fix: prevent KVO key path double-prefixing for bool properties already starting with "Is"

Author: glennawatson

src/ReactiveUI.Binding.SourceGenerators/Plugins/Observation/KVOObservationPlugin.cs

@@ -283,15 +283,16 @@ public void EmitInlineObservationVariable(
 
     /// <summary>
     /// Converts a .NET property name to a KVO key path using the standard naming convention.
-    /// Boolean properties get an "Is" prefix (e.g., <c>Enabled</c> → <c>"isEnabled"</c>).
+    /// Boolean properties get an "Is" prefix unless they already start with "Is"
+    /// (e.g., <c>Enabled</c> → <c>"isEnabled"</c>, but <c>IsEnabled</c> → <c>"isEnabled"</c>).
     /// All others: lowercase first character (e.g., <c>Text</c> → <c>"text"</c>).
     /// </summary>
     /// <param name="propertyName">The .NET property name.</param>
     /// <param name="propertyTypeFullName">The fully qualified property type (e.g., "bool", "string").</param>
     /// <returns>The KVO key path string.</returns>
     private static string ToKvoKeyPath(string propertyName, string propertyTypeFullName)
     {
-        if (propertyTypeFullName == "bool")
+        if (propertyTypeFullName == "bool" && !propertyName.StartsWith("Is", StringComparison.Ordinal))
         {
             propertyName = "Is" + propertyName;
         }

src/tests/ReactiveUI.Binding.SourceGenerators.Tests/Plugins/ObservationPluginTests.cs

@@ -666,6 +666,22 @@ public async Task KVOPlugin_BooleanProperty_UsesIsPrefix()
         await Assert.That(sb.ToString()).Contains("\"isEnabled\"");
     }
 
+    /// <summary>
+    /// Verifies KVO key path for boolean property already starting with "Is" does not double-prefix.
+    /// </summary>
+    /// <returns>A task representing the asynchronous test operation.</returns>
+    [Test]
+    public async Task KVOPlugin_BooleanPropertyAlreadyStartingWithIs_DoesNotDoublePrefix()
+    {
+        var plugin = new KVOObservationPlugin();
+        var sb = new StringBuilder();
+        var segment = ModelFactory.CreatePropertyPathSegment("IsEnabled", "bool");
+
+        plugin.EmitShallowObservation(sb, "obj", segment, "global::TestApp.MyView", isBeforeChange: false, includeStartWith: true);
+
+        await Assert.That(sb.ToString()).Contains("\"isEnabled\"");
+    }
+
     /// <summary>
     /// Verifies KVO key path for empty property name returns empty string.
     /// </summary>