feat: Added the fix for Extention and role module

Fix 1 — Role serialization (13 tests + Test057 as side-effect)
New file: Contentstack.Management.Core/Utils/RuleJsonConverter.cs

System.Text.Json only serializes the declared type when iterating a List<Rule>, so subclass fields like module and branches were silently dropped. The custom converter serializes the actual runtime type on Write, and dispatches on the "module" discriminator on Read. It uses the existing WithoutConverter<T>() helper to avoid infinite recursion.

Edit: ContentstackClient.cs Initialize()

Added SerializerOptions.Converters.Add(new RuleJsonConverter()) alongside the existing NodeJsonConverter and TextNodeJsonConverter registrations.

Fix 2 — Extension upload wrong file type (3 tests)
The Contentstack Extensions API requires an HTML source file. All three tests were uploading contentTypeSchema.json, which the API rejected with error_code 344: "upload: Not a valid html file".

New file: Contentstack.Management.Core.Tests/Mock/extension.html

Minimal valid HTML file accepted by the Extensions API.

Edit: Contentstack013_AssetTest.cs

Test002, Test003, Test004 — changed path from contentTypeSchema.json → extension.html and content type from "application/json" → "text/html".

Author: OMpawar-21

Contentstack.Management.Core.Tests/IntegrationTest/Contentstack013_AssetTest.cs

@@ -410,11 +410,11 @@ public async Task Test001_Should_Create_Asset()
         public async Task Test002_Should_Create_Dashboard()
         {
             TestOutputLogger.LogContext("TestScenario", "CreateDashboardWidget");
-            var path = Path.Combine(System.Environment.CurrentDirectory, "../../../Mock/contentTypeSchema.json");
+            var path = Path.Combine(System.Environment.CurrentDirectory, "../../../Mock/extension.html");
             try
             {
                 DashboardWidgetModel dashboard = new DashboardWidgetModel(
-                    path, "application/json", "Integration Test Dashboard",
+                    path, "text/html", "Integration Test Dashboard",
                     isEnable: true, defaultWidth: "half", tags: "dashboard,test");
                 ContentstackResponse response = await _stack.Extension().UploadAsync(dashboard);
                 TestOutputLogger.LogContext("StackAPIKey", _stack?.APIKey ?? "null");
@@ -439,12 +439,12 @@ public async Task Test002_Should_Create_Dashboard()
         public async Task Test003_Should_Create_Custom_Widget()
         {
             TestOutputLogger.LogContext("TestScenario", "CreateCustomWidget");
-            var path = Path.Combine(System.Environment.CurrentDirectory, "../../../Mock/contentTypeSchema.json");
+            var path = Path.Combine(System.Environment.CurrentDirectory, "../../../Mock/extension.html");
             try
             {
                 var scope = new ExtensionScope { ContentTypes = new List<string> { "$all" } };
                 CustomWidgetModel widget = new CustomWidgetModel(
-                    path, "application/json", "Integration Test Widget",
+                    path, "text/html", "Integration Test Widget",
                     tags: "widget,test", scope: scope);
                 ContentstackResponse response = await _stack.Extension().UploadAsync(widget);
                 TestOutputLogger.LogContext("StackAPIKey", _stack?.APIKey ?? "null");
@@ -469,11 +469,11 @@ public async Task Test003_Should_Create_Custom_Widget()
         public async Task Test004_Should_Create_Custom_field()
         {
             TestOutputLogger.LogContext("TestScenario", "CreateCustomField");
-            var path = Path.Combine(System.Environment.CurrentDirectory, "../../../Mock/contentTypeSchema.json");
+            var path = Path.Combine(System.Environment.CurrentDirectory, "../../../Mock/extension.html");
             try
             {
                 CustomFieldModel field = new CustomFieldModel(
-                    path, "application/json", "Integration Test Field",
+                    path, "text/html", "Integration Test Field",
                     dataType: "text", isMultiple: false, tags: "field,test");
                 ContentstackResponse response = await _stack.Extension().UploadAsync(field);
                 TestOutputLogger.LogContext("StackAPIKey", _stack?.APIKey ?? "null");

Contentstack.Management.Core/ContentstackClient.cs

@@ -203,6 +203,7 @@ protected void Initialize(HttpClient? httpClient = null)
             SerializerOptions.Converters.Add(new FieldJsonConverter()); // Re-enabled for ContentType support
             SerializerOptions.Converters.Add(new NodeJsonConverter());
             SerializerOptions.Converters.Add(new TextNodeJsonConverter());
+            SerializerOptions.Converters.Add(new RuleJsonConverter());
         }
 
         protected void BuildPipeline()

Contentstack.Management.Core/Utils/RuleJsonConverter.cs

@@ -0,0 +1,52 @@
+using System;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using Contentstack.Management.Core.Models;
+
+namespace Contentstack.Management.Core.Utils
+{
+    /// <summary>
+    /// Polymorphic converter for <see cref="Rule"/> so that derived types
+    /// (BranchRules, ContentTypeRules, etc.) are serialized with their own
+    /// properties when stored in a <c>List&lt;Rule&gt;</c>.
+    ///
+    /// System.Text.Json only serializes the declared type by default, which
+    /// drops subclass-only fields like "module" and "branches" from the payload,
+    /// causing the Management API to return HTTP 422.
+    ///
+    /// Register this converter in JsonSerializerOptions.Converters (not via
+    /// [JsonConverter] attribute) so that WithoutConverter&lt;T&gt;() can remove it
+    /// during recursive serialization and prevent infinite recursion.
+    /// </summary>
+    internal class RuleJsonConverter : JsonConverter<Rule>
+    {
+        public override void Write(Utf8JsonWriter writer, Rule value, JsonSerializerOptions options)
+        {
+            var opts = options.WithoutConverter<RuleJsonConverter>();
+            JsonSerializer.Serialize(writer, (object)value, value.GetType(), opts);
+        }
+
+        public override Rule? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        {
+            using var doc = JsonDocument.ParseValue(ref reader);
+            var opts = options.WithoutConverter<RuleJsonConverter>();
+
+            if (doc.RootElement.TryGetProperty("module", out var moduleProp))
+            {
+                return moduleProp.GetString() switch
+                {
+                    "branch"       => doc.RootElement.Deserialize<BranchRules>(opts),
+                    "branch_alias" => doc.RootElement.Deserialize<BranchAliasRules>(opts),
+                    "content_type" => doc.RootElement.Deserialize<ContentTypeRules>(opts),
+                    "asset"        => doc.RootElement.Deserialize<AssetRules>(opts),
+                    "folder"       => doc.RootElement.Deserialize<FolderRules>(opts),
+                    "environment"  => doc.RootElement.Deserialize<EnvironmentRules>(opts),
+                    "taxonomy"     => doc.RootElement.Deserialize<TaxonomyRules>(opts),
+                    _              => doc.RootElement.Deserialize<Rule>(opts),
+                };
+            }
+
+            return doc.RootElement.Deserialize<Rule>(opts);
+        }
+    }
+}