feat: initial pass at citations in request and response

src/AnthropicClient/Json/CitationConverter.cs

@@ -0,0 +1,28 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+using AnthropicClient.Models;
+
+namespace AnthropicClient.Json;
+
+class CitationConverter : JsonConverter<Citation>
+{
+  public override Citation Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+  {
+    using var jsonDocument = JsonDocument.ParseValue(ref reader);
+    var root = jsonDocument.RootElement;
+    var type = root.GetProperty("type").GetString();
+    return type switch
+    {
+      CitationType.CharacterLocation => JsonSerializer.Deserialize<CharacterLocationCitation>(root.GetRawText(), options)!,
+      CitationType.PageLocation => JsonSerializer.Deserialize<PageLocationCitation>(root.GetRawText(), options)!,
+      CitationType.ContentBlockLocation => JsonSerializer.Deserialize<ContentBlockLocationCitation>(root.GetRawText(), options)!,
+      _ => throw new JsonException($"Unknown content type: {type}")
+    };
+  }
+
+  public override void Write(Utf8JsonWriter writer, Citation value, JsonSerializerOptions options)
+  {
+    JsonSerializer.Serialize(writer, value, value.GetType(), options);
+  }
+}

src/AnthropicClient/Json/JsonSerializationOptions.cs

@@ -18,6 +18,7 @@ static class JsonSerializationOptions
       new ContentDeltaConverter(),
       new JsonStringEnumConverter(),
       new MessageBatchResultConverter(),
+      new CitationConverter(),
     },
     DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
   };