Add custom JSON converters for ISubContent and ISubContentImageSource to support polymorphic serialization

app/MindWork AI Studio/Provider/Anthropic/SubContentImageSourceConverter.cs

@@ -0,0 +1,32 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace AIStudio.Provider.Anthropic;
+
+/// <summary>
+/// Custom JSON converter for the ISubContentImageSource interface to handle polymorphic serialization.
+/// </summary>
+/// <remarks>
+/// This converter ensures that when serializing ISubContentImageSource objects, all properties
+/// of the concrete implementation (e.g., SubContentBase64Image, SubContentImageUrl) are serialized,
+/// not just the properties defined in the ISubContentImageSource interface.
+/// </remarks>
+public sealed class SubContentImageSourceConverter : JsonConverter<ISubContentImageSource>
+{
+    private static readonly ILogger<SubContentImageSourceConverter> LOGGER = Program.LOGGER_FACTORY.CreateLogger<SubContentImageSourceConverter>();
+
+    public override ISubContentImageSource? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        // Deserialization is not needed for request objects, as sub-content image sources are only serialized
+        // when sending requests to LLM providers.
+        LOGGER.LogError("Deserializing ISubContentImageSource is not supported. This converter is only used for serializing request messages.");
+        return null;
+    }
+
+    public override void Write(Utf8JsonWriter writer, ISubContentImageSource value, JsonSerializerOptions options)
+    {
+        // Serialize the actual concrete type (e.g., SubContentBase64Image, SubContentImageUrl) instead of just the ISubContentImageSource interface.
+        // This ensures all properties of the concrete type are included in the JSON output.
+        JsonSerializer.Serialize(writer, value, value.GetType(), options);
+    }
+}

app/MindWork AI Studio/Provider/BaseProvider.cs

@@ -1,8 +1,10 @@
 using System.Net;
 using System.Runtime.CompilerServices;
 using System.Text.Json;
+using System.Text.Json.Serialization;
 
 using AIStudio.Chat;
+using AIStudio.Provider.Anthropic;
 using AIStudio.Provider.OpenAI;
 using AIStudio.Settings;
 using AIStudio.Tools.PluginSystem;
@@ -40,7 +42,14 @@ public abstract class BaseProvider : IProvider, ISecretId
     protected static readonly JsonSerializerOptions JSON_SERIALIZER_OPTIONS = new()
     {
         PropertyNamingPolicy = JsonNamingPolicy.SnakeCaseLower,
-        Converters = { new AnnotationConverter(), new MessageBaseConverter() },
+        Converters =
+        {
+            new JsonStringEnumConverter(JsonNamingPolicy.SnakeCaseLower),
+            new AnnotationConverter(),
+            new MessageBaseConverter(),
+            new SubContentConverter(),
+            new SubContentImageSourceConverter(),
+        },
         AllowTrailingCommas = false
     };
 

app/MindWork AI Studio/Provider/SubContentConverter.cs

@@ -0,0 +1,34 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+using AIStudio.Provider.OpenAI;
+
+namespace AIStudio.Provider;
+
+/// <summary>
+/// Custom JSON converter for the ISubContent interface to handle polymorphic serialization.
+/// </summary>
+/// <remarks>
+/// This converter ensures that when serializing ISubContent objects, all properties
+/// of the concrete implementation (e.g., SubContentText, SubContentImageUrl) are serialized,
+/// not just the properties defined in the ISubContent interface.
+/// </remarks>
+public sealed class SubContentConverter : JsonConverter<ISubContent>
+{
+    private static readonly ILogger<SubContentConverter> LOGGER = Program.LOGGER_FACTORY.CreateLogger<SubContentConverter>();
+
+    public override ISubContent? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        // Deserialization is not needed for request objects, as sub-content is only serialized
+        // when sending requests to LLM providers.
+        LOGGER.LogError("Deserializing ISubContent is not supported. This converter is only used for serializing request messages.");
+        return null;
+    }
+
+    public override void Write(Utf8JsonWriter writer, ISubContent value, JsonSerializerOptions options)
+    {
+        // Serialize the actual concrete type (e.g., SubContentText, SubContentImageUrl) instead of just the ISubContent interface.
+        // This ensures all properties of the concrete type are included in the JSON output.
+        JsonSerializer.Serialize(writer, value, value.GetType(), options);
+    }
+}