row.IsEditable || _status == null)
             return;
+
+        if (!string.IsNullOrEmpty(_editingRowId))
+        {
+            if (string.Equals(_editingRowId, row.Id, StringComparison.Ordinal))
+                return;
+
+            if (!IsCurrentEditValid)
+            {
+                RevealHostFieldValidation();
+                _showInvalidHostEditModal = true;
+                await InvokeAsync(StateHasChanged);
+                return;
+            }
+
+            await CommitAndEndInlineEditAsync();
+        }
+
+        if (!Session.Ui.IsEditMode)
+            Session.Ui.EnterEditMode();
+
         var entry = FindManagedEntry(row);
         if (entry == null)
             return;
+        _showHostFieldValidation = false;
         _editingRowId = row.Id;
         _editAddress = entry.Address;
         _editNames = string.Join(", ", entry.Names);
+        await InvokeAsync(StateHasChanged);
+    }
+
+    private void AddManagedHostFromBadge()
+    {
+        if (IsInlineEditing)
+            return;
+        AddManagedHost();
+    }
+
+    private void AddManagedHost()
+    {
+        if (_status == null || string.IsNullOrWhiteSpace(_status.ManagedHostsFilePath) || IsInlineEditing)
+            return;
+        if (!Session.Ui.IsEditMode)
+            Session.Ui.EnterEditMode();
+
+        var list = CloneEntries(CurrentManagedEntries).ToList();
+        var nextLine = list.Count == 0 ? 1 : list.Max(e => e.LineNumber) + 1;
+        var id = "new:" + Guid.NewGuid().ToString("N");
+        list.Add(new HostEntry
+        {
+            LineNumber = nextLine,
+            Id = id,
+            Address = "",
+            Names = new List<string>(),
+            IsComment = false,
+            IsPassthrough = false
+        });
+
+        Session.Draft.SetManagedHostsDraft(
+            CloneEntries(_baselineManagedEntries),
+            list,
+            _status.ManagedHostsFilePath);
+        RebuildManagedOverlay();
+        InvalidateVisibleGroupsCache();
+        _showHostFieldValidation = false;
+        _editingRowId = id;
+        _editAddress = "";
+        _editNames = "";
+        StateHasChanged();
     }
 
     private void CancelEdit()
@@ -267,14 +510,90 @@ else
         _editingRowId = null;
         _editAddress = "";
         _editNames = "";
+        _showHostFieldValidation = false;
+    }
+
+    private void RevealHostFieldValidation() => _showHostFieldValidation = true;
+
+    private void OnInvalidEditContinue()
+    {
+        _showInvalidHostEditModal = false;
+        _refocusEditAfterRender = true;
+        StateHasChanged();
+    }
+
+    private async Task OnInvalidEditDiscardAsync()
+    {
+        if (string.IsNullOrEmpty(_editingRowId) || _status == null || string.IsNullOrWhiteSpace(_status.ManagedHostsFilePath))
+        {
+            _showInvalidHostEditModal = false;
+            CancelEdit();
+            await InvokeAsync(StateHasChanged);
+            return;
+        }
+
+        var list = CloneEntries(CurrentManagedEntries).ToList();
+        var entry = list.FirstOrDefault(MatchesEditingId);
+        if (entry != null && entry.Id.StartsWith("new:", StringComparison.Ordinal))
+        {
+            list.Remove(entry);
+            Session.Draft.SetManagedHostsDraft(
+                CloneEntries(_baselineManagedEntries),
+                list,
+                _status.ManagedHostsFilePath);
+            RebuildManagedOverlay();
+            InvalidateVisibleGroupsCache();
+        }
+
+        _showInvalidHostEditModal = false;
+        CancelEdit();
+        await InvokeAsync(StateHasChanged);
+    }
+
+    private async Task OnEditFieldKeyDown(KeyboardEventArgs e)
+    {
+        if (_showInvalidHostEditModal || string.IsNullOrEmpty(_editingRowId))
+            return;
+
+        if (e.Key == "Enter")
+        {
+            await TryFinishHostEditFromKeyboardAsync();
+            return;
+        }
+
+        if (e.Key != "Escape")
+            return;
+
+        if (IsCurrentEditValid)
+            await CommitAndEndInlineEditAsync();
+        else
+        {
+            RevealHostFieldValidation();
+            _showInvalidHostEditModal = true;
+            await InvokeAsync(StateHasChanged);
+        }
+    }
+
+    private async Task TryFinishHostEditFromKeyboardAsync()
+    {
+        if (string.IsNullOrEmpty(_editingRowId))
+            return;
+        if (IsCurrentEditValid)
+            await CommitAndEndInlineEditAsync();
+        else
+        {
+            RevealHostFieldValidation();
+            _showInvalidHostEditModal = true;
+            await InvokeAsync(StateHasChanged);
+        }
     }
 
     private async Task OnEditingRowFocusOut(FocusEventArgs _)
     {
-        if (string.IsNullOrEmpty(_editingRowId))
+        if (_showInvalidHostEditModal || string.IsNullOrEmpty(_editingRowId))
             return;
         await Task.Delay(10);
-        if (string.IsNullOrEmpty(_editingRowId))
+        if (_showInvalidHostEditModal || string.IsNullOrEmpty(_editingRowId))
             return;
 
         var outside = true;
@@ -289,24 +608,43 @@ else
         }
 
         if (outside)
+        {
+            if (IsCurrentEditValid)
                 await CommitAndEndInlineEditAsync();
+            else
+            {
+                RevealHostFieldValidation();
+                _showInvalidHostEditModal = true;
+                await InvokeAsync(StateHasChanged);
+            }
+        }
     }
 
     private async Task CommitAndEndInlineEditAsync()
     {
-        if (string.IsNullOrEmpty(_editingRowId) || _status == null)
+        if (string.IsNullOrEmpty(_editingRowId) || _status == null || string.IsNullOrWhiteSpace(_status.ManagedHostsFilePath))
             return;
-        var entry = _managedEntries.FirstOrDefault(MatchesEditingId);
+        var list = CloneEntries(CurrentManagedEntries).ToList();
+        var entry = list.FirstOrDefault(MatchesEditingId);
         if (entry == null)
         {
             CancelEdit();
             return;
         }
 
