Phase 0 — mechanical rename ZB.MOM.WW.LmxOpcUa.* → ZB.MOM.WW.OtOpcUa.*

Renames all 11 projects (5 src + 6 tests), the .slnx solution file, all source-file namespaces, all axaml namespace references, and all v1 documentation references in CLAUDE.md and docs/*.md (excluding docs/v2/ which is already in OtOpcUa form). Also updates the TopShelf service registration name from "LmxOpcUa" to "OtOpcUa" per Phase 0 Task 0.6.

Preserves runtime identifiers per Phase 0 Out-of-Scope rules to avoid breaking v1/v2 client trust during coexistence: OPC UA `ApplicationUri` defaults (`urn:{GalaxyName}:LmxOpcUa`), server `EndpointPath` (`/LmxOpcUa`), `ServerName` default (feeds cert subject CN), `MxAccessConfiguration.ClientName` default (defensive — stays "LmxOpcUa" for MxAccess audit-trail consistency), client OPC UA identifiers (`ApplicationName = "LmxOpcUaClient"`, `ApplicationUri = "urn:localhost:LmxOpcUaClient"`, cert directory `%LocalAppData%\LmxOpcUaClient\pki\`), and the `LmxOpcUaServer` class name (class rename out of Phase 0 scope per Task 0.5 sed pattern; happens in Phase 1 alongside `LmxNodeManager → GenericDriverNodeManager` Core extraction). 23 LmxOpcUa references retained, all enumerated and justified in `docs/v2/implementation/exit-gate-phase-0.md`.

Build clean: 0 errors, 30 warnings (lower than baseline 167). Tests at strict improvement over baseline: 821 passing / 1 failing vs baseline 820 / 2 (one flaky pre-existing failure passed this run; the other still fails — both pre-existing and unrelated to the rename). `Client.UI.Tests`, `Historian.Aveva.Tests`, `Client.Shared.Tests`, `IntegrationTests` all match baseline exactly. Exit gate compliance results recorded in `docs/v2/implementation/exit-gate-phase-0.md` with all 7 checks PASS or DEFERRED-to-PR-review (#7 service install verification needs Windows service permissions on the reviewer's box).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/AckAlarmWindow.axaml

@@ -0,0 +1,39 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Views.AckAlarmWindow"
+        Title="Acknowledge Alarm"
+        Width="420"
+        SizeToContent="Height"
+        MinHeight="240"
+        WindowStartupLocation="CenterOwner"
+        CanResize="False">
+    <StackPanel Margin="16" Spacing="12">
+        <TextBlock Text="Acknowledge Alarm" FontWeight="Bold" FontSize="16" />
+
+        <StackPanel Spacing="4">
+            <TextBlock Text="Source:" FontSize="12" Foreground="Gray" />
+            <TextBlock Name="SourceText" FontWeight="SemiBold" />
+        </StackPanel>
+
+        <StackPanel Spacing="4">
+            <TextBlock Text="Condition:" FontSize="12" Foreground="Gray" />
+            <TextBlock Name="ConditionText" />
+        </StackPanel>
+
+        <StackPanel Spacing="4">
+            <TextBlock Text="Comment:" FontSize="12" Foreground="Gray" />
+            <TextBox Name="CommentInput"
+                     Watermark="Enter acknowledgment comment"
+                     AcceptsReturn="True"
+                     Height="60"
+                     TextWrapping="Wrap" />
+        </StackPanel>
+
+        <TextBlock Name="ResultText" Foreground="Gray" />
+
+        <StackPanel Orientation="Horizontal" Spacing="8" HorizontalAlignment="Right">
+            <Button Name="AckButton" Content="Acknowledge" />
+            <Button Name="CancelButton" Content="Cancel" />
+        </StackPanel>
+    </StackPanel>
+</Window>

src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/AckAlarmWindow.axaml.cs

@@ -0,0 +1,67 @@
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Media;
+using ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+public partial class AckAlarmWindow : Window
+{
+    private readonly AlarmsViewModel _alarmsVm;
+    private readonly AlarmEventViewModel _alarm;
+
+    public AckAlarmWindow()
+    {
+        InitializeComponent();
+        _alarmsVm = null!;
+        _alarm = null!;
+    }
+
+    public AckAlarmWindow(AlarmsViewModel alarmsVm, AlarmEventViewModel alarm)
+    {
+        InitializeComponent();
+        _alarmsVm = alarmsVm;
+        _alarm = alarm;
+
+        var sourceText = this.FindControl<TextBlock>("SourceText");
+        if (sourceText != null) sourceText.Text = alarm.SourceName;
+
+        var conditionText = this.FindControl<TextBlock>("ConditionText");
+        if (conditionText != null) conditionText.Text = $"{alarm.ConditionName} (Severity: {alarm.Severity})";
+
+        var ackButton = this.FindControl<Button>("AckButton");
+        if (ackButton != null) ackButton.Click += OnAckClicked;
+
+        var cancelButton = this.FindControl<Button>("CancelButton");
+        if (cancelButton != null) cancelButton.Click += OnCancelClicked;
+    }
+
+    private async void OnAckClicked(object? sender, RoutedEventArgs e)
+    {
+        var commentInput = this.FindControl<TextBox>("CommentInput");
+        var resultText = this.FindControl<TextBlock>("ResultText");
+        if (commentInput == null || resultText == null) return;
+
+        var comment = commentInput.Text ?? string.Empty;
+
+        resultText.Foreground = Brushes.Gray;
+        resultText.Text = "Acknowledging...";
+
+        var (success, message) = await _alarmsVm.AcknowledgeAlarmAsync(_alarm, comment);
+
+        if (success)
+        {
+            Close();
+        }
+        else
+        {
+            resultText.Foreground = Brushes.Red;
+            resultText.Text = message;
+        }
+    }
+
+    private void OnCancelClicked(object? sender, RoutedEventArgs e)
+    {
+        Close();
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/AlarmsView.axaml

