Move options validation to constructor (#826)

This works around the breaking change to BackgroundService in
dotnet/runtime#116283 which launches
ExecuteAsync using Task.Run.

Author: halter73

src/ModelContextProtocol.AspNetCore/IdleTrackingBackgroundService.cs

@@ -4,16 +4,18 @@
 
 namespace ModelContextProtocol.AspNetCore;
 
-internal sealed partial class IdleTrackingBackgroundService(
-    StatefulSessionManager sessions,
-    IOptions<HttpServerTransportOptions> options,
-    IHostApplicationLifetime appLifetime,
-    ILogger<IdleTrackingBackgroundService> logger) : BackgroundService
+internal sealed partial class IdleTrackingBackgroundService : BackgroundService
 {
-    // Workaround for https://github.com/dotnet/runtime/issues/91121. This is fixed in .NET 9 and later.
-    private readonly ILogger _logger = logger;
+    private readonly StatefulSessionManager _sessions;
+    private readonly IOptions<HttpServerTransportOptions> _options;
+    private readonly IHostApplicationLifetime _appLifetime;
+    private readonly ILogger _logger;
 
-    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    public IdleTrackingBackgroundService(
+        StatefulSessionManager sessions,
+        IOptions<HttpServerTransportOptions> options,
+        IHostApplicationLifetime appLifetime,
+        ILogger<IdleTrackingBackgroundService> logger)
     {
         // Still run loop given infinite IdleTimeout to enforce the MaxIdleSessionCount and assist graceful shutdown.
         if (options.Value.IdleTimeout != Timeout.InfiniteTimeSpan)
@@ -23,14 +25,22 @@ protected override async Task ExecuteAsync(CancellationToken stoppingToken)
 
         ArgumentOutOfRangeException.ThrowIfLessThan(options.Value.MaxIdleSessionCount, 0);
 
+        _sessions = sessions;
+        _options = options;
+        _appLifetime = appLifetime;
+        _logger = logger;
+    }
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
         try
         {
-            var timeProvider = options.Value.TimeProvider;
+            var timeProvider = _options.Value.TimeProvider;
             using var timer = new PeriodicTimer(TimeSpan.FromSeconds(5), timeProvider);
 
             while (!stoppingToken.IsCancellationRequested && await timer.WaitForNextTickAsync(stoppingToken))
             {
-                await sessions.PruneIdleSessionsAsync(stoppingToken);
+                await _sessions.PruneIdleSessionsAsync(stoppingToken);
             }
         }
         catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
@@ -40,15 +50,15 @@ protected override async Task ExecuteAsync(CancellationToken stoppingToken)
         {
             try
             {
-                await sessions.DisposeAllSessionsAsync();
+                await _sessions.DisposeAllSessionsAsync();
             }
             finally
             {
                 if (!stoppingToken.IsCancellationRequested)
                 {
                     // Something went terribly wrong. A very unexpected exception must be bubbling up, but let's ensure we also stop the application,
                     // so that it hopefully gets looked at and restarted. This shouldn't really be reachable.
-                    appLifetime.StopApplication();
+                    _appLifetime.StopApplication();
                     IdleTrackingBackgroundServiceStoppedUnexpectedly();
                 }
             }

tests/ModelContextProtocol.AspNetCore.Tests/StreamableHttpServerConformanceTests.cs

@@ -57,11 +57,7 @@ public async ValueTask DisposeAsync()
         base.Dispose();
     }
 
-#if !NET10_0
     [Fact]
-#else
-    [Fact(Skip = "https://github.com/modelcontextprotocol/csharp-sdk/issues/823")]
-#endif
     public async Task NegativeNonInfiniteIdleTimeout_Throws_ArgumentOutOfRangeException()
     {
         Builder.Services.AddMcpServer().WithHttpTransport(options =>
@@ -73,11 +69,7 @@ public async Task NegativeNonInfiniteIdleTimeout_Throws_ArgumentOutOfRangeExcept
         Assert.Contains("IdleTimeout", ex.Message);
     }
 
-#if !NET10_0
     [Fact]
-#else
-    [Fact(Skip = "https://github.com/modelcontextprotocol/csharp-sdk/issues/823")]
-#endif
     public async Task NegativeMaxIdleSessionCount_Throws_ArgumentOutOfRangeException()
     {
         Builder.Services.AddMcpServer().WithHttpTransport(options =>