-        entry.Address = _editAddress.Trim();
-        entry.Names = ParseNamesList(_editNames);
-        ApplyManagedOverlay();
-        SyncManagedHostsDraft();
+        var trimmedAddr = _editAddress.Trim();
+        var newNames = ParseNamesList(_editNames);
+        if (!HostsEntryEditValidator.IsValid(trimmedAddr, newNames))
+            return;
+
+        entry.Address = trimmedAddr;
+        entry.Names = newNames;
+        Session.Draft.SetManagedHostsDraft(
+            CloneEntries(_baselineManagedEntries),
+            list,
+            _status.ManagedHostsFilePath!);
+        RebuildManagedOverlay();
+        InvalidateVisibleGroupsCache();
         CancelEdit();
         await InvokeAsync(StateHasChanged);
     }
@@ -318,7 +656,7 @@ else
     }
 
     private HostEntry? FindManagedEntry(HostsPageRow row) =>
-        _managedEntries.FirstOrDefault(e =>
+        CurrentManagedEntries.FirstOrDefault(e =>
             string.Equals(e.Id, row.Id, StringComparison.Ordinal) ||
             string.Equals($"managed:{e.LineNumber}", row.Id, StringComparison.Ordinal));
 
@@ -339,19 +677,6 @@ else
             IsPassthrough = e.IsPassthrough
         }).ToList();
 
-    private void SyncManagedHostsDraft()
-    {
-        if (_status == null || string.IsNullOrWhiteSpace(_status.ManagedHostsFilePath))
-            return;
-        var draft = CloneEntries(_managedEntries);
-        var original = CloneEntries(_originalManagedEntries);
-        var pending = new PendingManagedHostsChange(original, draft, _status.ManagedHostsFilePath);
-        if (pending.HasChanges)
-            Session.TrackManagedHostsChange(pending);
-        else
-            Session.RevertManagedHostsChange();
-    }
-
     private MarkupString RenderAddnHostsList()
     {
         if (_status?.AddnHostsPaths == null || _status.AddnHostsPaths.Count == 0)
@@ -372,9 +697,20 @@ else
 
     protected override async Task OnInitializedAsync()
     {
+        Session.Changed += OnSessionChanged;
         await Load();
     }
 
+    private void OnSessionChanged()
+    {
+        if (_status != null && !string.IsNullOrEmpty(_status.ManagedHostsFilePath))
+        {
+            RebuildManagedOverlay();
+            InvalidateVisibleGroupsCache();
+        }
+        _ = InvokeAsync(StateHasChanged);
+    }
+
     protected override async Task OnAfterRenderAsync(bool firstRender)
     {
         if (firstRender)
@@ -394,6 +730,21 @@ else
             {
             }
         }
+
+        if (_refocusEditAfterRender)
+        {
+            _refocusEditAfterRender = false;
+            if (!string.IsNullOrEmpty(_editingRowId))
+            {
+                try
+                {
+                    await _editAddressInputRef.FocusAsync();
+                }
+                catch (JSDisconnectedException)
+                {
+                }
+            }
+        }
     }
 
     private async Task RefreshStatusAsync()
@@ -406,14 +757,28 @@ else
         catch { /* ignore */ }
     }
 
+    private void ReconcileManagedHostsDraftAfterLoad()
+    {
+        if (_status == null || string.IsNullOrWhiteSpace(_status.ManagedHostsFilePath))
+            return;
+        var draft = Session.Draft.ManagedHostsDraft;
+        if (draft == null)
+            return;
+        if (!string.Equals(draft.ManagedHostsFilePath, _status.ManagedHostsFilePath, StringComparison.Ordinal))
+            return;
+        Session.Draft.SetManagedHostsDraft(
+            CloneEntries(_baselineManagedEntries),
+            CloneEntries(draft.NewEntries),
+            _status.ManagedHostsFilePath);
+    }
+
     private async Task Load()
     {
         _error = null;
         try
         {
             _status = await StatusClient.GetStatusAsync();
-            _managedEntries = (await HostsClient.GetHostsAsync()).ToList();
-            _originalManagedEntries = CloneEntries(_managedEntries);
+            _baselineManagedEntries = (await HostsClient.GetHostsAsync()).ToList();
 
             if (_status?.EffectiveConfig != null && !string.IsNullOrEmpty(_status.ManagedHostsFilePath))
             {
@@ -421,15 +786,17 @@ else
                 var domain = _status.EffectiveConfig.DomainValues?.FirstOrDefault();
                 var noHosts = _status.NoHosts;
                 var fromApi = await HostsClient.GetUnifiedRowsAsync(expandHosts, domain, noHosts, _status.ManagedHostsFilePath);
-                _unifiedRows = fromApi.ToList();
-                ApplyManagedOverlay();
+                _restUnifiedRows = fromApi.Where(r => r.SourceKind != HostsRowSourceKind.Managed).ToList();
+                ReconcileManagedHostsDraftAfterLoad();
+                RebuildManagedOverlay();
             }
             else
             {
+                _restUnifiedRows = new List<HostsPageRow>();
                 _unifiedRows = Array.Empty<HostsPageRow>();
             }
 
-            SyncManagedHostsDraft();
+            InvalidateVisibleGroupsCache();
         }
         catch (Exception ex)
         {
@@ -437,7 +804,7 @@ else
         }
     }
 
-    private void ApplyManagedOverlay()
+    private void RebuildManagedOverlay()
     {
         if (_status?.EffectiveConfig == null || string.IsNullOrEmpty(_status.ManagedHostsFilePath))
             return;
@@ -447,7 +814,7 @@ else
         var path = _status.ManagedHostsFilePath;
         var managedRows = new List<HostsPageRow>();
 
-        foreach (var e in _managedEntries.Where(x => !x.IsPassthrough))
+        foreach (var e in CurrentManagedEntries.Where(x => !x.IsPassthrough))
         {
             var names = e.Names ?? (IReadOnlyList<string>)Array.Empty<string>();
             var effective = HostsEffectiveNames.Expand(names, expandHosts, domain);
@@ -466,13 +833,14 @@ else
                 LineNumber: e.LineNumber));
         }
 
