feat(net): STJ overloads for HTTP JSON helpers, [Obsolete] Newtonsoft surface (#83 follow-up)

src/Fallout.Common/CI/GitHubActions/GitHubActions.Client.cs

@@ -29,7 +29,9 @@ private JObject GetJobDetails(long runId)
             .GetResponse()
             .AssertSuccessfulStatusCode();
 
+#pragma warning disable CS0618 // GetBodyAsJson(JObject) retires in v11; migrate to GetBodyAsJsonObject + System.Text.Json.Nodes.JsonObject access patterns then.
         return response.GetBodyAsJson().GetAwaiter().GetResult()
+#pragma warning restore CS0618
             .GetChildren("jobs")
             .Single(x => x.GetPropertyStringValue("name") == Job);
     }

src/Fallout.Common/Tools/Mastodon/MastodonTasks.cs

@@ -37,7 +37,9 @@ async Task<string> PostMediaFile(string file)
                     .AddStreamContent("file", stream, Path.GetFileName(file)))
                 .GetResponseAsync();
 
+#pragma warning disable CS0618 // GetBodyAsJson(JObject) retires in v11; migrate to GetBodyAsJsonObject + System.Text.Json.Nodes.JsonObject access patterns then.
             var json = await response.GetBodyAsJson();
+#pragma warning restore CS0618
             return json["id"].NotNull().ToString();
         }
 

src/Fallout.Common/Tools/Slack/SlackTasks.cs

@@ -51,7 +51,9 @@ public static async Task<string> SendOrUpdateSlackMessage(Configure<SlackMessage
             .WithJsonContent(message)
             .GetResponseAsync();
 
+#pragma warning disable CS0618 // GetBodyAsJson(JObject) retires in v11; migrate to GetBodyAsJsonObject + System.Text.Json.Nodes.JsonObject access patterns then.
         var jobject = await response.GetBodyAsJson();
+#pragma warning restore CS0618
         var error = jobject.GetPropertyValueOrNull<string>("error");
         Assert.True(error == null, error);
 

src/Fallout.Utilities.Net/Fallout.Utilities.Net.csproj

@@ -11,6 +11,7 @@
   <ItemGroup>
     <PackageReference Include="Newtonsoft.Json" />
     <PackageReference Include="System.Net.Http" />
+    <PackageReference Include="System.Text.Json" />
   </ItemGroup>
 
 </Project>

src/Fallout.Utilities.Net/HttpRequest.Content.cs

@@ -1,4 +1,4 @@
-// Copyright 2026 Maintainers of Fallout.
+// Copyright 2026 Maintainers of Fallout.
 // Originally based on NUKE by Matthias Koch and contributors.
 // Distributed under the MIT License.
 // https://github.com/ChrisonSimtian/Fallout/blob/main/LICENSE
@@ -10,14 +10,15 @@
 using System.Net.Http;
 using System.Net.Http.Headers;
 using System.Text;
+using System.Text.Json;
 using Newtonsoft.Json;
 
 namespace Fallout.Common.Utilities.Net;
 
 public static partial class HttpRequestExtensions
 {
     /// <summary>
-    /// Sets the JSON-serialized object as content via <see cref="JsonConvert.SerializeObject(object?)"/>.
+    /// Sets the JSON-serialized object as content via <see cref="Newtonsoft.Json.JsonConvert.SerializeObject(object?)"/>.
     /// </summary>
     public static HttpRequestBuilder WithJsonContent<T>(this HttpRequestBuilder builder, T obj)
     {
@@ -26,14 +27,24 @@ public static HttpRequestBuilder WithJsonContent<T>(this HttpRequestBuilder buil
     }
 
     /// <summary>
-    /// Sets the JSON-serialized object as content via <see cref="JsonConvert.SerializeObject(object?)"/>.
+    /// Sets the JSON-serialized object as content via <see cref="Newtonsoft.Json.JsonConvert.SerializeObject(object?)"/>.
     /// </summary>
+    [Obsolete("Use the JsonSerializerOptions overload instead. Newtonsoft.Json.JsonSerializerSettings is scheduled for removal in v11 as part of the System.Text.Json migration (#83).")]
     public static HttpRequestBuilder WithJsonContent<T>(this HttpRequestBuilder builder, T obj, JsonSerializerSettings settings)
     {
         var content = JsonConvert.SerializeObject(obj, settings);
         return builder.WithStringContent(content, "application/json");
     }
 