@@ -0,0 +1,39 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels"
+             x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Views.AlarmsView"
+             x:DataType="vm:AlarmsViewModel">
+    <DockPanel Margin="8">
+        <!-- Controls -->
+        <StackPanel DockPanel.Dock="Top" Spacing="8">
+            <TextBlock Text="Alarm Monitoring" FontWeight="Bold" />
+            <StackPanel Orientation="Horizontal" Spacing="8">
+                <TextBox Text="{Binding MonitoredNodeIdText}" Width="250" Watermark="Source Node ID (optional)" />
+                <NumericUpDown Value="{Binding Interval}" Minimum="100" Maximum="60000" Width="120" />
+                <Button Content="Subscribe" Command="{Binding SubscribeCommand}" />
+                <Button Content="Unsubscribe" Command="{Binding UnsubscribeCommand}" />
+                <Button Content="Refresh" Command="{Binding RefreshCommand}" />
+            </StackPanel>
+        </StackPanel>
+
+        <!-- Alarm Events -->
+        <DataGrid Name="AlarmsGrid"
+                  ItemsSource="{Binding AlarmEvents}"
+                  AutoGenerateColumns="False"
+                  IsReadOnly="True"
+                  HorizontalScrollBarVisibility="Auto"
+                  Margin="0,8,0,0"
+                  LoadingRow="OnDataGridLoadingRow">
+            <DataGrid.Columns>
+                <DataGridTextColumn Header="Time" Binding="{Binding Time, StringFormat='{}{0:yyyy-MM-dd HH:mm:ss}'}" Width="Auto" />
+                <DataGridTextColumn Header="Source" Binding="{Binding SourceName}" Width="Auto" />
+                <DataGridTextColumn Header="Condition" Binding="{Binding ConditionName}" Width="Auto" />
+                <DataGridTextColumn Header="Severity" Binding="{Binding Severity}" Width="Auto" />
+                <DataGridTextColumn Header="Message" Binding="{Binding Message}" Width="Auto" />
+                <DataGridCheckBoxColumn Header="Active" Binding="{Binding ActiveState}" Width="Auto" />
+                <DataGridCheckBoxColumn Header="Acked" Binding="{Binding AckedState}" Width="Auto" />
+                <DataGridCheckBoxColumn Header="Retain" Binding="{Binding Retain}" Width="Auto" />
+            </DataGrid.Columns>
+        </DataGrid>
+    </DockPanel>
+</UserControl>

src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/AlarmsView.axaml.cs

@@ -0,0 +1,79 @@
+using System.ComponentModel;
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Media;
+using Avalonia.VisualTree;
+using ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+public partial class AlarmsView : UserControl
+{
+    // Severity color bands (OPC UA severity 0-1000)
+    private static readonly IBrush InactiveBrush = new SolidColorBrush(Color.Parse("#F0F0F0"));     // light grey
+    private static readonly IBrush LowBrush = new SolidColorBrush(Color.Parse("#DBEAFE"));          // light blue (1-332)
+    private static readonly IBrush MediumBrush = new SolidColorBrush(Color.Parse("#FEF3C7"));       // light yellow (333-665)
+    private static readonly IBrush HighBrush = new SolidColorBrush(Color.Parse("#FEE2E2"));         // light red (666-899)
+    private static readonly IBrush CriticalBrush = new SolidColorBrush(Color.Parse("#FECACA"));     // red (900-1000)
+
+    public AlarmsView()
+    {
+        InitializeComponent();
+    }
+
+    protected override void OnLoaded(RoutedEventArgs e)
+    {
+        base.OnLoaded(e);
+
+        var grid = this.FindControl<DataGrid>("AlarmsGrid");
+        if (grid == null) return;
+
+        var contextMenu = new ContextMenu();
+        var ackItem = new MenuItem { Header = "Acknowledge..." };
+        ackItem.Click += OnAcknowledgeClicked;
+        contextMenu.Items.Add(ackItem);
+        contextMenu.Opening += OnContextMenuOpening;
+        grid.ContextMenu = contextMenu;
+    }
+
+    private void OnDataGridLoadingRow(object? sender, DataGridRowEventArgs e)
+    {
+        if (e.Row.DataContext is AlarmEventViewModel alarm)
+            e.Row.Background = GetSeverityBrush(alarm);
+    }
+
+    private static IBrush GetSeverityBrush(AlarmEventViewModel alarm)
+    {
+        if (!alarm.ActiveState)
+            return InactiveBrush;
+
+        return alarm.Severity switch
+        {
+            >= 900 => CriticalBrush,
+            >= 666 => HighBrush,
+            >= 333 => MediumBrush,
+            _ => LowBrush
+        };
+    }
+
+    private void OnContextMenuOpening(object? sender, CancelEventArgs e)
+    {
+        var grid = this.FindControl<DataGrid>("AlarmsGrid");
+        if (grid?.SelectedItem is not AlarmEventViewModel alarm || !alarm.CanAcknowledge)
+            e.Cancel = true;
+    }
+
+    private void OnAcknowledgeClicked(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is not AlarmsViewModel vm) return;
+
+        var grid = this.FindControl<DataGrid>("AlarmsGrid");
+        if (grid?.SelectedItem is not AlarmEventViewModel alarm || !alarm.CanAcknowledge) return;
+
+        var parentWindow = this.FindAncestorOfType<Window>();
+        if (parentWindow == null) return;
+
+        var ackWindow = new AckAlarmWindow(vm, alarm);
+        ackWindow.ShowDialog(parentWindow);
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/BrowseTreeView.axaml

