Add cross-platform OPC UA client stack: shared library, CLI tool, and Avalonia UI

Implements Client.Shared (IOpcUaClientService with connection lifecycle, failover,
browse, read/write, subscriptions, alarms, history, redundancy), Client.CLI (8 CliFx
commands mirroring tools/opcuacli-dotnet), and Client.UI (Avalonia desktop app with
tree browser, read/write, subscriptions, alarms, and history tabs). All three target
.NET 10 and are covered by 249 unit tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/ZB.MOM.WW.LmxOpcUa.Client.Shared/Helpers/AggregateTypeMapper.cs

@@ -0,0 +1,27 @@
+using Opc.Ua;
+using ZB.MOM.WW.LmxOpcUa.Client.Shared.Models;
+
+namespace ZB.MOM.WW.LmxOpcUa.Client.Shared.Helpers;
+
+/// <summary>
+/// Maps the library's AggregateType enum to OPC UA aggregate function NodeIds.
+/// </summary>
+public static class AggregateTypeMapper
+{
+    /// <summary>
+    /// Returns the OPC UA NodeId for the specified aggregate type.
+    /// </summary>
+    public static NodeId ToNodeId(AggregateType aggregate)
+    {
+        return aggregate switch
+        {
+            AggregateType.Average => ObjectIds.AggregateFunction_Average,
+            AggregateType.Minimum => ObjectIds.AggregateFunction_Minimum,
+            AggregateType.Maximum => ObjectIds.AggregateFunction_Maximum,
+            AggregateType.Count => ObjectIds.AggregateFunction_Count,
+            AggregateType.Start => ObjectIds.AggregateFunction_Start,
+            AggregateType.End => ObjectIds.AggregateFunction_End,
+            _ => throw new ArgumentOutOfRangeException(nameof(aggregate), aggregate, "Unknown AggregateType value.")
+        };
+    }
+}

src/ZB.MOM.WW.LmxOpcUa.Client.Shared/Helpers/FailoverUrlParser.cs

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+namespace ZB.MOM.WW.LmxOpcUa.Client.Shared.Helpers;
+
+/// <summary>
+/// Parses and normalizes failover URL sets for redundant OPC UA connections.
+/// </summary>
+public static class FailoverUrlParser
+{
+    /// <summary>
+    /// Parses a comma-separated failover URL string, prepending the primary URL.
+    /// Trims whitespace and deduplicates.
+    /// </summary>
+    /// <param name="primaryUrl">The primary endpoint URL.</param>
+    /// <param name="failoverCsv">Optional comma-separated failover URLs.</param>
+    /// <returns>An array with the primary URL first, followed by unique failover URLs.</returns>
+    public static string[] Parse(string primaryUrl, string? failoverCsv)
+    {
+        if (string.IsNullOrWhiteSpace(failoverCsv))
+            return new[] { primaryUrl };
+
+        var urls = new List<string> { primaryUrl };
+        foreach (var url in failoverCsv.Split(',', StringSplitOptions.RemoveEmptyEntries))
+        {
+            var trimmed = url.Trim();
+            if (!string.IsNullOrEmpty(trimmed) && !urls.Contains(trimmed, StringComparer.OrdinalIgnoreCase))
+                urls.Add(trimmed);
+        }
+        return urls.ToArray();
+    }
+
+    /// <summary>
+    /// Builds a failover URL set from the primary URL and an optional array of failover URLs.
+    /// </summary>
+    /// <param name="primaryUrl">The primary endpoint URL.</param>
+    /// <param name="failoverUrls">Optional failover URLs.</param>
+    /// <returns>An array with the primary URL first, followed by unique failover URLs.</returns>
+    public static string[] Parse(string primaryUrl, string[]? failoverUrls)
+    {
+        if (failoverUrls == null || failoverUrls.Length == 0)
+            return new[] { primaryUrl };
+
+        var urls = new List<string> { primaryUrl };
+        foreach (var url in failoverUrls)
+        {
+            var trimmed = url?.Trim();
+            if (!string.IsNullOrEmpty(trimmed) && !urls.Contains(trimmed, StringComparer.OrdinalIgnoreCase))
+                urls.Add(trimmed);
+        }
+        return urls.ToArray();
+    }
+}

src/ZB.MOM.WW.LmxOpcUa.Client.Shared/Helpers/SecurityModeMapper.cs

@@ -0,0 +1,42 @@
+using Opc.Ua;
+using ZB.MOM.WW.LmxOpcUa.Client.Shared.Models;
+
+namespace ZB.MOM.WW.LmxOpcUa.Client.Shared.Helpers;
+
+/// <summary>
+/// Maps between the library's SecurityMode enum and OPC UA SDK MessageSecurityMode.
+/// </summary>
+public static class SecurityModeMapper
+{
+    /// <summary>
+    /// Converts a <see cref="SecurityMode"/> to an OPC UA <see cref="MessageSecurityMode"/>.
+    /// </summary>
+    public static MessageSecurityMode ToMessageSecurityMode(SecurityMode mode)
+    {
+        return mode switch
+        {
+            SecurityMode.None => MessageSecurityMode.None,
+            SecurityMode.Sign => MessageSecurityMode.Sign,
+            SecurityMode.SignAndEncrypt => MessageSecurityMode.SignAndEncrypt,
+            _ => throw new ArgumentOutOfRangeException(nameof(mode), mode, "Unknown SecurityMode value.")
+        };
+    }
+
+    /// <summary>
+    /// Parses a string to a <see cref="SecurityMode"/> value, case-insensitively.
+    /// </summary>
+    /// <param name="value">The string to parse (e.g., "none", "sign", "encrypt", "signandencrypt").</param>
+    /// <returns>The corresponding SecurityMode.</returns>
+    /// <exception cref="ArgumentException">Thrown for unrecognized values.</exception>
+    public static SecurityMode FromString(string value)
+    {
+        return (value ?? "none").Trim().ToLowerInvariant() switch
+        {
+            "none" => SecurityMode.None,
+            "sign" => SecurityMode.Sign,
+            "encrypt" or "signandencrypt" => SecurityMode.SignAndEncrypt,
+            _ => throw new ArgumentException(
+                $"Unknown security mode '{value}'. Valid values: none, sign, encrypt, signandencrypt")
+        };
+    }
+}

src/ZB.MOM.WW.LmxOpcUa.Client.Shared/Helpers/ValueConverter.cs

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+namespace ZB.MOM.WW.LmxOpcUa.Client.Shared.Helpers;
+
+/// <summary>
+/// Converts raw string values into typed values based on the current value's runtime type.
+/// Ported from the CLI tool's OpcUaHelper.ConvertValue.
+/// </summary>
+public static class ValueConverter
+{
+    /// <summary>
+    /// Converts a raw string value into the runtime type expected by the target node.
+    /// </summary>
+    /// <param name="rawValue">The raw string supplied by the user.</param>
+    /// <param name="currentValue">The current node value used to infer the target type. May be null.</param>
+    /// <returns>A typed value suitable for an OPC UA write request.</returns>
+    public static object ConvertValue(string rawValue, object? currentValue)
+    {
+        return currentValue switch
+        {
+            bool => bool.Parse(rawValue),
+            byte => byte.Parse(rawValue),
+            short => short.Parse(rawValue),
+            ushort => ushort.Parse(rawValue),
+            int => int.Parse(rawValue),
+            uint => uint.Parse(rawValue),
+            long => long.Parse(rawValue),
+            ulong => ulong.Parse(rawValue),
+            float => float.Parse(rawValue),
+            double => double.Parse(rawValue),
+            _ => rawValue
+        };
+    }
+}