PR 5.4 — Write-by-classification parity scenarios

Both backends route a write through the same path keyed off the attribute's
SecurityClassification, so a single write request must produce the same
StatusCode on each:

- FreeAccess_or_Operate_write_returns_same_StatusCode_on_both_backends
  picks the first numeric FreeAccess/Operate attribute and writes 0.0.
- Configure_class_write_routes_through_secured_path_on_both_backends
  picks a Configure/Tune attribute, writes through the secured path,
  asserts StatusCode parity (the test doesn't care whether the write
  succeeds — only that both backends produce the same outcome).

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

tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.ParityTests/WriteByClassificationParityTests.cs

@@ -0,0 +1,71 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.ParityTests;
+
+/// <summary>
+///     PR 5.4 — Write-by-classification parity. Each driver routes writes by the
+///     attribute's <see cref="SecurityClassification"/>: <c>FreeAccess</c> /
+///     <c>Operate</c> use plain <c>Write</c>; <c>Tune</c> / <c>Configure</c> /
+///     <c>VerifiedWrite</c> use <c>WriteSecured</c>. Both backends must surface the
+///     same StatusCode for the same write request — successful for FreeAccess /
+///     Operate (assuming the dev Galaxy has at least one writable attribute) and
+///     failure for Configure when no auth principal is supplied.
+/// </summary>
+[Trait("Category", "ParityE2E")]
+[Collection(nameof(ParityCollection))]
+public sealed class WriteByClassificationParityTests
+{
+    private readonly ParityHarness _h;
+    public WriteByClassificationParityTests(ParityHarness h) => _h = h;
+
+    [Fact]
+    public async Task FreeAccess_or_Operate_write_returns_same_StatusCode_on_both_backends()
+    {
+        _h.RequireBoth();
+
+        var b = new RecordingAddressSpaceBuilder();
+        await ((ITagDiscovery)_h.LegacyDriver!).DiscoverAsync(b, CancellationToken.None);
+
+        var target = b.Variables.FirstOrDefault(v =>
+            v.AttributeInfo.SecurityClass is SecurityClassification.FreeAccess or SecurityClassification.Operate
+            && v.AttributeInfo.DriverDataType is DriverDataType.Float32 or DriverDataType.Float64 or DriverDataType.Int32);
+        if (target is null) Assert.Skip("no FreeAccess/Operate numeric writable attribute on dev Galaxy");
+
+        var request = new[] { new WriteRequest(target.AttributeInfo.FullName, 0.0) };
+        var results = await _h.RunOnAvailableAsync(
+            (driver, ct) => ((IWritable)driver).WriteAsync(request, ct),
+            CancellationToken.None);
+
+        results[ParityHarness.Backend.LegacyHost][0].StatusCode
+            .ShouldBe(results[ParityHarness.Backend.MxGateway][0].StatusCode,
+                $"FreeAccess/Operate StatusCode parity for '{target.AttributeInfo.FullName}'");
+    }
+
+    [Fact]
+    public async Task Configure_class_write_routes_through_secured_path_on_both_backends()
+    {
+        _h.RequireBoth();
+
+        var b = new RecordingAddressSpaceBuilder();
+        await ((ITagDiscovery)_h.LegacyDriver!).DiscoverAsync(b, CancellationToken.None);
+
+        var target = b.Variables.FirstOrDefault(v =>
+            v.AttributeInfo.SecurityClass is SecurityClassification.Configure or SecurityClassification.Tune);
+        if (target is null) Assert.Skip("no Configure/Tune attribute on dev Galaxy");
+
+        var request = new[] { new WriteRequest(target.AttributeInfo.FullName, 0.0) };
+        var results = await _h.RunOnAvailableAsync(
+            (driver, ct) => ((IWritable)driver).WriteAsync(request, ct),
+            CancellationToken.None);
+
+        // Both backends route through the secured-write path. The exact StatusCode
+        // depends on whether the running test identity has write permission on the
+        // dev Galaxy — what matters here is that they agree, not which value they
+        // produce. (Parity, not policy.)
+        results[ParityHarness.Backend.LegacyHost][0].StatusCode
+            .ShouldBe(results[ParityHarness.Backend.MxGateway][0].StatusCode,
+                $"Secured-write StatusCode parity for '{target.AttributeInfo.FullName}'");
+    }
+}