-        var rest = _unifiedRows.Where(r => r.SourceKind != HostsRowSourceKind.Managed).ToList();
-        _unifiedRows = managedRows.Concat(rest).ToList();
+        _unifiedRows = managedRows.Concat(_restUnifiedRows).ToList();
     }
 
     public void Dispose()
     {
+        Session.Changed -= OnSessionChanged;
         _ = CleanupHostsTableScrollCueAsync();
+        _ = CleanupHostsUiModuleAsync();
     }
 
     private async Task CleanupHostsTableScrollCueAsync()
@@ -491,4 +859,20 @@ else
 
         _hostsTableScrollCueModule = null;
     }
+
+    private async Task CleanupHostsUiModuleAsync()
+    {
+        if (_hostsUiModule == null)
+            return;
+
+        try
+        {
+            await _hostsUiModule.DisposeAsync();
+        }
+        catch (JSDisconnectedException)
+        {
+        }
+
+        _hostsUiModule = null;
+    }
 }

src/DnsmasqWebUI/Components/Pages/Hosts.razor.css

@@ -101,6 +101,21 @@
 }
 
 /* Group header row (colspan, not rowspan) */
+::deep .hosts-table .hosts-effective-names-th {
+    white-space: nowrap;
+}
+
+::deep .hosts-table .hosts-effective-names-help {
+    vertical-align: middle;
+    text-decoration: none;
+    line-height: 1;
+}
+
+::deep .hosts-table .hosts-effective-names-help:hover,
+::deep .hosts-table .hosts-effective-names-help:focus-visible {
+    color: var(--bs-primary) !important;
+}
+
 ::deep .hosts-table .hosts-group-header-cell {
     background: linear-gradient(180deg, #f8fafc 0%, #f6f8fb 100%);
     border-top: 1px solid #dbe3ec;
@@ -112,6 +127,10 @@
 }
 
 .hosts-group-header__content {
+    display: flex;
+    flex-direction: column;
+    align-items: flex-start;
+    gap: 0.35rem;
     width: 100%;
 }
 
@@ -121,13 +140,26 @@
     align-items: center;
     gap: 0.5rem;
     color: #0f172a;
+    min-width: 0;
+}
+
+.hosts-group-header__path {
+    display: flex;
+    flex-wrap: wrap;
+    align-items: center;
+    gap: 0.5rem;
+    min-width: 0;
+    width: 100%;
+    font-weight: 500;
+}
+
+.hosts-group-header__badge {
+    flex-shrink: 0;
 }
 
 .hosts-group-header__subtitle {
-    display: inline-flex;
-    align-items: center;
+    display: inline-block;
     line-height: 1.2;
-    margin-left: 0.25rem;
     font-weight: 500;
     white-space: nowrap;
     overflow: hidden;
@@ -147,6 +179,11 @@
     background-color: rgba(13, 110, 253, 0.06);
 }
 
+::deep .hosts-table .hosts-row--empty td.hosts-empty-group-message {
+    background: #fafbfc;
+    font-style: italic;
+}
+
 ::deep .hosts-row code {
     font-size: 0.93em;
     color: #0f172a;

src/DnsmasqWebUI/Infrastructure/Services/Dnsmasq/Hosts/HostsPageProjectionService.cs

@@ -63,6 +63,9 @@ public sealed class HostsPageProjectionService : IHostsPageProjectionService
                 ? first.InactiveReason
                 : null;
 
+            var isSourceEditable = first.SourceKind == HostsRowSourceKind.Managed
+                || sortedRows.Any(r => r.IsEditable);
+
             result.Add(new HostsPageGroup(
                 Key: $"{first.SourceKind}:{first.SourcePath}",
                 Title: title,
@@ -72,7 +75,8 @@ public sealed class HostsPageProjectionService : IHostsPageProjectionService
                 IsActive: sortedRows.Any(r => r.IsActive),
                 InactiveReason: inactiveReason,
                 VisibleRowCount: sortedRows.Count,
-                Rows: sortedRows));
+                Rows: sortedRows,
+                IsSourceEditable: isSourceEditable));
         }
 
         return result;

src/DnsmasqWebUI/Infrastructure/Services/EffectiveConfig/Abstractions/IEffectiveConfigDraft.cs

@@ -0,0 +1,37 @@
+using DnsmasqWebUI.Models.Dnsmasq.EffectiveConfig;
+using DnsmasqWebUI.Models.Hosts;
+
+namespace DnsmasqWebUI.Infrastructure.Services.EffectiveConfig.Abstractions;
+
+/// <summary>
+/// Pending effective-config changes, validation issues, and apply/save. Independent of edit-mode UI state.
+/// </summary>
+public interface IEffectiveConfigDraft
+{
+    event Action? Changed;
+
+    IReadOnlyList<PendingDnsmasqChange> PendingChanges { get; }
+    IReadOnlyDictionary<string, IReadOnlyList<FieldIssue>> FieldIssues { get; }
+    PendingManagedHostsChange? ManagedHostsDraft { get; }
+
+    void TrackCommit(EffectiveConfigEditCommittedArgs args);
+    void RevertChange(string sectionId, string optionName);
+
+    void SetManagedHostsDraft(
+        IReadOnlyList<HostEntry> baseline,
+        IReadOnlyList<HostEntry> draft,
+        string managedHostsFilePath);
+
+    void RevertManagedHostsDraft();
+
+    void SetFieldIssues(string fieldKey, IReadOnlyList<FieldIssue> issues);
+    void ClearFieldIssues(string fieldKey);
+    void SetCrossOptionIssues(IReadOnlyList<FieldIssue> issues);
+
+    bool HasBlockingValidationErrors();
+    IReadOnlyList<FieldIssue> GetValidationSummary();
+
+    Task<EffectiveConfigSaveResult> ApplyAsync(CancellationToken ct = default);
+    void AcceptAppliedChanges();
+    void DiscardAllDraft();
+}

src/DnsmasqWebUI/Infrastructure/Services/EffectiveConfig/Abstractions/IEffectiveConfigEditSession.cs

