Merge branch 'v0.3.1-theming' into v0.4-opcua

Trailing DataGridTemplateColumn had Width="Auto"; against the 2* star columns
it collapsed on first layout, clipping the Details button to a sliver. Pin to
Width="120" so the button always fits.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.paul/ROADMAP.md

@@ -6,9 +6,9 @@
 |---------|------|--------|--------|-----------|
 | v0.1 | Walking Skeleton (MTConnect) | 1 | ✅ Shipped | 2026-07-21 |
 | v0.2 | Machine Management UX | 2, 2.1 | ✅ Shipped (2.1 commit pending) | 2026-07-21 |
-| v0.3 | Data-Item Selection + UX | 3, 3.1 | 🚧 Phase 3 done, 3.1 (theming) next | - |
-| v0.4 | OPC UA Protocol | 4 | 📋 Planned | - |
-| v0.5 | Fanuc FOCAS Protocol | 5 | 📋 Planned | - |
+| v0.3 | Data-Item Selection + UX | 3, 3.1 | ✅ Shipped (branch v0.3.1-theming) | 2026-07-22 |
+| v0.4 | OPC UA Protocol | 4 | 🚧 In progress (branch v0.4-opcua) | - |
+| v0.5 | Fanuc FOCAS Protocol | 5 | ⏸️ Deferred (no native/Windows on dev host) | - |
 | v0.6 | History & Trends | 6 | 📋 Planned | - |
 
 ## 🚧 Active Milestone: v0.2 Machine Management UX

.paul/STATE.md

@@ -5,18 +5,24 @@
 See: .paul/PROJECT.md (updated 2026-07-21)
 
 **Core value:** Operators see live state of every configured machine across heterogeneous protocols in one place, adding machines/protocols without code.
-**Current focus:** v0.3 Phase 3 (item selection) shipped → PAUSED. Next: Phase 3.1 theming/UX.
+**Current focus:** Autonomous finish run — branch-per-milestone. v0.3.1 theming SHIPPED. Now v0.4 OPC UA.
 
 ## Current Position
 
-Milestone: v0.3 Data-Item Selection + UX
-Phase: 3 (item selection) ✓ SHIPPED — Phase 3.1 (theming/UX) NOT started
-Plan: v0.3-backend ✓, v0.3-appui ✓
-Status: PAUSED (user requested). Build 0/0, 138 tests + 2 docker-skip.
-Last activity: 2026-07-22 — v0.3 item selection: Machine.MonitoredItemIds (opt-in), IProtocolDriver.ProbeAsync, MTConnect probe+filter, Persistence col+migration, monitor.ProbeAsync, config probe→checklist UI (47 items live), detail empty-state.
+Milestone: v0.4 OPC UA Protocol
+Phase: 4 — IN PROGRESS (branch v0.4-opcua, from v0.3.1-theming)
+Status: Build 0/0, 148 tests + 2 docker-skip (after v0.3.1).
+Last activity: 2026-07-22 — v0.3.1 theming shipped on branch v0.3.1-theming (Fluent light/dark, per-protocol icons, curated layout, +10 converter tests). SDK decided for v0.4: OPCFoundation.NetStandard.Opc.Ua.Client 1.5.378.156 (MIT), plugin retargets net48, IUaClient seam for testability.
 
 Progress:
-- v0.3: Phase 3 done, Phase 3.1 (theming) pending
+- v0.3.1 theming ✓ (branch pushed)
+- v0.4 OPC UA: impl starting
+- v0.5 FOCAS: DEFERRED (no native fwlib32/Windows on Linux dev host)
+
+## Branch-per-milestone (user directive 2026-07-22)
+
+Chain, each branch from previous; user merges one at a time; push branches to origin, NO auto-merge to main:
+v0.3.1-theming (from main) ✓ → v0.4-opcua → v0.6-history (skips deferred v0.5).
 
 ## Loop Position
 

Junction.sln

@@ -19,6 +19,8 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "tests", "tests", "{362A84DF
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Junction.Tests", "tests\Junction.Tests\Junction.Tests.csproj", "{618E6634-A16C-4806-836A-185ECDEE7312}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Junction.Protocols.OpcUa", "src\Junction.Protocols.OpcUa\Junction.Protocols.OpcUa.csproj", "{93FC27CB-C147-4BE6-8E86-F46192B72099}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -52,6 +54,10 @@ Global
 		{618E6634-A16C-4806-836A-185ECDEE7312}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{618E6634-A16C-4806-836A-185ECDEE7312}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{618E6634-A16C-4806-836A-185ECDEE7312}.Release|Any CPU.Build.0 = Release|Any CPU
+		{93FC27CB-C147-4BE6-8E86-F46192B72099}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{93FC27CB-C147-4BE6-8E86-F46192B72099}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{93FC27CB-C147-4BE6-8E86-F46192B72099}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{93FC27CB-C147-4BE6-8E86-F46192B72099}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(NestedProjects) = preSolution
 		{EE2D0A1D-3135-4065-A9EF-AB99F4FCC062} = {6DDDE464-201D-4B4F-A23E-566B5FC111BC}
@@ -60,5 +66,6 @@ Global
 		{BBAD50B2-18B5-4F4B-B8E3-CE749DB46C83} = {6DDDE464-201D-4B4F-A23E-566B5FC111BC}
 		{965918A3-4C29-4F6A-B53D-0A72BDF4376C} = {6DDDE464-201D-4B4F-A23E-566B5FC111BC}
 		{618E6634-A16C-4806-836A-185ECDEE7312} = {362A84DF-21D2-4DA7-B8B5-8C5E3C6E8500}
+		{93FC27CB-C147-4BE6-8E86-F46192B72099} = {6DDDE464-201D-4B4F-A23E-566B5FC111BC}
 	EndGlobalSection
 EndGlobal

src/Junction.App/App.axaml

@@ -2,15 +2,113 @@
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:local="clr-namespace:Junction.App"
              xmlns:conv="clr-namespace:Junction.App.Converters"
-             x:Class="Junction.App.App">
+             x:Class="Junction.App.App"
+             RequestedThemeVariant="Default">
+    <!-- RequestedThemeVariant="Default" = follow the OS light/dark preference. -->
+
     <Application.Resources>
-        <conv:StatusKindToBrushConverter x:Key="StatusKindToBrush" />
+        <ResourceDictionary>
+            <!-- Per-variant palette. Fluent supplies the base chrome; these are Junction's
+                 accent + surface + status tokens, adapted for Light and Dark. -->
+            <ResourceDictionary.ThemeDictionaries>
+                <ResourceDictionary x:Key="Light">
+                    <SolidColorBrush x:Key="AccentBrush" Color="#2563EB" />
+                    <SolidColorBrush x:Key="AccentHoverBrush" Color="#1D4FD7" />
+                    <SolidColorBrush x:Key="AppBackgroundBrush" Color="#F4F6F9" />
+                    <SolidColorBrush x:Key="CardBackgroundBrush" Color="#FFFFFF" />
+                    <SolidColorBrush x:Key="CardBorderBrush" Color="#E2E6EC" />
+                    <SolidColorBrush x:Key="HeaderForegroundBrush" Color="#161A1F" />
+                    <SolidColorBrush x:Key="SubtleForegroundBrush" Color="#697586" />
+                    <SolidColorBrush x:Key="DangerBrush" Color="#C62828" />
+                    <SolidColorBrush x:Key="OnAccentBrush" Color="#FFFFFF" />
+                </ResourceDictionary>
+                <ResourceDictionary x:Key="Dark">
+                    <SolidColorBrush x:Key="AccentBrush" Color="#4C8DF6" />
+                    <SolidColorBrush x:Key="AccentHoverBrush" Color="#6BA1F8" />
+                    <SolidColorBrush x:Key="AppBackgroundBrush" Color="#1B1E23" />
+                    <SolidColorBrush x:Key="CardBackgroundBrush" Color="#24282E" />
+                    <SolidColorBrush x:Key="CardBorderBrush" Color="#3A3F46" />
+                    <SolidColorBrush x:Key="HeaderForegroundBrush" Color="#F2F4F7" />
+                    <SolidColorBrush x:Key="SubtleForegroundBrush" Color="#9AA3AF" />
+                    <SolidColorBrush x:Key="DangerBrush" Color="#EF5350" />
+                    <SolidColorBrush x:Key="OnAccentBrush" Color="#FFFFFF" />
+                </ResourceDictionary>
+            </ResourceDictionary.ThemeDictionaries>
+
+            <!-- Spacing scale (variant-invariant). -->
+            <Thickness x:Key="PageMargin">20</Thickness>
+
+            <!-- Variant-invariant converters. -->
+            <conv:StatusKindToBrushConverter x:Key="StatusKindToBrush" />
+            <conv:ProtocolIdToIconConverter x:Key="ProtocolIdToIcon" />
+        </ResourceDictionary>
     </Application.Resources>
+
     <Application.DataTemplates>
         <local:ViewLocator />
     </Application.DataTemplates>
+
     <Application.Styles>
         <FluentTheme />
         <StyleInclude Source="avares://Avalonia.Controls.DataGrid/Themes/Fluent.xaml" />
+
+        <!-- Inter (bundled via WithInterFont) as the shell default for a consistent, crisp face. -->
+        <Style Selector="Window">
+            <Setter Property="FontFamily" Value="avares://Avalonia.Fonts.Inter/Assets#Inter" />
+            <Setter Property="Background" Value="{DynamicResource AppBackgroundBrush}" />
+        </Style>
+
+        <!-- Reusable text roles. -->
+        <Style Selector="TextBlock.h1">
+            <Setter Property="FontSize" Value="22" />
+            <Setter Property="FontWeight" Value="SemiBold" />
+            <Setter Property="Foreground" Value="{DynamicResource HeaderForegroundBrush}" />
+        </Style>
+        <Style Selector="TextBlock.h2">
+            <Setter Property="FontSize" Value="16" />
+            <Setter Property="FontWeight" Value="SemiBold" />
+            <Setter Property="Foreground" Value="{DynamicResource HeaderForegroundBrush}" />
+        </Style>
+        <Style Selector="TextBlock.subtle">
+            <Setter Property="Foreground" Value="{DynamicResource SubtleForegroundBrush}" />
+        </Style>
+        <Style Selector="TextBlock.fieldLabel">
+            <Setter Property="FontWeight" Value="SemiBold" />
+            <Setter Property="Foreground" Value="{DynamicResource SubtleForegroundBrush}" />
+        </Style>
+
+        <!-- Card / section container. -->
+        <Style Selector="Border.card">
+            <Setter Property="Background" Value="{DynamicResource CardBackgroundBrush}" />
+            <Setter Property="BorderBrush" Value="{DynamicResource CardBorderBrush}" />
+            <Setter Property="BorderThickness" Value="1" />
+            <Setter Property="CornerRadius" Value="6" />
+            <Setter Property="Padding" Value="16" />
+        </Style>
+
+        <!-- Primary (accent) button. -->
+        <Style Selector="Button.accent">
+            <Setter Property="Background" Value="{DynamicResource AccentBrush}" />
+            <Setter Property="Foreground" Value="{DynamicResource OnAccentBrush}" />
+            <Setter Property="FontWeight" Value="SemiBold" />
+        </Style>
+        <Style Selector="Button.accent:pointerover /template/ ContentPresenter">
+            <Setter Property="Background" Value="{DynamicResource AccentHoverBrush}" />
+            <Setter Property="Foreground" Value="{DynamicResource OnAccentBrush}" />
+        </Style>
+
+        <!-- Destructive button. -->
+        <Style Selector="Button.danger">
+            <Setter Property="Background" Value="{DynamicResource DangerBrush}" />
+            <Setter Property="Foreground" Value="#FFFFFF" />
+            <Setter Property="FontWeight" Value="SemiBold" />
+        </Style>
+
+        <!-- Protocol glyph. -->
+        <Style Selector="PathIcon.protocol">
+            <Setter Property="Width" Value="16" />
+            <Setter Property="Height" Value="16" />
+            <Setter Property="Foreground" Value="{DynamicResource AccentBrush}" />
+        </Style>
     </Application.Styles>
 </Application>

