fix(adminui): reject AbLegacy array length >256 at author-time (review I-3)

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/AbLegacyTagConfigModel.cs

@@ -44,5 +44,19 @@ public sealed class AbLegacyTagConfigModel
 
     /// <summary>Validation hook; returns an error message or null when the model is valid.</summary>
     public string? Validate()
-        => string.IsNullOrWhiteSpace(Address) ? "Address is required." : null;
+    {
+        if (string.IsNullOrWhiteSpace(Address))
+            return "Address is required.";
+
+        // Array-length cap: PCCC data-file elements are limited to AbLegacyArray.MaxElements (256).
+        // The driver-agnostic materialiser uses the raw arrayLength to set OPC UA ArrayDimensions, but the
+        // driver clamps to 256 at runtime — so an authored length > 256 produces a Part 6 §5.3.2 mismatch.
+        // Reject it here at author-time so the error surfaces in the TagModal before the config is saved.
+        var isArray = TagConfigJson.GetBool(_bag, "isArray");
+        var arrayLength = TagConfigJson.GetInt(_bag, "arrayLength");
+        if (isArray && arrayLength > AbLegacyArray.MaxElements)
+            return $"AbLegacy array length cannot exceed {AbLegacyArray.MaxElements} (PCCC data-file element limit).";
+
+        return null;
+    }
 }

tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/AbLegacyTagConfigModelTests.cs

@@ -99,4 +99,34 @@ public sealed class AbLegacyTagConfigModelTests
 
         json.ShouldContain("\"deviceHostAddress\":\"ab://host\"");
     }
+
+    // Array-length cap (review I-3): authored arrayLength > 256 on an AbLegacy array tag must be
+    // rejected at author-time to prevent a Part 6 §5.3.2 ArrayDimensions mismatch at runtime.
+
+    [Fact]
+    public void Validate_returns_error_when_array_length_exceeds_256()
+    {
+        var m = AbLegacyTagConfigModel.FromJson("""{"address":"N7:0","isArray":true,"arrayLength":300}""");
+
+        var error = m.Validate();
+
+        error.ShouldNotBeNull();
+        error.ShouldContain("256");
+    }
+
+    [Fact]
+    public void Validate_returns_null_when_array_length_exactly_256()
+    {
+        var m = AbLegacyTagConfigModel.FromJson("""{"address":"N7:0","isArray":true,"arrayLength":256}""");
+
+        m.Validate().ShouldBeNull();
+    }
+
+    [Fact]
+    public void Validate_returns_null_for_scalar_tag_regardless_of_no_array_length()
+    {
+        var m = AbLegacyTagConfigModel.FromJson("""{"address":"N7:0"}""");
+
+        m.Validate().ShouldBeNull();
+    }
 }