fix(modbus): equipment tags carry unitId; ResolveHost keys per-unit via the resolver (CONV-4)

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Contracts/ModbusEquipmentTagParser.cs

@@ -55,10 +55,14 @@ public static class ModbusEquipmentTagParser
             // "writable" defaults to true when absent (today's value) — makes read-only equipment tags
             // authorable (UNDER-6). Node-level authz remains the effective write gate.
             var writable = TagConfigJson.ReadWritable(root);
+            // CONV-4: optional per-tag unitId (0–255). Absent ⇒ null ⇒ the driver-level UnitId via
+            // ModbusDriver.ResolveUnitId, so multi-unit equipment tags key their own per-host breaker.
+            // Scope: unitId ONLY — the remaining parser-strictness gaps are R2-11's.
+            var unitId = ReadOptionalByte(root, "unitId");
             def = new ModbusTagDefinition(
                 Name: reference, Region: region, Address: (ushort)address, DataType: dataType,
                 Writable: writable, ByteOrder: byteOrder, BitIndex: bitIndex, StringLength: stringLength,
-                ArrayCount: arrayCount);
+                ArrayCount: arrayCount, UnitId: unitId);
             return true;
         }
         catch (JsonException) { return false; }
@@ -109,6 +113,10 @@ public static class ModbusEquipmentTagParser
         => o.TryGetProperty(name, out var e) && e.ValueKind == JsonValueKind.Number
            && e.TryGetInt32(out var v) ? v : 0;
 
+    private static byte? ReadOptionalByte(JsonElement o, string name)
+        => o.TryGetProperty(name, out var e) && e.ValueKind == JsonValueKind.Number
+           && e.TryGetInt32(out var v) && v is >= 0 and <= 255 ? (byte)v : null;
+
     private static bool ReadBool(JsonElement o, string name)
         => o.TryGetProperty(name, out var e) && e.ValueKind == JsonValueKind.True;
 }