@@ -0,0 +1,31 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels"
+             x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Views.BrowseTreeView"
+             x:DataType="vm:BrowseTreeViewModel">
+    <TreeView ItemsSource="{Binding RootNodes}"
+              Name="BrowseTree"
+              SelectionMode="Multiple">
+        <TreeView.Styles>
+            <Style Selector="TreeViewItem" x:DataType="vm:TreeNodeViewModel">
+                <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
+            </Style>
+        </TreeView.Styles>
+        <TreeView.ItemTemplate>
+            <TreeDataTemplate ItemsSource="{Binding Children}">
+                <StackPanel Orientation="Horizontal" Spacing="6">
+                    <TextBlock Text="{Binding DisplayName}" VerticalAlignment="Center" />
+                    <TextBlock Text="{Binding NodeClass}"
+                               FontSize="10"
+                               Foreground="Gray"
+                               VerticalAlignment="Center" />
+                    <ProgressBar IsIndeterminate="True"
+                                 IsVisible="{Binding IsLoading}"
+                                 Width="50"
+                                 Height="8"
+                                 VerticalAlignment="Center" />
+                </StackPanel>
+            </TreeDataTemplate>
+        </TreeView.ItemTemplate>
+    </TreeView>
+</UserControl>

src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/BrowseTreeView.axaml.cs

@@ -0,0 +1,11 @@
+using Avalonia.Controls;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+public partial class BrowseTreeView : UserControl
+{
+    public BrowseTreeView()
+    {
+        InitializeComponent();
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/HistoryView.axaml

@@ -0,0 +1,65 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels"
+             xmlns:controls="using:ZB.MOM.WW.OtOpcUa.Client.UI.Controls"
+             x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Views.HistoryView"
+             x:DataType="vm:HistoryViewModel">
+    <DockPanel Margin="8">
+        <!-- Controls -->
+        <StackPanel DockPanel.Dock="Top" Spacing="10">
+            <TextBlock Text="History Read" FontWeight="Bold" />
+            <TextBlock Text="{Binding SelectedNodeId, FallbackValue='(no node selected)'}"
+                       Foreground="Gray" />
+
+            <!-- Row 1: Time range -->
+            <controls:DateTimeRangePicker StartDateTime="{Binding StartTime, Mode=TwoWay}"
+                                          EndDateTime="{Binding EndTime, Mode=TwoWay}" />
+
+            <!-- Row 2: Aggregate, Interval, Max Values, Read button -->
+            <StackPanel Orientation="Horizontal" Spacing="12">
+                <StackPanel Spacing="2">
+                    <TextBlock Text="Aggregate" FontSize="11" Foreground="Gray" />
+                    <ComboBox ItemsSource="{Binding AggregateTypes}"
+                              SelectedItem="{Binding SelectedAggregateType}"
+                              Width="150">
+                        <ComboBox.ItemTemplate>
+                            <DataTemplate>
+                                <TextBlock Text="{Binding, TargetNullValue='Raw'}" />
+                            </DataTemplate>
+                        </ComboBox.ItemTemplate>
+                    </ComboBox>
+                </StackPanel>
+                <StackPanel Spacing="2" IsVisible="{Binding IsAggregateRead}">
+                    <TextBlock Text="Interval (ms)" FontSize="11" Foreground="Gray" />
+                    <NumericUpDown Value="{Binding IntervalMs}" Minimum="1000" Maximum="86400000" Width="150" />
+                </StackPanel>
+                <StackPanel Spacing="2">
+                    <TextBlock Text="Max Values" FontSize="11" Foreground="Gray" />
+                    <NumericUpDown Value="{Binding MaxValues}" Minimum="1" Maximum="100000" Width="120" />
+                </StackPanel>
+                <Button Content="Read History"
+                        Command="{Binding ReadHistoryCommand}"
+                        VerticalAlignment="Bottom"
+                        Padding="16,6" />
+            </StackPanel>
+
+            <ProgressBar IsIndeterminate="True"
+                         IsVisible="{Binding IsLoading}"
+                         Height="4" />
+        </StackPanel>
+
+        <!-- Results -->
+        <DataGrid ItemsSource="{Binding Results}"
+                  AutoGenerateColumns="False"
+                  IsReadOnly="True"
+                  HorizontalScrollBarVisibility="Auto"
+                  Margin="0,8,0,0">
+            <DataGrid.Columns>
+                <DataGridTextColumn Header="Value" Binding="{Binding Value}" Width="Auto" />
+                <DataGridTextColumn Header="Status" Binding="{Binding Status}" Width="Auto" />
+                <DataGridTextColumn Header="Source Timestamp" Binding="{Binding SourceTimestamp}" Width="Auto" />
+                <DataGridTextColumn Header="Server Timestamp" Binding="{Binding ServerTimestamp}" Width="Auto" />
+            </DataGrid.Columns>
+        </DataGrid>
+    </DockPanel>
+</UserControl>