@@ -1,51 +1,15 @@
 using DnsmasqWebUI.Infrastructure.Services.Registration.Abstractions;
-using DnsmasqWebUI.Models.Dnsmasq.EffectiveConfig;
 
 namespace DnsmasqWebUI.Infrastructure.Services.EffectiveConfig.Abstractions;
 
 /// <summary>
-/// Scoped orchestrator for effective-config edit lifecycle: edit mode, active field, pending changes, validation, and apply.
-/// Components read state from here and call methods; the owning section re-renders after state changes.
+/// Scoped root for effective-config editing: <see cref="Draft"/> holds pending changes and validation;
+/// <see cref="Ui"/> holds edit mode and active field. Subscribe to <see cref="Changed"/> for any update.
 /// </summary>
 public interface IEffectiveConfigEditSession : IApplicationScopedService
 {
-    /// <summary>Raised when session state changes so UI (section and external widgets) can refresh.</summary>
     event Action? Changed;
 
-    bool IsEditMode { get; }
-    string? ActiveFieldKey { get; }
-    IReadOnlyList<PendingDnsmasqChange> PendingChanges { get; }
-
-    /// <summary>Per-field validation issues (errors block save; warnings can be confirmed).</summary>
-    IReadOnlyDictionary<string, IReadOnlyList<FieldIssue>> FieldIssues { get; }
-
-    void EnterEditMode();
-    void ExitEditModeDiscard();
-    void ActivateField(string fieldKey);
-    void DeactivateField();
-
-    void TrackCommit(EffectiveConfigEditCommittedArgs args);
-    void RevertChange(string sectionId, string optionName);
-    void TrackManagedHostsChange(PendingManagedHostsChange change);
-    void RevertManagedHostsChange();
-
-    void SetFieldIssues(string fieldKey, IReadOnlyList<FieldIssue> issues);
-    void ClearFieldIssues(string fieldKey);
-
-    /// <summary>Replaces all cross-option validation issues (e.g. no-resolv vs server). Merged with per-field issues for display and save guard.</summary>
-    void SetCrossOptionIssues(IReadOnlyList<FieldIssue> issues);
-
-    /// <summary>True if any field has one or more issues with <see cref="FieldIssueSeverity.Error"/>.</summary>
-    bool HasBlockingValidationErrors();
-    /// <summary>All issues across fields for summary display (e.g. toolbar count or save guard message).</summary>
-    IReadOnlyList<FieldIssue> GetValidationSummary();
-
-    Task<EffectiveConfigSaveResult> ApplyAsync(CancellationToken ct = default);
-
-    /// <summary>
-    /// Accepts that changes were applied to disk. Clears pending changes and optionally exits edit mode.
-    /// Call this after a successful write (even if restart failed), so the session state matches disk state.
-    /// </summary>
-    /// <param name="stayInEditMode">If true, keep edit mode active; if false, exit edit mode.</param>
-    void AcceptAppliedChanges(bool stayInEditMode);
+    IEffectiveConfigDraft Draft { get; }
+    IEffectiveConfigUiState Ui { get; }
 }

src/DnsmasqWebUI/Infrastructure/Services/EffectiveConfig/Abstractions/IEffectiveConfigUiState.cs

@@ -0,0 +1,18 @@
+namespace DnsmasqWebUI.Infrastructure.Services.EffectiveConfig.Abstractions;
+
+/// <summary>
+/// Edit affordance state only: whether the effective-config UI is in edit mode and which field is active.
+/// Does not own pending changes or validation.
+/// </summary>
+public interface IEffectiveConfigUiState
+{
+    event Action? Changed;
+
+    bool IsEditMode { get; }
+    string? ActiveFieldKey { get; }
+
+    void EnterEditMode();
+    void ExitEditMode();
+    void ActivateField(string fieldKey);
+    void DeactivateField();
+}

