Add InheritedDescriptionAttributes test from PR #7599

Includes AIFunctionFactory_InheritedDescriptionAttributes_OnOverride test
that validates inherited Description attributes on overridden methods,
including parameter descriptions and return value descriptions.
Covers both modern .NET and .NET Framework behavior differences.

Author: Copilot

test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs

@@ -510,6 +510,28 @@ public void AIFunctionNameAttribute_DisplayNameAttribute_StillHonoredWhenNoAIFun
         Assert.Equal("from-display-name", func.Name);
     }
 
+    [Fact]
+    public void AIFunctionFactory_InheritedDescriptionAttributes_OnOverride()
+    {
+        MethodInfo overrideMethod = typeof(DerivedDescribed).GetMethod(nameof(DerivedDescribed.Compute))!;
+        AIFunction f = AIFunctionFactory.Create(overrideMethod, new DerivedDescribed());
+
+        Assert.Equal("The compute method", f.Description);
+
+        JsonElement valueParam = f.JsonSchema.GetProperty("properties").GetProperty("value");
+        Assert.Equal("The input value", valueParam.GetProperty("description").GetString());
+
+        Assert.NotNull(f.ReturnJsonSchema);
+        Assert.Equal("integer", f.ReturnJsonSchema!.Value.GetProperty("type").GetString());
+#if NET
+        // On modern .NET the return-parameter inheritance walk is fixed, so the inherited description is read.
+        Assert.Equal("The computed result", f.ReturnJsonSchema!.Value.GetProperty("description").GetString());
+#else
+        // On .NET Framework the inherited return-parameter description cannot be read and is silently dropped.
+        Assert.False(f.ReturnJsonSchema!.Value.TryGetProperty("description", out _));
+#endif
+    }
+
     [Fact]
     public void AIFunctionFactoryCreateOptions_ValuesPropagateToAIFunction()
     {
@@ -1802,4 +1824,16 @@ private sealed class AIParameterNameAttributeRecursiveNode
     {
         public AIParameterNameAttributeRecursiveNode? Next { get; set; }
     }
+
+    private abstract class BaseDescribed
+    {
+        [Description("The compute method")]
+        [return: Description("The computed result")]
+        public abstract int Compute([Description("The input value")] int value);
+    }
+
+    private sealed class DerivedDescribed : BaseDescribed
+    {
+        public override int Compute(int value) => value;
+    }
 }