src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/HistoryView.axaml.cs

@@ -0,0 +1,11 @@
+using Avalonia.Controls;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+public partial class HistoryView : UserControl
+{
+    public HistoryView()
+    {
+        InitializeComponent();
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/MainWindow.axaml

@@ -0,0 +1,162 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:vm="using:ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels"
+        xmlns:views="using:ZB.MOM.WW.OtOpcUa.Client.UI.Views"
+        x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Views.MainWindow"
+        x:DataType="vm:MainWindowViewModel"
+        Title="OPC UA Client"
+        Width="1200"
+        Height="800">
+    <DockPanel>
+        <!-- Top Connection Bar -->
+        <Border DockPanel.Dock="Top" Background="#F0F0F0" Padding="12">
+            <StackPanel Spacing="4">
+                <!-- Always visible: URL + Connect/Disconnect -->
+                <StackPanel Orientation="Horizontal" Spacing="8">
+                    <StackPanel Spacing="2" VerticalAlignment="Bottom">
+                        <TextBlock Text="Endpoint URL" FontSize="11" Foreground="Gray" />
+                        <TextBox Text="{Binding EndpointUrl}"
+                                 Width="400"
+                                 Watermark="opc.tcp://host:port" />
+                    </StackPanel>
+                    <Button Content="Connect"
+                            Command="{Binding ConnectCommand}"
+                            VerticalAlignment="Bottom" Padding="16,6" />
+                    <Button Content="Disconnect"
+                            Command="{Binding DisconnectCommand}"
+                            VerticalAlignment="Bottom" Padding="16,6" />
+                </StackPanel>
+
+                <!-- Expandable settings -->
+                <Expander Header="Connection Settings" Padding="0,4">
+                    <StackPanel Spacing="10" Margin="4,8,4,4">
+                        <!-- Row 1: Authentication -->
+                        <StackPanel Orientation="Horizontal" Spacing="12">
+                            <StackPanel Spacing="2">
+                                <TextBlock Text="Username" FontSize="11" Foreground="Gray" />
+                                <TextBox Text="{Binding Username}"
+                                         Width="160"
+                                         Watermark="(anonymous)" />
+                            </StackPanel>
+                            <StackPanel Spacing="2">
+                                <TextBlock Text="Password" FontSize="11" Foreground="Gray" />
+                                <TextBox Text="{Binding Password}"
+                                         Width="160"
+                                         Watermark="(none)"
+                                         PasswordChar="*" />
+                            </StackPanel>
+                            <StackPanel Spacing="2">
+                                <TextBlock Text="Security Mode" FontSize="11" Foreground="Gray" />
+                                <ComboBox ItemsSource="{Binding SecurityModes}"
+                                          SelectedItem="{Binding SelectedSecurityMode}"
+                                          Width="160" />
+                            </StackPanel>
+                        </StackPanel>
+
+                        <!-- Row 2: Failover + Session -->
+                        <StackPanel Orientation="Horizontal" Spacing="12">
+                            <StackPanel Spacing="2">
+                                <TextBlock Text="Failover URLs (comma-separated)" FontSize="11" Foreground="Gray" />
+                                <TextBox Text="{Binding FailoverUrls}"
+                                         Width="400"
+                                         Watermark="opc.tcp://backup1:4840, opc.tcp://backup2:4840" />
+                            </StackPanel>
+                            <StackPanel Spacing="2">
+                                <TextBlock Text="Session Timeout (s)" FontSize="11" Foreground="Gray" />
+                                <NumericUpDown Value="{Binding SessionTimeoutSeconds}"
+                                               Minimum="1" Maximum="3600"
+                                               Width="120"
+                                               FormatString="0" />
+                            </StackPanel>
+                        </StackPanel>
+
+                        <!-- Row 3: Certificates -->
+                        <StackPanel Orientation="Horizontal" Spacing="12">
+                            <StackPanel Spacing="2">
