fix(code-review): resolve Batch 2 open findings (AbCip, AbLegacy, Galaxy, FOCAS)

- Driver.AbCip.Contracts-001: parse 'writable' from TagConfig JSON (default true) instead of hardcoding
- Driver.AbCip.Contracts-002/-003: Dt type comment; drop dead [Display]/[Range] annotations
- Driver.AbCip.Contracts-004: dedicated AbCipEquipmentTagParser test class (+15)
- Driver.AbCip-017: document Tick severity Low-fallback on Bad severity read
- Driver.AbLegacy.Contracts-002/-003/-004: isArray-scalar remarks (+tests), MaxTagBytes/ForFamily docs
- Driver.Galaxy.Browser-003 + Driver.Galaxy.Contracts-003: extract ResolveApiKey -> GalaxySecretRef (dedup)
- Driver.Galaxy-019: cache buffered-interval only on Ok + ILogger warnings + ClassifyIntervalReply (+tests)
- Driver.FOCAS.Contracts-002: thread WriteIdempotent through DiscoverAsync (+test)

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyEquipmentTagTests.cs

@@ -37,6 +37,32 @@ public sealed class AbLegacyEquipmentTagTests
         => AbLegacyEquipmentTagParser.TryParse(
             """{"address":"","dataType":"Int"}""", out _).ShouldBeFalse();
 
+    // -002 regression: isArray:true without a valid positive arrayLength → scalar (null ArrayLength).
+
+    [Fact]
+    public void IsArray_true_with_arrayLength_zero_produces_scalar()
+    {
+        var json = """{"address":"N7:0","dataType":"Int","isArray":true,"arrayLength":0}""";
+        AbLegacyEquipmentTagParser.TryParse(json, out var def).ShouldBeTrue();
+        def!.ArrayLength.ShouldBeNull();
+    }
+
+    [Fact]
+    public void IsArray_true_with_no_arrayLength_produces_scalar()
+    {
+        var json = """{"address":"N7:0","dataType":"Int","isArray":true}""";
+        AbLegacyEquipmentTagParser.TryParse(json, out var def).ShouldBeTrue();
+        def!.ArrayLength.ShouldBeNull();
+    }
+
+    [Fact]
+    public void IsArray_true_with_negative_arrayLength_produces_scalar()
+    {
+        var json = """{"address":"N7:0","dataType":"Int","isArray":true,"arrayLength":-5}""";
+        AbLegacyEquipmentTagParser.TryParse(json, out var def).ShouldBeTrue();
+        def!.ArrayLength.ShouldBeNull();
+    }
+
     /// <summary>
     ///     End-to-end driver-level proof: an AbLegacy driver with NO authored tags can still read an
     ///     equipment-tag ref (the raw TagConfig JSON) — the resolver parses it into a transient