review(Driver.AbLegacy): fix Bit write 1-byte/2-byte encode-decode mismatch (Medium)

Re-review at 7286d320. -014 (Medium): Bit EncodeValue (no bitIndex) wrote SetInt8 while
DecodeValue read GetInt16 on a 16-bit B-file element, so a false write could round-trip
as true (stale high byte). Fix: SetInt16 + TDD. -015: tests pass CancellationToken.

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

@@ -89,7 +89,7 @@ public sealed class AbLegacyCapabilityTests
 
         var afterUnsub = events.Count;
         tagRef.Value = 999;
-        await Task.Delay(300);
+        await Task.Delay(300, TestContext.Current.CancellationToken);
         events.Count.ShouldBe(afterUnsub);
     }
 
@@ -171,7 +171,7 @@ public sealed class AbLegacyCapabilityTests
             Probe = new AbLegacyProbeOptions { Enabled = true, ProbeAddress = null },
         }, "drv-1");
         await drv.InitializeAsync("{}", CancellationToken.None);
-        await Task.Delay(200);
+        await Task.Delay(200, TestContext.Current.CancellationToken);
 
         drv.GetHostStatuses().Single().State.ShouldBe(HostState.Unknown);
         await drv.ShutdownAsync(CancellationToken.None);

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

@@ -189,6 +189,40 @@ public sealed class AbLegacyReadWriteTests
         results.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.Good);
     }
 
+    /// <summary>
+    ///     Driver.AbLegacy-014 — a Bit-typed tag with no bit suffix (e.g. B3:0, DataType=Bit)
+    ///     takes the EncodeValue(Bit, bitIndex:null, …) path (not RMW). The encode must be
+    ///     symmetric with the DecodeValue path, which reads the full 16-bit word via GetInt16.
+    ///     Through the fake factory this verifies the driver dispatches through EncodeValue with
+    ///     the right arguments; the SetInt16/SetInt8 delta is exercised against a live PLC.
+    /// </summary>
+    [Fact]
+    public async Task Bit_tag_without_suffix_writes_via_EncodeValue_not_RMW()
+    {
+        // A Bit-typed tag with NO /N bit suffix — bitIndex is null, so write must NOT
+        // route through WriteBitInWordAsync (which requires bitIndex). Instead it goes
+        // through EncodeValue(Bit, null, value) on the tag's own runtime, not a parent runtime.
+        var factory = new FakeAbLegacyTagFactory();
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions("ab://10.0.0.5/1,0")],
+            Tags = [new AbLegacyTagDefinition("Flag", "ab://10.0.0.5/1,0", "B3:0", AbLegacyDataType.Bit)],
+            Probe = new AbLegacyProbeOptions { Enabled = false },
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest("Flag", true)], CancellationToken.None);
+
+        // Must succeed (Good) and route through the tag's own runtime, NOT a parent runtime.
+        results.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.Good);
+        factory.Tags.ShouldContainKey("B3:0");
+        factory.Tags.ShouldNotContainKey("B3");  // no parent-word runtime created
+        factory.Tags["B3:0"].WriteCount.ShouldBe(1);
+        // FakeAbLegacyTag.EncodeValue stores the raw value; verify it received true.
+        factory.Tags["B3:0"].Value.ShouldBe(true);
+    }
+
     /// <summary>Verifies that write exceptions surface as BadCommunicationError.</summary>
     [Fact]
     public async Task Write_exception_surfaces_BadCommunicationError()