test(ablegacy): bit write surfaces device rejection status (review)

Adds `Bit_write_surfaces_device_rejection_status` to AbLegacyBitRmwTests,
verifying that a non-zero libplctag status returned by the parent-word write
in WriteBitInWordAsync propagates as a non-Good OPC UA StatusCode rather than
being silently swallowed. Added a minimal `WriteStatusOverride` hook to
FakeAbLegacyTag (test-project-only) so the read half of the RMW still
returns 0/Good while the write half returns the seeded error code.

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyBitRmwTests.cs

@@ -177,4 +177,38 @@ public sealed class AbLegacyBitRmwTests
 
         Convert.ToInt32(factory.Tags["B3:0"].Value).ShouldBe(0xFF);
     }
+
+    /// <summary>
+    ///     A non-zero libplctag status returned by the parent-word write is surfaced as a non-Good
+    ///     OPC UA StatusCode — the PCCC device rejection propagates to the caller.
+    /// </summary>
+    [Fact]
+    public async Task Bit_write_surfaces_device_rejection_status()
+    {
+        // Arrange: the parent tag reads OK (Status = 0) but write returns a timeout error.
+        const int errorTimeout = (int)libplctag.Status.ErrorTimeout;
+        var factory = new FakeAbLegacyTagFactory
+        {
+            Customise = p => new FakeAbLegacyTag(p)
+            {
+                Value = (short)0b0001,
+                WriteStatusOverride = errorTimeout,
+            },
+        };
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions("ab://10.0.0.5/1,0")],
+            Tags = [new AbLegacyTagDefinition("F", "ab://10.0.0.5/1,0", "I:0/3", AbLegacyDataType.Bit)],
+            Probe = new AbLegacyProbeOptions { Enabled = false },
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        // Act
+        var results = await drv.WriteAsync([new WriteRequest("F", true)], CancellationToken.None);
+
+        // Assert: the write rejection must NOT be silently swallowed as Good.
+        var statusCode = results.Single().StatusCode;
+        statusCode.ShouldNotBe(AbLegacyStatusMapper.Good);
+        statusCode.ShouldBe(AbLegacyStatusMapper.MapLibplctagStatus(errorTimeout));
+    }
 }

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/FakeAbLegacyTag.cs

@@ -17,9 +17,16 @@ internal class FakeAbLegacyTag : IAbLegacyTagRuntime
     /// </summary>
     public object? ArrayValue { get; set; }
 
-    /// <summary>Gets or sets the tag status code.</summary>
+    /// <summary>Gets or sets the tag status code (returned by <see cref="GetStatus"/> for reads).</summary>
     public int Status { get; set; }
 
+    /// <summary>
+    ///     Gets or sets an optional status code that overrides <see cref="Status"/> once a write
+    ///     has been performed (i.e. after <see cref="WriteCount"/> becomes &gt; 0). Lets tests seed
+    ///     a write-rejection status without also failing the preceding read.
+    /// </summary>
+    public int? WriteStatusOverride { get; set; }
+
     /// <summary>Gets or sets a value indicating whether to throw on initialization.</summary>
     public bool ThrowOnInitialize { get; set; }
 
@@ -80,7 +87,8 @@ internal class FakeAbLegacyTag : IAbLegacyTagRuntime
 
     /// <summary>Gets the current tag status.</summary>
     /// <returns>The status code.</returns>
-    public virtual int GetStatus() => Status;
+    public virtual int GetStatus() =>
+        WriteStatusOverride.HasValue && WriteCount > 0 ? WriteStatusOverride.Value : Status;
 
     /// <summary>Decodes the tag value based on the specified data type and bit index.</summary>
     /// <param name="type">The AbLegacy data type.</param>