test(benchmarks): add C#/ASP.NET and TypeScript tasks

Six tasks with hidden checks: ASP.NET validation and 404 handling, C#
cancellation, and TypeScript overlap, deep merge, and debounce fixes, checked
with dotnet run and node --test.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/benchmarks/tasks/15-csharp-cancellation/hidden/Check/Check.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Reports\Reports.csproj" />
+  </ItemGroup>
+</Project>

scripts/benchmarks/tasks/15-csharp-cancellation/hidden/Check/Program.cs

@@ -0,0 +1,20 @@
+using System.Diagnostics;
+using Reports;
+
+var failures = new List<string>();
+var builder = new ReportBuilder();
+var complete = await builder.BuildAsync(new[] { "a", "b" });
+if (complete != "## a\n## b") failures.Add($"unexpected output {complete}");
+using var source = new CancellationTokenSource(TimeSpan.FromMilliseconds(150));
+var watch = Stopwatch.StartNew();
+try
+{
+    await builder.BuildAsync(Enumerable.Range(0, 50).Select(number => number.ToString()), source.Token);
+    failures.Add("no cancellation");
+}
+catch (OperationCanceledException)
+{
+    if (watch.ElapsedMilliseconds > 1000) failures.Add($"cancelled only after {watch.ElapsedMilliseconds} ms");
+}
+foreach (var failure in failures) Console.Error.WriteLine("FAIL " + failure);
+return failures.Count == 0 ? 0 : 1;

scripts/benchmarks/tasks/15-csharp-cancellation/repo/src/Reports/ReportBuilder.cs

@@ -0,0 +1,15 @@
+namespace Reports;
+
+public sealed class ReportBuilder
+{
+    public async Task<string> BuildAsync(IEnumerable<string> sections, CancellationToken cancellationToken = default)
+    {
+        var parts = new List<string>();
+        foreach (var section in sections)
+        {
+            await Task.Delay(100);
+            parts.Add($"## {section}");
+        }
+        return string.Join("\n", parts);
+    }
+}

scripts/benchmarks/tasks/15-csharp-cancellation/repo/src/Reports/Reports.csproj

@@ -0,0 +1,7 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+</Project>

scripts/benchmarks/tasks/15-csharp-cancellation/task.json

@@ -0,0 +1,13 @@
+{
+  "prompt": "Cancelling a report build does nothing: BuildAsync keeps running until every section is rendered. Make it honor cancellation promptly by throwing OperationCanceledException.",
+  "check": [
+    "dotnet",
+    "run",
+    "--project",
+    "bench_hidden/Check",
+    "--nologo"
+  ],
+  "workflow": {
+    "kind": "C#/ASP.NET change"
+  }
+}