src/Junction.App/Converters/ProtocolIdToIconConverter.cs

@@ -0,0 +1,75 @@
+using System;
+using System.Globalization;
+using Avalonia.Data.Converters;
+using Avalonia.Media;
+
+namespace Junction.App.Converters
+{
+    /// <summary>
+    /// Maps a machine's <c>ProtocolId</c> ("mtconnect", future "opcua"/"fanuc", …) to a vector
+    /// glyph (<see cref="Geometry"/>) for a <c>PathIcon</c>. Keeps view-models framework-agnostic:
+    /// the icon decision lives entirely in the view layer, mirroring
+    /// <see cref="StatusKindToBrushConverter"/>. Unknown/empty ids fall back to a generic glyph.
+    /// <para>Glyphs are line-only 24×24 path data (no arcs/curves) so they always parse and read
+    /// as distinct filled shapes. No external image assets — net48 packaging stays a single exe set.</para>
+    /// </summary>
+    public sealed class ProtocolIdToIconConverter : IValueConverter
+    {
+        public static readonly ProtocolIdToIconConverter Instance = new ProtocolIdToIconConverter();
+
+        // Signal-strength bars — a live telemetry feed.
+        private const string MtconnectData = "M4,14 H7 V20 H4 Z M10,10 H13 V20 H10 Z M16,5 H19 V20 H16 Z";
+
+        // Stacked diamonds — the OPC UA layered address space.
+        private const string OpcuaData = "M12,2 L20,7 L12,12 L4,7 Z M12,13 L20,18 L12,23 L4,18 Z";
+
+        // Plus/cross — an industrial CNC controller marker.
+        private const string FanucData = "M10,3 H14 V10 H21 V14 H14 V21 H10 V14 H3 V10 H10 Z";
+
+        // Octagon node — generic / unknown protocol.
+        private const string FallbackData = "M8,4 H16 L20,8 V16 L16,20 H8 L4,16 V8 Z";
+
+        private static Geometry? _mtconnect;
+        private static Geometry? _opcua;
+        private static Geometry? _fanuc;
+        private static Geometry? _fallback;
+
+        /// <summary>
+        /// Pure lookup of the raw path-data string for a protocol id. View-framework-free and
+        /// side-effect-free so it is unit-testable without an Avalonia platform. Known ids return a
+        /// distinct non-empty string; anything else returns the generic fallback. Never throws.
+        /// </summary>
+        public static string PathDataFor(string? protocolId)
+        {
+            switch (protocolId == null ? null : protocolId.Trim().ToLowerInvariant())
+            {
+                case "mtconnect":
+                    return MtconnectData;
+                case "opcua":
+                    return OpcuaData;
+                case "fanuc":
+                    return FanucData;
+                default:
+                    return FallbackData;
+            }
+        }
+
+        public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+        {
+            switch (PathDataFor(value as string))
+            {
+                case MtconnectData:
+                    return _mtconnect ?? (_mtconnect = Geometry.Parse(MtconnectData));
+                case OpcuaData:
+                    return _opcua ?? (_opcua = Geometry.Parse(OpcuaData));
+                case FanucData:
+                    return _fanuc ?? (_fanuc = Geometry.Parse(FanucData));
+                default:
+                    return _fallback ?? (_fallback = Geometry.Parse(FallbackData));
+            }
+        }
+
+        public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+            => throw new NotSupportedException();
+    }
+}

src/Junction.App/Junction.App.csproj

@@ -7,6 +7,8 @@
     <OutputType>WinExe</OutputType>
     <RootNamespace>Junction.App</RootNamespace>
     <AvaloniaUseCompiledBindingsByDefault>true</AvaloniaUseCompiledBindingsByDefault>
+    <!-- net48 needs binding redirects for the M.E.Logging/System.* shims the OPC UA SDK drags in. -->
+    <AutoGenerateBindingRedirects>true</AutoGenerateBindingRedirects>
   </PropertyGroup>
 
   <!-- Avalonia 11.3.x supports net48; Avalonia 12 DROPS net48. PIN 11.3.10 exact everywhere. -->
@@ -42,6 +44,8 @@
     <!-- Plugin = RUNTIME artifact, NOT a compile reference. Build-order-only so we can copy its output. -->
     <ProjectReference Include="..\Junction.Protocols.MTConnect\Junction.Protocols.MTConnect.csproj"
                       ReferenceOutputAssembly="false" Private="false" />
+    <ProjectReference Include="..\Junction.Protocols.OpcUa\Junction.Protocols.OpcUa.csproj"
+                      ReferenceOutputAssembly="false" Private="false" />
   </ItemGroup>
 
   <!-- Copy MTConnect plugin (dll + manifest) into OutDir/plugins/mtconnect/ after build. -->
@@ -53,4 +57,15 @@
     <Copy SourceFiles="@(MtconnectPluginFiles)" DestinationFolder="$(OutDir)plugins\mtconnect\" SkipUnchangedFiles="true" />
   </Target>
 
+  <!-- Copy OPC UA plugin (its dll + FULL transitive SDK closure + manifest) into OutDir/plugins/opcua/
+       after build. Host $(TargetFramework) is net48 or net8.0; the plugin multi-targets the same TFMs,
+       so copy the matching per-TFM output. -->
+  <Target Name="CopyOpcuaPlugin" AfterTargets="Build" Condition="'$(TargetFramework)' != ''">
+    <ItemGroup>
+      <OpcuaPluginFiles Include="$(MSBuildThisFileDirectory)..\Junction.Protocols.OpcUa\bin\$(Configuration)\$(TargetFramework)\*.dll" />
+      <OpcuaPluginFiles Include="$(MSBuildThisFileDirectory)..\Junction.Protocols.OpcUa\bin\$(Configuration)\$(TargetFramework)\plugin.manifest.json" />
+    </ItemGroup>
+    <Copy SourceFiles="@(OpcuaPluginFiles)" DestinationFolder="$(OutDir)plugins\opcua\" SkipUnchangedFiles="true" />
+  </Target>
+
 </Project>

src/Junction.App/MainWindow.axaml

@@ -5,7 +5,8 @@
         x:DataType="vm:MainWindowViewModel"
         x:CompileBindings="True"
         Title="Junction"
-        Width="800" Height="600">
+        Width="900" Height="640"
+        Background="{DynamicResource AppBackgroundBrush}">
     <!-- Shell: hosts the current page; ViewLocator maps the VM to its View. -->
     <ContentControl Content="{Binding CurrentPage}" />
 </Window>

src/Junction.App/Views/DashboardView.axaml

@@ -8,66 +8,82 @@
              x:DataType="vm:DashboardViewModel"
              x:CompileBindings="True">
 
-  <DockPanel Margin="16">
-    <Grid DockPanel.Dock="Top" ColumnDefinitions="*,Auto" Margin="0,0,0,12">
+  <DockPanel Margin="20">
+    <Grid DockPanel.Dock="Top" ColumnDefinitions="*,Auto" Margin="0,0,0,16">
       <TextBlock Grid.Column="0"
+                 Classes="h1"
                  Text="{Binding Title}"
-                 FontSize="22" FontWeight="SemiBold"
                  VerticalAlignment="Center" />
       <Button Grid.Column="1"
+              Classes="accent"
               Content="+ Add machine"
               Command="{Binding AddMachineCommand}"
               VerticalAlignment="Center" />
     </Grid>
 
-    <DataGrid ItemsSource="{Binding Machines}"
-              AutoGenerateColumns="False"
-              IsReadOnly="True"
-              CanUserReorderColumns="False"
-              CanUserResizeColumns="True"
-              GridLinesVisibility="Horizontal"
-              HeadersVisibility="Column">
-      <DataGrid.Columns>
-        <DataGridTextColumn Header="Machine"
-                            Binding="{Binding Name}"
-                            Width="2*"
-                            x:DataType="vm:MachineRowViewModel" />
+    <Border Classes="card" Padding="0">
+      <DataGrid ItemsSource="{Binding Machines}"
+                AutoGenerateColumns="False"
+                IsReadOnly="True"
+                CanUserReorderColumns="False"
+                CanUserResizeColumns="True"
+                GridLinesVisibility="Horizontal"
+                HeadersVisibility="Column"
+                Background="Transparent">
+        <DataGrid.Columns>
+          <DataGridTemplateColumn Header="Machine" Width="2*">
+            <DataGridTemplateColumn.CellTemplate>
+              <DataTemplate x:DataType="vm:MachineRowViewModel">
+                <StackPanel Orientation="Horizontal" Spacing="10"
+                            VerticalAlignment="Center" Margin="12,0">
+                  <PathIcon Classes="protocol"
+                            Data="{Binding ProtocolId, Converter={StaticResource ProtocolIdToIcon}}"
+                            ToolTip.Tip="{Binding ProtocolId}"
+                            VerticalAlignment="Center" />
+                  <TextBlock Text="{Binding Name}" FontWeight="SemiBold" VerticalAlignment="Center" />
+                </StackPanel>
+              </DataTemplate>
+            </DataGridTemplateColumn.CellTemplate>
+          </DataGridTemplateColumn>
 
-        <DataGridTemplateColumn Header="Status" Width="Auto">
-          <DataGridTemplateColumn.CellTemplate>
-            <DataTemplate x:DataType="vm:MachineRowViewModel">
-              <StackPanel Orientation="Horizontal" Spacing="6"
-                          VerticalAlignment="Center" Margin="8,0">
-                <Ellipse Width="10" Height="10" VerticalAlignment="Center"
-                         Fill="{Binding StatusKind, Converter={StaticResource StatusKindToBrush}}" />
-                <TextBlock Text="{Binding ConnectionState}"
-                           Foreground="{Binding StatusKind, Converter={StaticResource StatusKindToBrush}}"
-                           FontWeight="SemiBold" VerticalAlignment="Center" />
-              </StackPanel>
-            </DataTemplate>
-          </DataGridTemplateColumn.CellTemplate>
-        </DataGridTemplateColumn>
+          <DataGridTemplateColumn Header="Status" Width="Auto">
+            <DataGridTemplateColumn.CellTemplate>
+              <DataTemplate x:DataType="vm:MachineRowViewModel">
+                <StackPanel Orientation="Horizontal" Spacing="6"
+                            VerticalAlignment="Center" Margin="12,0">
+                  <Ellipse Width="10" Height="10" VerticalAlignment="Center"
+                           Fill="{Binding StatusKind, Converter={StaticResource StatusKindToBrush}}" />
+                  <TextBlock Text="{Binding ConnectionState}"
+                             Foreground="{Binding StatusKind, Converter={StaticResource StatusKindToBrush}}"
+                             FontWeight="SemiBold" VerticalAlignment="Center" />
+                </StackPanel>
+              </DataTemplate>
+            </DataGridTemplateColumn.CellTemplate>
+          </DataGridTemplateColumn>
 
-        <DataGridTextColumn Header="Last Datum"
-                            Binding="{Binding LastDatum}"
-                            Width="2*"
-                            x:DataType="vm:MachineRowViewModel" />
+          <DataGridTextColumn Header="Last Datum"
+                              Binding="{Binding LastDatum}"
+                              Width="2*"
+                              x:DataType="vm:MachineRowViewModel" />
 
-        <DataGridTextColumn Header="Last Seen"
-                            Binding="{Binding LastSeen}"
-                            Width="Auto"
-                            x:DataType="vm:MachineRowViewModel" />
+          <DataGridTextColumn Header="Last Seen"
+                              Binding="{Binding LastSeen}"
+                              Width="Auto"
+                              x:DataType="vm:MachineRowViewModel" />
 
-        <DataGridTemplateColumn Header="" Width="Auto">
-          <DataGridTemplateColumn.CellTemplate>
-            <DataTemplate x:DataType="vm:MachineRowViewModel">
-              <Button Content="Details"
-                      Command="{Binding OpenDetailCommand}"
-                      VerticalAlignment="Center" Margin="8,2" />
-            </DataTemplate>
-          </DataGridTemplateColumn.CellTemplate>
-        </DataGridTemplateColumn>
-      </DataGrid.Columns>
-    </DataGrid>
+          <!-- Fixed width: a trailing Auto column collapses against the 2* star columns,
+               clipping the Details button to a sliver on first layout. -->
+          <DataGridTemplateColumn Header="" Width="120">
+            <DataGridTemplateColumn.CellTemplate>
+              <DataTemplate x:DataType="vm:MachineRowViewModel">
+                <Button Content="Details"
+                        Command="{Binding OpenDetailCommand}"
+                        VerticalAlignment="Center" Margin="12,4" />
+              </DataTemplate>
+            </DataGridTemplateColumn.CellTemplate>
+          </DataGridTemplateColumn>
+        </DataGrid.Columns>
+      </DataGrid>
+    </Border>
   </DockPanel>
 </UserControl>

src/Junction.App/Views/MachineConfigView.axaml

@@ -8,122 +8,128 @@
              x:DataType="vm:MachineConfigViewModel"
              x:CompileBindings="True">
 
-  <DockPanel Margin="16">
+  <!-- header / body / footer -->
+  <Grid Margin="20" RowDefinitions="Auto,*,Auto">
 
     <!-- Header -->
-    <TextBlock DockPanel.Dock="Top"
+    <TextBlock Grid.Row="0" Classes="h1"
                Text="{Binding Title}"
-               FontSize="22" FontWeight="SemiBold"
                Margin="0,0,0,16" />
 
-    <!-- Action bar -->
-    <StackPanel DockPanel.Dock="Bottom" Orientation="Horizontal" Spacing="12" Margin="0,16,0,0">
-      <Button Content="Save" Command="{Binding SaveCommand}" IsDefault="True" />
-      <Button Content="Cancel" Command="{Binding CancelCommand}" />
-    </StackPanel>
+    <!-- Body: fixed form column + stretching data-items column -->
+    <Grid Grid.Row="1" ColumnDefinitions="Auto,*">
 
