fix: when serializing source use media type to deserialize to image or document source

src/AnthropicClient/Json/SourceConverter.cs

@@ -16,11 +16,20 @@ class SourceConverter : JsonConverter<Source>
     {
       SourceType.Text => JsonSerializer.Deserialize<TextSource>(root.GetRawText(), options)!,
       SourceType.Content => JsonSerializer.Deserialize<CustomSource>(root.GetRawText(), options)!,
-      SourceType.Base64 => JsonSerializer.Deserialize<Base64Source>(root.GetRawText(), options)!,
+      SourceType.Base64 => DeserializeBase64Source(root, options),
       _ => throw new JsonException($"Unknown content type: {type}")
     };
   }
 
+  private static Source DeserializeBase64Source(JsonElement root, JsonSerializerOptions options)
+  {
+    var mediaType = root.GetProperty("media_type").GetString() ?? throw new JsonException("Missing 'media_type' property");
+    var isImage = ImageType.IsValidImageType(mediaType);
+    return isImage
+      ? JsonSerializer.Deserialize<ImageSource>(root.GetRawText(), options)!
+      : JsonSerializer.Deserialize<DocumentSource>(root.GetRawText(), options)!;
+  }
+
   public override void Write(Utf8JsonWriter writer, Source value, JsonSerializerOptions options)
   {
     if (value is TextSource textSource)

tests/AnthropicClient.Tests/Unit/Models/MessageRequestTests.cs

@@ -74,7 +74,7 @@ public class MessageRequestTests : SerializationTest
         ""content"": [
           { 
             ""type"": ""image"", 
-            ""source"": { ""media_type"": ""image/jpeg"", ""data"": ""data"" } 
+            ""source"": { ""type"": ""base64"", ""media_type"": ""image/jpeg"", ""data"": ""data"" } 
           }
         ] 
       }