Unseal FunctionCallContent and FunctionResultContent

src/Libraries/Microsoft.Extensions.AI.Abstractions/Contents/FunctionCallContent.cs

@@ -14,7 +14,7 @@ namespace Microsoft.Extensions.AI;
 /// Represents a function call request.
 /// </summary>
 [DebuggerDisplay("{DebuggerDisplay,nq}")]
-public sealed class FunctionCallContent : AIContent
+public class FunctionCallContent : AIContent
 {
     /// <summary>
     /// Initializes a new instance of the <see cref="FunctionCallContent"/> class.

src/Libraries/Microsoft.Extensions.AI.Abstractions/Contents/FunctionResultContent.cs

@@ -13,7 +13,7 @@ namespace Microsoft.Extensions.AI;
 /// Represents the result of a function call.
 /// </summary>
 [DebuggerDisplay("{DebuggerDisplay,nq}")]
-public sealed class FunctionResultContent : AIContent
+public class FunctionResultContent : AIContent
 {
     /// <summary>
     /// Initializes a new instance of the <see cref="FunctionResultContent"/> class.

src/Libraries/Microsoft.Extensions.AI.Abstractions/Microsoft.Extensions.AI.Abstractions.json

@@ -1792,7 +1792,7 @@
       ]
     },
     {
-      "Type": "sealed class Microsoft.Extensions.AI.FunctionCallContent : Microsoft.Extensions.AI.AIContent",
+      "Type": "class Microsoft.Extensions.AI.FunctionCallContent : Microsoft.Extensions.AI.AIContent",
       "Stage": "Stable",
       "Methods": [
         {
@@ -1824,7 +1824,7 @@
       ]
     },
     {
-      "Type": "sealed class Microsoft.Extensions.AI.FunctionResultContent : Microsoft.Extensions.AI.AIContent",
+      "Type": "class Microsoft.Extensions.AI.FunctionResultContent : Microsoft.Extensions.AI.AIContent",
       "Stage": "Stable",
       "Methods": [
         {

test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/Contents/FunctionCallContentTests.cs

@@ -7,13 +7,15 @@
 using System.Linq;
 using System.Text.Json;
 using System.Text.Json.Nodes;
+using System.Text.Json.Serialization;
+using System.Text.Json.Serialization.Metadata;
 using System.Threading;
 using System.Threading.Tasks;
 using Xunit;
 
 namespace Microsoft.Extensions.AI;
 
-public class FunctionCallContentTests
+public partial class FunctionCallContentTests
 {
     [Fact]
     public void Constructor_PropsDefault()
@@ -322,4 +324,60 @@ public static void CreateFromParsedArguments_NullInput_ThrowsArgumentNullExcepti
         Assert.Throws<ArgumentNullException>("name", () => FunctionCallContent.CreateFromParsedArguments("{}", "callId", null!, _ => null));
         Assert.Throws<ArgumentNullException>("argumentParser", () => FunctionCallContent.CreateFromParsedArguments("{}", "callId", "functionName", null!));
     }
+
+    [Fact]
+    public static void DerivedFunctionCallContent_CanBeSerializedAndDeserialized()
+    {
+        // Arrange: Register the derived type
+        var options = new JsonSerializerOptions
+        {
+            TypeInfoResolver = JsonTypeInfoResolver.Combine(AIJsonUtilities.DefaultOptions.TypeInfoResolver, DerivedTypesJsonContext.Default),
+            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+        };
+        options.AddAIContentType<DerivedFunctionCallContent>("derivedFunctionCall");
+
+        var derivedContent = new DerivedFunctionCallContent("callId1", "testFunction", new Dictionary<string, object?> { ["param1"] = "value1" })
+        {
+            CustomProperty = "customValue"
+        };
+
+        // Act: Serialize as AIContent to test polymorphic serialization
+        var json = JsonSerializer.Serialize<AIContent>(derivedContent, options);
+        var deserialized = JsonSerializer.Deserialize<AIContent>(json, options);
+
+        // Assert
+        Assert.NotNull(deserialized);
+        Assert.IsType<DerivedFunctionCallContent>(deserialized);
+        var derivedDeserialized = (DerivedFunctionCallContent)deserialized;
+        Assert.Equal("callId1", derivedDeserialized.CallId);
+        Assert.Equal("testFunction", derivedDeserialized.Name);
+        Assert.NotNull(derivedDeserialized.Arguments);
+        Assert.Single(derivedDeserialized.Arguments);
+        Assert.Equal("value1", derivedDeserialized.Arguments["param1"]?.ToString());
+        Assert.Equal("customValue", derivedDeserialized.CustomProperty);
+    }
+
+    internal sealed class DerivedFunctionCallContent : FunctionCallContent
+    {
+        public DerivedFunctionCallContent(string callId, string name, IDictionary<string, object?>? arguments = null)
+            : base(callId, name, arguments)
+        {
+        }
+
+        public string? CustomProperty { get; set; }
+    }
+
+    internal sealed class DerivedFunctionResultContent : FunctionResultContent
+    {
+        public DerivedFunctionResultContent(string callId, object? result)
+            : base(callId, result)
+        {
+        }
+
+        public string? CustomProperty { get; set; }
+    }
+
+    [JsonSerializable(typeof(DerivedFunctionCallContent))]
+    [JsonSerializable(typeof(DerivedFunctionResultContent))]
+    internal sealed partial class DerivedTypesJsonContext : JsonSerializerContext;
 }

test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/Contents/FunctionResultContentTests.cs

@@ -3,6 +3,8 @@
 
 using System;
 using System.Text.Json;
+using System.Text.Json.Serialization;
+using System.Text.Json.Serialization.Metadata;
 using Xunit;
 
 namespace Microsoft.Extensions.AI;
@@ -91,4 +93,33 @@ public void ItShouldBeSerializableAndDeserializableWithException()
         Assert.Equal(sut.Result, deserializedSut.Result?.ToString());
         Assert.Null(deserializedSut.Exception);
     }
+
+    [Fact]
+    public void DerivedFunctionResultContent_CanBeSerializedAndDeserialized()
+    {
+        // Arrange: Register the derived type
+        var options = new JsonSerializerOptions
+        {
+            TypeInfoResolver = JsonTypeInfoResolver.Combine(AIJsonUtilities.DefaultOptions.TypeInfoResolver, FunctionCallContentTests.DerivedTypesJsonContext.Default),
+            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+        };
+        options.AddAIContentType<FunctionCallContentTests.DerivedFunctionResultContent>("derivedFunctionResult");
+
+        var derivedContent = new FunctionCallContentTests.DerivedFunctionResultContent("callId1", "test result")
+        {
+            CustomProperty = "customValue"
+        };
+
+        // Act: Serialize as AIContent to test polymorphic serialization
+        var json = JsonSerializer.Serialize<AIContent>(derivedContent, options);
+        var deserialized = JsonSerializer.Deserialize<AIContent>(json, options);
+
+        // Assert
+        Assert.NotNull(deserialized);
+        Assert.IsType<FunctionCallContentTests.DerivedFunctionResultContent>(deserialized);
+        var derivedDeserialized = (FunctionCallContentTests.DerivedFunctionResultContent)deserialized;
+        Assert.Equal("callId1", derivedDeserialized.CallId);
+        Assert.Equal("test result", derivedDeserialized.Result?.ToString());
+        Assert.Equal("customValue", derivedDeserialized.CustomProperty);
+    }
 }