-    <!-- Inline validation hint -->
-    <TextBlock DockPanel.Dock="Bottom"
-               Text="{Binding ValidationError}"
-               IsVisible="{Binding HasValidationError}"
-               Foreground="#C0392B"
-               TextWrapping="Wrap"
-               Margin="0,12,0,0" />
+      <!-- Form -->
+      <Border Grid.Column="0" Classes="card" Width="380" VerticalAlignment="Top">
+        <StackPanel Spacing="12">
 
-    <!-- Form -->
-    <StackPanel DockPanel.Dock="Top" Spacing="12" MaxWidth="480" HorizontalAlignment="Left">
+          <StackPanel Spacing="4">
+            <TextBlock Classes="fieldLabel" Text="Name" />
+            <TextBox Text="{Binding Name}" Watermark="Machine name" />
+          </StackPanel>
 
-      <StackPanel Spacing="4">
-        <TextBlock Text="Name" FontWeight="SemiBold" />
-        <TextBox Text="{Binding Name}" Watermark="Machine name" />
-      </StackPanel>
+          <StackPanel Spacing="4">
+            <TextBlock Classes="fieldLabel" Text="Protocol" />
+            <ComboBox ItemsSource="{Binding AvailableProtocols}"
+                      SelectedItem="{Binding SelectedProtocol}"
+                      HorizontalAlignment="Stretch"
+                      PlaceholderText="Select a protocol" />
+          </StackPanel>
 
-      <StackPanel Spacing="4">
-        <TextBlock Text="Protocol" FontWeight="SemiBold" />
-        <ComboBox ItemsSource="{Binding AvailableProtocols}"
-                  SelectedItem="{Binding SelectedProtocol}"
-                  HorizontalAlignment="Stretch"
-                  PlaceholderText="Select a protocol" />
-      </StackPanel>
+          <StackPanel Spacing="4">
+            <TextBlock Classes="fieldLabel" Text="Agent URL" />
+            <TextBox Text="{Binding AgentUrl}" Watermark="http://host:5000" />
+          </StackPanel>
 
-      <StackPanel Spacing="4">
-        <TextBlock Text="Agent URL" FontWeight="SemiBold" />
-        <TextBox Text="{Binding AgentUrl}" Watermark="http://host:5000" />
-      </StackPanel>
+          <StackPanel Spacing="4">
+            <TextBlock Classes="fieldLabel" Text="Poll Interval (seconds)" />
+            <TextBox Text="{Binding PollIntervalSeconds}" Width="120" HorizontalAlignment="Left" />
+          </StackPanel>
 
-      <StackPanel Spacing="4">
-        <TextBlock Text="Poll Interval (seconds)" FontWeight="SemiBold" />
-        <TextBox Text="{Binding PollIntervalSeconds}" Width="120" HorizontalAlignment="Left" />
-      </StackPanel>
-
-    </StackPanel>
-
-    <!-- Data items to monitor (fills remaining space) -->
-    <Border BorderThickness="1"
-            BorderBrush="{DynamicResource SystemControlForegroundBaseMediumLowBrush}"
-            CornerRadius="4"
-            Padding="12" Margin="0,16,0,0" MaxWidth="640" HorizontalAlignment="Left">
-      <DockPanel>
-
-        <TextBlock DockPanel.Dock="Top" Text="Data items to monitor"
-                   FontSize="16" FontWeight="SemiBold" Margin="0,0,0,8" />
-
-        <!-- Controls row -->
-        <StackPanel DockPanel.Dock="Top" Orientation="Horizontal" Spacing="8" Margin="0,0,0,8">
-          <Button Content="Load available items"
-                  Command="{Binding LoadItemsCommand}" />
-          <Button Content="Select all"
-                  Command="{Binding SelectAllCommand}" />
-          <Button Content="Select none"
-                  Command="{Binding SelectNoneCommand}" />
-          <ProgressBar IsIndeterminate="True"
-                       IsVisible="{Binding IsProbing}"
-                       Width="120" VerticalAlignment="Center" />
         </StackPanel>
+      </Border>
 
-        <!-- Status message -->
-        <TextBlock DockPanel.Dock="Top"
-                   Text="{Binding ItemsStatus}"
-                   IsVisible="{Binding HasItemsStatus}"
-                   Opacity="0.85" TextWrapping="Wrap" Margin="0,0,0,8" />
+      <!-- Data items to monitor (fills remaining width + height) -->
+      <Border Grid.Column="1" Classes="card" Margin="16,0,0,0" HorizontalAlignment="Stretch">
+        <DockPanel>
 
-        <!-- Column header -->
-        <Border DockPanel.Dock="Top"
-                BorderThickness="0,0,0,1"
-                BorderBrush="{DynamicResource SystemControlForegroundBaseMediumLowBrush}"
-                Padding="0,0,0,4" Margin="0,0,0,4">
-          <Grid ColumnDefinitions="Auto,2*,1.2*,1.2*,1*" Margin="0,0,8,0">
-            <TextBlock Grid.Column="0" Text="" Width="28" />
-            <TextBlock Grid.Column="1" Text="Name" FontWeight="Bold" />
-            <TextBlock Grid.Column="2" Text="Type" FontWeight="Bold" />
-            <TextBlock Grid.Column="3" Text="Category" FontWeight="Bold" />
-            <TextBlock Grid.Column="4" Text="Units" FontWeight="Bold" />
-          </Grid>
-        </Border>
+          <TextBlock DockPanel.Dock="Top" Classes="h2" Text="Data items to monitor"
+                     Margin="0,0,0,8" />
 
-        <!-- Scrollable checklist -->
-        <ScrollViewer MaxHeight="320">
-          <ItemsControl ItemsSource="{Binding AvailableItems}">
-            <ItemsControl.ItemTemplate>
-              <DataTemplate x:DataType="vm:SelectableDataItemViewModel">
-                <Grid ColumnDefinitions="Auto,2*,1.2*,1.2*,1*" Margin="0,3">
-                  <CheckBox Grid.Column="0" Width="28"
-                            IsChecked="{Binding IsSelected}"
-                            VerticalAlignment="Center" />
-                  <StackPanel Grid.Column="1" VerticalAlignment="Center">
-                    <TextBlock Text="{Binding Name}" FontWeight="SemiBold" TextWrapping="Wrap" />
-                    <TextBlock Text="{Binding Id}" FontSize="11" Opacity="0.6" TextWrapping="Wrap" />
-                  </StackPanel>
-                  <TextBlock Grid.Column="2" Text="{Binding Type}" VerticalAlignment="Center" TextWrapping="Wrap" />
-                  <TextBlock Grid.Column="3" Text="{Binding Category}" VerticalAlignment="Center" TextWrapping="Wrap" />
-                  <TextBlock Grid.Column="4" Text="{Binding Units}" VerticalAlignment="Center" TextWrapping="Wrap" />
-                </Grid>
-              </DataTemplate>
-            </ItemsControl.ItemTemplate>
-          </ItemsControl>
-        </ScrollViewer>
+          <!-- Controls row -->
+          <StackPanel DockPanel.Dock="Top" Orientation="Horizontal" Spacing="8" Margin="0,0,0,8">
+            <Button Content="Load available items"
+                    Command="{Binding LoadItemsCommand}" />
+            <Button Content="Select all"
+                    Command="{Binding SelectAllCommand}" />
+            <Button Content="Select none"
+                    Command="{Binding SelectNoneCommand}" />
+            <ProgressBar IsIndeterminate="True"
+                         IsVisible="{Binding IsProbing}"
+                         Width="120" VerticalAlignment="Center" />
+          </StackPanel>
 
-      </DockPanel>
-    </Border>
-  </DockPanel>
+          <!-- Status message -->
+          <TextBlock DockPanel.Dock="Top" Classes="subtle"
+                     Text="{Binding ItemsStatus}"
+                     IsVisible="{Binding HasItemsStatus}"
+                     TextWrapping="Wrap" Margin="0,0,0,8" />
+
+          <!-- Column header -->
+          <Border DockPanel.Dock="Top"
+                  BorderThickness="0,0,0,1"
+                  BorderBrush="{DynamicResource CardBorderBrush}"
+                  Padding="0,0,0,4" Margin="0,0,0,4">
+            <Grid ColumnDefinitions="Auto,2*,1.2*,1.2*,1*" Margin="0,0,8,0">
+              <TextBlock Grid.Column="0" Text="" Width="28" />
+              <TextBlock Grid.Column="1" Classes="fieldLabel" Text="Name" />
+              <TextBlock Grid.Column="2" Classes="fieldLabel" Text="Type" />
+              <TextBlock Grid.Column="3" Classes="fieldLabel" Text="Category" />
+              <TextBlock Grid.Column="4" Classes="fieldLabel" Text="Units" />
+            </Grid>
+          </Border>
+
+          <!-- Scrollable checklist (fills remaining height) -->
+          <ScrollViewer>
+            <ItemsControl ItemsSource="{Binding AvailableItems}">
+              <ItemsControl.ItemTemplate>
+                <DataTemplate x:DataType="vm:SelectableDataItemViewModel">
+                  <Grid ColumnDefinitions="Auto,2*,1.2*,1.2*,1*" Margin="0,3">
+                    <CheckBox Grid.Column="0" Width="28"
+                              IsChecked="{Binding IsSelected}"
+                              VerticalAlignment="Center" />
+                    <StackPanel Grid.Column="1" VerticalAlignment="Center">
+                      <TextBlock Text="{Binding Name}" FontWeight="SemiBold" TextWrapping="Wrap" />
+                      <TextBlock Text="{Binding Id}" Classes="subtle" FontSize="11" TextWrapping="Wrap" />
+                    </StackPanel>
+                    <TextBlock Grid.Column="2" Text="{Binding Type}" VerticalAlignment="Center" TextWrapping="Wrap" />
+                    <TextBlock Grid.Column="3" Text="{Binding Category}" VerticalAlignment="Center" TextWrapping="Wrap" />
+                    <TextBlock Grid.Column="4" Text="{Binding Units}" VerticalAlignment="Center" TextWrapping="Wrap" />
+                  </Grid>
+                </DataTemplate>
+              </ItemsControl.ItemTemplate>
+            </ItemsControl>
+          </ScrollViewer>
+
+        </DockPanel>
+      </Border>
+    </Grid>
+
+    <!-- Footer: validation hint + action bar, full width -->
+    <StackPanel Grid.Row="2" Spacing="0">
+      <!-- Inline validation hint -->
+      <TextBlock Text="{Binding ValidationError}"
+                 IsVisible="{Binding HasValidationError}"
+                 Foreground="{DynamicResource DangerBrush}"
+                 TextWrapping="Wrap"
+                 Margin="0,12,0,0" />
+
+      <!-- Action bar -->
+      <StackPanel Orientation="Horizontal" Spacing="12" Margin="0,16,0,0">
+        <Button Classes="accent" Content="Save" Command="{Binding SaveCommand}" IsDefault="True" />
+        <Button Content="Cancel" Command="{Binding CancelCommand}" />
+      </StackPanel>
+    </StackPanel>
+
+  </Grid>
 </UserControl>

src/Junction.App/Views/MachineDetailView.axaml

@@ -9,71 +9,70 @@
              x:CompileBindings="True">
 
   <Grid>
-  <DockPanel Margin="16">
+  <DockPanel Margin="20">
 
-    <!-- Header bar: Back + machine name + status badge + Edit/Delete -->
-    <Grid DockPanel.Dock="Top" ColumnDefinitions="Auto,Auto,*,Auto,Auto" Margin="0,0,0,12">
+    <!-- Header bar: Back + protocol glyph + machine name + status badge + Edit/Delete -->
+    <Grid DockPanel.Dock="Top" ColumnDefinitions="Auto,Auto,Auto,*,Auto,Auto" Margin="0,0,0,16">
       <Button Grid.Column="0" Content="← Back" Command="{Binding BackCommand}" VerticalAlignment="Center" />
-      <TextBlock Grid.Column="1" Text="{Binding MachineName}"
-                 FontSize="22" FontWeight="SemiBold"
-                 VerticalAlignment="Center" Margin="12,0" />
-      <Border Grid.Column="2"
+      <PathIcon Grid.Column="1" Classes="protocol" Width="20" Height="20"
+                Data="{Binding ProtocolId, Converter={StaticResource ProtocolIdToIcon}}"
+                ToolTip.Tip="{Binding ProtocolId}"
+                VerticalAlignment="Center" Margin="14,0,0,0" />
+      <TextBlock Grid.Column="2" Classes="h1" Text="{Binding MachineName}"
+                 VerticalAlignment="Center" Margin="10,0" />
+      <Border Grid.Column="3"
               Background="{Binding StatusKind, Converter={StaticResource StatusKindToBrush}}"
               CornerRadius="4" Padding="8,3" HorizontalAlignment="Left" VerticalAlignment="Center">
         <TextBlock Text="{Binding ConnectionState}" Foreground="White" FontWeight="SemiBold" FontSize="12" />
       </Border>
-      <Button Grid.Column="3" Content="Edit" Command="{Binding EditCommand}"
+      <Button Grid.Column="4" Content="Edit" Command="{Binding EditCommand}"
               VerticalAlignment="Center" Margin="0,0,8,0" />
-      <Button Grid.Column="4" Content="Delete" Command="{Binding RequestDeleteCommand}"
+      <Button Grid.Column="5" Classes="danger" Content="Delete" Command="{Binding RequestDeleteCommand}"
               VerticalAlignment="Center" />
     </Grid>
 
