fix(adminui): preserve un-edited Modbus tag fields across edit (review)

Capture the original ModbusTagDefinition as _source in ModbusTagRow and
rewrite ToDefinition() to use 'with {}', so StringByteOrder, ArrayCount,
Deadband, UnitId, and CoalesceProhibited survive a load→edit→save cycle.

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Pages/Clusters/Drivers/ModbusDriverPage.razor

@@ -490,20 +490,36 @@ else
         public int StringLength { get; set; }
         public bool WriteIdempotent { get; set; }
 
-        public ModbusTagRow Clone() => (ModbusTagRow)MemberwiseClone();
+        // Original record (null for newly-added rows). Preserves fields the editor doesn't expose
+        // (StringByteOrder, ArrayCount, Deadband, UnitId, CoalesceProhibited) across a load→save.
+        private ModbusTagDefinition? _source;
+
+        public ModbusTagRow Clone() => (ModbusTagRow)MemberwiseClone(); // _source is an immutable record ref — safe to share
 
         public static ModbusTagRow FromDefinition(ModbusTagDefinition d) => new()
         {
             Name = d.Name, Region = d.Region, Address = d.Address, DataType = d.DataType,
             Writable = d.Writable, ByteOrder = d.ByteOrder, BitIndex = d.BitIndex,
             StringLength = d.StringLength, WriteIdempotent = d.WriteIdempotent,
+            _source = d,
         };
 
-        public ModbusTagDefinition ToDefinition() => new(
+        public ModbusTagDefinition ToDefinition()
-            Name: Name.Trim(), Region: Region, Address: (ushort)Math.Clamp(Address, 0, 65535),
+        {
-            DataType: DataType, Writable: Writable, ByteOrder: ByteOrder,
+            var baseDef = _source ?? new ModbusTagDefinition(Name.Trim(), Region, 0, DataType);
-            BitIndex: (byte)Math.Clamp(BitIndex, 0, 255), StringLength: (ushort)Math.Clamp(StringLength, 0, 65535),
+            return baseDef with
-            WriteIdempotent: WriteIdempotent);
+            {
+                Name = Name.Trim(),
+                Region = Region,
+                Address = (ushort)Math.Clamp(Address, 0, 65535),
+                DataType = DataType,
+                Writable = Writable,
+                ByteOrder = ByteOrder,
+                BitIndex = (byte)Math.Clamp(BitIndex, 0, 255),
+                StringLength = (ushort)Math.Clamp(StringLength, 0, 65535),
+                WriteIdempotent = WriteIdempotent,
+            };
+        }
 
         public static string? ValidateRow(ModbusTagRow row, IReadOnlyList<ModbusTagRow> all, int? editIndex)
         {

tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/ModbusDriverPageFormSerializationTests.cs

@@ -151,4 +151,23 @@ public sealed class ModbusDriverPageFormSerializationTests
         ModbusDriverPage.ModbusTagRow.ValidateRow(new() { Name = "A" }, rows, null)
             .ShouldNotBeNull();
     }
+
+    [Fact]
+    public void ToDefinition_preserves_unedited_fields()
+    {
+        var original = new ModbusTagDefinition(
+            "T", ModbusRegion.HoldingRegisters, 5, ModbusDataType.Int16,
+            StringByteOrder: ModbusStringByteOrder.LowByteFirst,
+            ArrayCount: 10, Deadband: 0.5, UnitId: 3, CoalesceProhibited: true);
+        var row = ModbusDriverPage.ModbusTagRow.FromDefinition(original);
+        row.Name = "Renamed";
+
+        var back = row.ToDefinition();
+        back.Name.ShouldBe("Renamed");
+        back.UnitId.ShouldBe((byte)3);
+        back.ArrayCount.ShouldBe(10);
+        back.Deadband.ShouldBe(0.5);
+        back.StringByteOrder.ShouldBe(ModbusStringByteOrder.LowByteFirst);
+        back.CoalesceProhibited.ShouldBeTrue();
+    }
 }