+                                <TextBlock Text="Certificate Store Path" FontSize="11" Foreground="Gray" />
+                                <StackPanel Orientation="Horizontal" Spacing="4">
+                                    <TextBox Text="{Binding CertificateStorePath}"
+                                             Width="370"
+                                             IsReadOnly="True"
+                                             Watermark="(default: AppData/LmxOpcUaClient/pki)" />
+                                    <Button Name="BrowseCertPathButton"
+                                            Content="..."
+                                            Width="30"
+                                            ToolTip.Tip="Browse for folder" />
+                                </StackPanel>
+                            </StackPanel>
+                            <CheckBox IsChecked="{Binding AutoAcceptCertificates}"
+                                      Content="Auto-accept untrusted server certificates"
+                                      VerticalAlignment="Bottom"
+                                      Margin="0,0,0,4" />
+                        </StackPanel>
+                    </StackPanel>
+                </Expander>
+
+                <!-- Redundancy Info -->
+                <StackPanel Orientation="Horizontal"
+                            Spacing="16"
+                            IsVisible="{Binding RedundancyInfo, Converter={x:Static ObjectConverters.IsNotNull}}"
+                            Margin="0,2,0,0">
+                    <TextBlock Text="{Binding RedundancyInfo.Mode, StringFormat='Redundancy: {0}'}"
+                               FontSize="11" Foreground="Gray" />
+                    <TextBlock Text="{Binding RedundancyInfo.ServiceLevel, StringFormat='Service Level: {0}'}"
+                               FontSize="11" Foreground="Gray" />
+                    <TextBlock Text="{Binding RedundancyInfo.ApplicationUri, StringFormat='URI: {0}'}"
+                               FontSize="11" Foreground="Gray" />
+                </StackPanel>
+            </StackPanel>
+        </Border>
+
+        <!-- Bottom Status Bar -->
+        <Border DockPanel.Dock="Bottom" Background="#F0F0F0" Padding="8,4">
+            <StackPanel Orientation="Horizontal" Spacing="20">
+                <TextBlock Text="{Binding StatusMessage}" />
+                <TextBlock Text="{Binding SessionLabel}" Foreground="Gray" />
+                <TextBlock Text="{Binding SubscriptionCount, StringFormat='Subscriptions: {0}'}" />
+            </StackPanel>
+        </Border>
+
+        <!-- Main Content -->
+        <Grid ColumnDefinitions="300,8,*">
+            <!-- Left: Browse Tree -->
+            <Border Grid.Column="0" BorderBrush="#CCCCCC" BorderThickness="0,0,1,0">
+                <DockPanel>
+                    <TextBlock DockPanel.Dock="Top" Text="Browse Tree" FontWeight="Bold" Margin="8,8,8,4" />
+                    <views:BrowseTreeView DataContext="{Binding BrowseTree}"
+                                          Name="BrowseTreePanel">
+                        <views:BrowseTreeView.ContextMenu>
+                            <ContextMenu Name="TreeContextMenu">
+                                <MenuItem Header="Subscribe" Name="SubscribeMenuItem" />
+                                <MenuItem Header="View History" Name="ViewHistoryMenuItem" />
+                                <Separator />
+                                <MenuItem Header="Monitor Alarms" Name="MonitorAlarmsMenuItem" />
+                            </ContextMenu>
+                        </views:BrowseTreeView.ContextMenu>
+                    </views:BrowseTreeView>
+                </DockPanel>
+            </Border>
+
+            <!-- Splitter -->
+            <GridSplitter Grid.Column="1" Width="8" Background="Transparent" />
+
+            <!-- Right: Tab panels -->
+            <TabControl Grid.Column="2"
+                        IsEnabled="{Binding IsConnected}"
+                        SelectedIndex="{Binding SelectedTabIndex}">
+                <TabItem Header="Read/Write">
+                    <views:ReadWriteView DataContext="{Binding ReadWrite}" />
+                </TabItem>
+                <TabItem Header="{Binding SubscriptionsTabHeader}">
+                    <views:SubscriptionsView DataContext="{Binding Subscriptions}" />
+                </TabItem>
+                <TabItem Header="{Binding AlarmsTabHeader}">
+                    <views:AlarmsView DataContext="{Binding Alarms}" />
+                </TabItem>
+                <TabItem Header="History">
+                    <views:HistoryView DataContext="{Binding History}" />
+                </TabItem>
+            </TabControl>
+        </Grid>
+    </DockPanel>
+</Window>