src/DnsmasqWebUI/Infrastructure/Services/EffectiveConfig/EffectiveConfigDraft.cs

@@ -0,0 +1,149 @@
+using DnsmasqWebUI.Infrastructure.Services.EffectiveConfig.Abstractions;
+using DnsmasqWebUI.Models.Dnsmasq.EffectiveConfig;
+using DnsmasqWebUI.Models.Hosts;
+
+namespace DnsmasqWebUI.Infrastructure.Services.EffectiveConfig;
+
+public sealed class EffectiveConfigDraft : IEffectiveConfigDraft
+{
+    private readonly IEffectiveConfigSaveService _saveService;
+    private readonly List<PendingDnsmasqChange> _pending = new();
+    private readonly Dictionary<string, List<FieldIssue>> _fieldIssues = new(StringComparer.OrdinalIgnoreCase);
+    private readonly List<FieldIssue> _crossOptionIssues = new();
+
+    public EffectiveConfigDraft(IEffectiveConfigSaveService saveService)
+    {
+        _saveService = saveService;
+    }
+
+    public event Action? Changed;
+
+    private void NotifyChanged() => Changed?.Invoke();
+
+    public IReadOnlyList<PendingDnsmasqChange> PendingChanges => _pending;
+
+    public PendingManagedHostsChange? ManagedHostsDraft =>
+        _pending.OfType<PendingManagedHostsChange>().FirstOrDefault();
+
+    public IReadOnlyDictionary<string, IReadOnlyList<FieldIssue>> FieldIssues
+    {
+        get
+        {
+            var copy = new Dictionary<string, List<FieldIssue>>(StringComparer.OrdinalIgnoreCase);
+            foreach (var kv in _fieldIssues)
+                copy[kv.Key] = new List<FieldIssue>(kv.Value);
+            foreach (var issue in _crossOptionIssues)
+            {
+                if (!copy.TryGetValue(issue.FieldKey, out var list))
+                    copy[issue.FieldKey] = list = new List<FieldIssue>();
+                list.Add(issue);
+            }
+            return copy.ToDictionary(kv => kv.Key, kv => (IReadOnlyList<FieldIssue>)kv.Value, StringComparer.OrdinalIgnoreCase);
+        }
+    }
+
+    public void DiscardAllDraft()
+    {
+        _pending.Clear();
+        _fieldIssues.Clear();
+        _crossOptionIssues.Clear();
+        NotifyChanged();
+    }
+
+    public void SetFieldIssues(string fieldKey, IReadOnlyList<FieldIssue> issues)
+    {
+        if (string.IsNullOrEmpty(fieldKey)) return;
+        _fieldIssues[fieldKey] = issues.ToList();
+        NotifyChanged();
+    }
+
+    public void ClearFieldIssues(string fieldKey)
+    {
+        if (string.IsNullOrEmpty(fieldKey)) return;
+        _fieldIssues.Remove(fieldKey);
+        NotifyChanged();
+    }
+
+    public void SetCrossOptionIssues(IReadOnlyList<FieldIssue> issues)
+    {
+        _crossOptionIssues.Clear();
+        if (issues != null)
+            _crossOptionIssues.AddRange(issues);
+        NotifyChanged();
+    }
+
+    public bool HasBlockingValidationErrors()
+    {
+        if (_fieldIssues.Values.Any(list => list.Any(i => i.Severity == FieldIssueSeverity.Error)))
+            return true;
+        return _crossOptionIssues.Any(i => i.Severity == FieldIssueSeverity.Error);
+    }
+
+    public IReadOnlyList<FieldIssue> GetValidationSummary()
+    {
+        var list = new List<FieldIssue>(_fieldIssues.Values.SelectMany(x => x));
+        list.AddRange(_crossOptionIssues);
+        return list;
+    }
+
+    public void TrackCommit(EffectiveConfigEditCommittedArgs args)
+    {
+        _pending.RemoveAll(c => c is PendingOptionChange o && o.SectionId == args.SectionId && o.OptionName == args.OptionName);
+        if (!ValuesEqual(args.OldValue, args.NewValue))
+            _pending.Add(new PendingOptionChange(
+                args.SectionId, args.OptionName, args.OldValue, args.NewValue, args.CurrentSourceFilePath));
+        NotifyChanged();
+    }
+
+    public void RevertChange(string sectionId, string optionName)
+    {
+        _pending.RemoveAll(c => c is PendingOptionChange o && o.SectionId == sectionId && o.OptionName == optionName);
+        ClearFieldIssues($"{sectionId}:{optionName}");
+        NotifyChanged();
+    }
+
+    public void SetManagedHostsDraft(
+        IReadOnlyList<HostEntry> baseline,
+        IReadOnlyList<HostEntry> draft,
+        string managedHostsFilePath)
+    {
+        _pending.RemoveAll(c => c is PendingManagedHostsChange);
+        var pending = new PendingManagedHostsChange(baseline, draft, managedHostsFilePath);
+        if (pending.HasChanges)
+            _pending.Add(pending);
+        NotifyChanged();
+    }
+
+    public void RevertManagedHostsDraft()
+    {
+        _pending.RemoveAll(c => c is PendingManagedHostsChange);
+        NotifyChanged();
+    }
+
+    public async Task<EffectiveConfigSaveResult> ApplyAsync(CancellationToken ct = default)
+    {
+        if (_pending.Count == 0)
+            return EffectiveConfigSaveResult.NoChanges();
+
+        return await _saveService.SaveAsync(_pending.ToList(), ct);
+    }
+
+    public void AcceptAppliedChanges()
+    {
+        _pending.Clear();
+        _fieldIssues.Clear();
+        _crossOptionIssues.Clear();
+        NotifyChanged();
+    }
+
+    private static IReadOnlyList<string>? AsStringList(object? value) => value as IReadOnlyList<string>;
+
+    private static bool ValuesEqual(object? oldValue, object? newValue)
+    {
+        var oldList = AsStringList(oldValue);
+        var newList = AsStringList(newValue);
+        if (oldList != null || newList != null)
+            return (oldList ?? Array.Empty<string>()).SequenceEqual(newList ?? Array.Empty<string>(), StringComparer.Ordinal);
+        return Equals(oldValue, newValue);
+    }
+}

src/DnsmasqWebUI/Infrastructure/Services/EffectiveConfig/EffectiveConfigEditSession.cs

@@ -1,172 +1,24 @@
 using DnsmasqWebUI.Infrastructure.Services.EffectiveConfig.Abstractions;
-using DnsmasqWebUI.Models.Dnsmasq.EffectiveConfig;
 
 namespace DnsmasqWebUI.Infrastructure.Services.EffectiveConfig;
 
 public sealed class EffectiveConfigEditSession : IEffectiveConfigEditSession
 {
-    private readonly IEffectiveConfigSaveService _saveService;
-    private readonly List<PendingDnsmasqChange> _pending = new();
-    private readonly Dictionary<string, List<FieldIssue>> _fieldIssues = new(StringComparer.OrdinalIgnoreCase);
-    private readonly List<FieldIssue> _crossOptionIssues = new();
+    private readonly EffectiveConfigDraft _draft;
+    private readonly EffectiveConfigUiState _ui;
 
     public EffectiveConfigEditSession(IEffectiveConfigSaveService saveService)
     {
-        _saveService = saveService;
+        _draft = new EffectiveConfigDraft(saveService);
+        _ui = new EffectiveConfigUiState();
+        _draft.Changed += OnChildChanged;
+        _ui.Changed += OnChildChanged;
     }
 
     public event Action? Changed;
 
-    private void NotifyChanged() => Changed?.Invoke();
+    public IEffectiveConfigDraft Draft => _draft;
+    public IEffectiveConfigUiState Ui => _ui;
 
