fix(s7): treat ArrayCount>=1 as array so 1-element arrays read as arrays (review I-2)

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7/S7Driver.cs

@@ -442,11 +442,12 @@ public sealed class S7Driver
             ? parsed
             : S7AddressParser.Parse(tag.Address);
 
-        // Array path: a tag with a declared count > 1 reads a CONTIGUOUS block of
+        // Array path: a tag with a declared count >= 1 reads a CONTIGUOUS block of
         // count × element-bytes in a SINGLE round-trip (Plc.ReadBytesAsync), then decodes each
         // element from its big-endian slice into an element-typed CLR array. The scalar path
-        // (count null / <= 1) is left byte-for-byte unchanged below.
+        // (count null) is left byte-for-byte unchanged below. A count of 1 IS a valid 1-element
-        if (tag.ArrayCount is > 1)
+        // array (the foundation materialises a [1] OPC UA array node when isArray:true).
+        if (tag.ArrayCount is >= 1)
             return await ReadArrayAsync(plc, tag, addr, ct).ConfigureAwait(false);
 
         // S7.Net's string-based ReadAsync returns object where the boxed .NET type depends on
@@ -793,10 +794,10 @@ public sealed class S7Driver
         var folder = builder.Folder("S7", "S7");
         foreach (var t in _options.Tags)
         {
-            // A tag carrying an array count (> 1) surfaces as a 1-D OPC UA array node; a missing
+            // A tag carrying a non-null array count (>= 1) surfaces as a 1-D OPC UA array node.
-            // count or a count of 1 stays scalar (count == 1 array adds no information over a
+            // A null count stays scalar. A count of 1 IS a valid 1-element array: the foundation
-            // scalar and would force every read down the slower block path).
+            // materialises a [1] OPC UA array node when isArray:true, so the driver must agree.
-            var isArray = t.ArrayCount is > 1;
+            var isArray = t.ArrayCount is >= 1;
             folder.Variable(t.Name, t.Name, new DriverAttributeInfo(
                 FullName: t.Name,
                 DriverDataType: MapDataType(t.DataType),

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/S7ArrayReadTests.cs

@@ -216,9 +216,11 @@ public sealed class S7ArrayReadTests
         arr.ArrayDim.ShouldBe(8u);
     }
 
-    /// <summary>Verifies a tag with ArrayCount of 1 is treated as a scalar (no array node).</summary>
+    /// <summary>Verifies a tag with ArrayCount of 1 is treated as a 1-element array (not scalar).
+    /// The foundation materialises a [1] OPC UA array node when IsArray=true, so the driver must
+    /// honour isArray:true + arrayLength:1 — a 1-element array IS a valid array.</summary>
     [Fact]
-    public async Task DiscoverAsync_count_of_one_is_scalar()
+    public async Task DiscoverAsync_count_of_one_is_array()
     {
         var opts = new S7DriverOptions
         {
@@ -231,8 +233,40 @@ public sealed class S7ArrayReadTests
         await drv.DiscoverAsync(builder, TestContext.Current.CancellationToken);
 
         var one = builder.Variables.Single().Attr;
-        one.IsArray.ShouldBeFalse("count<=1 is scalar");
+        one.IsArray.ShouldBeTrue("ArrayCount=1 is a 1-element array, not scalar");
-        one.ArrayDim.ShouldBeNull();
+        one.ArrayDim.ShouldBe(1u);
+    }
+
+    /// <summary>Verifies that a tag with a null ArrayCount (scalar) is still discovered as scalar.</summary>
+    [Fact]
+    public async Task DiscoverAsync_null_ArrayCount_is_scalar()
+    {
+        var opts = new S7DriverOptions
+        {
+            Host = "192.0.2.1",
+            Tags = [new("Scalar", "DB1.DBW0", S7DataType.Int16, ArrayCount: null)],
+        };
+        using var drv = new S7Driver(opts, "s7-arr-null");
+
+        var builder = new RecordingBuilder();
+        await drv.DiscoverAsync(builder, TestContext.Current.CancellationToken);
+
+        var scalar = builder.Variables.Single().Attr;
+        scalar.IsArray.ShouldBeFalse("null ArrayCount is scalar");
+        scalar.ArrayDim.ShouldBeNull();
+    }
+
+    /// <summary>Verifies a read of an isArray:true arrayLength:1 equipment tag returns a 1-element typed array.</summary>
+    [Fact]
+    public void DecodeArrayBlock_count_of_one_returns_single_element_array()
+    {
+        // A 1-element Int16 array: one big-endian word.
+        var block = BeWords(0x0064); // 100
+        var result = S7Driver.DecodeArrayBlock(ArrTag(S7DataType.Int16, 1), Addr(S7Size.Word), block);
+
+        var arr = result.ShouldBeOfType<short[]>();
+        arr.Length.ShouldBe(1);
+        arr[0].ShouldBe((short)100);
     }
 
     // ── Equipment-tag resolver threads arrayLength → ArrayCount ───────────────────────────