src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/MainWindow.axaml.cs

@@ -0,0 +1,146 @@
+using System.ComponentModel;
+using System.Reflection;
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using SkiaSharp;
+using Svg.Skia;
+using ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+public partial class MainWindow : Window
+{
+    public MainWindow()
+    {
+        InitializeComponent();
+        LoadIcon();
+    }
+
+    private void LoadIcon()
+    {
+        try
+        {
+            var assembly = Assembly.GetExecutingAssembly();
+            using var stream = assembly.GetManifestResourceStream("ZB.MOM.WW.OtOpcUa.Client.UI.Assets.app-icon.svg");
+            if (stream == null) return;
+
+            using var svg = new SKSvg();
+            svg.Load(stream);
+            if (svg.Picture == null) return;
+
+            var size = 64;
+            using var bitmap = new SKBitmap(size, size);
+            using var canvas = new SKCanvas(bitmap);
+            canvas.Clear(SKColors.Transparent);
+
+            var bounds = svg.Picture.CullRect;
+            var scale = Math.Min(size / bounds.Width, size / bounds.Height);
+            canvas.Translate((size - bounds.Width * scale) / 2, (size - bounds.Height * scale) / 2);
+            canvas.Scale(scale);
+            canvas.DrawPicture(svg.Picture);
+
+            using var image = SKImage.FromBitmap(bitmap);
+            using var data = image.Encode(SKEncodedImageFormat.Png, 100);
+            using var pngStream = new MemoryStream(data.ToArray());
+            Icon = new WindowIcon(pngStream);
+        }
+        catch
+        {
+            // Icon loading is best-effort
+        }
+    }
+
+    protected override void OnLoaded(RoutedEventArgs e)
+    {
+        base.OnLoaded(e);
+
+        var browseTreeView = this.FindControl<BrowseTreeView>("BrowseTreePanel");
+        var treeView = browseTreeView?.FindControl<TreeView>("BrowseTree");
+        if (treeView != null) treeView.SelectionChanged += OnTreeSelectionChanged;
+
+        var contextMenu = this.FindControl<ContextMenu>("TreeContextMenu");
+        if (contextMenu != null) contextMenu.Opening += OnTreeContextMenuOpening;
+
+        var subscribeItem = this.FindControl<MenuItem>("SubscribeMenuItem");
+        if (subscribeItem != null) subscribeItem.Click += OnSubscribeClicked;
+
+        var viewHistoryItem = this.FindControl<MenuItem>("ViewHistoryMenuItem");
+        if (viewHistoryItem != null) viewHistoryItem.Click += OnViewHistoryClicked;
+
+        var monitorAlarmsItem = this.FindControl<MenuItem>("MonitorAlarmsMenuItem");
+        if (monitorAlarmsItem != null) monitorAlarmsItem.Click += OnMonitorAlarmsClicked;
+
+        var browseCertPath = this.FindControl<Button>("BrowseCertPathButton");
+        if (browseCertPath != null) browseCertPath.Click += OnBrowseCertPathClicked;
+    }
+
+    private void OnTreeSelectionChanged(object? sender, SelectionChangedEventArgs e)
+    {
+        if (DataContext is not MainWindowViewModel vm || sender is not TreeView treeView) return;
+
+        vm.SelectedTreeNode = treeView.SelectedItem as TreeNodeViewModel;
+
+        vm.SelectedTreeNodes.Clear();
+        foreach (var item in treeView.SelectedItems)
+            if (item is TreeNodeViewModel node)
+                vm.SelectedTreeNodes.Add(node);
+    }
+
+    private void OnTreeContextMenuOpening(object? sender, CancelEventArgs e)
+    {
+        if (DataContext is not MainWindowViewModel vm) return;
+
+        vm.UpdateHistoryEnabledForSelection();
+
+        var subscribeItem = this.FindControl<MenuItem>("SubscribeMenuItem");
+        var viewHistoryItem = this.FindControl<MenuItem>("ViewHistoryMenuItem");
+        var monitorAlarmsItem = this.FindControl<MenuItem>("MonitorAlarmsMenuItem");
+
+        if (subscribeItem != null)
+            subscribeItem.IsEnabled = vm.IsConnected && vm.SelectedTreeNodes.Count > 0;
+        if (viewHistoryItem != null)
+            viewHistoryItem.IsEnabled = vm.IsHistoryEnabledForSelection;
+        if (monitorAlarmsItem != null)
+            monitorAlarmsItem.IsEnabled = vm.IsConnected && vm.SelectedTreeNodes.Count > 0;
+    }
+
+    private async void OnSubscribeClicked(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is MainWindowViewModel vm)
+            await vm.SubscribeSelectedNodesCommand.ExecuteAsync(null);
+    }
+
+    private void OnViewHistoryClicked(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is MainWindowViewModel vm)
+            vm.ViewHistoryForSelectedNodeCommand.Execute(null);
+    }
+
+    private async void OnMonitorAlarmsClicked(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is MainWindowViewModel vm)
+            await vm.MonitorAlarmsForSelectedNodeCommand.ExecuteAsync(null);
+    }
+
+    private async void OnBrowseCertPathClicked(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is not MainWindowViewModel vm) return;
+
+        var dialog = new OpenFolderDialog
+        {
+            Title = "Select Certificate Store Folder",
+            Directory = vm.CertificateStorePath
+        };
+
+        var result = await dialog.ShowAsync(this);
+        if (!string.IsNullOrEmpty(result))
+            vm.CertificateStorePath = result;
+    }
+
+    protected override void OnClosing(WindowClosingEventArgs e)
+    {
+        if (DataContext is MainWindowViewModel vm)
+            vm.SaveSettings();
+        base.OnClosing(e);
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/ReadWriteView.axaml