-    public bool IsEditMode { get; private set; }
-    public string? ActiveFieldKey { get; private set; }
-    public IReadOnlyList<PendingDnsmasqChange> PendingChanges => _pending;
-    public IReadOnlyDictionary<string, IReadOnlyList<FieldIssue>> FieldIssues
-    {
-        get
-        {
-            var copy = new Dictionary<string, List<FieldIssue>>(StringComparer.OrdinalIgnoreCase);
-            foreach (var kv in _fieldIssues)
-                copy[kv.Key] = new List<FieldIssue>(kv.Value);
-            foreach (var issue in _crossOptionIssues)
-            {
-                if (!copy.TryGetValue(issue.FieldKey, out var list))
-                    copy[issue.FieldKey] = list = new List<FieldIssue>();
-                list.Add(issue);
-            }
-            return copy.ToDictionary(kv => kv.Key, kv => (IReadOnlyList<FieldIssue>)kv.Value, StringComparer.OrdinalIgnoreCase);
-        }
-    }
-
-    public void EnterEditMode()
-    {
-        IsEditMode = true;
-        ActiveFieldKey = null;
-        _pending.Clear();
-        _fieldIssues.Clear();
-        _crossOptionIssues.Clear();
-        NotifyChanged();
-    }
-
-    public void ExitEditModeDiscard()
-    {
-        _pending.Clear();
-        _fieldIssues.Clear();
-        _crossOptionIssues.Clear();
-        ActiveFieldKey = null;
-        IsEditMode = false;
-        NotifyChanged();
-    }
-
-    public void ActivateField(string fieldKey)
-    {
-        IsEditMode = true;
-        ActiveFieldKey = fieldKey;
-        NotifyChanged();
-    }
-
-    public void DeactivateField()
-    {
-        ActiveFieldKey = null;
-        NotifyChanged();
-    }
-
-    public void SetFieldIssues(string fieldKey, IReadOnlyList<FieldIssue> issues)
-    {
-        if (string.IsNullOrEmpty(fieldKey)) return;
-        _fieldIssues[fieldKey] = issues.ToList();
-        NotifyChanged();
-    }
-
-    public void ClearFieldIssues(string fieldKey)
-    {
-        if (string.IsNullOrEmpty(fieldKey)) return;
-        _fieldIssues.Remove(fieldKey);
-        NotifyChanged();
-    }
-
-    public void SetCrossOptionIssues(IReadOnlyList<FieldIssue> issues)
-    {
-        _crossOptionIssues.Clear();
-        if (issues != null)
-            _crossOptionIssues.AddRange(issues);
-        NotifyChanged();
-    }
-
-    public bool HasBlockingValidationErrors()
-    {
-        if (_fieldIssues.Values.Any(list => list.Any(i => i.Severity == FieldIssueSeverity.Error)))
-            return true;
-        return _crossOptionIssues.Any(i => i.Severity == FieldIssueSeverity.Error);
-    }
-
-    public IReadOnlyList<FieldIssue> GetValidationSummary()
-    {
-        var list = new List<FieldIssue>(_fieldIssues.Values.SelectMany(x => x));
-        list.AddRange(_crossOptionIssues);
-        return list;
-    }
-
-    public void TrackCommit(EffectiveConfigEditCommittedArgs args)
-    {
-        _pending.RemoveAll(c => c is PendingOptionChange o && o.SectionId == args.SectionId && o.OptionName == args.OptionName);
-        if (!ValuesEqual(args.OldValue, args.NewValue))
-            _pending.Add(new PendingOptionChange(
-                args.SectionId, args.OptionName, args.OldValue, args.NewValue, args.CurrentSourceFilePath));
-        ActiveFieldKey = null;
-        NotifyChanged();
-    }
-
-    public void RevertChange(string sectionId, string optionName)
-    {
-        _pending.RemoveAll(c => c is PendingOptionChange o && o.SectionId == sectionId && o.OptionName == optionName);
-        ClearFieldIssues($"{sectionId}:{optionName}");
-        NotifyChanged();
-    }
-
-    public void TrackManagedHostsChange(PendingManagedHostsChange change)
-    {
-        _pending.RemoveAll(c => c is PendingManagedHostsChange);
-        _pending.Add(change);
-        NotifyChanged();
-    }
-
-    public void RevertManagedHostsChange()
-    {
-        _pending.RemoveAll(c => c is PendingManagedHostsChange);
-        NotifyChanged();
-    }
-
-    public async Task<EffectiveConfigSaveResult> ApplyAsync(CancellationToken ct = default)
-    {
-        if (_pending.Count == 0)
-            return EffectiveConfigSaveResult.NoChanges();
-
-        return await _saveService.SaveAsync(_pending.ToList(), ct);
-    }
-
-    public void AcceptAppliedChanges(bool stayInEditMode)
-    {
-        _pending.Clear();
-        _fieldIssues.Clear();
-        _crossOptionIssues.Clear();
-        ActiveFieldKey = null;
-        IsEditMode = stayInEditMode;
-        NotifyChanged();
-    }
-
-    private static IReadOnlyList<string>? AsStringList(object? value)
-    {
-        return value as IReadOnlyList<string>;
-    }
-
-    private static bool ValuesEqual(object? oldValue, object? newValue)
-    {
-        var oldList = AsStringList(oldValue);
-        var newList = AsStringList(newValue);
-        if (oldList != null || newList != null)
-            return (oldList ?? Array.Empty<string>()).SequenceEqual(newList ?? Array.Empty<string>(), StringComparer.Ordinal);
-        return Equals(oldValue, newValue);
-    }
+    private void OnChildChanged() => Changed?.Invoke();
 }

src/DnsmasqWebUI/Infrastructure/Services/EffectiveConfig/EffectiveConfigPageEditor.cs

@@ -27,8 +27,8 @@ public sealed class EffectiveConfigPageEditor : IEffectiveConfigPageEditor
 
     public void EnsureEditMode()
     {
-        if (!_session.IsEditMode)
-            _session.EnterEditMode();
+        if (!_session.Ui.IsEditMode)
+            _session.Ui.EnterEditMode();
     }
 
     public EffectiveConfigFieldRef Field(string sectionId, string optionName)
@@ -69,8 +69,9 @@ public sealed class EffectiveConfigPageEditor : IEffectiveConfigPageEditor
             : descriptor.GetValue();
         var oldValue = pending?.OldValue ?? baseValue;
         var source = descriptor.GetSource() ?? descriptor.GetItems()?.FirstOrDefault()?.Source;
-        _session.TrackCommit(new EffectiveConfigEditCommittedArgs(
+        _session.Draft.TrackCommit(new EffectiveConfigEditCommittedArgs(
             field.SectionId, field.OptionName, oldValue, newValue, source?.FilePath));
+        _session.Ui.DeactivateField();
         RefreshCrossOptionIssues(status);
     }
 