     <!-- Machine info panel -->
-    <Border DockPanel.Dock="Top"
-            BorderThickness="1"
-            BorderBrush="{DynamicResource SystemControlForegroundBaseMediumLowBrush}"
-            CornerRadius="4"
-            Padding="12" Margin="0,0,0,12">
+    <Border DockPanel.Dock="Top" Classes="card" Margin="0,0,0,16">
       <Grid ColumnDefinitions="Auto,*,Auto,*" RowDefinitions="Auto,Auto,Auto,Auto" >
-        <TextBlock Grid.Row="0" Grid.Column="0" Text="Protocol" FontWeight="Bold" Margin="0,0,12,4" />
-        <TextBlock Grid.Row="0" Grid.Column="1" Text="{Binding ProtocolId}" Margin="0,0,24,4" />
-        <TextBlock Grid.Row="0" Grid.Column="2" Text="Poll Interval" FontWeight="Bold" Margin="0,0,12,4" />
-        <TextBlock Grid.Row="0" Grid.Column="3" Text="{Binding PollInterval}" Margin="0,0,0,4" />
+        <TextBlock Grid.Row="0" Grid.Column="0" Classes="fieldLabel" Text="Protocol" Margin="0,0,12,6" />
+        <TextBlock Grid.Row="0" Grid.Column="1" Text="{Binding ProtocolId}" Margin="0,0,24,6" />
+        <TextBlock Grid.Row="0" Grid.Column="2" Classes="fieldLabel" Text="Poll Interval" Margin="0,0,12,6" />
+        <TextBlock Grid.Row="0" Grid.Column="3" Text="{Binding PollInterval}" Margin="0,0,0,6" />
 
-        <TextBlock Grid.Row="1" Grid.Column="0" Text="Connection" FontWeight="Bold" Margin="0,0,12,4" />
+        <TextBlock Grid.Row="1" Grid.Column="0" Classes="fieldLabel" Text="Connection" Margin="0,0,12,6" />
         <TextBlock Grid.Row="1" Grid.Column="1" Text="{Binding ConnectionState}"
                    Foreground="{Binding StatusKind, Converter={StaticResource StatusKindToBrush}}"
-                   FontWeight="SemiBold" Margin="0,0,24,4" />
-        <TextBlock Grid.Row="1" Grid.Column="2" Text="Captured At" FontWeight="Bold" Margin="0,0,12,4" />
-        <TextBlock Grid.Row="1" Grid.Column="3" Text="{Binding CapturedAt}" Margin="0,0,0,4" />
+                   FontWeight="SemiBold" Margin="0,0,24,6" />
+        <TextBlock Grid.Row="1" Grid.Column="2" Classes="fieldLabel" Text="Captured At" Margin="0,0,12,6" />
+        <TextBlock Grid.Row="1" Grid.Column="3" Text="{Binding CapturedAt}" Margin="0,0,0,6" />
 
-        <TextBlock Grid.Row="2" Grid.Column="0" Text="Last Seen" FontWeight="Bold" Margin="0,0,12,4" />
-        <TextBlock Grid.Row="2" Grid.Column="1" Text="{Binding LastSeen}" Margin="0,0,24,4" />
-        <TextBlock Grid.Row="2" Grid.Column="2" Text="Machine Id" FontWeight="Bold" Margin="0,0,12,4" />
-        <TextBlock Grid.Row="2" Grid.Column="3" Text="{Binding MachineIdText}" Margin="0,0,0,4"
+        <TextBlock Grid.Row="2" Grid.Column="0" Classes="fieldLabel" Text="Last Seen" Margin="0,0,12,6" />
+        <TextBlock Grid.Row="2" Grid.Column="1" Text="{Binding LastSeen}" Margin="0,0,24,6" />
+        <TextBlock Grid.Row="2" Grid.Column="2" Classes="fieldLabel" Text="Machine Id" Margin="0,0,12,6" />
+        <TextBlock Grid.Row="2" Grid.Column="3" Text="{Binding MachineIdText}" Margin="0,0,0,6"
                    FontSize="11" Opacity="0.7" TextWrapping="Wrap" />
 
-        <TextBlock Grid.Row="3" Grid.Column="0" Text="Agent URL" FontWeight="Bold" Margin="0,0,12,0" />
+        <TextBlock Grid.Row="3" Grid.Column="0" Classes="fieldLabel" Text="Agent URL" Margin="0,0,12,0" />
         <TextBlock Grid.Row="3" Grid.Column="1" Grid.ColumnSpan="3" Text="{Binding AgentUrl}"
                    Margin="0,0,0,0" TextWrapping="Wrap" />
       </Grid>
     </Border>
 
     <!-- Data-items header -->
-    <TextBlock DockPanel.Dock="Top"
+    <TextBlock DockPanel.Dock="Top" Classes="h2"
                Text="{Binding ItemCount, StringFormat='Data Items ({0})'}"
-               FontSize="16" FontWeight="SemiBold" Margin="0,0,0,6" />
+               Margin="0,0,0,8" />
 
     <Border DockPanel.Dock="Top"
             BorderThickness="0,0,0,1"
-            BorderBrush="{DynamicResource SystemControlForegroundBaseMediumLowBrush}"
+            BorderBrush="{DynamicResource CardBorderBrush}"
             Padding="0,0,0,6" Margin="0,0,0,4"
             IsVisible="{Binding HasItems}">
       <Grid ColumnDefinitions="2*,2*,1.2*,1.2*">
-        <TextBlock Grid.Column="0" Text="Name" FontWeight="Bold" />
-        <TextBlock Grid.Column="1" Text="Value" FontWeight="Bold" />
-        <TextBlock Grid.Column="2" Text="Category" FontWeight="Bold" />
-        <TextBlock Grid.Column="3" Text="Timestamp" FontWeight="Bold" />
+        <TextBlock Grid.Column="0" Classes="fieldLabel" Text="Name" />
+        <TextBlock Grid.Column="1" Classes="fieldLabel" Text="Value" />
+        <TextBlock Grid.Column="2" Classes="fieldLabel" Text="Category" />
+        <TextBlock Grid.Column="3" Classes="fieldLabel" Text="Timestamp" />
       </Grid>
     </Border>
 
@@ -86,7 +85,7 @@
               <Grid ColumnDefinitions="2*,2*,1.2*,1.2*" Margin="0,5">
                 <StackPanel Grid.Column="0">
                   <TextBlock Text="{Binding Name}" FontWeight="SemiBold" TextWrapping="Wrap" />
-                  <TextBlock Text="{Binding Id}" FontSize="11" Opacity="0.6" TextWrapping="Wrap" />
+                  <TextBlock Text="{Binding Id}" Classes="subtle" FontSize="11" TextWrapping="Wrap" />
                 </StackPanel>
                 <TextBlock Grid.Column="1" Text="{Binding Value}" VerticalAlignment="Center" TextWrapping="Wrap" />
                 <TextBlock Grid.Column="2" Text="{Binding Category}" VerticalAlignment="Center" />
@@ -101,11 +100,10 @@
       <StackPanel IsVisible="{Binding HasNoItems}"
                   HorizontalAlignment="Center" VerticalAlignment="Center"
                   Spacing="6" MaxWidth="420">
-        <TextBlock Text="No monitored items"
-                   FontSize="16" FontWeight="SemiBold"
+        <TextBlock Classes="h2" Text="No monitored items"
                    HorizontalAlignment="Center" />
-        <TextBlock Text="Edit this machine to select which data items to monitor."
-                   Opacity="0.75" TextWrapping="Wrap" TextAlignment="Center" />
+        <TextBlock Classes="subtle" Text="Edit this machine to select which data items to monitor."
+                   TextWrapping="Wrap" TextAlignment="Center" />
       </StackPanel>
     </Grid>
   </DockPanel>
@@ -113,19 +111,16 @@
   <!-- Delete-confirmation overlay: dims the screen, names the machine, requires an explicit choice. -->
   <Border IsVisible="{Binding IsDeleteConfirmVisible}"
           Background="#99000000">
-    <Border Background="{DynamicResource SystemControlBackgroundAltHighBrush}"
-            BorderBrush="{DynamicResource SystemControlForegroundBaseMediumLowBrush}"
-            BorderThickness="1" CornerRadius="6"
-            Padding="20" MaxWidth="420"
+    <Border Classes="card" MaxWidth="420"
             HorizontalAlignment="Center" VerticalAlignment="Center">
       <StackPanel Spacing="14">
-        <TextBlock Text="{Binding DeleteConfirmPrompt}" FontSize="16" FontWeight="SemiBold" TextWrapping="Wrap" />
-        <TextBlock Text="This permanently removes the machine and stops monitoring it. This cannot be undone."
-                   Opacity="0.75" TextWrapping="Wrap" />
+        <TextBlock Classes="h2" Text="{Binding DeleteConfirmPrompt}" TextWrapping="Wrap" />
+        <TextBlock Classes="subtle"
+                   Text="This permanently removes the machine and stops monitoring it. This cannot be undone."
+                   TextWrapping="Wrap" />
         <StackPanel Orientation="Horizontal" HorizontalAlignment="Right" Spacing="8">
           <Button Content="Cancel" Command="{Binding CancelDeleteCommand}" />
-          <Button Content="Delete" Command="{Binding ConfirmDeleteCommand}"
-                  Background="#C62828" Foreground="White" FontWeight="SemiBold" />
+          <Button Classes="danger" Content="Delete" Command="{Binding ConfirmDeleteCommand}" />
         </StackPanel>
       </StackPanel>
     </Border>

src/Junction.Protocols.OpcUa/IUaClient.cs

@@ -0,0 +1,27 @@
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using Junction.Domain.Protocols;
+
+namespace Junction.Protocols.OpcUa
+{
+    /// <summary>
+    /// Transport seam over an OPC UA session, mirroring the HttpClient injection the MTConnect
+    /// driver uses. Deliberately keeps all <c>Opc.Ua.*</c> SDK types OUT of its signatures so
+    /// <see cref="OpcuaDriver"/> can be unit-tested against a mock with no live server.
+    /// </summary>
+    public interface IUaClient
+    {
+        /// <summary>Establish the session (connect + authenticate). Idempotent: safe to call before each op.</summary>
+        Task ConnectAsync(CancellationToken ct);
+
+        /// <summary>Read the Value attribute of each given node id. Order matches the input order.</summary>
+        Task<IReadOnlyList<UaReadResult>> ReadAsync(IReadOnlyList<string> nodeIds, CancellationToken ct);
+
+        /// <summary>
+        /// Recursively browse the address space from <paramref name="browseRoot"/>, returning one
+        /// descriptor per Variable node found.
+        /// </summary>
+        Task<IReadOnlyList<DataItemDescriptor>> BrowseAsync(string browseRoot, CancellationToken ct);
+    }
+}

src/Junction.Protocols.OpcUa/Junction.Protocols.OpcUa.csproj

@@ -0,0 +1,27 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <!-- Multi-target: net48 = shipped fleet (Win7/8); net8.0 = Linux dev host must load plugin too.
+         MTConnect is ns2.0 (loads on both), but the OPC UA SDK ships no ns2.0 asset, so target the
+         two host TFMs explicitly. -->
+    <TargetFrameworks>net48;net8.0</TargetFrameworks>
+    <RootNamespace>Junction.Protocols.OpcUa</RootNamespace>
+    <!-- Guarantees the full transitive closure (SDK + its deps) lands in bin per TFM so the App copy
+         target ships everything the plugin needs at runtime. -->
+    <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="OPCFoundation.NetStandard.Opc.Ua.Client" Version="1.5.378.156" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Junction.Domain\Junction.Domain.csproj" />
+  </ItemGroup>
+
+  <!-- Plugin manifest: ships beside built assembly. Condition keeps build green if file is absent. -->
+  <ItemGroup>
+    <None Include="plugin.manifest.json" Condition="Exists('plugin.manifest.json')" CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
+
+</Project>

