Restore OpenAPI 3.1 and fix numeric schemas rendered as string union

Microsoft.AspNetCore.OpenApi reflects JsonNumberHandling.AllowReadingFromString
(default under JsonSerializerDefaults.Web) by emitting numeric schemas as
type: ["integer","string"] with a bigint regex. Swagger UI rendered ints/decimals
as strings in bodies and broke query/path params; downgrading to 3.0 dropped the
type entirely with the same symptom. Add NumericStringUnionTransformer to strip
the string alternative and the regex, leaving pure integer/number. Switch
OpenApiVersion back to 3.1. Workaround for dotnet/aspnetcore#58882 and #64145.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: HaikAsatryan

src/SharedKernel/OpenApi/NumericStringUnionTransformer.cs

@@ -0,0 +1,74 @@
+using Microsoft.AspNetCore.OpenApi;
+using Microsoft.OpenApi;
+
+namespace SharedKernel.OpenApi;
+
+// Workaround for https://github.com/dotnet/aspnetcore/issues/58882 and #64145.
+// Microsoft.AspNetCore.OpenApi reflects JsonNumberHandling.AllowReadingFromString
+// (enabled by default via JsonSerializerDefaults.Web) by emitting numeric schemas as
+// type: ["integer","string"] with a bigint regex pattern. Swagger UI renders this as a
+// string in bodies and breaks query/path parameters; downgrading to OpenAPI 3.0 drops
+// the type entirely. We strip the string alternative so numbers stay numbers in the doc.
+// Runtime deserialization is unchanged: STJ still accepts quoted numbers if a client sends them.
+internal sealed class NumericStringUnionTransformer : IOpenApiSchemaTransformer
+{
+   public Task TransformAsync(OpenApiSchema schema,
+      OpenApiSchemaTransformerContext context,
+      CancellationToken cancellationToken)
+   {
+      Strip(schema);
+      return Task.CompletedTask;
+   }
+
+   private static void Strip(IOpenApiSchema? schema)
+   {
+      if (schema is not OpenApiSchema s)
+      {
+         return;
+      }
+
+      if (s.Type is { } t
+          && (t & JsonSchemaType.String) != 0
+          && (t & (JsonSchemaType.Integer | JsonSchemaType.Number)) != 0)
+      {
+         s.Type = t & ~JsonSchemaType.String;
+         s.Pattern = null;
+      }
+
+      if (s.Properties is not null)
+      {
+         foreach (var p in s.Properties.Values)
+         {
+            Strip(p);
+         }
+      }
+
+      Strip(s.Items);
+      Strip(s.AdditionalProperties);
+      Strip(s.Not);
+
+      if (s.AllOf is not null)
+      {
+         foreach (var sub in s.AllOf)
+         {
+            Strip(sub);
+         }
+      }
+
+      if (s.OneOf is not null)
+      {
+         foreach (var sub in s.OneOf)
+         {
+            Strip(sub);
+         }
+      }
+
+      if (s.AnyOf is not null)
+      {
+         foreach (var sub in s.AnyOf)
+         {
+            Strip(sub);
+         }
+      }
+   }
+}

src/SharedKernel/OpenApi/OpenApiExtensions.cs

@@ -30,10 +30,11 @@ public static WebApplicationBuilder AddOpenApi(this WebApplicationBuilder builde
          builder.Services.AddOpenApi(document.GroupName,
             options =>
             {
-               options.OpenApiVersion = OpenApiSpecVersion.OpenApi3_0;
+               options.OpenApiVersion = OpenApiSpecVersion.OpenApi3_1;
                options.AddDocumentTransformer<RemoveServersTransformer>();
                options.AddDocument(document, openApiConfiguration);
                options.AddSchemaTransformer<EnumSchemaTransformer>();
+               options.AddSchemaTransformer<NumericStringUnionTransformer>();
                options.UseApiSecuritySchemes(openApiConfiguration);
                options.AddDocumentTransformer<TagOrderingTransformer>();
                configureOptions?.Invoke(options);

src/SharedKernel/SharedKernel.csproj

@@ -21,8 +21,8 @@
         <PackageIcon>pandatech.png</PackageIcon>
         <PackageReadmeFile>README.md</PackageReadmeFile>
 
-        <Version>2.2.7</Version>
-        <PackageReleaseNotes>Downgrade OpenAPI 3.1 to 3.0</PackageReleaseNotes>
+        <Version>2.2.8</Version>
+        <PackageReleaseNotes>Restore OpenAPI 3.1 and fix numeric schemas rendered as string union (workaround for dotnet/aspnetcore#58882, #64145)</PackageReleaseNotes>
 
         <GenerateDocumentationFile>true</GenerateDocumentationFile>
         <IncludeSymbols>true</IncludeSymbols>