+    /// <summary>
+    /// Sets the JSON-serialized object as content via <see cref="System.Text.Json.JsonSerializer.Serialize{TValue}(TValue, JsonSerializerOptions?)"/>.
+    /// </summary>
+    public static HttpRequestBuilder WithJsonContent<T>(this HttpRequestBuilder builder, T obj, JsonSerializerOptions options)
+    {
+        var content = System.Text.Json.JsonSerializer.Serialize(obj, options);
+        return builder.WithStringContent(content, "application/json");
+    }
+
     /// <summary>
     /// Sets the string as content.
     /// </summary>

src/Fallout.Utilities.Net/HttpResponse.Body.cs

@@ -1,9 +1,12 @@
-// Copyright 2026 Maintainers of Fallout.
+// Copyright 2026 Maintainers of Fallout.
 // Originally based on NUKE by Matthias Koch and contributors.
 // Distributed under the MIT License.
 // https://github.com/ChrisonSimtian/Fallout/blob/main/LICENSE
 
+using System;
 using System.IO;
+using System.Text.Json;
+using System.Text.Json.Nodes;
 using System.Threading.Tasks;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Linq;
@@ -15,35 +18,64 @@ namespace Fallout.Common.Utilities.Net;
 public static partial class HttpResponseExtensions
 {
     /// <summary>
-    /// Reads the HTTP response body as JSON.
+    /// Reads the HTTP response body as JSON via <see cref="Newtonsoft.Json.JsonConvert.DeserializeObject{T}(string)"/>.
     /// </summary>
     public static async Task<T> GetBodyAsJson<T>(this HttpResponseInspector inspector)
     {
         return JsonConvert.DeserializeObject<T>(await inspector.GetBodyAsync());
     }
 
     /// <summary>
-    /// Reads the HTTP response body as JSON.
+    /// Reads the HTTP response body as a Newtonsoft <see cref="JObject"/>.
     /// </summary>
+    [Obsolete("Use GetBodyAsJsonObject (returns System.Text.Json.Nodes.JsonObject) instead. Newtonsoft.Json.Linq.JObject is scheduled for removal in v11 as part of the System.Text.Json migration (#83).")]
     public static async Task<JObject> GetBodyAsJson(this HttpResponseInspector inspector)
     {
         return await inspector.GetBodyAsJson<JObject>();
     }
 
     /// <summary>
-    /// Reads the HTTP response body as JSON.
+    /// Reads the HTTP response body as JSON via <see cref="Newtonsoft.Json.JsonConvert.DeserializeObject{T}(string, JsonSerializerSettings)"/>.
     /// </summary>
+    [Obsolete("Use the JsonSerializerOptions overload instead. Newtonsoft.Json.JsonSerializerSettings is scheduled for removal in v11 as part of the System.Text.Json migration (#83).")]
     public static async Task<T> GetBodyAsJson<T>(this HttpResponseInspector inspector, JsonSerializerSettings settings)
     {
         return JsonConvert.DeserializeObject<T>(await inspector.GetBodyAsync(), settings);
     }
 
     /// <summary>
-    /// Reads the HTTP response body as JSON.
+    /// Reads the HTTP response body as a Newtonsoft <see cref="JObject"/> using the given <paramref name="settings"/>.
     /// </summary>
+    [Obsolete("Use GetBodyAsJsonObject with JsonSerializerOptions instead. Newtonsoft types are scheduled for removal in v11 as part of the System.Text.Json migration (#83).")]
     public static async Task<JObject> GetBodyAsJson(this HttpResponseInspector inspector, JsonSerializerSettings settings)
     {
+#pragma warning disable CS0618 // Self-call into the obsolete settings-taking generic overload; both retire together in v11.
         return await inspector.GetBodyAsJson<JObject>(settings);
+#pragma warning restore CS0618
+    }
+
+    /// <summary>
+    /// Reads the HTTP response body as JSON via <see cref="System.Text.Json.JsonSerializer.Deserialize{TValue}(string, JsonSerializerOptions?)"/>.
+    /// </summary>
+    public static async Task<T> GetBodyAsJson<T>(this HttpResponseInspector inspector, JsonSerializerOptions options)
+    {
+        return System.Text.Json.JsonSerializer.Deserialize<T>(await inspector.GetBodyAsync(), options);
+    }
+
+    /// <summary>
+    /// Reads the HTTP response body as a System.Text.Json <see cref="JsonObject"/>.
+    /// </summary>
+    public static async Task<JsonObject> GetBodyAsJsonObject(this HttpResponseInspector inspector)
+    {
+        return JsonNode.Parse(await inspector.GetBodyAsync())?.AsObject();
+    }
+
+    /// <summary>
+    /// Reads the HTTP response body as a System.Text.Json <see cref="JsonObject"/> using the given <paramref name="options"/>.
+    /// </summary>
+    public static async Task<JsonObject> GetBodyAsJsonObject(this HttpResponseInspector inspector, JsonNodeOptions options)
+    {
+        return JsonNode.Parse(await inspector.GetBodyAsync(), nodeOptions: options)?.AsObject();
     }
 
     public static async Task WriteToFile(this HttpResponseInspector inspector, AbsolutePath path, FileMode mode = FileMode.CreateNew)