src/Junction.Protocols.OpcUa/OpcuaDriver.cs

@@ -0,0 +1,182 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using Junction.Domain;
+using Junction.Domain.Models;
+using Junction.Domain.Protocols;
+
+namespace Junction.Protocols.OpcUa
+{
+    /// <summary>
+    /// Per-machine OPC UA protocol driver. Reads the configured node values and browses the address
+    /// space through an injected <see cref="IUaClient"/> (the transport seam, mirroring the HttpClient
+    /// injection in <c>MtconnectDriver</c>). SDK types stay behind <see cref="IUaClient"/> so this
+    /// driver is unit-tested against a mock with no live server.
+    /// <para>
+    /// Never throws for expected transport failures: maps them to <see cref="Result{T}.Fail(OperationError)"/>
+    /// and honours cancellation via <see cref="Result{T}.Cancelled"/>.
+    /// </para>
+    /// </summary>
+    public sealed class OpcuaDriver : IProtocolDriver
+    {
+        private const string Source = "OpcuaDriver";
+
+        private readonly IUaClient _client;
+        private readonly Guid _machineId;
+        private readonly IReadOnlyList<string> _nodeIds;
+        private readonly string _browseRoot;
+        private readonly TimeSpan _timeout;
+
+        // Selected data item ids to keep in ReadCurrentAsync snapshots. Empty => opt-in "monitor nothing".
+        private readonly HashSet<string> _monitoredItemIds;
+
+        /// <summary>Protocol identifier this driver serves.</summary>
+        public string ProtocolId => "opcua";
+
+        /// <param name="client">Transport seam; injected for testability, owned by the factory.</param>
+        /// <param name="machineId">Machine this driver reads for; stamped onto the snapshot.</param>
+        /// <param name="nodeIds">Configured node ids to read in <see cref="ReadCurrentAsync"/>.</param>
+        /// <param name="browseRoot">Address-space browse start node for <see cref="ProbeAsync"/>.</param>
+        /// <param name="timeout">Per-operation timeout enforced via a linked <see cref="CancellationTokenSource"/>.</param>
+        /// <param name="monitoredItemIds">
+        /// DataItem ids the user selected to monitor. <see cref="ReadCurrentAsync"/> keeps only these
+        /// (opt-in); empty/null => "monitor nothing".
+        /// </param>
+        public OpcuaDriver(
+            IUaClient client,
+            Guid machineId,
+            IReadOnlyList<string>? nodeIds,
+            string browseRoot,
+            TimeSpan timeout,
+            IReadOnlyCollection<string>? monitoredItemIds = null)
+        {
+            _client = client ?? throw new ArgumentNullException(nameof(client));
+            _machineId = machineId;
+            _nodeIds = nodeIds ?? Array.Empty<string>();
+            _browseRoot = browseRoot ?? "";
+            if (timeout <= TimeSpan.Zero && timeout != Timeout.InfiniteTimeSpan)
+            {
+                throw new ArgumentOutOfRangeException(nameof(timeout), timeout, "Timeout must be positive or Timeout.InfiniteTimeSpan.");
+            }
+            _timeout = timeout;
+
+            _monitoredItemIds = new HashSet<string>(StringComparer.Ordinal);
+            if (monitoredItemIds != null)
+            {
+                foreach (var id in monitoredItemIds)
+                {
+                    if (!string.IsNullOrEmpty(id))
+                    {
+                        _monitoredItemIds.Add(id);
+                    }
+                }
+            }
+        }
+
+        /// <inheritdoc />
+        public async Task<Result<MachineSnapshot>> ReadCurrentAsync(CancellationToken cancellationToken)
+        {
+            if (cancellationToken.IsCancellationRequested)
+            {
+                return Result<MachineSnapshot>.Cancelled();
+            }
+
+            using var cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
+            cts.CancelAfter(_timeout);
+
+            IReadOnlyList<UaReadResult> reads;
+            try
+            {
+                await _client.ConnectAsync(cts.Token).ConfigureAwait(false);
+                reads = await _client.ReadAsync(_nodeIds, cts.Token).ConfigureAwait(false);
+            }
+            catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
+            {
+                return Result<MachineSnapshot>.Cancelled();
+            }
+            catch (OperationCanceledException ex)
+            {
+                return Fail("CURRENT_TIMEOUT", "OPC UA read timed out: " + ex.Message);
+            }
+            catch (Exception ex)
+            {
+                return Fail("CURRENT_READ_ERROR", "OPC UA read failed: " + ex.Message);
+            }
+
+            var items = new List<DataItem>(reads.Count);
+            foreach (UaReadResult r in reads)
+            {
+                items.Add(new DataItem(r.NodeId, r.NodeId, r.Value, "VARIABLE", r.SourceTimestamp));
+            }
+
+            var snapshot = new MachineSnapshot(_machineId, DateTimeOffset.UtcNow, ConnectionState.Connected, items);
+            return Result<MachineSnapshot>.Ok(FilterToMonitored(snapshot));
+        }
+
+        /// <inheritdoc />
+        public async Task<Result<IReadOnlyList<DataItemDescriptor>>> ProbeAsync(CancellationToken cancellationToken)
+        {
+            if (cancellationToken.IsCancellationRequested)
+            {
+                return Result<IReadOnlyList<DataItemDescriptor>>.Cancelled();
+            }
+
+            using var cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
+            cts.CancelAfter(_timeout);
+
+            IReadOnlyList<DataItemDescriptor> descriptors;
+            try
+            {
+                await _client.ConnectAsync(cts.Token).ConfigureAwait(false);
+                descriptors = await _client.BrowseAsync(_browseRoot, cts.Token).ConfigureAwait(false);
+            }
+            catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
+            {
+                return Result<IReadOnlyList<DataItemDescriptor>>.Cancelled();
+            }
+            catch (OperationCanceledException ex)
+            {
+                return ProbeFail("PROBE_TIMEOUT", "OPC UA browse timed out: " + ex.Message);
+            }
+            catch (Exception ex)
+            {
+                return ProbeFail("PROBE_BROWSE_ERROR", "OPC UA browse failed: " + ex.Message);
+            }
+
+            return Result<IReadOnlyList<DataItemDescriptor>>.Ok(descriptors);
+        }
+
+        /// <summary>
+        /// Returns a copy of <paramref name="snapshot"/> keeping only items whose id is in the monitored
+        /// selection. Empty selection yields an empty item set (opt-in). Connection state and capture
+        /// instant are preserved. Exact semantics as MtconnectDriver.
+        /// </summary>
+        private MachineSnapshot FilterToMonitored(MachineSnapshot snapshot)
+        {
+            if (_monitoredItemIds.Count == 0)
+            {
+                return new MachineSnapshot(
+                    snapshot.MachineId, snapshot.CapturedAt, snapshot.ConnectionState, Array.Empty<DataItem>());
+            }
+
+            var kept = new List<DataItem>();
+            for (int i = 0; i < snapshot.Items.Count; i++)
+            {
+                DataItem item = snapshot.Items[i];
+                if (_monitoredItemIds.Contains(item.Id))
+                {
+                    kept.Add(item);
+                }
+            }
+
+            return new MachineSnapshot(snapshot.MachineId, snapshot.CapturedAt, snapshot.ConnectionState, kept);
+        }
+
+        private static Result<MachineSnapshot> Fail(string code, string message) =>
+            Result<MachineSnapshot>.Fail(new OperationError(code, Source, message));
+
+        private static Result<IReadOnlyList<DataItemDescriptor>> ProbeFail(string code, string message) =>
+            Result<IReadOnlyList<DataItemDescriptor>>.Fail(new OperationError(code, Source, message));
+    }
+}

src/Junction.Protocols.OpcUa/OpcuaDriverFactory.cs

@@ -0,0 +1,220 @@
+using System;
+using System.Collections.Generic;
+using Junction.Domain;
+using Junction.Domain.Models;
+using Junction.Domain.Protocols;
+
+namespace Junction.Protocols.OpcUa
+{
+    /// <summary>
+    /// Plugin entrypoint for the OPC UA protocol. Resolved by the Core plugin loader from
+    /// <c>plugin.manifest.json</c> via <see cref="Activator.CreateInstance(Type)"/>, so it MUST
+    /// keep a public parameterless constructor.
+    /// <para>
+    /// Owns OPC UA config validation, mirroring <c>MtconnectDriverFactory</c> (case-insensitive
+    /// lookup, CONFIG_* fail codes). Builds a real <see cref="UaClient"/> and injects it into the
+    /// per-machine <see cref="OpcuaDriver"/>.
+    /// </para>
+    /// <para>Expected <see cref="Machine.ConnectionConfig"/> keys (case-insensitive):</para>
+    /// <list type="bullet">
+    ///   <item><description><c>EndpointUrl</c> (required) — absolute opc.tcp:// URL of the server.</description></item>
+    ///   <item><description><c>SecurityMode</c> (optional) — None|Sign|SignAndEncrypt, default None.</description></item>
+    ///   <item><description><c>SecurityPolicy</c> (optional) — default None.</description></item>
+    ///   <item><description><c>AuthMode</c> (optional) — Anonymous|UsernamePassword, default Anonymous.</description></item>
+    ///   <item><description><c>Username</c>/<c>Password</c> — required iff AuthMode=UsernamePassword.</description></item>
+    ///   <item><description><c>NodeIds</c> (optional CSV) — node ids read by ReadCurrentAsync.</description></item>
+    ///   <item><description><c>BrowseRoot</c> (optional) — browse start node, default "i=85".</description></item>
+    ///   <item><description><c>TimeoutSeconds</c> (optional) — positive int, default 10.</description></item>
+    /// </list>
+    /// </summary>
+    public sealed class OpcuaDriverFactory : IProtocolDriverFactory
+    {
+        private const string Source = "OpcuaDriverFactory";
+        private const string EndpointUrlKey = "EndpointUrl";
+        private const string SecurityModeKey = "SecurityMode";
+        private const string SecurityPolicyKey = "SecurityPolicy";
+        private const string AuthModeKey = "AuthMode";
+        private const string UsernameKey = "Username";
+        private const string PasswordKey = "Password";
+        private const string NodeIdsKey = "NodeIds";
+        private const string BrowseRootKey = "BrowseRoot";
+        private const string TimeoutKey = "TimeoutSeconds";
+
+        private const string DefaultBrowseRoot = "i=85";
+        private static readonly TimeSpan DefaultTimeout = TimeSpan.FromSeconds(10);
+
+        /// <summary>Protocol identifier this factory produces drivers for.</summary>
+        public string ProtocolId => "opcua";
+
+        /// <summary>Required by the plugin loader (Activator.CreateInstance).</summary>
+        public OpcuaDriverFactory()
+        {
+        }
+
+        /// <inheritdoc />
+        public Result<IProtocolDriver> Create(Machine machine)
+        {
+            if (machine is null)
+            {
+                return Fail("MACHINE_NULL", "Machine was null.");
+            }
+
+            var config = machine.ConnectionConfig;
+
+            // EndpointUrl: required, absolute, opc.tcp scheme.
+            var endpointUrl = GetValue(config, EndpointUrlKey);
+            if (string.IsNullOrWhiteSpace(endpointUrl))
+            {
+                return Fail("CONFIG_ENDPOINTURL_MISSING",
+                    "Required connection config key '" + EndpointUrlKey + "' is missing or empty.");
+            }
+            endpointUrl = endpointUrl!.Trim();
+            if (!Uri.TryCreate(endpointUrl, UriKind.Absolute, out var uri))
+            {
+                return Fail("CONFIG_ENDPOINTURL_INVALID",
+                    "Connection config key '" + EndpointUrlKey + "' is not an absolute URI: '" + endpointUrl + "'.");
+            }
+            if (!string.Equals(uri.Scheme, "opc.tcp", StringComparison.OrdinalIgnoreCase))
+            {
+                return Fail("CONFIG_ENDPOINTURL_SCHEME",
+                    "Connection config key '" + EndpointUrlKey + "' must use the 'opc.tcp' scheme: '" + endpointUrl + "'.");
+            }
+
+            // SecurityMode: optional, one of None|Sign|SignAndEncrypt (default None).
+            var securityMode = GetValue(config, SecurityModeKey);
+            if (string.IsNullOrWhiteSpace(securityMode))
+            {
+                securityMode = "None";
+            }
+            else
+            {
+                securityMode = securityMode!.Trim();
+                if (!IsOneOf(securityMode, "None", "Sign", "SignAndEncrypt"))
+                {
+                    return Fail("CONFIG_SECURITYMODE_INVALID",
+                        "Connection config key '" + SecurityModeKey + "' must be None, Sign or SignAndEncrypt: '" + securityMode + "'.");
+                }
+            }
+
+            // SecurityPolicy: optional, default None. Free-form (validated by the server on connect).
+            var securityPolicy = GetValue(config, SecurityPolicyKey);
+            if (string.IsNullOrWhiteSpace(securityPolicy))
+            {
+                securityPolicy = "None";
+            }
+
+            // AuthMode: optional, one of Anonymous|UsernamePassword (default Anonymous).
+            var authMode = GetValue(config, AuthModeKey);
+            if (string.IsNullOrWhiteSpace(authMode))
+            {
+                authMode = "Anonymous";
+            }
+            else
+            {
+                authMode = authMode!.Trim();
+                if (!IsOneOf(authMode, "Anonymous", "UsernamePassword"))
+                {
+                    return Fail("CONFIG_AUTHMODE_INVALID",
+                        "Connection config key '" + AuthModeKey + "' must be Anonymous or UsernamePassword: '" + authMode + "'.");
+                }
+            }
+
+            string? username = GetValue(config, UsernameKey);
+            string? password = GetValue(config, PasswordKey);
+            if (string.Equals(authMode, "UsernamePassword", StringComparison.OrdinalIgnoreCase))
+            {
+                if (string.IsNullOrWhiteSpace(username))
+                {
+                    return Fail("CONFIG_USERNAME_MISSING",
+                        "Connection config key '" + UsernameKey + "' is required when AuthMode=UsernamePassword.");
+                }
+                if (string.IsNullOrEmpty(password))
+                {
+                    return Fail("CONFIG_PASSWORD_MISSING",
+                        "Connection config key '" + PasswordKey + "' is required when AuthMode=UsernamePassword.");
+                }
+            }
+
+            // BrowseRoot: optional, default i=85.
+            var browseRoot = GetValue(config, BrowseRootKey);
+            if (string.IsNullOrWhiteSpace(browseRoot))
+            {
+                browseRoot = DefaultBrowseRoot;
+            }
+            browseRoot = browseRoot!.Trim();
+
+            // NodeIds: optional CSV of node ids to read.
+            var nodeIds = ParseCsv(GetValue(config, NodeIdsKey));
+
+            // TimeoutSeconds: optional positive int (default 10).
+            var timeout = DefaultTimeout;
+            var timeoutRaw = GetValue(config, TimeoutKey);
+            if (!string.IsNullOrWhiteSpace(timeoutRaw))
+            {
+                if (!int.TryParse(timeoutRaw, out var seconds) || seconds <= 0)
+                {
+                    return Fail("CONFIG_TIMEOUT_INVALID",
+                        "Connection config key '" + TimeoutKey + "' must be a positive integer (seconds): '" + timeoutRaw + "'.");
+                }
+                timeout = TimeSpan.FromSeconds(seconds);
+            }
+
+            var client = new UaClient(endpointUrl, securityMode!, authMode!, username, password, timeout);
+            var driver = new OpcuaDriver(client, machine.Id, nodeIds, browseRoot, timeout, machine.MonitoredItemIds);
+            return Result<IProtocolDriver>.Ok(driver);
+        }
+
+        private static IReadOnlyList<string> ParseCsv(string? raw)
+        {
+            if (string.IsNullOrWhiteSpace(raw))
+            {
+                return Array.Empty<string>();
+            }
+
+            var parts = raw!.Split(',');
+            var list = new List<string>(parts.Length);
+            foreach (var p in parts)
+            {
+                var trimmed = p.Trim();
+                if (trimmed.Length > 0)
+                {
+                    list.Add(trimmed);
+                }
+            }
+            return list;
+        }
+
+        private static bool IsOneOf(string value, params string[] allowed)
+        {
+            foreach (var a in allowed)
+            {
+                if (string.Equals(value, a, StringComparison.OrdinalIgnoreCase))
+                {
+                    return true;
+                }
+            }
+            return false;
+        }
+
+        private static string? GetValue(IReadOnlyDictionary<string, string> config, string key)
+        {
+            if (config is null)
+            {
+                return null;
+            }
+
+            foreach (var pair in config)
+            {
+                if (string.Equals(pair.Key, key, StringComparison.OrdinalIgnoreCase))
+                {
+                    return pair.Value;
+                }
+            }
+
+            return null;
+        }
+
+        private static Result<IProtocolDriver> Fail(string code, string message) =>
+            Result<IProtocolDriver>.Fail(new OperationError(code, Source, message));
+    }
+}