@@ -84,8 +85,9 @@ public sealed class EffectiveConfigPageEditor : IEffectiveConfigPageEditor
         var baseValues = descriptor.GetItems()?.Select(i => i.Value).ToList() ?? new List<string>();
         var oldValues = pending?.OldValue is IReadOnlyList<string> list ? list.ToList() : baseValues;
         var source = descriptor.GetSource() ?? descriptor.GetItems()?.FirstOrDefault()?.Source;
-        _session.TrackCommit(new EffectiveConfigEditCommittedArgs(
+        _session.Draft.TrackCommit(new EffectiveConfigEditCommittedArgs(
             field.SectionId, field.OptionName, oldValues, newValues.ToList(), source?.FilePath));
+        _session.Ui.DeactivateField();
         RefreshCrossOptionIssues(status);
     }
 
@@ -105,36 +107,36 @@ public sealed class EffectiveConfigPageEditor : IEffectiveConfigPageEditor
 
     public void Revert(EffectiveConfigFieldRef field)
     {
-        _session.RevertChange(field.SectionId, field.OptionName);
+        _session.Draft.RevertChange(field.SectionId, field.OptionName);
     }
 
     public void SetFieldIssues(EffectiveConfigFieldRef field, IReadOnlyList<FieldIssue> issues)
     {
-        _session.SetFieldIssues(field.FieldKey, issues);
+        _session.Draft.SetFieldIssues(field.FieldKey, issues);
     }
 
     public void ClearFieldIssues(EffectiveConfigFieldRef field)
     {
-        _session.ClearFieldIssues(field.FieldKey);
+        _session.Draft.ClearFieldIssues(field.FieldKey);
     }
 
     public void RefreshCrossOptionIssues(DnsmasqServiceStatus status)
     {
         var issues = _crossOptionValidation.Validate(
             status,
-            _session.PendingChanges.OfType<PendingOptionChange>().ToList());
-        _session.SetCrossOptionIssues(issues);
+            _session.Draft.PendingChanges.OfType<PendingOptionChange>().ToList());
+        _session.Draft.SetCrossOptionIssues(issues);
     }
 
     public void Activate(EffectiveConfigFieldRef field)
     {
         EnsureEditMode();
-        _session.ActivateField(field.FieldKey);
+        _session.Ui.ActivateField(field.FieldKey);
     }
 
     private PendingOptionChange? GetPendingOptionChange(EffectiveConfigFieldRef field)
     {
-        return _session.PendingChanges.OfType<PendingOptionChange>().FirstOrDefault(c =>
+        return _session.Draft.PendingChanges.OfType<PendingOptionChange>().FirstOrDefault(c =>
             string.Equals(c.SectionId, field.SectionId, StringComparison.OrdinalIgnoreCase) &&
             string.Equals(c.OptionName, field.OptionName, StringComparison.OrdinalIgnoreCase));
     }

src/DnsmasqWebUI/Infrastructure/Services/EffectiveConfig/EffectiveConfigUiState.cs

@@ -0,0 +1,38 @@
+using DnsmasqWebUI.Infrastructure.Services.EffectiveConfig.Abstractions;
+
+namespace DnsmasqWebUI.Infrastructure.Services.EffectiveConfig;
+
+public sealed class EffectiveConfigUiState : IEffectiveConfigUiState
+{
+    public event Action? Changed;
+
+    public bool IsEditMode { get; private set; }
+    public string? ActiveFieldKey { get; private set; }
+
+    public void EnterEditMode()
+    {
+        IsEditMode = true;
+        ActiveFieldKey = null;
+        Changed?.Invoke();
+    }
+
+    public void ExitEditMode()
+    {
+        IsEditMode = false;
+        ActiveFieldKey = null;
+        Changed?.Invoke();
+    }
+
+    public void ActivateField(string fieldKey)
+    {
+        IsEditMode = true;
+        ActiveFieldKey = fieldKey;
+        Changed?.Invoke();
+    }
+
+    public void DeactivateField()
+    {
+        ActiveFieldKey = null;
+        Changed?.Invoke();
+    }
+}