@@ -0,0 +1,39 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels"
+             x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Views.ReadWriteView"
+             x:DataType="vm:ReadWriteViewModel">
+    <StackPanel Spacing="8" Margin="8">
+        <!-- Selected Node -->
+        <TextBlock Text="Selected Node" FontWeight="Bold" />
+        <TextBlock Text="{Binding SelectedNodeId, FallbackValue='(none)'}"
+                   Foreground="Gray" />
+
+        <!-- Read Section -->
+        <Separator />
+        <TextBlock Text="Read Value" FontWeight="Bold" />
+        <Button Content="Read" Command="{Binding ReadCommand}" />
+        <Grid ColumnDefinitions="Auto,*" RowDefinitions="Auto,Auto,Auto,Auto" Margin="0,4,0,0">
+            <TextBlock Grid.Row="0" Grid.Column="0" Text="Value: " FontWeight="SemiBold" />
+            <TextBlock Grid.Row="0" Grid.Column="1" Text="{Binding CurrentValue}" TextWrapping="Wrap" />
+
+            <TextBlock Grid.Row="1" Grid.Column="0" Text="Status: " FontWeight="SemiBold" />
+            <TextBlock Grid.Row="1" Grid.Column="1" Text="{Binding CurrentStatus}" />
+
+            <TextBlock Grid.Row="2" Grid.Column="0" Text="Source Time: " FontWeight="SemiBold" />
+            <TextBlock Grid.Row="2" Grid.Column="1" Text="{Binding SourceTimestamp}" />
+
+            <TextBlock Grid.Row="3" Grid.Column="0" Text="Server Time: " FontWeight="SemiBold" />
+            <TextBlock Grid.Row="3" Grid.Column="1" Text="{Binding ServerTimestamp}" />
+        </Grid>
+
+        <!-- Write Section -->
+        <Separator />
+        <TextBlock Text="Write Value" FontWeight="Bold" />
+        <StackPanel Orientation="Horizontal" Spacing="8">
+            <TextBox Text="{Binding WriteValue}" Width="200" Watermark="Value to write" />
+            <Button Content="Write" Command="{Binding WriteCommand}" />
+        </StackPanel>
+        <TextBlock Text="{Binding WriteStatus}" Foreground="Gray" />
+    </StackPanel>
+</UserControl>

src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/ReadWriteView.axaml.cs

@@ -0,0 +1,11 @@
+using Avalonia.Controls;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+public partial class ReadWriteView : UserControl
+{
+    public ReadWriteView()
+    {
+        InitializeComponent();
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/SubscriptionsView.axaml

@@ -0,0 +1,35 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels"
+             x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Views.SubscriptionsView"
+             x:DataType="vm:SubscriptionsViewModel">
+    <DockPanel Margin="8">
+        <!-- Add/Remove Controls -->
+        <StackPanel DockPanel.Dock="Top" Spacing="8">
+            <TextBlock Text="Subscriptions" FontWeight="Bold" />
+            <StackPanel Orientation="Horizontal" Spacing="8">
+                <TextBox Text="{Binding NewNodeIdText}" Width="250" Watermark="Node ID (e.g., ns=2;s=MyNode)" />
+                <NumericUpDown Value="{Binding NewInterval}" Minimum="100" Maximum="60000" Width="120" />
+                <Button Content="Add" Command="{Binding AddSubscriptionCommand}" />
+                <Button Content="Remove" Command="{Binding RemoveSubscriptionCommand}" />
+            </StackPanel>
+        </StackPanel>
+
+        <!-- Active Subscriptions List -->
+        <DataGrid Name="SubscriptionsGrid"
+                  ItemsSource="{Binding ActiveSubscriptions}"
+                  SelectedItem="{Binding SelectedSubscription}"
+                  SelectionMode="Extended"
+                  AutoGenerateColumns="False"
+                  IsReadOnly="True"
+                  HorizontalScrollBarVisibility="Auto"
+                  Margin="0,8,0,0">
+            <DataGrid.Columns>
+                <DataGridTextColumn Header="Node ID" Binding="{Binding NodeId}" Width="Auto" />
+                <DataGridTextColumn Header="Value" Binding="{Binding Value}" Width="Auto" />
+                <DataGridTextColumn Header="Status" Binding="{Binding Status}" Width="Auto" />
+                <DataGridTextColumn Header="Timestamp" Binding="{Binding Timestamp}" Width="Auto" />
+            </DataGrid.Columns>
+        </DataGrid>
+    </DockPanel>
+</UserControl>

src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/SubscriptionsView.axaml.cs