src/Junction.Protocols.OpcUa/UaClient.cs

@@ -0,0 +1,332 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using Junction.Domain.Protocols;
+using Opc.Ua;
+using Opc.Ua.Client;
+using Opc.Ua.Configuration;
+
+namespace Junction.Protocols.OpcUa
+{
+    /// <summary>
+    /// Real <see cref="IUaClient"/> over the OPC Foundation .NET Standard SDK. Owns an
+    /// <see cref="ApplicationConfiguration"/> with a Directory PKI store under LocalApplicationData,
+    /// auto-generates the app-instance certificate, opens a <see cref="Session"/> and translates SDK
+    /// calls into the SDK-free DTOs the driver consumes.
+    /// <para>
+    /// This type is NOT unit-tested (it needs a live server); the driver is tested via a mocked
+    /// <see cref="IUaClient"/>. Exceptions raised here are caught by the driver and mapped to
+    /// <see cref="Junction.Domain.Result{T}"/> failures.
+    /// </para>
+    /// <para>
+    /// Uses the SDK's non-obsolete telemetry-threaded async surface throughout. The pinned SDK
+    /// (1.5.378.156) is mid-migration to an <c>ITelemetryContext</c>/DI-first API; a null telemetry
+    /// context is accepted and the SDK substitutes its default.
+    /// </para>
+    /// </summary>
+    public sealed class UaClient : IUaClient, IDisposable
+    {
+        private const string ApplicationName = "Junction";
+
+        private readonly string _endpointUrl;
+        private readonly string _securityMode;   // None | Sign | SignAndEncrypt
+        private readonly string _authMode;        // Anonymous | UsernamePassword
+        private readonly string? _username;
+        private readonly string? _password;
+        private readonly TimeSpan _timeout;
+
+        // Intentionally null: the SDK substitutes its default telemetry context. Typed non-nullable so
+        // the non-obsolete telemetry-threaded async overloads bind without nullable-analysis noise.
+        private readonly ITelemetryContext _telemetry = null!;
+
+        private ApplicationConfiguration? _appConfig;
+        private ISession? _session;
+
+        public UaClient(
+            string endpointUrl,
+            string securityMode,
+            string authMode,
+            string? username,
+            string? password,
+            TimeSpan timeout)
+        {
+            _endpointUrl = endpointUrl ?? throw new ArgumentNullException(nameof(endpointUrl));
+            _securityMode = string.IsNullOrWhiteSpace(securityMode) ? "None" : securityMode;
+            _authMode = string.IsNullOrWhiteSpace(authMode) ? "Anonymous" : authMode;
+            _username = username;
+            _password = password;
+            _timeout = timeout;
+        }
+
+        public async Task ConnectAsync(CancellationToken ct)
+        {
+            if (_session != null && _session.Connected)
+            {
+                return;
+            }
+
+            ApplicationConfiguration config = await BuildConfigurationAsync(ct).ConfigureAwait(false);
+
+            bool useSecurity = !string.Equals(_securityMode, "None", StringComparison.OrdinalIgnoreCase);
+
+            // Discover + pick the server endpoint matching the requested security.
+            EndpointDescription selected =
+                (await CoreClientUtils.SelectEndpointAsync(config, _endpointUrl, useSecurity, _telemetry, ct).ConfigureAwait(false))!;
+            var endpointConfiguration = EndpointConfiguration.Create(config);
+            var endpoint = new ConfiguredEndpoint(null, selected, endpointConfiguration);
+
+            IUserIdentity identity = BuildIdentity();
+
+            var factory = new DefaultSessionFactory(_telemetry);
+            _session = await factory.CreateAsync(
+                config,
+                endpoint,
+                updateBeforeConnect: false,
+                checkDomain: false,
+                sessionName: ApplicationName,
+                sessionTimeout: (uint)Math.Max(1000, _timeout.TotalMilliseconds),
+                identity: identity,
+                preferredLocales: null,
+                ct).ConfigureAwait(false);
+        }
+
+        public async Task<IReadOnlyList<UaReadResult>> ReadAsync(IReadOnlyList<string> nodeIds, CancellationToken ct)
+        {
+            await ConnectAsync(ct).ConfigureAwait(false);
+            ISession session = _session ?? throw new InvalidOperationException("OPC UA session not established.");
+
+            var results = new List<UaReadResult>(nodeIds.Count);
+            if (nodeIds.Count == 0)
+            {
+                return results;
+            }
+
+            var toRead = new ReadValueIdCollection();
+            foreach (var id in nodeIds)
+            {
+                toRead.Add(new ReadValueId { NodeId = new NodeId(id), AttributeId = Attributes.Value });
+            }
+
+            ReadResponse response =
+                await session.ReadAsync(null, 0, TimestampsToReturn.Both, toRead, ct).ConfigureAwait(false);
+            DataValueCollection values = response.Results;
+
+            for (int i = 0; i < nodeIds.Count; i++)
+            {
+                DataValue dv = (values != null && i < values.Count) ? values[i] : new DataValue(StatusCodes.BadUnexpectedError);
+                bool ok = StatusCode.IsGood(dv.StatusCode);
+                string value = dv.Value != null ? dv.Value.ToString() ?? "" : "";
+                DateTimeOffset ts = dv.SourceTimestamp == DateTime.MinValue
+                    ? DateTimeOffset.UtcNow
+                    : new DateTimeOffset(DateTime.SpecifyKind(dv.SourceTimestamp, DateTimeKind.Utc));
+                results.Add(new UaReadResult(nodeIds[i], value, ok, ts));
+            }
+
+            return results;
+        }
+
+        public async Task<IReadOnlyList<DataItemDescriptor>> BrowseAsync(string browseRoot, CancellationToken ct)
+        {
+            await ConnectAsync(ct).ConfigureAwait(false);
+            ISession session = _session ?? throw new InvalidOperationException("OPC UA session not established.");
+
+            NodeId root = string.IsNullOrWhiteSpace(browseRoot) ? ObjectIds.ObjectsFolder : new NodeId(browseRoot);
+            var descriptors = new List<DataItemDescriptor>();
+            var visited = new HashSet<string>(StringComparer.Ordinal);
+
+            await BrowseRecursiveAsync(session, root, descriptors, visited, ct).ConfigureAwait(false);
+            return descriptors;
+        }
+
+        private static async Task BrowseRecursiveAsync(
+            ISession session,
+            NodeId node,
+            List<DataItemDescriptor> descriptors,
+            HashSet<string> visited,
+            CancellationToken ct)
+        {
+            ct.ThrowIfCancellationRequested();
+            if (!visited.Add(node.ToString()))
+            {
+                return; // guard against cycles
+            }
+
+            var nodeToBrowse = new BrowseDescription
+            {
+                NodeId = node,
+                BrowseDirection = BrowseDirection.Forward,
+                ReferenceTypeId = ReferenceTypeIds.HierarchicalReferences,
+                IncludeSubtypes = true,
+                NodeClassMask = (uint)(NodeClass.Object | NodeClass.Variable),
+                ResultMask = (uint)BrowseResultMask.All,
+            };
+
+            BrowseResponse response = await session.BrowseAsync(
+                null, null, 0u, new BrowseDescriptionCollection { nodeToBrowse }, ct).ConfigureAwait(false);
+
+            if (response.Results == null || response.Results.Count == 0)
+            {
+                return;
+            }
+
+            BrowseResult result = response.Results[0];
+            var references = new ReferenceDescriptionCollection();
+            if (result.References != null)
+            {
+                references.AddRange(result.References);
+            }
+
+            // Follow continuation points to enumerate the full child set.
+            byte[] continuation = result.ContinuationPoint;
+            while (continuation != null && continuation.Length > 0)
+            {
+                ct.ThrowIfCancellationRequested();
+                BrowseNextResponse next = await session.BrowseNextAsync(
+                    null, false, new ByteStringCollection { continuation }, ct).ConfigureAwait(false);
+                if (next.Results == null || next.Results.Count == 0)
+                {
+                    break;
+                }
+                BrowseResult nr = next.Results[0];
+                if (nr.References != null)
+                {
+                    references.AddRange(nr.References);
+                }
+                continuation = nr.ContinuationPoint;
+            }
+
+            foreach (ReferenceDescription r in references)
+            {
+                NodeId? childId = ExpandedNodeId.ToNodeId(r.NodeId, session.NamespaceUris);
+                if (childId == null)
+                {
+                    continue;
+                }
+
+                if (r.NodeClass == NodeClass.Variable)
+                {
+                    string displayName = r.DisplayName != null ? r.DisplayName.Text : "";
+                    string dataType = await ReadDataTypeNameAsync(session, childId, ct).ConfigureAwait(false);
+                    descriptors.Add(new DataItemDescriptor(childId.ToString(), displayName, dataType, "VARIABLE", ""));
+                }
+
+                // Recurse into both objects and variables (variables can have variable children).
+                await BrowseRecursiveAsync(session, childId, descriptors, visited, ct).ConfigureAwait(false);
+            }
+        }
+
+        /// <summary>Reads a variable's DataType attribute and maps it to a built-in type name; "" on failure.</summary>
+        private static async Task<string> ReadDataTypeNameAsync(ISession session, NodeId variable, CancellationToken ct)
+        {
+            try
+            {
+                var toRead = new ReadValueIdCollection
+                {
+                    new ReadValueId { NodeId = variable, AttributeId = Attributes.DataType },
+                };
+                ReadResponse response =
+                    await session.ReadAsync(null, 0, TimestampsToReturn.Neither, toRead, ct).ConfigureAwait(false);
+                DataValueCollection values = response.Results;
+                if (values != null && values.Count > 0 && StatusCode.IsGood(values[0].StatusCode) && values[0].Value is NodeId dtId)
+                {
+                    BuiltInType bt = Opc.Ua.TypeInfo.GetBuiltInType(dtId);
+                    return bt != BuiltInType.Null ? bt.ToString() : dtId.ToString();
+                }
+            }
+            catch
+            {
+                // Best-effort enrichment; the descriptor is still valid without a data type.
+            }
+            return "";
+        }
+
+        private IUserIdentity BuildIdentity()
+        {
+            if (string.Equals(_authMode, "UsernamePassword", StringComparison.OrdinalIgnoreCase))
+            {
+                return new UserIdentity(_username ?? "", System.Text.Encoding.UTF8.GetBytes(_password ?? ""));
+            }
+            return new UserIdentity();
+        }
+
+        private async Task<ApplicationConfiguration> BuildConfigurationAsync(CancellationToken ct)
+        {
+            if (_appConfig != null)
+            {
+                return _appConfig;
+            }
+
+            string pkiRoot = Path.Combine(
+                Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
+                ApplicationName,
+                "pki");
+            string own = Path.Combine(pkiRoot, "own");
+            string trusted = Path.Combine(pkiRoot, "trusted");
+            string issuer = Path.Combine(pkiRoot, "issuer");
+            string rejected = Path.Combine(pkiRoot, "rejected");
+            Directory.CreateDirectory(own);
+            Directory.CreateDirectory(trusted);
+            Directory.CreateDirectory(issuer);
+            Directory.CreateDirectory(rejected);
+
+            bool secure = !string.Equals(_securityMode, "None", StringComparison.OrdinalIgnoreCase);
+            int operationTimeoutMs = (int)Math.Max(1000, _timeout.TotalMilliseconds);
+
+            var config = new ApplicationConfiguration
+            {
+                ApplicationName = ApplicationName,
+                ApplicationUri = "urn:localhost:" + ApplicationName,
+                ApplicationType = ApplicationType.Client,
+                SecurityConfiguration = new SecurityConfiguration
+                {
+                    ApplicationCertificate = new CertificateIdentifier
+                    {
+                        StoreType = CertificateStoreType.Directory,
+                        StorePath = own,
+                        SubjectName = "CN=" + ApplicationName + ", O=Junction",
+                    },
+                    TrustedPeerCertificates = new CertificateTrustList
+                    {
+                        StoreType = CertificateStoreType.Directory,
+                        StorePath = trusted,
+                    },
+                    TrustedIssuerCertificates = new CertificateTrustList
+                    {
+                        StoreType = CertificateStoreType.Directory,
+                        StorePath = issuer,
+                    },
+                    RejectedCertificateStore = new CertificateStoreIdentifier
+                    {
+                        StoreType = CertificateStoreType.Directory,
+                        StorePath = rejected,
+                    },
+                    // SecurityMode=None has no peer trust to establish, so accept untrusted server certs.
+                    AutoAcceptUntrustedCertificates = !secure,
+                    AddAppCertToTrustedStore = true,
+                },
+                TransportConfigurations = new TransportConfigurationCollection(),
+                TransportQuotas = new TransportQuotas { OperationTimeout = operationTimeoutMs },
+                ClientConfiguration = new ClientConfiguration { DefaultSessionTimeout = 60000 },
+                TraceConfiguration = new TraceConfiguration(),
+            };
+
+            await config.ValidateAsync(ApplicationType.Client, ct).ConfigureAwait(false);
+
+            var appInstance = new ApplicationInstance(config, _telemetry);
+            // Auto-generate the app-instance certificate if absent (silent, default lifetime).
+            await appInstance.CheckApplicationInstanceCertificatesAsync(true, null, ct).ConfigureAwait(false);
+
+            _appConfig = config;
+            return config;
+        }
+
+        public void Dispose()
+        {
+            // Session : IDisposable — disposing closes the channel/session.
+            _session?.Dispose();
+            _session = null;
+        }
+    }
+}