src/DnsmasqWebUI/Models/Dnsmasq/EffectiveConfig/ManagedHostsPendingChangeDiff.cs

@@ -0,0 +1,126 @@
+using DnsmasqWebUI.Models.Hosts;
+
+namespace DnsmasqWebUI.Models.Dnsmasq.EffectiveConfig;
+
+public enum ManagedHostsLineDiffKind
+{
+    Added,
+    Removed,
+    Modified,
+    /// <summary>Same entries (by id) but a different order in the file.</summary>
+    OrderOnly
+}
+
+/// <summary>One line-level change for display in the save modal (before → after).</summary>
+public readonly record struct ManagedHostsLineDiff(
+    ManagedHostsLineDiffKind Kind,
+    string? BeforeLine,
+    string? AfterLine);
+
+/// <summary>Builds a line-level diff between baseline and draft managed-hosts entries.</summary>
+public static class ManagedHostsPendingChangeDiff
+{
+    public static IReadOnlyList<ManagedHostsLineDiff> Build(PendingManagedHostsChange change) =>
+        Build(change.OldEntries, change.NewEntries);
+
+    public static IReadOnlyList<ManagedHostsLineDiff> Build(
+        IReadOnlyList<HostEntry> oldEntries,
+        IReadOnlyList<HostEntry> newEntries)
+    {
+        var oldMap = ToUniqueMap(oldEntries);
+        var newMap = ToUniqueMap(newEntries);
+        var keys = oldMap.Keys.Union(newMap.Keys, StringComparer.Ordinal).ToHashSet(StringComparer.Ordinal);
+        var list = new List<ManagedHostsLineDiff>();
+
+        foreach (var key in keys)
+        {
+            oldMap.TryGetValue(key, out var o);
+            newMap.TryGetValue(key, out var n);
+
+            if (o == null && n != null)
+                list.Add(new ManagedHostsLineDiff(ManagedHostsLineDiffKind.Added, null, FormatEntry(n)));
+            else if (o != null && n == null)
+                list.Add(new ManagedHostsLineDiff(ManagedHostsLineDiffKind.Removed, FormatEntry(o), null));
+            else if (o != null && n != null && !ContentEquals(o, n))
+                list.Add(new ManagedHostsLineDiff(ManagedHostsLineDiffKind.Modified, FormatEntry(o), FormatEntry(n)));
+        }
+
+        if (list.Count == 0 && DetectOrderOnly(oldEntries, newEntries))
+            list.Add(new ManagedHostsLineDiff(ManagedHostsLineDiffKind.OrderOnly, null, null));
+
+        return list
+            .OrderBy(d => SortOrder(d))
+            .ToList();
+    }
+
+    private static int SortOrder(ManagedHostsLineDiff d) => d.Kind switch
+    {
+        ManagedHostsLineDiffKind.Removed => 0,
+        ManagedHostsLineDiffKind.Modified => 1,
+        ManagedHostsLineDiffKind.OrderOnly => 2,
+        ManagedHostsLineDiffKind.Added => 3,
+        _ => 4
+    };
+
+    private static bool DetectOrderOnly(IReadOnlyList<HostEntry> oldList, IReadOnlyList<HostEntry> newList)
+    {
+        if (oldList.Count != newList.Count || oldList.Count == 0)
+            return false;
+        var oldKeys = oldList.Select(e => StableKey(e)).OrderBy(k => k, StringComparer.Ordinal).ToList();
+        var newKeys = newList.Select(e => StableKey(e)).OrderBy(k => k, StringComparer.Ordinal).ToList();
+        if (!oldKeys.SequenceEqual(newKeys, StringComparer.Ordinal))
+            return false;
+        for (var i = 0; i < oldList.Count; i++)
+        {
+            if (!string.Equals(StableKey(oldList[i]), StableKey(newList[i]), StringComparison.Ordinal))
+                return true;
+        }
+
+        return false;
+    }
+
+    private static Dictionary<string, HostEntry> ToUniqueMap(IReadOnlyList<HostEntry> entries)
+    {
+        var map = new Dictionary<string, HostEntry>(StringComparer.Ordinal);
+        foreach (var e in entries)
+        {
+            var k = StableKey(e);
+            if (!map.ContainsKey(k))
+                map[k] = e;
+        }
+
+        return map;
+    }
+
+    /// <summary>Matches <see cref="PendingManagedHostsChange"/> identity: Id, or managed:line when Id is empty.</summary>
+    public static string StableKey(HostEntry e) =>
+        !string.IsNullOrEmpty(e.Id) ? e.Id : $"managed:{e.LineNumber}";
+
+    public static string FormatEntry(HostEntry e)
+    {
+        if (e.IsPassthrough)
+            return string.IsNullOrEmpty(e.RawLine) ? "(unparsed line)" : e.RawLine.TrimEnd();
+        if (e.IsComment)
+            return string.IsNullOrEmpty(e.RawLine) ? "#" : e.RawLine.TrimEnd();
+        var names = e.Names ?? new List<string>();
+        if (string.IsNullOrWhiteSpace(e.Address) && names.Count == 0)
+            return "(empty)";
+        return $"{e.Address} {string.Join(' ', names)}".Trim();
+    }
+
+    private static bool ContentEquals(HostEntry a, HostEntry b)
+    {
+        if (string.Equals(a.Address ?? "", b.Address ?? "", StringComparison.Ordinal))
+        {
+            var an = a.Names ?? new List<string>();
+            var bn = b.Names ?? new List<string>();
+            if (an.SequenceEqual(bn, StringComparer.Ordinal)
+                && a.IsComment == b.IsComment
+                && a.IsPassthrough == b.IsPassthrough
+                && string.Equals(a.RawLine ?? "", b.RawLine ?? "", StringComparison.Ordinal))
+                return true;
+        }
+
+        return false;
+    }
+}

src/DnsmasqWebUI/Models/Hosts/HostsEntryEditValidator.cs

@@ -0,0 +1,35 @@
+using System.Net;
+
+namespace DnsmasqWebUI.Models.Hosts;
+
+/// <summary>Client-side checks for hosts table inline editing (IP + at least one name).</summary>
+public static class HostsEntryEditValidator
+{
+    public static IReadOnlyList<string> GetAddressFieldErrors(string addressTrimmed)
+    {
+        var errors = new List<string>();
+        if (string.IsNullOrWhiteSpace(addressTrimmed))
+            errors.Add("Address is required.");
+        else if (!IPAddress.TryParse(addressTrimmed, out _))
+            errors.Add("Address must be a valid IPv4 or IPv6 address.");
+        return errors;
+    }
+
+    public static IReadOnlyList<string> GetHostnameFieldErrors(IReadOnlyList<string> names)
+    {
+        if (names == null || names.Count == 0)
+            return new[] { "At least one hostname is required." };
+        return Array.Empty<string>();
+    }
+
+    public static IReadOnlyList<string> GetErrors(string addressTrimmed, IReadOnlyList<string> names)
+    {
+        var list = new List<string>();
+        list.AddRange(GetAddressFieldErrors(addressTrimmed));
+        list.AddRange(GetHostnameFieldErrors(names));
+        return list;
+    }
+
+    public static bool IsValid(string addressTrimmed, IReadOnlyList<string> names) =>
+        GetErrors(addressTrimmed, names).Count == 0;
+}

src/DnsmasqWebUI/Models/Hosts/HostsPageGroup.cs

@@ -12,4 +12,6 @@ public sealed record HostsPageGroup(
     bool IsActive,
     string? InactiveReason,
     int VisibleRowCount,
-    IReadOnlyList<HostsPageRow> Rows);
+    IReadOnlyList<HostsPageRow> Rows,
+    /// <summary>True when entries in this source can be edited in the UI (e.g. managed hosts file).</summary>
+    bool IsSourceEditable);

src/DnsmasqWebUI/wwwroot/js/modules/hosts-ui.js

@@ -0,0 +1,12 @@
+/**
+ * Touch / coarse-pointer devices: show Effective names help as a toast instead of relying on hover.
+ */
+export function preferEffectiveNamesHelpToast() {
+  try {
+    if (window.matchMedia("(pointer: coarse)").matches) return true;
+    if (window.matchMedia("(hover: none)").matches) return true;
+    return false;
+  } catch {
+    return false;
+  }
+}