@@ -0,0 +1,51 @@
+using Avalonia.Controls;
+using Avalonia.Input;
+using Avalonia.Interactivity;
+using Avalonia.VisualTree;
+using ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+public partial class SubscriptionsView : UserControl
+{
+    public SubscriptionsView()
+    {
+        InitializeComponent();
+    }
+
+    protected override void OnLoaded(RoutedEventArgs e)
+    {
+        base.OnLoaded(e);
+
+        var grid = this.FindControl<DataGrid>("SubscriptionsGrid");
+        if (grid != null)
+        {
+            grid.DoubleTapped += OnGridDoubleTapped;
+            grid.SelectionChanged += OnGridSelectionChanged;
+        }
+    }
+
+    private void OnGridSelectionChanged(object? sender, SelectionChangedEventArgs e)
+    {
+        if (DataContext is not SubscriptionsViewModel vm || sender is not DataGrid grid) return;
+
+        vm.SelectedSubscriptions.Clear();
+        foreach (var item in grid.SelectedItems)
+            if (item is SubscriptionItemViewModel sub)
+                vm.SelectedSubscriptions.Add(sub);
+
+        vm.RemoveSubscriptionCommand.NotifyCanExecuteChanged();
+    }
+
+    private void OnGridDoubleTapped(object? sender, TappedEventArgs e)
+    {
+        if (DataContext is not SubscriptionsViewModel vm) return;
+        if (vm.SelectedSubscription is not { } item) return;
+
+        var parentWindow = this.FindAncestorOfType<Window>();
+        if (parentWindow == null) return;
+
+        var writeWindow = new WriteValueWindow(vm, item.NodeId, item.Value);
+        writeWindow.ShowDialog(parentWindow);
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/WriteValueWindow.axaml

@@ -0,0 +1,37 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        x:Class="ZB.MOM.WW.OtOpcUa.Client.UI.Views.WriteValueWindow"
+        Title="Write Value"
+        Width="420"
+        SizeToContent="Height"
+        MinHeight="280"
+        WindowStartupLocation="CenterOwner"
+        CanResize="False">
+    <StackPanel Margin="16" Spacing="12">
+        <TextBlock Text="Write Value to Node" FontWeight="Bold" FontSize="16" />
+
+        <StackPanel Spacing="4">
+            <TextBlock Text="Node ID:" FontSize="12" Foreground="Gray" />
+            <TextBlock Name="NodeIdText" FontWeight="SemiBold" />
+        </StackPanel>
+
+        <StackPanel Spacing="4">
+            <TextBlock Text="Current Value:" FontSize="12" Foreground="Gray" />
+            <TextBlock Name="CurrentValueText" />
+        </StackPanel>
+
+        <StackPanel Spacing="4">
+            <TextBlock Text="New Value:" FontSize="12" Foreground="Gray" />
+            <TextBox Name="WriteValueInput" Watermark="Enter value to write" />
+        </StackPanel>
+
+        <StackPanel Spacing="4">
+            <TextBlock Name="ResultText" Foreground="Gray" />
+        </StackPanel>
+
+        <StackPanel Orientation="Horizontal" Spacing="8" HorizontalAlignment="Right">
+            <Button Name="WriteButton" Content="Write" />
+            <Button Name="CloseButton" Content="Close" />
+        </StackPanel>
+    </StackPanel>
+</Window>

src/ZB.MOM.WW.OtOpcUa.Client.UI/Views/WriteValueWindow.axaml.cs

@@ -0,0 +1,77 @@
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Media;
+using ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.UI.Views;
+
+public partial class WriteValueWindow : Window
+{
+    private readonly SubscriptionsViewModel _subscriptionsVm;
+    private readonly string _nodeId;
+
+    public WriteValueWindow()
+    {
+        InitializeComponent();
+        _subscriptionsVm = null!;
+        _nodeId = string.Empty;
+    }
+
+    public WriteValueWindow(SubscriptionsViewModel subscriptionsVm, string nodeId, string? currentValue)
+    {
+        InitializeComponent();
+        _subscriptionsVm = subscriptionsVm;
+        _nodeId = nodeId;
+
+        var nodeIdText = this.FindControl<TextBlock>("NodeIdText");
+        if (nodeIdText != null) nodeIdText.Text = nodeId;
+
+        var currentValueText = this.FindControl<TextBlock>("CurrentValueText");
+        if (currentValueText != null) currentValueText.Text = currentValue ?? "(null)";
+
+        // Pre-fill the write input with the current value
+        var writeInput = this.FindControl<TextBox>("WriteValueInput");
+        if (writeInput != null) writeInput.Text = currentValue ?? "";
+
+        var writeButton = this.FindControl<Button>("WriteButton");
+        if (writeButton != null) writeButton.Click += OnWriteClicked;
+
+        var closeButton = this.FindControl<Button>("CloseButton");
+        if (closeButton != null) closeButton.Click += OnCloseClicked;
+    }
+
+    private async void OnWriteClicked(object? sender, RoutedEventArgs e)
+    {
+        var input = this.FindControl<TextBox>("WriteValueInput");
+        var resultText = this.FindControl<TextBlock>("ResultText");
+        if (input == null || resultText == null) return;
+
+        var rawValue = input.Text;
+        if (string.IsNullOrEmpty(rawValue))
+        {
+            resultText.Foreground = Brushes.Red;
+            resultText.Text = "Please enter a value.";
+            return;
+        }
+
+        resultText.Foreground = Brushes.Gray;
+        resultText.Text = "Writing...";
+
+        var (success, message) = await _subscriptionsVm.ValidateAndWriteAsync(_nodeId, rawValue);
+
+        if (success)
+        {
+            Close();
+        }
+        else
+        {
+            resultText.Foreground = Brushes.Red;
+            resultText.Text = message;
+        }
+    }
+
+    private void OnCloseClicked(object? sender, RoutedEventArgs e)
+    {
+        Close();
+    }
+}