src/Junction.Protocols.OpcUa/UaReadResult.cs

@@ -0,0 +1,31 @@
+using System;
+
+namespace Junction.Protocols.OpcUa
+{
+    /// <summary>
+    /// Protocol-agnostic result of reading a single OPC UA node's Value attribute. Keeps SDK types
+    /// out of <see cref="IUaClient"/> so the driver is testable without a live server.
+    /// </summary>
+    public sealed class UaReadResult
+    {
+        /// <summary>The node id that was read (as configured, e.g. "ns=2;s=Temperature").</summary>
+        public string NodeId { get; }
+
+        /// <summary>Value rendered as string to stay type-agnostic; empty when null/unreadable.</summary>
+        public string Value { get; }
+
+        /// <summary>True when the read StatusCode was Good.</summary>
+        public bool StatusOk { get; }
+
+        /// <summary>Source timestamp reported by the server for the value.</summary>
+        public DateTimeOffset SourceTimestamp { get; }
+
+        public UaReadResult(string nodeId, string value, bool statusOk, DateTimeOffset sourceTimestamp)
+        {
+            NodeId = nodeId ?? "";
+            Value = value ?? "";
+            StatusOk = statusOk;
+            SourceTimestamp = sourceTimestamp;
+        }
+    }
+}

src/Junction.Protocols.OpcUa/plugin.manifest.json

@@ -0,0 +1,7 @@
+{
+  "protocolId": "opcua",
+  "displayName": "OPC UA",
+  "assemblyFile": "Junction.Protocols.OpcUa.dll",
+  "entryTypeName": "Junction.Protocols.OpcUa.OpcuaDriverFactory",
+  "apiVersion": "1.0"
+}

tests/Junction.Tests/Junction.Tests.csproj

@@ -26,6 +26,9 @@
     <ProjectReference Include="..\..\src\Junction.Core\Junction.Core.csproj" />
     <ProjectReference Include="..\..\src\Junction.Persistence\Junction.Persistence.csproj" />
     <ProjectReference Include="..\..\src\Junction.Protocols.MTConnect\Junction.Protocols.MTConnect.csproj" />
+    <ProjectReference Include="..\..\src\Junction.Protocols.OpcUa\Junction.Protocols.OpcUa.csproj" />
+    <!-- App reference resolves its net8.0 target (tests are net8.0-only); covers view-layer converters. -->
+    <ProjectReference Include="..\..\src\Junction.App\Junction.App.csproj" />
   </ItemGroup>
 
   <ItemGroup>

tests/Junction.Tests/Unit/OpcuaDriverFactoryTests.cs

@@ -0,0 +1,176 @@
+using System;
+using System.Collections.Generic;
+using Junction.Domain.Models;
+using Junction.Protocols.OpcUa;
+using Xunit;
+
+namespace Junction.Tests.Unit
+{
+    /// <summary>
+    /// Config-validation tests for <see cref="OpcuaDriverFactory"/>, mirroring
+    /// MtconnectDriverFactory tests: required/absolute/scheme checks, enum checks, the
+    /// UsernamePassword credential rule and case-insensitive key lookup.
+    /// </summary>
+    public sealed class OpcuaDriverFactoryTests
+    {
+        private static readonly Guid MachineId = Guid.Parse("99999999-8888-7777-6666-555555555555");
+        private const string EndpointUrl = "opc.tcp://opcua-server.test:4840";
+
+        private static Machine MachineWithConfig(IReadOnlyDictionary<string, string>? config) =>
+            new Machine(MachineId, "PLC-01", "opcua", config, TimeSpan.FromSeconds(5));
+
+        [Fact]
+        public void ProtocolId_IsOpcua()
+        {
+            Assert.Equal("opcua", new OpcuaDriverFactory().ProtocolId);
+        }
+
+        [Fact]
+        public void MissingEndpointUrl_ReturnsFail()
+        {
+            var result = new OpcuaDriverFactory().Create(MachineWithConfig(new Dictionary<string, string>()));
+
+            Assert.False(result.IsSuccess);
+            Assert.Contains(result.Errors, e => e.Code == "CONFIG_ENDPOINTURL_MISSING");
+        }
+
+        [Fact]
+        public void NonAbsoluteEndpointUrl_ReturnsFail()
+        {
+            var result = new OpcuaDriverFactory().Create(MachineWithConfig(
+                new Dictionary<string, string> { ["EndpointUrl"] = "not a uri" }));
+
+            Assert.False(result.IsSuccess);
+            Assert.Contains(result.Errors, e => e.Code == "CONFIG_ENDPOINTURL_INVALID");
+        }
+
+        [Fact]
+        public void WrongScheme_ReturnsFail()
+        {
+            var result = new OpcuaDriverFactory().Create(MachineWithConfig(
+                new Dictionary<string, string> { ["EndpointUrl"] = "http://opcua-server.test:4840" }));
+
+            Assert.False(result.IsSuccess);
+            Assert.Contains(result.Errors, e => e.Code == "CONFIG_ENDPOINTURL_SCHEME");
+        }
+
+        [Fact]
+        public void ValidEndpointUrl_ReturnsOkDriverWithOpcuaProtocolId()
+        {
+            var result = new OpcuaDriverFactory().Create(MachineWithConfig(
+                new Dictionary<string, string> { ["EndpointUrl"] = EndpointUrl }));
+
+            Assert.True(result.IsSuccess);
+            Assert.NotNull(result.Value);
+            Assert.Equal("opcua", result.Value.ProtocolId);
+        }
+
+        [Fact]
+        public void EndpointUrlKeyIsCaseInsensitive()
+        {
+            var result = new OpcuaDriverFactory().Create(MachineWithConfig(
+                new Dictionary<string, string> { ["endpointurl"] = EndpointUrl }));
+
+            Assert.True(result.IsSuccess);
+        }
+
+        [Fact]
+        public void InvalidSecurityMode_ReturnsFail()
+        {
+            var result = new OpcuaDriverFactory().Create(MachineWithConfig(new Dictionary<string, string>
+            {
+                ["EndpointUrl"] = EndpointUrl,
+                ["SecurityMode"] = "Bogus",
+            }));
+
+            Assert.False(result.IsSuccess);
+            Assert.Contains(result.Errors, e => e.Code == "CONFIG_SECURITYMODE_INVALID");
+        }
+
+        [Fact]
+        public void InvalidAuthMode_ReturnsFail()
+        {
+            var result = new OpcuaDriverFactory().Create(MachineWithConfig(new Dictionary<string, string>
+            {
+                ["EndpointUrl"] = EndpointUrl,
+                ["AuthMode"] = "Kerberos",
+            }));
+
+            Assert.False(result.IsSuccess);
+            Assert.Contains(result.Errors, e => e.Code == "CONFIG_AUTHMODE_INVALID");
+        }
+
+        [Fact]
+        public void UsernamePasswordWithoutUsername_ReturnsFail()
+        {
+            var result = new OpcuaDriverFactory().Create(MachineWithConfig(new Dictionary<string, string>
+            {
+                ["EndpointUrl"] = EndpointUrl,
+                ["AuthMode"] = "UsernamePassword",
+                ["Password"] = "secret",
+            }));
+
+            Assert.False(result.IsSuccess);
+            Assert.Contains(result.Errors, e => e.Code == "CONFIG_USERNAME_MISSING");
+        }
+
+        [Fact]
+        public void UsernamePasswordWithoutPassword_ReturnsFail()
+        {
+            var result = new OpcuaDriverFactory().Create(MachineWithConfig(new Dictionary<string, string>
+            {
+                ["EndpointUrl"] = EndpointUrl,
+                ["AuthMode"] = "UsernamePassword",
+                ["Username"] = "admin",
+            }));
+
+            Assert.False(result.IsSuccess);
+            Assert.Contains(result.Errors, e => e.Code == "CONFIG_PASSWORD_MISSING");
+        }
+
+        [Fact]
+        public void UsernamePasswordWithCredentials_ReturnsOk()
+        {
+            var result = new OpcuaDriverFactory().Create(MachineWithConfig(new Dictionary<string, string>
+            {
+                ["EndpointUrl"] = EndpointUrl,
+                ["AuthMode"] = "UsernamePassword",
+                ["Username"] = "admin",
+                ["Password"] = "secret",
+            }));
+
+            Assert.True(result.IsSuccess);
+        }
+
+        [Fact]
+        public void InvalidTimeout_ReturnsFail()
+        {
+            var result = new OpcuaDriverFactory().Create(MachineWithConfig(new Dictionary<string, string>
+            {
+                ["EndpointUrl"] = EndpointUrl,
+                ["TimeoutSeconds"] = "-5",
+            }));
+
+            Assert.False(result.IsSuccess);
+            Assert.Contains(result.Errors, e => e.Code == "CONFIG_TIMEOUT_INVALID");
+        }
+
+        [Fact]
+        public void FullValidConfig_ReturnsOk()
+        {
+            var result = new OpcuaDriverFactory().Create(MachineWithConfig(new Dictionary<string, string>
+            {
+                ["EndpointUrl"] = EndpointUrl,
+                ["SecurityMode"] = "SignAndEncrypt",
+                ["SecurityPolicy"] = "Basic256Sha256",
+                ["AuthMode"] = "Anonymous",
+                ["NodeIds"] = "ns=2;s=Temp, ns=2;s=Speed",
+                ["BrowseRoot"] = "i=85",
+                ["TimeoutSeconds"] = "15",
+            }));
+
+            Assert.True(result.IsSuccess);
+            Assert.Equal("opcua", result.Value.ProtocolId);
+        }
+    }
+}

