feat(abcip): 1-D array read via libplctag + IsArray discovery

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Contracts/AbCipDriverOptions.cs

@@ -135,6 +135,10 @@ public sealed record AbCipDeviceOptions(
 ///     GuardLogix controller; non-safety writes violate the safety-partition isolation and are
 ///     rejected by the PLC anyway. Surfaces the intent explicitly instead of relying on the
 ///     write attempt failing at runtime.</param>
+/// <param name="ElementCount">Phase 4c — number of array elements for a 1-D array tag. Defaults
+///     to 1 (scalar). When greater than 1 the tag discovers as an OPC UA array node
+///     (<c>IsArray</c> + <c>ArrayDim</c>) and reads via libplctag's <c>elem_count</c> into an
+///     element-typed CLR array. Ignored for <see cref="AbCipDataType.Structure"/>.</param>
 public sealed record AbCipTagDefinition(
     string Name,
     string DeviceHostAddress,
@@ -143,7 +147,8 @@ public sealed record AbCipTagDefinition(
     bool Writable = true,
     bool WriteIdempotent = false,
     IReadOnlyList<AbCipStructureMember>? Members = null,
-    bool SafetyTag = false);
+    bool SafetyTag = false,
+    int ElementCount = 1);
 
 /// <summary>
 ///     One declared member of a UDT tag. Name is the member identifier on the PLC (e.g. <c>Speed</c>,
@@ -155,7 +160,8 @@ public sealed record AbCipStructureMember(
     string Name,
     AbCipDataType DataType,
     bool Writable = true,
-    bool WriteIdempotent = false);
+    bool WriteIdempotent = false,
+    int ElementCount = 1);
 
 /// <summary>Which AB PLC family the device is — selects the profile applied to connection params.</summary>
 public enum AbCipPlcFamily

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Contracts/AbCipEquipmentTagParser.cs

@@ -31,9 +31,13 @@ public static class AbCipEquipmentTagParser
 
             var deviceHostAddress = ReadString(root, "deviceHostAddress");
             var dataType = ReadEnum(root, "dataType", AbCipDataType.DInt);
+            // Phase 4c — an isArray equipment tag carries arrayLength; thread it into the def's
+            // ElementCount so the read pulls the whole array via libplctag elem_count. When
+            // isArray is absent/false (or arrayLength is missing/<=1) the tag stays scalar.
+            var elementCount = ReadArrayElementCount(root);
             def = new AbCipTagDefinition(
                 Name: reference, DeviceHostAddress: deviceHostAddress, TagPath: tagPath,
-                DataType: dataType, Writable: true);
+                DataType: dataType, Writable: true, ElementCount: elementCount);
             return true;
         }
         catch (JsonException) { return false; }
@@ -41,6 +45,23 @@ public static class AbCipEquipmentTagParser
         catch (InvalidOperationException) { return false; }
     }
 
+    /// <summary>
+    ///     Resolve the 1-D array element count from an <c>isArray</c> / <c>arrayLength</c> pair.
+    ///     Returns 1 (scalar) unless <c>isArray</c> is truthy AND <c>arrayLength</c> is a number
+    ///     greater than 1; matches the sink's "isArray + arrayLength" carrier.
+    /// </summary>
+    private static int ReadArrayElementCount(JsonElement o)
+    {
+        var isArray = o.TryGetProperty("isArray", out var a) && a.ValueKind == JsonValueKind.True;
+        if (!isArray) return 1;
+        if (o.TryGetProperty("arrayLength", out var len)
+            && len.ValueKind == JsonValueKind.Number
+            && len.TryGetInt32(out var n)
+            && n > 1)
+            return n;
+        return 1;
+    }
+
     private static TEnum ReadEnum<TEnum>(JsonElement o, string name, TEnum fallback) where TEnum : struct, Enum
         => o.TryGetProperty(name, out var e) && e.ValueKind == JsonValueKind.String
            && Enum.TryParse<TEnum>(e.GetString(), ignoreCase: true, out var v) ? v : fallback;