tests/Junction.Tests/Unit/OpcuaDriverTests.cs

@@ -0,0 +1,218 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Junction.Domain.Models;
+using Junction.Domain.Protocols;
+using Junction.Protocols.OpcUa;
+using Moq;
+using Xunit;
+
+namespace Junction.Tests.Unit
+{
+    /// <summary>
+    /// Drives <see cref="OpcuaDriver"/> against a mocked <see cref="IUaClient"/> (no live server),
+    /// mirroring MtconnectDriverTests. Exercises the read/browse happy paths, the opt-in selection
+    /// filter, transport-failure mapping and cancellation.
+    /// </summary>
+    public sealed class OpcuaDriverTests
+    {
+        private static readonly Guid MachineId = Guid.Parse("11111111-2222-3333-4444-555555555555");
+        private const string BrowseRoot = "i=85";
+        private static readonly TimeSpan GenerousTimeout = TimeSpan.FromSeconds(30);
+
+        // Node ids configured for ReadCurrentAsync.
+        private static readonly string[] ConfiguredNodes = { "ns=2;s=Temp", "ns=2;s=Speed", "ns=2;s=State" };
+
+        private static IReadOnlyList<UaReadResult> FakeReads() => new List<UaReadResult>
+        {
+            new UaReadResult("ns=2;s=Temp", "21.5", true, DateTimeOffset.UtcNow),
+            new UaReadResult("ns=2;s=Speed", "1500", true, DateTimeOffset.UtcNow),
+            new UaReadResult("ns=2;s=State", "RUNNING", true, DateTimeOffset.UtcNow),
+        };
+
+        private static OpcuaDriver DriverWith(
+            IUaClient client,
+            IReadOnlyList<string>? nodeIds = null,
+            IReadOnlyCollection<string>? monitoredItemIds = null,
+            TimeSpan? timeout = null) =>
+            new OpcuaDriver(
+                client,
+                MachineId,
+                nodeIds ?? ConfiguredNodes,
+                BrowseRoot,
+                timeout ?? GenerousTimeout,
+                monitoredItemIds ?? ConfiguredNodes);
+
+        [Fact]
+        public void ProtocolId_IsOpcua()
+        {
+            var driver = DriverWith(new Mock<IUaClient>().Object);
+            Assert.Equal("opcua", driver.ProtocolId);
+        }
+
+        // ---- ReadCurrentAsync: happy path ----
+
+        [Fact]
+        public async Task ReadCurrentAsync_ReadsConfiguredNodes_ReturnsConnectedSnapshotStampedWithMachineId()
+        {
+            var mock = new Mock<IUaClient>();
+            mock.Setup(c => c.ConnectAsync(It.IsAny<CancellationToken>())).Returns(Task.CompletedTask);
+            mock.Setup(c => c.ReadAsync(It.IsAny<IReadOnlyList<string>>(), It.IsAny<CancellationToken>()))
+                .ReturnsAsync(FakeReads());
+
+            var driver = DriverWith(mock.Object);
+            var result = await driver.ReadCurrentAsync(CancellationToken.None);
+
+            Assert.True(result.IsSuccess);
+            Assert.False(result.WasCancelled);
+            Assert.Equal(MachineId, result.Value.MachineId);
+            Assert.Equal(ConnectionState.Connected, result.Value.ConnectionState);
+            Assert.Equal(3, result.Value.Items.Count);
+            Assert.Contains(result.Value.Items, i => i.Id == "ns=2;s=Temp" && i.Value == "21.5");
+            mock.Verify(c => c.ReadAsync(It.IsAny<IReadOnlyList<string>>(), It.IsAny<CancellationToken>()), Times.Once);
+        }
+
+        // ---- ReadCurrentAsync: opt-in selection filter ----
+
+        [Fact]
+        public async Task ReadCurrentAsync_SelectionSubset_KeepsOnlySelectedItems_PreservesConnectionState()
+        {
+            var mock = new Mock<IUaClient>();
+            mock.Setup(c => c.ReadAsync(It.IsAny<IReadOnlyList<string>>(), It.IsAny<CancellationToken>()))
+                .ReturnsAsync(FakeReads());
+
+            var selection = new[] { "ns=2;s=Temp", "ns=2;s=State" };
+            var driver = DriverWith(mock.Object, monitoredItemIds: selection);
+            var result = await driver.ReadCurrentAsync(CancellationToken.None);
+
+            Assert.True(result.IsSuccess);
+            Assert.Equal(2, result.Value.Items.Count);
+            Assert.Contains(result.Value.Items, i => i.Id == "ns=2;s=Temp");
+            Assert.Contains(result.Value.Items, i => i.Id == "ns=2;s=State");
+            Assert.DoesNotContain(result.Value.Items, i => i.Id == "ns=2;s=Speed");
+            Assert.Equal(ConnectionState.Connected, result.Value.ConnectionState);
+        }
+
+        [Fact]
+        public async Task ReadCurrentAsync_EmptySelection_ReturnsEmptyItems_PreservesConnectionState()
+        {
+            var mock = new Mock<IUaClient>();
+            mock.Setup(c => c.ReadAsync(It.IsAny<IReadOnlyList<string>>(), It.IsAny<CancellationToken>()))
+                .ReturnsAsync(FakeReads());
+
+            var driver = DriverWith(mock.Object, monitoredItemIds: Array.Empty<string>());
+            var result = await driver.ReadCurrentAsync(CancellationToken.None);
+
+            Assert.True(result.IsSuccess);
+            Assert.Empty(result.Value.Items);
+            Assert.Equal(ConnectionState.Connected, result.Value.ConnectionState);
+        }
+
+        // ---- ReadCurrentAsync: failure + cancellation ----
+
+        [Fact]
+        public async Task ReadCurrentAsync_ClientThrows_ReturnsFailNoThrow()
+        {
+            var mock = new Mock<IUaClient>();
+            mock.Setup(c => c.ReadAsync(It.IsAny<IReadOnlyList<string>>(), It.IsAny<CancellationToken>()))
+                .ThrowsAsync(new InvalidOperationException("server unreachable"));
+
+            var driver = DriverWith(mock.Object);
+            var result = await driver.ReadCurrentAsync(CancellationToken.None);
+
+            Assert.False(result.IsSuccess);
+            Assert.False(result.WasCancelled);
+            Assert.Contains(result.Errors, e => e.Code == "CURRENT_READ_ERROR");
+        }
+
+        [Fact]
+        public async Task ReadCurrentAsync_CancelledBeforeCall_ReturnsCancelled()
+        {
+            var mock = new Mock<IUaClient>();
+            var driver = DriverWith(mock.Object);
+            using var cts = new CancellationTokenSource();
+            cts.Cancel();
+
+            var result = await driver.ReadCurrentAsync(cts.Token);
+
+            Assert.False(result.IsSuccess);
+            Assert.True(result.WasCancelled);
+        }
+
+        [Fact]
+        public async Task ReadCurrentAsync_CancelledDuringCall_ReturnsCancelledNoThrow()
+        {
+            var mock = new Mock<IUaClient>();
+            using var cts = new CancellationTokenSource();
+            mock.Setup(c => c.ReadAsync(It.IsAny<IReadOnlyList<string>>(), It.IsAny<CancellationToken>()))
+                .Returns<IReadOnlyList<string>, CancellationToken>(async (_, ct) =>
+                {
+                    cts.Cancel();
+                    await Task.Delay(Timeout.Infinite, ct).ConfigureAwait(false);
+                    return FakeReads();
+                });
+
+            var driver = DriverWith(mock.Object);
+            var result = await driver.ReadCurrentAsync(cts.Token);
+
+            Assert.False(result.IsSuccess);
+            Assert.True(result.WasCancelled);
+        }
+
+        // ---- ProbeAsync: catalog ----
+
+        [Fact]
+        public async Task ProbeAsync_BrowsesFromRoot_ReturnsDescriptors()
+        {
+            var descriptors = new List<DataItemDescriptor>
+            {
+                new DataItemDescriptor("ns=2;s=Temp", "Temperature", "Double", "VARIABLE", ""),
+                new DataItemDescriptor("ns=2;s=Speed", "Speed", "Int32", "VARIABLE", ""),
+            };
+            var mock = new Mock<IUaClient>();
+            mock.Setup(c => c.BrowseAsync(BrowseRoot, It.IsAny<CancellationToken>()))
+                .ReturnsAsync(descriptors);
+
+            var driver = DriverWith(mock.Object);
+            var result = await driver.ProbeAsync(CancellationToken.None);
+
+            Assert.True(result.IsSuccess);
+            Assert.Equal(2, result.Value.Count);
+            var temp = result.Value.Single(d => d.Id == "ns=2;s=Temp");
+            Assert.Equal("Temperature", temp.Name);
+            Assert.Equal("Double", temp.Type);
+            Assert.Equal("VARIABLE", temp.Category);
+            mock.Verify(c => c.BrowseAsync(BrowseRoot, It.IsAny<CancellationToken>()), Times.Once);
+        }
+
+        [Fact]
+        public async Task ProbeAsync_ClientThrows_ReturnsFailNoThrow()
+        {
+            var mock = new Mock<IUaClient>();
+            mock.Setup(c => c.BrowseAsync(It.IsAny<string>(), It.IsAny<CancellationToken>()))
+                .ThrowsAsync(new InvalidOperationException("browse failed"));
+
+            var driver = DriverWith(mock.Object);
+            var result = await driver.ProbeAsync(CancellationToken.None);
+
+            Assert.False(result.IsSuccess);
+            Assert.Contains(result.Errors, e => e.Code == "PROBE_BROWSE_ERROR");
+        }
+
+        [Fact]
+        public async Task ProbeAsync_CancelledBeforeCall_ReturnsCancelled()
+        {
+            var mock = new Mock<IUaClient>();
+            var driver = DriverWith(mock.Object);
+            using var cts = new CancellationTokenSource();
+            cts.Cancel();
+
+            var result = await driver.ProbeAsync(cts.Token);
+
+            Assert.False(result.IsSuccess);
+            Assert.True(result.WasCancelled);
+        }
+    }
+}

tests/Junction.Tests/Unit/ProtocolIdToIconConverterTests.cs

@@ -0,0 +1,78 @@
+using Junction.App.Converters;
+using Xunit;
+
+namespace Junction.Tests.Unit
+{
+    /// <summary>
+    /// Data-level tests for the protocol → glyph mapping. Targets the pure
+    /// <see cref="ProtocolIdToIconConverter.PathDataFor"/> so no Avalonia platform is required
+    /// (the geometry parse in Convert needs a render backend). Mirrors the intent of the
+    /// StatusKind converter: known ids → distinct non-empty data, unknown → fallback, never throws.
+    /// </summary>
+    public class ProtocolIdToIconConverterTests
+    {
+        [Theory]
+        [InlineData("mtconnect")]
+        [InlineData("opcua")]
+        [InlineData("fanuc")]
+        public void KnownProtocol_ReturnsNonEmptyData(string protocolId)
+        {
+            var data = ProtocolIdToIconConverter.PathDataFor(protocolId);
+
+            Assert.False(string.IsNullOrWhiteSpace(data));
+        }
+
+        [Fact]
+        public void KnownProtocols_AreMutuallyDistinct()
+        {
+            var mtc = ProtocolIdToIconConverter.PathDataFor("mtconnect");
+            var opc = ProtocolIdToIconConverter.PathDataFor("opcua");
+            var fan = ProtocolIdToIconConverter.PathDataFor("fanuc");
+
+            Assert.NotEqual(mtc, opc);
+            Assert.NotEqual(mtc, fan);
+            Assert.NotEqual(opc, fan);
+        }
+
+        [Fact]
+        public void Lookup_IsCaseAndWhitespaceInsensitive()
+        {
+            var canonical = ProtocolIdToIconConverter.PathDataFor("mtconnect");
+
+            Assert.Equal(canonical, ProtocolIdToIconConverter.PathDataFor("  MtConnect  "));
+        }
+
+        [Theory]
+        [InlineData("unknown")]
+        [InlineData("modbus")]
+        [InlineData("")]
+        public void UnknownOrEmpty_ReturnsFallback(string protocolId)
+        {
+            var fallback = ProtocolIdToIconConverter.PathDataFor("definitely-not-a-protocol");
+            var data = ProtocolIdToIconConverter.PathDataFor(protocolId);
+
+            Assert.False(string.IsNullOrWhiteSpace(data));
+            Assert.Equal(fallback, data);
+        }
+
+        [Fact]
+        public void Null_ReturnsFallback_DoesNotThrow()
+        {
+            var fallback = ProtocolIdToIconConverter.PathDataFor("definitely-not-a-protocol");
+            var data = ProtocolIdToIconConverter.PathDataFor(null);
+
+            Assert.False(string.IsNullOrWhiteSpace(data));
+            Assert.Equal(fallback, data);
+        }
+
+        [Fact]
+        public void Fallback_DiffersFromEveryKnownProtocol()
+        {
+            var fallback = ProtocolIdToIconConverter.PathDataFor("unknown");
+
+            Assert.NotEqual(fallback, ProtocolIdToIconConverter.PathDataFor("mtconnect"));
+            Assert.NotEqual(fallback, ProtocolIdToIconConverter.PathDataFor("opcua"));
+            Assert.NotEqual(fallback, ProtocolIdToIconConverter.PathDataFor("fanuc"));
+        }
+    }
+}